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Sample records for geomagnetic secular variations

  1. Geomagnetic secular variation in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Heirtzler, J. R.; Nazarova, K.

    2003-02-01

    Annual repeat stations in Australia and in South Africa show that secular variation may change rapidly and over short geographical distances in the Indian Ocean area. Satellite models show large secular variations in the center of the Indian Ocean where there are few island geomagnetic observatories. This paper investigates marine geomagnetic measurements to see if they give more information about secular variations in this area. Between 1960 and 1988 there were more than 70 port-to-port cruises with ships towing proton precession magnetometers in the Indian Ocean. Change in field intensity from one cruise to another provides new information about the secular variation in this part of the world. Several methods were investigated to determine this change from the ship's data. Observing the change on closely parallel or crossing tracks provides an estimate of this change. These results indicate that there are short time and distance scales of secular variation in the Indian Ocean which have not been accounted for in geomagnetic field models.

  2. Geomagnetic field models incorporating physical constraints on the secular variation

    NASA Technical Reports Server (NTRS)

    Constable, Catherine; Parker, Robert L.

    1993-01-01

    This proposal has been concerned with methods for constructing geomagnetic field models that incorporate physical constraints on the secular variation. The principle goal that has been accomplished is the development of flexible algorithms designed to test whether the frozen flux approximation is adequate to describe the available geomagnetic data and their secular variation throughout this century. These have been applied to geomagnetic data from both the early and middle part of this century and convincingly demonstrate that there is no need to invoke violations of the frozen flux hypothesis in order to satisfy the available geomagnetic data.

  3. The geomagnetic secular variation S parameter: A mathematical artifact

    NASA Astrophysics Data System (ADS)

    Linder, J. M.; Gilder, S. A.

    2011-12-01

    Secular variation, the change in the Earth's magnetic field through time, reflects the energy state of the geodynamo. Secular variation is commonly quantified by the standard deviation of the angular distances of the virtual geomagnetic poles to their mean pole, known as the S value. The S value has long been thought to exhibit latitude dependence [S(λ)] whose origin is widely attributed to a combination of time-varying dipole and non-dipole components. The slope, magnitude and uncertainty of S(λ) are taken as a basis to model the geomagnetic field and understand its evolution. Here we show that variations in S stem from a mathematical aberration of the conversion from directions to poles. A new method to quantify secular variation is proposed.

  4. Secular Variations of the Geomagnetic Field in Europe

    NASA Astrophysics Data System (ADS)

    Sas-Uhrynowski, A.; Welker, E.

    2009-09-01

    The international project MagNetE (Magnetic Net For Europe) was undertaken in 2003. The project has been accepted by the International Association of Geomagnetism and Aeronomy of the IUGG. The common research on the geomagnetic field space and time distribution in Europe, as well as collecting data and its analysis, constitutes the grounds for theoretical works on geomagnetic field models and their parameters. It is also the basis for studying the genesis of the geomagnetic field secular variations and its mechanism. The results of the project enable to increase the accuracy of models on the global, regional, and also on local scale. It has a vital meaning for the regions where the geomagnetic data are not available or, where the existing data, because of their low accuracy, cannot be used. Information about the secular variations of the geomagnetic field makes it possible to update the magnetic data, which is needed in navigation, topography, telecommunication, geology and geophysics and other domains. The enclosed maps of isopors presented have been compiled using the results of measuring campaigns in the years 2004-2006 together with the archive data. They show the secular variations of the magnetic declination D, the length H of the horizontal intensity vector and the lenght F of the total intensity vector of the geomagnetic field, in the intervals 1995-2000 and 2000-2005. The maps of isopors for Europe have been worked out using data from not only the magnetic observatories, but also from some hundred magnetic secular variation stations (repeated stations), located in 23 European countries. The secular variation differences between data obtained from terrestrial surveys and data from the IGRF model (International Geomagnetic Reference Field) have been presented in the form of maps and histograms. In several regions of Europe the unexpectedly large secular variation anomalies are visible. Anomalies of so high frequency and large amplitude cannot exist. They are

  5. Localized sudden changes in the geomagnetic secular variation.

    USGS Publications Warehouse

    Alldredge, L.R.

    1987-01-01

    There is much debate as to whether there was a worldwide geomagnetic jerk in 1969 or 1970. It is agreed that there was an unusual sharp change in the secular variation in the east component, Y, in Europe at that time. This note points out how a localized sudden change in the secular variation pattern of one component in Europe can occur without having any large worldwide effects in any of the components. The accompanying changes in the spherical harmonic coefficients for such a localized change are also discussed. -after Author

  6. A model of geomagnetic secular variation for 1980-1983

    USGS Publications Warehouse

    Peddie, N.W.; Zunde, A.K.

    1987-01-01

    We developed an updated model of the secular variation of the main geomagnetic field during 1980 through 1983 based on annual mean values for that interval from 148 worldwide magnetic observatories. The model consists of a series of 80 spherical harmonics, up to and including those of degree and order 8. We used it to form a proposal for the 1985 revision of the International Geomagnetic Reference Field (IGRF). Comparison of the new model, whose mean epoch is approximately 1982.0, with the Provisional Geomagnetic Reference Field for 1975-1980 (PGRF 1975), indicates that the moment of the centered-dipole part of the geomagnetic field is now decreasing faster than it was 5 years ago. The rate (in field units) indicated by PGRF 1975 was about -25 nT a-1, while for the new model it is -28 nT a-1. ?? 1987.

  7. Geomagnetic Secular Variation Prediction with Thermal Heterogeneous Boundary Conditions

    NASA Technical Reports Server (NTRS)

    Kuang, Weijia; Tangborn, Andrew; Jiang, Weiyuan

    2011-01-01

    It has long been conjectured that thermal heterogeneity at the core-mantle boundary (CMB) affects the geodynamo substantially. The observed two pairs of steady and strong magnetic flux lobes near the Polar Regions and the low secular variation in the Pacific over the past 400 years (and perhaps longer) are likely the consequences of this CMB thermal heterogeneity. There are several studies on the impact of the thermal heterogeneity with numerical geodynamo simulations. However, direct correlation between the numerical results and the observations is found very difficult, except qualitative comparisons of certain features in the radial component of the magnetic field at the CMB. This makes it difficult to assess accurately the impact of thermal heterogeneity on the geodynamo and the geomagnetic secular variation. We revisit this problem with our MoSST_DAS system in which geomagnetic data are assimilated with our geodynamo model to predict geomagnetic secular variations. In this study, we implement a heterogeneous heat flux across the CMB that is chosen based on the seismic tomography of the lowermost mantle. The amplitude of the heat flux (relative to the mean heat flux across the CMB) varies in the simulation. With these assimilation studies, we will examine the influences of the heterogeneity on the forecast accuracies, e.g. the accuracies as functions of the heterogeneity amplitude. With these, we could be able to assess the model errors to the true core state, and thus the thermal heterogeneity in geodynamo modeling.

  8. Gravitational dynamos and the low-frequency geomagnetic secular variation

    PubMed Central

    Olson, P.

    2007-01-01

    Self-sustaining numerical dynamos are used to infer the sources of low-frequency secular variation of the geomagnetic field. Gravitational dynamo models powered by compositional convection in an electrically conducting, rotating fluid shell exhibit several regimes of magnetic field behavior with an increasing Rayleigh number of the convection, including nearly steady dipoles, chaotic nonreversing dipoles, and chaotic reversing dipoles. The time average dipole strength and dipolarity of the magnetic field decrease, whereas the dipole variability, average dipole tilt angle, and frequency of polarity reversals increase with Rayleigh number. Chaotic gravitational dynamos have large-amplitude dipole secular variation with maximum power at frequencies corresponding to a few cycles per million years on Earth. Their external magnetic field structure, dipole statistics, low-frequency power spectra, and polarity reversal frequency are comparable to the geomagnetic field. The magnetic variability is driven by the Lorentz force and is characterized by an inverse correlation between dynamo magnetic and kinetic energy fluctuations. A constant energy dissipation theory accounts for this inverse energy correlation, which is shown to produce conditions favorable for dipole drift, polarity reversals, and excursions. PMID:18048345

  9. Gravitational dynamos and the low-frequency geomagnetic secular variation.

    PubMed

    Olson, P

    2007-12-18

    Self-sustaining numerical dynamos are used to infer the sources of low-frequency secular variation of the geomagnetic field. Gravitational dynamo models powered by compositional convection in an electrically conducting, rotating fluid shell exhibit several regimes of magnetic field behavior with an increasing Rayleigh number of the convection, including nearly steady dipoles, chaotic nonreversing dipoles, and chaotic reversing dipoles. The time average dipole strength and dipolarity of the magnetic field decrease, whereas the dipole variability, average dipole tilt angle, and frequency of polarity reversals increase with Rayleigh number. Chaotic gravitational dynamos have large-amplitude dipole secular variation with maximum power at frequencies corresponding to a few cycles per million years on Earth. Their external magnetic field structure, dipole statistics, low-frequency power spectra, and polarity reversal frequency are comparable to the geomagnetic field. The magnetic variability is driven by the Lorentz force and is characterized by an inverse correlation between dynamo magnetic and kinetic energy fluctuations. A constant energy dissipation theory accounts for this inverse energy correlation, which is shown to produce conditions favorable for dipole drift, polarity reversals, and excursions.

  10. Geomagnetic secular variation timescales under rapid rotation constraints

    NASA Astrophysics Data System (ADS)

    Coutelier, Maélie; Amit, Hagay; Christensen, Uli

    2016-04-01

    Based on geomagnetic observations, numerical dynamo simulations and frozen-flux theory it has been argued that the secular variation (SV) timescale of the magnetic field varies as 1l (where l is the spherical harmonic degree), except for the dipole. The equatorial symmetry of the core flow, which is expected due to rapid rotation effects, allows SV timescale decomposition into symmetric and asymmetric parts. We show in geomagnetic field models and in numerical dynamo simulations that the 1/l scaling law applies for the symmetric and asymmetric timescales as well separately. In both observed and simulated data the symmetric/asymmetric SV timescales are smaller/larger respectively, than in that of the full dataset. The symmetric dipole time scale is well fitted by the 1/l law in the geomagnetic field models, but not in the dynamo models. The opposite holds for the symmetric quadrupole time scales. Assuming that the dynamo models are more representative of the long-term behavior than the geomagnetic field models due to the much longer averaging time of the former, this may suggest that during the historical era the symmetric dipole SV timescale was exceptionally large and the symmetric quadrupole SV timescale was exceptionally small. Since present-day symmetric dipole SV timescale is below the 1/l fit, this may further suggest that the nearly constant dipole tilt between 1840-1960 was anomalous. Failure to explain the dipole SV timescales (both axial and equatorial) by the scaling law may suggest strong diffusion effects for the lowest degrees. Overall, our analytical fits for the symmetric and asymmetric SV timescales provide new insight into the re-organization times of different length scales in Earth's outer core.

  11. The 1995 revision of the joint US/UK geomagnetic field models - I. Secular variation

    USGS Publications Warehouse

    Macmillan, S.; Barraclough, D.R.; Quinn, J.M.; Coleman, R.J.

    1997-01-01

    We present the methods used to derive mathematical models of global secular variation of the main geomagnetic field for the period 1985 to 2000. These secular-variation models are used in the construction of the candidate US/UK models for the Definitive Geomagnetic Reference Field at 1990, the International Geomagnetic Reference Field for 1995 to 2000, and the World Magnetic Model for 1995 to 2000 (see paper II, Quinn et al., 1997). The main sources of data for the secular-variation models are geomagnetic observatories and repeat stations. Over the areas devoid of these data secular-variation information is extracted from aeromagnetic and satellite data. We describe how secular variation is predicted up to the year 2000 at the observatories and repeat stations, how the aeromagnetic and satellite data are used, and how all the data are combined to produce the required models.

  12. Geomagnetic secular variations at the Permo-Triassic boundary

    NASA Astrophysics Data System (ADS)

    Pavlov, Vladimir; Veselovskiy, Roman; Fetisova, Anna; Latyshev, Anton; Fluteau, Frederic

    2014-05-01

    Study of changes in geomagnetic secular variations through geological time is essential to document the Earth's magnetic field evolution and provides an important constraint for geodynamo modeling. Moreover, knowledge of the secular variations value for any specific geological epoch (paleosecular variations - PSV) may give an additional tool to constrain the duration of emplacement and cooling of various magmatic bodies including flows, dykes and sills. In this report we present the result of study of the PSV at the Permo-Triassic boundary (~252 Ma), based on the paleomagnetic data, obtained from numerous (N>100) volcanic flows of the Siberian traps exposed in series of sections located in Norilsk and Maymecha-Kotuy regions in the North-West and North of the Siberian platform. Our data, taken together with similar data from other regions (Sementau, East Kazakhstan; Emeichan, China) indicates that the amplitude of PSV at the Permo-Triassic boundary was about the same or a little lower than in Late Cenozoic during last 5 milllions years. The low (comparing with expected one) value of PSV recorded in several large sills from Angara-Bratsk region (southern Siberian platform) indicates that these sills was formed very fast during the time interval less than, at least, several thousand years. Especially this conclusion is interesting for so called Tolstomyss sill, which, in fact, represents a huge field of associated tuffs, sills, dykes and volcanics, extended over the distance more than 200 km. This result can be considered as a further indication of very fast emplacement of the Siberian traps and their link with the Permo-Triassic catastrophe.

  13. Analysis of geomagnetic secular variation during 1980-1985 and 1985- 1990, and geomagnetic models proposed for the 1991 revision of the International Geomagnetic Reference Field

    USGS Publications Warehouse

    Peddie, N.W.

    1992-01-01

    The secular variation of the main geomagnetic field during the periods 1980-1985 and 1985-1990 was analyzed in terms of spherical harmonics up to the eighth degree and order. Data from worldwide magnetic observatories and the Navy's Project MAGNET aerial surveys were used. The resulting pair of secular-variation models was used to update the Definitive Geomagnetic Reference Field (DGRF) model for 1980, resulting in new mainfield models for 1985.0 and 1990.0. These, along with the secular-variation model for 1985-1990, were proposed for the 1991 revision of the International Geomagnetic Reference Field (IGRF). -Author

  14. On the Possibilities of Predicting Geomagnetic Secular Variation with Geodynamo Modeling

    NASA Technical Reports Server (NTRS)

    Kuang, Wei-Jia; Tangborn, Andrew; Sabaka, Terrance

    2004-01-01

    We use our MoSST core dynamics model and geomagnetic field at the core-mantle boundary (CMB) continued downward from surface observations to investigate possibilities of geomagnetic data assimilation, so that model results and current geomagnetic observations can be used to predict geomagnetic secular variation in future. As the first attempt, we apply data insertion technique to examine evolution of the model solution that is modified by geomagnetic input. Our study demonstrate that, with a single data insertion, large-scale poloidal magnetic field obtained from subsequent numerical simulation evolves similarly to the observed geomagnetic variation, regardless of the initial choice of the model solution (so long it is a well developed numerical solution). The model solution diverges on the time scales on the order of 60 years, similar to the time scales of the torsional oscillations in the Earth's core. Our numerical test shows that geomagnetic data assimilation is promising with our MoSST model.

  15. On secular changes of correlation between geomagnetic indices and variations in solar activity

    NASA Astrophysics Data System (ADS)

    Le Mouël, Jean-Louis; Blanter, Elena; Shnirman, Mikhail; Courtillot, Vincent

    2012-09-01

    Geomagnetic indices can be divided in two families, sometimes called “mean” and “range” families, which reflect different interactions between solar and terrestrial processes on time scales ranging from hourly to secular and longer. We are interested here in trying to evaluate secular change in the correlations between these indices and variations in solar activity as indicators of secular changes in solar behavior. We use on one hand daily values of geomagnetic indices Dst and ζ (members of the “mean” family), and Ap and aa (members of the “range” family), and on the other hand solar indices WN (sunspot number), F10.7 (radio flux), interplanetary magnetic field B and solar wind speed v over the period 1955-2005. We calculate correlations between pairs of geomagnetic indices, between pairs of solar indices (including the composite Bv2), and between pairs consisting in a geomagnetic vs a solar index, all averaged over one to eleven years. The relationship between geomagnetic indices depends on the evolution of solar activity; strong losses of correlation occur during the declining phase of solar cycle 20 and in solar cycle 23. We confirm the strong correlation between aa and Bv2 and to a lesser extent between Dst and B. On the other hand, correlations between aa or Dst and v are non-stationary and display strong increases between 1975 and 2000. Some geomagnetic indices can be used as proxies for the behavior of solar wind indices for times when these were not available. We discuss possible physical origins of sub-decadal to secular evolutions of correlations and their relation with the character of solar activity (correlation of DP2 substorms and main storm occurrence, generation of toroidal field of a new cycle during descending phase of old cycle and prediction of next cycle, and also links with coupling of nonlinear oscillators and abrupt regime changes).

  16. RESEARCH NOTE: A Late Holocene geomagnetic secular variation record from Erhai Lake, southwest China

    NASA Astrophysics Data System (ADS)

    Hyodo, Masayuki; Yoshihara, Arata; Kashiwaya, Kenji; Okimura, Takashi; Masuzawa, Toshiyuki; Nomura, Ryotaro; Tanaka, Shingo; Xing, Tang Bang; Qing, Liu Su; Jian, Liu Shi

    1999-03-01

    A secular variation record of the geomagnetic field direction for the last 6.5 kyr has been obtained from the magnetization of sediment cores from Erhai Lake, southwest China. In order to make a comparison with this record, secular variation in east-central China was investigated by combining available magnetic field data from historical records and archaeomagnetic measurements since about 350 bc. The secular variation in Erhai Lake shows features consistent with the combined record, except for the oldest three observed declination swings in Sian from 720 to 900 ad. Many features of declination and inclination in China also occur in Japan. From 500 to 1000 ad, declination was westerly ranging from about -20° to -5° in Erhai Lake, east-central China, and Japan.

  17. Time-causal decomposition of geomagnetic time series into secular variation, solar quiet, and disturbance signals

    USGS Publications Warehouse

    Rigler, E. Joshua

    2017-04-26

    A theoretical basis and prototype numerical algorithm are provided that decompose regular time series of geomagnetic observations into three components: secular variation; solar quiet, and disturbance. Respectively, these three components correspond roughly to slow changes in the Earth’s internal magnetic field, periodic daily variations caused by quasi-stationary (with respect to the sun) electrical current systems in the Earth’s magnetosphere, and episodic perturbations to the geomagnetic baseline that are typically driven by fluctuations in a solar wind that interacts electromagnetically with the Earth’s magnetosphere. In contrast to similar algorithms applied to geomagnetic data in the past, this one addresses the issue of real time data acquisition directly by applying a time-causal, exponential smoother with “seasonal corrections” to the data as soon as they become available.

  18. Bottom-up control of geomagnetic secular variation by the Earth's inner core.

    PubMed

    Aubert, Julien; Finlay, Christopher C; Fournier, Alexandre

    2013-10-10

    Temporal changes in the Earth's magnetic field, known as geomagnetic secular variation, occur most prominently at low latitudes in the Atlantic hemisphere (that is, from -90 degrees east to 90 degrees east), whereas in the Pacific hemisphere there is comparatively little activity. This is a consequence of the geographical localization of intense, westward drifting, equatorial magnetic flux patches at the core surface. Despite successes in explaining the morphology of the geomagnetic field, numerical models of the geodynamo have so far failed to account systematically for this striking pattern of geomagnetic secular variation. Here we show that it can be reproduced provided that two mechanisms relying on the inner core are jointly considered. First, gravitational coupling aligns the inner core with the mantle, forcing the flow of liquid metal in the outer core into a giant, westward drifting, sheet-like gyre. The resulting shear concentrates azimuthal magnetic flux at low latitudes close to the core-mantle boundary, where it is expelled by core convection and subsequently transported westward. Second, differential inner-core growth, fastest below Indonesia, causes an asymmetric buoyancy release in the outer core which in turn distorts the gyre, forcing it to become eccentric, in agreement with recent core flow inversions. This bottom-up heterogeneous driving of core convection dominates top-down driving from mantle thermal heterogeneities, and localizes magnetic variations in a longitudinal sector centred beneath the Atlantic, where the eccentric gyre reaches the core surface. To match the observed pattern of geomagnetic secular variation, the solid material forming the inner core must now be in a state of differential growth rather than one of growth and melting induced by convective translation.

  19. Simultaneous stochastic inversion for geomagnetic main field and secular variation. II - 1820-1980

    NASA Technical Reports Server (NTRS)

    Bloxham, Jeremy; Jackson, Andrew

    1989-01-01

    With the aim of producing readable time-dependent maps of the geomagnetic field at the core-mantle boundary, the method of simultaneous stochastic inversion for the geomagnetic main field and secular variation, described by Bloxham (1987), was applied to survey data from the period 1820-1980 to yield two time-dependent geomagnetic-field models, one for the period 1900-1980 and the other for 1820-1900. Particular consideration was given to the effect of crustal fields on observations. It was found that the existing methods of accounting for these fields as sources of random noise are inadequate in two circumstances: (1) when sequences of measurements are made at one particular site, and (2) for measurements made at satellite altitude. The present model shows many of the features in the earth's magnetic field at the core-mantle boundary described by Bloxham and Gubbins (1985) and supports many of their earlier conclusions.

  20. Dynamic Responses of the Earth's Outer Core to Assimilation of Observed Geomagnetic Secular Variation

    NASA Technical Reports Server (NTRS)

    Kuang, Weijia; Tangborn, Andrew

    2014-01-01

    Assimilation of surface geomagnetic observations and geodynamo models has advanced very quickly in recent years. However, compared to advanced data assimilation systems in meteorology, geomagnetic data assimilation (GDAS) is still in an early stage. Among many challenges ranging from data to models is the disparity between the short observation records and the long time scales of the core dynamics. To better utilize available observational information, we have made an effort in this study to directly assimilate the Gauss coefficients of both the core field and its secular variation (SV) obtained via global geomagnetic field modeling, aiming at understanding the dynamical responses of the core fluid to these additional observational constraints. Our studies show that the SV assimilation helps significantly to shorten the dynamo model spin-up process. The flow beneath the core-mantle boundary (CMB) responds significantly to the observed field and its SV. The strongest responses occur in the relatively small scale flow (of the degrees L is approx. 30 in spherical harmonic expansions). This part of the flow includes the axisymmetric toroidal flow (of order m = 0) and non-axisymmetric poloidal flow with m (is) greater than 5. These responses can be used to better understand the core flow and, in particular, to improve accuracies of predicting geomagnetic variability in future.

  1. Contributions to the geomagnetic secular variation from a reanalysis of core surface dynamics

    NASA Astrophysics Data System (ADS)

    Barrois, O.; Gillet, N.; Aubert, J.

    2017-10-01

    We invert for motions at the surface of Earth's core under spatial and temporal constraints that depart from the mathematical smoothings usually employed to ensure spectral convergence of the flow solutions. Our spatial constraints are derived from geodynamo simulations. The model is advected in time using stochastic differential equations coherent with the occurrence of geomagnetic jerks. Together with a Kalman filter, these spatial and temporal constraints enable the estimation of core flows as a function of length and time-scales. From synthetic experiments, we find it crucial to account for subgrid errors to obtain an unbiased reconstruction. This is achieved through an augmented state approach. We show that a significant contribution from diffusion to the geomagnetic secular variation should be considered even on short periods, because diffusion is dynamically related to the rapidly changing flow below the core surface. Our method, applied to geophysical observations over the period 1950-2015, gives access to reasonable solutions in terms of misfit to the data. We highlight an important signature of diffusion in the Eastern equatorial area, where the eccentric westward gyre reaches low latitudes, in relation with important up/downwellings. Our results also confirm that the dipole decay, observed over the past decades, is primarily driven by advection processes. Our method allows us to provide probability densities for forecasts of the core flow and the secular variation.

  2. Statistics of the geomagnetic secular variation for the past 5Ma

    NASA Technical Reports Server (NTRS)

    Constable, C. G.; Parker, R. L.

    1986-01-01

    A new statistical model is proposed for the geomagnetic secular variation over the past 5Ma. Unlike previous models, the model makes use of statistical characteristics of the present day geomagnetic field. The spatial power spectrum of the non-dipole field is consistent with a white source near the core-mantle boundary with Gaussian distribution. After a suitable scaling, the spherical harmonic coefficients may be regarded as statistical samples from a single giant Gaussian process; this is the model of the non-dipole field. The model can be combined with an arbitrary statistical description of the dipole and probability density functions and cumulative distribution functions can be computed for declination and inclination that would be observed at any site on Earth's surface. Global paleomagnetic data spanning the past 5Ma are used to constrain the statistics of the dipole part of the field. A simple model is found to be consistent with the available data. An advantage of specifying the model in terms of the spherical harmonic coefficients is that it is a complete statistical description of the geomagnetic field, enabling us to test specific properties for a general description. Both intensity and directional data distributions may be tested to see if they satisfy the expected model distributions.

  3. Statistics of the geomagnetic secular variation for the past 5 m.y

    NASA Technical Reports Server (NTRS)

    Constable, C. G.; Parker, R. L.

    1988-01-01

    A new statistical model is proposed for the geomagnetic secular variation over the past 5Ma. Unlike previous models, the model makes use of statistical characteristics of the present day geomagnetic field. The spatial power spectrum of the non-dipole field is consistent with a white source near the core-mantle boundary with Gaussian distribution. After a suitable scaling, the spherical harmonic coefficients may be regarded as statistical samples from a single giant Gaussian process; this is the model of the non-dipole field. The model can be combined with an arbitrary statistical description of the dipole and probability density functions and cumulative distribution functions can be computed for declination and inclination that would be observed at any site on Earth's surface. Global paleomagnetic data spanning the past 5Ma are used to constrain the statistics of the dipole part of the field. A simple model is found to be consistent with the available data. An advantage of specifying the model in terms of the spherical harmonic coefficients is that it is a complete statistical description of the geomagnetic field, enabling us to test specific properties for a general description. Both intensity and directional data distributions may be tested to see if they satisfy the expected model distributions.

  4. Constraints on geomagnetic secular variation modeling from electromagnetism and fluid dynamics of the Earth's core

    NASA Technical Reports Server (NTRS)

    Benton, E. R.

    1986-01-01

    A spherical harmonic representation of the geomagnetic field and its secular variation for epoch 1980, designated GSFC(9/84), is derived and evaluated. At three epochs (1977.5, 1980.0, 1982.5) this model incorporates conservation of magnetic flux through five selected patches of area on the core/mantle boundary bounded by the zero contours of vertical magnetic field. These fifteen nonlinear constraints are included like data in an iterative least squares parameter estimation procedure that starts with the recently derived unconstrained field model GSFC (12/83). Convergence is approached within three iterations. The constrained model is evaluated by comparing its predictive capability outside the time span of its data, in terms of residuals at magnetic observatories, with that for the unconstrained model.

  5. A new Holocene record of geomagnetic secular variation from Windermere, UK

    NASA Astrophysics Data System (ADS)

    Avery, Rachael S.; Xuan, Chuang; Kemp, Alan E. S.; Bull, Jonathan M.; Cotterill, Carol J.; Fielding, J. James; Pearce, Richard

    2016-04-01

    Palaeomagnetic secular variation (PSV) records serve as valuable independent stratigraphic correlation and dating tools for marine and terrestrial sediment sequences. The master Holocene UK PSV record, used to date regional Holocene sediment sequences, was established over three decades ago using older radiocarbon techniques and discrete sediment samples from Windermere and two other lakes (Turner and Thompson, 1981). We present a new radiocarbon-dated record of Holocene geomagnetic secular variation from Windermere, with a view to updating the UK master PSV curve. Our analyses used u-channel samples taken from the centre of four sediment cores retrieved from Windermere in 2012.The natural remnant magnetisation (NRM) of each U-channel was measured before and after stepwise alternating field demagnetisation on a 2G Enterprises superconducting rock magnetometer at 0.5 cm resolution for the first core, and 1 cm resolution for the remaining cores. The NRM data reveal a stable and well-defined primary magnetization. Principal Component Analysis (PCA) directions of the four Windermere cores, especially the inclination records, appear to correlate well on their independent radiocarbon age models. The new Windermere PSV records compare well with the existing UK master curve on millennial timescales, as well as with records from other European lakes and northern North Atlantic marine records. These observations suggest that millennial scale secular variations of the Earth's magnetic field in the Europe- North Atlantic region shared common driving mechanisms during the Holocene. The new Windermere PSV record may thus be used in a regional context for correlating and dating sediment sequences through the Holocene.

  6. Late Glacial and Holocene Geomagnetic secular variation in Western Lake Geneva (Switzerland)

    NASA Astrophysics Data System (ADS)

    Baster, I.; Heller, F.; Egli, R.; Rachoud-Schneider, A. M.; Wildi, W.

    2003-04-01

    secular variation curves extending back to 13'400 years B. P. recorded by sediments deposited in Lac du Joux, Switzerland, J. Geophys., 48, 139-147. Turner, G.M. &Thompson, R. (1981) Lake sediment record of the geomagnetic secular variation in Britain during Holocene times, Geophys. J. Roy. astr. Soc., 65, 703-725.

  7. Recent geomagnetic secular variation from Swarm and ground observatories as estimated in the CHAOS-6 geomagnetic field model

    NASA Astrophysics Data System (ADS)

    Finlay, Christopher C.; Olsen, Nils; Kotsiaros, Stavros; Gillet, Nicolas; Tøffner-Clausen, Lars

    2016-07-01

    We use more than 2 years of magnetic data from the Swarm mission, and monthly means from 160 ground observatories as available in March 2016, to update the CHAOS time-dependent geomagnetic field model. The new model, CHAOS-6, provides information on time variations of the core-generated part of the Earth's magnetic field between 1999.0 and 2016.5. We present details of the secular variation (SV) and secular acceleration (SA) from CHAOS-6 at Earth's surface and downward continued to the core surface. At Earth's surface, we find evidence for positive acceleration of the field intensity in 2015 over a broad area around longitude 90°E that is also seen at ground observatories such as Novosibirsk. At the core surface, we are able to map the SV up to at least degree 16. The radial field SA at the core surface in 2015 is found to be largest at low latitudes under the India-South-East Asia region, under the region of northern South America, and at high northern latitudes under Alaska and Siberia. Surprisingly, there is also evidence for significant SA in the central Pacific region, for example near Hawaii where radial field SA is observed on either side of a jerk in 2014. On the other hand, little SV or SA has occurred over the past 17 years in the southern polar region. Inverting for a quasi-geostrophic core flow that accounts for this SV, we obtain a prominent planetary-scale, anti-cyclonic, gyre centred on the Atlantic hemisphere. We also find oscillations of non-axisymmetric, azimuthal, jets at low latitudes, for example close to 40°W, that may be responsible for localized SA oscillations. In addition to scalar data from Ørsted, CHAMP, SAC-C and Swarm, and vector data from Ørsted, CHAMP and Swarm, CHAOS-6 benefits from the inclusion of along-track differences of scalar and vector field data from both CHAMP and the three Swarm satellites, as well as east-west differences between the lower pair of Swarm satellites, Alpha and Charlie. Moreover, ground observatory SV

  8. Using geomagnetic secular variation to separate remanent and induced sources of the crustal magnetic field

    NASA Astrophysics Data System (ADS)

    Lesur, Vincent; Gubbins, David

    2000-09-01

    Magnetic fields originating from magnetized crustal rocks dominate the geomagnetic spectrum at wavelengths of 0.1-100km. It is not known whether the magnetization is predominantly induced or remanent, and static surveys cannot discriminate between the two. Long-running magnetic observatories offer a chance, in principle, of separating the two sources because secular variation leads to a change in the main inducing field, which in turn causes a change in the induced part of the short-wavelength crustal field. We first argue that the induced crustal field, bI(t), is linearly related to the local core field, B(t), through a symmetric, trace-free matrix A: bI(t)=AB(t). We then subtract a core field model from the observatory annual means and invert the residuals for three components of the remanent field, bR(t), and the five independent elements of A. Applying the method to 20 European observatories, all of which have recorded for more than 50 years, shows that the most difficult task is to distinguish bR from the steady part of bI. However, for nine observatories a time-dependent induced field fits the data better than a steady remanent field at the 99 per cent confidence level, suggesting the presence of a significant induced component to the magnetization.

  9. Archaeomagnetic results from southern Italy and their bearing on geomagnetic secular variation

    NASA Astrophysics Data System (ADS)

    Evans, M. E.; Hoye, G. S.

    2005-07-01

    Archaeodirectional results from kilns and other baked structures in southern Italy are presented. They are generally compatible with the much larger data sets from France and Bulgaria. In particular, a summary of all the results associated with the well-known eruption of Vesuvius that destroyed Pompeii ( n = 9, D = 355°, I = 58°, α95 = 1.5°) provides a reliable archaeomagnetic anchor point supporting the French and Bulgarian master curves. It is extremely well-constrained in time and it comprises independent studies carried out in four different countries. Furthermore, it is derived from a diverse set of features agreement amongst which argues strongly against significant perturbations due to magnetic refraction, structural disturbance, or depositional shallowing. In terms of geomagnetic secular variation, we interpret the western European archaeomagnetic data summarized here in terms of an open loop caused by westward drift, followed by an inclination low spanning the first few centuries CE representing the signal of a static flux pulse that reaches a maximum magnetic moment of a few percent of the earth's main central dipole.

  10. Retrieving geomagnetic secular variations from lava flows: evidence from Mounts Arso, Etna and Vesuvius (southern Italy)

    NASA Astrophysics Data System (ADS)

    Incoronato, Alberto; Angelino, Antimo; Romano, Romolo; Ferrante, Agostino; Sauna, Renata; Vanacore, Gianpio; Vecchione, Claudio

    2002-06-01

    Mean directions of magnetization from Mounts Arso (Ischia Island, Gulf of Naples), Etna and Vesuvius lava flows have been determined based on very stringent linearity criteria. These indicate that, regardless of the source volcano, the lava flow mean directions of magnetization form a common path, the SISVC (Southern Italy Secular Variation Curve). This curve enables a reassessment of the age of eruption of several lavas. A date of AD 1169 is demonstrated to be the only possible time of emplacement for one Etna lava flow previously assigned an age of AD 812/1169. It is also demonstrated that two Etna lava flows, which, according to the literature, were emplaced in AD 1536 and 1595 respectively, were actually both emplaced around AD 1037. Three other Etna lava flows, one ascribed to AD 1566 and two to AD 1595, were actually emplaced between AD 1169 and 1284/85. The same time window also holds for a Vesuvius lava flow for which only an upper time threshold was previously available. Only one of the studied flows needs further sampling and analysis to verify whether this flow has been affected by a complete remagnetization or has an erroneous historical dating. The applied procedure seems to be the most appropriate one in carrying out palaeomagnetic surveys of lava flows, as also suggested by the broad agreement with some 17th and 19th century measurements of the geomagnetic field in Rome, relocated to Etna, and is likely to improve knowledge of past history of a volcano significantly.

  11. Geomagnetic field variations in Western Europe from 1500 BC to 200 AD. Part II: New intensity secular variation curve

    NASA Astrophysics Data System (ADS)

    Hervé, Gwenaël; Chauvin, Annick; Lanos, Philippe

    2013-05-01

    In order to extend the secular variation curve (SVC) of archaeointensity in Western Europe to the first millennium BC, we studied 24 kilns and hearths in place, two displaced hearths and six sets of pottery sherds from French archaeological sites. Archaeological artefacts, radiocarbon and dendrochronology dated the acquisition of the thermoremanent magnetization (TRM) carried by the studied objects. Rock magnetism experiments suggest that the main carrier of the magnetization is a Ti-poor titanomagnetite. Archaeointensity was determined by the Thellier-Thellier classical protocol with pTRM-checks. A strict criteria set was applied to select only the most reliable results with linear NRM-TRM diagrams (55% of total specimens). This study demonstrates that pottery sherds with two TRMs give reliable archaeointensities in the low-temperature interval, if the NRM-TRM diagram is adequately adjusted. Eighteen new mean archaeointensities (14 corrected from the anisotropy of TRM and 16 from cooling rate) were computed. The comparison with previously published Western Europe paleointensities show a strong dispersion between data primarily due to their variable quality. Western Europe data were weighted following the archaeointensity protocol, the number of specimens per site and the type of studied materials, in order to better highlight the secular variation of archaeointensity during the first millennium BC. The SVC, built with sliding windows of 160 years shifted every 50 years, presents (at Paris) a maximum of 90 μT around 800 BC and a minimum of 60 μT around 250 BC. These archaeointensity maximum and minimum correspond to cusps of the geomagnetic field direction in Western Europe. This new curve is consistent with Mesopotamian and Eastern Europe data. The archaeointensity secular variation in Western Europe predicted by global geomagnetic models CALS3k.4, ARCH3k.1 and ARCH3k_cst.1 is smoother than our SVC. We used our directional dataset (Hervé et al., 2013) to build

  12. Bulgarian Geomagnetic Reference Field (BulGRF) for 2015.0 and secular variation prediction model up to 2020

    NASA Astrophysics Data System (ADS)

    Metodiev, Metodi; Trifonova, Petya

    2017-09-01

    The Bulgarian Geomagnetic Reference Field (BulGRF) for 2015.0 epoch and its secular variation model prediction up to 2020.0 is produced and presented in this paper. The main field model is based on the well-known polynomial approximation in latitude and longitude of the geomagnetic field elements. The challenge in our modelling strategy was to update the absolute field geomagnetic data from 1980.0 up to 2015.0 using secular measurements unevenly distributed in time and space. As a result, our model gives a set of six coefficients for the horizontal H, vertical Z, total field F, and declination D elements of the geomagnetic field. The extrapolation of BulGRF to 2020 is based on an autoregressive forecasting of the Panagyurishte observatory annual means. Comparison of the field values predicted by the model with Panagyurishte (PAG) observatory annual mean data and two vector field measurements performed in 2015 shows a close match with IGRF-12 values and some difference with the real (measured) values, which is probably due to the influence of crustal sources. BulGRF proves to be a reliable alternative to the global geomagnetic field models which together with its simplicity makes it a useful tool for reducing magnetic surveys to a common epoch carried out over the Bulgarian territory up to 2020.

  13. New evidence of a fast secular variation of the geomagnetic field 1000 BCE: archaeomagnetic study of Bavarian potteries

    NASA Astrophysics Data System (ADS)

    Hervé, G.; Gilder, S.; Fassbinder, J.; Metzler-Nebelsick, C.; Schnepp, E.; Geisweid, L.; Putz, A.; Reuss, S.; Riedel, G.; Westhausen, I.; Wittenborn, F.

    2016-12-01

    This study presents new archaeointensity results obtained on 350 pottery sherds from 45 graves and pits from 12 sites around Munich (Germany). The features are dated between 1400 and 400 BCE by ceramic and metallic artifacts, radiocarbon and dendrochronology. We collected only red- or partly red-colored sherds in order to minimize mineralogical alteration during laboratory experiments. Rock magnetism analyses show that the remanent magnetization is mainly carried by titanomagnetite. Archaeointensities were determined using the Thellier-Thellier protocol with corrections of TRM anisotropy and cooling rate on one to three specimens per sherd. The experiments were completed using Triaxe and multispecimen (MSP-DSC) methods. Around 60 per cent of the sherds provide reliable results, allowing the computation of 35 mean archaeointensity values. This quadruples the number of previously published data in Western Europe. The secular variation of the geomagnetic field strength is low from 1400 to 1200 BCE with intensities close to 50 µT then the intensity increased to 70 µT around 1000-900 BCE. After a minimum 50 µT near 750 BCE, the intensity increased again to 90 µT at 650 BCE. This high secular variation rate (0.4 µT/year) is especially apparent in the sherds from a fountain dated between 750 and 650 BCE. Next, the intensity remained high until 400 BCE before rapidly decreasing to 200 BCE. As the sharp change in geomagnetic direction around 800 BCE is not contemporaneous with an intensity high, this period is probably not characterized by an archaeomagnetic jerk. The trend of secular variation with two intensity maxima is similar to the one observed in the Near East. The Virtual Axial Dipole Moments of the two regions are approximately the same after 700 BCE, but before they are systematically 1-2 × 1022 Am2 higher in the Near East. This difference may be a further proof of a geomagnetic field anomaly in this area 1000 BCE, yet there is no evidence for a geomagnetic

  14. Improving total field geomagnetic secular variation modeling from a new set of cross-over marine data

    NASA Astrophysics Data System (ADS)

    Pavón-Carrasco, F. Javier; Torta, J. Miquel; Catalán, Manuel; Talarn, Àngela; Ishihara, Takemi

    2013-03-01

    A new set of cross-over marine data has been used to generate a regional model for the secular variation of the total geomagnetic field, showing the potential of the suggested approach for gaining a better knowledge of the field over oceanic regions. The model, which is valid for the Northern Atlantic region during the temporal interval 1960-2000, was obtained using spherical cap harmonic analysis (SCHA) in space and penalized splines in time. The maximum spatial expansion is equivalent to degree 9 in ordinary spherical harmonic analysis. Annual mean intensity data from different geomagnetic observatories have been used to improve the spatial and temporal resolution of the original dataset. Results indicate that the regional model improves, in terms of the root mean square error, the prediction given by the 11th generation of IGRF and CM4 global models, especially for the geomagnetic observatories considered. We also provide the uncertainty of the model coefficients and the secular variation prediction given by a bootstrap algorithm. The model is available in the EarthRef. org Digital Archive at http://earthref.org/ERDA/1728/.

  15. Geomagnetic Secular Variation in Texas over the Last 17,000 Years: High-Intensity Geomagnetic Field 'Spike' Observed at ca. 3000 cal BP

    NASA Astrophysics Data System (ADS)

    Bourne, M. D.; Feinberg, J. M.; Waters, M. R.; Stafford, T. W., Jr.; Forman, S. L.; Lundelius, E. L.

    2015-12-01

    By observing the fluctuations in direction and intensity of the Earth's magnetic field through time, we increase our understanding of the fluid motions in the Earth's outer core that sustain the geomagnetic field, the geodynamo. Recent archaeomagnetic studies in the Near East have proposed extremely rapid increases - 'spikes' - in geomagnetic field intensity ca. 3000 years ago that have proved problematic for our current understanding of core-flow. However, until now, these geomagnetic spikes had not been observed outside of the Near East, where they have been found in metallurgical slag and mud brick walls. We present a new fully-oriented, geomagnetic secular variation and relative palaeointensity (RPI) record for the last 17,000 years from Hall's Cave, Texas. Sediment washed into the cave has formed a continuous stratigraphic sequence that is at least 3.5 m thick. Within the stable, cool climate of the cave, pedogenic and bioturbation processes are almost non-existent, thereby limiting post-depositional physical and geochemical alteration of the magnetic record. The sub-aerial and subterranean setting of the sedimentary sequence in Hall's Cave enabled us to collect oriented palaeomagnetic cubes from an excavated section through the sequence. The palaeomagnetic samples yielded high-quality vectors. An age model for the sequence, determined using 57 AMS 14C-dates on individual bones from microvertebrate, was combined with the palaeomagnetic data to construct a secular variation record. The record is in broad agreement with predictions by Holocene field models for the site's location. However, at ca. 3000 years ago, the RPI data indicate an almost four-fold increase in geomagnetic field intensity lasting several hundred years and contemporaneous with the more short-lived, decadal-scale spikes reported from the Near East. Evidence for this extreme intensity event outside of the Near East has major implications for our current understanding of core-dynamics.

  16. An Online Observatory and Satellite-Based Model for the Geomagnetic Field in Antarctica and its Secular Variation

    NASA Astrophysics Data System (ADS)

    De Santis, A.; Gaya-Pique', L.; Torta, M. J.; Caprara, F.; De Santis, A.

    2002-05-01

    The recently proposed Antarctic geomagnetic Reference Model (ARM) is now available online. The model, developed applying Spherical Cap Harmonic Analysis, is capable of synthesizing the main field and its secular variation over Antarctica, and was based on the annual means of X, Y, and Z components recorded by Antarctic Observatories during the last forty years as well as on a selected subset of Oersted satellite total field values measured in periods characterized by very low magnetic activity between December 1999 and January 2000. ARM presents a clear improvement with respect to the IGRF2000 model when representing the field and, especially, its secular variation, so it would be recommended the use of ARM when magnetic surveys in Antarctica, carried out at different times, are reduced to the same epoch. To facilitate the work to the scientific community involved on the study of Antarctic magnetic features like the anomaly field, ARM is accessible through the homepage of the Italian Istituto Nazionale di Geofisica e Vulcanologia (www.ingv.it), allowing the user to compute the values of the geomagnetic field over Antarctica for a 3-D position (latitude, longitude, altitude) from 1960 to 2000, being also useful to predict the field ahead, although the errors are expected to increase with time. To further improving the model we intend to add the sampling of data corresponding to the quiet-day selection from Oersted, CHAMP and the Oersted-2 experiment onboard SAC-C, made available for this Session.

  17. Geomagnetic secular variation in Sicily and revised ages of historic lavas from Mount Etna

    NASA Astrophysics Data System (ADS)

    Tanguy, J. C.; Bucur, I.; Thompson, J. F. C.

    1985-12-01

    The variation of geomagnetic field direction in Sicily during the past 700 yr has tentatively been determined using lavas of known date from Mount Etna1. Additional palaeomagnetic studies on several hundred volcanic samples, combined with archaeomagnetic investigations carried out on Norman buildings, have improved the previous results and permit a reconstruction of the geomagnetic variation curve to about AD 1000. This curve agrees well with those obtained for other European countries2-6 and may be used as a reference for checking the ages attributed to archaeological structures as well as volcanic products in southern Italy during the past 1,000 yr. The present results cast serious doubts on the true ages of numerous historically dated lavas from Mount Etna, most of which are at least several centuries older than previously believed. The conclusions have implications for the succession of eruptions, effusion rates, magmatic evolution, and so on, and demonstrate the inconsistency of eruptive models based on historical records alone.

  18. Multi-decadal ingredients of the secular variation of the geomagnetic field. Insights from long time series of observatory data

    NASA Astrophysics Data System (ADS)

    Demetrescu, Crisan; Dobrica, Venera

    2014-06-01

    The temporal evolution of the geomagnetic field is shown, on data from 24 observatories with 100-150 years long time series of annual means, to be composed of several ingredients, which we call the steady, the ∼80-year, the 22-year, and the 11-year variations. The latter is the result of incomplete averaging out in the annual mean of external effects and shows a characteristic 11-year solar-cycle-related evolution with an amplitude of 10-40 nT in H and Z and within ±0.05° in D. The other three characterize the main field. While the steady variation carries the largest part of the main field and is smoothly increasing or decreasing in time, the ∼80-year variation shows changes with amplitudes amounting to several hundred nT in the intensity components H and Z, and of 0.2-0.7° in declination; the 22-year variation changes with much smaller amplitudes, of 20-60 nT in H and somewhat larger in Z (20-100 nT), and of about 0.05-0.15° in D. The analysis of the first time derivative of declination for the 24 study observatories showed that the ∼80-year variation dominated the secular variation in the last 100 years and that the 22-year variation has gotten its importance in defining the time evolution of the first time derivative of declination, jerks included, since 1960. The external contribution is decisive though in establishing the very short time scale characterizing jerks and, to some extent, also the amplitude and timing of the jerk. The analysis of 400 years-long declination time-series from three European locations (London, Munich, Rome) resulted in tracing back of the ∼80-year variation to the 15th century and showed that what we called 'steady variation', based on 150 years of observatory data, proves to be only a part of a larger timescale variation, when 400 years of data are available. According to our results, the term 'jerk' loses its presently accepted meaning of sudden change in the temporal evolution of secular variation. A more complex

  19. Importance of selecting archaeomagnetic data for geomagnetic modelling: example of the new Western Europe directional and intensity secular variation curves from 1500 BC to 200 AD

    NASA Astrophysics Data System (ADS)

    Herve, Gwenael; Chauvin, Annick; Lanos, Philippe

    2014-05-01

    At the regional scale, the dispersion between archaeomagnetic data and especially archaeointensities suggests that some of them may be biased. As a consequence, it appears necessary to perform a selection of available data before to compute mean regional secular variation curves or geomagnetic models. However the definition of suitable selection criteria is not obvious and we need to know how to manage "old" data acquired during the 60-70s. The Western Europe directional and intensity data set from 1500 BC to 200 AD allows to discuss these issues. It has recently been enhanced by 39 new archaeodirections and 23 new archaeointensities (Hervé et al., 2013a and 2013b data sets and 5 unpublished data). First, the whole Western Europe data set was selected but the strong dispersion restricted the accuracy and the reliability of the new Western Europe secular variation curves at Paris. The causes of the dispersion appear different between archaeodirections and archaeointensities. In the directional data set, the main problem comes from some age errors in the oldest published data. Since their publication their archaeological dating may have changed of 50 years or more. For intensity data that were acquired much more recently, the dispersion mainly results from the use of unreliable archaeointensity protocols. We propose a weighting approach based on the number of specimens and the use of pTRM-checks, anisotropy and cooling rate corrections. Only 63% of available archaeodirections and 32% of archaeointensities were used to build the new Western Europe secular variation curves from 1500 BC to 200 AD. These curves reveal that selecting the reference data avoids wrong estimations of the shape of the secular variation curves, the secular variation rate, the dating of archaeomagnetic jerks... Finally, it is worth pointing out that current geomagnetic global models take into account almost all the data that we decided to reject. It could partly explain why their predictions at

  20. Holocene geomagnetic secular variation recorded by volcanic deposits at Mount St. Helens, Washington

    USGS Publications Warehouse

    Hagstrum, J.T.; Hoblitt, R.P.; Gardner, C.A.; Gray, T.E.

    2002-01-01

    A compilation of paleomagnetic data from volcanic deposits of Mount St. Helens is presented in this report. The database is used to determine signature paleomagnetic directions of products from its Holocene eruptive events, to assign sampled units to their proper eruptive period, and to begin the assembly of a much larger database of paleomagnetic directions from Holocene volcanic rocks in western North America. The paleomagnetic results from Mount St. Helens are mostly of high quality, and generally agree with the division of its volcanic deposits into eruptive episodes based on previous geologic mapping and radiocarbon dates. The Muddy River andesite's paleomagnetic direction, however, indicates that it is more likely part of the Pine Creek eruptive period rather than the Castle Creek period. In addition, the Two-Fingers andesite flow is more likely part of the Middle Kalama eruptive period and not part of the Goat Rocks period. The paleomagnetic data from Mount St. Helens and Mount Hood document variation in the geomagnetic field's pole position over the last ~2,500 years. A distinct feature of the new paleosecular variation (PSV) record, similar to the Fish Lake record (Oregon), indicates a sudden change from rapid clockwise movement of the pole about the Earth's spin axis to relatively slow counterclockwise movement at ???800 to 900 years B.P.

  1. A directional Secular Variation Curve for Greece for the last 4500 years: Comparison with regional and global geomagnetic field models

    NASA Astrophysics Data System (ADS)

    de Marco, E.; Tema, E.; Lanos, P.; Kondopoulou, D.

    2009-12-01

    A total of 64 Greek archaeomagnetic directional data have been used for the establishment of the variation of the Earth’s magnetic field in Greece over the past 4500 years. Most of the data come from archaeological material but some data from Santorini lava flows are also included. The data ages range from Minoan times (~2500 BC) up to the last century with a gap around 10th to 6th century BC. All data have been relocated to Athens (37.97° N, 23.72° E) using the virtual geomagnetic pole method. Data coming from direct measurements available in Greece for the last four centuries have been also added. The secular variation (SV) curves for declination and inclination have been obtained using hierarchical Bayesian modelling. For comparison, the dataset has been also analysed using the bi-variate moving average window technique with 150 years time window shifted by 75 years. The obtained smoothed curves accompanied by a 95 % confidence envelope are compared with archaeomagnetic data from Mediterranean area and with SV curves from nearby countries. The Greek curves have also been compared with the predictions of the SCHA.DIF.3K regional and the CALS7K and ARCH3K global geomagnetic field models. Despite the differences recognised between these models, the Greek archaeomagnetic SV curve is in reasonably good agreement with their basic trends. The proposed directional SV curve can contribute, together with the intensity SV curve previously published for Greece, to the reliable archaeomagnetic dating of Greek artefacts based on the full description of the Earth’s magnetic field (declination, inclination, intensity). It is clear that the continuous update of the dataset with new results from well-dated archaeological material will increase the precision of the SV curve, especially for the time periods poorly covered by data.

  2. Secular variation of the geomagnetic field over the past 4000 years recorded in the lavas and pyroclastics of the Northern Group of Kamchatka volcanoes: New data

    NASA Astrophysics Data System (ADS)

    Latyshev, A. V.; Kushlevich, D. O.; Ponomareva, V. V.; Pevzner, M. M.; Fedyukin, I. V.

    2017-09-01

    New paleomagnetic determinations satisfying the up-to-date methodical and instrumental standards of paleomagnetic studies are obtained from the lava flows and volcanic ash of the Northern Group of Kamchatka volcanoes. In the past 4000 years, 12 stratigraphic levels with tephrostratigraphic ages are explored. The obtained directions of the geomagnetic field fill a gap in the data on the secular variation for northeastern Asia and can be used for developing global models. Besides, a promising outlook for the use of the variations of the geomagnetic field for the regional correlation of volcanic events is demonstrated.

  3. Prospect of Using Numerical Dynamo Model for Prediction of Geomagnetic Secular Variation

    NASA Technical Reports Server (NTRS)

    Kuang, Weijia; Tangborn, Andrew

    2003-01-01

    Modeling of the Earth's core has reached a level of maturity to where the incorporation of observations into the simulations through data assimilation has become feasible. Data assimilation is a method by which observations of a system are combined with a model output (or forecast) to obtain a best guess of the state of the system, called the analysis. The analysis is then used as an initial condition for the next forecast. By doing assimilation, not only we shall be able to predict partially secular variation of the core field, we could also use observations to further our understanding of dynamical states in the Earth's core. One of the first steps in the development of an assimilation system is a comparison between the observations and the model solution. The highly turbulent nature of core dynamics, along with the absence of any regular external forcing and constraint (which occurs in atmospheric dynamics, for example) means that short time comparisons (approx. 1000 years) cannot be made between model and observations. In order to make sensible comparisons, a direct insertion assimilation method has been implemented. In this approach, magnetic field observations at the Earth's surface have been substituted into the numerical model, such that the ratio of the multiple components and the dipole component from observation is adjusted at the core-mantle boundary and extended to the interior of the core, while the total magnetic energy remains unchanged. This adjusted magnetic field is then used as the initial field for a new simulation. In this way, a time tugged simulation is created which can then be compared directly with observations. We present numerical solutions with and without data insertion and discuss their implications for the development of a more rigorous assimilation system.

  4. Investigations on geomagnetic secular variation anomalies through tectonomagnetic monitoring in the seismoactive zone of the Narmada-Son Lineament, Central India

    NASA Astrophysics Data System (ADS)

    Waghmare, S. Y.

    2009-12-01

    Data from repeated geomagnetic observations at exactly same location on the five profiles i.e. Katangi-Mandla (AA'), Mandla-Lakhnadon (BB'), Lakhnadon-Narsimhapur (CC'), Narsimhapur-Jabalpur (DD') and Jabalpur-Seoni (EE') have revealed secular variation of the total geomagnetic field in the tectonically/seismically active zone of the Narmada-Son Lineament (NSL), Central India. The seismicity in NSL, associated with the activation of boundary fault near Jabalpur, might have been responsible for the release of stress accumulated due to continuous northward movement of the Indian plate. The external magnetic field contributions (ionospheric/magnetospheric currents) as well as internal (secular trend of main field due to Earth's core electric currents) have been eliminated due to the operation of the reference base station within study area at Seismic Observatory Jabalpur. Proton Precession Magnetometers (PPMs) with sensitivity 0.1 nT were used simultaneously for measuring the total geomagnetic field intensity at the repeated-survey stations and reference station. The survey sites were visited annually wherein seven cycles of repeated observations were performed from 2003 to 2009. The simple difference method was used in data analysis and the residuals have been calculated as secular variations of the total geomagnetic field with values ranging from ±0.1 nT/yr to ±9.5 nT/yr at different stations. However, measurable seismic activity was not registered during the repeated survey period. It is proposed that secular changes originate from stress and tension on the NSL fault system and crustal blocks as a tectonomagnetic effect. However, the Geomagnetic Depth Sounding (GDS) experiment in Jabalpur area revealed high electrical conductivity anomaly (Satpura conductor) which has been interpreted due to fluids/saline water in the crust. There is a possibility for the fluids to flow through the porous rocks thereby generating electric currents to produce the electrokinetic

  5. Geomagnetic field model for the last 5 My: time-averaged field and secular variation

    NASA Astrophysics Data System (ADS)

    Hatakeyama, Tadahiro; Kono, Masaru

    2002-11-01

    Structure of the geomagnetic field has bee studied by using the paleomagetic direction data of the last 5 million years obtained from lava flows. The method we used is the nonlinear version, similar to the works of Gubbins and Kelly [Nature 365 (1993) 829], Johnson and Constable [Geophys. J. Int. 122 (1995) 488; Geophys. J. Int. 131 (1997) 643], and Kelly and Gubbins [Geophys. J. Int. 128 (1997) 315], but we determined the time-averaged field (TAF) and the paleosecular variation (PSV) simultaneously. As pointed out in our previous work [Earth Planet. Space 53 (2001) 31], the observed mean field directions are affected by the fluctuation of the field, as described by the PSV model. This effect is not excessively large, but cannot be neglected while considering the mean field. We propose that the new TAF+PSV model is a better representation of the ancient magnetic field, since both the average and fluctuation of the field are consistently explained. In the inversion procedure, we used direction cosines instead of inclinations and declinations, as the latter quantities show singularity or unstable behavior at the high latitudes. The obtained model gives reasonably good fit to the observed means and variances of direction cosines. In the TAF model, the geocentric axial dipole term ( g10) is the dominant component; it is much more pronounced than that in the present magnetic field. The equatorial dipole component is quite small, after averaging over time. The model shows a very smooth spatial variation; the nondipole components also seem to be averaged out quite effectively over time. Among the other coefficients, the geocentric axial quadrupole term ( g20) is significantly larger than the other components. On the other hand, the axial octupole term ( g30) is much smaller than that in a TAF model excluding the PSV effect. It is likely that the effect of PSV is most clearly seen in this term, which is consistent with the conclusion reached in our previous work. The PSV

  6. Low Amplitude of Geomagnetic Secular Variations Recorded in Traps of the Southern Siberian Platform: Very Fast Emplacement or Regional Remagnetization?

    NASA Astrophysics Data System (ADS)

    Veselovskiy, R. V.; Latyshev, A. V.; Pavlov, V. E.

    2011-12-01

    We have studied the lowest part of the Permo-Triassic Siberian trap sequence which is located in the middle course of the Angara river (Southern Siberia). This sequenced is composed by 200m thick volcanoclastic rocks (tuffs with bombs of different composition) and includes numerous mafic subvolcanic bodies (dykes and sills). Altogether more than 20 sites representing tuffs, bombs, dykes and sills stretched along the valley of the Angara river over the distance more than 30 km have been sampled and studied. Obtained site mean paleomagnetic directions are tightly grouped, showing very lower scatter. Taking into account that amplitude of geomagnetic secular variation at the P-T boundary was about of same order as in Late Cenozoic (Pavlov et al., 2011) this lower scatter can be either a sequence of very fast traps emplacement which could have disastrous environmental impact or a result of subsequent regional remagnetization. The only geological event in the region which seems to be capable to cause this remagnetization is emplacement of Early Triassic sills in nearby areas. In such the case we should expect that mean paleomagnetic directions from these sills will be very close to these ones obtained from site presented in this report. We present results of paleomagnetic studies of these sills and make a choice in favor of one of discussed options. This work was supported by grants NSF EAR 0807585 ("The Siberian Traps and end-Permian extinction") and RFBR 09-05-01180, 10-05-00557.

  7. Using “domino” model to study the secular variation of the geomagnetic dipolar moment

    NASA Astrophysics Data System (ADS)

    Duka, B.; Peqini, K.; De Santis, A.; Pavón-Carrasco, F. J.

    2015-05-01

    Aiming to understand the physical processes underneath the reversals events of geomagnetic field, different numerical models have been conceived. We considered here the so named “domino” model, an Ising-Heisenberg model of interacting magnetic macrospins aligned along a ring. This model was proposed by Mazaud and Laj (1989) and then applied by Mori et al. (2013) to study geomagnetic field reversals. The long series of the axial magnetic moment (dipolar moment or “magnetization”) generated by the “domino” model are empirically studied by varying all model parameters. We present here some results which are slightly different from those given by Mori et al. (2013), and will provide our explanation on the presence of these differences. We also define the set of parameters that supply the longest mean time between reversals. Using this set of parameters, a large number of time series of axial magnetic moment are also generated. After de-noising the fluctuation of these time series and averaging them, we compared the resulting averaged series with the series of axial dipolar magnetic moment values supplied by CALS7k.2, and CALS10k.1b models, finding similar behavior for the all time series. In a similar way, we also compared the averaged 14,000 years long series of dipolar moment with the dipolar magnetic moment obtained by the model SHA.DIF.14k.

  8. Geomagnetic secular variation recorded by sediments deposited during the Cretaceous normal superchron at low latitude

    NASA Astrophysics Data System (ADS)

    Linder, Julia; Gilder, Stuart A.

    2011-08-01

    Paleosecular variation of the Earth's magnetic field reflects the convective vigor of the geodynamo. To investigate the energy regime of the geodynamo during the Cretaceous normal superchron, we collected 534 samples for a paleosecular variation study from a 1400 m-long, paleontologically well-described section in northern Peru. Thermal demagnetization isolates stable magnetization directions carried by greigite. Arguments are equivocal whether this remanence is syn-diagenetic, acquired during the Cretaceous normal superchron, or a secondary overprint, acquired during a chron of solely normal polarity in the upper Cenozoic, yet pre-Bruhnes (>800 kyr). We explore the ramifications on the S value, which quantifies paleosecular variation, that arises from directional analysis, sun compass correction, bedding correction, sampling frequency, outlying directions and different recording media. The sum of these affects can readily raise the S value by more than 20%. S values from northern Peru are indistinguishable from other S values for the Cretaceous normal superchron as well as those for the last 5 Ma. Summing over all the potential uncertainties, we come to the pessimistic conclusion that the S value is an unsuitable parameter to constrain geodynamo models. Alternatively, no statistical difference in paleosecular variation exists during much of the Cretaceous normal superchron and during the last 5 Ma.

  9. Paleomagnetic directions and thermoluminescence dating from a bread oven-floor sequence in Lübeck (Germany): A record of 450 years of geomagnetic secular variation

    NASA Astrophysics Data System (ADS)

    Schnepp, Elisabeth; Pucher, Rudolf; Goedicke, Christian; Manzano, Ana; Müller, Uwe; Lanos, Philippe

    2003-02-01

    A record of about 450 years of geomagnetic secular variation is presented from a single archaeological site in Lübeck (Germany) where a sequence of 25 bread oven floors has been preserved in a bakery from medieval times until today. The age dating of the oven-floor sequence is based on historical documents, 14C-dating and thermoluminescence dating. It confines the time interval from about 1300 to 1800 A.D. Paleomagnetic directions have been determined from each oven floor by means of 198 oriented hand samples. After alternating field as well as thermal demagnetization experiments, the characteristic remanent magnetization direction was obtained using principal component analysis. The mean directions of 24 oven floors are characterized by high Fisherian precision parameters (>146) and small α95 confidence limits (1.2°-4.6°). For obtaining a smooth curve of geomagnetic secular variation for Lübeck, a spherical spline function was fitted to the data using a Bayesian approach, which considers not only the obtained ages, but also stratigraphic order. Correlation with historical magnetic records suggests that the age estimation for the upper 10 layers was too young and must date from the end of the sixteenth to the mid of the eighteenth century. For the lowermost 14 layers, dating is reliable and provides a secular variation curve for Germany. The inclination shows a minimum in the fourteenth century and then increases by more than 10°. Declination shows a local minimum around 1400 A.D. followed by a maximum in the seventeenth century. This is followed by the movement of declination about 30° to western directions.

  10. Long-term secular variation of the geomagnetic field during the last 200 kyr recorded in sediment cores from the western equatorial Pacific

    NASA Astrophysics Data System (ADS)

    Yamazaki, Toshitsugu; Ioka, Noboru

    1994-12-01

    We have conducted a paleomagnetic study of five hemipelagic-clay cores of 4-7 m in length obtained from the West Caroline Basin, western equatorial Pacific. The purpose of this study is to clarify the long-term secular variation of the geomagnetic field during the last 200 kyr, using both intensity and directional changes. One core was dated using oxygen isotope ratios (delta O-18), and characteristic magnetic susceptibility variations of about a factor of four allowed precise correlation between all cores. The magentic mineralogy is estimated to be dominated by magnetite of single-domain (SD) and/or pseudo-single-domain (PSD) state. The magnetic mineralogy and grain size are uniform throughout the cores, which enabled us to obtain relative paleointensity variations as well as directional changes. Remanent intensity normalized by anhysteretic remanent magnetization (ARM) indicates that sharp intensity drops (to less than or = 20% of the present field) occurred at about 40 and 190 kyr B.P., with a broader decrease around 110 kyr B. P. The former two are accompanied by anomalous remanent directions, suggesting short polarity reversals or excursions. Their ages are close to those of the previously reported Laschamp excursion and Biwa I event. A prominent intensity peak occurred immediately preceding the possible excursion at 40 kyr B.P. Our results are in general similar to the recently reported datasets spanning the last 80-140 kyr from the Somali Basin, the Mediterranean, and the Sulu Sea. The inclination record shows long-term cyclic changes of several degrees in amplitude. The intervals of the recurring variation are 40-50 kyr, which is longer than the core's memory and is close to the Milankovitch frequency associated with the change in obliquity of Earth's rotational axis. We infer that an external force such as orbital forcing could be a cause of the long-term secular variation.

  11. Secular variation of the middle and late Miocene geomagnetic field recorded by the Columbia River Basalt Group in Oregon, Idaho and Washington, USA

    NASA Astrophysics Data System (ADS)

    Dominguez, Ada R.; Van der Voo, Rob

    2014-06-01

    This study of 118 discrete volcanic flows from the Columbia River Basalt Group is aimed to determine their distribution of geomagnetic field directions and virtual geomagnetic poles (VGPs) and to compare the inherent secular variation parameters with those from other studies. The magnetic signature of these rocks is uniformly carried by primary titanomagnetite, indicating that magnetic changes are due to variations in the magnetic field. Although most flows are flat lying, those that are tilted pass the Tauxe and Watson tilt test. Sequential flows with statistically similar site means were grouped, and directions that were considered outliers were evaluated and removed using the Vandamme cut-off method. Three normal-polarity (N-polarity) and three reversed-polarity (R-polarity) intervals are revealed by the stratigraphically ordered flows and have mean directions of N polarity (dec/inc = 6.6°/+61.2°, k = 29.3, α95 = 4.2°), and R polarity (dec/inc = 178.2°/-59.2°, k = 16, α95 = 5.5°). Regression analysis indicates that the secular variation analysis has not been affected by regional rotation, and that apparent polar wander is negligible. The VGP distribution is almost perfectly circular and supports the preference of VGP positions for the dispersion analysis. Dispersion parameters with corrections for within-site scatter (Sb) show a range of 14.3°-25.5°, including error limits, and were consistently higher for R-polarity results than for those of N polarity. Published dispersion parameters for extrusives <5 Ma show Sb values slightly lower than ours, yielding values of 16°-19°, although the difference is not statistically significant. In contrast, published dispersion parameters from high quality data from the Cretaceous Normal Superchron are lower than those for the Neogene, which suggests that the noisiness of the magnetic field correlates with the frequency of reversals. Our new results allow us to extend the Plio-Pleistocene palaeosecular variation

  12. Evaluation of using R-SCHA to simultaneously model main field and secular variation multilevel geomagnetic data for the North Atlantic

    NASA Astrophysics Data System (ADS)

    Talarn, Àngela; Pavón-Carrasco, F. Javier; Torta, J. Miquel; Catalán, Manuel

    2017-02-01

    One efficient approach to modelling the Earth's core magnetic field involves the inclusion of crossover marine data which cover areas lacking in observatory and repeat station data for epochs when precise three-component satellite magnetic field measurements were not common. In this study, we show how the Revised Spherical Cap Harmonic Analysis (R-SCHA) can appropriately provide a continuous-time field model for the North Atlantic region by using multilevel sets of geomagnetic data such as marine, repeat station, observatory, and satellite data. Taking advantage of the properties of the R-SCHA basis functions we can model the radial and horizontal variations of the main field and its secular variation with the most suitable spatial and temporal wavelengths. To assess the best compromise between the data fit and the model roughness, temporal and spatial regularization matrices were implemented in the modelling approach. Two additional strategies were also used to obtain a satisfactory regional model: the opportunity to fit the anomaly bias at each observatory location, and constraining the regional model to the CHAOS-6 model at the end of its period of validity, i.e. 1999-2000, allowing a smooth transition with the predictions of this recent model. In terms of the root mean square error, the degree of success was limited partly because of the high uncertainties associated with some of the datasets (especially the marine ones), but we have produced a model that performs comparably to the global models for the period 1960-2000, thus showing the benefits of using this regional technique.

  13. Palaeomagnetic investigations on lake sediments from NE China: a new record of geomagnetic secular variations for the last 37 ka

    NASA Astrophysics Data System (ADS)

    Frank, Ute

    2007-04-01

    Detailed palaeomagnetic investigations were carried out on two 23 m long sediment cores from Erlongwan maar lake, NE China. The sediment composition of both cores is nearly identical. Based on a macroscopical inspection of the cores 410 graded layers intercalated into the laminated sediments were identified. Measurements of the anisotropy of the magnetic susceptibility revealed that these layers have not disturbed the sediment structure in general, but only in intervals where their thicknesses exceeds 50 cm. The age model for Erlongwan is based on 15 AMS 14C-datings on bulk sediment, showing that the sediment profile spans the last 37 ka cal BP. Although one of the sediment cores has been slightly deformed during core recovery, similar inclination and declination records could be obtained by standard palaeomagnetic methods. The stacked inclination and declination records show both variations similar to those known from palaeosecular variation records from Eastern China and Japan. Therefore, the presented study is a contribution to the ongoing process of compiling a PSV mastercurve for East Asia.

  14. A paleomagnetic study of secular variation in New Zealand

    USGS Publications Warehouse

    Cox, A.

    1969-01-01

    Ancient secular variation in New Zealand was determined from paleomagnetic measurements on 22 volcanic formations with ages of less than 0.68 m.y. The angular standard deviation from the field of an axial dipole is 13.2?? with 95% confidence limits between 10.9?? and 16.7??. The angular standard deviation of the corresponding virtual geomagnetic poles is 19.6?? with confidence limits between 16.2?? and 24.7??. These values are larger than those predicted by most models for secular variation. No difference was detected between the angular secular variation in New Zealand and that at the same latitude in North America. ?? 1969.

  15. Main field and recent secular variation.

    USGS Publications Warehouse

    Alldredge, L.R.

    1983-01-01

    As Cain (1979) indicated might happen in the last IUGG quadrennial report, added resources were made available during the past few years and a real impulse was added to the geomagnetic work in the US by the launching of the MAGSAT Satellite. This new effort paid off in terms of new charts, additional long wavelength studies, and external source studies. As before, however, the future funding for new starts in geomagnetism does not look bright at the present time. A single MAGSAT in orbit a little more than seven months did wonders for main field (M.F.) charting, but did little or nothing for secular variation (S.V.) charting. It would take a number of repeated MAGSATS to help the S.V. picture. Meanwhile, the world magnetic observatory net and surface repeat stations remain as the main source of S.V. data. -from Author

  16. Paleomagnetic secular variation study of Ar-Ar dated lavas flows from Tacambaro area (Central Mexico): Possible evidence of Intra-Jaramillo geomagnetic excursion in volcanic rocks

    NASA Astrophysics Data System (ADS)

    Peña, Rafael Maciel; Goguitchaichvili, Avto; Guilbaud, Marie-Noëlle; Martínez, Vicente Carlos Ruiz; Rathert, Manuel Calvo; Siebe, Claus; Reyes, Bertha Aguilar; Morales, Juan

    2014-04-01

    More than 350 oriented paleomagnetic cores were obtained for rock-magnetic and paleomagnetic analysis from radiometrically dated (40Ar-39Ar) magmatic rocks occurring in the southern segment (Jorullo and Tacámbaro areas) of the Michoacán-Guanajuato Volcanic Field in the Trans-Mexican Volcanic Belt. Most of the lavas (37) stem from monogenetic volcanoes dated at less than 4 Ma. Two additional sites were sampled from the plutonic basement dated at 33-30 Ma. Primary remanences carried by low-Ti titanomagnetites allowed to determining 34 reliable site-mean directions of mostly normal (27) but also reversed (7) polarities. The mean directions of these two populations are antipodal, and suggest neither major vertical-axis rotations with respect to the North America craton nor tilting in the region for the last 4 Ma (rotation and flattening of the inclination parameters being less than -5.9 ± 3.8 and 0.1 ± 3.9, respectively). The corresponding paleomagnetic pole obtained for Pliocene-Pleistocene times is PLAT = 83.4°, PLON = 2.4° (N = 32, A95 = 2.7°). Virtual geomagnetic poles also contribute to the time averaged field global database and to the paleosecular variation (PSV) investigations at low latitudes from lavas for the last 5 Ma, showing a geomagnetic dispersion value that is in agreement with available PSV models. When comparing the magnetic polarities and corresponding radiometric ages of the studied sites with the Cenozoic geomagnetic polarity time scale (GPTS), a good correlation is observable. This finding underscores the suitability of data obtained on lavas in Central Mexico for contributing to the GPTS. Furthermore, the detection of short-lived geomagnetic features seems possible, since the possible evidence of Intra-Jaramillo geomagnetic excursion could be documented for the first time in these volcanic rocks.

  17. Secular trends in storm-level geomagnetic activity

    USGS Publications Warehouse

    Love, J.J.

    2011-01-01

    Analysis is made of K-index data from groups of ground-based geomagnetic observatories in Germany, Britain, and Australia, 1868.0-2009.0, solar cycles 11-23. Methods include nonparametric measures of trends and statistical significance used by the hydrological and climatological research communities. Among the three observatory groups, German K data systematically record the highest disturbance levels, followed by the British and, then, the Australian data. Signals consistently seen in K data from all three observatory groups can be reasonably interpreted as physically meaninginful: (1) geomagnetic activity has generally increased over the past 141 years. However, the detailed secular evolution of geomagnetic activity is not well characterized by either a linear trend nor, even, a monotonic trend. Therefore, simple, phenomenological extrapolations of past trends in solar and geomagnetic activity levels are unlikely to be useful for making quantitative predictions of future trends lasting longer than a solar cycle or so. (2) The well-known tendency for magnetic storms to occur during the declining phase of a sunspot-solar cycles is clearly seen for cycles 14-23; it is not, however, clearly seen for cycles 11-13. Therefore, in addition to an increase in geomagnetic activity, the nature of solar-terrestrial interaction has also apparently changed over the past 141 years. ?? Author(s) 2011.

  18. Historic and paleomagnetic secular variation and the earth's core dynamo process.

    NASA Astrophysics Data System (ADS)

    Lund, S. P.; Olson, P.

    1987-06-01

    This paper attempts to summarize briefly the recent and ongoing efforts of the geomagnetism and paleomagnetism community to understand both the earth's magnetic-field secular variation, and its implications for the core dynamo process.

  19. Secular variations of tropospheric ozone

    NASA Astrophysics Data System (ADS)

    Khrgian, A. Kh.

    1988-02-01

    The dependence of secular variations of tropospheric ozone on decreases of temperature and cloud growth in Central Europe is assessed on the basis of Vienna, Paris, and Athens data for 1853-1920. Decreases in ozone content occurring with a certain time lag after major volcanic eruptions (e.g., Krakatoa) are examined. The effect of the Tungusk-meteorite fall on ozone content is also discussed.

  20. A study of alternative schemes for extrapolation of secular variation at observatories

    USGS Publications Warehouse

    Alldredge, L.R.

    1976-01-01

    The geomagnetic secular variation is not well known. This limits the useful life of geomagnetic models. The secular variation is usually assumed to be linear with time. It is found that attenative schemes that employ quasiperiodic variations from internal and external sources can improve the extrapolation of secular variation at high-quality observatories. Although the schemes discussed are not yet fully applicable in worldwide model making, they do suggest some basic ideas that may be developed into useful tools in future model work. ?? 1976.

  1. Secular obliquity variations for Ceres

    NASA Astrophysics Data System (ADS)

    Bills, Bruce; Scott, Bryan R.; Nimmo, Francis

    2016-10-01

    We have constructed secular variation models for the orbit and spin poles of the asteroid (1) Ceres, and used them to examine how the obliquity, or angular separation between spin and orbit poles, varies over a time span of several million years. The current obliquity is 4.3 degrees, which means that there are some regions near the poles which do not receive any direct Sunlight. The Dawn mission has provided an improved estimate of the spin pole orientation, and of the low degree gravity field. That allows us to estimate the rate at which the spin pole precesses about the instantaneous orbit pole.The orbit of Ceres is secularly perturbed by the planets, with Jupiter's influence dominating. The current inclination of the orbit plane, relative to the ecliptic, is 10.6 degrees. However, it varies between 7.27 and 11.78 degrees, with dominant periods of 22.1 and 39.6 kyr. The spin pole precession rate parameter has a period of 205 kyr, with current uncertainty of 3%, dominated by uncertainty in the mean moment of inertia of Ceres.The obliquity varies, with a dominant period of 24.5 kyr, with maximum values near 26 degrees, and minimum values somewhat less than the present value. Ceres is currently near to a minimum of its secular obliquity variations.The near-surface thermal environment thus has at least 3 important time scales: diurnal (9.07 hours), annual (4.60 years), and obliquity cycle (24.5 kyr). The annual thermal wave likely only penetrates a few meters, but the much long thermal wave associated with the obliquity cycle has a skin depth larger by a factor of 70 or so, depending upon thermal properties in the subsurface.

  2. Refined permo-triassic paleomagnetic pole for the Siberian platform and geomagnetic secular variations at the Paleozoic-Mesozoic boundary as recorded in volcanic traps key sections of northern Siberia

    NASA Astrophysics Data System (ADS)

    Pavlov, V. E.; Veselovskiy, R. V.; Khokhlov, A.; Latyshev, A. V.; fluteau, F.

    2011-12-01

    Two new volcanic key sections of the Siberian traps erupted ~ 250 million years ago have been studied in the Norilsk region (NW of the Siberian platform). Along with results obtained earlier from both this area (Heunemann et al., 2004) and Maymecha-Kotuy region (northern Siberian platform, Pavlov et al., 2011) these data constitute rather extensive database, including paleomagnetic information on about 200 volcanic flows. Using this information we can not only get refined permo-triassic paleomagnetic pole for the Siberian platform, based exceptionally on lava flows data, but also estimate amplitude of geomagnetic secular variation at the Paleozoic-Mesozoic boundary and check their compatibility with statistic models, suggested for description of recent (Late Cenozoic) Earth's magnetic field. Moreover, our results can be also used to obtain additional time constraints on duration of the trap emplacement and to isolate volcanic pulses within the traps sections. We present a report where we discuss all these topics. This work was supported by grants NSF # EAR 0807585 and RBRF #09-05-01180, 11-05-00601,10-05- 00557.

  3. Magnetic Navigation in Sea Turtles: Insights from Secular Variation

    NASA Astrophysics Data System (ADS)

    Putman, N. F.; Lohmann, K.

    2011-12-01

    Sea turtles are iconic migrants that posses a sensitive magnetic-sense that guides their long-distance movements in a variety of contexts. In the first few hours after hatching turtles use the magnetic field to maintain an offshore compass heading to reach deeper water, out of the reach of nearshore predators. Young turtles engage in directed swimming in response to regional magnetic fields that exist along their transoceanic migratory path. Older turtles also use magnetic information to relocate foraging sites and islands used for nesting after displacement. Numerous hypotheses have been put forth to explain how magnetic information functions in these movements, however, there is little consensus among animal navigation researchers. A particular vexing issue is how magnetic navigation can function under the constraints of the constant, gradual shifting of the earth's magnetic field (secular variation). Here, I present a framework based on models of recent geomagnetic secular variation to explore several navigational mechanisms proposed for sea turtles. I show that while examination of secular variation likely falsifies some hypothetical navigational strategies, it provides key insights into the selective pressures that could maintain other navigational mechanisms. Moreover, examination of secular variation's influence on the navigational precision in reproductive migrations of sea turtles offers compelling explanations for the population structure along sea turtle nesting beaches as well as spatiotemporal variation in nesting turtle abundance.

  4. Mineral magnetism and geomagnetic secular variation of marine and lacustrine sediments from central Italy: timing and nature of local and regional Holocene environmental change

    NASA Astrophysics Data System (ADS)

    Rolph, Timothy C.; Vigliotti, Luigi; Oldfield, Frank

    2004-07-01

    Sediment core palaeomagnetic and mineral magnetic records from two crater lakes in central Italy and from the western margin of the Adriatic Sea have been used to evaluate local and regional responses to Holocene environmental change. In all cores, sediment magnetism reflects the interplay between catchment material and the in situ production of bacterial magnetite (magnetotactic bacteria). In the lakes, the earliest Holocene sediments record a waning catchment input that we attribute to rising lake levels and increased tree cover in the catchment. From ˜9000 to 5000 yr BP, both lakes become anoxic, a consequence of water-mass stratification driven by high lake levels. Bottom-water anoxia also developed in the Adriatic, with sapropel S1 produced between ˜9000 and 7000 yr BP. Subsequently, the lake and Adriatic mineral magnetic records show evidence for increased catchment delivery, consistent with pollen evidence for Bronze Age deforestation. In the lakes, this evidence is first recorded at ˜4300 yr BP and a number of distinct clearance events are recorded. In comparison, at Adriatic site RF93-30, lithogenic input increases abruptly at ˜3500 yr BP and is followed by a slowly changing record of waxing and waning sediment delivery. Inter-site comparisons of palaeomagnetic data point to a possible link between the magnitude of the bacterial magnetite component and the recorded magnetic inclination. The sites are at near identical latitudes and have similar sediment accumulation rates but the Adriatic sites have a core-average magnetic inclination that is some 10° steeper than the lake average values. We suggest that the large dipole moment of the magnetosome chains, which in life produce the passive alignment of the bacterium along the local geomagnetic field line, produce a more faithful (albeit smoothed) record of the geomagnetic field.

  5. Secular Variation in Slip (Invited)

    NASA Astrophysics Data System (ADS)

    Cowgill, E.; Gold, R. D.

    2010-12-01

    Faults show temporal variations in slip rate at time scales ranging from the hours following a major rupture to the millions of years over which plate boundaries reorganize. One such behavior is secular variation in slip (SVS), which we define as a pulse of accelerated strain release along a single fault that occurs at a frequency that is > 1 order of magnitude longer than the recurrence interval of earthquakes within the pulse. Although numerous mechanical models have been proposed to explain SVS, it has proven much harder to measure long (5-500 kyr) records of fault displacement as a function of time. Such fault-slip histories may be obtained from morphochronologic data, which are measurements of offset and age obtained from faulted landforms. Here we describe slip-history modeling of morphochronologic data and show how this method holds promise for obtaining long records of fault slip. In detail we place SVS in the context of other types of time-varying fault-slip phenomena, explain the importance of measuring fault-slip histories, summarize models proposed to explain SVS, review current approaches for measuring SVS in the geologic record, and illustrate the slip-history modeling approach we advocate here using data from the active, left-slip Altyn Tagh fault in NW Tibet. In addition to SVS, other types of temporal variation in fault slip include post-seismic transients, discrepancies between geologic slip rates and those derived from geodetic and/or paleoseismic data, and single changes in slip rate resulting from plate reorganization. Investigating secular variation in slip is important for advancing understanding of long-term continental deformation, fault mechanics, and seismic risk. Mechanical models producing such behavior include self-driven mode switching, changes in pore-fluid pressure, viscoelasticity, postseismic reloading, and changes in local surface loads (e.g., ice sheets, large lakes, etc.) among others. However, a key problem in testing these

  6. Improving late Holocene radiocarbon-based chronologies by matching paleomagnetic secular variations to geomagnetic field models - Examples from Nam Co (Tibet) and Lake Kalimpaa (Sulawesi)

    NASA Astrophysics Data System (ADS)

    Haberzettl, T.; Kasper, T.; St-Onge, G.; Behling, H.; Daut, G.; Doberschütz, S.; Kirleis, W.; Mäusbacher, R.; Nowaczyk, N.

    2010-12-01

    Precise age control is a prerequisite for reliable paleoenvironmental reconstruction. Almost all Holocene chronologies of lacustrine sequences are based on radiocarbon dating. Most reliable ages are obtained from fragile terrestrial vegetation remnants (e.g., leaves) as these neither yield a reservoir or hard water effect nor are reworked as they would be destroyed during this process. However, in many records no terrestrial plant remains or macro remains in general are found in the sediments. In this case the only option to establish a radiocarbon based chronology is to date bulk sediment. This sediment sometimes contains reworked material or, in hard water lakes, aquatic organic remains which contain old carbon - both resulting in older ages. Here we present two records dated by bulk material showing these inconveniences. Nam Co is a hard water lake on the Tibetan Plateau (30.5°N, 91°E). Previous studies from various sites in this lake revealed different hard water effects. A radiocarbon date of bulk sediment from the top of a gravity core yielded an age of 1420 ±40 BP for the sediment/water interface. In order to test if this value can be constantly extrapolated back in time we established a reservoir corrected chronology with this value. Subsequently, we compared inclination and declination data to the CALS3k.3 and the CALS7k geomagnetic field models which currently provide the best representation of the late Holocene geomagnetic field. This showed excellent accordance for the period covered by the gravity core, i.e., ~4000 cal BP. Lake Kalimpaa (1.3°S, 120.3°E) is located on the island of Sulawesi, Indonesia. Radiocarbon-dated bulk samples also showed inconsistencies. Most likely not only the autochthonous carbon fraction was dated but also some allochthonous organic matter was incorporated into the samples. If this is the case, all ages are tentatively too old. Following a conservative approach, in order to minimize this error, only the youngest dates

  7. Are secular correlations between sunspots, geomagnetic activity, and global temperature significant?

    USGS Publications Warehouse

    Love, J.J.; Mursula, K.; Tsai, V.C.; Perkins, D.M.

    2011-01-01

    Recent studies have led to speculation that solar-terrestrial interaction, measured by sunspot number and geomagnetic activity, has played an important role in global temperature change over the past century or so. We treat this possibility as an hypothesis for testing. We examine the statistical significance of cross-correlations between sunspot number, geomagnetic activity, and global surface temperature for the years 1868-2008, solar cycles 11-23. The data contain substantial autocorrelation and nonstationarity, properties that are incompatible with standard measures of cross-correlational significance, but which can be largely removed by averaging over solar cycles and first-difference detrending. Treated data show an expected statistically- significant correlation between sunspot number and geomagnetic activity, Pearson p < 10-4, but correlations between global temperature and sunspot number (geomagnetic activity) are not significant, p = 0.9954, (p = 0.8171). In other words, straightforward analysis does not support widely-cited suggestions that these data record a prominent role for solar-terrestrial interaction in global climate change. With respect to the sunspot-number, geomagnetic-activity, and global-temperature data, three alternative hypotheses remain difficult to reject: (1) the role of solar-terrestrial interaction in recent climate change is contained wholly in long-term trends and not in any shorter-term secular variation, or, (2) an anthropogenic signal is hiding correlation between solar-terrestrial variables and global temperature, or, (3) the null hypothesis, recent climate change has not been influenced by solar-terrestrial interaction. ?? 2011 by the American Geophysical Union.

  8. Historical variation of the geomagnetic axial dipole

    NASA Astrophysics Data System (ADS)

    Finlay, Christopher C.

    2008-09-01

    The geomagnetic axial dipole (hereinafter denoted g10) is the largest component of our planet's magnetic field. Its magnitude determines the morphology of solar-terrestrial electrical current systems and it is the most fundamental diagnostic property of the core-generated geodynamo. Elucidating past and future variations of g10(t) is consequently of central importance in geomagnetism. Previous historical geomagnetic field models, such as gufm1 of Jackson et al. [Jackson, A., Jonkers, A.R.T., Walker, M.R., 2000. Four centuries of geomagnetic secular variation from historical records. Philos. Trans. R. Soc. Lond. A 358, 957-990], used direct observations to constrain g10(t) only after 1840 A.D.; before this time a crude linear extrapolation of the post-1840 A.D. rate of change (15 nT/year) was employed. In this contribution I construct historical field models with g10(t) instead constrained from 1590 A.D. to 1840 A.D. by an archaeointensity dataset compiled by Korte et al. [Korte, M., Genevey, A., Constable, C.G., Frank, U., Schnepp, E., 2005. Continuous geomagnetic field models for the past 7 millennia. 1. A new global data compilation. Geochem. Geophys. Geosyst. 6, doi:10.1029/2004GC000800]. A range of possible linear models of the form g10(t)=g10(1840)+β(t-1840) are first explored; β=2.74±42.32 nT/year is found to explain the archaeointensity dataset with maximum likelihood, consistent with the recent findings of Gubbins et al. [Gubbins, D., Jones, A.L., Finlay, C.C., 2006. Fall in Earth's magnetic field is erratic. Science 312, 900-902]. Relaxing the linear constraint in an effort to find more physically plausible models, I find it is necessary to artificially increase the weight given to the archaeointensity data in order to obtain acceptable models. Despite satisfactorily explaining both the historical and archaeointensity data, and possessing reasonable spatial and temporal complexity, such free evolution models perform worse than the simpler linearly

  9. Secular variations around 2000 obtained from satellite and observatory data

    NASA Astrophysics Data System (ADS)

    Bondar, T.; Golovkov, V.; Yakovleva, S.

    2003-04-01

    SECULAR VARIATIONS AROUND 2000 OBTAINED FROM SATELLITE AND OBSERVATORY DATA T. Bondar, V. Golovkov and S. Yakovleva Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation RAS IZMIRAN, Troitsk, Moscow Reg., 142190, Russia golovkov@izmiran.rssi.ru/FAX: +7-095-3340124 Using coefficients of models, developed on base of the satellite measurements of the geomagnetic vector (missions Magsat and Oersted), as well as SV coefficients in model by Olsen (2002) a space-time model of the geomagnetic field changes on the time interval of 20 yrs duration was developed. Coefficients of this ST model were obtained as the Taylor series up to second derivative. Obtained parabolic space-time model was compared with data series from magnetic observatories. It is shown that deviation of this completely satellite based model relative observatory time series is rather big due to the geomagnetic jerk about 1990. Space-time model derived from data from observatories describes variations better but only for area covered enough with observatories. False foci over SE Pacific reach hundreds nT. A new approach of joint use of satellite and observatory data is proposed. This technique of space-time analysis permits decreasing averaged errors to a few tens nT on whole time interval and whole Earth’s surface including large ocean areas.

  10. Lunar nitrogen: Secular variation or mixing?

    NASA Technical Reports Server (NTRS)

    Norris, S. J.; Wright, I. P.; Pillinger, C. T.

    1986-01-01

    The two current models to explain the nearly 40% variation of the lunar nitrogen isotopic composition are: (1) secular variation of solar wind nitrogen; and (2) a two component mixing model having a constant, heavy solar wind admixed with varying amounts of indigenous light lunar N (LLN). Both models are needed to explain the step pyrolysis extraction profile. The secular variation model proposes that the low temperature release is modern day solar wind implanted into grain surfaces, the 900 C to 1100 C release is from grain surfaces which were once exposed to the ancient solar wind but which are now trapped inside agglutinates, and the >1100 C release as spallogenic N produced by cosmic rays. The mixing model ascribes the components to solar wind, indigenous lunar N and spallogenic N respectively. An extension of either interpretation is that the light N seen in lunar breccias or deep drill cores represent conditions when more N-14 was available to the lunar surface.

  11. Two-scale model of a geomagnetic field variation

    NASA Technical Reports Server (NTRS)

    Braginsky, S. I.; Le Mouel, J. L.

    1993-01-01

    The effect of the vertical scale is investigated by considering a simple kinematic two-scale model of fluid flow inducing a variable magnetic field. Depending on the time constant, the induced magnetic field displays a variety of behaviors and geometries. In the high-frequency case, for example, a strong magnetic field tangential to the core mantle boundary, and hidden in the Delta layer, can be generated. A detailed computation and description of this magnetic field are presented. Some possible features of the secular variation of the actual geomagnetic field are discussed in the light of the model proposed here.

  12. Independently dated paleomagnetic secular variation records from the Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Haberzettl, T.; Henkel, K.; Kasper, T.; Ahlborn, M.; Su, Y.; Appel, E.; St-Onge, G.; Stoner, J. S.; Daut, G.; Wang, J.; Zhu, L.; Maeusbacher, R.

    2014-12-01

    Magnetostratigraphy has been serving as a valuable tool for dating and confirming chronologies of lacustrine sediments in many parts of the world. However, suitable paleomagnetic records on the Tibetan Plateau (TP) and adjacent areas are extremely scarce. Here, independently radiocarbon dated sediments of two lakes on the southern central TP, Tangra Yumco and Taro Co some 250 km further west, were investigated for their potential to record paleomagnetic secular variations. Multiple sediment cores resemble a very similar inclination pattern for the past 4000 years. This demonstrates the high potential of inclination to compare records over the Tibetan Plateau and eventually date other Tibetan records stratigraphically. Comparisons to an existing record from Nam Co, a lake 350 km west of Tangra Yumco, a varve dated record from the Makran Accretionary Wedge, and a stack record from East Asia reveal many similarities. However, model output data of geomagnetic field models for the coordinates of Tangra Yumco do not agree with our findings.

  13. Evaluation of the 1985-1990 IGRF secular variation candidates

    USGS Publications Warehouse

    Cain, J.C.; Kluth, C.

    1987-01-01

    The IGRF secular variation model for 1985-1990 was adopted by the International Association of Geomagnetism and Aeronomy at its Prague meeting in August 1985 as an average of the three candidate models submitted to the committee. We compared the three models at epoch 1985.0 against each other and against a new model based on observatory data available as of July 1, 1985. These comparisons showed that one of the three candidate models disagreed more with the other two and our model, especially in the eastern Pacific. None of the candidate models was seen to respond to a change in the secular variation of the vertical component that appears to have taken place most strongly in the western Pacific area since 1982. The lack of satellite data was seen to be a significant handicap towards prediction of the field change over most of the Earth's surface, especially the southern oceans. Maximum errors of any model are estimated to be of the order of 80 nT a-1. ?? 1987.

  14. Secular obliquity variations of Ceres and Pallas

    NASA Astrophysics Data System (ADS)

    Bills, Bruce G.; Scott, Bryan R.

    2017-03-01

    We examine variations in the orientations of the orbit poles and spin poles of Ceres and Pallas, on time scales of a few million years. We consider these two bodies together because they have similar orbits, but very different present states of knowledge concerning internal mass distribution and spin pole orientation. For Ceres, the Dawn mission has recently provided accurate estimates of the current spin pole orientation, and the degree 2 spherical harmonics of the gravitational potential. The polar moment of inertia is not as well constrained, but plausible bounds are known. For Pallas, we have estimates of the shape of the body, and spin pole orientation and angular rate, all derived from optical light curves. Using those input parameters, and the readily computed secular variations in the orbit pole, we can compute long term variations in the spin pole orientation. This provides information concerning long term variations in insolation, which controls stability of surface volatiles.

  15. Evaluation of a new paleosecular variation activity index as a diagnostic tool for geomagnetic field variations

    NASA Astrophysics Data System (ADS)

    Panovska, Sanja; Constable, Catherine

    2015-04-01

    Geomagnetic indices like Dst, K and A, have been used since the early twentieth century to characterize activity in the external part of the modern geomagnetic field and as a diagnostic for space weather. These indices reflect regional and global activity and serve as a proxy for associated physical processes. However, no such tools are yet available for the internal geomagnetic field driven by the geodynamo in Earth's liquid outer core. To some extent this reflects limited spatial and temporal sampling for longer timescales associated with paleomagnetic secular variation, but recent efforts in both paleomagnetic data gathering and modeling activity suggest that longer term characterization of the internal geomagnetic weather/climate and its variability would be useful. Specifically, we propose an index for activity in paleosecular variation, useful as both a local and global measure of field stability during so-called normal secular variation and as a means of identifying more extreme behavior associated with geomagnetic excursions and reversals. To date, geomagnetic excursions have been identified by virtual geomagnetic poles (VGPs) deviating more than some conventional limit from the geographic pole (often 45 degrees), and/or by periods of significant intensity drops below some critical value, for example 50% of the present-day field. We seek to establish a quantitative definition of excursions in paleomagnetic records by searching for synchronous directional deviations and lows in relative paleointensity. We combine paleointensity variations with deviations from the expected geocentric axial dipole (GAD) inclination in a single parameter, which we call the paleosecular variation (PSV) activity index. This new diagnostic can be used on any geomagnetic time series (individual data records, model predictions, spherical harmonic coefficients, etc.) to characterize the level of paleosecular variation activity, find excursions, or even study incipient reversals

  16. RESEARCH PAPERS : Secular variation of the poloidal magnetic field at the core-mantle boundary

    NASA Astrophysics Data System (ADS)

    Bhattacharyya, Archana

    1998-01-01

    A region of enhanced conductivity at the base of the mantle is modelled by an infinitesimally thin sheet of uniform effective conductance adjacent to the core-mantle boundary. Currents induced in this sheet by the temporally varying magnetic field produced by the geodynamo give rise to a discontinuity in the horizontal components of the poloidal magnetic field on crossing the sheet, while the radial component is continuous across the sheet. Treating the rest of the mantle as an insulator, the horizontal components of the poloidal magnetic field and their secular variation at the top of the core are determined from geomagnetic field, secular variation and secular acceleration models. It is seen that for an assumed effective conductance of the sheet of 108 S, which may be not unrealistic, the changes produced in the horizontal components of the poloidal field at the top of the core are usually <=10 per cent, but corrections to the secular variation in these components at the top of the core are typically 40 per cent, which is greater than the differences that exist between different secular variation models for the same epoch. Given the assumption that all the conductivity of the mantle is concentrated into a thin shell, the present method is not restricted to a weakly conducting mantle. Results obtained are compared with perturbation solutions.

  17. Fluctuations in tides and geomagnetic variations

    NASA Astrophysics Data System (ADS)

    Kohsiek, A.; Kiefer, M.; Meek, C. E.; Manson, A. H.

    Middle atmosphere tidal winds and the daily geomagnetic Sq-variation show a day-to-day variability, both with a local behaviour. Due to the main cause of the Sq-variation, the ionospheric dynamo effect, day-to-day fluctuation of Sq could be raised by fluctuations in tides. This coupling of fluctuations is investigated with radar wind data measured at Saskatoon at around 100 km height and with magnetic data from four observatories in the vicinity of the radar. We show that our definition of fluctuations exhibits properties of atmospheric tides in the winds and that the magnetic data can be assumed to represent a local behaviour. We find that there are some significant correlations between fluctuations in winds and magnetic variations. Apparently the local fluctuation of geomagnetic variations is weakly coupled not only to the fluctuations of the semidiurnal tides but also to those of the mean winds.

  18. Secular variation of the Earth's magnetic field and application to paleomagnetic dating of historical lava flows in Chile

    NASA Astrophysics Data System (ADS)

    Roperch, Pierrick; Chauvin, Annick; Lara, Luis E.; Moreno, Hugo

    2015-05-01

    The recent geomagnetic secular variation is mainly characterized by the large growth of the South Atlantic Magnetic Anomaly during the last three centuries, first documented by the geomagnetic model gufm1 (Jackson et al., 2000). We report new paleomagnetic results (directions and paleointensities) from several sites in two well dated lava flows in Chile, the 1835 AD eruption of the Osorno volcano and the 1751 AD eruption of the Llaima volcano. In addition, paleointensities were obtained on 14 samples from bricks of shelters built along the main road across the Andes from Santiago (Chile) to Mendoza (Argentina) in 1770 ± 5 AD. The results confirm the high reliability of the global geomagnetic model gufm1 for the last three centuries with a large amplitude of the secular variation in inclination (∼20°) and intensity (∼25 μT). Results from three 14C dated volcanic units in the time interval 1400-1750 AD indicate that more paleomagnetic results in well dated lava flows are necessary to improve the robustness of existing global geomagnetic models. At this stage, precise paleomagnetic or archeomagnetic dating in South America using global models should be restricted to the last 3 centuries. To illustrate the potential of paleomagnetic dating in region and time interval with very large geomagnetic secular variation, we report paleomagnetic data from several sites in historical lava flows (1700-1900 AD) from the Antuco, Llaima and Villarrica volcanoes that permit to refine the ages of the major historical effusive volcanic events.

  19. Solar generated quasi-biennial geomagnetic variation

    NASA Technical Reports Server (NTRS)

    Sugiura, M.; Poros, D. J.

    1977-01-01

    The existence of highly correlated quasi-biennial variations in the geomagnetic field and in solar activity is demonstrated. The analysis uses a numerical filter technique applied to monthly averages of the geomagnetic horizontal component and of the Zurich relative sunspot number. Striking correlations are found between the quasi-biennial geomagnetic variations determined from several magnetic observatories located at widely different longitudes, indicating a worldwide nature of the obtained variation. The correlation coefficient between the filtered Dst index and the filtered relative sunspot number is found to be -0.79 at confidence level greater than 99% with a time-lag of 4 months, with solar activity preceding the Dst variation. The correlation between the unfiltered data of Dst and of the sunspot number is also high with a similar time-lag. Such a timelag has not been discussed in the literature, and a further study is required to establish the mode of sun-earth relationship that gives this time delay.

  20. Secular variation of the Earth magnetic field recorded in Holocene lava flows from Chile

    NASA Astrophysics Data System (ADS)

    Roperch, Pierrick; Chauvin, Annick; Lara, Luis; Moreno, Hugo

    2014-05-01

    The recent secular variation of the Earth's magnetic field is mainly characterized by the large growth of the South Atlantic Magnetic Anomaly during the last three centuries, first documented in the geomagnetic field model GUFM (Jackson et al., 2000). This present-day magnetic anomaly is characterized in Chile by low magnetic inclinations and low intensities of the geomagnetic field (-40° and 25.7µT at 40°S). In order to better describe the secular variation during the Holocene, we sampled 21 dated lava flows or pyroclastic flows from several Chilean volcanoes (Lonquimay, Llaima, Solipulli, Villarrica, Mocho-Choshuenco, Osorno, Calbuco). Juvenile clasts from basaltic-andesitic pyroclastic flow deposits provide reliable paleomagnetic results (Roperch et al, 2014). We also sampled 56 sites in Holocene lava flows with only relative ages with respect of the dated units. Paleomagnetic results were obtained from several sites in two well-dated historic lava flows; 9 sites and 11 paleointensity results (PI) from the 1835AD eruption of the Osorno volcano and 8 sites and 23 PIs from the 1751AD eruption of the Llaima volcano. In addition, 14 PIs were obtained in bricks from shelters built along the main path across the Andes from Santiago (Chile) to Mendoza (Argentina) in 1768AD. These results confirm the high reliability of the global geomagnetic model GUFM for the last three centuries. At Villarrica, results from 10 sites in lava flows (calibrated age 1440AD±30) provide paleomagnetic directions that are different from the CALS3k.4 model (Korte et al., 2011) indicating that more paleomagnetic results in well dated lava flows are necessary to improve the robustness of global geomagnetic models prior to 1700AD. The steepest inclination of the geomagnetic field (-71.6°) and the highest intensity (70µT±5) are found in the time range 850-900AD. This observation is made from paleomagnetic results from a pyroclastic flow from the Osorno volcano (calibrated age range of 782

  1. Secular variation and core-flow modelling with stable strafication at the top of the core

    NASA Astrophysics Data System (ADS)

    Holme, Richard; Buffett, Bruce

    2015-04-01

    Observed geomagnetic secular variation has been used for many years to provide an observational constraint on the dynamics of the core through the modelling of its surface flow. Recent results in both seismology and mineral physics provide strong evidence of a stably stratified layer at the top of the core, which has substantial implications for the calculation of such flows. It has been assumed for many years that the dynamic state at the core surface is close to tangentially geostrophic, and pure stable stratification also requires a flow to be toroidal. Combining these two conditions requires variations in flow that are completely zonal toroidal, which are known not to provide an adequate explanation of the observed secular variation. However, a stably stratified layer can support flow instabilities of a more general character. Buffett (2014) has recently provided a model in which zonal toroidal motions are associated with the excitation of a zonal poloidal instability. This model is able to explain the broad variation of the axial dipole over the past 100 years, and also to explain feature of geomagnetic jerks that cannot be explained by purely torsional motions. This model has inspired a new generation of core-flow models, with a substantial time-varying zonal poloidal component, something that is absent from most models of core surface flow. Here, we present these new models, and consider to what extent this flow structure can explain the details of secular variation. We also consider the implications for the connection between core-surface flow and length-of-day variation - a stably stratified layer has implications for the interpretation of core flow and the Earth's angular momentum budget. Finally, we consider the ability of core-surface flow models to probe the structure of the stably- stratified layer. Buffett (2014). Geomagnetic fluctuations reveal stable stratification at the top of the Earth's core, Nature 507, 484-487, doi:10.1038/nature13122

  2. Derivation and use of core surface flows for forecasting secular variation

    NASA Astrophysics Data System (ADS)

    Whaler, K. A.; Beggan, C. D.

    2015-03-01

    Improving forecasts of the temporal and spatial changes of the Earth's main magnetic field over periods of less than 5 years has important scientific and economic benefits. Various methods for forecasting the rate of change, or secular variation, have been tried over the past few decades, ranging from the extrapolation of trends in ground observatory measurements to computational geodynamo modeling with data assimilation from historical magnetic field models. We examine the utility of an intermediate approach, using temporally varying core surface flow models derived from relatively short periods of magnetic field data to produce, by advection, secular variation estimates valid for the Earth's surface. We describe a new method to compute a core flow changing linearly with time from magnetic secular variation and acceleration data. We invert a combination of data from the CHAMP satellite mission and ground observatories over the period 2001.0 to 2010.0 for a series of such models. We assess their ability to forecast magnetic field changes by comparing them to CHAOS-4, a state-of-the-art model using data from 1997 to 2014.5. We show that the magnetic field predictions tend to have a lower root-mean-square difference from CHAOS-4 than the International Geomagnetic Reference Field or World Magnetic Map series of secular variation models.

  3. Holocene paleomagnetic secular variation records from the East China Sea

    NASA Astrophysics Data System (ADS)

    Zheng, Y.; Zheng, H.; Kissel, C.; Laj, C. E.; Deng, C.

    2011-12-01

    Paleomagnetic study on marine sediments can provide continuous, high-resolution records of short-term fluctuations of the Earth's magnetic field, which can be used for inter-core correlations at regional scale. However, Holocene paleomagnetic secular variation (PSV) records from marine sediment are still rare. Detailed paleomagnetic and rock magnetic studies were conducted on u-channel samples from rapidly deposited sediment core MD06-3040 (27.72°N, 121.78°E; 46 m water depth), on the East China Sea (ECS) inner continental shelf Holocene marine sequence, during IMAGES XIV Marco Polo 2 cruise on the R. V. Marion Dufresne (IPEV). The 19.22 m long core spans the entire Holocene, with theoretical high-resolution of about 20-year for paleomagnetic studies, and paleomagnetic secular variation (PSV) for the last 7500 years was retrieved from the uppermost 15.8 m fine-grained sediments. The dominant carrier of the remanent magnetization is magnetite, with some contributions from iron sulfide, such as greigite below 3.5 m, due to post-depositional diagenesis. The Characteristic Remanent magnetization (ChRM) is well defined by a single magnetization component and Maximum Angular Deviations (MAD) lower than 5°. Therefore, the information of paleomagnetic directions is still preserved after diagenetic alteration. Inclination of core MD06-3040 presents seven relatively high peaks, and declination presents four obvious eastern ward drifts during the last 7500 years. These variations can be well compared to that obtained from lakes in Japan, and some features are also comparable to the records from Europe with temporal offset. The power spectrum analysis shows that the inclination has significant power at the period of ~660 years, and declination at the period of ~3500 years and 1300 years. These periods are similar to that from Japan and North America, in which the period of ~1300 years for declination has been reported in many areas around the world. The observed PSV from

  4. Variations in the geomagnetic dipole moment during the Holocene and the past 50 kyr

    NASA Astrophysics Data System (ADS)

    Knudsen, Mads Faurschou; Riisager, Peter; Donadini, Fabio; Snowball, Ian; Muscheler, Raimund; Korhonen, Kimmo; Pesonen, Lauri J.

    2008-07-01

    All absolute paleointensity data published in peer-reviewed journals were recently compiled in the GEOMAGIA50 database. Based on the information in GEOMAGIA50, we reconstruct variations in the geomagnetic dipole moment over the past 50 kyr, with a focus on the Holocene period. A running-window approach is used to determine the axial dipole moment that provides the optimal least-squares fit to the paleointensity data, whereas associated error estimates are constrained using a bootstrap procedure. We subsequently compare the reconstruction from this study with previous reconstructions of the geomagnetic dipole moment, including those based on cosmogenic radionuclides ( 10Be and 14C). This comparison generally lends support to the axial dipole moments obtained in this study. Our reconstruction shows that the evolution of the dipole moment was highly dynamic, and the recently observed rates of change (5% per century) do not appear unique. We observe no apparent link between the occurrence of archeomagnetic jerks and changes in the geomagnetic dipole moment, suggesting that archeomagnetic jerks most likely represent drastic changes in the orientation of the geomagnetic dipole axis or periods characterized by large secular variation of the non-dipole field. This study also shows that the Holocene geomagnetic dipole moment was high compared to that of the preceding ˜ 40 kyr, and that ˜ 4 · 10 22 Am 2 appears to represent a critical threshold below which geomagnetic excursions and reversals occur.

  5. Long Term Geomagnetic Variations and Whole-Mantle Convection Processes

    NASA Astrophysics Data System (ADS)

    Biggin, A. J.; Steinberger, B. M.; Aubert, J.; Suttie, N.; Holme, R.; Torsvik, T. H.; van der Meer, D.; Van Hinsbergen, D. J.

    2012-12-01

    It has long been suspected that palaeomagnetically-observed variations in geomagnetic behaviour occurring over tens to hundreds of millions of years result from changes in core-mantle boundary (CMB) heat flow, itself controlled by lower mantle dynamics. Furthermore, the last few decades have seen numerous claims of causal relations between the palaeomagnetic record and surface events inferred from the geological record that invoke whole-mantle convection processes (sinking slabs, rising plumes, and true polar wander). Recent findings in seismology, geodynamics, and the numerical simulation of both mantle convection and the geodynamo do provide qualitative support for such ideas. CMB heat flow is probably highly heterogeneous and susceptible to substantial changes through variations in locations and rates of subduction, plume flux, or simply by rotations of the entire pattern with respect to the geodynamo via true polar wander (TPW). Numerical geodynamo modelling suggests that long term geomagnetic behaviour is sensitive to changes in total heat flow and its spatial pattern but cannot yet quantitatively confirm that the variations we expect to see in CMB heat flow over tens to hundreds of Myr (up to several tens of percent) are sufficient to modify the behaviour as observed. The most dramatic change in long-term geomagnetic behaviour observed in the last 200 Myr was between the mid-Jurassic (~ 170 Myr ago) and the mid-Cretaceous (~ 120 Myr ago) when average reversal frequency decreased from > 8 Myr-1 to < 0.1 Myr-1, mean field intensity appeared to increase by a factor of ~ 2, and the pattern of secular variation became much more stable. This transition was coincident with a major TPW event that probably moved patches of high CMB heat flux towards higher latitudes, a process which geodynamo models suggest would cause changes to geomagnetic behaviour similar to those observed. Consequently, we suspect that TPW played a role in causing this transition. TPW may not be

  6. Secular variation curves of Mexico, progress, problems and needs

    NASA Astrophysics Data System (ADS)

    Soler-Arechalde, A. M.

    2013-05-01

    Three cases of secular variation of Mexico will be analyzed. The first is the preliminary results of the record of the transition Bruhnes-Matuyama in a paleosol sequence. The second is the research of a rock shelter since late Pliocene-early Holocene to Posclassic (AD 900-1527). Finally the improvement of the first archaeomagnetic secular variation curve of Mesoamerica from 1973 to 2012 with the inclusion of new results like La Ciudadela and Teopancazco of Teotihuacan, Tlatelolco and Templo Mayor of Mexico City and Tula. Our results will be compared with previous records from lake sediments and volcanic rocks, the models available like CALS*K or other published curves.

  7. Geomagnetic Field Variations as Determined from Bulgarian Archaeomagnetic Data. Part II: The Last 8000 Years

    NASA Astrophysics Data System (ADS)

    Kovacheva, Mary; Jordanova, Neli; Karloukovski, Vassil

    The knowledge about past secular variations of the geomagnetic field is achieved on the basis of archaeomagnetic researches of which the Bulgarian studies form an extended data set. In Part I (Kovacheva and Toshkov, 1994), the methodology used in the Sofia palaeomagnetic laboratory was described and the secular variation curves for the last 2000 years were shown. In Part II (this paper), the basic characteristics of the prehistoric materials used in the archaeomagnetic studies are emphasised, particularly in the context of the rock magnetic studies used in connection with palaeointensity determinations. The results of magnetic anisotropy studies of the prehistoric ovens and other fired structures are summarised, including the anisotropy correction of the palaeointensity results for prehistoric materials, different from bricks and pottery. Curves of the direction and intensity of the geomagnetic field during the last 8000 years in Bulgaria are given. The available directional and intensity values have been used to calculate the variation curve of the virtual dipole moment (VDM) for the last 8000 years based on different time interval averages. The path of virtual geomagnetic pole (VGP) positions is discussed.

  8. Secular Variation Across the Oceans: a Retrospective Study from 35 Years of Shipboard Total Field Measurements in the NE Atlantic

    NASA Technical Reports Server (NTRS)

    Williams, C. A.; Verhoef, J.; Macnab, R.

    1992-01-01

    This is a pilot study to determine whether secular variation information can be retrieved from underway shipboard total field measurements with sufficient accuracy to complement geomagnetic data from land-based observatories. Applying the various new techniques described in this report, we extracted values of the total field at 42,677 crossovers or ship track intersection points contained in data sets collected between 18 degrees N and 50 degress N in the NE Atlantic, and extending temporally from 1955 to 1990. We used an edited subset of these total field values to derive the secular variation at 30,140 different locations in the study area, and compared the results with DGRF secular variation over the study area, calculated at 5 year intervals. The derived and DGRF values agree well, showing that indeed marine data can be a source for secular variations. However the analysis demonstrated that due to inherent noise in the marine data, only minor improvements on the DGRF values for the secular variation can be achieved.

  9. Secular variation study from non-welded pyroclastic deposits from Montagne Pelée volcano, Martinique (West Indies)

    NASA Astrophysics Data System (ADS)

    Genevey, A.; Gallet, Y.; Boudon, G.

    2002-07-01

    We present palaeomagnetic data obtained from large clasts collected in non-welded pyroclastic deposits from Montagne Pelée volcano (Martinique Island, West Indies). These deposits, dated by the 14C method from 5000 yr BP to the present, comprise block- and ash-flows, ash- and pumice-flows and pumice fallouts. Alternating fields treatment was as a routine chosen to demagnetise large samples for which the magnetisation was measured with a specially designed inductometer. The mean directions obtained from block- and ash-flow deposits of the 1902 and 1929 eruptions are in good agreement with the expected geomagnetic directions at these times in Martinique. The so-called P1 eruption (˜1345 AD), which is characterised by a rarely observed transition from a Peléean to a Plinian eruptive style, allows a direct comparison of the palaeomagnetic directions obtained from the three types of pyroclastic deposits. All deposits provide identical mean directions, which further demonstrates the suitability of the non-welded pyroclastic deposits for geomagnetic secular variation study with a very good accuracy and precision. The possibility of using pyroclastic deposits is promising for obtaining a wider distribution of sampling sites, which may better allow us to constrain our knowledge on the geomagnetic secular variation. We find that large geomagnetic changes occurred in Martinique during the last millennium, while the variations appear more limited prior to this period.

  10. The quasi-biennial variation in the geomagnetic field: a global characteristics analysis

    NASA Astrophysics Data System (ADS)

    Ou, Jiaming; Du, Aimin

    2016-04-01

    The periodicity of 1.5-3 years, namely the quasi-biennial oscillation (QBO), has been identified in the solar, geophysical, and atmospheric variability. Sugiura (1976) investigated the observatory annual means over 1900-1970 and confirmed the QBO in the geomagnetic field. At present, studying the quasi-biennial oscillation becomes substantial for separating the internal/external parts in the geomagnetic observations. For the internal field, two typical periodicities, namely the 6-year oscillation in the geomagnetic secular acceleration (SA) and the geomagnetic jerk (occurs in 1-2 years), have close period to the QBO. Recently, a global quasi-biennial fluctuation was identified in the geomagnetic core field model (Silva et al., 2012). Silva et al. speculated this 2.5 years signal to either external source remaining in the core field model or consequence of the methods used to construct the model. As more high-quality data from global observatories are available, it is a good opportunity to characterize the geomagnetic QBO in the global range. In this paper, we investigate the QBO in the observatory monthly geomagnetic field X, Y, and Z components spanning 1985-2010. We employ the observatory hourly means database from the World Data Center for Geomagnetism (WDC) for the investigation. Wavelet analysis is used to detect and identify the QBO, while Fast Fourier Transform (FFT) analysis to obtain the statistics of the QBO. We apply the spherical harmonic analysis on QBO's amplitude, in order to quantify and separate internal and external sources. Three salient periods respectively at 2.9, 2.2, and 1.7 years, are identified in the amplitude spectrum over 1988-2008. The oscillation with the period of ~2.2 years is most prominent in all field components and further studied. In the X component the QBO is attenuated towards the polar regions, while in the Z component the amplitude of QBO increases with increasing of the geomagnetic latitude. At the high latitudes, the QBO

  11. Secular variation of a metallic asteroid dynamo

    NASA Astrophysics Data System (ADS)

    Bryson, J. F. J.; Harrison, R. J.; Neufeld, J. A.; Nimmo, F.; Herrero-Albillos, J.; Kronast, F.; Weiss, B. P.

    2015-12-01

    The mechanisms by which inward core solidification may drive dynamo activity, and the properties of any fields that may result from this process, are highly uncertain. The fast cooling rates of the IVA iron meteorites suggest that their parent core had its silicate mantle removed by planetary collisions during the early solar system. Due to the resulting rapid radiative surface cooling, the IVA parent core solidified from the top-down, permitting a cold metallic crust that feasibly experienced fields generated by the hot interior liquid as it inwardly solidified. The IVA meteorites therefore potentially contain unique paleomagnetic information regarding top-down solidification. Through x-ray microscopy of the cloudy zone in the Steinbach and Chinautla meteorites and traditional paleomagnetic measurements on silicates extracted from the Steinbach, Bishop Canyon and São João Nepomuceno meteorites, we argue that the IVA parent core generated an intense (>100 μT) and secularly varying (time-scale <100 kyr) field during top-down solidification. These results show that certain iron meteorites are capable of having experienced dynamo fields, and that asteroids can generate directionally varying magnetic activity, strengthening claims that the fundamentals of dynamo activity are consistent across small and large bodies. Models of the thermochemical evolution and solidification of an unmantled core suggest that this field resulted from liquid motion induced by the repeated delamination and sinking of material from the base of the inwardly solidifying crust. This efficient dynamo generation mechanism was likely capable of readily creating magnetic activity at the slow cooling rates expected within mantled, inwardly solidifying cores (e.g., Mercury, Ganymede, many asteroids). Combining this observation with that of efficient solidification-driven dynamos during bottom-up asteroid core solidification, it is likely that magnetic activity was widespread in the early solar

  12. Long-term variation in the upper atmosphere as seen in the geomagnetic solar quiet daily variation

    NASA Astrophysics Data System (ADS)

    Shinbori, Atsuki; Koyama, Yukinobu; Nose, Masahito; Hori, Tomoaki; Otsuka, Yuichi; Yatagai, Akiyo

    2014-12-01

    Characteristics of long-term variation in the amplitude of solar quiet (Sq) geomagnetic field daily variation have been investigated using 1-h geomagnetic field data obtained from 69 geomagnetic observation stations within the period of 1947 to 2013. The Sq amplitude observed at these geomagnetic stations showed a clear dependence on the 10- to 12-year solar activity cycle and tended to be enhanced during each solar maximum phase. The Sq amplitude was the smallest around the minimum of solar cycle 23/24 in 2008 to 2009. The relationship between the solar F10.7 index and Sq amplitude was approximately linear but about 53% of geomagnetic stations showed a weak nonlinear relation to the solar F10.7 index. In order to remove the effect of solar activity seen in the long-term variation of the Sq amplitude, we calculated a linear or second-order fitting curve between the solar F10.7 index and Sq amplitude during 1947 to 2013 and examined the residual Sq amplitude, which is defined as the deviation from the fitting curve. As a result, the majority of trends in the residual Sq amplitude that passed through a trend test showed negative values over a wide region. This tendency was relatively strong in Europe, India, the eastern part of Canada, and New Zealand. The relationship between the magnetic field intensity at 100-km altitude and residual Sq amplitude showed an anti-correlation for about 71% of the geomagnetic stations. Furthermore, the residual Sq amplitude at the equatorial station (Addis Ababa) was anti-correlated with the absolute value of the magnetic field inclination. This implies movement of the equatorial electrojet due to the secular variation of the ambient magnetic field.

  13. Secular trends and geographical variations in sex ratio at birth.

    PubMed

    Pavic, Dario

    2015-12-01

    Numerous studies have established the presence of secular trends and geographical variations in sex ratio at birth, albeit with mixed and often contradictory results. In addition, a multitude of environmental, social, economic, demographic and other factors has been proposed to influence the sex ratio at birth, thus complicating the interpretation of both secular trends and geographical variations. In this paper, the current state of knowledge on these issues is presented and critically assessed. Analyzing longer time series of sex ratio at birth with possible cycles and random components is given priority over establishing simple linear trends in the data. In analyzing the geographical variation in the sex ratio at birth, two different levels of analysis are distinguished (global and local), and two different sets of factors affecting the sex ratio at birth are proposed accordingly. Some key guidelines and future research directions are also proposed.

  14. Geomagnetic Variations of Near-polar Regions and Human Health

    NASA Astrophysics Data System (ADS)

    Tchistova, Z. B.; Kutinov, Y. G.

    In polar region geomagnetic variations play active role to non-linear tectonic processes. This analysis is based on spatial-time spectral representation of geomagnetic variation and wave migration transformation. Many perturbations in electromagnetic fields may because by external factors (e.g. magnetic storms, ionosphere anomalies and other phenomena related to solar activity) "trigging" tectonic processes but having no direct relation to the processes of their preparation. Geophysical processes are responsible for perturbations in Earth's rotation and orientation on wide range of time-scale, from less than a day of millions of years. The geological structure of some sites of Earth's crust promotes occurrence of wave guides a number of geophysical fields (acoustic, seismic, electromagnetic), usually of transportation of acoustic, seismic, electromagnetic energy in Earth's crust are coincide spatially. During last 250 mln years Arctic Segment has been developing as an autonomous region with circumpolar zonality of geomagnetic fields, and mass - and-energy transfer in its bowlers as well as shitting of lithospheric plates and expansion of ocean are caused by rotation forces under of expanding planet. The dynamic structure of the geomagnetic variations may be characteriz ed by the variations of the order-chaos state. The order manifest itself in the rhythmic change of the medium state. Analysis of amplitude and phase of geomagnetic variations can be information on ecological state of regions. Geomagnetic variations is intrincically a multiscale process in time and space. One of the most important features of geomagnetic variations is multicyclic character, whish predetermined both extent and character of geomagnetic show, and specific features. Recently, there are collected many facts, show dependence between the processes in the Earth's biosphere, the elements of it, gelio- geo- physical and meteorological factors. The recent experimental data gives us opportunity

  15. A Secular Variation Model for Igrf-12 Based on Swarm Data and Inverse Geodynamo Modelling

    NASA Astrophysics Data System (ADS)

    Fournier, A.; Aubert, J.; Erwan, T.

    2014-12-01

    We are proposing a secular variation candidate model for the 12th generation of the international geomagnetic reference field, spanning the years 2015-2020. The novelty of our approach stands in the initialization of a 5-yr long integration of a numerical model of Earth's dynamo by means of inverse geodynamo modelling, as introduced by Aubert (GJI, 2014). This inverse technique combines the information coming from the observations (in the form of an instantaneous estimate of the Gauss coefficients for the magnetic field and its secular variation) with that coming from the multivariate statistics of a free run of a numerical model of the geodynamo. The Gauss coefficients and their error covariance properties are determined from Swarm data along the lines detailed by Thébault et al. (EPS, 2010). The numerical model of the geodynamo is the so-called Coupled Earth Dynamo model (Aubert et al., Nature, 2013), whose variability possesses a strong level of similarity with that of the geomagnetic field. We illustrate and assess the potential of this methodology by applying it to recent time intervals, with an initialization based on CHAMP data, and conclude by presenting our SV candidate, whose initialization is based on the 1st year of Swarm data This work is supported by the French "Agence Nationale de la Recherche" under the grant ANR-11-BS56-011 (http://avsgeomag.ipgp.fr) and by the CNES. References: Aubert, J., Geophys. J. Int. 197, 1321-1334, 2014, doi: 10.1093/gji/ggu064 Aubert, J., Finlay, C., Fournier, F. Nature 502, 219-223, 2013, doi: 10.1038/nature12574 Thébault E. , A. Chulliat, S. Maus, G. Hulot, B. Langais, A. Chambodut and M. Menvielle, Earth Planets Space, Vol. 62 (No. 10), pp. 753-763, 2010.

  16. An empirical model of the quiet daily geomagnetic field variation

    USGS Publications Warehouse

    Yamazaki, Y.; Yumoto, K.; Cardinal, M.G.; Fraser, B.J.; Hattori, P.; Kakinami, Y.; Liu, J.Y.; Lynn, K.J.W.; Marshall, R.; McNamara, D.; Nagatsuma, T.; Nikiforov, V.M.; Otadoy, R.E.; Ruhimat, M.; Shevtsov, B.M.; Shiokawa, K.; Abe, S.; Uozumi, T.; Yoshikawa, A.

    2011-01-01

    An empirical model of the quiet daily geomagnetic field variation has been constructed based on geomagnetic data obtained from 21 stations along the 210 Magnetic Meridian of the Circum-pan Pacific Magnetometer Network (CPMN) from 1996 to 2007. Using the least squares fitting method for geomagnetically quiet days (Kp ??? 2+), the quiet daily geomagnetic field variation at each station was described as a function of solar activity SA, day of year DOY, lunar age LA, and local time LT. After interpolation in latitude, the model can describe solar-activity dependence and seasonal dependence of solar quiet daily variations (S) and lunar quiet daily variations (L). We performed a spherical harmonic analysis (SHA) on these S and L variations to examine average characteristics of the equivalent external current systems. We found three particularly noteworthy results. First, the total current intensity of the S current system is largely controlled by solar activity while its focus position is not significantly affected by solar activity. Second, we found that seasonal variations of the S current intensity exhibit north-south asymmetry; the current intensity of the northern vortex shows a prominent annual variation while the southern vortex shows a clear semi-annual variation as well as annual variation. Thirdly, we found that the total intensity of the L current system changes depending on solar activity and season; seasonal variations of the L current intensity show an enhancement during the December solstice, independent of the level of solar activity. Copyright 2011 by the American Geophysical Union.

  17. Estimating the change in asymptotic direction due to secular changes in the geomagnetic field

    NASA Technical Reports Server (NTRS)

    Flueckiger, E. O.; Smart, D. F.; Shea, M. A.; Gentile, L. C.; Bathurat, A. A.

    1985-01-01

    The concept of geomagnetic optics, as described by the asymptotic directions of approach, is extremely useful in the analysis of cosmic radiation data. However, when changes in cutoff occur as a result of evolution in the geomagnetic field, there are corresponding changes in the asymptotic cones of acceptance. A method is introduced of estimating the change in the asymptotic direction of approach for vertically incident cosmic ray particles from a reference set of directions at a specific epoch by considering the change in the geomagnetic cutoff.

  18. Comments on 'Remarks on the secular change in the energy density spectrum of the geomagnetic field' by Joachim Meyer.

    USGS Publications Warehouse

    Alldredge, L.R.

    1986-01-01

    Meyer has discussed only the Rn aspect of the Alldredge (1984) paper he is criticising. He has ignored the pictorial demonstration of the need for higher harmonics to properly describe the secular variation field than the main field as demonstrated. This more or less independent demonstration supports the general conclusion of that paper. -from Author

  19. Interplanetary magnetic field and geomagnetic Dst variations.

    NASA Technical Reports Server (NTRS)

    Patel, V. L.; Desai, U. D.

    1973-01-01

    The interplanetary magnetic field has been shown to influence the ring current field represented by Dst. Explorer 28 hourly magnetic field observations have been used with the hourly Dst values. The moderate geomagnetic storms of 60 gammas and quiet-time fluctuations of 10 to 30 gammas are correlated with the north to south change of the interplanetary field component perpendicular to the ecliptic. This change in the interplanetary field occurs one to three hours earlier than the corresponding change in the Dst field.

  20. A first secular variation curve for the Iberian Peninsula

    NASA Astrophysics Data System (ADS)

    Núñez, J. I.; Osete, M. L.; Ruiz-Martínez, V. C.; Fabien, A.; Tarling, D. H.

    2003-04-01

    A palaeomagnetic study has been carried out at 22 archaeological sites in the Iberian Peninsula. These new results together with data from 4 sites previously studied in Iberia and data from neighbouring countries (southern of France and northern Morocco) have been compiled in order to obtain a first Secular Variation Curve for the Iberian Peninsula. Data from France and Morocco were selected from the Archaeomagnetic Database compiled by the Dept. of Geological Sciences, University of Plymouth, UK (D. Tarling). The selection criteria adopted was the following: Dating errors <50 years, number of samples > 5 and α95 < 3^o. A total amount of 54 data points with ages ranging from 200 BC up to 1500 AD have been used to construct the Madrid Preliminary Secular Variation Curve for the Iberian Peninsula, albeit with a gap between the 7th and 10th centuries. Palaeomagnetic directions were corrected to Madrid, using the Via-Pole Conversion method (Noel and Batt, 1990, Geoph. J. Inter, 70, 201--204). A 100 year something window moving in 50 years increments was applied to the data.

  1. Holocene Full-Vector Secular Variation from African Lakes

    NASA Astrophysics Data System (ADS)

    Lund, S.; Platzman, E. S.; Johnson, T. C.; Scholz, C. A.; Cohen, A. S.; Russell, J. M.

    2014-12-01

    We are developing a regional pattern of Holocene paleomagnetic secular variation (PSV) from four lakes in East Africa - Lake Turkana (3°N), Lake Victoria (1°S), Lake Tanganyika (5°S), and Lake Malawi (10°S). Detailed paleomagnetic and rock magnetic measurements have been made on two cores from Lake Malawi (9m meters in depth, last ~10,000 years), two cores from Lake Victoria (8 m, last ~8,000 years), 11 cores from Lake Turkana (2-9 m, last ~10,000 years), and one core from Lake Tanganyika (5 m, last ~5,000 years). Our rock magnetic studies identify significant intervals of magnetic mineral dissolution in Lakes Victoria and Tanganyika making parts of these cores unsuitable for relative paleointensity studies. On the other hand, rock magnetic variability in the Lake Malawi and Lake Turkana cores are stable and correlatable among cores. We have recovered directional secular variation records from Lakes Malawi, Victoria, and Turkana. Millennial-scale inclination and declination features can be correlated among cores at each lake and between lakes. We have also recovered relative paleointensity records from Lakes Malawi and Turkana. More than 20 radiocarbon dates and detailed seismic stratigraphy (Turkana) provide critical added information for correlating and dating the paleomagnetic records.

  2. Features of the Geomagnetic Variations In the Moscow Region

    NASA Astrophysics Data System (ADS)

    Riabova, Svetlana; Spivak, Alexander

    2017-04-01

    The results of instrumental observations indicate the presence of significant amplitude variations in Earth's magnetic field. The data obtained in the research of geomagnetic variations allow us to not only establish and classify their sources, but also to form the basis for the improvement and development of new source models of magnetospheric and ionospheric disturbances, new methods of magnetotelluric and magnetovariational sensing and diagnostic methods of geodynamic state of the Earth's crust and the research of meteorological processes in the atmosphere. In this research we used the results of instrumental observations of geomagnetic field, carried out in the period of 2009 - 2015 at Geophysical Observatory "Mikhnevo" of Institute of Geosphere Dynamics of Russian Academy of Sciences. The observatory (54,960N; 37,774E) is located in the Moscow region. The analysis shows that in general the geophysical situation in the Moscow region is disturbed. The tendency to increasing in geomagnetic activity over time is established (the number of days with a perturbed state of the geomagnetic field is increased by 7.6 times during the period of 2009 - 2015). Repeatability of geomagnetic disturbances is characterized by clearly pronounced periodicity with characteristic periods of about 14, 27, 60, 182 and 365 days.

  3. Fast geomagnetic field intensity variations between 1400 and 400 BCE: New archaeointensity data from Germany

    NASA Astrophysics Data System (ADS)

    Hervé, Gwenaël; Faβbinder, Jörg; Gilder, Stuart A.; Metzner-Nebelsick, Carola; Gallet, Yves; Genevey, Agnès; Schnepp, Elisabeth; Geisweid, Leonhard; Pütz, Anja; Reuβ, Simone; Wittenborn, Fabian; Flontas, Antonia; Linke, Rainer; Riedel, Gerd; Walter, Florian; Westhausen, Imke

    2017-09-01

    Thirty-five mean archaeointensity data were obtained on ceramic sherds dated between 1400 and 400 BCE from sites located near Munich, Germany. The 453 sherds were collected from 52 graves, pits and wells dated by archaeological correlation, radiocarbon and/or dendrochronology. Rock magnetic analyses indicate that the remanent magnetization was mainly carried by magnetite. Data from Thellier-Thellier experiments were corrected for anisotropy and cooling rate effects. Triaxe and multispecimen (MSP-DSC) protocols were also measured on a subset of specimens. Around 60% of the samples provide reliable results when using stringent criteria selection. The 35 average archaeointensity values based on 154 pots are consistent with previous data and triple the Western Europe database between 1400 and 400 BCE. A secular variation curve for central-western Europe, built using a Bayesian approach, shows a double oscillation in geomagnetic field strength with intensity maxima of ∼70 μT around 1000-900 BCE and another up to ∼90 μT around 600-500 BCE. The maximum rate of variation was ∼0.25 μT/yr circa 700 BCE. The secular variation trend in Western Europe is similar to that observed in the Middle East and the Caucasus except that we find no evidence for hyper-rapid field variations (i.e. geomagnetic spikes). Virtual Axial Dipole Moments from Western Europe, the Middle East and central Asia differ by more than 2·1022 A·m2 prior to 600 BCE, which signifies a departure from an axial dipole field especially between 1000 and 600 BCE. Our observations suggest that the regional Levantine Iron Age anomaly has been accompanied by an increase of the axial dipole moment together with a tilt of the dipole.

  4. Long-term variation in the upper atmosphere as seen in the geomagnetic solar quiet (Sq) daily variation

    NASA Astrophysics Data System (ADS)

    Shinbori, A.; Koyama, Y.; Yatagai, A. I.; Nose, M.; Hori, T.; Otsuka, Y.

    2012-12-01

    It has been well-known that geomagnetic solar quiet (Sq) daily variation is produced by the global ionospheric currents flowing in the E-region, which are generated by dynamo process via interaction between the neutral wind and ionospheric plasma in a region of the lower thermosphere and ionosphere. Then, to investigate the Sq amplitude is essential for understanding the long-term variations in the ionospheric conductivity and neutral wind of the lower thermosphere and ionosphere. Recently, Elias et al. [2010] reported that the Sq amplitude tends to increase by 5.4-9.9 % in the middle latitudes in a period of 1961-2001. They mentioned that the long-term variation of ionospheric conductivity associated with geomagnetic secular variation mainly determines the Sq trend, but that the rest component is due to ionospheric conductivity enhancement associated with cooling effect in the thermosphere due to increasing greenhouse gas. In the present study, we clarify the characteristics of the long-term variation in the Sq amplitude using the long-term observation data of geomagnetic field and neutral wind. In the present analysis, we used the F10.7 solar flux as a good indicator of the variation in the solar irradiance in the EUV and UV range as well as geomagnetic field data with time resolution of 1 hour observed at 184 geomagnetic stations. The definition of the Sq amplitude is the difference of the H-component between the maximum and minimum every day when the Kp index is less than 4. As a result, the long-term variation in the Sq amplitude at all the geomagnetic stations shows a strong correlation with the solar F10.7 flux which depends on 11-year solar activity. The relationship between the Sq amplitude and F10.7 flux was not linear but nonlinear. This nonlinearity could be interpreted as the decrease of production rate of electrons and ions in the ionosphere for the strong EUV and UV fluxes as already reported by Balan et al. [1993]. In order to minimize the solar

  5. New Data for the Mesoamerican Directional Secular Variation Curve

    NASA Astrophysics Data System (ADS)

    Soler-Arechalde, A. M.

    2015-12-01

    The Mesoamerican direction secular variation curve is an endless project, new data has been incorporated each year. The new data have radiocarbon dates associated. Wolfman in 1990 proposed the First Curve of Mesoamerica from 1 to 1200 DC. Since 2000 the UNAM´s Archaeomagnetism team has been working continuously by sampling 9 new sites and resampling new stages of Teotihuacan, Teopancazco and Tula. As a result of these investigations more than 70 new data has been annexed and the curve grows until 1600 DC. Data from El Tejar and DuBois has allowed to expand the curve until 1200 BC. An analysis of the incorporation of these new data is presented and the resultant curve is compared to the ARCH3K model.

  6. Cosmic rays flux and geomagnetic field variations at midlatitudes

    NASA Astrophysics Data System (ADS)

    Morozova, Anna; Ribeiro, Paulo; Tragaldabas Collaboration Team

    2014-05-01

    It is well known that the cosmic rays flux is modulated by the solar wind and the Earth's magnetic field. The Earth's magnetic field deflects charged particles in accordance with their momentum and the local field strength and direction. The geomagnetic cutoffs depend both on the internal and the external components of the geomagnetic field, therefore reflecting the geodynamo and the solar activity variations. A new generation, high performance, cosmic ray detector Tragaldabas was recently installed at the University of Santiago de Compostela (Spain). The detector has been acquiring test data since September 2013 with a rate of about 80 events/s over a solid angle of ~5 srad. around the vertical direction. To take full advantage of this new facility for the study of cosmic rays arriving to the Earth, an international collaboration has been organized, of about 20 researchers from 10 laboratories of 5 European countries. The Magnetic Observatory of Coimbra (Portugal) has been measuring the geomagnetic field components for almost 150 years since the first measurements in 1866. It is presently equipped with up-to-date instruments. Here we present a preliminary analysis of the global cosmic ray fluxes acquired by the new Tragaldabas detector in relation to the geomagnetic field variations measured by the Coimbra observatory. We also compare the data from the new cosmic rays detector with results obtained by the Castilla-La Mancha Neutron Monitor (CaLMa, Gadalajara, Spain) that is in operation since October 2011.

  7. De-noising Diurnal Variation Data in Geomagnetic Field Modelling

    NASA Astrophysics Data System (ADS)

    Onovughe, E.

    2017-01-01

    Ground based geomagnetic observatory series have been used to investigate and describe the residuals between a continuous geomagnetic field model and observed diurnal variation for noise-removal of signal due to external field of magnetospheric ring current sources. In all the observatories studied, the residuals in the X-direction consistently show the noisiest signal. Results show that the residuals in the X-direction correlates closely with the RC-index, suggesting an origin from unmodelled external field variation. Notable cross-correlation is also seen between the residuals and the RC-index at zero-lag. Removal/reduction of this unmodelled signal enhances resolution of fine-scale detail in diurnal variation studies.

  8. Archeointensities in Greece during the Neolithic period: New insights into material selection and secular variation curve

    NASA Astrophysics Data System (ADS)

    Fanjat, G.; Aidona, E.; Kondopoulou, D.; Camps, P.; Rathossi, C.; Poidras, T.

    2013-02-01

    Numerous archeomagnetic studies have provided high quality data for both the direction and the intensity of the geomagnetic field, essentially in Europe for the last 10 millennia. In particular, Greece supplies a lot of archeological materials due to its impressive cultural heritage and volcanic activity, so that numerous data have been obtained from burnt clays or historical lava flows. The most recent Greek secular variation curves are available for the last 8 millennia for the intensity and the last 6 millennia for the direction. Nevertheless, the coverage still presents several gaps for periods older than 2500 BC. In an effort to complete the Greek curve and extend it to older times, we present the archeointensity results from three Neolithic settlements in Northern Greece. The samples are of two different natures: burnt structures from Avgi (5250 ± 150 BC) and Vasili (4800 ± 200 BC), as well as ceramics from Dikili Tash (4830 ± 80 BC) and Vasili (4750 ± 250 BC). The samples have been subjected to standard rock magnetic analyses in order to estimate the thermal stability and the domain state of the magnetic carriers before archeointensity measurements. Surprisingly, very few ceramic samples provided reliable archeointensities whereas samples from burnt structures presented a very good success rate. Complementary studies showed that a detailed examination of the matrix color, following archeological information and classification standards can be a decisive test for pre-selection of sherds. In spite of these unsuccessful measurements from ceramics, we obtained an intensity value of 73.5 ± 1.1 μT for Dikili Tash, a higher value than the other data obtained in the same area, during the same period. However we do not have evidences for a technical artefact during the experiment. The burnt structures yielded two reliable archeointensities of 36.1 ± 1.8 μT and 46.6 ± 3.4 μT for Avgi and Vasili, respectively. Finally, we achieved a new archeomagnetic dating

  9. Secular variation of the Earth's magnetic field in the Balkan region during the last eight millennia based on archaeomagnetic data

    NASA Astrophysics Data System (ADS)

    Tema, E.; Kondopoulou, D.

    2011-08-01

    The first archaeomagnetic secular variation (SV) curves for the whole Southern Balkan Peninsula are presented. These are based on all data within a 700 km circle centred at Thessaloniki (40.60oN, 23.00oE). This data set consists of 325 directional and 625 intensity data mainly from Greece, Bulgaria, Serbia and southern Hungary. Some data from southern Italy are also included. The sliding moving window technique, was used to calculate a continuous SV curve for intensity while the directional SV curves were calculated using the bivariate extension of the Fisher statistics. These curves are well constrained and clearly show the main features of the geomagnetic field variation in this region during the last eight millennia. Comparisons with the predictions of the SCHA.DIF.3K and SCHA.DIF.8K regional and the CALS7K.2 and ARCH3K.1 global geomagnetic field models show a good agreement for the last 3000 years but differences for older times. The Balkan SV curves identify several rapid changes of the geomagnetic field in eastern Europe and can be used as reference curves for archaeomagnetic dating in the Balkan Peninsula.

  10. The Dst index underestimates the solar cycle variation of geomagnetic activity.

    PubMed

    Temerin, Michael; Li, Xinlin

    2015-07-01

    It is known that the correction of the Kyoto Dst index for the secular variation of the Earth's internal field produces a discontinuity in the Kyoto Dst index at the end of each year. We show that this secular correction also introduces a significant baseline error to the Kyoto Dst index that leads to an underestimate of the solar cycle variation of geomagnetic activity and of the strength of the ring current as measured by the Kyoto Dst index. Thus, the average value of the Kyoto Dst index would be approximately 13 nT more negative for the active year 2003 compared to quiet years 2006 and 2009 if the Kyoto Dst index properly measured the effects of the ring current and other currents that influence the Dst observatories. Discontinuities in the Kyoto Dst index at the end of each year have an average value of about 5 nT, but the discontinuity at the end of year 2002 was approximately 12 nT, and the discontinuity at the end of year 1982 may have been as large as 20 nT.

  11. The visible spectrum of Pluto: secular and longitudinal variation

    NASA Astrophysics Data System (ADS)

    Lorenzi, Vania; Pinilla-Alonso, Noemí; Emery, Joshua P.; Licandro, Javier; Cruikshank, Dale P.; Grundy, Will; Binzel, Richard P.

    2015-11-01

    Continuous near-infrared spectroscopic observations during the last 30 years enabled the characterization of the Pluto's surface and the study of its variability. Nevertheless, only few data are available in the visible range, where the nature of the complex-organics can be studied.For this reason, we started an observational campaign to obtain the Pluto's relative reflectance in the visible range, with the aim of characterizing the different components of its surface, and providing ground based observations in support of the New Horizons mission. We observed Pluto on six nights in 2014, with the imager/spectrograph ACAM@WHT (La Palma, Spain). We obtained six spectra in the 0.40 - 0.93 µm range, that covered a whole Pluto's rotational period (6.4 days).To study longitudinal variations, we computed for all the spectra the spectral slope, and the position and the depth of the methane ice absorption bands. Also, to search for secular or seasonal variations we compared our data with previously published results.All the spectra present a red slope, indicating the presence of complex organics on Pluto's surface, and show the methane ice absorption bands between 0.73 and 0.90 μm. We also report the detection of the CH4 absorption band at 0.62 μm, already detected in the spectra of Makemake and Eris. The measurement of the band depth at 0.62 μm in the new spectra of Pluto, and in the spectra of Makemake and Eris, permits us to estimate the Lambert coefficient, not measured yet at this wavelength, at a temperature of 30 K and 40 K.We find that all the CH4 bands present a blue shift. This shift is minimum at the Charon-facing hemisphere, where the CH4 is also more abundant, indicating a higher degree of saturation of CH4 in the CH4:N2 dilution at this hemisphere.Comparing with data in the literature, we found that the longitudinal and secular variations of the parameters measured in our spectra are in accordance with previous results and with the distribution of the dark

  12. Secular variations of the photometric parameters of Mira Ceti variables and semiregular variables

    NASA Astrophysics Data System (ADS)

    Marsakova, V. I.

    2014-06-01

    The photometric properties of long-period variable stars and problems related to their traditional classification are analyzed. A general review of secular variations of such light-curve parameters studied in our previous papers as the period, amplitude, and mean brightness is given. Several types of Mira Ceti stars that differ in the secular period variation pattern are identified. A connection between the secular amplitude variations of certain variables with the effect of multiperiodicity is revealed. It is shown that the pattern of these variations and their numerical properties may be used to classify these variable stars.

  13. A study of geomagnetic field variations along the 80° S geomagnetic parallel

    NASA Astrophysics Data System (ADS)

    Lepidi, Stefania; Cafarella, Lili; Francia, Patrizia; Piancatelli, Andrea; Pietrolungo, Manuela; Santarelli, Lucia; Urbini, Stefano

    2017-01-01

    The availability of measurements of the geomagnetic field variations in Antarctica at three sites along the 80° S geomagnetic parallel, separated by approximately 1 h in magnetic local time, allows us to study the longitudinal dependence of the observed variations. In particular, using 1 min data from Mario Zucchelli Station, Scott Base and Talos Dome, a temporary installation during 2007-2008 Antarctic campaign, we investigated the diurnal variation and the low-frequency fluctuations (approximately in the Pc5 range, ˜ 1-7 mHz). We found that the daily variation is clearly ordered by local time, suggesting a predominant effect of the polar extension of midlatitude ionospheric currents. On the other hand, the pulsation power is dependent on magnetic local time maximizing around magnetic local noon, when the stations are closer to the polar cusp, while the highest coherence between pairs of stations is observed in the magnetic local nighttime sector. The wave propagation direction observed during selected events, one around local magnetic noon and the other around local magnetic midnight, is consistent with a solar-wind-driven source in the daytime and with substorm-associated processes in the nighttime.

  14. Spatial and Temporal Variations in the Geomagnetic Field Determined From the Paleomagnetism of Sediment Cores From Scientific Ocean Drilling

    NASA Astrophysics Data System (ADS)

    Acton, G.

    2014-12-01

    Quantifying the spatial and temporal variations of the main geomagnetic field at Earth's surface is important for understanding underlying geodynamo processes and conditions near the core-mantle boundary. Much of the geomagnetic variability, known as secular variation, occurs on timescales of tens of years to many thousands of years, requiring the use of paleomagnetic observations to derive continuous records of the ancient field, referred to as paleosecular variation (PSV) records. Marine depositional systems where thick sedimentary sections accumulate at high sedimentation rates provide some of the best locations for obtaining long continuous PSV records that can reveal both the short- and long-term changes in the field. Scientific ocean drilling has been successful at recovering many such sections and the paleomagnetic records from these reveal how the amplitude of PSV differs between sites and through time. In this study, several such records cored during Ocean Drilling Program (ODP), Integrated Ocean Drilling Program (IODP), and other cruises from high, mid, and low latitudes will be used to quantify time intervals of low and high PSV, to examine time-average properties of the field, to map spatial variations in the angular dispersion of the virtual geomagnetic pole (VGP), and to assess whether the spatial variation in angular dispersion changes with time.

  15. Solar daily variation at geomagnetic observatories in Pakistan

    NASA Astrophysics Data System (ADS)

    Rahim, Zain; Kumbher, Abdul Salam

    2016-03-01

    A study of solar daily variation is performed using the famous Chapman-Miller method for solar cycles 22 & 23 (1986-2007). The objective is to study the characteristics of Sq variation at Pakistani geomagnetic observatories using solar harmonics and a more traditional five quietest day's method. The data recorded at the Karachi geomagnetic observatory for SC 22 and 23 and data sets from other Pakistani geomagnetic observatories; Sonmiani, Quetta and Islamabad are analyzed for H, D and Z components of the geomagnetic field. Except for the D and Z components at Karachi and Sonmiani and H component at Islamabad, the two solar daily variations correlated well with each other. Also, the synthesized daily variation from the solar harmonics of H, D and Z components explained the equivalent Sq current system reasonably well for all seasons. For H component, the first solar harmonic (s1) obtained from spherical harmonic analysis of the data, appeared as the largest harmonic with no significant changes for the seasonal division of data. However, for D and Z components, amplitudes are comparable, but undergo distinct variations. s1 for H and D components increases with magnetic activity while for Z component it is the largest for the medium phase of magnetic activity. With the sunspot number division of data, the weighted mean of the Wolf ratio of all three components is in good agreement with the previous studies. The synthesized solar daily variation for D component, S(D), at Karachi, Sonmiani, Quetta and Islamabad did not show any signs of winter anomaly for the period studied. However, S(D) variation at Karachi during winter season showed morning minimum followed by a maximum at local noon and another minimum in the afternoon. We suggest this could be the effects of Equatorial Ionospheric Anomaly (EIA) observable at the Karachi observatory only during the winter season. Similarly, much disturbed in equinoctial and summer months, S(Z) illustrated an unwavering daily

  16. Character of Holocene paleomagnetic secular variation in the tangent cylinder: Evidence from the Chukchi Sea

    NASA Astrophysics Data System (ADS)

    Lund, Steve; Keigwin, Lloyd; Darby, Dennis

    2016-07-01

    We have carried out a paleomagnetic study on three deep-sea cores from the Chukchi Sea (72°N) in order to characterize the Holocene paleomagnetic secular variation (PSV) in this high-latitude region. The Chukchi Sea lies within the geomagnetic-field tangent cylinder and PSV variability in this region might be expected to have a different pattern than PSV at sites located outside the tangent cylinder at lower latitudes. We have recovered correlatable directional PSV records and relative paleointensity records from all three cores. 15 radiocarbon dates were used to develop a chronostratigraphy for the PSV records. These records constitute the highest-resolution full-vector PSV records ever recovered from such high latitudes. We have compared our results with other previous studies from the region and find that our overall PSV is consistent with these other studies, although there are sometimes age differences up to 1000 years between correlatable PSV features. Our statistical PSV characteristics indicate that field variability (VGP angular dispersion) is lower than in regions just south of the Chukchi Sea and outside the tangent cylinder, but our records are probably not long enough to completely characterize PSV. However, our results are consistent with the only other published VGP angular dispersion results from inside the tangent cylinder (Antarctica, 79°S).

  17. Diurnal variations of cosmic ray geomagnetic cut-off threshold rigidities

    NASA Technical Reports Server (NTRS)

    Dvornikov, V. M.; Sdobnov, V. E.; Sergeev, A. V.; Danilova, O. A.; Tyasto, M. I.

    1985-01-01

    The spectrographic global survey method was used to investigate the rigidity variations Rc of geomagnetic cut-off as a function of local time and the level of geomagnetic disturbance for a number of stations of the world wide network. It is shown that geomagnetic cut-off threshold rigidities undergo diurnal variations. The diurnal wave amplitude decreases with increasing threshold rigidity Rc, and the wave maximum occurs at 2 to 4 hr LT. The amplitude of diurnal variations increases with increasing geomagnetic activity. The results agree with those from trajectory calculations made for an asymmetric model of the magnetosphere during different geomagnetic disturbance conditions.

  18. Statistical Model of Secular Variation and Excursions and Drilling to the Moho

    NASA Astrophysics Data System (ADS)

    Harrison, C. G.

    2007-12-01

    Almost all models for Earth's magnetic field secular variation derived from paleomagnetic results disregard results that give low latitude Virtual Geomagnetic Poles (VGPs). These results are regarded as "unusual" or "not part of the regular secular variation process". These low latitude VGPs are regarded as being produced at a time when the field is undergoing an excursion or a reversal and that therefore they should not be included in a secular variation study. However, it is almost impossible to determine logically the latitude of VGP below which results should be dismissed from study of the secular variation. And for some studies, it is important to include all results to arrive at a valid conclusion. This is the case with the paleomagnetic evidence that will be collected during the drilling through the oceanic crust to the Mohorovicic discontinuity, marking the top of the mantle. Accordingly, the results from the data set originally used by McElhinny and McFadden (1997) updated by addition of new results was expanded to include all the results giving low latitude VGPs that were left out of the updated data set. These expanded results were subjected to statistical analysis based on different latitude bands of the observation sites. This showed that for all latitude bands, the Fisher distribution gave a very bad fit to the data. However the data from every observational latitude band could be fitted by a Fisher distribution for about 90% of the data, plus a uniform distribution in latitude for the other 10% of the data. In addition, the Fisher distribution angular standard deviation showed a linear increase with observation latitude, rising from 11.5º at 10º latitude to 20º at 66º latitude. These results can be used to define a simple model which allows us to estimate the scatter to be found at any latitude, and in particular to determine the scatter in inclination that would be obtained from unoriented samples of basalt recovered during the Integrated Ocean

  19. Secular variation from Mexican stalagmites: their potential and problems

    NASA Astrophysics Data System (ADS)

    Latham, A. G.; Ford, D. C.; Schwarcz, H. P.; Birchall, T.

    1989-07-01

    As part of a feasibility study to see whether stalagmites could provide useful records of secular variation, nine oriented stalagmites were collected from the states of Chiapas and San Luis Potosí, Mexico. Of these, six have yielded measurable natural remanent magnetizations (NRMs) throughout their length. The cleaned magnetizations of one of these samples were shown unequivocally to have recorded the ambient field, and there is no reason to believe that this is not true of the primary magnetizations of other samples. The sequences of palaeofield directions, up the samples' length, have varying degrees of resolution and serial correlation, depending on the rate of field change as averaged by the stalagmite growth rate and the thickness of the measured specimens. Ages and growth rates were estimated by the U-Th method. The main problem in stalagmite palaeomagnetic analysis is a weak NRM, although this may be avoided by judicious choice of the sample. Samples which possess significant viscous components may be cleaned by alternating field or thermally if there is sufficient magnetic material. Unlike many sediments, stalagmites do not appear to suffer from depositional error problems. Dating problems may include low initial U-content, yielding ages with large errors, and the presence of allogenic 230Th in detritus, which causes older apparent ages. The dating limit is ˜ 350 ka. It is usually not possible to obtain long records comparable with those of most lake sediments, and there are aesthetic reasons for not spoiling caves adorned with stalagmites. The method is seen to be complementary to the use of sedimentary sequences to study palaeosecular variation. Studies of the rock magnetism of stalagmites are presented to suggest the mineral carriers of the magnetization and the origins of the natural remanence.

  20. AN UPDATE OF ITALIAN ARCHEAOINTENSITY DATA AND GEOMAGNETIC FIELD STRENGTH VARIATION DURING THE LAST THREE MILLENNIA

    NASA Astrophysics Data System (ADS)

    Tema, E.; Goguitchaichrili, A.

    2009-12-01

    Beside of the impressive cultural heritage and the abundant archaeological sites, Italian archaeointensity data are still sparse. We present here a new compilation and analysis of existing absolute intensity data in order to estimate the variation of the Earth’s magnetic field over the past three millennia. The current dataset consists of 140 intensity data mainly belonging to southern Italy. Vesuvius and Etna contribute 83 per cent of total while only 17 per cent comes from archaeological material. The time distribution is also irregular with the majority of determinations concentrated at the last four centuries. Still, older periods are very poorly covered. All data have been reduced at the latitude of Viterbo (42.45° N, 12.03° E) and plotted versus time. Data coming from historical volcanic eruptions show important discrepancies while those coming from archaeological material are still not sufficiently numerous to reliably describe the fine characteristics of geomagnetic field intensity variations. In order to increase the representativity of the data, archaeointensity results from nearby regions (approximately 700 km and 900 km radius from Viterbo) have been considered. The 700 km circle dataset still remains poor with only 20 additional data added. In contrast, the 900 km dataset includes 122 more archaeointensity data mainly coming from France, Switzerland, Czech Republic, Slovakia, Hungary, Greece and Bulgaria that partially fill the gap between 4-7th centuries BC and 3-4th and 9-11th AD for which no Italian data are available. A preliminary Italian intensity secular variation curve has been calculated by using sliding windows of 100 years shifted by 50 years. The results have been compared with regional and global models predictions. Clearly more Italian archaeointensity data are still needed in order to draw a robust Italian intensity secular variation curve that could be used for archaeomagnetic dating in combination with directional data.

  1. Marine Magnetic Anomalies, Oceanic Crust Magnetization, and Geomagnetic Time Variations

    NASA Astrophysics Data System (ADS)

    Dyment, J.; Arkani-Hamed, J.

    2005-12-01

    Since the classic paper of Vine and Matthews (Nature, 1963), marine magnetic anomalies are commonly used to date the ocean floor through comparison with the geomagnetic polarity time scale and proper identification of reversal sequences. As a consequence, the classical model of rectangular prisms bearing a normal / reversed magnetization has been dominant in the literature for more than 40 years. Although the model explains major characteristics of the sea-surface magnetic anomalies, it is contradicted by (1) recent advances on the geophysical and petrologic structure of the slow-spreading oceanic crust, and (2) the observation of short-term geomagnetic time variations, both of which are more complex than assumed in the classical model. Marine magnetic anomalies may also provide information on the magnetization of the oceanic crust as well as short-term temporal fluctuations of the geomagnetic field. The "anomalous skewness", a residual phase once the anomalies have been reduced to the pole, has been interpreted either in terms of geomagnetic field variations or crustal structure. The spreading-rate dependence of anomalous skewness rules out the geomagnetic hypothesis and supports a spreading-rate dependent magnetic structure of the oceanic crust, with a basaltic layer accounting for most of the anomalies at fast spreading rates and an increasing contribution of the deeper layers with decreasing spreading rate. The slow cooling of the lower crust and uppermost mantle and serpentinization, a low temperature alteration process which produces magnetite, are the likely cause of this contribution, also required to account for satellite magnetic anomalies over oceanic areas. Moreover, the "hook shape" of some sea-surface anomalies favors a time lag in the magnetization acquisition processes between upper and lower magnetic layers: extrusive basalt acquires a thermoremanent magnetization as soon as emplaced, whereas the underlying peridotite and olivine gabbro cool slowly

  2. The Study of the Geomagnetic Variation for Sq current System

    NASA Astrophysics Data System (ADS)

    Zhao, X.; Du, A.

    2012-04-01

    The solar quiet variation (Sq) with a period of 24 hrs is a typical one of the quiet variations. Sq is generally caused by atmospheric tide-dynamo in ionosphere and it is controlled by the electric field, electric conductivity in ionosphere and neutral wind in middle-high altitude atmosphere. In our work, the geomagnetic field data observed by 90 ground-based observatories is used to analyze the local time variation of Sq. Sq is derived from five quiet-day geomagnetic data in every month by the FFT method. According to the pattern of geomagnetic X component in Sq, there is a prenoon-postnoon (before noon and after noon) asymmetry. This asymmetry is obvious in spring, summer and winter. The X component at 12:00-13:00 LT is about 5 nT larger than it at 11:00-12:00 LT. The ratio between the X component of daily variable amplitude and Y component of daily variable amplitude in middle and low (high) latitude regions in summer is greater (smaller) than that in winter. Used the sphere harmonic analysis method, the Sq equivalent current system is obtained. From the pattern of Sq current system, the prenoon-postnoon asymmetry may be caused by the electric field in the high latitude region. This electric field has two effects: the one is that the electric field from high latitude maps to the low latitude region; the other is this electric field penetrate to the middle latitude region directly. The combined action of these two effects makes the prenoon-postnoon asymmetry of Sq. The asymmetry also has an obvious seasonal effect. It may relate to the polar Sq and DP2 in the high latitude region.

  3. Reconstruction of secular variation in seawater sulfate concentrations

    NASA Astrophysics Data System (ADS)

    Algeo, T. J.; Luo, G. M.; Song, H. Y.; Lyons, T. W.; Canfield, D. E.

    2015-04-01

    Long-term secular variation in seawater sulfate concentrations ([SO42-]SW) is of interest owing to its relationship to the oxygenation history of Earth's surface environment. In this study, we develop two complementary approaches for quantification of sulfate concentrations in ancient seawater and test their application to late Neoproterozoic (635 Ma) to Recent marine units. The "rate method" is based on two measurable parameters of paleomarine systems: (1) the S-isotope fractionation associated with microbial sulfate reduction (MSR), as proxied by Δ34SCAS-PY, and (2) the maximum rate of change in seawater sulfate, as proxied by &partial; δ 34SCAS/∂ t(max). The "MSR-trend method" is based on the empirical relationship of Δ34SCAS-PY to aqueous sulfate concentrations in 81 modern depositional systems. For a given paleomarine system, the rate method yields an estimate of maximum possible [SO42-]SW (although results are dependent on assumptions regarding the pyrite burial flux, FPY), and the MSR-trend method yields an estimate of mean [SO42-]SW. An analysis of seawater sulfate concentrations since 635 Ma suggests that [SO42-]SW was low during the late Neoproterozoic (<5 mM), rose sharply across the Ediacaran-Cambrian boundary (~5-10 mM), and rose again during the Permian (~10-30 mM) to levels that have varied only slightly since 250 Ma. However, Phanerozoic seawater sulfate concentrations may have been drawn down to much lower levels (~1-4 mM) during short (<~2 Myr) intervals of the Cambrian, Early Triassic, Early Jurassic, and Cretaceous as a consequence of widespread ocean anoxia, intense MSR, and pyrite burial. The procedures developed in this study offer potential for future high-resolution quantitative analyses of paleo-seawater sulfate concentrations.

  4. Duration of eruption at the Giant Crater lava field, Medicine Lake volcano, California, based on paleomagnetic secular variation

    NASA Astrophysics Data System (ADS)

    Champion, Duane E.; Donnelly-Nolan, Julie M.

    1994-08-01

    Nearly 500 cores were collected from the postglacial Giant Crater lava field on the south flank of Medicine Lake volcano. The basaltic lavas form a continuous set of lava flows which display strong chemical zonation from initially erupted calc-alkaline basaltic andesite to final primitive basalt of tholeiitic affinity. Six chemical-stratigraphic groups have been recognized and mapped. The eruptive sequence was sampled at numerous sites both to determine the characteristic paleomagnetic direction of each chemical group and to estimate the duration of the eruption inferred from secular variation of the geomagnetic field. Well-grouped mean directions of magnetization were obtained for 41 sites in the Giant Crater lava field. Mean directions of magnetization determined for the lava field are nearly identical. The likelihood of any extended time interval for the eruption of the different lava types is extremely small, and the data suggest an eruptive event of less than 30 years duration, analogous to historic Hawaiian eruptions. However, the average of groups 1-4, which cannot be distinguished paleomagnetically from each other, is slightly different statistically from that of the average of groups 5 and 6, which have similar directions. A time gap of 10 +/- 5 years is inferred between eruption of group 4 and 5 lavas based on analysis of the probability of the observed angular difference of 1.27 deg +/- 0.84 deg between their mean directions and by comparison of this angular difference to calculated filed directions with similar declination and inclination determined from spherical harmonic models of the geomagnetic field for the time period 1945-1990. About 200 oriented cores were also collected from predecessor and successor basaltic lava flows on the upper flanks of the volcano. Together with remanent directions from lavas of the Snake River Plain the data define a clockwise loop of secular variation.

  5. Active experiments in the ionosphere and geomagnetic field variations

    NASA Astrophysics Data System (ADS)

    Sivokon, V. P.; Cherneva, N. V.; Khomutov, S. Y.; Serovetnikov, A. S.

    2014-11-01

    Variations of ionospheric-magnetospheric relation energy, as one of the possible outer climatology factors, may be traced on the basis of analysis of natural geophysical phenomena such as ionosphere artificial radio radiation and magnetic storms. Experiments on active impact on the ionosphere have been carried out for quite a long time in Russia as well. The most modern heating stand is located in Alaska; it has been used within the HAARP Program. The possibility of this stand to affect geophysical fields, in particular, the geomagnetic field is of interest.

  6. New archaeointensity results from archaeological sites and variation of the geomagnetic field intensity for the last 7 millennia in Greece

    NASA Astrophysics Data System (ADS)

    De Marco, E.; Spatharas, V.; Gómez-Paccard, M.; Chauvin, A.; Kondopoulou, D.

    In this study six new intensity determinations are presented, obtained from five well dated archaeological sites, located in northern Greece and in Paros, Cyclades Islands. The fired structures consisted of ceramic and pottery kilns belonging to the Hellenistic, Roman and Byzantine periods. Between 8 and 21 samples of highly fired baked clays, tiles and bricks were taken, homogeneously distributed over the structures. The samples were analysed using the classical Thellier method, providing the past intensities and directions of the geomagnetic field recorded at each site. The intensity values have been corrected for anisotropy of thermal remanent magnetisation and cooling rate effects. Differences in the mean archaeointensities per site ranging from 1% to 11%, before and after TRM anisotropy and cooling rate corrections, were obtained. The new results indicate a decrease of 20% of the geomagnetic field strength in Greece, during the last four centuries BC. In order to compare our results with previously published data, a catalogue of archaeo- and palaeointensity results for the Aegean area has been established, covering the last 7 millennia. It consists of 336 data from Greece, western Turkey and Former Yugoslavia, collected from various authors. Weighting factors have been applied to these data, that then have been treated with a hierarchical Bayesian modelling, and a geomagnetic field intensity variation curve for Greece was constructed. A good agreement is observed when comparing the curve for Greece with the Bulgarian secular variation curve (SVC) for intensity. Satisfactory coincidence is also found with the archaeointensity data from Mesopotamia. Despite the presence of some time gaps, a more precise secular variation intensity curve has been constructed for Greece which, combined with a forthcoming directional SVC, will help for dating purposes.

  7. Empirical evidence for latitude dependence and asymmetry of geomagnetic spatial variation in mainland China

    NASA Astrophysics Data System (ADS)

    Lu, Shikun; Zhang, Hao; Li, Xihai; Liu, Daizhi; Wang, Xiqin

    2016-05-01

    Spatiotemporal geomagnetic variation is a significant research topic of geomagnetism and space physics. Generated by convection and flows within the fluid outer core, latitude dependence and asymmetry, as the inherent spatiotemporal properties of geomagnetic field, have been extensively studied. We apply and modify an extension of existing method, Hidden Markov Model (HMM), which is an efficient tool for modeling the statistical properties of time series. Based on ground magnetic measurement data set in mainland China, first, we find the parameters of HMM can be used as the geomagnetic statistical signature to represent the spatiotemporal geomagnetic variations for each site. The results also support the existence of the geomagnetic latitude dependence more apparently. Furthermore, we provide solid empirical evidence for geomagnetic asymmetry relying on such ground magnetic measurement data set.

  8. The use of geomagnetic field models in magnetic surveys

    NASA Technical Reports Server (NTRS)

    Regan, R. D.; Gain, J. C.

    1974-01-01

    The importance of global geomagnetic field models for the reduction of magnetic surveys is discussed. It is demonstrated that a numerical model with adequate secular variation correction, provides a suitable representation of the regional field. The limitations of the presently available models are reported, with emphasis on the International Geomagnetic Reference Field.

  9. Assessment of extreme values in geomagnetic and geoelectric field variations for Canada

    NASA Astrophysics Data System (ADS)

    Nikitina, L.; Trichtchenko, L.; Boteler, D. H.

    2016-07-01

    Disturbances of the geomagnetic field produced by space weather events can have an impact on power systems and other critical infrastructure. To mitigate these risks it is important to determine the extreme values of geomagnetic activity that can occur. More than 40 years of 1 min magnetic data recorded at 13 Canadian geomagnetic observatories have been analyzed to evaluate extreme levels in geomagnetic and geoelectric activities in different locations of Canada. The hourly ranges of geomagnetic field variations and hourly maximum in rate of change of the magnetic variations have been used as measures of geomagnetic activity. Geoelectric activity is estimated by the hourly peak amplitude of the geoelectric fields calculated with the use of Earth resistivity models specified for different locations in Canada. A generalized extreme value distribution was applied to geomagnetic and geoelectric indices to evaluate extreme geomagnetic and geoelectric disturbances, which could happen once per 50 and once per 100 years with 99% confidence interval. Influence of geomagnetic latitude and Earth resistivity models on the results for the extreme geomagnetic and geoelectric activity is discussed. The extreme values provide criteria for assessing the vulnerability of power systems and other technology to geomagnetic activity for design or mitigation purposes.

  10. Correlation of the earth's rotation rate and the secular change of the geomagnetic field. [power spectra/harmonic analysis

    NASA Technical Reports Server (NTRS)

    Jin, R. S.

    1975-01-01

    Power spectral density analysis using Burg's maximum entropy method was applied to the geomagnetic dipole field and its rate of change for the years 1901 to 1969. Both spectra indicate relative maxima at 0.015 cycles/year and its harmonics. These maxima correspond approximately to 66, 33, 22, 17, 13, 11, and 9-year spectral lines. The application of the same analysis techniques to the length-of-day (l.o.d) fluctuations for the period 1865 to 1961 reveal similar spectral characteristics. Although peaks were observed at higher harmonics of the fundamental frequency, the 22-year and 11-year lines are not attributed unambiguously to the solar magnetic cycle and the solar cycle. It is suggested that the similarity in the l.o.d fluctuations and the dipole field variations is related to the motion within the earth's fluid core during the past one hundred years.

  11. Johann von Lamont: A Pioneer in Geomagnetism

    NASA Astrophysics Data System (ADS)

    Soffel, Heinrich

    2006-06-01

    The 200th birthday of John Lamont (1805-1879, Figure 1), a pioneer in the study of geomagnetism, was marked on 13 December 2005. Lamont founded the Munich Geomagnetic Observatory in 1840 and was a member of the group of scientists including Carl Friedrich Gauss, Alexander von Humboldt, Eduard Sabine, Jonas Angstrøm, Humphret Lloyd, Adolf Kupffer, Karl Kreil, and Adolphe Quetelet who composed the Göttingen Magnetic Union. They organized an international network of geomagnetic observatories [Barraclough et al., 1992]. The present knowledge of the geomagnetic field and its secular variation is largely based on the data collected by the global network of geomagnetic observatories during the last 170 years. Lamont's talents and his dedication and enthusiasm for discovery are reflected in the depth and scope of his contributions to a broad variety of natural sciences such as astronomy, meteorology, geomagnetism, and geodesy. However, this article just touches on his merits in geomagnetism.

  12. A 17,000 yr paleomagnetic secular variation record from the southeast Alaskan margin: Regional and global correlations

    NASA Astrophysics Data System (ADS)

    Walczak, M. H.; Stoner, J. S.; Mix, A. C.; Jaeger, J.; Rosen, G. P.; Channell, J. E. T.; Heslop, D.; Xuan, C.

    2017-09-01

    High-resolution sedimentary records on two cores from the Gulf of Alaska margin allow development of a ∼17,400-yr reconstruction of paleomagnetic secular variation (PSV). General agreement between the two records on their independent chronologies confirms that local PSV is recorded, demonstrating that such archives, notwithstanding complexities due to variable sedimentary regimes, deposition rates, and diagenetic conditions, provide meaningful information on past changes of the geomagnetic field. Comparisons with other independently dated sedimentary paleomagnetic records from the NE Pacific indicate largely coherent inclination records that in combination create a NE Pacific sedimentary inclination anomaly stack (NEPSIAS) capturing the common signal over an area spanning >30° longitude and latitude from Alaska through Oregon to Hawaii. Comparisons of NEPSIAS with high quality declination records from the northern North Atlantic (NNA) show that negative (shallow) inclination anomalies in NEPSIAS are associated with eastward NNA declinations while positive (steep) inclination anomalies in NEPSIAS are associated with westward NNA declinations. Comparison of these directional records to regional geomagnetic intensities over the past ∼3000 yrs in North America and back nearly 8000 yrs in the Euro/Mediterranean region, are consistent with a driving mechanism of oscillations in the relative strength of the North American and Euro/Mediterranean flux lobes. The persistence of these dynamics through the Holocene implicates a long-lived organizing structure likely imposed on the geomagnetic field by the lower mantle and/or inner core. These observations underscore a fundamental connection between directional PSV in the North Pacific with that of the North Atlantic, supporting the potential for long-distance correlation of directional PSV as a chronostratigraphic tool.

  13. Paleosecular variation record of geomagnetic full vector during late Miocene, from the Nayarit area, Mexico

    NASA Astrophysics Data System (ADS)

    Goguitchaichvili, Avto; Alva Valdivia, Luis M.; Elguera, Jose Rosas; Fucugauchi, Jaime Urrutia; Cervantes, Miguel Angel; Morales, Juan

    2002-11-01

    results support the theoretical suggestion about an inverse relationship between secular variation and local field strength as result of electromagnetic coupling between the solid inner core and liquid outer core, with the inner core tending to stabilise core convection, and hence the field, when intensity is high. Some fluctuation of absolute intensity was detected within the same directional group (DG) indicating that the intensity of the geomagnetic field varies faster than its direction.

  14. Long-term variation in the upper atmosphere as seen in the amplitude of the geomagnetic solar quiet daily variation

    NASA Astrophysics Data System (ADS)

    Shinbori, A.; Koyama, Y.; Hayashi, H.; Nose, M.; Hori, T.; Otsuka, Y.; Tsuda, T.

    2011-12-01

    It has been well-known that geomagnetic solar quiet (Sq) daily variation is produced by global ionospheric currents flowing in the E-region from middle latitudes to the magnetic equator. These currents are generated by a dynamo process via interaction between the neutral wind and ionospheric plasma in a region of the thermosphere and ionosphere. From the Ohm's equation, the ionospheric currents strongly depend on the ionospheric conductivity, polarization electric field and neutral wind. Then, to investigate the Sq amplitude is essential for understanding the long-term variations in the ionospheric conductivity and neutral wind of the thermosphere and ionosphere. Elias et al. [2010] found that the Sq amplitude tends to increase by 5.4-9.9 % in the middle latitudes from 1961 to 2001. They mentioned that the long-term variation of ionospheric conductivity associated with geomagnetic secular variation mainly determines the Sq trend, but that the rest component is ionospheric conductivity enhancement associated with cooling effects in the thermosphere due to increasing the greenhouse gases. In this talk, we clarify the characteristics of the long-term variation in the Sq amplitude using the long-term observation data of geomagnetic field and neutral wind. These observation data have been provided by the IUGONET (Inter-university Upper atmosphere Global Observation NETwork) project. In the present analysis, we used the F10.7 flux as an indicator of the variation in the solar irradiance in the EUV and UV range, geomagnetic field data with time resolution of 1 hour. The definition of the Sq amplitude is the difference of the H-component between the maximum and minimum per day when the Kp index is less than 4. As a result, the Sq amplitude at all the stations strongly depends on 11-year solar activity, and tends to enhance more during the high activities (19- and 22- solar cycles) than during the low activity (20-solar cycle). The Fourier spectra of the F10.7 flux and Sq

  15. Numerical simulations of geomagnetic field variations: from jerks to superchrons

    NASA Astrophysics Data System (ADS)

    Sakuraba, A.

    2011-12-01

    In the last two decades, computer simulations of the geodynamo have brought progress in our understanding of geomagnetic field variations of various timescales. For example, geomagnetic polarity reversals and their statistical properties have been successfully simulated by an MHD dynamo model. The origin of superchrons are discussed in the framework of the evolution of the whole Earth system (e.g. Driscoll & Olson, 2011). However, it is still true that our dynamo models do not exactly mimic the Earth. The most fundamental problem is that our model viscosity is too high. In terms of nondimensional numbers, the Ekman number (E) is still larger than 10-6 in most studies; that is, our E is nearly 10 orders of magnitude larger than the real Earth value. One current approach is to decrease this parameter using power of modern parallel computers. It is now possible to decrease E less than 10-6. In this low-viscosity regime, convection seems to change in a qualitative way. For example, the length scale of convective vortices becomes very small in the presence of a weak magnetic field, but can be as large as the core depth when the generated magnetic field intensity is strong enough. These two length scales may coexist inside the fluid core (Sakuraba & Roberts, 2009). The low-E approach is the most straightforward and ideal approach to better understanding of the geodynamo but still expensive to simulate million-year-scale polarity reversals. In this presentation, I show some results of numerical simulations of short-term geomagnetic field variations using recent low-viscosity models. The topic will cover the westward drift and torsional oscillations. The low-E approach should be continued in parallel with development of supercomputers, but another approach may be possible to overcome the geodynamo problem. That is so-called the magnetostrophic dynamo model, which was theoretically studied by J. B. Taylor (1963). This model totally neglects viscosity and assumes infinitely

  16. Latitudinal variation of the polar cusp during a geomagnetic storm

    SciTech Connect

    Meng, C.

    1982-01-01

    Large amplitude latitudinal variation of the polar cusp position was observed during the intense geomagnetic storm of 15--16 February 1980. The observation of the polar cusp, identified as the region of intense but extremely soft electron precipitation, was made by two nearly noon-midnight orbit DMSP satellites over both northern and southern hemispheres. The latitudinal shift of the polar cusp is observed to be related to the intensity variation of the ring current indicated by the hourly Dst values. The polar cusp region moved from its normal location at approx.76/sup 0/ gm lat down to approx.62/sup 0/ gm lat at the peak of this storm. This movement took about 5 hours and was detected over both hemispheres. A drastic variation in the width of the cusp region was also observed; it is very narrow (approx.1/sup 0/) during the equatorial shift and expands to > or approx. =5/sup 0/ during the poleward recovery. Variation of the polar cusp latitude with that of the Dst index was also seen during the period before the intense storm.

  17. VO-ESD: a virtual observatory approach to describe the geomagnetic field temporal variations with application to Swarm data

    NASA Astrophysics Data System (ADS)

    Saturnino, Diana; Langlais, Benoit; Amit, Hagay; Mandea, Mioara; Civet, François; Beucler, Éric

    2017-04-01

    A complete description of the main geomagnetic field temporal variation is crucial to understand dynamics in the core. This variation, termed secular variation (SV), is known with high accuracy at ground magnetic observatory locations. However the description of its spatial variability is hampered by the globally uneven distribution of the observatories. For the past two decades a global coverage of the field changes has been allowed by satellites. Their surveys of the geomagnetic field have been used to derive and improve global spherical harmonic (SH) models through some strict data selection schemes to minimise external field contributions. But discrepancies remain between ground measurements and field predictions by these models. Indeed, the global models do not reproduce small spatial scales of the field temporal variations. To overcome this problem we propose a modified Virtual Observatory (VO) approach by defining a globally homogeneous mesh of VOs at satellite altitude. With this approach we directly extract time series of the field and its temporal variation from satellite measurements as it is done at observatory locations. As satellite measurements are acquired at different altitudes a correction for the altitude is needed. Therefore, we apply an Equivalent Source Dipole (ESD) technique for each VO and each given time interval to reduce all measurements to a unique location, leading to time series similar to those available at ground magnetic observatories. Synthetic data is first used to validate the new VO-ESD approach. Then, we apply our scheme to measurements from the Swarm mission. For the first time, a 2.5 degrees resolution global mesh of VO times series is built. The VO-ESD derived time series are locally compared to ground observations as well as to satellite-based model predictions. The approach is able to describe detailed temporal variations of the field at local scales. The VO-ESD time series are also used to derive global SH models. Without

  18. Paleosecular variations of the geomagnetic field during the Holocene from Eastern Asia

    NASA Astrophysics Data System (ADS)

    Yang, Xiaoqiang; Liu, Qingsong; Yu, Kefu; Huang, Wenya; Zhu, Liyan; Zhang, Huodai; Liu, Jian; Li, JinHua

    2016-05-01

    High-resolution paleomagnetic secular variation (PSV) records bear great information of dynamics processes of the Earth's geomagnetic field, and can be further used for inter-profile correlation and for dating sediments. However, effects of changes in the depositional environment on PSV records have not been fully determined. This study constructed Holocene PSV records for the gravity piston core (ZSQD34) obtained from the northern South China Sea. Rock magnetic and Transmission Electron Microscope (TEM) results indicate that single (SD) and PSD domain magnetites are the main carrier of the natural remanent magnetization. Comparable to the records derived from the freshwater lakes and the modeling results, we observed that direction curves from these two environments of contrasting salinity content are rather consistent. The direction curves are independent of the constructed salinity. However, the gradual increasing trend of relative intensity since about 5 kyr might be related to the decreasing sea surface salinity. Furthermore, on the centennial and millennial time scale, the relative intensity and salinity show some positive relation, suggesting a potential contribution of salinity to the paleomagnetic relative intensity recording processes.

  19. Geomagnetic main field modeling using magnetohydrodynamic constraints

    NASA Technical Reports Server (NTRS)

    Estes, R. H.

    1985-01-01

    The influence of physical constraints are investigated which may be approximately satisfied by the Earth's liquid core on models of the geomagnetic main field and its secular variation. A previous report describes the methodology used to incorporate nonlinear equations of constraint into the main field model. The application of that methodology to the GSFC 12/83 field model to test the frozen-flux hypothesis and the usefulness of incorporating magnetohydrodynamic constraints for obtaining improved geomagnetic field models is described.

  20. Latitudinal and MLT dependence of the seasonal variation of geomagnetic field around auroral zone

    NASA Astrophysics Data System (ADS)

    Zhu, Jin; Du, Aimin; Ou, Jiaming; Xu, Wenyao

    2017-08-01

    Seasonal variation of geomagnetic field around auroral zone is analyzed in terms of geomagnetic latitude, magnetic local time (MLT) and geomagnetic condition in this study. The study uses horizontal component (H) of geomagnetic field obtained from 6 observatories located in geomagnetic latitude of 57.8°N-73.8°N along 115°E longitudinal line. The results indicate that seasonal variations of geomagnetic field around auroral zone are different combinations of annual and semiannual variations at different latitudinal ranges. Both annual and semiannual variations show distinct MLT dependency: (1) At dayside auroral latitudes (around 72°N geomagnetic latitude), geomagnetic field shows distinct annual variation under both quiet and disturbed conditions. Furthermore, the annual component is mainly contributed by data of dusk sector. (2) At nightside auroral latitudes (around 65°N), geomagnetic field shows semiannual dominated seasonal variation. Under quiet conditions the annual component is comparable to the semiannual component, while under disturbed conditions, the semiannual component is twice as much as the annual component. Under quiet conditions, the semiannual component is mainly contributed by 1300-1400 MLT, while the annual component has two peaks: one is around 1100-1300 MLT and the other is around 2000-2200 MLT. Under disturbed conditions, the semiannual component is mainly contributed by data around midnight, while the annual component is mainly contributed by dusk sector. (3) At subauroral latitudes (around 60°N), annual variation is comparable to semiannual variation under both quiet and disturbed conditions. Both annual and semiannual components show similar MLT dependencies as that of nightside auroral latitudes.

  1. Spatial structure of connection between the troposphere heat content and variations in solar and geomagnetic activities

    NASA Astrophysics Data System (ADS)

    Vasil'eva, L. A.; Molodykh, S. I.; Kovalenko, V. A.

    2016-03-01

    We have carried out correlation analysis of connection between the heat content of different tropospheric layers and variations of solar (F10.7cm) and geomagnetic activity (AA index) in 1950-2007. The heat content response to effects of solar and geomagnetic activity has been found to have an explicit spatial structure. The heat content of the most of the troposphere correlates with solar and geomagnetic activity; however, we have observed significant anticorrelation in some regions. The degree of connection between the tropospheric heat content change and variations of solar and geomagnetic activity have been shown to depend on the time scale (time averaging period). The time averaging period increasing from 5 to 7 years, the correlation coefficient grows in most regions (up to 0.6-0.7), but if the increase continues, only weaker growth is observed. This time-scale dependence can be explained by the fact that the majority of variations in tropospheric heat content on the time-scale of less than 5 years are affected by processes having no connection with solar or geomagnetic activity. We have performed analysis of the influence of atmospheric circulation on connection between the tropospheric heat content change and variations of solar and geomagnetic activity. The heat content change in regions that are frequently occupied by the cyclones is shown to have practically no connection with variations of solar and geomagnetic activity.

  2. Variations of angular elements of the geomagnetic field in Europe during the last 24 centuries

    NASA Astrophysics Data System (ADS)

    Burakov, K. S.; Nachasova, I. E.

    2011-05-01

    The analysis of variations in angular elements of the geomagnetic field during the period since 350 B.C. to the present day according to the findings from the study of thermal magnetization of baked archaeological samples from England, France, and East Europe showed that the key feature in the behavior of the geomagnetic inclination in all three regions is a millennial variation. The trend in the behavior of the inclination of the geomagnetic field can be regarded as a manifestation of a variation with a characteristic time scale of several thousand years. Despite the general likeness of variations in inclination and declination of the ancient geomagnetic field, they also exhibit a noticeable dissimilarity. The paths of the virtual geomagnetic pole reconstructed from the variations of angular elements of the geomagnetic field in East Europe indicate that the geomagnetic polar motion is quasi-cyclic. The duration of the first cycle was about 1000 years, while the second cycle has not been completed due to the change of the motion to the opposite direction in the middle of the XVII century.

  3. Lunar Daily Geomagnetic Variations in Japan Generated by Tidal Currents in Ocean and Ionosphere

    NASA Astrophysics Data System (ADS)

    Yamazaki, K.

    2016-12-01

    In the present work, lunar daily geomagnetic variations (i.e. tidal variations) in Japan are estimated by using data at ground observatories. Tidal variations in the geomagnetic field are mainly arising from two sources, ocean and ionosphere. Recent works on geomagnetic tidal variations often use satellite data; however, ground observatories possibly provides details of oceanic variations because of the vicinity of observations. Three component geomagnetic data at 18 observatories in Japan during 2001-2015 are used in the present study. To determine tidal componentsthese, Chapman-Millar method (Chapman and Millar, 1940) are applied to these data. The separation is conducted by using a method proposed by Malin (1970), which is based on an assumption that ionospheric contribution at local midnight is negligibly small. Lunar daily geomagnetic variations at considered sites are successfully determined. Many of the results are. For example, horizontal components of ionospheric variations are nearly uniform in the region, as demonstrated by earlier studies for other regions (e.g. McKnight 1995). However, non-trivial results are also obtained for oceanic component. At some pairs of site whose distances are less than few tens of kilometers, significant differences in oceanic contribution are recognized. Because oceanic contributions of the geomagnetic variation consists of electric currents driven by sea-water movements and counter electric currents in the surrounding crust, this result possibly provides information on conductivity anomalies in the crust.

  4. Statistical analysis of extreme values for geomagnetic and geoelectric field variations for Canada

    NASA Astrophysics Data System (ADS)

    Nikitina, Lidia; Trichtchenko, Larisa; Boteler, David

    2016-04-01

    Disturbances of the geomagnetic field produced by space weather events cause variable geoelectric fields at Earth's surface which drive electric currents in power systems, resulting in hazardous impacts on electric power transmission. In extreme cases, as during the magnetic storm in March 13, 1989, this can result in burnt-out transformers and power blackouts. To make assessment of geomagnetic and geoelectric activity in Canada during extreme space weather events, extreme value statistical analysis has been applied to more than 40 years of magnetic data from the Canadian geomagnetic observatories network. This network has archived digital data recordings for observatories located in sub-auroral, auroral, and polar zones. Extreme value analysis was applied to hourly ranges of geomagnetic variations as an index of geomagnetic activity and to hourly maximum of rate-of-change of geomagnetic field. To estimate extreme geoelectric fields, the minute geomagnetic data were used together with Earth conductivity models for different Canadian locations to calculate geoelectric fields. The extreme value statistical analysis was applied to hourly maximum values of the horizontal geoelectric field. This assessment provided extreme values of geomagnetic and geoelectric activity which are expected to happen once per 50 years and once per 100 years. The results of this analysis are designed to be used to assess the geomagnetic hazard to power systems and help the power industry mitigate risks from extreme space weather events.

  5. Two populations of sunspots and secular variations of their characteristics

    NASA Astrophysics Data System (ADS)

    Nagovitsyn, Yu. A.; Pevtsov, A. A.; Osipova, A. A.; Tlatov, A. G.; Miletskii, E. V.; Nagovitsyna, E. Yu.

    2016-10-01

    We investigate the magnetic fields and total areas of mid- and low-latitude sunspots based on observations at the Greenwich and Kislovodsk (sunspot areas) and Mount Wilson, Crimean, Pulkovo, Ural, IMIS, Ussuriysk, IZMIRAN, and Shemakha (magnetic fields) observatories. We show that the coefficients in the linear form of the dependence of the logarithm of the total sunspot area S on its maximum magnetic field H change with time. Two distinct populations of sunspots are identified using the twodimensional H-log S occurrence histogram: small and large, separated by the boundaries log S = 1.6 ( S = 40 MSH) and H = 2050 G. Analysis of the sunspot magnetic flux also reveals the existence of two lognormally distributed populations with the mean boundary between them Φ = 1021 Mx. At the same time, the positions of the flux occurrence maxima for the populations change on a secular time scale: by factors of 4.5 and 1.15 for small and large sunspots, respectively. We have confirmed that the sunspots form two physically distinct populations and show that the properties of these populations change noticeably with time. This finding is consistent with the hypothesis about the existence of two magnetic field generation zones on the Sun within the framework of a spatially distributed dynamo.

  6. Toward using millennial-scale geomagnetic field models to constrain in situ cosmogenic nuclide production rate variations

    NASA Astrophysics Data System (ADS)

    Lifton, N. A.

    2005-12-01

    The geomagnetic field exerts a strong influence on the trajectories of charged primary cosmic-ray particles incident on the Earth's atmosphere (and therefore, on the geographic distribution of their progeny). The resulting cascade of secondary particles then interacts with the top few meters of the Earth's surface to produce various nuclides in situ (in situ cosmogenic nuclides, or CNs). With appropriate interpretive models, concentrations of these nuclides measured in terrestrial materials can be used to infer the duration of surface exposure (or of burial following exposure) and rates of various surficial processes. However, the potential precision with which CNs can be applied is limited by how well their production rates are known. Nuclide production rates are typically determined by measuring CN concentrations in surficial rocks with well-constrained exposure histories. Scaling these time-integrated production rates to other locations with different exposure durations, though, requires knowledge or assumptions of how instantaneous production rates have varied in space and time. Spatial scaling of CN production rates is typically described by models based on modern secondary cosmic-ray measurements, ordered by parameters linked to the geomagnetic field. In general, the most robust parameter for ordering these measurements is the effective vertical cutoff rigidity (RC), a measure of the energy required for primary cosmic rays to penetrate the geomagnetic and magnetospheric fields and interact with the atmosphere at a given location. Temporal variations in CN production rates at a given site result primarily from changes in the orientation and intensity of the geomagnetic field. These geomagnetic variations have been modeled for CN applications using estimates of Holocene variations in dipole orientation combined with records of global dipole intensity variations. It has typically been assumed in CN research that secular variation of the geomagnetic pole averages

  7. Equatorial E region electric fields at the dip equator: 2. Seasonal variabilities and effects over Brazil due to the secular variation of the magnetic equator

    NASA Astrophysics Data System (ADS)

    Moro, J.; Denardini, C. M.; Resende, L. C. A.; Chen, S. S.; Schuch, N. J.

    2016-10-01

    In this work, the seasonal dependency of the E region electric field (EEF) at the dip equator is examined. The eastward zonal (Ey) and the daytime vertical (Ez) electric fields are responsible for the overall phenomenology of the equatorial and low-latitude ionosphere, including the equatorial electrojet (EEJ) and its plasma instability. The electric field components are studied based on long-term backscatter radars soundings (348 days for both systems) collected during geomagnetic quiet days (Kp ≤ 3+), from 2001 to 2010, at the São Luís Space Observatory (SLZ), Brazil (2.33°S, 44.20°W), and at the Jicamarca Radio Observatory (JRO), Peru (11.95°S, 76.87°W). Among the results, we observe, for the first time, a seasonal difference between the EEF in these two sectors in South America based on coherent radar measurements. The EEF is more intense in summer at SLZ, in equinox at JRO, and has been highly variable with season in the Brazilian sector compared to the Peruvian sector. In addition, the secular variation on the geomagnetic field and its effect on the EEJ over Brazil resulted that as much farther away is the magnetic equator from SLZ, later more the EEJ is observed (10 h LT) and sooner it ends (16 h LT). Moreover, the time interval of type II occurrence decreased significantly after the year 2004, which is a clear indication that SLZ is no longer an equatorial station due to the secular variation of the geomagnetic field.

  8. Archeointensities during the Neolithic period in Greece: new data to constraint the secular variation curves

    NASA Astrophysics Data System (ADS)

    Fanjat, G.; Aidona, E.; Camps, P.; Poidras, T.; Kondopoulou, D.

    2011-12-01

    Archaeomagnetism has been continuously developed over the last three decades. Backed archaeological features such as pottery, kilns or burnt structures, provide reliable data as they usually carry a strong and stable thermo-remanent magnetization acquired during the last firing. Numerous studies have provided high quality data for both the direction and intensity of the geomagnetic field essentially in Europe (e. g. compilations Genevey et al 2008, G3, Kovacheva et al, 2009, G3). In particular, Greece provides a lot of archaeological materials and numerous data are available (e. g. Aitken et al 1984, PEPI, Aitken et al 1989, PEPI, De Marco et al, 2008, Phys. Chem. Earth) from archaeomagnetic features or historical lava flows (Spassov et al, 2010, G3). The Greek secular variation curves (SVCs) are available for the last 8 millennia for the intensity and the last 6 millenia for the direction. Nevertheless, the coverage of the archaeological periods remains with several gaps for periods older than 2500 BC (Genevey et al, 2008, G3 and Kovacheva et al, 2009, G3). In this study, we present paleointensity results from Neolithic settlements in Northern Greece. Samples have been collected from four different archaeological sites: burnt structures and ceramics in Avgi (Kastoria, 5400-5100 B.C.) and Vasili (Farsala, 6000 B.C.), one kiln with the associated ceramics from Sossandra (Aridaia, 5000-4600 B.C.) and one ceramic collection from Dikili Tash (Kavala, 4800 B.C.). The samples have been subjected to a standard magnetic analysis in order to define the stability of the magnetic carriers and fulfil all the required criteria for the estimation of the palaeointensity. We obtained two reliable palaeointensities for the Avgi and Vasili sites of 38 and 48 μT respectively and a high mean paleointensity value arround 85 μT for the Dikili Tash site. These results are compared with the SVCs from neighbouring countries as well as with recent compilations and global models. We

  9. The relationship of air temperature variations over the northern hemisphere during the secular and 11-year solar cycles

    NASA Technical Reports Server (NTRS)

    Ryzhakov, L. Y.; Tomskaya, A. S.

    1978-01-01

    A comparison was made of air temperature anomaly maps for the months of January and July against a background of high and low secular solar activity, with and without regard for the 11 year cycle. By comparing temperature variations during the 11 year and secular cycles, it is found that the 11 year cycle influences thermal conditions more strongly than the secular cycle, and that temperature differences between extreme phases of the solar cycles are greater in January than in July.

  10. New Sediment Data to Constrain Southern Atlantic Holocene Secular Variation

    NASA Astrophysics Data System (ADS)

    Korte, M. C.; Frank, U.; Nowaczyk, N. R.; Frederichs, T.; Brown, M. C.

    2014-12-01

    The present day geomagnetic field shows a notable weak zone stretching from South America to southern Africa. This is known as the South Atlantic Anomaly caused by a growing patch of reversed magnetic flux at the core-mantle boundary. The investigation of existence and evolution of similar features over the past millennia using global spherical harmonic models is hampered by the fact that at present only very few paleomagnetic data from equatorial and many southern hemisphere regions are available to constrain models well in these regions. Here, we present the results of paleomagnetic investigations of sediment cores from four locations at low latitudes. OPD 1078 and 1079 lie off the coast of Angola, GeoB6517-2 and ODP 1076D are located in the Congo Fan and M35003-4 is situated southeast of Grenada in the Tobago Basin. In addition to the paleomagnetic work all cores were subjected to a comprehensive set of rock magnetic measurements. Detailed age models based on radiocarbon dating are available for all locations, since the sites were already subjects of different aspects of climatic studies. We include these new records and previously presented data from two Ethiopian locations in millennial scale global models of the CALSxk type. Agreement of the new data to previous models and modifications of models due to the additional data are discussed, focussing in particular on magnetic field structures resembling the present-day South Atlantic Anomaly.

  11. Effect of March 9, 2016 Total Solar Eclipse on geomagnetic field variation

    NASA Astrophysics Data System (ADS)

    Ruhimat, Mamat; Winarko, Anton; Nuraeni, Fitri; Bangkit, Harry; Aris, M. Andi; Suwardi; Sulimin

    2016-11-01

    During solar eclipse, solar radiation to the Earth is blocked by the Moon. Thus, the ionization process in the ionosphere is disrupted, as well as the variation of geomagnetic field. The disturbance of geomagnetic field is caused by electric current in the E layer of the ionosphere. At low latitude, the current which is dominant in quiet day is the Sq currents. The blocking of solar radiation cause decrement in electron density in the blocked region. The aim of the research is to find the effect of total solar eclipse to the geomagnetic field. The measurement of the geomagnetic field variation during total solar eclipse on March 9, 2016 was carried out at the Meteorological station of BMKG in Ternate (0° 49' 45.20 "N; 127° 22' 54.00" E). By eliminating the geomagnetic disturbance that occurred in a daily geomagnetic field variation, the pattern of quiet day which is usually in a shape of smooth curve became affected. During the total solar eclipse on March 9, 2016 from 00:30 until 02:00 UT, we found that the geomagnetic field variation of the quiet day decreased by -5 nT.

  12. The effect of cosmic ray intensity variations and geomagnetic disturbances on the physiological state of aviators

    NASA Astrophysics Data System (ADS)

    Papailiou, M.; Mavromichalaki, H.; Kudela, K.; Stetiarova, J.; Dimitrova, S.; Giannaropoulou, E.

    2011-09-01

    Over the last few years various researches have reached the conclusion that cosmic ray variations and geomagnetic disturbances are related to the condition of the human physiological state. In this study medical data regarding 4018 Slovak aviators were analyzed in relation to daily variations of cosmic ray and geomagnetic activity. Specifically daily data concerning mean values of heart rate which were registered during the medical examinations of the Slovak aviators, were related to daily variations of cosmic ray intensity, as measured by the Neutron Monitor Station on Lomnicky Stit (http://neutronmonitor.ta3.sk/realtime.php3) and the high resolution neutron monitor database (http://www.nmdb.eu) and daily variations of Dst and Ap geomagnetic indices. All subjects were men in good health of age 18-60 yrs. This particular study refers to the time period from 1 January 1994 till 31 December 2002. Statistical methods were applied to establish a statistical significance of the effect of geomagnetic activity levels and cosmic ray intensity variations on the aforementioned physiological parameters for the whole group. The Pearson r-coefficients were calculated and the Analysis of Variance (ANOVA) method was applied to establish the statistical significance levels (p-values) of the effect of geomagnetic activity and cosmic ray intensity variations on heart rate up to three days before and three days after the respective events. Results show that there is an underlying effect of geomagnetic activity and cosmic ray intensity variations on the cardiovascular functionality.

  13. Dynamo currents representing geomagnetic L variation demonstrated by a multi-layer ionospheric model

    NASA Astrophysics Data System (ADS)

    Xu, W.-Y.; Tschu, K.-K.; Matsushita, S.

    1984-05-01

    A multi-layer ionospheric model and lunar (2,2) tidal mode have been used to calculate dynamo current systems representing lunar geomagnetic semidiurnal variations. Since both the height variation of the ionospheric conductivities and latitudinal dependence of the height of the conductivity peaks have been taken into account, the dynamo current systems agree with equivalent ones (estimated from geomagnetic data) better than those for a thin shell model of the ionospheric conductivity, especially in the polar region.

  14. Modeling the Jovian magnetic field and its secular variation using all available magnetic field observations

    NASA Astrophysics Data System (ADS)

    Ridley, Victoria A.; Holme, Richard

    2016-03-01

    We present new models of Jupiter's internal magnetic field and secular variation from all available direct measurements from three decades of spacecraft observation. A regularized minimum norm approach allows the creation of smooth, numerically stable models displaying a high degree of structure. External field from the magnetodisk is modeled iteratively for each orbit. Jupiter's inner magnetosphere is highly stable with time, with no evidence for variation with solar activity. We compare two spherical harmonic models, one assuming a field constant in time and a second allowing for linear time variation. Including secular variation improves data fit with fewer additional parameters than increasing field complexity. Our favored solution indicates a ˜0.012% yr-1 increase in Jupiter's dipole magnetic moment from 1973 to 2003; this value is roughly one quarter of that for Earth. Inaccuracies in determination of the planetary reference frame cannot explain all the observed secular variation. Should more structure be allowed in the solutions, we find the northern hemispherical configuration resembles recent models based on satellite auroral footprint locations, and there is also evidence of a possible patch of reversed polar flux seen at the expected depth of the dynamo region, resembling that found at Earth and with implications for the Jovian interior. Finally, using our preferred model, we infer flow dynamics at the top of Jupiter's dynamo source. Though highly speculative, the results produce several gyres with some symmetry about the equator, similar to those seen at Earth's core-mantle boundary, suggesting motion on cylinders aligned with the rotation axis.

  15. Decadal to millennial scale geomagnetic field variations in the Levantine archaeointensity curve (LAC): methodology and applications

    NASA Astrophysics Data System (ADS)

    Shaar, Ron; Tauxe, Lisa; Ron, Hagai; Agnon, Amotz; Ben-Yosef, Erez; Finkelstein, Israel; Zuckerman, Sharon; Levy, Thomas E.

    2014-05-01

    ) according to the dating method employed (archaeological, historical, radiocarbon). In addition, we cross check results from multiple archaeological sites using different source materials dated using different methodologies. The results of this effort are summarized in a regional compilation namely Levantine Archaeomagnetic Curve - LAC. The initial version of the LAC includes recently published data from ancient copper production sites, and new data from two important biblical archaeological mounds in Israel - Tel Megiddo ("Armageddon") and Tel Hazor. In this talk we review our working methodologies, report the current status of the LAC, and discuss its implications on our understanding of geomagnetic secular variations.

  16. Worldwide Geomagnetic Data Collection and Management

    NASA Astrophysics Data System (ADS)

    Mandea, Mioara; Papitashvili, Vladimir

    2009-11-01

    Geomagnetic data provided by different platforms piece together a global picture of Earth's magnetic field and its interaction with geospace. Furthermore, a great diversity of the geomagnetic field changes, from secular (over decades to centuries) to short time variations (down to minutes and seconds), can be detected only through continued observations. An international effort to watch and record geomagnetic changes first began in the 1830s with a network of scientific observers organized by Karl Friedrich Gauss in Germany, and this effort has continued since then. One of the most remarkable achievements in understanding the geomagnetic field morphology and time behavior was made possible by the International Geophysical Year (IGY), an exploration and research effort that lasted for 18 months, starting on 1 July 1957. The IGY encompassed 11 geoscience disciplines, including geomagnetism. The IGY has represented a giant step forward in the quality and quantity of worldwide geomagnetic measurements, as well as in the widespread interest in magnetic measurements. A half century of probing the geomagnetic field spatial and temporal variations has produced a number of outstanding results, and the interested reader can find recent reviews on various geomagnetic field topics (from measurements to modeling) in Encyclopedia of Geomagnetism and Paleomagnetism [Gubbins and Herrero-Bervera, 2007] or Treatise on Geophysics: Geomagnetism [Kono, 2007].

  17. New archeointensity data from Novgorod (North-Western Russia) between c. 1100 and 1700 AD. Implications for the European intensity secular variation

    NASA Astrophysics Data System (ADS)

    Salnaia, Natalia; Gallet, Yves; Genevey, Agnès; Antipov, Ilya

    2017-08-01

    Reconstructing the secular variation of Europe's geomagnetic field over the past millennium is challenging because of the lack of recently acquired archeomagnetic data from Western Russia. In this paper, we report on nine new archeointensity values obtained from groups of brick fragments sampled in Novgorod (North-Western Russia) and its vicinities. These fragments were collected from churches whose precise ages range from the beginning of the 12th century to the end of the 17th century AD. All the archeointensity measurements were carried out using the Triaxe experimental protocol, which takes into account the thermoremanent magnetization (TRM) anisotropy effect. Intensity determinations were performed using fast and slow cooling rates for laboratory-TRM acquisition. The results confirm that the Triaxe protocol overcomes the TRM cooling rate dependence. The new data shows that geomagnetic field intensities in North-Western Russia have decreased in the past millennium. Comparisons were made with other data previously obtained in Western Europe, the Balkans and Russia, as well as with intensity values expected in Novgorod from global geomagnetic field models. These comparisons yielded three main results: 1) The new archeointensity data do not show the occurrence of large intensity variations in North-Western Russia, as those observed in the Balkan dataset. Conversely, they appear more compatible with Western European results, which suggests a limited non-dipole field effect across Europe during the past millennium; 2) Our data are weaker than the intensity values expected in Novgorod from the available global geomagnetic field models. This suggests that the field models are inaccurate for the Novgorod area; 3) A constant linear decrease of the geocentric axial dipole moment since 1600 AD does not appear compatible with our younger data.

  18. ong-term trends of foE and geomagnetic activity variations

    NASA Astrophysics Data System (ADS)

    Mikhailov, A. V.; de La Morena, B. A.

    2003-03-01

    A relationship between foE trends and geomagnetic activity long-term variations has been revealed for the first time. By analogy with earlier obtained results on the foF2 trends it is possible to speak about the geomagnetic control of the foE long-term trends as well. Periods of increasing geomagnetic activity correspond to negative foE trends, while these trends are positive for the decreasing phase of geomagnetic activity. This natural relationship breaks down around 1970 (on some stations later) when pronounced positive foE trends have appeared on most of the stations considered. The dependence of foE trends on geomagnetic activity can be related with nitric oxide variations at the E-layer heights. The positive foE trends that appeared after the break down effect may also be explained by the [NO] decrease which is not related to geomagnetic activity variations. But negative trends or irregular foE variations on some stations for the same time period require some different mechanism. Chemical pollution of the lower thermosphere due to the anthropogenic activity may be responsible for such abnormal foE behavior after the end of the 1960s.

  19. Dependence of Quiet Time Geomagnetic Activity Seasonal Variation on the Solar Magnetic Polarity

    NASA Astrophysics Data System (ADS)

    Oh, Suyeon

    2013-03-01

    The geomagnetic activity shows the semiannual variation stronger in vernal and autumnal equinoxes than in summer and winter solstices. The semiannual variation has been explained by three main hypotheses such as Axial hypothesis, Equinoctial hypothesis, and Russell-McPherron Effect. Many studies using the various geomagnetic indices have done to support three main hypotheses. In recent, Oh & Yi (2011) examined the solar magnetic polarity dependency of the geomagnetic storm occurrence defined by Dst index. They reported that there is no dependency of the semiannual variation on the sign of the solar polar fields. This study examines the solar magnetic polarity dependency of quiet time geomagnetic activity. Using Dxt index (Karinen & Mursula 2005) and Dcx index (Mursula & Karinen 2005) which are recently suggested, in addition to Dst index, we analyze the data of three-year at each solar minimum for eight solar cycles since 1932. As a result, the geomagnetic activity is stronger in the period that the solar magnetic polarity is anti-parallel with the Earth's magnetic polarity. There exists the difference between vernal and autumnal equinoxes regarding the solar magnetic polarity dependency. However, the difference is not statistically significant. Thus, we conclude that there is no solar magnetic polarity dependency of the semiannual variation for quiet time geomagnetic activity.

  20. Geophysical variables and behavior: XXI. Geomagnetic variation as possible enhancement stimuli for UFO reports preceding earthtremors.

    PubMed

    Persinger, M A

    1985-02-01

    The contribution of geomagnetic variation to the occurrence of UFORs (reports of UFOs) within the New Madrid States during the 6-mo. increments before increases in the numbers of IV-V or less intensity earthquakes within the central USA was determined. Although statistically significant zero-order correlations existed between measures of earthquakes, UFORs and geomagnetic variability, the association between the latter two deteriorated markedly when their shared variance with earthquakes was held constant. These outcomes are compatible with the hypothesis that geomagnetic variability (or phenomena associated with it) may enhance UFORs but only if tectonic stress and strain are increasing within the region.

  1. Secular trends in seasonal variation in birth weight.

    PubMed

    Jensen, Camilla B; Gamborg, Michael; Raymond, Kyle; McGrath, John; Sørensen, Thorkild I A; Heitmann, Berit L

    2015-06-01

    Many environmental factors have been shown to influence birth weight (BW) and one of these are season of birth. The aim of the present study was to investigate the seasonal variation in BW in Denmark during 1936-1989, and to see if the variation could be explained by sunshine exposure during pregnancy. The study population was selected from the Copenhagen School Health Records Register and included 276 339 children born between 1936 and 1989. Seasonal variation was modeled using a non-stationary sinusoidal model that allowed the underlying trend in BW and the amplitude and phase of the yearly cycles to change. There was a clear seasonal pattern in BW which, however, changed gradually across the study period. The highest BWs were seen during fall (September - October) from 1936 to 1963, but a new peak gradually grew from the early 1940s during early summer (May - June) and became the highest from 1964 to 1989. The amplitude of the fall peak started at 25.5 (95%CI 24.6; 25.9) grams and gradually disappeared. The amplitude of the early summer peak gradually arose from nothing to a peak of 18.6 (95%CI 17.7; 19.6) grams in the mid 1980s where it started to decrease again. Sunshine did not explain the seasonal variation in BW. There was a clear seasonal pattern in BW in Denmark 1936-1989, which however changed across the study period. Throughout the study period we observed a peak in BW during the fall, but gradually, starting in the early 1940s, an additional early summer peak emerged and became the highest from 1964 and onwards. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

  2. Exploring the use of paleomagnetic secular variations to date young sediments from the hardwater lake Tangra Yumco (Tibet)

    NASA Astrophysics Data System (ADS)

    Haberzettl, T.; Kasper, T.; Long, H.; Su, Y.; Ahlborn, M.; Appel, E.; Daut, G.; Henkel, K.; St-Onge, G.; Wang, J.; Zhu, L.; Maeusbacher, R.

    2013-12-01

    Magnetostratigraphy has been serving as a valuable tool for dating and confirming chronologies of lacustrine sediments. Although the coverage of suitable paleomagnetic records on the Tibetan Plateau (TP) and around has been extremely scarce, recently emerging records enable a validation of existing age-depth models using magnetostratigraphy. This is very important, since almost all radiocarbon ages obtained from lacustrine sediments on the TP are affected by a reservoir effect. For example at Nam Co (co = lake) on the eastern TP the chronology for the past 4 ka cal BP was supported by the comparison of paleomagnetic secular variation (PSV) and results from spherical harmonic geomagnetic field models. In addition, this approach was confirmed by comparison of the directional data of Nam Co to a varved record from the Makran accretionary wedge which is much further to the south-west but shows remarkable similarities. Here we present PSV data from multiple sediment cores from lake Tangra Yumco, located ~400 km west of Nam Co. Inclination and declination data from the different sediment cores are very similar, but only one core has been sufficiently dated yet. Unfortunately, validation of the reservoir corrected radiocarbon based age scale from this core is very poor although it contains one age from a part of wood (which because of its terrestrial nature was not reservoir corrected). On this chronology, the Tangra Yumco PSV data shows neither similarities with the Nam Co record, nor with geomagnetic field model outputs. Interestingly, if the chronology from Tangra Yumco is tuned to the chronology of the validated Nam Co record using inclination data, the minerogenic input proxies become almost identical. The minerogenic input is indicative of runoff and hence hydrological variations due to changes in the monsoon strength. Very similar hydrological variations can also be observed in the independently-dated Hongyuan peat bog (further to the north-east) which suggests

  3. Present-day secular variations in the zonal harmonics of earth's geopotential

    NASA Technical Reports Server (NTRS)

    Mitrovica, J. X.; Peltier, W. R.

    1993-01-01

    The mathematical formulation required for predicting secular variation in the geopotential is developed for the case of a spherically symmetric, self-gravitating, viscoelastic earth model and an arbitrary surface load which can include a gravitational self-consistent ocean loading component. The theory is specifically applied to predict the present-day secular variation in the zonal harmonics of the geopotenial arising from the surface mass loading associated with the late Pleistocene glacial cycles. A procedure is outlined in which predictions of the present-day geopotential signal due to the late Pleistocene glacial cycles may be used to derive bounds on the net present-day mass flux from the Antarctic and Greenland ice sheets to the local oceans.

  4. Present-day secular variations in the zonal harmonics of earth's geopotential

    NASA Technical Reports Server (NTRS)

    Mitrovica, J. X.; Peltier, W. R.

    1993-01-01

    The mathematical formulation required for predicting secular variation in the geopotential is developed for the case of a spherically symmetric, self-gravitating, viscoelastic earth model and an arbitrary surface load which can include a gravitational self-consistent ocean loading component. The theory is specifically applied to predict the present-day secular variation in the zonal harmonics of the geopotenial arising from the surface mass loading associated with the late Pleistocene glacial cycles. A procedure is outlined in which predictions of the present-day geopotential signal due to the late Pleistocene glacial cycles may be used to derive bounds on the net present-day mass flux from the Antarctic and Greenland ice sheets to the local oceans.

  5. Solar neutrino production of long-lived isotopes and secular variations in the sun

    SciTech Connect

    Haxton, W.C.; Cowan, G.A.

    1980-11-21

    Long-lived isotopes produced in the earth's crust by solar neutrinos may provide a method of probing secular variations in the rate of energy production in the sun's core. Only one isotope, calcium-41, appears to be suitable from the dual standpoints of reliable nuclear physics and manageable backgrounds. The proposed measurement also may be interesting in view of recent evidence for neutrino oscillations.

  6. High-resolution chronology of sediment below CCD based on Holocene paleomagnetic secular variations in the Tohoku-oki earthquake rupture zone

    NASA Astrophysics Data System (ADS)

    Kanamatsu, Toshiya; Usami, Kazuko; McHugh, Cecilia M. G.; Ikehara, Ken

    2017-08-01

    Using high-resolution paleomagnetic data, we examined the potential for obtaining precise ages from sediment core samples recovered from deep-sea basins close to rupture zones of the 2011 and earlier earthquakes off Tohoku, Japan. Obtaining detailed stratigraphic ages from deep-sea sediments below the calcium compensation depth (CCD) is difficult, but we found that the samples contain excellent paleomagnetic secular variation records to constrain age models. Variations in paleomagnetic directions obtained from the sediments reveal systematic changes in the cores. A stacked paleomagnetic profile closely matches the Lake Biwa data sets in southwest Japan for the past 7000 years, one can establish age models based on secular variations of the geomagnetic field on sediments recovered uniquely below the CCD. Comparison of paleomagnetic directions near a tephra and a paleomagnetic direction of contemporaneous pyroclastic flow deposits acquired by different magnetization processes shows precise depositional ages reflecting the magnetization delay of the marine sediment record.Plain Language SummaryGenerally obtaining detailed ages from deep-sea sediments is difficult, because available dating method is very limited. We found that the deep-see sediment off North Japan recorded past sequential <span class="hlt">geomagnetic</span> directions. If those records correlate well with the reference record in past 7000 years, then we could estimate age of sediment by pattern matching. Additionally a volcanic ash emitted in 915 A.D., which was intercalated in our samples, indicates a time lag in our age model. This observation makes our age model more precise.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015IzPSE..51..574N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015IzPSE..51..574N"><span><span class="hlt">Variations</span> in <span class="hlt">geomagnetic</span> field and temperature in Spain during the past millennium</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nachasova, I. E.; Burakov, K. S.; Pilipenko, O. V.; Markov, G. P.</p> <p>2015-07-01</p> <p>The archaeomagnetic studies are conducted for the collection of coated ceramic samples from the Albarracin archaeological monument in Spain dated to the 10-20th centuries A.D. The pattern of <span class="hlt">variations</span> in <span class="hlt">geomagnetic</span> field intensity during this time interval is identified. The behavior of <span class="hlt">geomagnetic</span> intensity is dominated by a decreasing trend (from ˜80 to 40 μT). The <span class="hlt">variation</span> with a characteristic time of a few hundred years is the most striking one. Investigation of the material from this collection by the method of rehydroxylation provided the temperature estimates for this region of Spain for the time interval of pottery production. The temperature <span class="hlt">variations</span> generally tend to increase, while the main trend in the <span class="hlt">variations</span> of <span class="hlt">geomagnetic</span> intensity is decreasing. The time series of temperature and intensity of the main magnetic field contain <span class="hlt">variations</span> with close characteristic times shifted in time so that the changes in temperature go somewhat ahead of the changes in the <span class="hlt">geomagnetic</span> field. It was previously suggested to improve the accuracy and resolution of the obtained <span class="hlt">variations</span> in the past magnetic field using the method of archaeomagnetic dating of the material from archaeological monuments. The method was tested by dating the pottery kiln material from the El Molon monument, Spain, with the use of the virtual <span class="hlt">geomagnetic</span> pole curve based on the past magnetic field in the East Europe. The method proved to be quite efficient and promising for dating the archaeological material from all over Europe.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMGP43A1117Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMGP43A1117Y"><span>Paleosecular <span class="hlt">variations</span> of <span class="hlt">geomagnetic</span> field from the Last Glacial Maximum to the Holocene in the north of South China Sea</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yang, X.; Huang, W.; Liu, Q.</p> <p>2012-12-01</p> <p>The high-resolution <span class="hlt">geomagnetic</span> field records from the Last Glacial Maximum to the Holocene, which possessed of a notable climate change, were scarce in the global area. In this abstract, two gravity piston cores ZSQD2 (114.16oE, 19.58oN, ~190 cm in length, water depth 681m) and ZSQD34 (114.74oE, 19.05oN, ~184 cm in length, water depth 1820 m), situated in the north of South China Sea, were selected to study the <span class="hlt">secular</span> <span class="hlt">variations</span> of <span class="hlt">geomagnetic</span> field in this area. Radiocarbon ages of G.sacculifer suggest that the deposition rate varied with 56.1 cm/kyr and 3.7 cm/kyr during the Last Glacial and the Holocene, respectively. Rock magnetic results indicate that the pseudo-single domain magnetite with low coercivity dominate the properties of sediments. The characteristic remanent magnetization (ChRM) values are evaluated using the 5-8 AF steps when MAD values are generally <5. Constrained by the radiocarbon chronology, the <span class="hlt">secular</span> <span class="hlt">variation</span> curves since ~18 cal. kyr can be constructed using the ChRM directions and NRM/ARM ratios (as a proxy of relative intensity). Comparing the Holocene SV with that from terrestrial lakes in Southern China, similar shape corroborates the reliability of records and uniform pattern of non-dipole magnetic field. Two significant features on SV curves present the <span class="hlt">geomagnetic</span> field characteristics from ~17 cal. kyr to the early Holocene. One is that the direction <span class="hlt">variations</span> lag behind the relative intensity on the millennium time scale. Such as a major direction shift occurred around 13 cal. kyr while the relative intensity low was about 14 cal. kyr. Another feature is the fast and frequent wiggles both in direction and intensity between ~17 to ~14.5 cal. kyr. During this period, two significant negative inclination anomalies occurred at ~16.4 and ~15.4 cal. kyr associated with low intensity, respectively. Nevertheless, the corresponding declinations did not show the reversed features although they had also some slight fluctuations. The</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JGeod.tmp...41Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JGeod.tmp...41Y"><span>Contribution of solar radiation and <span class="hlt">geomagnetic</span> activity to global structure of 27-day <span class="hlt">variation</span> of ionosphere</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yao, Yibin; Zhai, Changzhi; Kong, Jian; Liu, Lei</p> <p>2017-04-01</p> <p>Twenty-seven-day <span class="hlt">variation</span> caused by solar rotation is one of the main periodic effects of solar radiation influence on the ionosphere, and there have been many studies on this periodicity using peak electron density N_{mF2} and solar radio flux index F10.7. In this paper, the global electron content (GEC) and observation of Solar EUV Monitor (SEM) represent the whole ionosphere and solar EUV flux, respectively, to investigate the 27-day <span class="hlt">variation</span>. The 27-day period components of indices (GEC_{27}, SEM_{27}, F10.7_{27}, Ap_{27}) are obtained using Chebyshev band-pass filter. The comparison of regression results indicates that the index SEM has higher coherence than F10.7 with 27-day <span class="hlt">variation</span> of the ionosphere. The regression coefficients of SEM_{27 } varied from 0.6 to 1.4 and the coefficients of Ap_{27} varied from - 0.6 to 0.3, which suggests that EUV radiation seasonal <span class="hlt">variations</span> are the primary driver for the 27-day <span class="hlt">variations</span> of the ionosphere for most periods. TEC map grid points on three meridians where IGS stations are dense are selected for regression, and the results show that the contribution of solar EUV radiation is positive at all <span class="hlt">geomagnetic</span> latitudes and larger than <span class="hlt">geomagnetic</span> activity in most latitudes. The contribution of <span class="hlt">geomagnetic</span> activity is negative at high <span class="hlt">geomagnetic</span> latitude, increasing with decreasing <span class="hlt">geomagnetic</span> latitudes, and positive at low <span class="hlt">geomagnetic</span> latitudes. The global structure of 27-day <span class="hlt">variation</span> of ionosphere is presented and demonstrates that there are two zonal anomaly regions along with the <span class="hlt">geomagnetic</span> latitudes lines and two peaks in the north of Southeast Asia and the Middle Pacific where TEC_{27} magnitude values are notably larger than elsewhere along zonal anomaly regions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015IAUGA..2235993H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015IAUGA..2235993H"><span>Analysis of the Solar Diameter <span class="hlt">Variations</span> at July, 1986 and the <span class="hlt">Geomagnetic</span> Storm of March, 1989</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Humberto Andrei, Alexandre; Garcia, Marcos A.; Papa, Andres R. R.; Calderari Boscardin, Sergio; Lousada Penna, Jucira; Sigismondi, Costantino</p> <p>2015-08-01</p> <p>In this work, we have a well-known event in scientific literature used to illustrate our investigation on the viability of the solar diameter <span class="hlt">variation</span> be a precursor for the occurrence of sets of coronal mass ejections, and thus, for <span class="hlt">geomagnetic</span> storms, as noted in previous works of our group, but now, in a time scale of a few days. The selected event was that of March 13, 1989, a strong <span class="hlt">geomagnetic</span> storm that made the Hydro-Quebec power grid fall down by 9 hours, damaging the local economy in millions of dollars. At the same time we have investigated a time interval belonging to a solar minimum period, on July 1986, prior to the rising phase and solar maximum of Solar Cycle 22, to compare with the <span class="hlt">geomagnetic</span> pattern, as well as with the solar diameter behavior along these periods of low solar and <span class="hlt">geomagnetic</span> activity. We used the time series of the CERGA’s astrolabe (because its dataset is long enough as to comprise both time periods of the analysis), the <span class="hlt">geomagnetic</span> index AP and the H <span class="hlt">geomagnetic</span> component from the Tatuoca Magnetic Observatory (because it is near to the <span class="hlt">geomagnetic</span> equator and with the extra aim of checking the sensitivity of its magnetometers to global events).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70015817','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70015817"><span>What do we mean by accuracy in <span class="hlt">geomagnetic</span> measurements?</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Green, A.W.</p> <p>1990-01-01</p> <p>High accuracy is what distinguishes measurements made at the world's magnetic observatories from other types of <span class="hlt">geomagnetic</span> measurements. High accuracy in determining the absolute values of the components of the Earth's magnetic field is essential to studying <span class="hlt">geomagnetic</span> <span class="hlt">secular</span> <span class="hlt">variation</span> and processes at the core mantle boundary, as well as some magnetospheric processes. In some applications of <span class="hlt">geomagnetic</span> data, precision (or resolution) of measurements may also be important. In addition to accuracy and resolution in the amplitude domain, it is necessary to consider these same quantities in the frequency and space domains. New developments in <span class="hlt">geomagnetic</span> instruments and communications make real-time, high accuracy, global <span class="hlt">geomagnetic</span> observatory data sets a real possibility. There is a growing realization in the scientific community of the unique relevance of <span class="hlt">geomagnetic</span> observatory data to the principal contemporary problems in solid Earth and space physics. Together, these factors provide the promise of a 'renaissance' of the world's <span class="hlt">geomagnetic</span> observatory system. ?? 1990.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013E%26PSL.363..168F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013E%26PSL.363..168F"><span>First archeointensity determinations on Maya incense burners from Palenque temples, Mexico: New data to constrain the Mesoamerica <span class="hlt">secular</span> <span class="hlt">variation</span> curve</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fanjat, G.; Camps, P.; Alva Valdivia, L. M.; Sougrati, M. T.; Cuevas-Garcia, M.; Perrin, M.</p> <p>2013-02-01</p> <p>We present archeointensity data carried out on pieces of incense burners from the ancient Maya city of Palenque, Chiapas, Mexico, covering much of the Mesoamerican Classic period, from A.D. 400 to A.D. 850. We worked on pieces from 24 incense burners encompassing the five Classic ceramic phases of Palenque: Motiepa (A.D. 400-500), Cascadas (A.D. 500-600), Otulum (A.D. 600-700), Murcielagos (A.D. 700-770), and Balunté (A.D. 770-850). All the samples come from highly elaborate, flanged pedestal of incense burners that are undoubtedly assigned to a ceramic phase by means of their iconographic, morphological and stylistic analyses. Archeointensity measurements were performed with the Thellier-Thellier's method on pre-selected samples by means of their magnetic properties. We obtained archeointensities of very good technical quality from 19 of 24 pieces, allowing the determination of a precise mean value for each ceramic phase, between 29.1±0.9 μT and 32.5±1.2 μT. The firing temperatures of ceramics were estimated with Mössbauer spectroscopy between 700 °C and 1000 °C. These values ensure that a full thermo-remanent magnetization was acquired during the original heating. Our results suggest a relative stability of the field intensity during more than 400 years in this area. The abundance of archeological material in Mesoamerica contrasts with the small amount of archeomagnetic data available that are, in addition, of uneven quality. Thus, it is not possible to establish a trend of intensity <span class="hlt">variations</span> in Mesoamerica, even using the global databases and <span class="hlt">secular</span> <span class="hlt">variation</span> predictions from global models. In this context, our high technical quality data represent a strong constraint for the Mesoamerican <span class="hlt">secular</span> <span class="hlt">variation</span> curve during the first millennium AD. The corresponding Virtual Axial Dipole Moments (VADM) are substantially smaller than the ones predicted by the last global <span class="hlt">geomagnetic</span> models CALS3k.4, suggesting the need for additional data to develop a</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010ASPC..424...88G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010ASPC..424...88G"><span>Analysis of <span class="hlt">Geomagnetic</span> Disturbances and Cosmic Ray Intensity <span class="hlt">Variations</span> in Relation to Medical Data from Rome</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Giannaropoulou, E.; Papailiou, M.; Mavromichalaki, H.; Tsipis, A.</p> <p>2010-07-01</p> <p>Over the last few years many studies have been conducted concerning the possible influence of <span class="hlt">geomagnetic</span> and solar activity and cosmic ray activity on human physiological state and in particular on human cardio - health state. As it is shown the human organism is sensitive to environmental changes and reacts to them through a series of <span class="hlt">variations</span> of its physiological parameters such as heart rate, arterial systolic and diastolic blood pressure, etc. In this paper daily mean values of heart rate, as they were registered for a group of 2.028 volunteers during medical examinations in the Polyclinico Tor Vergata, Rome, Italy are analyzed in relation to daily cosmic ray intensity <span class="hlt">variations</span>, as measured by the Neutron Monitor of the University of Athens and daily <span class="hlt">variations</span> of the <span class="hlt">geomagnetic</span> indices Dst, Ap and Kp. The results from this study show that <span class="hlt">geomagnetic</span> activity changes and cosmic rays intensity <span class="hlt">variations</span> may regulate the human homeostasis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005KFNTS...5..165K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005KFNTS...5..165K"><span><span class="hlt">Secular</span> behaviour of <span class="hlt">geomagnetic</span> indices IHV, C9, aa since 1901 and presumed rising of solar open magnetic field flux</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kobylinski, Z.; Trebicka, R.; Izdebska, I.</p> <p>2005-06-01</p> <p>We examine long-term series of IHV and C9 <span class="hlt">geomagnetic</span> indices calculated from the data derived during the 20th century in St.-Petersburg, Pavlovsk, Swider, Cheltenham, Fredericksburg, Kakioka, and Honolulu in order to verify the conclusion of Lockwood et al. [8] that the total magnetic flux leaving the Sun increased by a factor of 2.3 since 1901. It was supported on the analysis of aa <span class="hlt">geomagnetic</span> index which shows a drift upward from the 12th-13th solar cycle to the 22nd cycle. The mean level of the annual averages of indices used here have been approximately constant or showed the clearly smaller rising than aa drift upward from 1901 till 1960. We conclude that the double rising of solar magnetic flux during the 20th century is questionable.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMGP53C1166V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMGP53C1166V"><span>The Effect of a Heterogeneous Thin Electrically Conducting Lower Mantle Layer on <span class="hlt">Secular</span> <span class="hlt">Variation</span> in the Geodynamo</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vilim, R.; Dumberry, M.; Stanley, S.</p> <p>2013-12-01</p> <p>Recent studies have shown that the rate of <span class="hlt">secular</span> <span class="hlt">variation</span> is not constant over the Earth. Particularly, the Pacific Ocean is remarkably devoid of any quickly time varying magnetic field components. While this could be due to factors intrinsic to the dynamo, the Earth's lowest mantle displays a remarkable heterogeneity that could also help explain the pattern of <span class="hlt">secular</span> <span class="hlt">variation</span> if this deep mantle heterogeneity can couple to the dynamo. There have been several recent studies that discuss the possibility of an electrically conducting lower mantle, either because of the metallization of FeO, or from the deep penetration of iron into the mantle due to morphological instabilities. If a thin lower mantle layer is heterogeneous in electrical conductivity it could couple to the flow via the Lorenz force and brake the eddies which contribute to <span class="hlt">secular</span> <span class="hlt">variation</span>, lowering both the field amplitude and the rate of <span class="hlt">secular</span> <span class="hlt">variation</span>. A conducting mantle layer will also preferentially damp the quickly time varying components of the magnetic field via the electromagnetic screening effect, reducing the <span class="hlt">secular</span> <span class="hlt">variation</span> we observe at the surface of the Earth. While other studies have investigated the thermal effects of a heterogeneous lower mantle on the dynamo, we investigate the effects of a thin electrically conducting lower mantle layer. We use a numerical geodynamo model to determine whether this layer can cause the spatial pattern of <span class="hlt">secular</span> <span class="hlt">variation</span> rates observed for the Earth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMGP51B1338L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMGP51B1338L"><span>Temporal correlation of U. S. Great Basin lake sediments below the Mono Lake Excursion using paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liddicoat, J. C.; Coe, R. S.; Negrini, R. M.; Knott, J. R.; Lund, S.; Benson, L. V.</p> <p>2015-12-01</p> <p>Beginning nearly 50 years ago with a paleomagnetic study of exposed lacustrine sediments in the Mono Basin, CA (Denham and Cox, 1971), there have been subsequent studies to document paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> (PSV) in the basin and to establish a chronology for that record (Vazquez and Lidzbarski, 2012). We report a paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> (PSV) investigation of lacustrine sediments in the Mono Basin, CA, that extends the base of the PSV record of Lund et al. (1988) by about 20 percent. We did our investigation at two localities separated by about 4 km on the southeastern and eastern sides of Mono Lake: South Shore Cliffs (SSC) and Warm Springs (WS). The sampled interval at SSC is from 0.1 m above to 2.2 m below Wilson Creek Ash 19 in the tephrostratigraphy of Lajoie (1968), ending in loose sand. At WS, we sampled from Ash 17 to 1.0 m below Ash 19, a total of 2 m. At SSC using back-to-back horizons 2-cm thick containing one to three samples each that were a.f. or thermally demagnetized, we found rapidly fluctuating PSV in the interval from ~ 0.3 to 1.0 m below Ash 19. The fluctuating PSV contains a change in declination of ~ 80˚ from 308˚ (n = 3, α-95: 6.1˚) to 29˚ (n = 3, α-95: 11.5˚) within a single hand sample that spans 14 cm. Inclination during that change in declination gradually rose from 56˚ to 63˚ and increased to 70˚ before reducing to a minimum of 29.9˚. The path of the Virtual <span class="hlt">Geomagnetic</span> Poles when the declination is most westerly forms a narrow loop that reaches 49.7˚ N latitude near 170˚ E longitude. At WS the westerly swing in declination is absent, but the easterly declination and relatively steep inclination described above are recorded. A study of the relative paleomagnetic intensity (RPI) shows that the maximum RPI is ~1.5 m below Ash 19 and decreases to a minimum ~6 cm above the ash. Distinct PSV and RPI features below the Mono Lake excursion correlate well between records from the periphery of Mono Lake and those from</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMSA41C4075S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMSA41C4075S"><span>Characteristics of long-term <span class="hlt">variation</span> in the amlitude of the <span class="hlt">geomagnetic</span> solar quiet (Sq) daily <span class="hlt">variation</span> using the Inter-university Upper atmosphere Gobal Observation NETwork (IUGONET) data analysis system</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shinbori, A.; Koyama, Y.; Nose, M.; Hori, T.; Otsuka, Y.; Yatagai, A. I.</p> <p>2014-12-01</p> <p>Characteristics of long-term <span class="hlt">variation</span> in the amplitude of solar quiet <span class="hlt">geomagnetic</span> field daily <span class="hlt">variation</span> (Sq) have been investigated using 1-hour <span class="hlt">geomagnetic</span> field data obtained from 69 <span class="hlt">geomagnetic</span> stations in a period of 1947-2013. In the present data analysis, we took advantage of the IUGONET data analysis system. The Sq amplitude clearly showed a 10-12 year solar activity dependence and it tended to enhance during each solar maximum. During the minimum of solar cycle 23/24 in 2008-2009, the Sq amplitude became the smallest in the investigated period. The relationship between the solar F10.7 index and Sq amplitude is approximately linear but 64 percent of <span class="hlt">geomagnetic</span> stations show a weak nonlinear dependence on the solar F10.7 index. In order to remove the effect of solar activity seen in the long-term <span class="hlt">variation</span> of the Sq amplitude, we calculated a linear or second order fitting curve between the solar F10.7 index and Sq amplitude during 1947-2013, and examined the residual Sq amplitude, which is defined as the deviation from the fitting curve. As a result, a majority of the trends in the residual Sq amplitude that passed through a trend test showed a negative value in a wide region. This tendency was relatively strong in Europe, India, the eastern part of Canada, and New Zealand. The relationship between the magnetic field intensity and residual Sq amplitude showed an anti-correlation for about 71 percent of <span class="hlt">geomagnetic</span> stations. On the other hand, the residual Sq amplitude in the equatorial station (Addis Ababa) was anti-correlated with the absolute value of the magnetic field inclination. This implies the movement of the equatorial electrojet due to the <span class="hlt">secular</span> <span class="hlt">variation</span> of the ambient magnetic field.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMGP53A3757I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMGP53A3757I"><span>Spherical Cap Harmonic Modelling of 400 Years of <span class="hlt">Secular</span> <span class="hlt">Variation</span> in the South-west Pacific</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ingham, M.; Alfheid, M.; Ingham, E. M.; Turner, G. M.</p> <p>2014-12-01</p> <p>Historical magnetic data recorded in ship's logs on voyages of exploration and trade in the south-west Pacific have been used as a basis for constructing a model of <span class="hlt">secular</span> <span class="hlt">variation</span> in the region using spherical cap harmonic (SCH) analysis. The spherical cap used is centred on colatitude 115° and longitude 160° and has a radius of 50°, thus covering New Zealand, Australia and parts of Antarctica. Gaps in the observational data have been filled by an iterative procedure started by using IGRF field values to obtain SCH models for 2000, 1950 and 1900 and assuming that the spherical cap coefficients have a linear <span class="hlt">variation</span> in time over the 400 year time period of the model, as is observed to a first approximation for Gauss coefficients calculated from a global spherical harmonic analysis. The resulting field models have generally smooth spatial and temporal <span class="hlt">variations</span> in declination, inclination and intensity which show some differences from the <span class="hlt">variations</span> calculated using the global spherical harmonic model gufm1. The technique clearly shows promise for producing more refined models of <span class="hlt">secular</span> <span class="hlt">variation</span> in the south-west Pacific when the historical data are supplemented by archeomagnetic and paleomagnetic data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920023411','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920023411"><span>Steady induction effects in <span class="hlt">geomagnetism</span>. Part 1A: Steady motional induction of <span class="hlt">geomagnetic</span> chaos</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Voorhies, Coerte V.</p> <p>1992-01-01</p> <p><span class="hlt">Geomagnetic</span> effects of magnetic induction by hypothetically steady fluid motion and steady magnetic flux diffusion near the top of Earth's core are investigated using electromagnetic theory, simple magnetic earth models, and numerical experiments with <span class="hlt">geomagnetic</span> field models. The problem of estimating a steady fluid velocity field near the top of Earth's core which induces the <span class="hlt">secular</span> <span class="hlt">variation</span> indicated by broad-scale models of the observed <span class="hlt">geomagnetic</span> field is examined and solved. In Part 1, the steady surficial core flow estimation problem is solved in the context of the source-free mantle/frozen-flux core model. In the first paper (IA), the theory underlying such estimates is reviewed and some consequences of various kinematic and dynamic flow hypotheses are derived. For a frozen-flux core, fluid downwelling is required to change the mean square normal magnetic flux density averaged over the core-mantle boundary. For surficially geostrophic flow, downwelling implies poleward flow. The solution of the forward steady motional induction problem at the surface of a frozen-flux core is derived and found to be a fine, easily visualized example of deterministic chaos. <span class="hlt">Geomagnetic</span> effects of statistically steady core surface flow may well dominate <span class="hlt">secular</span> <span class="hlt">variation</span> over several decades. Indeed, effects of persistent, if not steady, surficially geostrophic core flow are described which may help explain certain features of the present broad-scale <span class="hlt">geomagnetic</span> field and perhaps paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010SpWea...8.5001K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010SpWea...8.5001K"><span>Solar energetic particle cutoff <span class="hlt">variations</span> during the 29-31 October 2003 <span class="hlt">geomagnetic</span> storm</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kress, B. T.; Mertens, C. J.; Wiltberger, M.</p> <p>2010-05-01</p> <p>At low latitudes to midlatitudes the Earth's magnetic field usually shields the upper atmosphere and spacecraft in low Earth orbit from solar energetic particles (SEPs). During severe <span class="hlt">geomagnetic</span> storms, distortion of the Earth's field suppresses <span class="hlt">geomagnetic</span> shielding, allowing SEPs access to the midlatitudes. A case study of the 26-31 October 2003 solar-<span class="hlt">geomagnetic</span> event is used to examine how a severe <span class="hlt">geomagnetic</span> storm affects SEP access to the Earth. <span class="hlt">Geomagnetic</span> cutoffs are numerically determined in model <span class="hlt">geomagnetic</span> fields using code developed by the Center for Integrated Space Weather Modeling (CISM) at Dartmouth College. The CISM-Dartmouth <span class="hlt">geomagnetic</span> cutoff model is being used in conjunction with the High Energy and Charge Transport code (HZETRN) at the NASA Langley Research Center to develop a real-time data-driven prediction of radiation exposure at commercial airline altitudes. In this work, cutoff rigidities are computed on global grids and along several high-latitude flight routes before and during the <span class="hlt">geomagnetic</span> storm. It is found that significant <span class="hlt">variations</span> in SEP access to the midlatitudes and high latitudes can occur on time scales of an hour or less in response to changes in the solar wind dynamic pressure and interplanetary magnetic field. The maximum suppression of the cutoff is ˜1 GV occurring in the midlatitudes during the main phase of the storm. The cutoff is also significantly suppressed by the arrival of an interplanetary shock. The maximum suppression of the cutoff due to the shock is approximately one half of the maximum suppression during the main phase of the storm.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_9 --> <div id="page_10" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="181"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1914631O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1914631O"><span>Annual <span class="hlt">Variations</span> of the <span class="hlt">Geomagnetic</span> Field in the Earth's Polar Regions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ou, Jiaming; Du, Aimin</p> <p>2017-04-01</p> <p>The annual <span class="hlt">variations</span> of the <span class="hlt">geomagnetic</span> field play an important role in the coupling processes between the solar wind, magnetosphere and ionosphere. The annual <span class="hlt">variation</span> is a well-established feature of the <span class="hlt">geomagnetic</span> field, and usually is applied for modeling the conductivity of the lower mantle [Parkinson, 1983], and for long-term space weather forecasting [Bartels, 1932; Malin and Mete Isikara, 1976; Gonzalez et al., 1994]. Considerable effort has been devoted toward understanding the causes of the <span class="hlt">geomagnetic</span> field <span class="hlt">variations</span>, but the suggested physical mechanisms differ widely. The annual <span class="hlt">variation</span> is relatively weak in many magnetic indices, but it has a distinct signature in the <span class="hlt">geomagnetic</span> components. Thus, we use the components for this analysis. The components have a positive peak in northern summer and a negative dip in winter [Vestine, 1954]. Vestine [1954] suggested that the annual <span class="hlt">variation</span> is caused by an ionospheric dynamo in which electric currents in the ionosphere are generated by meridional winds. The winds blow from north-to-south during northern summer, and south-to-north in northern winter. Malin and Mete Isikara [1976], using near-midnight <span class="hlt">geomagnetic</span> data, concluded that the annual <span class="hlt">variation</span> results from a latitudinal movement of the auroral electrojet or the ring current. Stauning [2011] derived of the seasonal <span class="hlt">variation</span> of the quiet daily <span class="hlt">variations</span> and examined the influence of the sector structure of the interplanetary magnetic field. Ziegger and Mursula [1998] have suggested a third mechanism: that the cause is related to an asymmetric solar wind speed distribution across the heliographic equator. In this paper, we study the annual <span class="hlt">variation</span> problem using long-term magnetic observation and ionospheric conductivity. The sunlight incident on the ionosphere will be calculated. Although a global analysis is done, particular focus will be placed on the polar regions. This study covers the interval 1990-2010, and the cause of the well</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4233730','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4233730"><span><span class="hlt">Geomagnetic</span> imprinting predicts spatio-temporal <span class="hlt">variation</span> in homing migration of pink and sockeye salmon</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Putman, Nathan F.; Jenkins, Erica S.; Michielsens, Catherine G. J.; Noakes, David L. G.</p> <p>2014-01-01</p> <p>Animals navigate using a variety of sensory cues, but how each is weighted during different phases of movement (e.g. dispersal, foraging, homing) is controversial. Here, we examine the <span class="hlt">geomagnetic</span> and olfactory imprinting hypotheses of natal homing with datasets that recorded <span class="hlt">variation</span> in the migratory routes of sockeye (Oncorhynchus nerka) and pink (Oncorhynchus gorbuscha) salmon returning from the Pacific Ocean to the Fraser River, British Columbia. Drift of the magnetic field (i.e. <span class="hlt">geomagnetic</span> imprinting) uniquely accounted for 23.2% and 44.0% of the <span class="hlt">variation</span> in migration routes for sockeye and pink salmon, respectively. Ocean circulation (i.e. olfactory imprinting) predicted 6.1% and 0.1% of the <span class="hlt">variation</span> in sockeye and pink migration routes, respectively. Sea surface temperature (a variable influencing salmon distribution but not navigation, directly) accounted for 13.0% of the <span class="hlt">variation</span> in sockeye migration but was unrelated to pink migration. These findings suggest that <span class="hlt">geomagnetic</span> navigation plays an important role in long-distance homing in salmon and that consideration of navigation mechanisms can aid in the management of migratory fishes by better predicting movement patterns. Finally, given the diversity of animals that use the Earth's magnetic field for navigation, <span class="hlt">geomagnetic</span> drift may provide a unifying explanation for spatio-temporal <span class="hlt">variation</span> in the movement patterns of many species. PMID:25056214</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25056214','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25056214"><span><span class="hlt">Geomagnetic</span> imprinting predicts spatio-temporal <span class="hlt">variation</span> in homing migration of pink and sockeye salmon.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Putman, Nathan F; Jenkins, Erica S; Michielsens, Catherine G J; Noakes, David L G</p> <p>2014-10-06</p> <p>Animals navigate using a variety of sensory cues, but how each is weighted during different phases of movement (e.g. dispersal, foraging, homing) is controversial. Here, we examine the <span class="hlt">geomagnetic</span> and olfactory imprinting hypotheses of natal homing with datasets that recorded <span class="hlt">variation</span> in the migratory routes of sockeye (Oncorhynchus nerka) and pink (Oncorhynchus gorbuscha) salmon returning from the Pacific Ocean to the Fraser River, British Columbia. Drift of the magnetic field (i.e. <span class="hlt">geomagnetic</span> imprinting) uniquely accounted for 23.2% and 44.0% of the <span class="hlt">variation</span> in migration routes for sockeye and pink salmon, respectively. Ocean circulation (i.e. olfactory imprinting) predicted 6.1% and 0.1% of the <span class="hlt">variation</span> in sockeye and pink migration routes, respectively. Sea surface temperature (a variable influencing salmon distribution but not navigation, directly) accounted for 13.0% of the <span class="hlt">variation</span> in sockeye migration but was unrelated to pink migration. These findings suggest that <span class="hlt">geomagnetic</span> navigation plays an important role in long-distance homing in salmon and that consideration of navigation mechanisms can aid in the management of migratory fishes by better predicting movement patterns. Finally, given the diversity of animals that use the Earth's magnetic field for navigation, <span class="hlt">geomagnetic</span> drift may provide a unifying explanation for spatio-temporal <span class="hlt">variation</span> in the movement patterns of many species.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008GeoJI.175..462C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008GeoJI.175..462C"><span>Palaeomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> and rock-magnetic studies of Holocene sediments from a maar lake (Hoya de San Nicolas) in Central Mexico</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chaparro, Marcos A. E.; Böhnel, Harald N.; Byrne, Roger; Nowaczyk, Norbert R.; Molina-Garza, Roberto S.; Park, Jungjae; Negendank, Jörg F. W.</p> <p>2008-11-01</p> <p>Three up to 520-cm-long sediment cores from Hoya San Nicolas in Guanajuato, Mexico, were analysed for various magnetic properties in order to better define a palaeomagnetic <span class="hlt">secular</span> curve for Central Mexico. The results-magnetic susceptibility, hysteresis cycles, anhysteretic and isothermal remanent magnetization-suggest that the remanent magnetization of the sediments is controlled by ferrimagnetic minerals (pseudo-single domain magnetite), which are suitable recorders of the <span class="hlt">geomagnetic</span> field. The age-depth model indicates average deposition rates of 0.32 (interval 146-198 cm) and 0.45 mm yr-1 (interval 200-520 cm) and a basal age of about 11 600 calibrated years BP (cal. yr BP). We used magnetic susceptibility and natural remanent magnetization to correlate the three cores. A composite palaeomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> (SV) record was obtained from the cores with a stretching and stacking process, and a chronology established with accelerator mass spectrometer dates on microscopic charcoal and stratigraphic correlations with other well dated Holocene records from Mexico and Guatemala. The declination and inclination results show oscillatory behaviour varying in a narrow range, although a distinctive directional swing is evident between 9060 and 9810 cal. yr BP. The San Nicolas palaeomagnetic SV curve is similar to palaeomagnetic master curves from Europe and North America, in shape, occurrence and synchronicity of directional features, especially with respect to inclination.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SpWea..14..210A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SpWea..14..210A"><span>PAMELA's measurements of <span class="hlt">geomagnetic</span> cutoff <span class="hlt">variations</span> during the 14 December 2006 storm</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Adriani, O.; Barbarino, G. C.; Bazilevskaya, G. A.; Bellotti, R.; Boezio, M.; Bogomolov, E. A.; Bongi, M.; Bonvicini, V.; Bottai, S.; Bruno, A.; Cafagna, F.; Campana, D.; Carlson, P.; Casolino, M.; Castellini, G.; De Donato, C.; Nolfo, G. A.; De Santis, C.; De Simone, N.; Di Felice, V.; Galper, A. M.; Karelin, A. V.; Koldashov, S. V.; Koldobskiy, S.; Krutkov, S. Y.; Kvashnin, A. N.; Leonov, A.; Malakhov, V.; Marcelli, L.; Martucci, M.; Mayorov, A. G.; Menn, W.; Mergé, M.; Mikhailov, V. V.; Mocchiutti, E.; Monaco, A.; Mori, N.; Munini, R.; Osteria, G.; Palma, F.; Panico, B.; Papini, P.; Pearce, M.; Picozza, P.; Ricci, M.; Ricciarini, S. B.; Sarkar, R.; Scotti, V.; Simon, M.; Sparvoli, R.; Spillantini, P.; Stozhkov, Y. I.; Vacchi, A.; Vannuccini, E.; Vasilyev, G. I.; Voronov, S. A.; Yurkin, Y. T.; Zampa, G.; Zampa, N.</p> <p>2016-03-01</p> <p>Data from the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) satellite experiment were used to measure the <span class="hlt">geomagnetic</span> cutoff for high-energy (≳ 80MeV) protons during the 14 December 2006 <span class="hlt">geomagnetic</span> storm. The <span class="hlt">variations</span> of the cutoff latitude as a function of rigidity were studied on relatively short timescales, corresponding to spacecraft orbital periods (˜94 min). Estimated cutoff values were compared with those obtained by means of a trajectory-tracing approach based on a dynamical empirical modeling of the Earth's magnetosphere. We found significant <span class="hlt">variations</span> in the cutoff latitude, with a maximum suppression of ˜7° at lowest rigidities during the main phase of the storm. The observed reduction in the <span class="hlt">geomagnetic</span> shielding and its temporal evolution were related to the changes in the magnetospheric configuration, investigating the role of interplanetary magnetic field, solar wind, and <span class="hlt">geomagnetic</span> parameters. PAMELA's results represent the first direct measurement of <span class="hlt">geomagnetic</span> cutoffs for protons with kinetic energies in the sub-GeV and GeV region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11540872','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11540872"><span><span class="hlt">Secular</span> <span class="hlt">variation</span> in carbon isotope ratios from Upper Proterozoic successions of Svalbard and East Greenland.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Knoll, A H; Hayes, J M; Kaufman, A J; Swett, K; Lambert, I B</p> <p>1986-06-26</p> <p>Analyses of stratigraphically continuous suites of samples from Upper Proterozoic sedimentary successions of East Greenland, Spitsbergen and Nordaustlandet (Svalbard) provide an approximation to the <span class="hlt">secular</span> <span class="hlt">variation</span> in carbon isotope ratios during a geologically and biologically important period of change from around 900 million years ago to the beginning of the Cambrian period. Late Riphean carbonates and organic material show a stratigraphically useful pattern of enrichment in 13C relative to Phanerozoic or earlier Proterozoic samples. Isotopic compositions of isolated samples from other localities are consistent with a worldwide extended interval of enhanced organic burial and consequent net survival of oxidized material, probably O2, just before the initial radiation of metazoans.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.474....1B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.474....1B"><span>Retrodiction of <span class="hlt">secular</span> <span class="hlt">variations</span> in deep-sea CaCO3 burial during the Cenozoic</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Boudreau, Bernard P.; Luo, Yiming</p> <p>2017-09-01</p> <p>Deep-sea sediments record changes in oceanic carbonate chemistry and CaCO3 sedimentation rate through temporal <span class="hlt">variations</span> in the total burial of CaCO3 and the position of the carbonate snowline, i.e., the ocean depth at which CaCO3-free sediments are first recorded. This paper links mathematically <span class="hlt">secular</span> changes in snowline to those in the burial rate through a set of relatively simple equations. When the available Cenozoic deep-sea burial records are employed to predict <span class="hlt">secular</span> <span class="hlt">variations</span> in snowline, the process fails at some time in the past, indicating that these records are not consistent with each other. The burial records are more likely the source of this problem, as they involve far more uncertainties than the snowline records. As a consequence, we introduce a method for estimating carbonate burial through the use of a canonical CaCO3-depth profile, which can respond dynamically to <span class="hlt">secular</span> changes in carbonate sedimentation and the positions of both the snowline and the carbonate saturation horizon. The resulting synthetic CaCO3 burial record is consistent with snowline records and indicates that the burial rates offered by Davies and Worsley (1981) are generally too high, with highly questionable maxima at 25 and 47 Ma BP. Our estimates of burial are more consistent with the range advanced by Mackenzie and Morse (1992); nevertheless, our results differ from the latter with respect to timing and magnitude of the <span class="hlt">variations</span>. Our approach allows simultaneous calculation of the mean carbonate ion concentration of the deep sea. We find that carbonate-ion levels fell through the Cenozoic and are similar to those calculated by Tyrrell and Zeebe (2004), using a different model. <span class="hlt">Secular</span> <span class="hlt">variations</span> in CaCO3 burial are found to be primarily driven by changes in the Ca2+-CO3 2 - ion product within the bottom-waters, with an increase in the sedimentation rate of CaCO3 of secondary importance over the Cenozoic.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMGP23A1276B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMGP23A1276B"><span>Global <span class="hlt">Secular</span> <span class="hlt">Variation</span> and Excursions Within the Brunhes - is it Real?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Barckhausen, U.; Weske, M.</p> <p>2015-12-01</p> <p>We analyzed 64 high quality magnetic profiles crossing the Central Indian Ridge and the Southeast Indian Ridge between 21°S and 28°S. All profiles cover the entire Anomaly 1 and they do not cross discontinuities, major faults, or significant isolated bathymetric features. When stacked over single ridge segments, correlated <span class="hlt">variations</span> in the magnetic field become apparent. However, these <span class="hlt">variations</span> change from one ridge segment to the next and when stacked over the entire ridge, all correlated <span class="hlt">variations</span> are lost. Therefore we conclude that the correlated <span class="hlt">variations</span> represent local effects, in this case mainly caused by bathymetry and irregularities of the spreading process which are typically limited to one ridge segment. Since we do not see any anomalies associated to <span class="hlt">geomagnetic</span> excursions, we carried out forward modelling which shows that any excursion lasting for longer than 10.000 years should become visible in our data, thus putting an upper limit of 10.000 years to the maximum duration of <span class="hlt">geomagnetic</span> excursions during the Brunhes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeoRL..42.7933T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeoRL..42.7933T"><span>Evidence for a new <span class="hlt">geomagnetic</span> jerk in 2014</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Torta, J. Miquel; Pavón-Carrasco, F. Javier; Marsal, Santiago; Finlay, Christopher C.</p> <p>2015-10-01</p> <p>The production of quasi-definitive data at Ebre observatory has enabled us to detect a new <span class="hlt">geomagnetic</span> jerk in early 2014. This has been confirmed by analyzing data at several observatories in the European-African and Western Pacific-Australian sectors in the classical fashion of looking for the characteristic V shape of the <span class="hlt">geomagnetic</span> <span class="hlt">secular</span> <span class="hlt">variation</span> trend. A global model produced with the latest available satellite and observatory data supports these findings, giving a global perspective on both the jerk and a related <span class="hlt">secular</span> acceleration pulse at the core-mantle boundary. We conclude that the jerk was most visible in the Atlantic and European sectors.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015IzPSE..51..709N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015IzPSE..51..709N"><span>The <span class="hlt">geomagnetic</span> field intensity <span class="hlt">variations</span> in the Iberian Peninsula during the last millennium</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nachasova, I. E.; Akimova, S. V.</p> <p>2015-09-01</p> <p>The pattern of <span class="hlt">variations</span> in the intensity of the <span class="hlt">geomagnetic</span> field starting from the middle of the sixth millennium B.C. is reconstructed from the data about the intensity of the ancient <span class="hlt">geomagnetic</span> field in the region of the Iberian Peninsula provided by the archaeomagnetic studies of ceramics from archaeological monuments. In this time interval, the intensity of the field widely varies from ~30 to ~90 µT. The smooth <span class="hlt">variation</span> of the field is superimposed by the <span class="hlt">variations</span> with characteristic times from thousands to hundreds of years. The intensity <span class="hlt">variations</span> can be subdivided into two groups: rather sharp <span class="hlt">variations</span> with a characteristic duration of about 200 years and smooth quasi-harmonic fluctuations with a duration of a few hundred years.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11605400','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11605400"><span>[Biotropic effects of <span class="hlt">geomagnetic</span> storms and their seasonal <span class="hlt">variations</span>].</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kuleshova, V P; Pulinets, S A; Sazanova, E A; Kharchenko, A M</p> <p>2001-01-01</p> <p>A substantial effect of <span class="hlt">geomagnetic</span> storms on human health with a confidential probability P = 0.95 was revealed. The quantitative estimates of the biotropic effect are presented. For example, the frequency of occurrence of bursts exceeding the average number of hospitalized patients with mental and cardiovascular diseases during magnetic storms increases approximately 2 times compared with quiet periods (based on the data on 1983-84). The frequency of occurrence of myocardial infarction, angina pectoris, violation of cardial rhythm, acute violation of brain blood circulation during storms increases 2.1; 1.6; 1.6; 1.5 times, respectively compared with magnetically quiet periods (based on the data of 1992-96). A similarity of the seasonal distribution of the magnitude of the biotropic effect is revealed in the case of myocardial infarction and the number of magnetic storms: a maximum in the equinox and a minimum in summer.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930037356&hterms=field+magnetic+Earth&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dfield%2Bmagnetic%2BEarth','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930037356&hterms=field+magnetic+Earth&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dfield%2Bmagnetic%2BEarth"><span>The steady part of the <span class="hlt">secular</span> <span class="hlt">variation</span> of the Earth's magnetic field</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bloxham, Jeremy</p> <p>1992-01-01</p> <p>The <span class="hlt">secular</span> <span class="hlt">variation</span> of the Earth's magnetic field results from the effects of magnetic induction in the fluid outer core and from the effects of magnetic diffusion in the core and the mantle. Adequate observations to map the magnetic field at the core-mantle boundary extend back over three centuries, providing a model of the <span class="hlt">secular</span> <span class="hlt">variation</span> at the core-mantle boundary. Here we consider how best to analyze this time-dependent part of the field. To calculate steady core flow over long time periods, we introduce an adaptation of our earlier method of calculating the flow in order to achieve greater numerical stability. We perform this procedure for the periods 1840-1990 and 1690-1840 and find that well over 90 percent of the variance of the time-dependent field can be explained by simple steady core flow. The core flows obtained for the two intervals are broadly similar to each other and to flows determined over much shorter recent intervals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015IzPSE..51...44N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015IzPSE..51...44N"><span><span class="hlt">Variations</span> in the intensity of the <span class="hlt">geomagnetic</span> field in Siberia during the last 13000 years</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nachasova, I. E.; Burakov, K. S.; Pilipenko, O. V.</p> <p>2015-01-01</p> <p>The thermal magnetization of the samples from the archaeological sites in Siberia is studied. The magnetization of the collected samples was studied using the authors' modification of the Thellier method amended by the magnetic anisotropy and chemical alterations. Resulting from the study of the burned material from the Kazachka site, the time series of the <span class="hlt">geomagnetic</span> field intensity in Siberia spanning the time interval from 10000 to 1000 B.C. is obtained. These data are unique in terms of the duration and representativeness. For the first time, the main <span class="hlt">variation</span> in the intensity of the <span class="hlt">geomagnetic</span> field is traced by studying the magnetization of the samples from a single archeological site. The pattern of the <span class="hlt">variations</span> in the intensity of the <span class="hlt">geomagnetic</span> field in Siberia from 11000 B.C. to 2000 A.D., which is reconstructed from the data of the Kazachka, Ust-Karenga, and some other sites of Cis-Baikalia, indicates that the characteristics time of the long-period oscillation in the intensity of the <span class="hlt">geomagnetic</span> field is about 8000 years. It also suggests the existence of rapid <span class="hlt">variations</span> superimposed on the main oscillation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006EP%26S...58..697T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006EP%26S...58..697T"><span>Long-term seafloor <span class="hlt">geomagnetic</span> station in the northwest Pacific: A possible candidate for a seafloor <span class="hlt">geomagnetic</span> observatory</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Toh, H.; Hamano, Y.; Ichiki, M.</p> <p>2006-06-01</p> <p>For two years, <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> have been measured at the seafloor in the northwest Pacific. The seafloor data consist of the <span class="hlt">geomagnetic</span> vector field measured by a three-component fluxgate magnetometer and the absolute scalar total force measured by an Overhauser (1953) magnetometer with attitude measurements for both orientation and tilt. Using the attitude data, the <span class="hlt">geomagnetic</span> data at a site in the northwest Pacific (41o06'08″N, 159°57'47″E, -5580 m), hereafter referred to as NWP, were converted into the same reference frame as land and satellite measurements. Short-period <span class="hlt">variations</span> of the converted vector data were examined by Hamano's (2002) global time domain analysis method, which showed compatibility of the seafloor <span class="hlt">geomagnetic</span> observatory data with the existing land observatory network. The smooth and gradual change of the Earth's main field (i.e., the <span class="hlt">geomagnetic</span> <span class="hlt">secular</span> <span class="hlt">variation</span>) was also found consistent with those predicted by the latest International <span class="hlt">Geomagnetic</span> Reference Field (IGRF-10; IAGA, 2005) and by Ørsted Satellite (Olsen, 2002) for not only the scalar field but also the vector field. This means that observation of the <span class="hlt">geomagnetic</span> vector <span class="hlt">secular</span> <span class="hlt">variation</span> is now feasible on the seafloor.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.3681C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.3681C"><span>Solar and <span class="hlt">Geomagnetic</span> Activity <span class="hlt">Variations</span> Correlated to Italian M6+ Earthquakes Occurred in 2016</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cataldi, Gabriele; Cataldi, Daniele; Straser, Valentino</p> <p>2017-04-01</p> <p>Between August 2016 and October 2016 in Italy were recorded three strong earthquakes: M6.2 on August 2016 at 01:36:32 UTC; M6.1 on October 26, 2016 at 19:18:08 UTC and M6,6 on October 30, 2016 at 06:40:18 UTC. The authors of this study wanted to verify the existence of a correlation between these earthquakes and solar/<span class="hlt">geomagnetic</span> activity. To confirming or not the presence of this kind of correlation, the authors analyzed the conditions of Spaceweather "near Earth" and the characteristics of the Earth's <span class="hlt">geomagnetic</span> field in the hours that preceded the three earthquakes. The data relating to the three earthquakes were provided by the United States Geological Survey (USGS). The data on ion density used to realize the correlation study are represented by: solar wind ion density <span class="hlt">variation</span> detected by ACE (Advanced Composition Explorer) Satellite, in orbit near the L1 Lagrange point, at 1.5 million of km from Earth, in direction of the Sun. The instrument used to perform the measurement of the solar wind ion density is the Electron, Proton, and Alpha Monitor (EPAM) instrument, equipped on the ACE Satellite. To conduct the study, the authors have taken in consideration the <span class="hlt">variation</span> of the solar wind protons density of three different energy fractions: differential proton flux 1060-1900 keV (p/cm^2-sec-ster-MeV); differential proton flux 761-1220 keV (p/cm^2-sec-ster-MeV); differential proton flux 310-580 keV (p/cm^2-sec-ster-MeV). <span class="hlt">Geomagnetic</span> activity data were provided by Tromsø <span class="hlt">Geomagnetic</span> Observatory (TGO), Norway; by Scoresbysund <span class="hlt">Geomagnetic</span> Observatory (SCO), Greenland, Denmark; Dikson <span class="hlt">Geomagnetic</span> Observatory (DIK), Russia and by Pushkov Institute of terrestrial magnetism, ionosphere and radio wave propagation (IZMIRAN), Troitsk, Moscow Region. The results of the study, in agreement with what already ascertained by authors from 2012, have confirmed that the three strong Italian earthquakes were preceded by a clear increase of the solar wind proton density which</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFMGP43C..01J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFMGP43C..01J"><span><span class="hlt">Geomagnetic</span> <span class="hlt">secular</span> <span class="hlt">variation</span> as a window on the dynamics of Earth's core (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jackson, A.</p> <p>2010-12-01</p> <p>One of the forefront questions of planetary geophysics is to understand how magnetic fields can be spontaneously created by so-called dynamo action. Giant strides have been taken in recent years in understanding the theory of convectively driven dynamos; yet equally important is the marriage between theory and observation. I will argue that we are on the cusp of a new level of understanding brought about by new methods for incorporating observations and theory. In 1950 Sir Edward Bullard wrote an influential paper entitled "The westward drift of the Earth's magnetic field", with coauthors C Freedman, H Gellman and J Nixon. A comprehensive study of observations was tied together with the then nascent dynamo theory to infer properties of the dynamics of the core. Sixty years on, we have a much enriched understanding of the theory of convectively driven dynamos, and an even more comprehensive database of observations stretching back several centuries. Equally important are the new satellite observations that provide global coverage with unprecedented accuracy over the last decade. In this talk I will try to show how the interplay between theory and observation can lead to understanding of force balances in the core, and interactions between the core and the overlying mantle.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1981Ge%26Ae..21.1064Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1981Ge%26Ae..21.1064Z"><span>Separation of <span class="hlt">variations</span> of the <span class="hlt">geomagnetic</span> field into normal and anomalous parts on a bounded territory</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhdanov, M. S.; Plotnikov, S. V.</p> <p>1981-12-01</p> <p>A method based on convolution integrals is developed for separating <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> into normal and anomalous parts. It is shown for a number of typical models of normal geoelectric section that the kernels of the integral transforms have the form of spatial windows which fluctuate (depending on the <span class="hlt">variation</span> period) from several tens to several hundreds of kilometers. This indicates the possibility of separating fields specified on a bounded territory into normal and anomalous parts.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004cosp...35.1353D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004cosp...35.1353D"><span>Relationship Between Human Physiological Parameters And <span class="hlt">Geomagnetic</span> <span class="hlt">Variations</span> Of Solar Origin</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dimitrova, S.</p> <p></p> <p> <span class="hlt">variations</span> of solar origin. The examinations and analyses performed show that space weather prediction may be utilized for the purpose of pharmacological and regime measures to limit the adverse physiological reactions to <span class="hlt">geomagnetic</span> storms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1981JATP...43..607C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1981JATP...43..607C"><span>Annual and semiannual <span class="hlt">variations</span> of the <span class="hlt">geomagnetic</span> field at equatorial locations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Campbell, W. H.</p> <p>1981-06-01</p> <p>The annual and semiannual <span class="hlt">variations</span> of the quiet-sun year (1965) <span class="hlt">geomagnetic</span> field are examined using <span class="hlt">geomagnetic</span> records obtained from observatories located between about 0 and 30 deg N <span class="hlt">geomagnetic</span> latitude. Three separate contributions are analyzed: (1) the quiet-day midnight level (MDT), (2) the solar-quiet daily <span class="hlt">variation</span> (Sq), and (3) the quiet-time lunar semidiurnal tidal <span class="hlt">variation</span> (L). Methods of three recent studies (Campbell, 1980a, 1980b) are used to emphasize the equatorial features, and the differences in the seasonal amplitude and phase changes, obtained from a Fourier analysis of annual and semiannual components in the three orthogonal magnetic-field directions, are illustrated. Conclusions are presented, including: (1) the equatorial MDT <span class="hlt">variations</span> of the northward and vertical components at quiet periods seem to represent the expected seasonal nighttime magnetospheric distortions, (2) the seasonal equatorial region Sq follows closely the annual and semiannual patterns expected to be caused by ionospheric conductivity and heating <span class="hlt">variations</span> that give rise to a dynamo current at E-region heights, and (3) the lunar seasonal <span class="hlt">variations</span> show characteristics of dayside ionospheric electrojet origin.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMGP23A1324V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMGP23A1324V"><span>Ultra-High Resolution Late Pleistocene Paleomagnetic <span class="hlt">Secular</span> <span class="hlt">Variation</span> Records From the Gulf of Alaska (IODP Exp. 341 Sites U1418 and U1419)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Velle, J. H.; St-Onge, G.; Stoner, J. S.; Mix, A. C.; Walczak, M.; Asahi, H.; Forwick, M.</p> <p>2016-12-01</p> <p>IODP Expedition 341 in the Gulf of Alaska drilled the upper Surveyor Fan on the continental rise at Site U1418 (58°46.6'N 144°29.6'W; 3667 m water depth) and the continental slope at Site U1419 (59°319'N 144°8'W; 684 m water depth). U-channel paleomagnetic data has so far been collected to depths of 65 m (CCSF-A) at Site U1418 and 112 m (CCSF-A) at Site U1419. The preliminary oxygen isotope (U1418 and U1419) and radiocarbon-based age models (U1419) constrain the studied sequences to approximately 30,000 and 50,000 years, respectively. Sedimentation rates > 300 cm/kyr were resolved in some intervals, and these exceptionally expanded records allow paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> (PSV) from the northeastern Pacific to be studied in high-resolution. Alternating field (AF) demagnetization of u-channel samples and hysteresis data from Site U1418 reveal a low coercivity magnetization consistent with pseudo-single domain (PSD) magnetite with only slight down-core <span class="hlt">variations</span>, resulting in a strong, well-defined (MAD <5°), single component magnetization being preserved. U-channel measurements of Site U1419 display a weaker, but still stable, low coercivity magnetization, also consistent with PSD magnetite as the primary remanence carrier. Inclination patterns can be correlated between Site U1418 and U1419, as well as to other regional records, suggesting that these features are <span class="hlt">geomagnetic</span> in origin, and that the Gulf of Alaska sedimentary sequences have captured regional scale paleomagnetic <span class="hlt">secular</span> <span class="hlt">variations</span>. Normalization of the natural remanent magnetization (NRM) at Site U1418 with anhysteretic remanent magnetization (ARM) over 7 AF demagnetization steps are consistent with relative paleointensity, suggesting the potential for a NE Pacific regional template for stratigraphic correlation through the Late Pleistocene.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_10 --> <div id="page_11" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="201"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AnGeo..35...39D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AnGeo..35...39D"><span>Induction effects of <span class="hlt">geomagnetic</span> disturbances in the geo-electric field <span class="hlt">variations</span> at low latitudes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Doumbia, Vafi; Boka, Kouadio; Kouassi, Nguessan; Didier Franck Grodji, Oswald; Amory-Mazaudier, Christine; Menvielle, Michel</p> <p>2017-01-01</p> <p>In this study we examined the influences of <span class="hlt">geomagnetic</span> activity on the Earth surface electric field <span class="hlt">variations</span> at low latitudes. During the International Equatorial Electrojet Year (IEEY) various experiments were performed along 5° W in West Africa from 1992 to 1995. Among other instruments, 10 stations equipped with magnetometers and telluric electric field lines operated along a meridian chain across the <span class="hlt">geomagnetic</span> dip equator from November 1992 to December 1994. In the present work, the induced effects of space-weather-related <span class="hlt">geomagnetic</span> disturbances in the equatorial electrojet (EEJ) influence area in West Africa were examined. For that purpose, <span class="hlt">variations</span> in the north-south (Ex) and east-west (Ey) components of telluric electric field were analyzed, along with that of the three components (H, D and Z) of the <span class="hlt">geomagnetic</span> field during the <span class="hlt">geomagnetic</span> storm of 17 February 1993 and the solar flare observed on 4 April 1993. The most important induction effects during these events are associated with brisk impulses like storm sudden commencement (ssc) and solar flare effect (sfe) in the <span class="hlt">geomagnetic</span> field <span class="hlt">variations</span>. For the moderate <span class="hlt">geomagnetic</span> storm that occurred on 17 February 1993, with a minimum Dst index of -110 nT, the geo-electric field responses to the impulse around 11:00 LT at LAM are Ex = 520 mV km-1 and Ey = 400 mV km-1. The geo-electric field responses to the sfe that occurred around 14:30 LT on 4 April 1993 are clearly observed at different stations as well. At LAM the crest-to-crest amplitude of the geo-electric field components associated with the sfe are Ex = 550 mV km-1 and Ey = 340 mV km-1. Note that the sfe impact on the geo-electric field <span class="hlt">variations</span> decreases with the increasing distance of the stations from the subsolar point, which is located at about 5.13° N on 4 April. This trend does not reflect the sfe increasing amplitude near the dip equator due the high Cowling conductivity in the EEJ belt.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70010407','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70010407"><span>Spectral characteristics of <span class="hlt">geomagnetic</span> field <span class="hlt">variations</span> at low and equatorial latitudes</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Campbell, W.H.</p> <p>1977-01-01</p> <p><span class="hlt">Geomagnetic</span> field spectra from eight standard observations at <span class="hlt">geomagnetic</span> latitudes below 30?? were studied to determine the field characteristics unique to the equatorial region. Emphasis was placed upon those <span class="hlt">variations</span> having periods between 5 min and 4 hr for a selection of magnetically quiet, average, and active days in 1965. The power spectral density at the equator was about ten times that the near 30?? latitude. The initial manifestation of the equatorial electrojet as evidenced by the east-west alignment of the horizontal field or the change in vertical amplitudes occurred below about 20?? latitude. Induced current effects upon the vertical component from which the Earth conductivity might be inferred could best be obtained at times and latitudes unaffected by the electrojet current. Values of about 1.6 ?? 103 mhos/m for an effective skin depth of 500-600 km were determined. The spectral amplitudes increased linearly with <span class="hlt">geomagnetic</span> activity index, Ap. The spectral slope had a similar behavior at all latitudes. The slope changed systematically with Ap-index and showed a diurnal <span class="hlt">variation</span>, centered on local noon, that changed form with <span class="hlt">geomagnetic</span> activity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMGP21A..05O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMGP21A..05O"><span><span class="hlt">Geomagnetic</span> superchrons and time <span class="hlt">variations</span> in the cooling rate of the core</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Olson, P.</p> <p>2015-12-01</p> <p>Polarity reversal systematics from numerical dynamos are used to explore the relationship between <span class="hlt">geomagnetic</span> reversal frequency, including <span class="hlt">geomagnetic</span> superchrons, and time <span class="hlt">variations</span> in the rate of the cooling of the core. We develop a parameterization of the average reversal frequency from numerical dynamos in terms of the core heat flux normalized by the difference between the present-day core heat flux and the core heat flux at <span class="hlt">geomagnetic</span> superchron onset. A low-order polynomial fit of this parameterization to the 0-300 Ma <span class="hlt">Geomagnetic</span> Polarity Time Scale (GPTS) reveals that a decrease in core heat flux relative to present-day of approximately 30% can account for the Cretaceous Normal Polarity and Kiaman Reversed Polarity Superchrons, whereas the hyper-reversing periods in the Jurassic GPTS imply a core heat flux approximately 20% higher than at present-day. Low heat flux and slow cooling of the core inferred during the Kiaman Reversed Polarity Superchron is qualitatively consistent with predictions from mantle global circulation models (mantle GCMs) that show a reduction in mantle convective activity during the time of Pangea, whereas these same mantle GCMs and most plate motion reconstructions predict fast core cooling during the Cretaceous Normal Polarity Superchron, suggesting that the cooling rate of the core is not generally in phase with <span class="hlt">variations</span> in plate motions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JGRA..120.3829X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JGRA..120.3829X"><span>Multiday thermospheric density oscillations associated with <span class="hlt">variations</span> in solar radiation and <span class="hlt">geomagnetic</span> activity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xu, Jiyao; Wang, Wenbin; Zhang, Shunrong; Liu, Xiao; Yuan, Wei</p> <p>2015-05-01</p> <p>Thermospheric densities observed by Challenging Minisatellite Payload and Gravity Recovery and Climate Experiment satellites during 2002-2010 and the globally averaged thermospheric densities from 1967 to 2007 have been used to investigate latitudinal, longitudinal, and height dependences of the multiday oscillations of thermospheric densities. The data show that the main multiday oscillations in thermospheric densities are 27, 13.5, 9, and 7 day oscillations. The high-correlation coefficients between the density oscillations and the F10.7 or Ap index indicate that these oscillations are externally driven. The 27 day density oscillation, being the strongest, is induced by <span class="hlt">variations</span> in solar radiation, as well as recurrent <span class="hlt">geomagnetic</span> activity that is the result of corotating interaction regions (CIRs) and high-speed solar wind streams of coronal hole origin. Density oscillations at periods of 13.5, 9, and 7 days at solar minimum and during the declining phase are stronger than those at solar maximum. These oscillations are mainly associated with recurrent <span class="hlt">geomagnetic</span> activity due to coronal hole high-speed streams and CIRs. The multiday, periodic oscillations of thermospheric density exhibit strong latitudinal and longitudinal <span class="hlt">variations</span> in the <span class="hlt">geomagnetic</span> coordinate and oscillate synchronously at different heights. Oscillations with zonal wave number 0 oscillate globally, whereas those with nonzero wave numbers are strong at high <span class="hlt">geomagnetic</span> latitudes, and hemispherically asymmetric. They are stronger in the Southern Hemisphere. The spectral distributions of thermospheric densities at different heights have almost the same latitude and longitude structures, but the spectral magnitudes increase with height.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012IzPSE..48..434N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012IzPSE..48..434N"><span><span class="hlt">Variations</span> in <span class="hlt">geomagnetic</span> intensity and temperature in the second Millennium B.C. in Spain</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nachasova, I. E.; Burakov, K. S.</p> <p>2012-05-01</p> <p>The Bronze ceramics of the Baeza archeological monument in Spain is studied by archaeomagnetic methods. In the 19th and 18th centuries B.C, the intensity of the <span class="hlt">geomagnetic</span> field varied from 40 to 60 mkT. The <span class="hlt">variations</span> are smooth; they attained their maximum in the 16th to 15th centuries B.C. The obtained data on the <span class="hlt">variations</span> in the <span class="hlt">geomagnetic</span> intensity perfectly agree with the results of previous investigations for the ceramics from the Bronze Age multilayered archeological monuments Azuer and Ubeda. The temperature in the region of the Baeza monument is estimated in the interval from the 18th to the 13th centuries B.C. It experiences wave-like <span class="hlt">variation</span>, ranging from ˜15 to 23°C and attains its maximum in the 16th century B.C.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011GeoJI.185.1220P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011GeoJI.185.1220P"><span>A new 200 Ma paleomagnetic pole for Africa, and paleo-<span class="hlt">secular</span> <span class="hlt">variation</span> scatter from Central Atlantic Magmatic Province (CAMP) intrusives in Morocco (Ighrem and Foum Zguid dykes)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Palencia-Ortas, A.; Ruiz-Martínez, V. C.; Villalaín, J. J.; Osete, M. L.; Vegas, R.; Touil, A.; Hafid, A.; McIntosh, G.; van Hinsbergen, D. J. J.; Torsvik, T. H.</p> <p>2011-06-01</p> <p>Available apparent polar wander (APW) paths for the 200 Ma configuration of Pangea, just prior to the opening of the Central Atlantic Ocean, differ as much as 10o in arc length. Here, we add new data from northwest Africa for this time, obtained from the northeast-trending Foum-Zguid and Ighrem dykes (ca. 200 Ma). These dykes form part of the northern domain of the Central Atlantic Magmatic Province (CAMP), and crosscut the Anti-Atlas Ranges in Morocco, and compositionally correspond to quartz-normative tholeiites intruded in continental lithosphere shortly before the opening of the Central Atlantic Ocean. The Foum-Zguid dyke has been intensively studied, whereas the Ighrem dyke has received less scientific focus. We sampled both dykes for paleomagnetic investigation along 100 km of each dyke (12 sites for Foum-Zguid and 11 for Ighrem, 188 samples included in the final analyses). Rock magnetic experiments indicate a mixture of multidomain and single-domain magnetite and/or low-Ti titanomagnetite particles as the principal remanence carriers. In both dykes, the primary nature of the characteristic remanent magnetization is supported by positive contact tests, related to Fe-metasomatism or baked overprints of the corresponding sedimentary country rocks. The directions of the characteristic magnetization exhibit exclusively normal polarity. Site-mean virtual <span class="hlt">geomagnetic</span> poles are differently grouped in each dyke, suggesting distinct <span class="hlt">geomagnetic</span> <span class="hlt">secular</span> <span class="hlt">variation</span> records. The Foum-Zguid paleomagnetic pole (N= 12, PLat= 67.9°N, PLon= 247.9°E, κ= 125, A95= 3.9°) plots close to that of Ighrem (N= 11, PLat= 78.4°N, PLon= 238.2°E, κ= 47, A95= 6.7°), confirming those mineralogical and geochemical evidences supporting that they represent dissimilar magmatic stages. Virtual <span class="hlt">geomagnetic</span> poles dispersion from both dykes (S= 10.5°13.0°8.1°) is in line with those obtained from recent studies of a CAMP-related dyke in Iberia and results from CAMP lavas in the Argana</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19720010021','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19720010021"><span>Natural <span class="hlt">variations</span> in the <span class="hlt">geomagnetically</span> trapped electron population</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Vampola, A. L.</p> <p>1972-01-01</p> <p>Temporal <span class="hlt">variations</span> in the trapped natural electron flux intensities and energy spectra are discussed and demonstrated using recent satellite data. These data are intended to acquaint the space systems engineer with the types of natural <span class="hlt">variations</span> that may be encountered during a mission and to augment the models of the electron environment currently being used in space system design and orbit selection. An understanding of the temporal <span class="hlt">variations</span> which may be encountered should prove helpful. Some of the <span class="hlt">variations</span> demonstrated here which are not widely known include: (1) addition of very energetic electrons to the outer zone during moderate magnetic storms: (2) addition of energetic electrons to the inner zone during major magnetic storms; (3) inversions in the outer zone electron energy spectrum during the decay phase of a storm injection event and (4) occasional formation of multiple maxima in the flux vs altitude profile of moderately energetic electrons.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMGP13B1307Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMGP13B1307Y"><span>Study on the <span class="hlt">Geomagnetic</span> Short Period <span class="hlt">Variations</span> of the Northwestern Yunnan</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yuan, Y.; Li, Q.; Cai, J.</p> <p>2015-12-01</p> <p>The Northwestern Yunnan is located in the interaction area between the Eurasian plate and the India plate. This area has been the ideal place for the research of continental dynamics and the prediction for risk region of strong earthquake for its complex tectonic environment and frequent seismic activity. Therefore the study on the <span class="hlt">geomagnetic</span> short period <span class="hlt">variations</span> is of great significance in the exploration of deep electrical structure, analysis of the seismic origin and deep geodynamics in the Northwestern Yunnan of China . This paper is based on the <span class="hlt">geomagnetic</span> data from the magnetometer array with 8 sites built in the northwestern Yunnan to explore the deep electrical structure by the method of <span class="hlt">geomagnetic</span> depth sounding. Firstly, we selected a total of 183 <span class="hlt">geomagnetic</span> short period events at the range of 6min to 120min period. And we found a north northwest dividing line, of which two sides has the opposite value in the vertical component <span class="hlt">variation</span> amplitude, which indicates the obvious conductivity anomaly underground. Secondly, the contour maps of the ratio of vertical component and horizontal component <span class="hlt">variation</span> amplitude ΔZ/ΔH in different periods reflects the changes of a high conductivity belt's direction and position. In addition, the induction arrows maps within the period of 2 - 256min also shows that on the two sides of the dividing line the induction vectors deviate from each other, and the amplitude and direction of vectors varies with periods regularly. In the light of this, we infer that a high conductivity belt probably exists, which stretches from the deep crust to uppermost mantle and changes with depth constantly with the reference of magnetotelluric sounding. In the end of this paper, the staggered grid finite difference method is used to model the simplified three-dimensional high conductivity anomaly, and the result shows magnetic field distributions are consistent with the observed <span class="hlt">geomagnetic</span> short period <span class="hlt">variations</span> characteristics in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014Ge%26Ae..54..269R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014Ge%26Ae..54..269R"><span>First <span class="hlt">geomagnetic</span> measurements in the Antarctic region</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Raspopov, O. M.; Demina, I. M.; Meshcheryakov, V. V.</p> <p>2014-05-01</p> <p>Based on data from literature and archival sources, we have further processed and analyzed the results of <span class="hlt">geomagnetic</span> measurements made during the 1772-1775 Second World Expedition by James Cook and the 1819-1821 overseas Antarctic Expedition by Russian mariners Bellingshausen and Lazarev. Comparison with the GUFM historical model showed that there are systematic differences in the spatial structure of both the declination and its <span class="hlt">secular</span> <span class="hlt">variation</span>. The results obtained can serve as a basis for the construction of regional models of the <span class="hlt">geomagnetic</span> field for the Antarctic region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004AnGeo..22...93C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004AnGeo..22...93C"><span>Origins of the semiannual <span class="hlt">variation</span> of <span class="hlt">geomagnetic</span> activity in 1954 and 1996</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cliver, E.; Svalgaard, L.; Ling, A.</p> <p>2004-01-01</p> <p>. We investigate the cause of the unusually strong semiannual <span class="hlt">variation</span> of <span class="hlt">geomagnetic</span> activity observed in the solar minimum years of 1954 and 1996. For 1996 we separate the contributions of the three classical modulation mechanisms (axial, equinoctial, and Russell-McPherron) to the six-month wave in the index and find that all three contribute about equally. This is in contrast to the longer run of <span class="hlt">geomagnetic</span> activity (1868-1998) over which the equinoctial effect accounts for 70% of the semiannual <span class="hlt">variation</span>. For both 1954 and 1996, we show that the Russell-McPherron effect was enhanced by the Rosenberg-Coleman effect (an axial polarity effect) which increased the amount of the negative (toward Sun) [positive (away from Sun)] polarity field observed during the first [second] half of the year; such fields yield a southward component in GSM coordinates. Because this favourable condition occurs only for alternate solar cycles, the marked semiannual <span class="hlt">variation</span> in 1954 and 1996 is a manifestation of the 22-year cycle of <span class="hlt">geomagnetic</span> activity. The 11-year evolution of the heliospheric current sheet (HCS) also contributes to the strong six-month wave during these years. At solar minimum, the streamer belt at the base of the HCS is located near the solar equator, permitting easier access to high speed streams from polar coronal holes when the Earth is at its highest heliographic latitudes in March and September. Such an axial <span class="hlt">variation</span> in solar wind speed was observed for 1996 and is inferred for 1954.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70034109','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70034109"><span>Spring-fall asymmetry of substorm strength, <span class="hlt">geomagnetic</span> activity and solar wind: Implications for semiannual <span class="hlt">variation</span> and solar hemispheric asymmetry</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Mursula, K.; Tanskanen, E.; Love, J.J.</p> <p>2011-01-01</p> <p>We study the seasonal <span class="hlt">variation</span> of substorms, <span class="hlt">geomagnetic</span> activity and their solar wind drivers in 1993-2008. The number of substorms and substorm mean duration depict an annual <span class="hlt">variation</span> with maxima in Winter and Summer, respectively, reflecting the annual change of the local ionosphere. In contradiction, substorm mean amplitude, substorm total efficiency and global <span class="hlt">geomagnetic</span> activity show a dominant annual <span class="hlt">variation</span>, with equinoctial maxima alternating between Spring in solar cycle 22 and Fall in cycle 23. The largest annual <span class="hlt">variations</span> were found in 1994 and 2003, in the declining phase of the two cycles when high-speed streams dominate the solar wind. A similar, large annual <span class="hlt">variation</span> is found in the solar wind driver of substorms and <span class="hlt">geomagnetic</span> activity, which implies that the annual <span class="hlt">variation</span> of substorm strength, substorm efficiency and <span class="hlt">geomagnetic</span> activity is not due to ionospheric conditions but to a hemispherically asymmetric distribution of solar wind which varies from one cycle to another. Our results imply that the overall semiannual <span class="hlt">variation</span> in global <span class="hlt">geomagnetic</span> activity has been seriously overestimated, and is largely an artifact of the dominant annual <span class="hlt">variation</span> with maxima alternating between Spring and Fall. The results also suggest an intimate connection between the asymmetry of solar magnetic fields and some of the largest <span class="hlt">geomagnetic</span> disturbances, offering interesting new pathways for forecasting disturbances with a longer lead time to the future. Copyright ?? 2011 by the American Geophysical Union.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.agu.org/pubs/crossref/2011/2011GL046751.shtml','USGSPUBS'); return false;" href="http://www.agu.org/pubs/crossref/2011/2011GL046751.shtml"><span>Spring-fall asymmetry of substorm strength, <span class="hlt">geomagnetic</span> activity and solar wind: Implications for semiannual <span class="hlt">variation</span> and solar hemispheric asymmetry</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Marsula, K.; Tanskanen, E.; Love, J.J.</p> <p>2011-01-01</p> <p>We study the seasonal <span class="hlt">variation</span> of substorms, <span class="hlt">geomagnetic</span> activity and their solar wind drivers in 1993–2008. The number of substorms and substorm mean duration depict an annual <span class="hlt">variation</span> with maxima in Winter and Summer, respectively, reflecting the annual change of the local ionosphere. In contradiction, substorm mean amplitude, substorm total efficiency and global <span class="hlt">geomagnetic</span> activity show a dominant annual <span class="hlt">variation</span>, with equinoctial maxima alternating between Spring in solar cycle 22 and Fall in cycle 23. The largest annual <span class="hlt">variations</span> were found in 1994 and 2003, in the declining phase of the two cycles when high-speed streams dominate the solar wind. A similar, large annual <span class="hlt">variation</span> is found in the solar wind driver of substorms and <span class="hlt">geomagnetic</span> activity, which implies that the annual <span class="hlt">variation</span> of substorm strength, substorm efficiency and <span class="hlt">geomagnetic</span> activity is not due to ionospheric conditions but to a hemispherically asymmetric distribution of solar wind which varies from one cycle to another. Our results imply that the overall semiannual <span class="hlt">variation</span> in global <span class="hlt">geomagnetic</span> activity has been seriously overestimated, and is largely an artifact of the dominant annual <span class="hlt">variation</span> with maxima alternating between Spring and Fall. The results also suggest an intimate connection between the asymmetry of solar magnetic fields and some of the largest <span class="hlt">geomagnetic</span> disturbances, offering interesting new pathways for forecasting disturbances with a longer lead time to the future.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015RAA....15..742A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015RAA....15..742A"><span>Statistical analysis of <span class="hlt">geomagnetic</span> field <span class="hlt">variations</span> during the partial solar eclipse on 2011 January 4 in Turkey</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ateş, Abdullah; Ekinci, Yunus Levent; Buyuksarac, Aydin; Aydemir, Attila; Demirci, Alper</p> <p>2015-05-01</p> <p>Some geophysical parameters, such as those related to gravitation and the <span class="hlt">geomagnetic</span> field, could change during solar eclipses. In order to observe <span class="hlt">geomagnetic</span> fluctuations, <span class="hlt">geomagnetic</span> measurements were carried out in a limited time frame during the partial solar eclipse that occurred on 2011 January 4 and was observed in Canakkale and Ankara, Turkey. Additionally, records of the <span class="hlt">geomagnetic</span> field spanning 24 hours, obtained from another observatory (in Iznik, Turkey), were also analyzed to check for any peculiar <span class="hlt">variations</span>. In the data processing stage, a polynomial fit, following the application of a running average routine, was applied to the <span class="hlt">geomagnetic</span> field data sets. <span class="hlt">Geomagnetic</span> field data sets indicated there was a characteristic decrease at the beginning of the solar eclipse and this decrease can be well-correlated with previous <span class="hlt">geomagnetic</span> field measurements that were taken during the total solar eclipse that was observed in Turkey on 2006 March 29. The behavior of the <span class="hlt">geomagnetic</span> field is also consistent with previous observations in the literature. As a result of these analyses, it can be suggested that eclipses can cause a shielding effect on the <span class="hlt">geomagnetic</span> field of the Earth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70012123','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70012123"><span>Annual and semiannual <span class="hlt">variations</span> of the <span class="hlt">geomagnetic</span> field at equatorial locations</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Campbell, W.H.</p> <p>1981-01-01</p> <p>For a year of quiet solar-activity level, <span class="hlt">geomagnetic</span> records from American hemisphere observatories located between about 0?? and 30?? north <span class="hlt">geomagnetic</span> latitude were used to compare the annual and semiannual <span class="hlt">variations</span> of the <span class="hlt">geomagnetic</span> field associated with three separate contributions: (a) the quiet-day midnight level, MDT; (b) the solar-quiet daily <span class="hlt">variation</span>, Sq; (c) the quiet-time lunar semidiurnal tidal <span class="hlt">variation</span>, L(12). Four Fourier spectral constituents (24, 12, 8, 6 h periods) of Sq were individually treated. All three orthogonal elements (H, D and Z) were included in the study. The MDT changes show a dominant semiannual <span class="hlt">variation</span> having a range of about 7 gammas in H and a dominant annual <span class="hlt">variation</span> in Z having a range of over 8 gammas. These changes seem to be a seasonal response to the nightside distortions by magnetospheric currents. There is a slow decrease in MDT amplitudes with increasing latitude. The Sq changes follow the patterns expected from an equatorial ionospheric dynamo electrojet current system. The dominant seasonal <span class="hlt">variations</span> occur in H having a range of over 21 gammas for the 24 h period and over 12 gammas for the 12 h period spectral components. The higher-order components are relatively smaller in size. The Sq(H) amplitudes decrease rapidly with increasing latitude. Magnetospheric contributions to the equatorial Sq must be less than a few per cent of the observed magnitude. The L(12) <span class="hlt">variation</span> shows the ionospheric electrojet features by the dominance of H and the rapid decrease in amplitude with latitude away from the equator. However, the seasonal <span class="hlt">variation</span> range of over 7 gammas has a maximum in early February and minimum in late June that is not presently explainable by the known ionospheric conductivity and tidal behavior. ?? 1981.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMSA23D2365S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMSA23D2365S"><span>Long-term <span class="hlt">variation</span> in the ionosphere and lower thermosphere as seen in the <span class="hlt">geomagnetic</span> solar quiet daily <span class="hlt">variation</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shinbori, A.; Koyama, Y.; Hori, T.; Nose, M.; Otsuka, Y.</p> <p>2015-12-01</p> <p>In order to investigate characteristics of the long-term <span class="hlt">variation</span> in the ionosphere and lower thermosphere, we analyzed the amplitude of <span class="hlt">geomagnetic</span> solar quiet (Sq) field daily <span class="hlt">variation</span> using 1-h <span class="hlt">geomagnetic</span> field data obtained from 69 <span class="hlt">geomagnetic</span> stations within the period of 1947-2013. In the present data analysis, we took advantage of the Inter-university Upper atmosphere Global Observation NETwork (IUGONET) products (metadata database and analysis software) for finding and handling the long-term observation data obtained at many observatories. The Sq amplitude observed at these <span class="hlt">geomagnetic</span> stations showed a clear solar activity dependence and tended to be enhanced during each solar maximum phase. The Sq amplitude was the smallest around the minimum of solar cycle 23/24 in 2008-2009. This significant depression implies that the solar extreme ultraviolet (EUV) radiation responsible for ionization of the upper atmosphere decreased during this solar cycle minimum. In order to examine a global distribution of the long-term trend in the Sq amplitude, we derived the residual Sq amplitude from the deviation from the fitting curve between the solar F10.7 index and Sq amplitude. As a result, a majority of the trends in the residual Sq amplitude showed negative values over a wide region. This tendency was relatively strong in Europe, India, the eastern part of Canada, and New Zealand. Moreover, we estimate the neutral wind in the lower thermosphere from the Sq amplitude and height-integrated ionospheric conductivity in order to know the physical mechanism of the long-term trend in the residual Sq amplitude. As a result, the estimated thermospheric zonal and meridional winds showed a seasonal <span class="hlt">variation</span> with a period of one year or less, but the solar activity dependence was unclear. This result suggests that the solar cycle dependence of the Sq amplitude may be mainly attributed to the <span class="hlt">variation</span> of the ionospheric conductivity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JAsGe...6..104D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JAsGe...6..104D"><span>The Egyptian <span class="hlt">geomagnetic</span> reference field to the Epoch, 2010.0</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Deebes, H. A.; Abd Elaal, E. M.; Arafa, T.; Lethy, A.; El Emam, A.; Ghamry, E.; Odah, H.</p> <p>2017-06-01</p> <p>The present work is a compilation of two tasks within the frame of the project ;<span class="hlt">Geomagnetic</span> Survey & Detailed <span class="hlt">Geomagnetic</span> Measurements within the Egyptian Territory; funded by the ;Science and Technology Development Fund agency (STDF);. The National Research Institute of Astronomy and Geophysics (NRIAG), has conducted a new extensive land <span class="hlt">geomagnetic</span> survey that covers the whole Egyptian territory. The field measurements have been done at 3212 points along all the asphalted roads, defined tracks, and ill-defined tracks in Egypt; with total length of 11,586 km. In the present work, the measurements cover for the first time new areas as: the southern eastern borders of Egypt including Halayeb and Shlatin, the Quattara depresion in the western desert, and the new roads between Farafra and Baharia oasis. Also marine <span class="hlt">geomagnetic</span> survey have been applied for the first time in Naser lake. Misallat and Abu-Simble <span class="hlt">geomagnetic</span> observatories have been used to reduce the field data to the Epoch 2010. During the field measurements, whenever possible, the old stations occupied by the previous observers have been re-occupied to determine the <span class="hlt">secular</span> <span class="hlt">variations</span> at these points. The <span class="hlt">geomagnetic</span> anomaly maps, the normal <span class="hlt">geomagnetic</span> field maps with their corresponding <span class="hlt">secular</span> <span class="hlt">variation</span> maps, the normal <span class="hlt">geomagnetic</span> field equations of the <span class="hlt">geomagnetic</span> elements (EGRF) and their corresponding <span class="hlt">secular</span> <span class="hlt">variations</span> equations, are outlined. The anomalous sites, as discovered from the anomaly maps are, only, mentioned. In addition, a correlation between the International <span class="hlt">Geomagnetic</span> Reference Field (IGRF) 2010.0 and the Egyptian <span class="hlt">Geomagnetic</span> Reference Field (EGRF) 2010 is indicated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002EGSGA..27.1267F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002EGSGA..27.1267F"><span>The Identification of Seismo and Volcanomagnetic Events Using Non-stationary Analysis of <span class="hlt">Geomagnetic</span> Field <span class="hlt">Variations</span>.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fedi, M.; Gonçalves, P.; Johnston, M.; La Manna, M.</p> <p></p> <p>Many studies have shown a clear correlation between volcanic and/or seismic activ- ity and time <span class="hlt">variations</span> of local <span class="hlt">geomagnetic</span> fields, called seismomagnetic (SM) and /or volcanomagnetic (VM) effects. SM and VM can be generated from various phys- ical process, such as piezomagnetism, tectonomagnetism and electrokinetism. Rele- vant parameters are the event duration, the event magnitude and the magnetometer sample rate. Here, we present some results obtained from a non-stationary analysis of <span class="hlt">geomagnetic</span> time series that focuses on automatic detection of possible SM and VM events. Several approaches are considered. The first one, based on the continuous wavelet transform, provides us with a multiresolution lecture of the signal, expanded in time-scale space. The second uses a time-variant adaptive algorithm (RLS) that al- lows the detection of some time intervals where important statistical <span class="hlt">variations</span> of the signal occur. Finally, we investigate a third technique relying on multifractal analy- sis. This latter allows estimation of local regularity of a time series path, in order to detect unusual singularities. Different multifractal models were used for testing the methodology, such as multifractional Brownian Motions (mbmSs), before applying it to synthetic simulations of <span class="hlt">geomagnetic</span> signals. In our simulations, we took into account theoretical SM and/or VM effects deriving from fault rupture and overpres- sured magma chambers. We applied these methodologies to two different real world data sets, recorded on Mt Etna (volcanic area) during the volcanic activity occurred in 1981, and in North Palm Springs (seismic area) during the seism of July 8th 1986, respectively. In both cases, all techniques were effective in automatically identifying the <span class="hlt">geomagnetic</span> time-<span class="hlt">variations</span> likely inferred by volcanic and/or seismic activity and the results are in good agreement with the indices provided by real volcanic and seismic measurements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002EGSGA..27.1255F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002EGSGA..27.1255F"><span>The Identification of Seismo and Volcanomagnetic Events Using Non-stationary Analysis of <span class="hlt">Geomagnetic</span> Field <span class="hlt">Variations</span>.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fedi, M.; Gonçalves, P.; Johnston, M.; La Manna, M.</p> <p></p> <p>Many studies have shown a clear correlation between volcanic and/or seismic activ- ity and time <span class="hlt">variations</span> of local <span class="hlt">geomagnetic</span> fields, called seismomagnetic (SM) and /or volcanomagnetic (VM) effects. SM and VM can be generated from various phys- ical process, such as piezomagnetism, tectonomagnetism and electrokinetism. Rele- vant parameters are the event duration, the event magnitude and the magnetometer sample rate. Here, we present some results obtained from a non-stationary analysis of <span class="hlt">geomagnetic</span> time series that focuses on automatic detection of possible SM and VM events. Several approaches are considered. The first one, based on the continuous wavelet transform, provides us with a multiresolution lecture of the signal, expanded in time-scale space. The second uses a time-variant adaptive algorithm (RLS) that al- lows the detection of some time intervals where important statistical <span class="hlt">variations</span> of the signal occur. Finally, we investigate a third technique relying on multifractal analy- sis. This latter allows estimation of local regularity of a time series path, in order to detect unusual singularities. Different multifractal models were used for testing the methodology, such as multifractional Brownian Motions (mbm 's), before applying it to synthetic simulations of <span class="hlt">geomagnetic</span> signals. In our simulations, we took into account theoretical SM and/or VM effects deriving from fault rupture and overpres- sured magma chambers. We applied these methodologies to two different real world data sets, recorded on Mt Etna (volcanic area) during the volcanic activity occurred in 1981, and in North Palm Springs (seismic area) during the seism of July 8th 1986, respectively. In both cases, all techniques were effective in automatically identifying the <span class="hlt">geomagnetic</span> time-<span class="hlt">variations</span> likely inferred by volcanic and/or seismic activity in fact we obtained results in good agreement with the indices provided by real volcanic and seismic measurements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014cosp...40E1977M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014cosp...40E1977M"><span>Analysis of <span class="hlt">geomagnetic</span> data and cosmic ray <span class="hlt">variations</span> in periods of magnetic perturbations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mandrikova, Oksana; Zalyaev, Timur; Solovev, Igor; Shevtsov, Boris</p> <p></p> <p>indent=0.63cm In the present paper we have suggested a model of the <span class="hlt">geomagnetic</span> field <span class="hlt">variation</span>, which allows us to present the characteristic <span class="hlt">variation</span> of the field and local perturbations formed in periods of increased <span class="hlt">geomagnetic</span> activity. The model is based on wavelets and has the following form: [ f(t)= sum_n c_{j,n} phi_{j,n} + sum_{(j_{dist},n)in I_1} d_{j_{dist},n}Psi_{j_{dist},n}(t) + sum_{(j_{dist},n)in I_2} d_{j_{dist},n}Psi_{j_{dist},n}(t) + e(t) ] where component sum_n c_{j,n} phi_{j,n} presents the characteristic <span class="hlt">variation</span>; component \\sum_{(j_{dist},n)in I_1} d_{j_{dist},n}Psi_{j_{dist},n}(t) presents weak <span class="hlt">geomagnetic</span> perturbations; component \\sum_{(j_{dist},n)in I_2} d_{j_{dist},n}Psi_{j_{dist},n}(t) presents strong <span class="hlt">geomagnetic</span> perturbations; j is the scale; I_1, I_2 are the sets of indices; e(t) is the noise; Psi_j = \\{Psi_{j,n}\\}_{n in Z} is the wavelet basis; phi_j = \\{phi_{j,n}\\}_{n in Z} is the scaling function; c_{j,n}=< f, phi_{j,n} > ,d_{j,n}=< f, Psi_{j,n} >. Using the proposed model we have developed a technique of identifying the characteristic <span class="hlt">variation</span> of the <span class="hlt">geomagnetic</span> field (in periods of quiet magnetosphere) and components presenting different conditions of the field in periods of perturbations. The technique can be used for various data registration stations and is useful for studying the dynamics of electric current systems in the magnetosphere, the interaction between such systems, and their spatial and temporal distribution. We have also created special rules for estimating the storminess degree of the <span class="hlt">geomagnetic</span> field. The suggested theoretical tools allow us to determine time points when <span class="hlt">geomagnetic</span> perturbations arise and to obtain quantitative estimates of the storminess degree. Furthermore, it is also possible to implement these rules in the automatic mode. The theoretical tools mentioned above are also aimed at developing and improving mathematical tools for estimating and monitoring the condition of the <span class="hlt">geomagnetic</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11130715','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11130715"><span><span class="hlt">Geomagnetic</span> intensity <span class="hlt">variations</span> over the past 780 kyr obtained from near-seafloor magnetic anomalies.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gee, J S; Cande, S C; Hildebrand, J A; Donnelly, K; Parker, R L</p> <p>2000-12-14</p> <p>Knowledge of past <span class="hlt">variations</span> in the intensity of the Earth's magnetic field provides an important constraint on models of the geodynamo. A record of absolute palaeointensity for the past 50 kyr has been compiled from archaeomagnetic and volcanic materials, and relative palaeointensities over the past 800 kyr have been obtained from sedimentary sequences. But a long-term record of <span class="hlt">geomagnetic</span> intensity should also be carried by the thermoremanence of the oceanic crust Here we show that near-seafloor magnetic anomalies recorded over the southern East Pacific Rise are well correlated with independent estimates of <span class="hlt">geomagnetic</span> intensity during the past 780 kyr. Moreover, the pattern of absolute palaeointensity of seafloor glass samples from the same area agrees with the well-documented dipole intensity pattern for the past 50 kyr. A comparison of palaeointensities derived from seafloor glass samples with global intensity <span class="hlt">variations</span> thus allows us to estimate the ages of surficial lava flows in this region. The record of <span class="hlt">geomagnetic</span> intensity preserved in the oceanic crust should provide a higher-time-resolution record of crustal accretion processes at mid-ocean ridges than has previously been obtainable.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_11 --> <div id="page_12" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="221"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/177466','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/177466"><span>Semiannual <span class="hlt">variations</span> of great <span class="hlt">geomagnetic</span> storms: Solar sources of great storms. (Reannouncement with new availability information)</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Cliver, E.W.; Crooker, N.U.; Cane, H.V.</p> <p>1992-01-01</p> <p>The authors report preliminary results of an investigation of the solar sources of 25 great <span class="hlt">geomagnetic</span> storms with D sub st < or = {minus}250 nT occurring from 1957-1990. These storms exhibit a clear semiannual <span class="hlt">variation</span> with 14 events occurring within {+-} 30 days of the equinoxes vs. 5 storms within {+-} 30 days of the solstices. This seasonal <span class="hlt">variation</span> appears to result from a variable threshold for the size of a solar event required to produce a great <span class="hlt">geomagnetic</span> storm, in the sense that weaker solar events, such as disappearing solar filaments, are more likely to produce great storms at the equinoxes than near the solstices. The great problem storms of the last four solar cycles, i.e., those storms lacking commensurate preceding solar activity, are all found to occur relatively near the equinoxes. Conversely, four of the five great storms that occurred near the solstices were preceded by truly outstanding solar flares. About half (11/25) of the great storms had obvious precursor <span class="hlt">geomagnetic</span> activity, i.e., periods of approximately > 1 day with D sub st approximately < {minus}30 nT. The precursors can enable some weaker solar events to be more geoeffective than would otherwise be the case in two ways: (1) compression and amplification of pre-existing southward (precursor) fields by the transient shock, and (2) establishment of a lower D sub st baseline , making it easier for transient events to drive D sub st to values < or = {minus}250 nT.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2000EP%26S...52..237O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2000EP%26S...52..237O"><span>Daily <span class="hlt">variations</span> of <span class="hlt">geomagnetic</span> H D and Z-field at equatorial latitudes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Okeke, F. N.; Hamano, Y.</p> <p>2000-04-01</p> <p>With the establishment of the new <span class="hlt">geomagnetic</span> field observations in the Ocean Hemisphere Network Project (OHP) in Japan, minutes values of <span class="hlt">geomagnetic</span> components, H D and Zhave been recorded. The hourly mean values were used to study the <span class="hlt">variations</span> in these three components at these new equatorial electrojet regions. The results of the analysis carried out revealed that the amplitude of dHhas diurnal <span class="hlt">variation</span> which peaks during the day at about local noon in all the three equatorial electrojet regions. This diurnal <span class="hlt">variation</span> in Hwith Sq(H) enhancement in all the three regions are attributed to the enhanced dynamo action at these regions. Diurnal <span class="hlt">variation</span> as observed in Dindicates that the equatorial electrojet current system has both east-west and north-south components. The pronounced magnitude of Zvariation as observed in Kiritimati is attributed mainly to sea induction. Also some abnormal features were observed on 23rd of January at Huancayo, in the components. Seasonal <span class="hlt">variations</span> with more pronounced equinoctial maximum were observed in Hthan in Z. Dcomponent showed no consistent seasonal <span class="hlt">variation</span> in all the regions. The equinoctial maximum is due to enhanced equatorial electron density at equinox. More research work, if carried out in these new regions will be useful in making more new contributions to the field of the dynamics of the equatorial electrojet region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017SerAJ.194...87C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017SerAJ.194...87C"><span>Solar Flares and <span class="hlt">Variation</span> of Local <span class="hlt">Geomagnetic</span> Field: Measurements by the Huancayo Observatory over 2001-2010</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Carlos Reyes, Rafael E.; Gárate Ayesta, Gabriel A.; Reyes Navarro, Felipe A.</p> <p>2017-06-01</p> <p>We study the local <span class="hlt">variation</span> of the <span class="hlt">geomagnetic</span> field measured by the Huancayo <span class="hlt">Geomagnetic</span> Observatory, Peru, during 2001-2010. Initially, we sought to relate the SFI values, stored daily in the NOAA's National Geophysical Data Center, with the corresponding <span class="hlt">geomagnetic</span> index; however, no relation was observed. Nonetheless, subsequently, a comparison between the monthly <span class="hlt">geomagnetic</span>-activity index and the monthly SFI average allowed observing a temporal correlation between these average indices. This correlation shows that the effect of the solar flares does not simultaneously appear on the corresponding magnetic indices. To investigate this, we selected the most intense X-class flares; then, we checked the magnetic field disturbances observed in the Huancayo <span class="hlt">Geomagnetic</span> Observatory magnetograms. We found some disturbances of the local <span class="hlt">geomagnetic</span> field in the second and third day after the corresponding solar flare; however, the disturbance strength of the local <span class="hlt">geomagnetic</span> field is not correlated with the X-class of the solar flare. Finally, there are some disturbances of the local <span class="hlt">geomagnetic</span> field that are simultaneous with the X-class solar flares and they show a correlation with the total flux of the solar flare.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017SerAJ.tmp....2C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017SerAJ.tmp....2C"><span>Solar Flares and <span class="hlt">Variation</span> of Local <span class="hlt">Geomagnetic</span> Field: Measurements by the Huancayo Observatory over 2001-2010</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Carlos Reyes, Rafael E.; Gárate Ayesta, Gabriel A.; Reyes Navarro, Felipe A.</p> <p>2017-02-01</p> <p>We study the local <span class="hlt">variation</span> of the <span class="hlt">geomagnetic</span> field measured by the Huancayo <span class="hlt">Geomagnetic</span> Observatory, Peru, during 2001-2010. Initially, we sought to relate the SFI values, stored daily in the NOAA's National Geophysical Data Center, with the corresponding <span class="hlt">geomagnetic</span> index; however, no relation was observed. Nonetheless, subsequently, a comparison between the monthly <span class="hlt">geomagnetic</span>-activity index and the monthly SFI average allowed observing a temporal correlation between these average indices. This correlation shows that the effect of the solar flares does not simultaneously appear on the corresponding magnetic indices. To investigate this, we selected the most intense X-class flares; then, we checked the magnetic field disturbances observed in the Huancayo <span class="hlt">Geomagnetic</span> Observatory magnetograms. We found some disturbances of the local <span class="hlt">geomagnetic</span> field in the second and third day after the corresponding solar flare; however, the disturbance strength of the local <span class="hlt">geomagnetic</span> field is not correlated with the X-class of the solar flare. Finally, there are some disturbances of the local <span class="hlt">geomagnetic</span> field that are simultaneous with the X-class solar flares and they show a correlation with the total flux of the solar flare.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMGP41A1113D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMGP41A1113D"><span>Paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> at the Azores during the last 3 ka</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Di Chiara, A.; Speranza, F.; Porreca, M.</p> <p>2012-12-01</p> <p>We report on 33 new paleomagnetic directions obtained from 16 lava flows emplaced in the last 3 ka on São Miguel, the largest island of the Azores. The data provide 27 directions from historical or 14C dated flows which, together with 6 directions previously gathered from the same flows by Johyson et al., (1998), yield the first paleomagnetic record of the last 3 ka from the Atlantic Ocean. Within-flow directions are consistent, suggesting that inclination swings from 60° to 25° and declination changes between -10° to 20° reflect <span class="hlt">variations</span> in the <span class="hlt">geomagnetic</span> field over the last 3 ka. To a first approximation, the declination record is consistent with predictions from CALS3k.4 and gufm1 global field models. Conversely, inclination values are lower than model predictions at two different ages: 1) four different sites from the 1652 AD flow yield I=48° instead of I=63° predicted by gufm1; 2) data from several flows nicely mimic the inclination minimum of 800-1400 AD, but inclination values are lower by ca. 10° than CALS3k.4 model predictions. By interpolating a cubic spline fit on declination / inclination versus age data, we tentatively infer the directional evolution of the <span class="hlt">geomagnetic</span> field at the Azores from 1000 BC to 1600 AD.The obtained curve shows three tracks in virtual overlap during the 1000-800 BC, 800-500 BC, and 400-700 AD time spans; Cubic spline interpolation of flow mean declinations (a) and inclinations (b) versus respective calendar ages; c) directions derived every 100 years from cubic spline interpolation, superimposed on paleomagnetic directions (and relative confidence cones) from three loosely-dated flows (Fig. 1). For ages older than 750 AD the fit line is dashed, as it is constrained by a limited number of data. Vertical error bars for declination and inclination data are α95 /cos(I) and α95 values, respectively</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/437386','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/437386"><span>On the <span class="hlt">secular</span> <span class="hlt">variations</span> in the composition of Phanerozoic marine potash evaporites</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Holland, H.D.; Horita, J.; Seyfried, W.E. Jr.</p> <p>1996-11-01</p> <p>In a recent paper, L.A. Hardie proposed that the <span class="hlt">secular</span> changes in the mineralogy of marine nonskeletal limestones and in the mineralogy of marine potash evaporites during the Phanerozoic are the result of changes in the composition of seawater caused primarily by fluctuations in the flux of seawater through mid-ocean ridges. He suggested that even quite small <span class="hlt">variations</span> (25%) in this flux have a profound effect on the composition of seawater. We show that the effects of changes in the hydrothermal flux are much smaller than he proposed. Nevertheless, a doubling of the hydrothermal flux could probably alter the composition of seawater sufficiently to affect the mineralogy of marine potash evaporites. An alternative explanation for the <span class="hlt">variations</span> in the mineralogy of these deposits invokes differences in the degree of dolomitization during the evaporation of seawater. The apparent near constancy of the K{sup +} content of seawater during the Phanerozoic supports this hypothesis. It seems likely that during periods of rapid seafloor spreading the rate of seawater cycling is greater than today, that sea level is higher, that very large carbonate platforms are more abundant, and that changes in seawater chemistry together with increases in dolomitization during the evaporation of seawater lead to MgSO{sub 4}-free potash deposits. The relative importance of these several effects can probably be determined with certainty only when we have analyses of relatively unaltered seawater from the several Phanerozoic periods. 27 refs., 1 fig., 1 tab.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PEPI..269....1G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PEPI..269....1G"><span>New and revised palaeomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> records from post-glacial volcanic materials in New Zealand</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Greve, Annika; Turner, Gillian M.</p> <p>2017-08-01</p> <p>Global databases suffer from a paucity of palaeomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> (PSV) data from the SW Pacific region and are often affected by inconsistencies in data quality, or available age control of the sampled units. Here we present new PSV records obtained from post-glacial (≤15 kyrs BP) volcanic materials (mainly lavas) from New Zealand. The new dataset incorporates a compilation and critical assessment of all previous discrete PSV data and their age controls, and the results of new sampling in the Taupo Volcanic Zone. The overall dataset includes 23 directional and 10 absolute palaeointensity records primarily from lavas of rhyolitic or andesitic composition. Age constraints on the rhyolitic lavas are available from correlation with distal, radiocarbon dated tephra deposits, age controls on the andesites from field relationships or from 40Ar/39Ar dating. Directional swings, ranging from 326.5° to 26.0° declination and -81.4 to -46.3° inclination and intensity <span class="hlt">variations</span> from 37.0 to 71.6 μT, fall well into the range of PSV expected for this time-frame in New Zealand and reproduce features of continuous sediment records.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EP%26S...69...58P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EP%26S...69...58P"><span>Effect of a huge crustal conductivity anomaly on the H-component of <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> recorded in central South America</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Padilha, Antonio L.; Alves, Livia R.; Silva, Graziela B. D.; Espinosa, Karen V.</p> <p>2017-04-01</p> <p>We describe here an analysis of the H-component of the <span class="hlt">geomagnetic</span> field recorded in several temporary stations operating simultaneously in the central-eastern region of Brazil during nighttime pulsation events in 1994 and the sudden commencement of the St. Patrick's Day magnetic storm in 2015. A significant amplification in the amplitude of the <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> is consistently observed in one of these stations. Magnetovariational analysis indicates that the amplification factor is period dependent with maximum amplitude around 100 s. Integrated magnetotelluric (MT) and <span class="hlt">geomagnetic</span> depth soundings (GDS) have shown that this station is positioned just over a huge 1200-km-long crustal conductor (estimated bulk conductivity greater than 1 S/m). We propose that the anomalous signature of the <span class="hlt">geomagnetic</span> field at this station is due to the high reflection coefficient of the incident electromagnetic wave at the interface with the very good conductor and by skin effects damping the electromagnetic wave in the conducting layers overlying the conductor. There are some indication from the GDS data that the conductor extends southward beneath the sediments of the Pantanal Basin. In this region is being planned the installation of a new <span class="hlt">geomagnetic</span> observatory, but its preliminary data suggest anomalous <span class="hlt">geomagnetic</span> <span class="hlt">variations</span>. We understand that a detailed MT survey must be carried out around the chosen observatory site to evaluate the possible influence of induced currents on the local <span class="hlt">geomagnetic</span> field.[Figure not available: see fulltext.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeoRL..41.6627P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeoRL..41.6627P"><span>Constraints on the <span class="hlt">secular</span> <span class="hlt">variation</span> of Mercury's magnetic field from the combined analysis of MESSENGER and Mariner 10 data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Philpott, Lydia C.; Johnson, Catherine L.; Winslow, Reka M.; Anderson, Brian J.; Korth, Haje; Purucker, Michael E.; Solomon, Sean C.</p> <p>2014-10-01</p> <p>Observations of Mercury's internal magnetic field from the Magnetometer on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft have revealed a dipole moment of 190 nT RM3 offset about 480 km northward from the planetary equator, where RM is Mercury's radius. We have reanalyzed magnetic field observations acquired by the Mariner 10 spacecraft during its third flyby of Mercury (M10-III) in 1975 to constrain the <span class="hlt">secular</span> <span class="hlt">variation</span> in the internal field over the past 40 years. With the application of techniques developed in the analysis of MESSENGER data, we find that the dipole moment that best fits the M10-III data is 188 nT RM3 offset 475 km northward from the equator. Our results are consistent with no <span class="hlt">secular</span> <span class="hlt">variation</span>, although <span class="hlt">variations</span> of up to 10%, 16%, and 35%, respectively, are permitted in the zonal coefficients g10, g20, and g30 in a spherical harmonic expansion of the internal field.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1983ged..book.....H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1983ged..book.....H"><span>The <span class="hlt">geomagnetic</span> elements in Denmark 1928-1980</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hansen, H. A.</p> <p></p> <p><span class="hlt">Geomagnetic</span> surveys in Denmark from 1928 till 1980 are reported. The Danish Meteorological Institute initiated a new, <span class="hlt">geomagnetic</span> survey of Denmark in 1928 by the establishment of 10 repeat statins for observation of the <span class="hlt">geomagnetic</span>, <span class="hlt">secular</span> <span class="hlt">variation</span>. The stations were visited again in 1930 and since then every fifth year. The general survey was started in 1939 and continued during the years 1946 to 1957 with the mapping of Northern Jutland. In 1967 the survey taken with a coarser spacing of the measured points during the following years succeeded in completing the mapping of the country with primary consideration to the declination. The observations on the repeat stations during the time 1928-1980 allowed development of mathematical formulas for the <span class="hlt">secular</span> change of the magnetic elements D, H and Z at any arbitrary point in the country.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016cosp...41E.202B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016cosp...41E.202B"><span>Cosmic rays, conditions in interplanetary space and <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> during solar cycles 19-24</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Biktash, Lilia</p> <p>2016-07-01</p> <p>We have studied conditions in interplanetary space, which can have an influence on galactic and solar cosmic rays (CRs). In this connection the solar wind and interplanetary magnetic field parameters and CRs <span class="hlt">variations</span> have been compared with <span class="hlt">geomagnetic</span> activity represented by the equatorial Dst and Kp indices beginning from 1955 to the end 2015. The indices are in common practice in the solar wind-magnetosphere-ionosphere interaction studies and they are the final product of this interaction. The important drivers in interplanetary medium which have effect on cosmic rays as CMEs (coronal mass ejections) and CIRs (corotating interaction regions) undergo very strong changes during their propagation to the Earth. Correlation of sunspot numbers and long-term <span class="hlt">variations</span> of cosmic rays do not adequately reflect peculiarities concerned with the solar wind arrival to 1 AU also. Moreover records of in situ space measurements of the IMF and most other indicators of solar activity cover only a few decades and have a lot of gaps for calculations of long-term <span class="hlt">variations</span>. Because of this, in such investigations, the <span class="hlt">geomagnetic</span> indices have some inestimable advantage as continuous series other the solar wind measurements. We have compared the yearly average <span class="hlt">variations</span> of the indices and of the solar wind parameters with cosmic ray data from Moscow, Climax, Halekala and Oulu neutron monitors during the 20-24 solar cycles. During the descending phases of the solar cycles the long-lasting solar wind high speed streams occurred frequently and were the primary contributors to the recurrent Dst <span class="hlt">variations</span> and had effects on cosmic rays <span class="hlt">variations</span>. We show that long-term Dst and Kp <span class="hlt">variations</span> in these solar cycles were correlated with cosmic ray count rates and can be used for prediction of CR <span class="hlt">variations</span>. Climate change in connection with evolution of CRs <span class="hlt">variations</span> is discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2000GeoJI.143..545D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2000GeoJI.143..545D"><span>A global analysis of the 1991 <span class="hlt">geomagnetic</span> jerk</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>De Michelis, Paola; Cafarella, Lili; Meloni, Antonio</p> <p>2000-12-01</p> <p>A recent examination of the <span class="hlt">geomagnetic</span> annual mean values for the European magnetic observatories has shown the existence of a sudden change in the <span class="hlt">secular</span> acceleration in about 1991 (Cafarella & Meloni 1995; Macmillan 1996). Using first differences of the Y (east <span class="hlt">geomagnetic</span> field component) mean values from 74 observatories, the worldwide character of the 1991 impulse has been determined (De Michelis et al. 1998). Using data from 109 observatories widely distributed all over the world, the structure of the <span class="hlt">secular</span> <span class="hlt">variation</span> for the X (north) and Z (vertical) magnetic field intensities around 1990 was investigated, and evidence of this most recent jerk was found. External effects were removed from the annual mean data by comparing the long-term <span class="hlt">variations</span> of the <span class="hlt">geomagnetic</span> field components at individual observatories with the long-term <span class="hlt">variations</span> of two <span class="hlt">geomagnetic</span> indices, aa and Dst, and of a solar index, the Wolf number R. A careful analysis has been carried out on the amplitude of the external disturbance, on its dependence on latitude, and on the weights of the <span class="hlt">geomagnetic</span> indices in the evaluation of the resulting external field. The <span class="hlt">secular</span> <span class="hlt">variation</span> has been evaluated from the corrected annual means. Around 1990, the <span class="hlt">secular</span> <span class="hlt">variation</span> can be fitted at many observatories by two straight lines with a sudden and marked change in slope. In this manner the jerk occurrence time and the intensity of the step in the second time derivative (ΔX'', ΔY'' and ΔZ'') were computed. Maps of ΔX'', ΔY'' and ΔZ'' provide information on the worldwide intensity distribution of the examined event. Maps of the jerk occurrence-time distributions are also given. The mean jerk occurrence time is 1990.1+/-0.6. Finally, a spherical harmonic analysis was used to complete the quantitative description of this phenomenon in order to study the trend of the energy density spectrum as a function of the harmonic degree n.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012Tectp.524...29T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012Tectp.524...29T"><span><span class="hlt">Geomagnetic</span> <span class="hlt">variations</span> possibly associated with the Pisco earthquake on 15 August 2007, Peru</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Takla, E. M.; Yumoto, K.; Ishitsuka, J.; Rosales, D.; Dutra, S.; Uozumi, T.; Abe, S.</p> <p>2012-02-01</p> <p>On 15 August 2007, Pisco earthquake (magnitude 8.0) hit the central coast of Peru near the MAGDAS Ancon (ANC) station. <span class="hlt">Geomagnetic</span> data from ANC and other reference stations have been analyzed to detect any signature related to this great earthquake. Results indicate the presence of annual <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> in the vertical component at ANC and Huancayo (HUA) stations (in the vicinity of the epicenter of Pisco earthquake). These <span class="hlt">variations</span> have a quasi-sinusoidal waveform with amplitudes of about 10 and 5 nT for ANC and HUA stations respectively. They appeared clearly during the period preceding the onset of the Pisco earthquake especially at ANC station. By using HUA, Eusebio (EUS) and Kourou (KOU) as reference stations in the vicinity and away from the epicenter of Pisco earthquake, a clear disappearance of the diurnal <span class="hlt">variation</span> of the vertical component was observed at ANC station during the day of earthquake. Moreover, the Pisco earthquake and another earthquake (on 29 March 2008) near ANC station were found to occur concurrently with the depressions in the polarization ratio (Z/H) of Pc 3 (10-45 s) amplitude. Such anomalous <span class="hlt">variations</span> appear to be a result of changes in the crustal stress field and the lithospheric conductivity in the studied region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PNAS..114.2160B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PNAS..114.2160B"><span>Six centuries of <span class="hlt">geomagnetic</span> intensity <span class="hlt">variations</span> recorded by royal Judean stamped jar handles</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ben-Yosef, Erez; Millman, Michael; Shaar, Ron; Tauxe, Lisa; Lipschits, Oded</p> <p>2017-02-01</p> <p>Earth’s magnetic field, one of the most enigmatic physical phenomena of the planet, is constantly changing on various time scales, from decades to millennia and longer. The reconstruction of <span class="hlt">geomagnetic</span> field behavior in periods predating direct observations with modern instrumentation is based on geological and archaeological materials and has the twin challenges of (i) the accuracy of ancient paleomagnetic estimates and (ii) the dating of the archaeological material. Here we address the latter by using a set of storage jar handles (fired clay) stamped by royal seals as part of the ancient administrative system in Judah (Jerusalem and its vicinity). The typology of the stamp impressions, which corresponds to changes in the political entities ruling this area, provides excellent age constraints for the firing event of these artifacts. Together with rigorous paleomagnetic experimental procedures, this study yielded an unparalleled record of the <span class="hlt">geomagnetic</span> field intensity during the eighth to second centuries BCE. The new record constitutes a substantial advance in our knowledge of past <span class="hlt">geomagnetic</span> field <span class="hlt">variations</span> in the southern Levant. Although it demonstrates a relatively stable and gradually declining field during the sixth to second centuries BCE, the new record provides further support for a short interval of extreme high values during the late eighth century BCE. The rate of change during this “<span class="hlt">geomagnetic</span> spike” [defined as virtual axial dipole moment > 160 ZAm2 (1021 Am2)] is further constrained by the new data, which indicate an extremely rapid weakening of the field (losing ˜27% of its strength over ca. 30 y).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70011657','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70011657"><span>A proposed International <span class="hlt">Geomagnetic</span> Reference Field for 1965- 1985.</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Peddie, N.W.; Fabiano, E.B.</p> <p>1982-01-01</p> <p>A set of spherical harmonic models describing the Earth's main magnetic field from 1965 to 1985 has been developed and is proposed as the next revision of the International <span class="hlt">Geomagnetic</span> Reference Field (IGRF). A tenth degree and order spherical harmonic model of the main field was derived from Magsat data. A series of eighth degree and order spherical harmonic models of the <span class="hlt">secular</span> <span class="hlt">variation</span> of the main field was derived from magnetic observatory annual mean values. Models of the main field at 1965, 1970, 1975, and 1980 were obtained by extrapolating the main-field model using the <span class="hlt">secular</span> <span class="hlt">variation</span> models.-Authors spherical harmonic models Earth main magnetic field Magsat data</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016QuRes..85..391R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016QuRes..85..391R"><span>Paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> and environmental magnetism of Holocene-age sediments from Tulare Lake, CA</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Roza, Janine; Jackson, Brandon; Heaton, Eric; Negrini, Rob</p> <p>2016-05-01</p> <p>The lake-level record from Tulare Lake, CA has been shown to provide valuable constraints on late Pleistocene and Holocene runoff from the Sierra Nevada mountain range into the San Joaquin Valley of California, one of the world's most prolific agricultural centers. This project uses the magnetic properties of the Tulare Lake sediments in order to date the sediments and to constrain the relative lake level at the time of deposition. Shallowing lake conditions were identified leading up to a prominent unconformity; magnetic mineralogy and grain size indicators, primarily decreasing ARM/IRM and S-Ratio values suggest coarser grain sizes and more oxidizing conditions. Approximately half of the samples possessed well-behaved paleomagnetic directions suitable for paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> dating. The results indicate that the sediments below the unconformity were deposited approximately 7600-8500 cal yr BP, and the sediments above the unconformity were deposited approximately 2500-800 cal yr BP. The ages of the corresponding sediments are consistent with the time intervals during which previous studies indicate that lake level was above the elevation of this site, before and after a mid Holocene regression.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMGC41E1133R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMGC41E1133R"><span>Paleomagnetic <span class="hlt">Secular</span> <span class="hlt">Variation</span> and Environmental Magnetism of Holocene-aged Sediments from Tulare Lake, CA</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Roza, J.; Jackson, B.; Heaton, E.; Negrini, R. M.</p> <p>2015-12-01</p> <p>The lake-level record from Tulare Lake, CA has been shown to provide valuable constraints on late Pleistocene and Holocene channelized runoff from the Sierra Nevada mountain range into the San Joaquin Valley of California, one of the world's most prolific agricultural centers. This project focuses on the use of magnetic properties of the Tulare Lake sediments in order to test previous results by dating the sediments and determining the relative lake level at the time of deposition. Shallowing lake conditions were identified leading up to a prominent unconformity from magnetic mineralogy and grain size indicators, primarily decreasing ARM/IRM and S-Ratio values suggesting coarser grain sizes and more oxidizing conditions. Approximately half of the samples possessed well-behaved paleomagnetic directions suitable for paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> dating. The results indicate that the sediments below the unconformity were deposited approximately 7600-6700 14C years ago (~7600 to 8500 cal yr B.P.), and the sediments above the unconformity were deposited approximately 2200-500 14C years ago. The ages of the corresponding sediments are consistent with the time intervals during which lake level was predicted to be above the elevation of the Poso Canal site before and after a mid-Holocene regression.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..1411956O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..1411956O"><span>Improved Land-Sea Correlations in Iceland Based on Paleomagnetic <span class="hlt">Secular</span> <span class="hlt">Variations</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ölafsdóttir, S.; Geirsdóttir, Á.; Miller, G. H.; Stoner, J. S.</p> <p>2012-04-01</p> <p>High-resolution paleoclimatic reconstructions from both terrestrial and nearby marine archives are available from Iceland. Independently dated tephras and radiocarbon dates could theoretically synchronize these records, thereby allowing evaluation of leads and lags in the climate record. However, direct comparisons between records are limited by the difficulties in deriving precise age control. Here, Paleomagnetic <span class="hlt">Secular</span> <span class="hlt">Variation</span> (PSV) records reconstructed through alternating field demagnetization of u-channel samples from two lacustrine archives (HAK-1B & HVT-1A) are compared to the PSV records from a well-dated marine record (MD99-2269) taken from North Iceland shelf. Over the past 10 ka of the sediment records 40 to 60 tie points are utilized, based on diagnostic tephra layers and unique features in the PSV records, to synchronize the three sediment cores within a lock-in depth uncertainty. The uncertainties are likely to be on the order of decades due to the high accumulation rate, allowing all records to be placed on a common time scale. Using the well-dated marine core as a chronological template demonstrates the difference between linearly-interpreted tephra-based age model and the more time-variable PSV age model. The high frequency of tie points allows the reconstruction of sediment accumulation rate changes in the lacustrine records that were not apparent from the tephrochonological controls. The resulting PSV synchronized paleoclimate records from land and sea add valuable information about forcing and responses of the Holocene climate system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.P24B..07W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.P24B..07W"><span>Predicting Juno's Possible Internal Field and <span class="hlt">Secular</span> <span class="hlt">Variation</span> Models Based on Numerical Dynamo Simulations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wicht, J.; Holme, R. T.; Gastine, T.; Duarte, L.</p> <p>2016-12-01</p> <p>We use numerical simulations to model Jupiter's internal dynamo and to predict the information Juno's magnetometer may reveal about the internal magnetic field and dynamics. The simulations were performed with the MHD code MagIC, cover 99% of Jupiter's radius below the one bar level, and use an electrical conductivity profile that includes the metallic inner as well as the molecular outer hydrogen layer. Surface magnetic fields closely resemble known magnetic field models. The flow is dominated by a realistic prograde equatorial jet but lacks multiple mid to high latitude jets which, according to our simulations, seem incompatible with a Jupiter like magnetic field. Using the Juno mission trajectory and assuming an isotropic measurement error of 100 nT we could recover the numerical model field to spheric harmonic degree 18, and <span class="hlt">secular</span> <span class="hlt">variation</span> (SV) perhaps to degree 5. The field shows characteristic bands where the equatorial jet reaches down to higher conductivities and promotes a secondary local dynamo effect. The presence of these bands as well as the SV caused by zonal flow advection may offer important clues on the depth of the zonal jets. The form of the spectrum can provide additional information on the general depth of the dynamo region: The numerical simulations suggest that dynamo action starts at the radius where the magnetic Reynolds number, the ratio of Ohmic dissipation time to convective turnover time, exceeds about 50. This roughly agrees with the depth where the magnetic power spectrum is white for spherical harmonics degrees beyond four.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015sptz.prop12011P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015sptz.prop12011P"><span>Rotationally Resolved Study Of The Surface Of Pluto: seasonal/<span class="hlt">secular</span> <span class="hlt">variations</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pinilla-Alonso, Noemi; Bauer, James; Buratti, Bonnie; Cruikshank, Dale P.; Grundy, Will M.; Emery, Joshua P.; Fernandez, Yan; Lisse, Casey M.; Stansberry, John</p> <p>2015-10-01</p> <p>We propose Warm Spitzer/IRAC GO observations of the Pluto system, to monitorize the <span class="hlt">secular</span> and/or seasonal changes on Pluto's surface composition. The aim of this proposal is to characterize the surface heterogeneity of Pluto through photometric observations at the 3.6 and 4.5 µm IRAC channels after the New Horizons encounter on July 2014. We ask for observations at 18 longitudes (~ every 20o). The surface of Pluto, formed by patches of CH4, N2 and CO, is a dynamic and variable system, with a timescale on the order of months to years. Spitzer holds a unique place in the solar system to observe Pluto, above the Earth's atmosphere in a stable Earth-trailing environment. Relative differences in the albedo of Pluto in ch1 and ch2 is an effective tool to study the different mixing ratios of the ices on the surface. This is also promising for the search of other candidate materials that have not yet been identified in the vis/NIR, e.g CO2 that has its fundamental absorption band in the wavelength range of ch2. In 2004, under a Spitzer program during the cryogenic mission (PI. Cruikshank), low-resolution light curves were obtained at 8 different longitudes. In 2014, under a Cycle 10 program (PI. Pinilla-Alonso) we obtained data at ch1 and ch2 at 18 longitudes. The analysis of these data shows clear indications not only of surface heterogeneity, but also on possible <span class="hlt">secular</span> <span class="hlt">variations</span>. These data are under analysis and show a great potential for the mapping of volatiles ices all over the surface of Pluto. Two parallel observational programs are in progress involving people in this group, one of near-infrared spectroscopy (~0.9-2.5 µm) at the NASA Infrared Telescope Facility (PI. Grundy) and one of visible spectroscopy (0.4-0.95 µm) at WHT, La Palma (PI. Pinilla-Alonso). The combination of these datasets, covering different wavelength regions, provide unique and complementary information, and is very important in deriving full benefit of data from the NASA New Horizons</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_12 --> <div id="page_13" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="241"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFMGP33A0103M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFMGP33A0103M"><span>Do <span class="hlt">Geomagnetic</span> <span class="hlt">Variations</span> Affect the Foliar Spiral Direction of Coconut Palms?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Minorsky, P. V.; Bronstein, N. B.</p> <p>2005-12-01</p> <p>In coconut palms, leaves are attached to the stem in either an ascending clockwise (left-handed or L) or counter-clockwise (right-handed or R) spiral (1). Foliar spiral direction (FSD) is a classic case of morphological antisymmetry, in which dextral and sinistral forms are not inherited and are equally common within a species (2). FSD would seem a simple stochastic process unworthy of further study if not for the observation, based on data collected from 71,640 coconut palms in 42 locations around the world, that the FSD of coconut palms varies with latitude: R-trees predominate in the N Hemisphere and L-trees predominate in the S Hemisphere (3). Hemispheric asymmetries in FSD are significantly better correlated with magnetic latitude than with geographic or <span class="hlt">geomagnetic</span> latitude, suggesting that latitudinal asymmetries in FSD might be associated with the temporally varying component of Earth's magnetic field (4). Here, we present two new lines of evidence that <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> may underlie asymmetries in palm FSD. First, we show that asymmetries occur in the FSD of palm populations on opposite sides of islands, and second, that asymmetries in FSD vary with the 11-year solar cycle. The prediction that asymmetries in coconut palm FSD should exist on opposite sides of islands arises from the fact that because seawater is more electrically conductive than land, induced earth currents divide and stream past an island more strongly in one particular direction. The "<span class="hlt">geomagnetic</span> island effect" is characterized by a complete reversal of the vertical Z component of short-period <span class="hlt">geomagnetic</span> field anomalies at observation points on opposite sides of islands (5). To examine whether FSD varied around the circumferences of islands, we collected data on 6 islands (Puerto Rico, n = 4311; Antigua, n = 2038; Hawaii, n = 3552; Maui, n = 2175; Tahiti, n = 1582; Moorea, n = 2116). For each population, the degree of asymmetry was determined by calculating an "asymmetry quotient</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1980MsT..........1T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1980MsT..........1T"><span>Data acquisition system for use in the study of <span class="hlt">geomagnetic</span> <span class="hlt">variations</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Thomas, H. H.</p> <p>1980-12-01</p> <p>The study of the <span class="hlt">variations</span> in the <span class="hlt">geomagnetic</span> field requires a small, low power digital acquisition system. This thesis describes the design of a digital data acquisition system for such use. The design uses the complementary metal-oxide-semiconductor (CMOS) version of the INTEL 8048 single chip microcomputer and a high density data recorder. The microcomputers do not take data internally, instead they route data over a separate data bus. Two intermediate data memories are used; alternating between being written onto by the acquisition circuit and being read from for writing to the data recorder.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1982JGG....34..213D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1982JGG....34..213D"><span>A correlation between measured E-region current and <span class="hlt">geomagnetic</span> daily <span class="hlt">variation</span> at equatorial latitude</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Duhau, S.; Osella, A. M.</p> <p></p> <p>The usual methods of separation of the <span class="hlt">geomagnetic</span> daily <span class="hlt">variations</span> into parts of external and internal origin at equatorial latitudes have been revised to remove any previous assumption about the internal current, so that the separation may be performed in a zone of anomalous earth conductivity. The resulting procedure has been applied to obtain the distribution of the ionospheric current from the external field, at the South American dip equator and the result has been compared with previous measurements of the E-region current.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1715893R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1715893R"><span>Synchronous <span class="hlt">Variations</span> of the Free Aquifer Groundwater Level and <span class="hlt">Geomagnetic</span> Field</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ryabova, Svetlana A.; Spivak, Alexander A.</p> <p>2015-04-01</p> <p>We consider long period <span class="hlt">variations</span> of the magnetic field at the Earth's crust surface and its relation to seasonal change of the groundwater regime at the middle latitude geophysical observatory "Mikhnevo", situated at 85 km south of Moscow. Observatory is located away from large industrial projects allowing one to realize correct recording of geophysical fields. Results of synchronous observations of <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> and groundwater regime were used as basic data. Measurements of the local <span class="hlt">variations</span> of the magnetic field were carried out in special <span class="hlt">geomagnetic</span> pavilion using flux-gate magnetometer LEMI-018 (measurement range ±68 000 nT, resolution capacity 10 pT). Received digital data rows with discretization 1 s resulted in sequence of values in 1 min. Measurements of the groundwater <span class="hlt">variations</span> in water-table aquifer were carried out in the well of 30 m depth using sensitive sensor of water level LMP308i (resolving capacity 0.1 mm). Magnetic tipper, which is very sensitive to changes of the Earth's crust properties, was considered as characteristics of the magnetic <span class="hlt">variations</span>, and in the same time as an indicator of the change of the electric properties of the medium. Results of calculations demonstrate clear marked annual <span class="hlt">variation</span> of both real and imaginary composites of magnetic tipper describing relation between vertical component of magnetizing force and its horizontal components. Increase of thickness of the layer of watered rock resulting from rise of underground water level in water-table aquifer causes an increase of electrical conductivity of subsurface Earth's crust plot. It results in synchronous magnetic tipper <span class="hlt">variations</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SSRv..tmp...53Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SSRv..tmp...53Y"><span>Sq and EEJ—A Review on the Daily <span class="hlt">Variation</span> of the <span class="hlt">Geomagnetic</span> Field Caused by Ionospheric Dynamo Currents</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yamazaki, Y.; Maute, A.</p> <p>2016-09-01</p> <p>A record of the <span class="hlt">geomagnetic</span> field on the ground sometimes shows smooth daily <span class="hlt">variations</span> on the order of a few tens of nano teslas. These daily <span class="hlt">variations</span>, commonly known as Sq, are caused by electric currents of several μA/m2 flowing on the sunlit side of the E-region ionosphere at about 90-150 km heights. We review advances in our understanding of the <span class="hlt">geomagnetic</span> daily <span class="hlt">variation</span> and its source ionospheric currents during the past 75 years. Observations and existing theories are first outlined as background knowledge for the non-specialist. Data analysis methods, such as spherical harmonic analysis, are then described in detail. Various aspects of the <span class="hlt">geomagnetic</span> daily <span class="hlt">variation</span> are discussed and interpreted using these results. Finally, remaining issues are highlighted to provide possible directions for future work.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017SSRv..206..299Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017SSRv..206..299Y"><span>Sq and EEJ—A Review on the Daily <span class="hlt">Variation</span> of the <span class="hlt">Geomagnetic</span> Field Caused by Ionospheric Dynamo Currents</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yamazaki, Y.; Maute, A.</p> <p>2017-03-01</p> <p>A record of the <span class="hlt">geomagnetic</span> field on the ground sometimes shows smooth daily <span class="hlt">variations</span> on the order of a few tens of nano teslas. These daily <span class="hlt">variations</span>, commonly known as Sq, are caused by electric currents of several μ A/m2 flowing on the sunlit side of the E-region ionosphere at about 90-150 km heights. We review advances in our understanding of the <span class="hlt">geomagnetic</span> daily <span class="hlt">variation</span> and its source ionospheric currents during the past 75 years. Observations and existing theories are first outlined as background knowledge for the non-specialist. Data analysis methods, such as spherical harmonic analysis, are then described in detail. Various aspects of the <span class="hlt">geomagnetic</span> daily <span class="hlt">variation</span> are discussed and interpreted using these results. Finally, remaining issues are highlighted to provide possible directions for future work.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMGP11A..07T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMGP11A..07T"><span>New Insights on Long Term <span class="hlt">Geomagnetic</span> Moment <span class="hlt">Variation</span> from Cosmogenic Nuclide and Paleointensity Signatures along Ocean Sediment Cores.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Thouveny, N.; Bourles, D. L.; Valet, J. P.; Bassinot, F. C.; Ménabréaz, L.; Simon, Q.; Demory, F.; Valery, G.; Vidal, L.; Beaufort, L.; de Garidel-Thoron, T.</p> <p>2015-12-01</p> <p>Some numerical and experimental simulations suggest that precession might supply enough power to influence planetary dynamos. The demonstration of a causal relationship between the Earth's orbital motion and <span class="hlt">variations</span> of the <span class="hlt">geomagnetic</span> field intensity, would open interesting perspective for modelling the past and future <span class="hlt">geomagnetic</span> field behaviour and its eventual relationships to past and future orbitally constrained, climatic changes. Although pristine <span class="hlt">geomagnetic</span> signals can be extracted by filtering and stacking multiple normalized intensity records, the reconstruction of high resolution <span class="hlt">geomagnetic</span> field <span class="hlt">variations</span> still raises questions. Namely, significant variance at orbital frequencies in relative paleointensity (RPI) records are generally considered as clues of residual contamination by paleoclimatically induced <span class="hlt">variations</span> of magnetic carriers size ranges or mineralogy. Such questions can be adressed using other indicators of the <span class="hlt">geomagnetic</span> dipole moment <span class="hlt">variation</span>, such as the cosmogenic production modulated by the magnetospheric shielding. During the MAGORB project (ANR-09-BLAN-053-001) cosmogenic nuclide geochemistry, d18O, and paleomagnetic records were constructed along thick clayey-carbonate sequences deposited in the equatorial pacific and indian oceans over the last million of years. Authigenic 10Be/9Be ratio and RPI <span class="hlt">variations</span> generally exhibit similar ranges of oscillations. However significant offsets appear between some RPI lows and their corresponding 10Be/9Be peaks, suggesting delayed lock-in of the remanent magnetization. After transfer on time scales the new <span class="hlt">geomagnetic</span> moment series can be compared with the PISO-1500 and SINT-2000 stacks, and with the 10Be ice core record of EPICA Dome C. These new authigenic 10Be/9Be ratio records provide new opportunities to: 1) assess the validity of high resolution RPI records, 2) evaluate address the question of the presence of orbital periods in the paleo-field <span class="hlt">geomagnetic</span> spectrum, and 3) to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19990018406','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19990018406"><span>Evidence for Solar-Cycle Forcing and <span class="hlt">Secular</span> <span class="hlt">Variation</span> in the Armagh Observatory Temperature Record</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wilson, Robert M.</p> <p>1998-01-01</p> <p>A prominent feature of previous long-term temperature studies has been the appearance of warming since the 1880s, this often being taken as evidence for anthropogenic-induced global warming. In this investigation, the long-term, annual, mean temperature record (1844-1992) of the Armagh Observatory (Armagh, North Ireland), a set of temperature data based on maximum and minimum thermometers that predates the 1880s and correlates well with northern hemispheric and global standards, is examined for evidence of systematic <span class="hlt">variation</span>, in particular, as related to solar-cycle forcing and <span class="hlt">secular</span> <span class="hlt">variation</span>. Indeed, both appear to be embedded within the Armagh data. Removal of these effects, each contributing about 8% to the overall reduction in variance, yields residuals that are randomly distributed. Application of the 10-year moving average to the residuals, furthermore, strongly suggests that the behavior of the residuals is episodic, inferring that (for extended periods of time) temperatures at Armagh sometimes were warmer or cooler (than expected), while at other times they were stable. Comparison of cyclic averages of annual mean temperatures against the lengths of the associated Hale cycles (i.e., the length of two, sequentially numbered, even-odd sunspot cycle pairs) strongly suggests that the temperatures correlate inversely (r = -0.886 at less than 2% level of significance) against the length of the associated Hale cycle. Because sunspot cycle 22 ended in 1996, the present Hale cycle probably will be shorter than average, implying that temperatures at Armagh over this Hale cycle will be warmer (about 9.31 q 0.23 C at the 90% confidence level) than average (= 9.00 C).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhRvD..91d4009M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhRvD..91d4009M"><span>Cosmological <span class="hlt">variation</span> of the MOND constant: <span class="hlt">Secular</span> effects on galactic systems</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Milgrom, Mordehai</p> <p>2015-02-01</p> <p>The proximity of the MOND acceleration constant with cosmological accelerations—for example, a0≈c H0/2 π —points to its possibly decreasing with cosmic time. I begin to consider the <span class="hlt">secular</span> changes induced in galactic systems by such presumed <span class="hlt">variations</span>, which are assumed to be adiabatic. It is important to understand these effects, in isolation from other evolutionary influences, in order to identify or constrain a0 <span class="hlt">variations</span> by detection of induced effects, or lack thereof. I find that as long as the system is fully in the deep-MOND regime—as applies to many galactic systems—the adiabatic response of the system obeys simple scaling laws. For example, in a system that would be stationary for fixed a0, the system expands homologously as a0-1 /4, while internal velocities decrease uniformly as a01 /4. If a0∝c H at all relevant times, this change amounts to a factor of ˜2.5 since redshift 10. For rotating systems, the angular frequency Ω ∝a01 /2. The accelerations increase relative to a0 as a0-1 /4, pushing the system towards the Newtonian regime. All this follows from the appearance of a0 in MOND and the scale invariance of the deep-MOND limit—two basic tenets of MOND. More complicated evolution ensues when parts of the system become Newtonian, or are so from inception. For example, these parts may become unstable since they are not protected by MOND's stabilizing effects. The existence of such regions also modifies the MONDian regime since they affect the potential everywhere, and constituents might migrate between the Newtonian and MONDian regimes. Studying these last effects would require detailed numerical calculations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1984JGR....89.7773P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1984JGR....89.7773P"><span>The pattern of anomalous <span class="hlt">geomagnetic</span> <span class="hlt">variation</span> fields over the midcontinent gravity high</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Prugger, Arnfinn F.; Woods, Dennis V.</p> <p>1984-09-01</p> <p>Magnetometer array data, collected by H. Porath and co-workers from the University of Texas at Dallas in the midwest United States during the fall of 1969, have been reanalyzed to further define the nature of the reported <span class="hlt">geomagnetic</span> <span class="hlt">variation</span> anomaly in the region of the midcontinent gravity high. <span class="hlt">Variation</span> events with a wide range of horizontal source field polarization and frequency have been digitized from the original film records. These data have been used in a vertical-field response arrow (induction vector) analysis. The results indicate that there is no significant overall conductivity anomaly associated with the geologic structure causing the gravity feature. Rather, the pattern of anomalous <span class="hlt">variation</span> fields is one of isolated anomalies at high frequency. These anomalies are coincident with postulated fault structures perpendicular to the gravity high lineament and with localized regions of high heat flow.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015Ge%26Ae..55.1026G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015Ge%26Ae..55.1026G"><span>Reconstruction of the long term <span class="hlt">variations</span> of the total solar irradiance from <span class="hlt">geomagnetic</span> data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Georgieva, K.; Nagovitsyn, Yu.; Kirov, B.</p> <p>2015-12-01</p> <p>The total solar irradiance (TSI) is considered one of the main factors determining the terrestrial climate, and its <span class="hlt">variations</span> are included in many numerical models evaluating the effects of natural as compared to anthropogenic factors of climate change. For the purposes of climate change, it is important to estimate both past and future TSI <span class="hlt">variations</span>, which are caused by <span class="hlt">variations</span> of the solar magnetic fields. Various proxies are used for reconstructing the long term evolution of TSI, which have some inevitable limitations leading to big uncertainties. We suggest an independent proxy-<span class="hlt">geomagnetic</span> activity records, and present a reconstruction of TSI which supports higher long term TSI variability than generally accepted, and a prediction for a decrease in TSI in the following cycles, which can be taken into account in models of the expected future climate variability.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70011454','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70011454"><span>International <span class="hlt">Geomagnetic</span> Reference Field: the third generation.</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Peddie, N.W.</p> <p>1982-01-01</p> <p>In August 1981 the International Association of <span class="hlt">Geomagnetism</span> and Aeronomy revised the International <span class="hlt">Geomagnetic</span> Reference Field (IGRF). It is the second revision since the inception of the IGRF in 1968. The revision extends the earlier series of IGRF models from 1980 to 1985, introduces a new series of definitive models for 1965-1976, and defines a provisional reference field for 1975- 1980. The revision consists of: 1) a model of the main <span class="hlt">geomagnetic</span> field at 1980.0, not continuous with the earlier series of IGRF models together with a forecast model of the <span class="hlt">secular</span> <span class="hlt">variation</span> of the main field during 1980-1985; 2) definitive models of the main field at 1965.0, 1970.0, and 1975.0, with linear interpolation of the model coefficients specified for intervening dates; and 3) a provisional reference field for 1975-1980, defined as the linear interpolation of the 1975 and 1980 main-field models.-from Author</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JESS..124.1721V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JESS..124.1721V"><span><span class="hlt">Variation</span> of surface electric field during <span class="hlt">geomagnetic</span> disturbed period at Maitri, Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Victor, N. Jeni; Panneerselvam, C.; Anil Kumar, C. P.</p> <p>2015-12-01</p> <p>The paper discusses on the <span class="hlt">variations</span> of the atmospheric vertical electric field measured at sub-auroral station Maitri (70∘75'S, 11∘75'E), and polar station Vostok (78.5∘S, 107∘E) during the <span class="hlt">geomagnetic</span> disturbances on 25-26 January 2006. Diurnal <span class="hlt">variation</span> of surface electric field measured at Maitri shows a similar <span class="hlt">variation</span> with worldwide thunderstorm activity, whereas the departure of the field is observed during disturbed periods. This part of the field corresponds to the magnetospheric/ionospheric (an additional generator in the polar regions) voltage generators. Solar wind parameters and planetary indices represent the temporal <span class="hlt">variation</span> of the disturbances, and digital fluxgate magnetometer <span class="hlt">variation</span> continuously monitored to trace the auroral movement at Maitri. We have observed that the electrojet movement leaves its signature on vertical and horizontal components of the DFM in addition; the study infers the position of auroral current wedge with respect to Maitri. To exhibit the auroral oval, OVATION model is obtained with the aid of DMSP satellite and UV measurements. It is noted that the Maitri is almost within the auroral oval during the periods of disturbances. To examine the simultaneous changes in the vertical electric field associated with this magnetic disturbance, the dawn-dusk potential is studied for every UT hours; the potential was obtained from Weimer model and SuperDARN radar. The comparison reveals the plausible situation for the superposition of dawn-dusk potential on surface electric field over Maitri. This observation also shows that the superposition may not be consistent with the phase of the electrojet. Comparison of surface electric field at Maitri and Vostok shows that the parallel <span class="hlt">variation</span> exhibits with each other, but during the period of <span class="hlt">geomagnetic</span> disturbances, the influence is not much discerned at Vostok.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFMGP41A..06B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFMGP41A..06B"><span><span class="hlt">Secular</span> <span class="hlt">Variation</span> and Paleomagnetic Studies of Southern Patagonian Plateau Lavas, 46S to 52S, Argentina</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brown, L.; Gorring, M.; Mason, D.; Condit, C.; Lillydahl-Schroeder, H.</p> <p>2007-12-01</p> <p>Regional studies of paleosecular <span class="hlt">variation</span> of the Earth's magnetic field can provide us with information beyond that available from one location. Southern Patagonia, Argentina (46S to 52S latitude and 68W to 72W longitude) is a place where numerous Plio-Pleistocene lava flows are available for such a study. Volcanic activity in this area is related to back arc volcanism due to slab window activity as the South Chile Ridge is subducted beneath western South America, producing Neogene volcanic centers capping Mesozoic basement extending far to the east of the active plate boundary. Published studies on young lavas from both the northern (Meseta del Lago Buenos Aires, Brown et al, 2004) and southern (Pali Aike Volcanic Field, Mejia et al, 2004) portions provide stable paleomagnetic data on nearly 70 lava flows. Paleosecular <span class="hlt">variation</span> values for the two studies differ, with 17.1 degrees obtained from the Pali Aike field and 20.0 degrees from the Lago Buenos Aires field. Recent fieldwork in the plateau lavas between these two locations has provided some 80 new sites allowing us to better investigate <span class="hlt">secular</span> <span class="hlt">variation</span> and the time-averaged field over this entire region during the past 5 myr. Rock magnetic studies on selected new samples (isothermal remanent magnetization and hysteresis measurements) as well as optical observations indicate low titanium magnetite as the primary carrier of remanence. Hysteresis properties range from 0.1 to 0.4 for Mr/Ms and 1.4 to 3.0 for Hcr/Hc indicating psuedo-single domain behavior. Mean destructive fields for AF demagnetization average 40 to 60 mT. Thirty-three new sites, mostly from Gran Meseta Central (48°S), yield a mean direction of inclination -61.8, declination of 356.6 with an alpha-95 of 5.7 degrees. These directions, with additional sites recently collected from Meseta de la Muerte south to Rio Santa Cruz, will allow us to further investigate paleosecular <span class="hlt">variation</span> over this wide region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012Ge%26Ae..52..121V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012Ge%26Ae..52..121V"><span>Long-term <span class="hlt">variations</span> in the flux of cosmogenic isotope 10Be over the last 10000 years: <span class="hlt">Variations</span> in the <span class="hlt">geomagnetic</span> field and climate</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vasiliev, S. S.; Dergachev, V. A.; Raspopov, O. M.; Jungner, H.</p> <p>2012-02-01</p> <p>A spectral analysis of data on the flux of cosmogenic 10Be in ice core samples from the Central Greenland (project GRIP) over the last 10 thousand years have been carried out. It has been shown that the 10Be flux varies cyclically; the most significant cycle is of about 2300 years. <span class="hlt">Variations</span> in the position of the virtual <span class="hlt">geomagnetic</span> pole over 8000 years have been analyzed. Significant components, pointing to the cyclic <span class="hlt">variation</span> in the position of the <span class="hlt">geomagnetic</span> pole with a period of about 2300 years, have been revealed in a periodogram of the virtual <span class="hlt">geomagnetic</span> pole longitude. In addition to the nearly 2300-year-long cycle, some lines are observable in the 10Be flux periodogram, which can be considered as a manifestation of the 1000-year-long cycle of the 10Be deposition rate on the ice surface. The relationship between the cyclicity of the <span class="hlt">geomagnetic</span> pole position and the 10Be flux is discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFM.B21D..07R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFM.B21D..07R"><span>Effect of <span class="hlt">secular</span> <span class="hlt">variation</span> in oceanic Mg/Ca on calcareous biomineralization</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ries, J. B.; Stanley, S. M.</p> <p>2006-12-01</p> <p>The polymorph mineralogy of simple, hypercalcifying marine organisms has generally varied in synchroneity with the polymorph mineralogy of abiotic CaCO3 precipitates (ooids, marine cements) throughout the Phanerozoic Eon. This synchroneity is caused by <span class="hlt">secular</span> <span class="hlt">variation</span> in the Mg/Ca ratio of seawater (SW; mMg/Ca > 2 = aragonite + high-Mg calcite; mMg/Ca < 2 = calcite), determined primarily by the mixing rate of mid-ocean-ridge/large-igneous-province hydrothermal brines and river water, driven by the global rate of ocean crust production. Here, we present experiments evaluating the effect of seawater Mg/Ca on the biomineralization and growth of extant representatives of hypercalcifying taxa that have been subjected to fluctuations in oceanic Mg/Ca in the past. Codiacean algae (arag), scleractinian corals (arag), coccolithophores (low-high Mg-calc), coralline algae (high Mg-calc), various reef-dwelling animals (echinoids, crabs, shrimp, calcareous serpulid worms; high Mg- calc), and calcifying microbial mats (arag + high-Mg calc) were grown in artificial SW formulated over the range of mMg/Ca (1.0 to 5.2) that occurred throughout each taxon's history. Codiacean algae and scleractinian corals exhibited higher rates of calcification and growth in artificial SW favoring their aragonite mineralogy and, significantly, produced a portion of their CaCO3 as calcite in the artificial calcite SW. Coccolithophores (low-high Mg calc.) showed higher calcification and growth rates and produced low-Mg calcite in the calcite SW. Likewise, coralline algae and the reef-dwelling animals (high-Mg calc) varied skeletal Mg/Ca with seawater Mg/Ca. The calcifying microbial mats grew equally well in the calcite and aragonite SW and varied their mineral polymorph commensurate with the SW (mMg/Ca<2 = low- Mg calc; mMg/Ca>2 = arag + high-Mg calc), suggesting a nearly abiotic mode of calcification. The precipitation of low-Mg calcite + aragonite by codiacean algae and scleractinian corals (arag</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..1212635M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..1212635M"><span>Marine sediments and Beryllium-10 record of the <span class="hlt">geomagnetic</span> moment <span class="hlt">variations</span> during the Brunhes period.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ménabréaz, Lucie; Thouveny, Nicolas; Bourlès, Didier; Demory, François</p> <p>2010-05-01</p> <p>Over millennial time scales, the atmospheric production of the cosmonuclid 10Be (half-life 1.387 ± 0.012 Ma [Shmeleff et al., 2009; Korschinek et al., 2009]) is modulated by the <span class="hlt">geomagnetic</span> field strength, following a negative power law (e.g. Lal, 1988; Masarik and Beer, 2009). With respect to paleomagnetic reconstructions, 10Be-derived paleointensity records can therefore constitute an alternative, global and independent reading of the dipole moment <span class="hlt">variations</span>. During the last years, efforts have been made to extract a <span class="hlt">geomagnetic</span> signal from single and stacked 10Be records in natural archives such as ice and marine sediments (e.g. Carcaillet et al., 2004; Christl et al., 2007; Muscheler et al., 2005). In marine sediments, the 10Be concentration results from complex interplay of several processes: cosmogenic production, adsorption on sediment particles, redistribution by fluviatile and oceanic transport, and deposition. Therefore, a correction procedure is required to consider both sediment redistribution and enhanced scavenging, which can alter the primary signatures. To reconstruct the succession of field intensity lows accompanying excursions during the Brunhes chron, we investigated authigenic 10Be/9Be record of marine sequences also studied for paleomagnetism and oxygen isotopes. Mid and low latitude sites were preferred in order to benefit from the most efficient modulation by the magnetospheric shielding. We present a high resolution authigenic 10Be/9Be record of the last 50 ka recovered from the Portuguese Margin, that deciphers the cosmonuclide 10Be overproduction created by the <span class="hlt">geomagnetic</span> dipole low associated with the Laschamp excursion. This record is compared to other proxy records of the <span class="hlt">geomagnetic</span> field <span class="hlt">variations</span> for the same time interval: (1) the relative paleointensity (RPI) reconstructed from the same sediments and the GLOPIS-75 record (Laj et al., 2004), (2) the absolute VDM record based on absolute paleointensities measured on lava flows</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Ge%26Ae..56..342S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Ge%26Ae..56..342S"><span>Klimovskaya: A new <span class="hlt">geomagnetic</span> observatory</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Soloviev, A. A.; Sidorov, R. V.; Krasnoperov, R. I.; Grudnev, A. A.; Khokhlov, A. V.</p> <p>2016-05-01</p> <p>In 2011 Geophysical Center RAS (GC RAS) began to deploy the Klimovskaya <span class="hlt">geomagnetic</span> observatory in the south of Arkhangelsk region on the territory of the Institute of Physiology of Natural Adaptations, Ural Branch, Russian Academy of Sciences (IPNA UB RAS). The construction works followed the complex of preparatory measures taken in order to confirm that the observatory can be constructed on this territory and to select the optimal configuration of observatory structures. The observatory equipping stages are described in detail, the technological and design solutions are described, and the first results of the registered data quality control are presented. It has been concluded that Klimovskaya observatory can be included in INTERMAGNET network. The observatory can be used to monitor and estimate <span class="hlt">geomagnetic</span> activity, because it is located at high latitudes and provides data in a timely manner to the scientific community via the web-site of the Russian-Ukrainian <span class="hlt">Geomagnetic</span> Data Center. The role of ground observatories such as Klimovskaya remains critical for long-term observations of <span class="hlt">secular</span> <span class="hlt">variation</span> and for complex monitoring of the <span class="hlt">geomagnetic</span> field in combination with low-orbiting satellite data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AIPC.1203..748P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AIPC.1203..748P"><span>Analysis of Changes of Cardiological Parameters at Middle Latitude Region in Relation to <span class="hlt">Geomagnetic</span> Disturbances and Cosmic Ray <span class="hlt">Variations</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Papailiou, M.; Dimitrova, S.; Babayev, E. S.; Mavromichalaki, H.</p> <p>2010-01-01</p> <p>Collaborating scientific groups from Athens (Greece), Baku (Azerbaijan) and Sofia (Bulgaria) have conducted a research work on the possible effects of <span class="hlt">geomagnetic</span> field disturbances (GMF) and cosmic ray intensity (CRI) <span class="hlt">variations</span> on human homeostasis, particularly, the cardio-health state. Electrocardiograms (ECGs) of seven functionally healthy persons were digitally registered at the joint Laboratory of Heliobiology located in the Medical Centre INAM, Baku, on working days and Saturdays. Heart rate values, estimated from ECGs, were analysed in relation to daily values of CRI, as measured by the Neutron Monitor of the University of Athens and daily <span class="hlt">variations</span> of Dst and Ap <span class="hlt">geomagnetic</span> indices and some significant results had been revealed in previous studies. Researches were continued by study of additional cardiologic parameters estimated from the same ECG data. In this study digital data of RR interval (the time elapsing between two consecutive R waves in the ECG), namely RRminimum, RRmaximum and RRaverage were analyzed taking into consideration different levels of GMF disturbances (estimated through <span class="hlt">variations</span> of Dst and Ap indices) and cosmic ray activity (through CRI <span class="hlt">variations</span>). The data refer to the time period 15 July 2006-31 March 2008. <span class="hlt">Variations</span> of RR intervals show connection to GMF disturbances and CRI <span class="hlt">variations</span>. The revealed effects are more pronounced for high levels of <span class="hlt">geomagnetic</span> activity (when <span class="hlt">geomagnetic</span> storms occur) and large CRI decreases as well as on the days before and after these <span class="hlt">variations</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850026720','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850026720"><span>The cosmic ray differential diurnal <span class="hlt">variation</span> dependences on the zenith angle and the <span class="hlt">geomagnetic</span> disturbance</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kavlakov, S.; Georgiev, L.</p> <p>1985-01-01</p> <p>Simultaneous and continuous muon measurements in two opposite azimuthal directions under equal zenith angles demonstrated the importance of this method for cosmic ray diurnal <span class="hlt">variation</span> investigations. Lately these measurements were extended by means of improved telescopes. The obtained cosmic ray diurnal <span class="hlt">variations</span> were presented as intensity differential curves. Theoretical investigations connected the properties of these curves with some interplanetary spece parameters. The harmonics of these curves were interpreted physically. Some order difference curves were introduced. In earlier works some dependences between the parameters characterizing the first and the second harmonics of the differential intensity curves and the <span class="hlt">geomagnetic</span> activity were found. Then all measurements were carried out under only one zenith angle. The results of investigations of similar dependences using data of simultaneous measurements under three different zenith angles are presented.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_13 --> <div id="page_14" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="261"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatSR...623411V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatSR...623411V"><span>Palaeomagnetism of the Upper Miocene- Lower Pliocene lavas from the East Carpathians: contribution to the paleosecular <span class="hlt">variation</span> of <span class="hlt">geomagnetic</span> field</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vişan, Mădălina; Panaiotu, Cristian G.; Necula, Cristian; Dumitru, Anca</p> <p>2016-03-01</p> <p>Investigations of the paleosecular <span class="hlt">variation</span> of the <span class="hlt">geomagnetic</span> field on geological timescales depend on globally distributed data sets from lava flows. We report new paleomagnetic results from lava flows of the East Carpathian Mountains (23.6°E, 46.4°N) erupted between 4 and 6 Ma. The average virtual <span class="hlt">geomagnetic</span> pole position (76 sites) includes the North Geographic Pole and the dispersion of virtual <span class="hlt">geomagnetic</span> poles is in general agreement with the data of the Time Averaged <span class="hlt">geomagnetic</span> Field Initiative. Based on this study and previous results from the East Carpathians obtained from 0.04–4 Ma old lava flows, we show that high value of dispersion are characteristic only for 1.5–2.8 Ma old lava flows. High values of dispersion during the Matuyama chron are also reported around 50°N, in the global paleosecular <span class="hlt">variation</span> data set. More data are needed at a global level to determine if these high dispersions reflect the behaviour of the <span class="hlt">geomagnetic</span> field or an artefact of inadequate number of sites. This study of the East Carpathians volcanic rocks brings new data from southeastern Europe and which can contribute to the databases for time averaged field and paleosecular <span class="hlt">variation</span> from lavas in the last 6 Ma.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4800496','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4800496"><span>Palaeomagnetism of the Upper Miocene- Lower Pliocene lavas from the East Carpathians: contribution to the paleosecular <span class="hlt">variation</span> of <span class="hlt">geomagnetic</span> field</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Vişan, Mădălina; Panaiotu, Cristian G.; Necula, Cristian; Dumitru, Anca</p> <p>2016-01-01</p> <p>Investigations of the paleosecular <span class="hlt">variation</span> of the <span class="hlt">geomagnetic</span> field on geological timescales depend on globally distributed data sets from lava flows. We report new paleomagnetic results from lava flows of the East Carpathian Mountains (23.6°E, 46.4°N) erupted between 4 and 6 Ma. The average virtual <span class="hlt">geomagnetic</span> pole position (76 sites) includes the North Geographic Pole and the dispersion of virtual <span class="hlt">geomagnetic</span> poles is in general agreement with the data of the Time Averaged <span class="hlt">geomagnetic</span> Field Initiative. Based on this study and previous results from the East Carpathians obtained from 0.04–4 Ma old lava flows, we show that high value of dispersion are characteristic only for 1.5–2.8 Ma old lava flows. High values of dispersion during the Matuyama chron are also reported around 50°N, in the global paleosecular <span class="hlt">variation</span> data set. More data are needed at a global level to determine if these high dispersions reflect the behaviour of the <span class="hlt">geomagnetic</span> field or an artefact of inadequate number of sites. This study of the East Carpathians volcanic rocks brings new data from southeastern Europe and which can contribute to the databases for time averaged field and paleosecular <span class="hlt">variation</span> from lavas in the last 6 Ma. PMID:26997549</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26997549','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26997549"><span>Palaeomagnetism of the Upper Miocene- Lower Pliocene lavas from the East Carpathians: contribution to the paleosecular <span class="hlt">variation</span> of <span class="hlt">geomagnetic</span> field.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Vişan, Mădălina; Panaiotu, Cristian G; Necula, Cristian; Dumitru, Anca</p> <p>2016-03-21</p> <p>Investigations of the paleosecular <span class="hlt">variation</span> of the <span class="hlt">geomagnetic</span> field on geological timescales depend on globally distributed data sets from lava flows. We report new paleomagnetic results from lava flows of the East Carpathian Mountains (23.6°E, 46.4°N) erupted between 4 and 6 Ma. The average virtual <span class="hlt">geomagnetic</span> pole position (76 sites) includes the North Geographic Pole and the dispersion of virtual <span class="hlt">geomagnetic</span> poles is in general agreement with the data of the Time Averaged <span class="hlt">geomagnetic</span> Field Initiative. Based on this study and previous results from the East Carpathians obtained from 0.04-4 Ma old lava flows, we show that high value of dispersion are characteristic only for 1.5-2.8 Ma old lava flows. High values of dispersion during the Matuyama chron are also reported around 50°N, in the global paleosecular <span class="hlt">variation</span> data set. More data are needed at a global level to determine if these high dispersions reflect the behaviour of the <span class="hlt">geomagnetic</span> field or an artefact of inadequate number of sites. This study of the East Carpathians volcanic rocks brings new data from southeastern Europe and which can contribute to the databases for time averaged field and paleosecular <span class="hlt">variation</span> from lavas in the last 6 Ma.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110012855','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110012855"><span>MoSST DAS: The First Working <span class="hlt">Geomagnetic</span> Data Assimilation System</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kuang, Weijia; Wei, Zigang; Tangborn, Andrew</p> <p>2011-01-01</p> <p>The Earth possesses an internal magnetic field (<span class="hlt">geomagnetic</span> field) generated by convection in the outer core (geodynamo). Previous efforts have been focused along two distinct paths: (1) numerical geodynamo modeling to understand the origin of the <span class="hlt">geomagnetic</span> field, and the mechanisms of <span class="hlt">geomagnetic</span> <span class="hlt">secular</span> <span class="hlt">variations</span> (SV); and (2) <span class="hlt">geomagnetic</span> field modeling to map the spatial/temporal <span class="hlt">variations</span> of the field from <span class="hlt">geomagnetic</span> data, and to derive core properties, e.g. inversion of core flow near the core-mantle boundary (CMB). <span class="hlt">Geomagnetic</span> data assimilation is a new approach emerged over the past 5 years: surface observations are assimilated with geodynamo models for better understanding of the core dynamical state, and accurately prediction of SV. In collaboration with several <span class="hlt">geomagnetic</span> research groups, we have developed the first working <span class="hlt">geomagnetic</span> data assimilation system, Modular, Scalable, Self-consistent, and Three-dimensional (MoSST) DAS, that includes the MoSST numerical dynamo model; 7000 years of <span class="hlt">geomagnetic</span> field maps from several field models utilizing satellite and ground observatory data, historical magnetic records and archeo/paleo magnetic data; and an ensemble based optimal interpolation (01) assimilation algorithm. With this system, we have demonstrated clearly that the assimilated core dynamical state is substantially different from those of pure geodynamo simulations. Ensemble assimilation runs also show the convergence of the assimilated solutions inside the core, suggesting that the simulation state is pulled closer to the truth via data assimilation. The forecasts from this system are also very accurate: the 5-year forecast of the <span class="hlt">geomagnetic</span> field agrees very well with the observations; and the 5-year <span class="hlt">secular</span> <span class="hlt">variation</span> forecast is more accurate than the IGRF SV forecast models in the past. Using <span class="hlt">geomagnetic</span> records up to 2009, we have made an SV forecast for the period from 2010-2015, and is a candidate SV model for IGRF-11.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PEPI..257..205G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PEPI..257..205G"><span>New archeointensity data from French Early Medieval pottery production (6th-10th century AD). Tracing 1500 years of <span class="hlt">geomagnetic</span> field intensity <span class="hlt">variations</span> in Western Europe</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Genevey, Agnès; Gallet, Yves; Jesset, Sébastien; Thébault, Erwan; Bouillon, Jérôme; Lefèvre, Annie; Le Goff, Maxime</p> <p>2016-08-01</p> <p>Nineteen new archeointensity results were obtained from the analysis of groups of French pottery fragments dated to the Early Middle Ages (6th to 10th centuries AD). They are from several medieval ceramic production sites, excavated mainly in Saran (Central France), and their precise dating was established based on typo-chronological characteristics. Intensity measurements were performed using the Triaxe protocol, which takes into account the effects on the intensity determinations of both thermoremanent magnetization anisotropy and cooling rate. Intensity analyses were also carried out on modern pottery produced at Saran during an experimental firing. The results show very good agreement with the <span class="hlt">geomagnetic</span> field intensity directly measured inside and around the kiln, thus reasserting the reliability of the Triaxe protocol and the relevance of the quality criteria used. They further demonstrate the potential of the Saran pottery production for archeomagnetism. The new archeointensity results allow a precise and coherent description of the <span class="hlt">geomagnetic</span> field intensity <span class="hlt">variations</span> in Western Europe during the Early Medieval period, which was until now poorly documented. They show a significant increase in intensity during the 6th century AD, high intensity values from the 7th to the 9th century, with a minimum of small amplitude at the transition between the 7th and the 8th centuries and finally an important decrease until the beginning of the 11th century. Together with published intensity results available within a radius of 700 km around Paris, the new data were used to compute a master curve of the Western European <span class="hlt">geomagnetic</span> intensity <span class="hlt">variations</span> over the past 1500 years. This curve clearly exhibits five intensity maxima: at the transition between the 6th and 7th century AD, at the middle of the 9th century, during the 12th century, in the second part of the 14th century and at the very beginning of the 17th century AD. Some of these peaks are smoothed, or</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeCoA.160..188G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeCoA.160..188G"><span>Fossil corals as an archive of <span class="hlt">secular</span> <span class="hlt">variations</span> in seawater chemistry since the Mesozoic</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gothmann, Anne M.; Stolarski, Jarosław; Adkins, Jess F.; Schoene, Blair; Dennis, Kate J.; Schrag, Daniel P.; Mazur, Maciej; Bender, Michael L.</p> <p>2015-07-01</p> <p>Numerous archives suggest that the major ion and isotopic composition of seawater have changed in parallel with large <span class="hlt">variations</span> in geologic processes and Earth's climate. However, our understanding of the mechanisms driving <span class="hlt">secular</span> changes in seawater chemistry on geologic timescales is limited by the resolution of data in time, large uncertainties in seawater chemistry reconstructions, and ambiguities introduced by sample diagenesis. We validated the preservation of a suite of ∼60 unrecrystallized aragonitic fossil scleractinian corals, ranging in age from Triassic through Recent, for use as new archives of past seawater chemistry. Optical and secondary electron microscopy (SEM) studies reveal that fossil coral crystal fabrics are similar to those of modern coralline aragonite. X-ray diffractometry (XRD), cathodoluminescence microscopy (CL), and Raman studies confirm that these specimens contain little to no secondary calcite. In order to screen for geochemical changes indicative of alteration, we measured 87Sr/86Sr ratios, clumped isotopes, and trace element ratios sensitive to diagenesis (e.g., Mn/Ca). We retain samples when these tests either fail to identify any diagenetic modifications, or identify specific domains free of detectable alteration. Using the validated fossil coral archive we reconstruct seawater Mg/Ca and Sr/Ca ratios, measured by Secondary Ion Mass Spectrometry (SIMS), back to ∼230 Ma. The effects of temperature on coral trace element incorporation cannot explain the trends observed in our fossil coral Mg/Ca and Sr/Ca data. In agreement with independent records, seawater Mg/Ca molar ratios inferred from corals are low (Mg/Ca ∼1) during the Cretaceous and Jurassic, and increase between the Early Cenozoic and present (Mg/Ca = 5.2). Seawater Sr/Ca ratios from corals vary systematically between ∼8 and 13 mmol/mol since 230 Ma, with maximum values in the Cretaceous and Paleogene. The coral Sr/Ca record disagrees with records from</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMSA13B..04S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMSA13B..04S"><span>Seasonal and solar activity dependence of the ionospheric electric fields estimated with <span class="hlt">geomagnetic</span> solar quiet daily <span class="hlt">variation</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shinbori, A.; Koyama, Y.; Nose, M.; Hori, T.; Otsuka, Y.</p> <p>2016-12-01</p> <p>In order to investigate the seasonal and solar activity dependence of the ionospheric electric field estimated with the <span class="hlt">geomagnetic</span> solar quiet (Sq) daily <span class="hlt">variation</span> from 1958 to 2015, we analyzed 1-hour <span class="hlt">geomagnetic</span> field data obtained from 83 <span class="hlt">geomagnetic</span> observatories from the middle-latitude to equatorial regions with an aid of the IUGONET data analysis tool. These <span class="hlt">geomagnetic</span> field data were provided by WDC for <span class="hlt">Geomagnetism</span>, Kyoto University. In this analysis, we first selected <span class="hlt">geomagnetic</span> field data corresponding to a period of the solar quiet day when the Kp index is less than 4 throughout a day. Next, we identified the Sq <span class="hlt">variation</span> as a deviation from the value at midnight in both the X and Y components of the <span class="hlt">geomagnetic</span> field data. Finally, we obtained the monthly-mean ionospheric electric fields by solving Ohm's equation with the two-dimensional height-integrated ionospheric conductivity and <span class="hlt">geomagnetic</span> Sq <span class="hlt">variation</span>. As a result, the ionospheric zonal and meridional electric fields shows a clear seasonal <span class="hlt">variation</span> and 11-year solar activity dependence for all of the investigated <span class="hlt">geomagnetic</span> stations. The power spectra of the zonal electric field shows three dominant peaks at 6, 12 and 132 months. Moreover, the 4-month periodic component was also found in the middle-latitude regions. The intensity of the zonal electric field is positively correlated with the F10.7 index near the equatorial region (|θ| < 20 degrees, θ: magnetic latitude) with no time lag while it is negatively correlated in the middle-latitude region (|θ| > 20 degrees). The latitudinal difference of the correlation coefficient between the F10.7 index and the zonal electric field intensity is seen over the entire range of geographic longitude analyzed in this study. As a cause of the negative correlation in the middle latitudes, it can be thought that the neutral wind originating from solar tidal waves in the lower thermosphere becomes weaker during a high solar activity due to the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003JGRB..108.2228G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003JGRB..108.2228G"><span>Eight thousand years of <span class="hlt">geomagnetic</span> field intensity <span class="hlt">variations</span> in the eastern Mediterranean</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Genevey, AgnèS.; Gallet, Yves; Margueron, Jean-Claude</p> <p>2003-05-01</p> <p>Twenty new intensity determinations of the ancient <span class="hlt">geomagnetic</span> field have been obtained from groups of potsherds and brick fragments from Syria. These artifacts, archeologically well dated from ˜6000 B.C. to approximately A.D. 1200, have been analyzed using the [1959] method as modified by [1967]. Intensity values have been corrected for the effects of anisotropy of thermal remanent magnetization and cooling rate. Our results indicate that field intensities were moderate in Syria from ˜6000 B.C. to ˜3500 B.C., with values of ˜30-40 μT. There was a significant increase in intensity by a factor of 2 from ˜3500 B.C. to ˜700 B.C., which was interrupted by a moderate decrease between ˜2550 B.C. and ˜1750 B.C. During more recent periods, our results show an intensity minimum approximately A.D. 200 and a maximum around the tenth century. Comparison with different data sets from the eastern Mediterranean and central Asia shows that <span class="hlt">geomagnetic</span> field intensity <span class="hlt">variations</span> were consistent at this large regional scale, at least over the last 5 millennia.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014cosp...40E2179M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014cosp...40E2179M"><span>On cosmic rays flux <span class="hlt">variations</span> in midlatitudes and their relations to <span class="hlt">geomagnetic</span> and atmospheric conditions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Morozova, Anna; Blanco, Juan Jose; Mendes Ribeiro, Paulo Fernando</p> <p></p> <p>The cosmic rays flux is globally modulated by the solar cycle and shows anti-correlation with the sunspot number. Near to the Earth it is modulated by the solar wind and the Earth's magnetic field. The analysis of the secondary cosmic rays produced when they interact in the low stratosphere allows extracting information about solar wind structures surrounding Earth's orbit, the magnetic field of the Earth and the temperature of the stratosphere. Recently, a new cosmic ray detector, the TRAGALDABAS, composed by RPC (Resistive Plate Chamber) planes, has been developed and installed to go deeper into the understanding of the cosmic rays arriving to the Earth surface. An international collaboration has been organized for keeping the detector operative and for analyzing the data. Here we present the analysis of the cosmic rays flux <span class="hlt">variations</span> measured by two cosmic rays detectors of different types located in Spain (Castilla-La Mancha Neutron Monitor - CaLMa - in Guadalajara and TRAGALDABAS in Santiago de Compostela) and their comparison to changes both in the <span class="hlt">geomagnetic</span> field components measured by the Coimbra <span class="hlt">Geomagnetic</span> Observatory (Portugal) and in the atmospheric conditions (tropo- and stratosphere) measured by Spanish and Portuguese meteorological stations. The study is focused on a number of recent cosmic rays events and pays specific attention to the comparison of the CaLMa series and the preliminary TRAGALDABAS data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19900033678&hterms=geomagnetic+storm&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dgeomagnetic%2Bstorm','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19900033678&hterms=geomagnetic+storm&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dgeomagnetic%2Bstorm"><span>On the mechanisms responsible for high-latitude thermospheric composition <span class="hlt">variations</span> during the recovery phase of a <span class="hlt">geomagnetic</span> storm</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Burns, A. G.; Killeen, T. L.; Crowley, G.; Emery, B. A.; Roble, R. G.</p> <p>1989-01-01</p> <p>The causal mechanisms for the recovery of the perturbed high-latitude thermospheric composition to the unperturbed state in the period following a <span class="hlt">geomagnetic</span> storm are investigated. Model runs of the NCAR thermosphere/ionosphere GCM (TIGCM) and thermosphere GCM are used to calculate the averaged mass mixing ratio <span class="hlt">variations</span> and the forcing terms responsible for these <span class="hlt">variations</span> during the recovery phase of a <span class="hlt">geomagnetic</span> storm. High latitude compositional recovery is found to occur in the NCAR TIGCM on a time scale of about 12 hr to 1 day. This time scale is in agreement with previously observed time scales for typical poststorm F region electron density recoveries. Neither molecular diffusion nor large-scale horizontal advection is the dominant process in determining the compositional state during the recovery period. Thermospheric compositional recovery at high <span class="hlt">geomagnetic</span> latitudes is driven primarily by vertical advection.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011EP%26S...63..469C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011EP%26S...63..469C"><span>Monitoring the ionospheric total electron content <span class="hlt">variations</span> over the Korean Peninsula using a GPS network during <span class="hlt">geomagnetic</span> storms</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Choi, Byung-Kyu; Lee, Sang-Jeong; Park, Jong-Uk</p> <p>2011-06-01</p> <p>We have established a regional ionospheric model (RIM) for investigating changes in the total electron content (TEC) over South Korea using 38 Korean GPS reference stations. The inverse distance weighted (IDW) interpolation method was applied to create a two-dimensional ionospheric map of vertical TEC units (TECU) based on a grid. To examine the diurnal patterns of ionospheric TEC over South Korea, we first processed the GPS data from a <span class="hlt">geomagnetically</span> quiet period of 10 days. In a second step, we compared the estimated GPS-TEC <span class="hlt">variations</span> with the changes in <span class="hlt">geomagnetic</span> activity indices (the K p and D st indices) and the auroral electrojet index (AE) as a function of universal time (UT) on 4 and 20 November, 2003. The GPS-TEC responses for those storm events were proportional to the <span class="hlt">geomagnetic</span> activity at this mid-latitude location. The sudden increases in ionospheric TEC (SITEC) caused by the <span class="hlt">geomagnetic</span> storms were detected. The <span class="hlt">variations</span> in GPS-TEC may help reveal the processes of ionospheric disturbances caused by <span class="hlt">geomagnetic</span> storms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.8343M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.8343M"><span>Improving <span class="hlt">geomagnetic</span> observatory data in the South Atlantic Anomaly</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Matzka, Jürgen; Morschhauser, Achim; Brando Soares, Gabriel; Pinheiro, Katia</p> <p>2016-04-01</p> <p>The Swarm mission clearly proofs the benefit of coordinated <span class="hlt">geomagnetic</span> measurements from a well-tailored constellation in order to recover as good as possible the contributions of the various <span class="hlt">geomagnetic</span> field sources. A similar truth applies to <span class="hlt">geomagnetic</span> observatories. Their scientific value can be maximised by properly arranging the position of individual observatories with respect to the geometry of the external current systems in the ionosphere and magnetosphere, with respect to regions of particular interest for <span class="hlt">secular</span> <span class="hlt">variation</span>, and with respect to regions of anomalous electric conductivity in the ground. Here, we report on our plans and recent efforts to upgrade <span class="hlt">geomagnetic</span> observatories and to recover unpublished data from <span class="hlt">geomagnetic</span> observatories at low latitudes in the South Atlantic Anomaly. In particular, we target the magnetic equator with the equatorial electrojet and low latitudes to characterise the Sq- and ring current. The observatory network that we present allows also to study the longitudinal structure of these external current systems. The South Atlantic Anomaly region is very interesting due to its <span class="hlt">secular</span> <span class="hlt">variation</span>. We will show newly recovered data and comparisons with existing data sets. On the technical side, we introduce low-power data loggers. In addition, we use mobile phone data transfer, which is rapidly evolving in the region and allows timely data access and quality control at remote sites that previously were not connected to the internet.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFMSM23B1717Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFMSM23B1717Y"><span>Physical Meaning of the Equinoctial Effect for Seasonal <span class="hlt">Variation</span> of <span class="hlt">Geomagnetic</span> Activity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yoshida, A.</p> <p>2008-12-01</p> <p>The general tendency for magnetic disturbances to be more stormy at equinoxes than at solstices has been recognised for more than 150 years. To explain the seasonal <span class="hlt">variation</span> three principal hypotheses have been proposed; the axial hypothesis (Cortie, 1912), the equinoctial hypothesis (Bartels, 1932; McIntosh, 1959), and the Russell and McPherron (RM) hypothesis (Russell and McPherron, 1973). The RM hypothesis, which is based on the recognition that the magnetic field in the solar equatorial plane tends to have the largest southward component in geocentric solar magnetospheric (GSM) coordinates in early April and October, has been largely accepted for many years. However, recent studies have confirmed that the RM effect accounts for only a subordinate proportion of the seasonal <span class="hlt">variation</span> of <span class="hlt">geomagnetic</span> activity, and that the larger part of the phenomenon is attributable to the equinoctial effect in which the angle between the solar wind flow and the dipole axis of the Earth plays an essential role (Cliver, Kamide and Ling, 2000; Cliver, Kamide, Ling and Yokoyama, 2001; O'Brien and McPherron, 2002). In this paper physical meaning of the equinoctial effect is investigated based on the data of three-hourly am index and solar wind parameters acquired by the ACE satellite. The am indices are well correlated with BsVxVx, where Bs is the southward component of the interplanetary magnetic field (IMF) and Vx is the solar wind velocity in the sun-earth direction. It is found, however, that the am - BsVxVx relation depends on the range of VxVx: The am in higher ranges of VxVx tends to be larger than am in lower ranges of VxVx for both equinoctial and solstitial epochs for the same value of BsVxVx. Using the data sets of the same VxVx range, it is shown that distribution of points in the am - BsVxVx diagram at the solstitial epochs overlaps with that at the equinoctial epochs and the average am values in each BsVxVx bin in solstitial epochs are almost equal to those in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003E%26PSL.213..321L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003E%26PSL.213..321L"><span>Paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> at Vulcano (Aeolian Islands) during the last 135 kyr</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lanza, Roberto; Zanella, Elena</p> <p>2003-08-01</p> <p>Paleosecular <span class="hlt">variation</span> (PSV) of the Earth’s magnetic field during the last 135 kyr has been investigated in lavas, scoriae and pyroclastic rocks of Vulcano (Aeolian Islands). About 1000 samples have been collected at 77 sites from 25 distinct volcanic units, whose age is either known from published isotopical data or constrained on the grounds of statigraphical relationships. Magnetic mineralogy investigation shows that Ti-magnetite is the main ferromagnetic mineral. At most sites, secondary magnetization components are either absent or easily removed by stepwise thermal or alternating field demagnetization. The mean site direction of the characteristic remanent magnetization is usually well-defined, since the semi-angle of confidence is greater than 5° at only four sites. The mean paleomagnetic direction over the last 135 kyr (D=9.4°, I=53.2°, α95=3.5°) differs from the geocentric axial dipole (GAD) at Vulcano (D=0°, I=57.8°) and might be interpreted as the effect of a long-term, non-axial-dipolar component. The PSV record from Vulcano agrees well with those from the lacustrine sediments of Lago Grande di Monticchio (100 kyr BP) and Lago di Mezzano (30 kyr BP), located in the Italian peninsula [Brandt et al., Quat. Sci. Rev. 18 (1999) 961-976]. The inclination anomaly ΔI found at Vulcano corresponds to about half of the shallowing observed in the sediments of the two lakes and the declination anomaly ΔD may be used to tie the declination values, derived from azimuthally unoriented cores, to the geographical reference system. In order to find the optimum site to be used as reference for PSV studies in Italy, the angular values of the Earth’s magnetic field measured at the 113 repeat stations of the Italian <span class="hlt">Geomagnetic</span> Network [Coticchia et al., Boll. Geod. Sci. Aff. 40 (2001) 277-291] have been analyzed with the relocation via pole method [Noel and Batt, Geophys. J. Int. 102 (1990) 753-756]. The Viterbo station (lat. 42°27‧N, long. 12°02</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5128336','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5128336"><span>Paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> as an intra-basinal and extra-basinal correlation tool for Pleistocene lake sediments</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Negrini, R.M.; Erbes, D.B. . Dept. of Physics and Geology); Roberts, A.P.; Verosub, K.L.</p> <p>1993-04-01</p> <p>High-resolution age control is a serious problem encountered by those studying middle to late Pleistocene lake sediments, especially saline lake deposits which commonly are low in organic content obviating the use of bulk sediment radiocarbon dating. Paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span>, the low amplitude <span class="hlt">variation</span> in the direction and intensity of the Earth's magnetic field, can be recorded accurately in lake sediments. In this case if offers a high-resolution correlation tool which can be used for intra- and extra-basinal correlations. In principal, this could extend geographically as far away as marine environments enabling on to tie non-marine stratigraphy into the well-dated chronology common to marine sediment records. Examples are given of correlations based on this technique. The examples, in turn, are based on ongoing paleomagnetic and lithostratigraphic studies in the sediments of Pleistocene Lakes Chewaucan, Lahontan and previously-published paleomagnetic records from Pleistocene Lake Russell and from two un-named Pleistocene lakes. Intrabasinal correlations in Lake Chewaucan support the contention that <span class="hlt">secular</span> <span class="hlt">variation</span> can be used to correlate outcrop exposures (three samples per horizon) on a depth scale of several centimeters which probably corresponds to a temporal resolution of a few hundred years or less.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFMSM51C2105L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFMSM51C2105L"><span>On the decadal to multi-decadal evolution and correlations of <span class="hlt">geomagnetic</span> indices in relation to <span class="hlt">variations</span> in solar activity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Le Mouel, J.; Blanter, E.; Shnirman, M.; Courtillot, V.</p> <p>2011-12-01</p> <p>Magnetic indices measure magnetic activity occurring over periods of time from minutes to hours, as recorded at <span class="hlt">geomagnetic</span> observatories. They address in principle specific features of <span class="hlt">geomagnetic</span> activity, with an origin in Earth's ionosphere or magnetosphere. In the present study, we use daily indices, which can be arranged in two classes: roughly speaking, some reflect properties of magnetic field disturbances integrated over one day (1st family or A-type), whereas others reflect the maximal values of these disturbances (ranges) for that day (2nd family or B type). We analyze correlations between the evolutions of classical (daily) indices aa, Ap (B-type) and Dst and recently introduced absolute 3-day slopes ζ (A-type) at decadal time scales. Pairs of indices (aa and Ap on one hand, Dst and ζ on the other hand) display decade-long periods of high correlation interrupted by shorter periods of reduced correlation and even anti-correlation. Decadal <span class="hlt">variations</span> of mutual correlation between A and B-type indices are governed by solar cycle evolution. Loss of correlation between <span class="hlt">geomagnetic</span> indices coincides with loss of correlation between <span class="hlt">geomagnetic</span> indices and solar activity. In the past half-century, such sharp losses have occurred in the declining phases and minima of solar cycles 20 and 23. Differences between these two solar cycles in terms of correlation properties of <span class="hlt">geomagnetic</span> indices will be briefly discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010SSRv..155..247F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010SSRv..155..247F"><span>An Introduction to Data Assimilation and Predictability in <span class="hlt">Geomagnetism</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fournier, Alexandre; Hulot, Gauthier; Jault, Dominique; Kuang, Weijia; Tangborn, Andrew; Gillet, Nicolas; Canet, Elisabeth; Aubert, Julien; Lhuillier, Florian</p> <p>2010-08-01</p> <p>Data assimilation in <span class="hlt">geomagnetism</span> designates the set of inverse methods for <span class="hlt">geomagnetic</span> data analysis which rely on an underlying prognostic numerical model of core dynamics. Within that framework, the time-dependency of the magnetohydrodynamic state of the core need no longer be parameterized: The model trajectory (and the <span class="hlt">secular</span> <span class="hlt">variation</span> it generates at the surface of the Earth) is controlled by the initial condition, and possibly some other static control parameters. The primary goal of <span class="hlt">geomagnetic</span> data assimilation is then to combine in an optimal fashion the information contained in the database of <span class="hlt">geomagnetic</span> observations and in the dynamical model, by adjusting the model trajectory in order to provide an adequate fit to the data. The recent developments in that emerging field of research are motivated mostly by the increase in data quality and quantity during the last decade, owing to the ongoing era of magnetic observation of the Earth from space, and by the concurrent progress in the numerical description of core dynamics. In this article we review briefly the current status of our knowledge of core dynamics, and elaborate on the reasons which motivate <span class="hlt">geomagnetic</span> data assimilation studies, most notably (a) the prospect to propagate the current quality of data backward in time to construct dynamically consistent historical core field and flow models, (b) the possibility to improve the forecast of the <span class="hlt">secular</span> <span class="hlt">variation</span>, and (c) on a more fundamental level, the will to identify unambiguously the physical mechanisms governing the <span class="hlt">secular</span> <span class="hlt">variation</span>. We then present the fundamentals of data assimilation (in its sequential and <span class="hlt">variational</span> forms) and summarize the observations at hand for data assimilation practice. We present next two approaches to <span class="hlt">geomagnetic</span> data assimilation: The first relies on a three-dimensional model of the geodynamo, and the second on a quasi-geostrophic approximation. We also provide an estimate of the limit of the predictability of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFMGC41A0690M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFMGC41A0690M"><span>GRACE Hydrologic Mass Balance <span class="hlt">Secular</span> Trends and <span class="hlt">Variations</span> on Arctic Permafrost Watersheds</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Muskett, R. R.</p> <p>2008-12-01</p> <p>Permafrost is largest component of the Arctic cryosphere by area extent. Over the last century, substantial changes in storage and cycling of fresh water have been observed. Observations of the globally distributed hydrologic mass balance (water equivalent thickness change relative to the geoid) from the Gravity Recovery and Climate Experiment mission offer to provide a greater understanding of the processes controlling redistribution of water mass (groundwater storage, discharge, snow water equivalent storage, vegetation water storage, and ice sheet mass balance) under ongoing effects of climate warming. Using newly processed monthly GRACE grids, Level-3 Release 4, de-striped, adjusted for post-glacial rebound I investigate the hydrologic mass balance of the Arctic watershed regions. Regionally-averaged monthly time series show strong seasonal periodicity, with maxima occurring in April/May and minima in September/October. Eurasian watersheds have significant positive <span class="hlt">secular</span> trends. The Ob-Irtysh watershed shows a water equivalent gain of 22.7 ± 13.5 km3/yr, and the Lena watershed shows a water equivalent gain of 44.7 ± 0.8 km3/yr from August 2002 through March 2008. The Mackenzie watershed shows a water equivalent volume change of -5.6 ± 7.2 km3/yr in the same time period. The permafrost area extent in the watersheds investigated shows the Ob-Irtysh draining the least continuous permafrost extent and the Lena draining the most. The Mackenzie watershed drains a mixture of continuous and discontinuous permafrost area extents. Regionally-average snow water equivalent time series show seasonal periodicity whose maxima and minima occur one month ahead of the GRACE time series. <span class="hlt">Secular</span> trends of snow water equivalent show neither significant gain nor loss over the time period. This removes snow water equivalent (a component of surface water storage) as being the source of the GRACE <span class="hlt">secular</span> trends. A subsurface source of water mass exchange of the GRACE <span class="hlt">secular</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1982RSPTA.306..161V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1982RSPTA.306..161V"><span><span class="hlt">Geomagnetic</span> Excursions: A Critical Assessment of the Evidence as Recorded in Sediments of the Brunhes Epoch</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Verosub, K. L.</p> <p>1982-08-01</p> <p><span class="hlt">Geomagnetic</span> excursions have tantalized geophysicists since the earliest suggestion of their occurrence over 15 years ago. Either as large-scale <span class="hlt">geomagnetic</span> <span class="hlt">secular</span> <span class="hlt">variation</span>, <span class="hlt">geomagnetic</span> reversals of short duration or aborted reversals, they held great promise of providing new insights into the nature of the origin of the <span class="hlt">geomagnetic</span> field. Unfortunately the evidence for <span class="hlt">geomagnetic</span> excursions from the palaeomagnetic record of Brunhes age sediments is not as compelling as the theoretical arguments. A critical assessment of the available data indicates that the Gothenburg excursion is unlikely to have occurred and the Erieau excursion is very unlikely. The Mono Lake excursion probably occurred, but its absence in nearby contemporaneous sites creates profound problems. The Blake Event appears to be an actual short reversal of complex character, but confirmation of its global nature may be quite difficult.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JGRA..119.2160L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JGRA..119.2160L"><span>Altitude <span class="hlt">variations</span> in the thermosphere mass density response to <span class="hlt">geomagnetic</span> activity during the recent solar minimum</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, X.; Thayer, J. P.; Burns, A.; Wang, W.; Sutton, E.</p> <p>2014-03-01</p> <p>Accelerometer data from coplanar orbits of Challenging Minisatellite Payload (CHAMP) and Gravity Recovery and Climate Experiment (GRACE) satellites were used to study the complex altitude and latitude <span class="hlt">variations</span> of the thermosphere mass density response to <span class="hlt">geomagnetic</span> activity during 1-10 December 2008 near 09 LT. Helium number densities near 500 km altitude were extracted from the CHAMP and GRACE measurements and clearly show the presence of a winter hemisphere helium bulge. This recent extreme solar minimum indicates that wintertime helium concentrations exceed NRLMSISE-00 model estimates by 30%-70% during quiet <span class="hlt">geomagnetic</span> activity after adjusting F10.7 input into MSIS. The perturbation in mass density from quiet to active conditions is found to be less enhanced in the winter hemisphere at the higher GRACE altitudes (25%) than at the lower CHAMP altitudes (60%) and is attributed to dynamic behavior in the helium/oxygen transition. The investigation revealed the maximum storm time density perturbation to occur near the He/O transition region with a much weaker maximum near the O/N2 transition region. The altitude of maximum density perturbation occurs where the perturbation in the weighted pressure scale height is equal and opposite to the perturbation in the weighted mean molecular weight scale height. The altitude structure of density scale height perturbation is significantly influenced by the changes in the molecular weight scale height and can account for 50% of the change in mass density scale height in a region correspondingly close to the He/O transition during the 2008 solar minimum period.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_14 --> <div id="page_15" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="281"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.6823C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.6823C"><span>Chinese Mobile <span class="hlt">Geomagnetic</span> Monitoring Array</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, Bin; Ni, Zhe; Chen, Shuanggui; Yuan, Jiehao</p> <p>2017-04-01</p> <p>From 2010, we have set up Chinese Mobile <span class="hlt">Geomagnetic</span> Monitoring Array (CMGMA) gradually for seismic monitoring and forecasting. Today, the array includes 973 <span class="hlt">geomagnetic</span> repeat survey stations, the mean intervals between adjacent 2 stations is about 70km in east of China and 150km in west, covers 7'680'000km2 monitoring eara. We measure total intensity (F), declination (D) and indensity (I) on each station one time every year, and then remove dural <span class="hlt">variation</span> using minutely averages data on the nearest observatory and remove main field using "Chinese <span class="hlt">Geomagnetic</span> Reference Field (CGRF) -Spherical Cap Harmonic model". After removing <span class="hlt">secular</span> <span class="hlt">variation</span> using a natural orthogonal component (NOC) model base hourly averages data from 1995 to now on 31 observatories in China, we calculate the <span class="hlt">variations</span> of lithosphere magnetic field between each adjacent two years.After analyse the <span class="hlt">variations</span> of lithoshpere magnetic field before all 25 earthquakes with magnitude bigger than 5 in our monitoring eara, 2 kinds of anomarlies were found during 1-18 months before 20 earthquakes of 25 samples. The first kind was typical called "Quiet Island", and the variant kind called "frozen area" or "quiet byland". The main character of these 2 kind anomalies is the <span class="hlt">variations</span> of lithosphere magnetic field are smaller near the epicenter than surronding. When we draw the horizontal varistions (ΔBy, ΔBx) as an arrow at level, the <span class="hlt">variations</span> are identical, scale and direction, in a wide range, as a liquid river flowing from one side to the other.However, the <span class="hlt">variations</span> near the further epicenter show their difference, with low value and different dirction. Even we have picked these anomlies out before the earthquakes in each July, just soon after our field survey. We are not clear why these nomlies are there, and can not further propose a perfect idea about magnitude and original times.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeoJI.202..533K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeoJI.202..533K"><span>Crustal structure of Precambrian terranes in the southern African subcontinent with implications for <span class="hlt">secular</span> <span class="hlt">variation</span> in crustal genesis</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kachingwe, Marsella; Nyblade, Andrew; Julià, Jordi</p> <p>2015-07-01</p> <p>New estimates of crustal thickness, Poisson's ratio and crustal shear wave velocity have been obtained for 39 stations in Angola, Botswana, the Democratic Republic of Congo, Malawi, Mozambique, Namibia, Rwanda, Tanzania and Zambia by modelling P-wave receiver functions using the H-κ stacking method and jointly inverting the receiver functions with Rayleigh-wave phase and group velocities. These estimates, combined with similar results from previous studies, have been examined for <span class="hlt">secular</span> trends in Precambrian crustal structure within the southern African subcontinent. In both Archean and Proterozoic terranes we find similar Moho depths [38-39 ± 3 km SD (standard deviation)], crustal Poisson's ratio (0.26 ± 0.01 SD), mean crustal shear wave velocity (3.7 ± 0.1 km s-1 SD), and amounts of heterogeneity in the thickness of the mafic lower crust, as defined by shear wave velocities ≥4.0 km s-1. In addition, the amount of variability in these crustal parameters is similar within each individual age grouping as between age groupings. Thus, the results provide little evidence for <span class="hlt">secular</span> <span class="hlt">variation</span> in Precambrian crustal structure, including between Meso- and Neoarchean crust. This finding suggests that (1) continental crustal has been generated by similar processes since the Mesoarchean or (2) plate tectonic processes have reworked and modified the crust through time, erasing <span class="hlt">variations</span> in structure resulting from crustal genesis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22282767','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22282767"><span>An independent constraint on the <span class="hlt">secular</span> rate of <span class="hlt">variation</span> of the gravitational constant from pulsating white dwarfs</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Córsico, Alejandro H.; Althaus, Leandro G.</p> <p>2013-06-01</p> <p>A <span class="hlt">secular</span> <span class="hlt">variation</span> of the gravitational constant modifies the structure and evolutionary time scales of white dwarfs. Using an state-of-the-art stellar evolutionary code and an up-to-date pulsational code we compute the effects of a <span class="hlt">secularly</span> varying G on the pulsational properties of variable white dwarfs. Comparing the the theoretical results obtained taking into account the effects of a running G with the observed periods and measured rates of change of the periods of two well studied pulsating white dwarfs, G117-B15A and R548, we place constraints on the rate of <span class="hlt">variation</span> of Newton's constant. We derive an upper bound Ġ/G ∼ −1.8 × 10{sup −10} yr{sup −1} using the variable white dwarf G117-B15A, and Ġ/G ∼ −1.3 × 10{sup −10} yr{sup −1} using R548. Although these upper limits are currently less restrictive than those obtained using other techniques, they can be improved in a future measuring the rate of change of the period of massive white dwarfs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006GRA.....8.2699C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006GRA.....8.2699C"><span>Observational investigation of ionospheric turbulent spectral content in relation to <span class="hlt">geomagnetic</span> field <span class="hlt">variations</span> and local seismicity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Contadakis, M. E.; Arambelos, D.; Asteriadis, G.; Pikridas, Ch.; Spatalas, S.; Chatzinikos, M.</p> <p>2006-04-01</p> <p>Atmospheric and underground explosions as well as shallow earthquakes producing strong vertical ground displacement, are known to produce pressure waves that propagates at infrasonic speeds in the atmosphere. At ionospheric altitudes these waves are coupled to ionospheric gravity waves and induce <span class="hlt">variations</span> in the ionospheric electron density. On the other hand local lithospheric density, ion inhalation, temperature or electromagnetic field <span class="hlt">variations</span>, produced by the local tectonic activity during the earthquake preparation period, induces near surface atmospheric <span class="hlt">variations</span> and affect the ionospheric density through the Lithospher-Atmosphere- Ionosphere Coupling. That is the lithospheric near surface tectonic activity results to local pre- co- and post seismic disturbances on the ionospheric Total Electron Content (TEC). Nevertheless these disturbances are mixed with disturbances induced to the ionospher by a number of agents such as tropospheric jets, magnetic storms and sub-storms, solar activity, ionosphere-magnetosphere coupling etc, and a major problem is to discriminate the influence of those agents from the influence of the local tectonic activity. In this paper we present the results of the wavelet analysis of TVEC <span class="hlt">variations</span> over a network of 4 GPS stations, depicted from EUREF-EPN network, covering the whole area of Greece. Our results indicate that 1) Disturbances with period higher than 3 hours have a Universal origin i.e. earth-tides, Aurora or Equatorial anomaly. 2) Disturbances with periods equal or smaller than 3 hours are of local origin. 3) Strong <span class="hlt">Variations</span> of <span class="hlt">geomagnetic</span> field affect the disturbances of all periods. 4) Disturbances with period 3 hours present a good coherency in the measurements of more than one GPS stations. In concluding disturbances with period equal or less than 3 hours are suitable for de</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Ge%26Ae..57..266K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Ge%26Ae..57..266K"><span>Effects of <span class="hlt">geomagnetic</span> disturbances in daytime <span class="hlt">variations</span> of the atmospheric electric field in polar regions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kleimenova, N. G.; Kubicki, M.; Odzimek, A.; Malysheva, L. M.; Gromova, L. I.</p> <p>2017-05-01</p> <p>We have studied the influence of daytime polar substorms (<span class="hlt">geomagnetic</span> bays under the IMF Bz > 0) on <span class="hlt">variations</span> of the vertical gradient of the atmospheric electric field potential ( Ez) observed at the Polish Hornsund Station (Svalbard, Norway). Only the observations of Ez under "fair weather" conditions were used, i.e. in the absence of strong wind, precipitations, low cloud cover, etc. We studied more than 20 events of daytime polar substorms registered by the Scandinavian chain of IMAGE magnetometers in 2010-2014 during the "fair weather" periods at the Hornsund Station. Analysis of the observations showed that Ez significantly deviates from the its background <span class="hlt">variations</span> during daytime, as a rule, when the Hornsund Station is in the region of projection of the daytime auroral oval, the position of which was determined from OVATION data. It was shown that the development of a daytime polar substorm leads to fluctuating enhance of Ez values. It was found that Ez surges are accompanied by intensification of field-aligned electric currents outflowing from the ionosphere, which were calculated from the data of low-orbit communication satellites of the AMPERE project.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EP%26S...68...23K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EP%26S...68...23K"><span>Morphology of the southern African <span class="hlt">geomagnetic</span> field derived from observatory and repeat station survey observations: 2005-2014</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kotzé, P. B.; Korte, M.</p> <p>2016-02-01</p> <p><span class="hlt">Geomagnetic</span> field data from four observatories and annual field surveys between 2005 and 2015 provide a detailed description of Earth's magnetic field changes over South Africa, Namibia and Botswana on time scales of less than 1 year. The southern African area is characterized by rapid changes in the <span class="hlt">secular</span> <span class="hlt">variation</span> pattern and lies in close proximity to the South Atlantic Anomaly (SAA) where the <span class="hlt">geomagnetic</span> field intensity is almost 30 % weaker than in other regions at similar latitudes around the globe. Several <span class="hlt">geomagnetic</span> <span class="hlt">secular</span> acceleration (SA) pulses (<span class="hlt">geomagnetic</span> jerks) around 2007, 2010 and 2012 could be identified over the last decade in southern Africa. We present a new regional field model for declination and horizontal and vertical intensity over southern Africa (Southern African REGional (SAREG)) which is based on field survey and observatory data and covering the time interval from 2005 to 2014, i.e. including the period between 2010 and 2013 when no low Earth-orbiting vector field satellite data are available. A comparative evaluation between SAREG and global field models like CHAOS-5, the CHAMP, Orsted and SAC-C model of the Earth's magnetic field and International <span class="hlt">Geomagnetic</span> Reference Field (IGRF-12) reveals that a simple regional field model based on a relatively dense ground network is able to provide a realistic representation of the <span class="hlt">geomagnetic</span> field in this area. We particularly note that a global field model like CHAOS-5 does not always indicate similar short-period patterns in the field components as revealed by observatory data, while representing the general <span class="hlt">secular</span> <span class="hlt">variation</span> reasonably well during the time interval without near-Earth satellite vector field data. This investigation further shows the inhomogeneous occurrence and distribution of <span class="hlt">secular</span> <span class="hlt">variation</span> impulses in the different <span class="hlt">geomagnetic</span> field components and at different locations in southern African.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeoJI.209.1660N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoJI.209.1660N"><span><span class="hlt">Secular</span> <span class="hlt">variations</span> in zonal harmonics of Earth's geopotential and their implications for mantle viscosity and Antarctic melting history due to the last deglaciation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nakada, Masao; Okuno, Jun'ichi</p> <p>2017-06-01</p> <p><span class="hlt">Secular</span> <span class="hlt">variations</span> in zonal harmonics of Earth's geopotential based on the satellite laser ranging observations, {\\dot{J}_n}, contain important information about the Earth's deformation due to the glacial isostatic adjustment (GIA) and recent melting of glaciers and the Greenland and Antarctic ice sheets. Here, we examine the GIA-induced {\\dot{J}_n}, \\dot{J}_n^{GIA} (2 ≤ n ≤ 6), derived from the available geopotential zonal <span class="hlt">secular</span> rate and recent melting taken from the IPCC 2013 Report (AR5) to explore the possibility of additional information on the depth-dependent lower-mantle viscosity and GIA ice model inferred from the analyses of the \\dot{J}_2^{GIA} and relative sea level changes. The sensitivities of the \\dot{J}_n^{GIA} to lower-mantle viscosity and GIA ice model with a global averaged eustatic sea level (ESL) of ∼130 m indicate that the <span class="hlt">secular</span> rates for n = 3 and 4 are mainly caused by the viscous response of the lower mantle to the melting of the Antarctic ice sheet regardless of GIA ice models adopted in this study. Also, the analyses of the \\dot{J}_n^{GIA} based on the available geopotential zonal <span class="hlt">secular</span> rates indicate that permissible lower-mantle viscosity structure satisfying even zonal <span class="hlt">secular</span> rates of n = 2, 4 and 6 is obtained for the GIA ice model with an Antarctic ESL component of ∼20 or ∼30 m, but there is no viscosity solution satisfying \\dot{J}_3^{GIA} and \\dot{J}_5^{GIA} values. Moreover, the inference model for the lower-mantle viscosity and GIA ice model from each odd zonal <span class="hlt">secular</span> rate is distinctly different from that satisfying GIA-induced even zonal <span class="hlt">secular</span> rate. The discrepancy between the inference models for the even and odd zonal <span class="hlt">secular</span> rates may partly be attributed to uncertainties of the geopotential zonal <span class="hlt">secular</span> rates for n > 2 and particularly those for odd zonal <span class="hlt">secular</span> rates due to weakness in the orbital geometry. If this problem is overcome at least for the <span class="hlt">secular</span> rates of n < 5, then the analyses of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014cosp...40E.801E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014cosp...40E.801E"><span>Studies of ionospheric <span class="hlt">variations</span> during <span class="hlt">geomagnetic</span> activities at the low-latitude station, Ile-Ife, Nigeria</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Emmanuel, Ariyibi</p> <p></p> <p>The dual frequency SCINDA NovAtel GSV 4004B GPS receiver installed at the Ile-Ife (low-latitude station) has been in operation since December 2009. Data records for the year 2010 were processed to obtain Total Electron Content (TEC) and S 4 index. These were interpreted to analyze the ionospheric condition during low <span class="hlt">geomagnetic</span> activity period (when Dst is from -40 to 0 nT) and during <span class="hlt">geomagnetic</span> storm events (with Dst about -100 nT). Seasonal <span class="hlt">variations</span> of the TEC and S 4 index were also investigated. The occurrence of scintillations is closely linked to the peak value of TEC during the daytime; this is very evident during the equinox months when TEC ≥ 30 TECu. When the maximum TEC value is below 30 TECu, as shown by most of the days in the summer months, the scintillation phenomenon does not occur. During <span class="hlt">geomagnetic</span> storms, the daytime segment of the TEC plot experiences fluctuations (even bifurcations) in values with the peak TEC value of about 40 TECu. From the interpreted data, the occurrence of <span class="hlt">geomagnetic</span> storm does not necessarily suggest an increase in the level of scintillations at a low-latitude region. Also, there is a remarkable difference between the IRI 2007 model and the observed TEC values, as the daytime TEC peak differs in magnitude and time of occurrence from the observed TEC.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AcGeo..61..223A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AcGeo..61..223A"><span>Studies of ionospheric <span class="hlt">variations</span> during <span class="hlt">geomagnetic</span> activities at the low-latitude station, Ile-Ife, Nigeria</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ariyibi, Emmanuel; Joshua, Emanuel; Rabiu, Babatunde</p> <p>2013-02-01</p> <p>The dual frequency SCINDA NovAtel GSV 4004B GPS receiver installed at the Ile-Ife (low-latitude station) has been in operation since December 2009. Data records for the year 2010 were processed to obtain Total Electron Content (TEC) and S 4 index. These were interpreted to analyze the ionospheric condition during low <span class="hlt">geomagnetic</span> activity period (when Dst is from -40 to 0 nT) and during <span class="hlt">geomagnetic</span> storm events (with Dst about -100 nT). Seasonal <span class="hlt">variations</span> of the TEC and S 4 index were also investigated. The occurrence of scintillations is closely linked to the peak value of TEC during the daytime; this is very evident during the equinox months when TEC ≥ 30 TECu. When the maximum TEC value is below 30 TECu, as shown by most of the days in the summer months, the scintillation phenomenon does not occur. During <span class="hlt">geomagnetic</span> storms, the daytime segment of the TEC plot experiences fluctuations (even bifurcations) in values with the peak TEC value of about 40 TECu. From the interpreted data, the occurrence of <span class="hlt">geomagnetic</span> storm does not necessarily suggest an increase in the level of scintillations at a low-latitude region. Also, there is a remarkable difference between the IRI 2007 model and the observed TEC values, as the daytime TEC peak differs in magnitude and time of occurrence from the observed TEC.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19830007484','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19830007484"><span><span class="hlt">Geomagnetic</span> modeling by optimal recursive filtering</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Gibbs, B. P.; Estes, R. H.</p> <p>1981-01-01</p> <p>The results of a preliminary study to determine the feasibility of using Kalman filter techniques for <span class="hlt">geomagnetic</span> field modeling are given. Specifically, five separate field models were computed using observatory annual means, satellite, survey and airborne data for the years 1950 to 1976. Each of the individual field models used approximately five years of data. These five models were combined using a recursive information filter (a Kalman filter written in terms of information matrices rather than covariance matrices.) The resulting estimate of the <span class="hlt">geomagnetic</span> field and its <span class="hlt">secular</span> <span class="hlt">variation</span> was propogated four years past the data to the time of the MAGSAT data. The accuracy with which this field model matched the MAGSAT data was evaluated by comparisons with predictions from other pre-MAGSAT field models. The field estimate obtained by recursive estimation was found to be superior to all other models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMSM33C2518C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMSM33C2518C"><span>Solar Cycle and <span class="hlt">Geomagnetic</span> Activity <span class="hlt">Variation</span> of Topside Ionospheric Upflow as Measured by DMSP</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Coley, W. R.; Hairston, M. R.</p> <p>2016-12-01</p> <p>Under the proper conditions a considerable amount of plasma can escape the Earth's ionosphere into the magnetosphere. Indeed, there are indications that at least part of the time the ionosphere may be the dominant source of ions for the plasma sheet and near-Earth portion of the magnetosphere. The upward flux of thermal O+ from the lower part of the topside ionosphere actively provides plasma into intermediate altitudes where they may be given escape energy by various mechanisms. Previous work has indicated that there is considerable time <span class="hlt">variation</span> of upwelling low energy ionospheric plasma to these intermediate altitudes during moderate to high solar activity. Here we use the SSIES thermal plasma instruments on board the Defense Meteorological Satellite Program (DMSP) F13-F19 series of spacecraft to examine the vertical flux of thermal O+ from the deep solar minimum of 2008-2009 to the moderately active period of 2012-2015. Separately integrating the upward and downward fluxes over the high-latitude region (auroral zone and polar cap) allows the observation of the total upflow/downflow as a function of the current <span class="hlt">geomagnetic</span> conditions, solar cycle, and solar wind conditions. In particular we investigate the incidence of high upward flux events as a function of solar wind velocity and density during the deepest solar minimum since the space age began.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011PEPI..188..214R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011PEPI..188..214R"><span>A coupled low order dynamo/turbulent shell model for <span class="hlt">geomagnetic</span> field <span class="hlt">variations</span> and reversals</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ryan, David A.; Sarson, Graeme R.</p> <p>2011-10-01</p> <p>We couple a low order αω dynamo model to a shell model of turbulence, with the dynamo α-effect being identified with the helicity of the shell model. Fluctuations ('noise') in this term lead to lognormal-like statistics in the magnetic field, as was noted for inter-reversal duration by Ryan and Sarson (2007). Here we extend the analysis to shorter time-scale field <span class="hlt">variations</span> (viz. Virtual Axial Dipole Moments, VADMs), and find that a lognormal distribution is also a significant fit for this quantity, both for the output from our model and for the observed paleomagnetic data. This shared lognormality - which Ryan and Sarson (2007) argued arose from a common source in terms of 'multiplicative noise' in the underlying dynamo mechanism - makes the synthetic and observed data comparable; we also note some similarities in the patterns of VADM fluctuations (including asymmetric decay and recovery, epitomised in an extreme form by the controversial 'saw-tooth' pattern) and in reversal inter-event times (chrons) of widely varying duration. We describe the dynamics behind our coupled model, and discuss the effect of certain model parameters on the synthetic chron durations, including the occurrence of superchrons. Implications for the observed <span class="hlt">geomagnetic</span> field behaviour are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMGP23A1296S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMGP23A1296S"><span><span class="hlt">Secular</span> <span class="hlt">variation</span> between 5 and 10c CE in Japan: remeasurements of 2000 samples collected between 1960-70's from Sueki earthenware kilns in Osaka.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shibuya, H.; Mochizuki, N.; Hatakeyama, T.</p> <p>2015-12-01</p> <p>In Japan, archeomagnetic measurements are vigorously developed for years, though it is not well known to paleomagnetism community in english. One of the works is massive archeomagnetic study of Suemura kiln group carried out in Osaka University in 1960's to early 70's. More than 500 kilns were excavated in Sakai city and vicinities, Osaka Prefecture, Japan. The kiln group is called as Suemura Kilns, and are for Sueki earthenware of 5c to 10c CE. About 300 kilns were sampled and most of the samples were measured at the time, and the results are reported in e.g. Hirooka (1971) and Shibuya (1980). However, the results have significant scatter in direction, which may be due to the limitation of old astatic magnetometer measurements and handwriting graphic determination of magnetic direction, and/or the lack of demagnetization. We recently inherited many of those samples and remeasured them with spinner magnetometer applying alternation field demagnetization (afd). The magnetizations are generally very stable, as usual as other archeomagnetic samples, and afd does not change the magnetic direction mostly. However, significant number of sites show large scatter in magnetic directions, which might be due to the wrong identification of kiln floor or disturbance at the time of collapsing or excavation. Taking kilns of α95<4o, we recovered 131 paleomagnetic directions. Although third of them are dated by pottery shape chronology, the range of each pottery style is not precisely known and the relation of the baked floor and the potteries excavated around kilns are not always clear. The carbon dating of those kilns are very scares. Thus we first try to draw <span class="hlt">secular</span> <span class="hlt">variation</span> curve in declination-inclination plot. With the rough ages of those kilns, it is pretty easy to draw the SVC. It is also numerically determined taking the distance of each direction from nearest point in SVC and the velocity change of the SVC as penalty function, within a couple of degrees in the error</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23532042','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23532042"><span>Arabidopsis thaliana root elongation growth is sensitive to lunisolar tidal acceleration and may also be weakly correlated with <span class="hlt">geomagnetic</span> <span class="hlt">variations</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Barlow, Peter W; Fisahn, Joachim; Yazdanbakhsh, Nima; Moraes, Thiago A; Khabarova, Olga V; Gallep, Cristiano M</p> <p>2013-05-01</p> <p>Correlative evidence suggests a relationship between the lunisolar tidal acceleration and the elongation rate of arabidopsis roots grown under free-running conditions of constant low light. Seedlings of Arabidopsis thaliana were grown in a controlled-climate chamber maintained at a constant temperature and subjected to continuous low-level illumination from fluorescent tubes, conditions that approximate to a 'free-running' state in which most of the abiotic factors that entrain root growth rates are excluded. Elongation of evenly spaced, vertical primary roots was recorded continuously over periods of up to 14 d using high temporal- and spatial-resolution video imaging and were analysed in conjunction with geophysical variables. The results confirm the lunisolar tidal/root elongation relationship. Also presented are relationships between the hourly elongation rates and the contemporaneous <span class="hlt">variations</span> in <span class="hlt">geomagnetic</span> activity, as evaluated from the disturbance storm time and ap indices. On the basis of time series of root elongation rates that extend over ≥4 d and recorded at different seasons of the year, a provisional conclusion is that root elongation responds to <span class="hlt">variation</span> in the lunisolar force and also appears to adjust in accordance with <span class="hlt">variations</span> in the <span class="hlt">geomagnetic</span> field. Thus, both lunisolar tidal acceleration and the <span class="hlt">geomagnetic</span> field should be considered as modulators of root growth rate, alongside other, stronger and more well-known abiotic environmental regulators, and perhaps unexplored factors such as air ions. Major changes in atmospheric pressure are not considered to be a factor contributing to oscillations of root elongation rate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014E%26PSL.392..217C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014E%26PSL.392..217C"><span><span class="hlt">Geomagnetic</span> intensity <span class="hlt">variations</span> for the past 8 kyr: New archaeointensity results from Eastern China</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cai, Shuhui; Tauxe, Lisa; Deng, Chenglong; Pan, Yongxin; Jin, Guiyun; Zheng, Jianming; Xie, Fei; Qin, Huafeng; Zhu, Rixiang</p> <p>2014-04-01</p> <p>In this study, we have carried out paleointensity experiments on 918 specimens spanning the last ∼7 kyr, including pottery fragments, baked clay and slag, collected from Shandong, Liaoning, Zhejiang and Hebei Provinces in China. Approximately half of the specimens yielded results that passed strict data selection criteria and give high-fidelity paleointensities. The virtual axial dipole moments (VADMs) of our sites range from ∼2×1022 to ∼13×1022 Am. At ∼2250 BCE our results suggest a paleointensity low of ∼2×1022 Am, which increases to a high of ∼13×1022 Am by ∼1300 BCE. This rapid (less than 1000 yrs) six-fold change in the paleointensity may have important implications for the dynamics of core flow at this time. Our data from the last ∼3 kyr are generally in good agreement with the ARCH3k.1 model, but deviate significantly at certain time periods from the CALS3k.4 and CALS10k.1b model, which is likely due to differences in the data used to constrain these models. At ages older than ∼3 ka, where only the CALS10k.1b model is available for comparison, our data deviate significantly from the model. Combining our new results with the published data from China and Japan, we provide greatly improved constraints for the regional model of Eastern Asia. When comparing the <span class="hlt">variations</span> of <span class="hlt">geomagnetic</span> field in three global representative areas of Eastern Asia, the Middle East and Southern Europe, a common general trend of sinusoidal <span class="hlt">variations</span> since ∼8 ka is shown, likely dominated by the dipole component. However, significant disparities are revealed as well, which we attribute to non-dipolar components caused by movement of magnetic flux patches at the core-mantle boundary.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015E%26PSL.430..178K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015E%26PSL.430..178K"><span>Holocene <span class="hlt">geomagnetic</span> field intensity <span class="hlt">variations</span>: Contribution from the low latitude Canary Islands site</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kissel, C.; Laj, C.; Rodriguez-Gonzalez, A.; Perez-Torrado, F.; Carracedo, J. C.; Wandres, C.</p> <p>2015-11-01</p> <p>New absolute paleomagnetic intensity (PI) are investigated from 37 lava flows located at Tenerife and Gran Canaria (Canary Islands). They complete previously published directional results from the same flows and therefore allow to examine the time <span class="hlt">variations</span> of the full <span class="hlt">geomagnetic</span> vector. Twenty-eight flows are radiocarbon dated between 1706 AD and about 13 200 BC and one is historical. Eight other flows are not dated but they have stratigraphic links with the dated flows and archeomagnetic ages had been attributed to them based on their paleomagnetic directions. Various mineralogical analyses were conducted, giving access to the nature of the magnetic minerals and to their grain size. We performed the original Thellier and Thellier paleointensity (PI) experiments with a success rate of about 65% coupling this experiment with the strict set of selection criteria PICRIT-03. The mean PIs at the flow level are based on 3 to 12 independent PI determinations except for one site in which only one reliable determination could be obtained. The data indicate some variability in the local field intensity with a prominent PI peak centered around 600 BC and reaching 80 μT (VADM 16 ×1022 Am2), documented for the first time in this region. Combined with the published data obtained from western Africa, Spain, Portugal, Morocco and the Azores within a 2000 km-radius around the Canary Islands, our data allow to construct a curve illustrating the Earth magnetic field intensity fluctuations for Southwestern Europe/Western Africa. This curve, compared to the one produced for the Middle East and one calculated for Central Asia shows that maximum intensity patches have a very large geographical extent. They do not yet appear clearly in the models of <span class="hlt">variations</span> of the dipolar field intensity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001AGUFMGP51A0286D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001AGUFMGP51A0286D"><span><span class="hlt">Geomagnetic</span> Paleointensity <span class="hlt">Variations</span> as a Cheap, High-Resolution Geochronometer for Recent Mid-Ocean Ridge Processes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>DYMENT, J.; HEMOND, C.</p> <p>2001-12-01</p> <p>The sequence of <span class="hlt">geomagnetic</span> field reversals is widely used to date events younger than 160 Ma, with a resolution of a million years. In oceanic domains, Vine and Matthews (1963) magnetic anomalies have been successfully used for more than 35 years. The major limitation of this chronometer is its low temporal resolution, especially for the recent times: the youngest polarity reversal, between Brunhes normal and Matuyama reversed periods, is dated ~800 ka. Studies of pelagic sedimentary cores have shown the existence of consistent <span class="hlt">variations</span> of the <span class="hlt">geomagnetic</span> field intensity within this period. If accurately dated, these <span class="hlt">variations</span> may refine the magnetic geochronometer to a much higher resolution of 10-100 ka. Recent studies have demonstrated that the "tiny wiggles" of lower amplitude and shorter wavelength superimposed to the Vine and Matthews anomalies are of <span class="hlt">geomagnetic</span> origin and correspond to the paleointensity <span class="hlt">variations</span> identified on sediment cores. Using a large set of magnetic data acquired in 1996 on the Mid-Atlantic Ridge at 21° N (surface and submersible magnetic anomalies, natural remanent magnetization and absolute paleointensities measured on samples), we have shown that the oceanic crust confidently records the <span class="hlt">geomagnetic</span> intensity <span class="hlt">variations</span>. It was unfortunately impossible to date the samples, made of basalt too depleted in K2O and in trace elements required by the various methods of radiochronology. In 2000 we have collected a similar data set at the Central Indian Ridge axis at 19° S (surface, deep-tow, and submersible magnetic anomalies, natural remanent magnetization and absolute paleointensities measured on samples). This area offers the advantages of 1) a faster spreading rate, and therefore a higher temporal resolution of the <span class="hlt">geomagnetic</span> signal, and 2) the presence of moderately enriched basalt as a consequence of the interaction of the ridge with the nearby Reunion hotspot, making possible radiochronologic dating. Our first evaluation</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..1414276D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..1414276D"><span>The <span class="hlt">variations</span> of <span class="hlt">geomagnetic</span> field in the region of the Sulaksky cascade of hydro-electric power station</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Daniyalov, M. G.; Suleymanov, A. I.</p> <p>2012-04-01</p> <p>Technogenic intervention in nature while creation of large water basins disturbs developed dynamic balance in rock mass and activates seismic processes, i.e. causes the so-called exited earthquakes which are connected with water basin operation. Local changes of a magnetic field of the Earth can be the result of various physical processes, but the most probable - electromagnetic and piezomagnetic processes. In our case the rock piezomagnetism is considered to be the principal cause of local <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> - change of their magnetization under the influence of mechanical pressure. The measurements were made 2 times a day at the same time to reveal the connection of <span class="hlt">geomagnetic</span> field components <span class="hlt">variations</span> with water basin level fluctuations. According to <span class="hlt">geomagnetic</span> measurements of 1983-1989 it is determined, that relative changes of a vertical component δΖ much more exceed respective alterations of the module of a full vector δT that is indirect acknowledgement of magnetoelastic effect under natural conditions. We determined that in the period of intensive rising of water level and weight the sharp reduction of a vertical component in water basin is observed which depends not only on loading value, but also on filling speed. At stable level of a water basin slight increase of δΖ is observed which is explained by internal pressure relaxation process in the water basin basis. The empirical formula for calculation of changes of a vertical component of a field ΔΖ under the influence of loading during the water basin filling is observed. The numerical value of coefficient k,, calculated by the least square method as the interconnection coefficient between vertical component changes and changes of level of the Chirkeysky water basin according to measurements of 1983-1989 is: 5, 66 10-4 nano-tesla / Pa. Ju. Skovorodkin obtained the numerical value of k coefficient: 6, 3 10-6 nano-tesla / Pa during the <span class="hlt">variations</span> measurements of full vector module of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014Ge%26Ae..54..666S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014Ge%26Ae..54..666S"><span><span class="hlt">Geomagnetic</span> field <span class="hlt">variations</span> induced by internal and surface waves in the four-layer model of the marine environment</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smagin, V. P.; Semkin, S. V.; Savchenko, V. N.</p> <p>2014-09-01</p> <p>The layered model of the marine environment, including the atmosphere, two seawater layers with different conductivity and density, and the bottom rock layer, has been considered. The <span class="hlt">geomagnetic</span> field <span class="hlt">variations</span>, generated by internal and surface waves with different frequency and propagation direction, have been found in the scope of this model. The effect of magnetic permeability and electric conductivity of bottom rocks on induced magnetic field has been taken into account. The transfer functions and spectral densities of these <span class="hlt">variations</span> have been analytically determined and numerically estimated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1814994G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1814994G"><span>Local <span class="hlt">geomagnetic</span> indices and their role in space weather</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Guerrero, Antonio; Cid, Consuelo; Saiz, Elena; Palacios, Judith; Cerrato, Yolanda</p> <p>2016-04-01</p> <p>The analysis of local <span class="hlt">geomagnetic</span> disturbances (specific longitude and latitude) have recently proved to play an important role in space weather research. Localized strong (high intensity) and impulsive (fast developed and fast recovered) <span class="hlt">geomagnetic</span> disturbances are typically recorded at high latitudes and commonly related to field-aligned currents. These type of disturbances are also recorded, less frequently, at mid and low latitudes, representing an important hazard for technology. In order to obtain <span class="hlt">geomagnetic</span> disturbances (<span class="hlt">geomagnetic</span> index) from the records at a certain observatory, a baseline has to be removed. The baseline is usually determined taking into account <span class="hlt">geomagnetic</span> <span class="hlt">secular</span> <span class="hlt">variation</span> and solar quiet time. At mid-latitudes the shape of the daily solar quiet component presents a strong day-to-day variability difficult to predict. In this work we present a new technique capable to determine the baseline at mid-latitudes which allows us to obtain a high resolution local <span class="hlt">geomagnetic</span> index with the highest accuracy ever obtained at mid-latitudes.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017SpWea..15..606H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017SpWea..15..606H"><span><span class="hlt">Variation</span> and modeling of ultraviolet auroral oval boundaries associated with interplanetary and <span class="hlt">geomagnetic</span> parameters</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hu, Ze-Jun; Yang, Qiu-Ju; Liang, Ji-Min; Hu, Hong-Qiao; Zhang, Bei-Chen; Yang, Hui-Gen</p> <p>2017-04-01</p> <p>A large data set of auroral poleward/equatorward boundary, which are automatically identified from more than 60,000 images acquired by Polar ultraviolet imager, is used to study the <span class="hlt">variation</span> of auroral boundaries associated with the interplanetary/<span class="hlt">geomagnetic</span> environments and dynamic parameters of the magnetosphere. A total number of 3,805,000/1,215,000 points for poleward/equatorward boundary were identified from the data set. It is found that the poleward/equatorward boundaries show an equatorward movement with the increase of Kan-Lee electric field. The poleward/equatorward boundaries in the nightside sector (1800-0600 magnetic local time (MLT)) show an equatorward motion with the increase of the value of IMF By and the north-south electric field. The equatorward boundary (1800-0300 MLT) shows a quasi-linear equatorward displacement with the increase of solar wind dynamic pressure and speed. The poleward boundary (excluding midday sector) and equatorward boundary expand equatorward with the increase of AE index. The auroral oval boundary model with input parameters of the three components of IMF, solar wind speed and density, and AE is developed by using multivariate regression method. Evaluation of the model shows that the mean absolute deviation of the model in every MLT sector is 1.3-2.1° magnetic latitude (MLAT) for the poleward boundary and 1.3-2.5° MLAT for the equatorward boundary, respectively, when input parameters are within valid value coverage (three components of IMF are each from -8 to +8 nT, and the values of solar wind speed and density, and AE are not more than 550 km/s, 20/cm-3, and 520 nT, respectively).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.T13A1135G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.T13A1135G"><span>Mapping <span class="hlt">Geomagnetic</span> Field <span class="hlt">Variations</span> in the Cretaceous Quiet Zone with Unmanned Airborne Vehicles</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gee, J. S.; Cande, S. C.; Kent, D. V.</p> <p>2007-12-01</p> <p>About one quarter of the present seafloor was generated during the constant normal polarity interval from 121 to 83 Ma (Cretaceous Quiet Zone or KQZ), and the lack of temporal markers limits tectonic reconstructions in these areas. Although magnetostratigraphic studies provide strong evidence that the KQZ formed during predominantly normal polarity, there are nonetheless relatively large amplitude <span class="hlt">variations</span> in many sea surface magnetic anomaly profiles crossing KQZ crust. To evaluate the relative importance of <span class="hlt">geomagnetic</span> and crustal variables (thickness, geochemistry) in generating these anomalies, we collected multibeam bathymetry and magnetic data on 19 profiles crossing anomaly 34 and extending 500 km into the KQZ in the southwest Pacific. The relatively fast spreading (60 km/m.y. half rate), minimal sediment cover and high paleolatitude of formation make this area ideal for evaluating the magnetic anomaly pattern. An additional 10,000 km of magnetic anomaly data were acquired using an autonomous unmanned airborne vehicle (UAV). Although land-launched UAVs have been used in a variety of research applications, the nine successful flights during our cruise represent the first deployment from a UNOLS research vessel. The UAV (operated by Fugro Airborne) was launched from a pneumatic catapult and captured by a wingtip clip that attaches to a rope suspended from a retractable boom on the fantail. The Cs-vapor magnetometer data from the UAV compare favorably with results from the surface-towed magnetometer, with minor differences related primarily to the higher elevation (120m above sea level) of the UAV. The resulting magnetic coverage indicates that, as with younger seafloor, quasi-linear short wavelength anomalies are present within the KQZ. These anomalies can vary on spatial scales smaller than the multibeam swath width, highlighting the utility of obtaining additional coverage with the UAVs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JAsGe...6..131F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JAsGe...6..131F"><span>Investigation of <span class="hlt">geomagnetic</span> induced current at high latitude during the storm-time <span class="hlt">variation</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Falayi, E. O.; Ogunmodimu, O.; Bolaji, O. S.; Ayanda, J. D.; Ojoniyi, O. S.</p> <p>2017-06-01</p> <p>During the <span class="hlt">geomagnetic</span> disturbances, the <span class="hlt">geomagnetically</span> induced current (GIC) are influenced by the geoelectric field flowing in conductive Earth. In this paper, we studied the variability of GICs, the time derivatives of the <span class="hlt">geomagnetic</span> field (dB/dt), <span class="hlt">geomagnetic</span> indices: Symmetric disturbance field in H (SYM-H) index, AU (eastward electrojet) and AL (westward electrojet) indices, Interplanetary parameters such as solar wind speed (v), and interplanetary magnetic field (Bz) during the <span class="hlt">geomagnetic</span> storms on 31 March 2001, 21 October 2001, 6 November 2001, 29 October 2003, 31 October 2003 and 9 November 2004 with high solar wind speed due to a coronal mass ejection. Wavelet spectrum based approach was employed to analyze the GIC time series in a sequence of time scales of one to twenty four hours. It was observed that there are more concentration of power between the 14-24 h on 31 March 2001, 17-24 h on 21 October 2001, 1-7 h on 6 November 2001, two peaks were observed between 5-8 h and 21-24 h on 29 October 2003, 1-3 h on 31 October 2003 and 18-22 h on 9 November 2004. Bootstrap method was used to obtain regression correlations between the time derivative of the <span class="hlt">geomagnetic</span> field (dB/dt) and the observed values of the <span class="hlt">geomagnetic</span> induced current on 31 March 2001, 21 October 2001, 6 November 2001, 29 October 2003, 31 October 2003 and 9 November 2004 which shows a distributed cluster of correlation coefficients at around r = -0.567, -0.717, -0.477, -0.419, -0.210 and r = -0.488 respectively. We observed that high energy wavelet coefficient correlated well with bootstrap correlation, while low energy wavelet coefficient gives low bootstrap correlation. It was noticed that the <span class="hlt">geomagnetic</span> storm has a influence on GIC and <span class="hlt">geomagnetic</span> field derivatives (dB/dt). This might be ascribed to the coronal mass ejection with solar wind due to particle acceleration processes in the solar atmosphere.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.2617C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.2617C"><span><span class="hlt">Variations</span> of terrestrial <span class="hlt">geomagnetic</span> activity correlated to M6+ global seismic activity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cataldi, Gabriele; Cataldi, Daniele; Straser, Valentino</p> <p>2013-04-01</p> <p>From the surface of the Sun, as a result of a solar flare, are expelled a coronal mass (CME or Coronal Mass Ejection) that can be observed from the Earth through a coronagraph in white light. This ejected material can be compared to an electrically charged cloud (plasma) mainly composed of electrons, protons and other small quantities of heavier elements such as helium, oxygen and iron that run radially from the Sun along the lines of the solar magnetic field and pushing into interplanetary space. Sometimes the CME able to reach the Earth causing major disruptions of its magnetosphere: mashed in the region illuminated by the Sun and expanding in the region not illuminated. This interaction creates extensive disruption of the Earth's <span class="hlt">geomagnetic</span> field that can be detected by a radio receiver tuned to the ELF band (Extreme Low Frequency 0-30 Hz). The Radio Emissions Project (scientific research project founded in February 2009 by Gabriele Cataldi and Daniele Cataldi), analyzing the change in the Earth's <span class="hlt">geomagnetic</span> field through an induction magnetometer tuned between 0.001 and 5 Hz (bandwidth in which possible to observe the <span class="hlt">geomagnetic</span> pulsations) was able to detect the existence of a close relationship between this <span class="hlt">geomagnetic</span> perturbations and the global seismic activity M6+. During the arrival of the CME on Earth, in the Earth's <span class="hlt">geomagnetic</span> field are generated sudden and intensive emissions that have a bandwidth including between 0 and 15 Hz, an average duration of 2-8 hours, that preceding of 0-12 hours M6+ earthquakes. Between 1 January 2012 and 31 December 2012, all M6+ earthquakes recorded on a global scale were preceded by this type of signals which, due to their characteristics, have been called "Seismic <span class="hlt">Geomagnetic</span> Precursors" (S.G.P.). The main feature of Seismic <span class="hlt">Geomagnetic</span> Precursors is represented by the close relationship that they have with the solar activity. In fact, because the S.G.P. are <span class="hlt">geomagnetic</span> emissions, their temporal modulation depends</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20090011775','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20090011775"><span>Predicting the Size of Sunspot Cycle 24 on the Basis of Single- and Bi-<span class="hlt">Variate</span> <span class="hlt">Geomagnetic</span> Precursor Methods</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wilson, Robert M.; Hathaway, David H.</p> <p>2009-01-01</p> <p>Examined are single- and bi-<span class="hlt">variate</span> <span class="hlt">geomagnetic</span> precursors for predicting the maximum amplitude (RM) of a sunspot cycle several years in advance. The best single-<span class="hlt">variate</span> fit is one based on the average of the ap index 36 mo prior to cycle minimum occurrence (E(Rm)), having a coefficient of correlation (r) equal to 0.97 and a standard error of estimate (se) equal to 9.3. Presuming cycle 24 not to be a statistical outlier and its minimum in March 2008, the fit suggests cycle 24 s RM to be about 69 +/- 20 (the 90% prediction interval). The weighted mean prediction of 11 statistically important single-<span class="hlt">variate</span> fits is 116 +/- 34. The best bi-<span class="hlt">variate</span> fit is one based on the maximum and minimum values of the 12-mma of the ap index; i.e., APM# and APm*, where # means the value post-E(RM) for the preceding cycle and * means the value in the vicinity of cycle minimum, having r = 0.98 and se = 8.2. It predicts cycle 24 s RM to be about 92 +/- 27. The weighted mean prediction of 22 statistically important bi-<span class="hlt">variate</span> fits is 112 32. Thus, cycle 24's RM is expected to lie somewhere within the range of about 82 to 144. Also examined are the late-cycle 23 behaviors of <span class="hlt">geomagnetic</span> indices and solar wind velocity in comparison to the mean behaviors of cycles 2023 and the <span class="hlt">geomagnetic</span> indices of cycle 14 (RM = 64.2), the weakest sunspot cycle of the modern era.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EOSTr..90..208M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EOSTr..90..208M"><span><span class="hlt">Geomagnetic</span> and Archeomagnetic Jerks: Where Do We Stand?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mandea, Mioara; Olsen, Nils</p> <p>2009-06-01</p> <p>The Earth's magnetic field is generated mainly by a self-sustaining dynamo in the fluid outer core. Known as the core or main field, the dynamo's magnetic field is not constant but changes with time, a phenomenon denoted as <span class="hlt">secular</span> <span class="hlt">variation</span>. Unfortunately, no common agreement exists about the definition of <span class="hlt">secular</span> <span class="hlt">variation</span>: While some use this term for the temporal changes of the core field in general, others use the term only for its linear part (first time derivative). Two more terms are linked to core field temporal <span class="hlt">variations</span>: <span class="hlt">geomagnetic</span> jerks and archeomagnetic jerks. They are used to describe specific magnetic field signatures in the observations, implying a phenomenological classification. We suggest that a characterization of magnetic field changes based on the physics of the underlying core process may be more useful. Such a classification is proposed here to help avoid further misunderstanding through terminology.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ESASP.740E.274B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ESASP.740E.274B"><span><span class="hlt">Geomagnetic</span> Jerks in the Swarm Era</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brown, William; Beggan, Ciaran; Macmillan, Susan</p> <p>2016-08-01</p> <p>The timely provision of <span class="hlt">geomagnetic</span> observations as part of the European Space Agency (ESA) Swarm mission means up-to-date analysis and modelling of the Earth's magnetic field can be conducted rapidly in a manner not possible before. Observations from each of the three Swarm constellation satellites are available within 4 days and a database of close-to-definitive ground observatory measurements is updated every 3 months. This makes it possible to study very recent <span class="hlt">variations</span> of the core magnetic field. Here we investigate rapid, unpredictable internal field <span class="hlt">variations</span> known as <span class="hlt">geomagnetic</span> jerks. Given that jerks represent (currently) unpredictable changes in the core field and have been identified to have happened in 2014 since Swarm was launched, we ask what impact this might have on the future accuracy of the International <span class="hlt">Geomagnetic</span> Reference Field (IGRF). We assess the performance of each of the IGRF-12 <span class="hlt">secular</span> <span class="hlt">variation</span> model candidates in light of recent jerks, given that four of the nine candidates are novel physics-based predictive models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AdSpR..37.1251D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AdSpR..37.1251D"><span>Relationship between human physiological parameters and <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> of solar origin</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dimitrova, S.</p> <p></p> <p>Results presented concern influence of increased <span class="hlt">geomagnetic</span> activity on some human physiological parameters. The blood pressure and heart rate of 86 volunteers were measured on working days in autumn 2001 (01/10 09/11) and in spring 2002 (08/04 28/05). These periods were chosen because of maximal expected <span class="hlt">geomagnetic</span> activity. Altogether 2799 recordings were obtained and analysed. Questionnaire information about subjective psycho-physiological complaints was also gathered. MANOVA was employed to check the significance of the influence of three factors on the physiological parameters under consideration. The factors were the following: (1) planetary <span class="hlt">geomagnetic</span> activity level estimated by Ap-index and divided into five levels; (2) gender males and females; (3) blood pressure degree persons in the group examined were divided into hypotensive, normotensive and hypertensive. Post hoc analysis was performed to elicit the significance of differences in the factors’ levels. The average arterial blood pressure of the group was found to increase significantly with the increase of <span class="hlt">geomagnetic</span> activity level. The average increment of systolic and diastolic blood pressure of the group examined reached 9%. This effect was present irrespectively of gender. Results obtained suppose that hypertensive persons have the highest sensitivity and the hypotensive persons have the lowest sensitivity of the arterial blood pressure to increase of <span class="hlt">geomagnetic</span> activity. The results did not show significant changes in the heart rate. The percentage of the persons who reported subjective psycho-physiological complaints was also found to increase significantly with the <span class="hlt">geomagnetic</span> activity increase and the highest sensitivity was revealed for the hypertensive females.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014cosp...40E1898L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014cosp...40E1898L"><span>Long-term observations of the solar wind speed from the high latitude <span class="hlt">geomagnetic</span> observatories</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lukianova, Renata; Kozlovsky, Alexander</p> <p></p> <p>Solar wind speed is an important driver of the magnetospheric dynamics. The solar wind high speed streams (HSSs) affects the ionosphere and even the neutral atmosphere. Analysis of the <span class="hlt">geomagnetic</span> <span class="hlt">secular</span> <span class="hlt">variation</span> at polar and auroral latitudes reveals a signal of the HSS as a significant deflection of the observatory annual means in the corresponding <span class="hlt">secular</span> <span class="hlt">variation</span>. A major reduction of the horizontal <span class="hlt">geomagnetic</span> component at auroral latitudes and to a notable strengthening of the vertical component in both polar caps indicates an extreme intensity in the westward substorm auroral electrojet (WEJ) current detected in the strongest HSS years during the declining phase of each solar cycle. The near polar cap boundary observatories in Antarctic show the largest effect. The longest available time series from Godhavn and Sodankyla observatories allows monitoring the WEJ intensity during the last 100 years and makes it possible to associate the WEJ intensity with the extreme HSS.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EP%26S...69...84K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EP%26S...69...84K"><span>Statistical evaluation of global <span class="hlt">geomagnetic</span> field models over Southern Africa during 2015</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kotzé, P. B.</p> <p>2017-06-01</p> <p>Global <span class="hlt">geomagnetic</span> field models using spherical harmonic basis functions are important in space physics research, space weather and applications like navigation and mineral resources exploration. These models are based on various <span class="hlt">geomagnetic</span> field data sets ranging from Earth surface magnetic observatory measurements to low-Earth orbit satellites equipped with highly sensitive and accurate magnetometers. Although these field models are derived by fitting harmonic functions to data distributed across the Earth, they are applied on regional scales within fixed boundaries in many instances and one can therefore question how well do these models perform on restricted areas. Three recently published global <span class="hlt">geomagnetic</span> field models, IGRF-12, CHAOS-6 and POMME-10, have been statistically evaluated over Southern Africa using repeat station data as well as measurements from 4 INTERMAGNET observatories located at Hermanus and Hartebeesthoek in South Africa as well as Tsumeb and Keetmanshoop in Namibia for 2015. Apart from the observatory data, the field survey repeat station data do not form part of the data set on which these global field models are based and therefore can be regarded as an independent test of these field models over an area like Southern Africa which is well known for its rapid change of the <span class="hlt">geomagnetic</span> field. Results obtained in this investigation for both main field and <span class="hlt">secular</span> <span class="hlt">variation</span> models clearly showed the importance of timely ground-based <span class="hlt">geomagnetic</span> field observations in the derivation of accurate field models, particularly in regions characterised by rapid and unpredictable <span class="hlt">secular</span> <span class="hlt">variation</span> changes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20060035442&hterms=comparison+total&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dcomparison%2Btotal','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20060035442&hterms=comparison+total&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dcomparison%2Btotal"><span><span class="hlt">Variations</span> of total electron content during <span class="hlt">geomagnetic</span> disturbances: A model/observation comparison</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Roble, G. Lu X. Pi A. D. Richmond R. G.</p> <p>1997-01-01</p> <p>This paper studies the ionospheric response to major <span class="hlt">geomagnetic</span> storm of October 18-19, 1995, using the thermosphere-ionosphere electrodynamic general circulation model (TIE-GCM) simulations and the global ionospheric maps (GIM) of total electron content (TEC) observations from the Global Positioning System (GPS) worldwide network.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005IJMPA..20.6699K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005IJMPA..20.6699K"><span>Global Cosmic Ray Intensity Changes, Solar Activity <span class="hlt">Variations</span> and <span class="hlt">Geomagnetic</span> Disturbances as North Atlantic Hurricane Precursors</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kavlakov, S. P.</p> <p></p> <p>It was shown that specific changes of the sunspots (SS) number, cosmic ray (CR) intensity and <span class="hlt">geomagnetic</span> activity indices AP and KP were statistically noticeable in the interval of 30 days before the appearance of a cyclonic rotational system over the North Atlantic, developing gradually in a major hurricane.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JGRA..122.4512G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JGRA..122.4512G"><span>On the <span class="hlt">variation</span> in the ionospheric response to <span class="hlt">geomagnetic</span> storms with time of onset</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Greer, K. R.; Immel, T.; Ridley, A.</p> <p>2017-04-01</p> <p>Recent observations from Immel and Mannucci (2013) have indicated that <span class="hlt">geomagnetic</span> storms cause larger enhancements in the ionospheric plasma density and total electron content (TEC) in the American sector than anywhere else on the planet. This suggests that the presence of a UT storm onset effect is important for correctly understanding the impact, longitudinal structure, and timing of <span class="hlt">geomagnetic</span> storms. Using the Global Ionosphere-Thermosphere Model (GITM), we conduct a modeling experiment of the August 2011 <span class="hlt">geomagnetic</span> storm by modifying the storm arrival time (UT) in Earth's daily rotation and examining the subsequent system response. We find that the simulations reflect the recent studies indicating that the strongest enhancements of TEC are in the American and Pacific longitude sectors of storms with onsets between 1600 UT and 2400 UT. The underlying mechanisms of the strong TEC increases during storm times in these longitude sectors are also examined. Some of the resulting TEC structures may be explained by changes in the [O]/[N2] ratio (especially in the high latitudes), but it is unable to explain all of the variability in the equatorial regions. Storm time neutral winds and vertical ion motions coupled to Earth's asymmetrical <span class="hlt">geomagnetic</span> topology appear to be driving the longitude sector variability due to UT storm onset times.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AdSpR..55..401K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AdSpR..55..401K"><span><span class="hlt">Variations</span> of solar, interplanetary, and <span class="hlt">geomagnetic</span> parameters with solar magnetic multipole fields during Solar Cycles 21-24</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kim, Bogyeong; Lee, Jeongwoo; Yi, Yu; Oh, Suyeon</p> <p>2015-01-01</p> <p>In this study we compare the temporal <span class="hlt">variations</span> of the solar, interplanetary, and <span class="hlt">geomagnetic</span> (SIG) parameters with that of open solar magnetic flux from 1976 to 2012 (from Solar Cycle 21 to the early phase of Cycle 24) for a purpose of identifying their possible relationships. By the open flux, we mean the average magnetic field over the source surface (2.5 solar radii) times the source area as defined by the potential field source surface (PFSS) model of the Wilcox Solar Observatory (WSO). In our result, most SIG parameters except the solar wind dynamic pressure show rather poor correlations with the open solar magnetic field. Good correlations are recovered when the contributions from individual multipole components are counted separately. As expected, solar activity indices such as sunspot number, total solar irradiance, 10.7 cm radio flux, and solar flare occurrence are highly correlated with the flux of magnetic quadrupole component. The dynamic pressure of solar wind is strongly correlated with the dipole flux, which is in anti-phase with Solar Cycle (SC). The <span class="hlt">geomagnetic</span> activity represented by the Ap index is correlated with higher order multipole components, which show relatively a slow time <span class="hlt">variation</span> with SC. We also found that the unusually low <span class="hlt">geomagnetic</span> activity during SC 23 is accompanied by the weak open solar fields compared with those in other SCs. It is argued that such dependences of the SIG parameters on the individual multipole components of the open solar magnetic flux may clarify why some SIG parameters vary in phase with SC and others show seemingly delayed responses to SC <span class="hlt">variation</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3631336','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3631336"><span>Arabidopsis thaliana root elongation growth is sensitive to lunisolar tidal acceleration and may also be weakly correlated with <span class="hlt">geomagnetic</span> <span class="hlt">variations</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Barlow, Peter W.; Fisahn, Joachim; Yazdanbakhsh, Nima; Moraes, Thiago A.; Khabarova, Olga V.; Gallep, Cristiano M.</p> <p>2013-01-01</p> <p>Background Correlative evidence suggests a relationship between the lunisolar tidal acceleration and the elongation rate of arabidopsis roots grown under free-running conditions of constant low light. Methods Seedlings of Arabidopsis thaliana were grown in a controlled-climate chamber maintained at a constant temperature and subjected to continuous low-level illumination from fluorescent tubes, conditions that approximate to a ‘free-running’ state in which most of the abiotic factors that entrain root growth rates are excluded. Elongation of evenly spaced, vertical primary roots was recorded continuously over periods of up to 14 d using high temporal- and spatial-resolution video imaging and were analysed in conjunction with geophysical variables. Key Results and Conclusions The results confirm the lunisolar tidal/root elongation relationship. Also presented are relationships between the hourly elongation rates and the contemporaneous <span class="hlt">variations</span> in <span class="hlt">geomagnetic</span> activity, as evaluated from the disturbance storm time and ap indices. On the basis of time series of root elongation rates that extend over ≥4 d and recorded at different seasons of the year, a provisional conclusion is that root elongation responds to <span class="hlt">variation</span> in the lunisolar force and also appears to adjust in accordance with <span class="hlt">variations</span> in the <span class="hlt">geomagnetic</span> field. Thus, both lunisolar tidal acceleration and the <span class="hlt">geomagnetic</span> field should be considered as modulators of root growth rate, alongside other, stronger and more well-known abiotic environmental regulators, and perhaps unexplored factors such as air ions. Major changes in atmospheric pressure are not considered to be a factor contributing to oscillations of root elongation rate. PMID:23532042</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EP%26S...69...17K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EP%26S...69...17K"><span>The 2014 <span class="hlt">geomagnetic</span> jerk as observed by southern African magnetic observatories</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kotzé, P. B.</p> <p>2017-01-01</p> <p>Rapid <span class="hlt">secular</span> <span class="hlt">variation</span> pulses in the Earth's <span class="hlt">geomagnetic</span> field have been identified during the last decade. In particular, the 2014 jerk is the latest in a series of localised rapid <span class="hlt">secular</span> <span class="hlt">variation</span> events observed at the Earth's surface which are thought to be the result of rapid oscillations at the core surface approximately at a depth of 3000 km. In Southern Africa, the 2014 jerk has been analysed using data from four observatories located at Hermanus, Hartebeesthoek, Keetmanshoop and Tsumeb and found that this event occurred with varying strengths in the different components at a particular observatory, while different observatories in the region showed strong individual characteristics. The changes in the <span class="hlt">secular</span> <span class="hlt">variation</span> patterns at individual magnetic observatories in this study took place in an area characterised by rapid changes in the <span class="hlt">geomagnetic</span> field with time. Of particular interest is that global field models like CHAOS-6 and POMME 10 derived from various combinations of ground and satellite data do not always indicate similar short-period patterns in X, Y and Z as revealed by observatory measurements. This has been confirmed by comparing the <span class="hlt">secular</span> <span class="hlt">variation</span> pattern at the Kourou magnetic observatory located in French Guiana, a station close to the current centre of the South Atlantic Anomaly.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70011876','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70011876"><span>International <span class="hlt">geomagnetic</span> reference field 1980: a report by IAGA Division I working group.</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Peddie, N.W.</p> <p>1982-01-01</p> <p>Describes the recommendations of the working group, which suggested additions to IGRF because of the cumulative effect of the inevitable uncertainties in the <span class="hlt">secular</span> <span class="hlt">variation</span> models which had led to unacceptable inaccuracies in the IGRF by the late 1970's. The recommendations were accepted by the International Association of <span class="hlt">Geomagnetism</span> and Aeronomy on August 15, 1981 at the 4th Scientific Assembly, Edinburgh. An extended table sets out spherical harmonic coefficients of the IGRF 1980.-R.House</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeoJI.207.1332C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeoJI.207.1332C"><span>New archaeomagnetic direction results from China and their constraints on palaeosecular <span class="hlt">variation</span> of the <span class="hlt">geomagnetic</span> field in Eastern Asia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cai, Shuhui; Tauxe, Lisa; Deng, Chenglong; Qin, Huafeng; Pan, Yongxin; Jin, Guiyun; Chen, Xuexiang; Chen, Wei; Xie, Fei; Zhu, Rixiang</p> <p>2016-11-01</p> <p>We carried out an archaeomagnetic directional study on 38 oriented samples (bricks and baked clays) collected from four archaeological locations at three provinces in China. The ages of our samples, spanning from ˜3000 BCE to ˜1300 CE, were constrained using a combination of archaeological context, radiocarbon dating and stratigraphic information. Rock magnetic results demonstrate that the main magnetic minerals of the studied samples are magnetite and/or hematite in single domain and superparamagnetic states. A total of 20 new reliable archaeodirectional data from 12 independent sites are obtained after thermal demagnetization experiments. These are the first set of archaeodirectional data in China produced since the 1990s. The published data are largely from the past 2 kyr and data from older time periods are rare. Our new data, especially those from period older than 3 ka, fill many gaps of the presently published dataset and will provide strong constraints on palaeosecular <span class="hlt">variation</span> of the <span class="hlt">geomagnetic</span> field in Eastern Asia and on the improvement of global models. Quite a few inflection points in the direction of the <span class="hlt">geomagnetic</span> field are recorded in Eastern Asia over the past 10 kyr and some of them synchronize with the maximums or minimums of the palaeointensity. The palaeosecular <span class="hlt">variation</span> rates are very low (based on present data distribution) before 2000 BCE and then start to increase and fluctuate afterward, which is generally consistent with the pattern of palaeointensity <span class="hlt">variations</span> in this area.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFMGP43A..05I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFMGP43A..05I"><span>Refining the Late Quaternary Paleomagnetic <span class="hlt">Secular</span> <span class="hlt">Variation</span> record in the Mediterranean Region as a Chronologic Tool for Marine Geology Investigations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Iorio, M.; Liddicoat, J. C.; Budillon, F.; Incoronato, A.; Coe, R.; Insinga, D.; Lubritto, C.; Cassata, W. S.; Tiano, P.; Petruccione, E.</p> <p>2011-12-01</p> <p>Together, piston cores C1067, C1201 and C1202 from the continental shelf and slope in the Salerno Gulf and Cilento offshore in the Eastern Tyrrhenian Sea record long-term change (Paleomagnetic <span class="hlt">Secular</span> <span class="hlt">Variation</span> - PSV) of Earth's magnetic field during the last approximately 115,000 years. Each core contains the last 24,000 years except for the interval from about 20,000 to 11,000 years that is absent in C1067 and C1202 because of erosion on the continental slope. The PSV for the Eastern Tyrrhenian Sea is correlated to curves of global relative paleomagnetic field intensity in other marine cores (Stoner et al., 2002) and dated lacustrine records of PSV for western Europe (Thouveny et al., 1990) and Great Britain (Turner and Thompson, 1981). Tephrochronolgy and radiometric dates (C14 and Ar/Ar) also are used for assigning an age to the record. Along with an improved record of PSV for the Mediterranean region, the PSV in the Salerno Gulf and Cilento offshore piston cores has application for placing time constraints on the marine geology and stratigraphy on the continental shelf and slope. The result is that catastrophic events such as large-scale submarine slumps, volcanic eruptions, turbidite deposition, and abrupt changes in sedimentation rate are dated. The changes in sedimentation rate seem to be linked to global rapid sea-level pulses and climate events that induced concurrent reduction and/or abundance in the sediment supply from the adjacent coastal margin.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002EGSGA..27..631M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002EGSGA..27..631M"><span>Changes In Atmosphere and Ionosphere Caused By Solar-<span class="hlt">geomagnetic</span> Activity, Within Belgrade Area</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mitic, M.; Djordjevic, A.; Mihajlovic, S. J.</p> <p></p> <p>Results of the different solar-climatic and terrestrial investigations show mutual con- nection between changes in the solar activity, <span class="hlt">geomagnetic</span> field and meteorological parameters, such as: temperature, humidity and air pressure. In order to determine the influence of solar-<span class="hlt">geomagnetic</span> activity on atmosphere and ionosphere within Bel- grade area, characteristic parameters were selected: - temperature T, as the atmosphere parameter; - critical frequency foF2 as the ionosphere parameter; - horisontal com- ponent H, as the <span class="hlt">geomagnetic</span> field parameter; - Ri, relative Sunspot number, as the parameter of solar activity. Investigation has been done for the period from 1958-1995, which has been taken as the time interval. This period belongs to the descendent branch of the 19-th, 20- th, 21-st and 22-nd solar cycle. Values of the ionosphere parameters were considered for the 21-st cycle (as that data was available to the author). During the observation, mentioned parameters were compared in different ways. Changes were observed as behavior of mid-monthly and mid-yearly values of parameters through specific time intervals, seasons, minimums and maximums of Sun activity. It has been established that the temperature and the horisontal component of <span class="hlt">geomagnetic</span> field have period of about 22-years and 11-years lasting period for relative Sunspots number Ri. Changes in values of ionosphere parameters were well correlated with changes of horizontal component for quiet days, values of temperature and the Sunspots number, as it was suspected. Further, <span class="hlt">secular</span> <span class="hlt">variations</span> were formed for more detailed investigations. The <span class="hlt">secular</span> <span class="hlt">variation</span> of values, for any parameter, is presented as a function of change of consec- utive yearly values in a particular time interval. By application of Fourier Transforma- tion, a spectral analysis of <span class="hlt">secular</span> <span class="hlt">variations</span> has been done. Changes were separated in duration of 6 and 9 months, 1, 2 and 3.5 years. In order to make a "view" on <span class="hlt">secular</span></p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19930060109&hterms=severino&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dseverino','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19930060109&hterms=severino&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dseverino"><span>Periodic <span class="hlt">variation</span> in the <span class="hlt">geomagnetic</span> activity - A study based on the Ap index</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>De Gonzalez, Alicia L. C.; Gonzalez, Walter D.; Dutra, Severino L. G.; Tsurutani, Bruce T.</p> <p>1993-01-01</p> <p>The monthly and daily samples of the Ap index for the interval from 1932 through 1982 were studied using the power spectrum technique. Results obtained for Bartel's period (about 27 days), the semiannual period, the dual-peak solar cycle distribution of <span class="hlt">geomagnetic</span> storms, and certain other medium-scale periodicities are examined in detail. In addition, results on the cumulative occurrence number of storms per decade as a function of the Ap and Dst indices for the storm are presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016cosp...41E1813S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016cosp...41E1813S"><span>Latitudinal <span class="hlt">variation</span> of 732.0 nm dayglow emission under <span class="hlt">geomagnetic</span> storm conditions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Singh, Vir; Dharwan, Maneesha</p> <p>2016-07-01</p> <p>A comprehensive model is developed to study 732.0 nm dayglow emission. The Solar2000 EUV (extreme ultraviolet) flux model, neutral atmosphere model (NRLMSISE-00), latest transition probabilities and updated reaction rate coefficients are incorporated in the present model. The modeled volume emission rates (VER) are compared with the measurements as provided by Atmosphere Explorer-C satellite, Dynamics Explorer-2 spacecraft and WINDII measurements. The model is found in very good agreement with the measurements. This model is used to study the effects of <span class="hlt">geomagnetic</span> storm on the 732.0 nm dayglow emission at various latitudes in northern hemisphere. It is found that the VER decreases as the latitude increases. The decrease in VER from low to mid latitudes is due to the decrease in atomic oxygen number density with latitude. The zenith intensity at the maximum <span class="hlt">geomagnetic</span> activity is about 15% higher than the zenith intensity before the start of the <span class="hlt">geomagnetic</span> storm in equatorial region. However, no appreciable change in the zenith intensity is found at higher latitudes (above 50° N). Further a negative correlation is found between the volume emission rate and DST index at all latitudes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001GeCoA..65.2995M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001GeCoA..65.2995M"><span>Correction of in situ cosmogenic nuclide production rates for <span class="hlt">geomagnetic</span> field intensity <span class="hlt">variations</span> during the past 800,000 years</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Masarik, Jozef; Frank, Martin; Schäfer, Jörg M.; Wieler, Rainer</p> <p>2001-09-01</p> <p>We present integrated relative production rates for cosmogenic nuclides in rock surfaces, which take into account reported <span class="hlt">variations</span> of the <span class="hlt">geomagnetic</span> field intensity during the past 800,000 yr. The calculations are based on the model simulating cosmic ray particle interactions with the Earth's atmosphere given by Masarik and Beer ["Simulation of particle fluxes and cosmogenic nuclide production in the Earth's atmosphere," J. Geophys. Res. 104(D10), 12099-12111, 1999]. Corrections are nearly independent on altitude between sea level and at least 5000 m. The correction factors are essentially identical for all stable and radioactive cosmogenic nuclides with half-lives longer than a few hundred thousand years. At the equator, integrated production rates for exposure ages between ˜40,000 to 800,000 yr are 10 to 12% higher than the present-day values, whereas at latitudes >40°, <span class="hlt">geomagnetic</span> field intensity <span class="hlt">variations</span> have hardly influenced in situ cosmogenic nuclide production. Correction factors for in situ 14C production rates differ from those of longer-lived nuclides. They are always smaller than ˜2% because the magnetic field intensity remained rather constant during the past ˜10 kyr, when the major fraction of the 14C extant today was produced.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19960042566','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19960042566"><span><span class="hlt">Secular</span> <span class="hlt">variation</span> of activity in comets 2P/Encke and 9P/Tempel 1</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Haken, Michael; AHearn, Michael F.; Feldman, Paul D.; Budzien, Scott A.</p> <p>1995-01-01</p> <p>We compare production rates of H20 derived from International Ultraviolet Explorer (IUE) spectra from multiple apparitions of 2 comets, 2P/Encke and 9P/Tempel 1, whose orbits are in near-resonance with that of the Earth. Since model-induced errors are primarily a function of observing geometry, the close geometrical matches afforded by the resonance condition results in the cancellation of such errors when taking ratios of production rates. Giving careful attention to the <span class="hlt">variation</span> of model parameters with solar activity, we find marginal evidence of change in 2P/Encke: a 1-sigma pre-perihelion decrease averaging 4%/revolution over 4 apparitions from 1980-1994, and a 1-sigma post-perihelion increase of 16%/revolution for 2 successive apparitions in 1984 and 1987. We find for 9P/Tempel 1, however, a 7-sigma decrease of 29%/revolution over 3 apparitions from 1983-1994, even after correcting for a tracking problem which made the fluxes systematically low. We speculate on a possible association of the character of long-term brightness <span class="hlt">variations</span> with physical properties of the nucleus, and discuss implications for future research.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFMGP23A1018G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFMGP23A1018G"><span>Improving our knowledge of the rapid <span class="hlt">geomagnetic</span> field intensity <span class="hlt">variation</span> observed in Europe around 800 AD</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gómez-Paccard, M.; Chauvin, A.; Lanos, P.; Dufresne, P.; Kovacheva, M.; Hill, M. J.; Beamud, E.; Gutiérrez-Lloret, S.; Cañavate, V.; Blain, S.; Bouvier, A.; Oberlin, C.; Guibert, P.; Sapin, C.; Pringent, D.</p> <p>2011-12-01</p> <p>Available European data indicate that during the past 2500 years there have been periods of rapid intensity <span class="hlt">geomagnetic</span> fluctuations interspersed with periods of little change. The challenge now is to precisely describe these rapid changes. The aim of this study is to obtain an improved description of the sharp <span class="hlt">geomagnetic</span> intensity change that took place in Western Europe around 800 yrs AD as well as to investigate if this peak is observed at a continental scale. For this purpose 13 precisely dated early medieval Spanish pottery fragments, 4 archeological French kilns and a 3 collections of bricks used for the construction of different historical buildings from France and with ages ranging between 330 to 1290 AD have been studied. The material collected has been dated by archeological/historical constraints together with radiocarbon,thermoluminiscence (TL) and archeomagentic analysis. From classical Thellier experiments including TRM anisotropy and cooling rate corrections upon archeointensity estimates and conducted on 164 specimens (119 of them giving reliable results) ten new high-quality mean intensities have been obtained. The new intensity data together with a selection of the most reliable data from Western Europe have been relocated to the latitude of Paris and confirm the existence of an intensity maxima of ~85 μT centred at ~850 AD and related to intensity changes up to 20 μT per century. The results also indicate that a previous abrupt intensity change (reaching a maximum value of ~ 90 μT) took place in Western Europe around 650 AD. A selection of high-quality intensity data from Bulgaria, Italy and Greece indicate a very similar intensity trend for Eastern Europe. Although available data indicate that the duration of such periods of high intensities may be of less than one century more data are needed to infer the exact duration of these maximums. A comparison between the selected data and regional and global <span class="hlt">geomagnetic</span> field models indicates that</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGRA..121.7193M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGRA..121.7193M"><span><span class="hlt">Geomagnetic</span> control of the midlatitude daytime foF1 and foF2 long-term <span class="hlt">variations</span>: Physical interpretation using European observations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mikhailov, A. V.; Perrone, L.</p> <p>2016-07-01</p> <p>Morphological analysis of Slough/Chilton and Juliusruh foF2 and foF1 long-term <span class="hlt">variations</span> for the period including recent observations made in the previous paper (PM) has shown that the <span class="hlt">geomagnetic</span> control is valid in the 21st century, moreover, the dependence on <span class="hlt">geomagnetic</span> activity has become more pronounced and explicit after 1990. A new method to retrieve thermospheric neutral composition (O, O2, and N2), exospheric temperature Tex, and the total solar EUV flux with λ < 1050 Å from routine foF1 ionosonde observations has been developed to understand the mechanism of this <span class="hlt">geomagnetic</span> control. The method was tested using CHAMP/STAR neutral gas density measurements. The retrieved for the first time thermospheric parameters at Slough/Chilton and Juliusruh over the period of ~ 5 solar cycles were used to analyze the mechanism of foF1 and foF2 long-term <span class="hlt">variations</span> in the light of the <span class="hlt">geomagnetic</span> control concept. It was shown that the control was provided via two channels: [O] and [O]/[N2] <span class="hlt">variations</span>. <span class="hlt">Geomagnetic</span> activity presented by 11 year running mean weighted index Ap11y controls the (O/N2)11y ratio <span class="hlt">variations</span>, while solar activity presented by (F10.7)11y controls atomic oxygen [O]11y <span class="hlt">variations</span>. Atomic oxygen, the main aeronomic parameter controlling daytime foF1 and foF2 <span class="hlt">variations</span>, manifests solar cycle and long-term (for some solar cycles) <span class="hlt">variations</span> with the rising phase in 1965-1985 and the falling phase in 1985-2008. These long-term [O] <span class="hlt">variations</span> are reflected in foF2 and foF1 long-term <span class="hlt">variations</span>. The origin of these long-term <span class="hlt">variations</span> is in the Sun. The empirical thermospheric model Mass Spectrometer Incoherent Scatter-86 driven by Ap and F10.7 indices manifests [O]11y and (O/N2 )11y <span class="hlt">variations</span> similar to the retrieved ones including the period of deep solar minimum with a very low atomic oxygen concentration in 2008. This confirms the basic idea of the <span class="hlt">geomagnetic</span> control concept that ionospheric long-term <span class="hlt">variations</span> have a natural (not</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1811817K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1811817K"><span>Holocene <span class="hlt">geomagnetic</span> field <span class="hlt">variations</span> from low latitude site: contribution from the Canary Islands</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kissel, Catherine; Laj, Carlo; Rodriguez-Gonzalez, Alejandro; Perez-Torrado, Francisco; Carrracedo, Juan-Carlos; Wandres, Camille</p> <p>2016-04-01</p> <p>Full <span class="hlt">geomagnetic</span> vector information was retrieved from 37 lava flows (corresponding to 38 sites because one flow was sampled at two different localities) located in Tenerife and Gran Canaria (Canary Islands). Twenty-eight flows are dated between 1706 AD and about 13200 BC and one is historical. Eight other non-dated flows have stratigraphic links with the dated flows and at the end, our study allowed us to attribute to them archeomagnetic ages based on their paleomagnetic characteristics. Various mineralogical analyses were conducted, giving access to the nature and grain size of the magnetic minerals. Full stepwise (about 13 steps) thermal and AF demagnetizations were conducted on more than 400 samples to determine the paleomagnetic directions. The individual MAD values are on the average about 2° and the mean precision parameter at the flow scale (alpha95) is 4.2°. For paleointensities (PI), we performed the original Thellier and Thellier experiments with a success rate of about 65%, coupling it with the strict set of selection criteria PICRIT-03. The mean PIs at the flow level are based on 3 to 12 independent PI determinations except for one site in which only one reliable determination could be obtained. The obtained data are unique in this area over the 1000-14000 BC period and they are complementary to the dataset obtained in the Canary Islands for the last 500 years. Over the last 3 kyr, they indicate some variability in the local field intensity with a prominent PI peak centered around 600 BC and reaching 80 μT (VADM 16 x 10 ^22 Am ^2), documented by four different flows and associated to significantly easterly deviated declinations. The directional data are rather consistent with the most recent models proposed for that area but the obtained PI indicate that models largely underestimate the paleointensities. Combined with published data obtained from western Africa, Spain, Portugal, Morocco and the Azores within a 2000 km-radius around the Canary</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920045063&hterms=Russell&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DRussell','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920045063&hterms=Russell&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DRussell"><span>The semiannual <span class="hlt">variation</span> of great <span class="hlt">geomagnetic</span> storms and the postshock Russell-Mcpherron effect preceding coronal mass ejecta</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Crooker, N. U.; Cliver, E. W.; Tsurutani, B. T.</p> <p>1992-01-01</p> <p>Recent results indicate that the intense southward interplanetary magnetic fields (IMFs) responsible for great storms can reside in the postshock plasma preceding the driver gas of coronal mass ejections (CMEs) as well as in the driver gas itself. It is proposed here that strong southward fields in the postshock flow result from a major increase in the Russell-McPherron polarity effect through a systematic pattern of compression and draping within the ecliptic plane. Differential compression at the shock increases the Parker spiral angle and, consequently, the azimuthal field component that projects as a southward component onto earth's dipole axis. The resulting prediction is that southward fields in the postshock plasma maximize at the spring (fall) equinox in CMEs emerging from toward (away) sectors. This pattern produces a strong semiannual <span class="hlt">variation</span> in postshock IMF orientation and may account at least in part for the observed semiannual <span class="hlt">variation</span> of the occurrence of great <span class="hlt">geomagnetic</span> storms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920045063&hterms=russell&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Drussell','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920045063&hterms=russell&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Drussell"><span>The semiannual <span class="hlt">variation</span> of great <span class="hlt">geomagnetic</span> storms and the postshock Russell-Mcpherron effect preceding coronal mass ejecta</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Crooker, N. U.; Cliver, E. W.; Tsurutani, B. T.</p> <p>1992-01-01</p> <p>Recent results indicate that the intense southward interplanetary magnetic fields (IMFs) responsible for great storms can reside in the postshock plasma preceding the driver gas of coronal mass ejections (CMEs) as well as in the driver gas itself. It is proposed here that strong southward fields in the postshock flow result from a major increase in the Russell-McPherron polarity effect through a systematic pattern of compression and draping within the ecliptic plane. Differential compression at the shock increases the Parker spiral angle and, consequently, the azimuthal field component that projects as a southward component onto earth's dipole axis. The resulting prediction is that southward fields in the postshock plasma maximize at the spring (fall) equinox in CMEs emerging from toward (away) sectors. This pattern produces a strong semiannual <span class="hlt">variation</span> in postshock IMF orientation and may account at least in part for the observed semiannual <span class="hlt">variation</span> of the occurrence of great <span class="hlt">geomagnetic</span> storms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGRB..121.7716S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGRB..121.7716S"><span>Authigenic 10Be/9Be ratio signatures of the cosmogenic nuclide production linked to <span class="hlt">geomagnetic</span> dipole moment <span class="hlt">variation</span> since the Brunhes/Matuyama boundary</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Simon, Quentin; Thouveny, Nicolas; Bourlès, Didier L.; Valet, Jean-Pierre; Bassinot, Franck; Ménabréaz, Lucie; Guillou, Valéry; Choy, Sandrine; Beaufort, Luc</p> <p>2016-11-01</p> <p><span class="hlt">Geomagnetic</span> dipole moment <span class="hlt">variations</span> associated with polarity reversals and excursions are expressed by large changes of the cosmogenic nuclide beryllium-10 (10Be) production rates. Authigenic 10Be/9Be ratios (proxy of atmospheric 10Be production) from oceanic cores therefore complete the classical information derived from relative paleointensity (RPI) records. This study presents new authigenic 10Be/9Be ratio results obtained from cores MD05-2920 and MD05-2930 collected in the west equatorial Pacific Ocean. Be ratios from cores MD05-2920, MD05-2930 and MD90-0961 have been stacked and averaged. <span class="hlt">Variations</span> of the authigenic 10Be/9Be ratio are analyzed and compared with the <span class="hlt">geomagnetic</span> dipole low series reported from global RPI stacks. The largest 10Be overproduction episodes are related to dipole field collapses (below a threshold of 2 × 1022 Am2) associated with the Brunhes/Matuyama reversal, the Laschamp (41 ka) excursion, and the Iceland Basin event (190 ka). Other significant 10Be production peaks are correlated to <span class="hlt">geomagnetic</span> excursions reported in literature. The record was then calibrated by using absolute dipole moment values drawn from the Geomagia and Pint paleointensity value databases. The 10Be-derived <span class="hlt">geomagnetic</span> dipole moment record, independent from sedimentary paleomagnetic data, covers the Brunhes-Matuyama transition and the whole Brunhes Chron. It provides new and complementary data on the amplitude and timing of millennial-scale <span class="hlt">geomagnetic</span> dipole moment <span class="hlt">variations</span> and particularly on dipole moment collapses triggering polarity instabilities.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19810064430&hterms=wind+exposure&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dwind%2Bexposure','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19810064430&hterms=wind+exposure&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dwind%2Bexposure"><span><span class="hlt">Secular</span> <span class="hlt">variations</span> in composition of the solar wind - Evidence and causes</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kerridge, J. F.</p> <p>1980-01-01</p> <p><span class="hlt">Variations</span> in the composition of the regolith due to irradiation by the solar wind are examined by categorizing the exposure history recorded in each sample. The history can be defined by two parameters: the duration of solar wind exposure (maturity) and a measure of how long the exposure took place (antiquity). Three partially successful methods for determining antiquity are described: the regolith contains small amounts of unsupported, trapped radiogenic noble gases, the most common being Ar-40. Assuming relatively prompt outgassing of the lunar interior, the amount of Ar-40 implanted per unit time should be proportional to the lunar content of K-40, and thus should have decayed exponentially over the lifetime of the moon. Normalization to constant exposure duration is achieved by taking the ratio Ar-40/Ar-36 in trapped gas, Ar-36 being an efficiently trapped solar wind species. The second method involves the interaction between galactic cosmic rays and lunar material producing certain spallogenic nuclides which may be analyzed in terms of a cosmic ray exposure age. The third method deals with the fact that there is a general tendency for depth within a core to be related to time deposition; two variants of this method are presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PEPI..252...49U','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PEPI..252...49U"><span>High resolution Holocene paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> records from Bay of Bengal</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Usapkar, A.; Dewangan, P.; Badesab, F. K.; Mazumdar, A.; Ramprasad, T.; Krishna, K. S.; Basavaiah, N.</p> <p>2016-03-01</p> <p>We present high resolution paleosecular <span class="hlt">variation</span> (PSV) records up to 8 cal. kyr BP from three piston cores, MD161/8, MD161/11 and MD161/13 acquired in the Krishna-Godavari (KG) basin, Bay of Bengal. During the Holocene period, high sedimentation rates are recorded at MD161/8 (38.8-248.3 cm/kyr), MD161/11 (137-336 cm/kyr) and MD161/13 (∼573 cm/kyr). Rock magnetic data analysis suggests that the remanence signal is carried by titanomagnetite/titanohematite grains in stable single domain (SSD)/pseudo single domain (PSD) state. The PSV records of MD161/11 and MD161/13 show good correlation in the uppermost sediments despite significant <span class="hlt">variation</span> in the sedimentation rates; however, poor correlation of PSV records is observed for the core MD161/8 probably due to local effects. Paleoinclination records of MD161/8, MD161/11 and MD161/13 show a low between ∼2.4 and 2.0 cal. kyr BP, an increase between 2.0 and 1.4 cal. kyr BP and a decrease towards the present. To varying degrees these trends can be observed in the other Asian PSV records of Shuangchiling (SCL) and Biwa lakes. However, the magnitude of the observed inclination anomaly in KG basin is higher (∼40°) compared to those reported from SCL (∼25°) and Biwa (∼10°) lakes. Paleodeclination records of MD161/11 and MD161/13 show a decline between ∼4.0 and 2.9 cal. kyr BP, an increase between 2.9 and 2.1 cal. kyr BP, a substantial decrease between ∼2.1 and 1.0 cal. kyr BP and an increase towards the present. Similar trends can be observed in the other Asian PSV records of SCL and Biwa lakes with a minor age offset of 0.2-0.5 kyr. The available models CALS7k.2 and CALS10k.1 are evaluated for their capability in predicting the inclination and declination anomalies from the Asian regions. The CALS7k.2 model can predict most of the inclination anomalies while the CALS10k.1 is unable to predict many of them. The CALS7k.2 model shows that the observed inclination anomalies can be attributed to the presence of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JGRA..119.2836M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JGRA..119.2836M"><span>Spatial <span class="hlt">variation</span> in the plasma sheet composition: Dependence on <span class="hlt">geomagnetic</span> and solar activity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Maggiolo, R.; Kistler, L. M.</p> <p>2014-04-01</p> <p>We study the spatial distribution of plasma sheet O+ and H+ ions using data from the COmposition and DIstribution Function (CODIF) instrument on board the Cluster spacecraft from 2001 to 2005. The densities are mapped along magnetic field lines to produce bidimensional density maps at the magnetospheric equatorial plane for various <span class="hlt">geomagnetic</span> and solar activity levels (represented by the Kp and F10.7 indexes). We analyze the correlation of the O+ and H+ density with Kp and F10.7 in the midtail region at geocentric distances between 15 and 20 RE and in the near-Earth regions at radial distances between 7 and 8 RE. Near Earth the H+ density slightly increases with Kp and F10.7 while in the midtail region it is not correlated with Kp and F10.7. On the contrary, the amount of O+ ions significantly increases with Kp and F10.7 independently of the region. In the near-Earth region, the effects of solar EUV and <span class="hlt">geomagnetic</span> activity on the O+ density are comparable. In the midtail region, the O+ density increases at a lower rate with solar EUV flux but strongly increases with <span class="hlt">geomagnetic</span> activity although the effect is modulated by the solar EUV flux level. We also evidence a strong increase of the proportion of O+ ions with decreasing geocentric distance below ~10 RE. These results confirm the direct entry of O+ ions into the near-Earth plasma sheet and suggest that both energetic outflows from the auroral zone and cold outflow from the high-latitude ionosphere may contribute to feed the near-Earth plasma sheet with ionospheric ions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23410284','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23410284"><span>Domino model for <span class="hlt">geomagnetic</span> field reversals.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Mori, N; Schmitt, D; Wicht, J; Ferriz-Mas, A; Mouri, H; Nakamichi, A; Morikawa, M</p> <p>2013-01-01</p> <p>We solve the equations of motion of a one-dimensional planar Heisenberg (or Vaks-Larkin) model consisting of a system of interacting macrospins aligned along a ring. Each spin has unit length and is described by its angle with respect to the rotational axis. The orientation of the spins can vary in time due to spin-spin interaction and random forcing. We statistically describe the behavior of the sum of all spins for different parameters. The term "domino model" in the title refers to the interaction among the spins. We compare the model results with <span class="hlt">geomagnetic</span> field reversals and dynamo simulations and find strikingly similar behavior. The aggregate of all spins keeps the same direction for a long time and, once in a while, begins flipping to change the orientation by almost 180 degrees (mimicking a <span class="hlt">geomagnetic</span> reversal) or to move back to the original direction (mimicking an excursion). Most of the time the spins are aligned or antialigned and deviate only slightly with respect to the rotational axis (mimicking the <span class="hlt">secular</span> <span class="hlt">variation</span> of the <span class="hlt">geomagnetic</span> pole with respect to the geographic pole). Reversals are fast compared to the times in between and they occur at random times, both in the model and in the case of the Earth's magnetic field.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V54A..08R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V54A..08R"><span><span class="hlt">Secular</span> <span class="hlt">variations</span> of iron isotopes in ferromanganese crusts: evidences for deeply sourced iron in the Pacific Ocean?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rouxel, O. J.; Gueguen, B.</p> <p>2016-12-01</p> <p>Ferromanganese (Fe-Mn) crusts are potential archive of the Fe isotope composition of deep seawater through time. Here, we report Fe isotope composition of two pairs of Fe-Mn crusts collected on two volcanic seamounts from the Northern Pacific Ocean (Apuupuu Seamount, Hawaii) and the Southern Pacific Ocean (near Rurutu Island, Austral archipelago of French Polynesia). This approach allows (a) a direct comparison of the Fe isotope record in Fe-Mn crusts from the same seamount in order to address local effects, and (b) a comparison of geochemical composition of crusts between North and South Pacific in order to address the effect of more global geochemical processes. The results show that, despite different growth rates, diagenetic history, textures and geochemical patterns, Fe-Mn crusts from both North and South Pacific Oceans have fairly homogenous Fe isotope compositions over the last 17 Ma, yielding average δ56Fe values of -0.22 ± 0.20‰ (1sd, n = 54). The results also show striking correlations between Fe and Pb isotope ratios, indicating that local mixing between water masses is the main factor controlling Fe isotope composition in FeMn crusts. Recently, Horner et al. (2015) reported a range of δ56Fe values from -1.12‰ to 1.54‰ along a 76 Ma-old FeMn crust from the central pacific. However, <span class="hlt">secular</span> <span class="hlt">variations</span> of Fe isotopes inferred from other FeMn crusts in the Central North Pacific and Western Pacific (Yang and Rouxel, unpublished) show different patterns over the last 40 Ma, with δ56Fe ranging from -0.07 to -0.61‰ (n=81). Hence, the application of Fe isotopes as paleoceanographic proxies to trace deeply sourced iron at the scale of oceanic basins should be used with caution, prompting for an integrative approach combining diverse yet complimentary geochemical proxies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013GeoJI.193..635B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013GeoJI.193..635B"><span>Late Devonian palaeomagnetism of the North Tien Shan, Kyrgyzstan: can <span class="hlt">secular</span> <span class="hlt">variation</span> vary on a short timescale?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bazhenov, Mikhail L.; Van der Voo, Rob; Levashova, Natalia M.; Dominguez, Ada R.</p> <p>2013-05-01</p> <p>We studied more than 80 lava flows from a ˜600-m-thick pile of Upper Devonian (Frasnian) basalts and andesites of the Aral Formation in the North Tien Shan (Kyrgyzstan, Central Asia). With the aid of stepwise thermal demagnetization, a high-temperature, dual-polarity component was reliably isolated from most flows. The primary origin of the high-temperature component is demonstrated by positive reversal, conglomerate and fold tests. The most prominent and intriguing feature of this Late Devonian data set involves a clear distinction in angular dispersion between the lower and upper parts of the studied section. A rather low concentration parameter (k = 13) and several directional anomalies characterize the lower section; in contrast, a much better grouping (k = 46) and a lack of directional outliers is observed for the dual-polarity vectors from the upper flow sequence of the formation. We analysed different mechanisms to account for this directional pattern and found that it is possible in just two ways. One is to assume that <span class="hlt">secular</span> <span class="hlt">variation</span> (SV) in the upper sequence is strongly underrepresented, and it is a coincidence that the mean directions of both polarities are statistically antipodal, and the corresponding concentration parameters are statistically equal. The other explanation is to hypothesize that the magnitude of SV can vary several-fold at the same palaeolatitude and over time intervals estimated as 105-106 yr. This is in sharp contrast with other models of SV, where this magnitude has been assumed to be rather time-independent (for a given latitude). Our hypothesis accounts for the observed irregularities in palaeomagnetic data, but makes attempts to establish a correlation between SV and other parameters (geographic latitude, reversal frequency, age, etc.) more difficult. We are aware, however, that more data are needed to refute or confirm it.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009BGD.....6.7325R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009BGD.....6.7325R"><span>Review: the effects of <span class="hlt">secular</span> <span class="hlt">variation</span> in seawater Mg/Ca on marine biocalcification</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ries, J. B.</p> <p>2009-07-01</p> <p>Synchronized transitions in the polymorph mineralogy of the major reef-building and sediment-producing calcareous marine organisms and abiotic CaCO3 precipitates (ooids, marine cements) throughout Phanerozoic time is believed to have been caused by tectonically-induced <span class="hlt">variations</span> in seawater molar Mg/Ca (>2="aragonite seas"; <2="calcite seas"). Here, I review a series of experiments in which extant calcifying taxa were reared in experimental seawater formulated over the range of mMg/Ca ratios (1.0 to 5.2) that occurred throughout their geologic history. Aragonite-secreting bryopsidalean algae and scleractinian corals and calcite-secreting coccolithophores exhibited higher rates of calcification and growth in the experimental seawaters that favored their skeletal mineral. These results support the assertion that seawater Mg/Ca played an important role in determining which hypercalcifying marine organisms were the major reef-builders and sediment-producers throughout Earth history. The observation that primary production increased along with calcification in mineralogically-favorable seawater is consistent with the hypothesis that calcification promotes photosynthesis within autotrophs through the liberation of CO2. The Mg/Ca ratio of calcite secreted by the coccolithophores, coralline algae and reef-dwelling animals (crustacea, urchins, calcareous tube worms) declined with reductions in seawater Mg/Ca. Calcifying microbial biofilms varied their mineral polymorph with seawater Mg/Ca (mMg/Ca<2=low Mg calc; mMg/Ca>2=arag+high Mg calc), suggesting a nearly abiotic mode of calcification. These results indicate that biomineralogical control can be partially overridden by ambient seawater Mg/Ca and suggests that modern high Mg calcite organisms probably secreted low Mg calcite in calcite seas of the past. Notably, Mg fractionation in autotrophic organisms was more strongly influenced by changes in seawater Mg/Ca, a probable consequence of them inducing a less controlled</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JGRB..120.2056C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JGRB..120.2056C"><span>New constraints on the <span class="hlt">variation</span> of the <span class="hlt">geomagnetic</span> field during the late Neolithic period: Archaeointensity results from Sichuan, southwestern China</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cai, Shuhui; Chen, Wei; Tauxe, Lisa; Deng, Chenglong; Qin, Huafeng; Pan, Yongxin; Yi, Liang; Zhu, Rixiang</p> <p>2015-04-01</p> <p>We have carried out an archaeomagnetic study on a late Neolithic locality (Liujiazhai) in Sichuan, southwestern China. We pull together various dating techniques, including radiocarbon analysis, optically stimulated luminescence dating, stratigraphic information as well as archaeological and archaeomagnetic estimations, to constrain the age of the studied samples. Rock magnetic results indicate thermally stable fine-grained magnetite or titanomagnetite as the dominant magnetic carriers. More than half of the specimens (141/246) in the paleointensity experiment pass the selection criteria and are considered to record robust intensity values. The virtual axial dipole moments range from approximately (2.8 to 7.8) × 1022 Am2 with an average of 5.9 × 1022 Am2, indicating that the <span class="hlt">geomagnetic</span> intensity around 3000 before the Common Era (B.C.E.) is overall lower than the present field intensity (9.8 × 1022 Am2) of this area. The new results from Liujiazhai are generally consistent with the published data of similar age but deviate from the only available model of CALS10k.1b at certain time periods, making them important for future improvements of the model. Those data are significant for constraining the <span class="hlt">variation</span> of <span class="hlt">geomagnetic</span> field intensity between ~3100 and 2600 B.C.E. and improving the regional model of eastern Asia.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMGP13B1133M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMGP13B1133M"><span>Marine sediments and Beryllium-10 record of the <span class="hlt">geomagnetic</span> moment <span class="hlt">variations</span> of the 20-50ka interval</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ménabréaz, L.; Thouveny, N.; Bourles, D. L.</p> <p>2012-12-01</p> <p>To better constrain the Earth's dipole moment changes at the time of the Laschamp and Mono Lake excursions, we reconstructed the cosmogenic nuclide 10Be production <span class="hlt">variations</span> in the atmosphere using authigenic 10Be/9Be records measured along two marine sediment sequences from the north-east Atlantic (Portuguese margin) and west-equatorial Pacific (Papua-New Guinea margin) oceans. These two records evidence an almost doubling of the 10Be production at ~41 ka, thus assignable to the <span class="hlt">geomagnetic</span> dipole low associated to the Laschamp excursion. The compilation of authigenic 10Be/9Be marine records provides a stack which indicates that the global 10Be production rates at 41 ka were enhanced by a ~1.5 factor compared to the average over the 20-50 ka interval. The comparison of this authigenic 10Be/9Be marine stack with the Greenland 10Be flux record (smoothed by 1000-year averaging) evidences a good coherency of the timing and amplitude of 10Be production recorded at high, mid and low latitudes. This confirms that the 10Be overproduction signal has a global significance, as expected from a <span class="hlt">geomagnetic</span> dipole moment loss. The calibration of the 10Be/9Be stack using absolute virtual dipole moment values provides an independent tool to reconstruct <span class="hlt">geomagnetic</span> dipole moment <span class="hlt">variations</span>. This allows computing the loss rate leading to the Laschamp dipole minimum (~ -1.5 x 1022 A.m2.ka-1), which constitutes an interesting criterion to assess the loss rate of the historical field. In constrast with relative paleointensity records and absolute paleointensity data sets, the absence of significant cosmogenic enhancement at the age of 34 ka suggests that the Mono Lake dipole low was not sufficient to trigger a significant cosmogenic overproduction. This demonstrates that if the Mono lake excursion really occurred at that time, the duration and amplitude of the dipole weakening were very limited compared to that of the Laschamp. The 10Be overproduction quantified in this study</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70022403','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70022403"><span>The 2000 revision of the joint UK/US <span class="hlt">geomagnetic</span> field models and an IGRF 2000 candidate model</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Macmillan, S.; Quinn, J.M.</p> <p>2000-01-01</p> <p>The method of derivation of the joint UK/US spherical harmonic <span class="hlt">geomagnetic</span> main-field and <span class="hlt">secular-variation</span> models is presented. Early versions of these models, with the main field truncated at degree 10, are the UK/US candidates for the IGRF 2000 model. The main-field model describes the Earth's magnetic field at the 2000.0 epoch, while the <span class="hlt">secular-variation</span> model predicts the evolution of this field between 2000.0 and 2005.0. A revised 1995.0 main-field model was also generated. Regional models for the continental US, Alaska and Hawaii were also produced as a by-product of the UK/US global modelling effort. Copy right?? The Society of <span class="hlt">Geomagnetism</span> and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015IAUGA..2241881V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015IAUGA..2241881V"><span>Earth orientation parameters: excitation by atmosphere, oceans and <span class="hlt">geomagnetic</span> jerks</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vondrak, Jan; Ron, Cyril</p> <p>2015-08-01</p> <p>It is well known that geophysical fluids (atmosphere, oceans) excite Earth orientation. The influence is known to be dominant for polar motion, partly responsible for length-of-day changes, and very small effects are now observable also in nutation. Very recently several authors (Holme and de Viron 2005, Gibert and le Mouel 2008, Malkin 2013) noted that sudden changes of Earth's speed of rotation and phase/amplitude of the free motions of its spin axis (Chandler wobble, Free core nutation) occur near the epochs of <span class="hlt">geomagnetic</span> jerks (GMJ - rapid changes of the <span class="hlt">secular</span> <span class="hlt">variations</span> of <span class="hlt">geomagnetic</span> field). By using the numerical integration of broad-band Liouville equations (Brzezinski 1994) we demonstrate that if non-periodical bell-like excitations of limited length (app. 1 year) around the epochs of GMJ are added to atmospheric and oceanic excitations, the agreement between observed and calculated Earth orientation parameters is improved significantly.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EP%26S...67...79T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EP%26S...67...79T"><span>International <span class="hlt">Geomagnetic</span> Reference Field: the 12th generation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Thébault, Erwan; Finlay, Christopher C.; Beggan, Ciarán D.; Alken, Patrick; Aubert, Julien; Barrois, Olivier; Bertrand, Francois; Bondar, Tatiana; Boness, Axel; Brocco, Laura; Canet, Elisabeth; Chambodut, Aude; Chulliat, Arnaud; Coïsson, Pierdavide; Civet, François; Du, Aimin; Fournier, Alexandre; Fratter, Isabelle; Gillet, Nicolas; Hamilton, Brian; Hamoudi, Mohamed; Hulot, Gauthier; Jager, Thomas; Korte, Monika; Kuang, Weijia; Lalanne, Xavier; Langlais, Benoit; Léger, Jean-Michel; Lesur, Vincent; Lowes, Frank J.; Macmillan, Susan; Mandea, Mioara; Manoj, Chandrasekharan; Maus, Stefan; Olsen, Nils; Petrov, Valeriy; Ridley, Victoria; Rother, Martin; Sabaka, Terence J.; Saturnino, Diana; Schachtschneider, Reyko; Sirol, Olivier; Tangborn, Andrew; Thomson, Alan; Tøffner-Clausen, Lars; Vigneron, Pierre; Wardinski, Ingo; Zvereva, Tatiana</p> <p>2015-05-01</p> <p>The 12th generation of the International <span class="hlt">Geomagnetic</span> Reference Field (IGRF) was adopted in December 2014 by the Working Group V-MOD appointed by the International Association of <span class="hlt">Geomagnetism</span> and Aeronomy (IAGA). It updates the previous IGRF generation with a definitive main field model for epoch 2010.0, a main field model for epoch 2015.0, and a linear annual predictive <span class="hlt">secular</span> <span class="hlt">variation</span> model for 2015.0-2020.0. Here, we present the equations defining the IGRF model, provide the spherical harmonic coefficients, and provide maps of the magnetic declination, inclination, and total intensity for epoch 2015.0 and their predicted rates of change for 2015.0-2020.0. We also update the magnetic pole positions and discuss briefly the latest changes and possible future trends of the Earth's magnetic field.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016E%26PSL.453...78C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016E%26PSL.453...78C"><span>Persistent high paleosecular <span class="hlt">variation</span> activity in southern hemisphere for at least 10 000 years</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Constable, Catherine; Korte, Monika; Panovska, Sanja</p> <p>2016-11-01</p> <p>Direct observations of the <span class="hlt">geomagnetic</span> field show that <span class="hlt">secular</span> <span class="hlt">variation</span> is strong in the Atlantic hemisphere, and comparatively reduced in the Pacific region. The dipole has been decaying since at least 1840 AD, driven by growth and migration of reverse flux patches in the southern hemisphere. We investigate whether anything like this modern pattern of <span class="hlt">geomagnetic</span> <span class="hlt">secular</span> <span class="hlt">variation</span> persists and can be detected in global paleomagnetic field models. Synthesis of results from two new time-varying spherical harmonic models shows that geographically distinct <span class="hlt">geomagnetic</span> <span class="hlt">secular</span> <span class="hlt">variation</span> extends to at least 10 000 BP. The models use the same database but differ in methodology, leading to some regional differences in results. Consistent large-scale surface features include strong average fields in the northern hemisphere and weaker fields with greater overall variability in the south. Longitudinal structure is present, with weaker average fields in the western Pacific than in the east, and prominent negative inclination anomalies extending beneath Indonesia, across Africa and to Brazil, but weaker anomalies in the central Pacific. Marginally positive inclination anomalies occur west of the Americas. Paleosecular <span class="hlt">variation</span> activity peaks at high southern latitudes, and there is a pattern of reduced activity at equatorial and mid-latitudes beneath the Pacific. Although the dipole has exhibited both growth and decay over the interval 0-10 000 BP, our results show that <span class="hlt">geomagnetic</span> paleosecular <span class="hlt">variation</span> is preferentially focused in similar geographic regions to <span class="hlt">secular</span> <span class="hlt">variation</span> seen in the modern field.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PEPI..270..128S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PEPI..270..128S"><span>Detection of <span class="hlt">secular</span> acceleration pulses from magnetic observatory data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Soloviev, Anatoly; Chulliat, Arnaud; Bogoutdinov, Shamil</p> <p>2017-09-01</p> <p><span class="hlt">Geomagnetic</span> <span class="hlt">secular</span> <span class="hlt">variation</span> (SV) models for the epochs before the space era are based on magnetic observatory data, which represent relatively rough and noisy time series due to magnetic storms, anthropogenic spikes and gaps. These models are often strongly regularized in time, so that fast <span class="hlt">variations</span> in the SV are smoothed out. However, recent studies show that at least some of the <span class="hlt">geomagnetic</span> jerks observed at the Earth's surface emanate from increasing and decreasing phases of <span class="hlt">secular</span> acceleration (SA) pulses at the core surface. The latter ones are direct manifestation of the dynamic processes taking place in the liquid core. They were first detected from satellite data, which are both of higher quality and more homogeneous in terms of geographical coverage than ground data. Herein we attempt to carry out similar studies based on observatory data available for a longer period. The proposed method of SV modeling and recognition of SA pulses relies on a new technique of processing time series based on fuzzy mathematics. Comparison with the SV modeling results derived from satellite data shows their high conformity with the proposed method. Stability and reliability of the SA pulse recognition are demonstrated by the examples of well-studied SA pulses in 2006, 2009 and 2012. Moreover, several new SA pulses around 1996, 1999, 2002 and 2014 are discovered as a result of the new approach application to multi-observatory data analysis. The latter provides a basis for applying the method to older historical data and investigate SA pulses and <span class="hlt">geomagnetic</span> jerks further back in time.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.3001A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.3001A"><span><span class="hlt">Geomagnetic</span> inverse problem and data assimilation: a progress report</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Aubert, Julien; Fournier, Alexandre</p> <p>2013-04-01</p> <p>In this presentation I will present two studies recently undertaken by our group in an effort to bring the benefits of data assimilation to the study of Earth's magnetic field and the dynamics of its liquid iron core, where the geodynamo operates. In a first part I will focus on the <span class="hlt">geomagnetic</span> inverse problem, which attempts to recover the fluid flow in the core from the temporal <span class="hlt">variation</span> of the magnetic field (known as the <span class="hlt">secular</span> <span class="hlt">variation</span>). <span class="hlt">Geomagnetic</span> data can be downward continued from the surface of the Earth down to the core-mantle boundary, but not further below, since the core is an electrical conductor. Historically, solutions to the <span class="hlt">geomagnetic</span> inverse problem in such a sparsely observed system were thus found only for flow immediately below the core mantle boundary. We have recently shown that combining a numerical model of the geodynamo together with magnetic observations, through the use of Kalman filtering, now allows to present solutions for flow throughout the core. In a second part, I will present synthetic tests of sequential <span class="hlt">geomagnetic</span> data assimilation aiming at evaluating the range at which the future of the geodynamo can be predicted, and our corresponding prospects to refine the current <span class="hlt">geomagnetic</span> predictions. Fournier, Aubert, Thébault: Inference on core surface flow from observations and 3-D dynamo modelling, Geophys. J. Int. 186, 118-136, 2011, doi: 10.1111/j.1365-246X.2011.05037.x Aubert, Fournier: Inferring internal properties of Earth's core dynamics and their evolution from surface observations and a numerical geodynamo model, Nonlinear Proc. Geoph. 18, 657-674, 2011, doi:10.5194/npg-18-657-2011 Aubert: Flow throughout the Earth's core inverted from <span class="hlt">geomagnetic</span> observations and numerical dynamo models, Geophys. J. Int., 2012, doi: 10.1093/gji/ggs051</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008E%26PSL.267..468W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008E%26PSL.267..468W"><span>The 2003 <span class="hlt">geomagnetic</span> jerk and its relation to the core surface flows</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wardinski, I.; Holme, R.; Asari, S.; Mandea, M.</p> <p>2008-03-01</p> <p>In this paper we examine the core surface flow obtained by an inversion of a continuous model of the <span class="hlt">geomagnetic</span> field and its temporal <span class="hlt">variation</span> using the diffusion-less induction equation. The continuous CHAOS model is derived from satellite data up to spherical harmonic degree 14 and covers the period 1999 to 2006. The CHAOS <span class="hlt">secular</span> <span class="hlt">variation</span>, when downward continued to the core surface, shows stripe-like features, which can be attributed to spherical harmonic degree 12 and higher. These contributions are removed by applying a tapering method, and the resulting tapered model is then inverted for the core surface flow. Satellite-based field models have a high spatial resolution; however, their temporal resolution is limited. In order to enhance the temporal resolution of the flow, we additionally constrain the flow to fit the <span class="hlt">secular</span> <span class="hlt">variation</span> from ground-based observatory data. A range of solutions, subject to different constraints, are computed, two flow hypotheses being considered: purely toroidal flow and tangentially geostrophic flow. We show that both flow types provide similar results; however, the purely toroidal flow provides a better fit to the <span class="hlt">secular</span> <span class="hlt">variation</span> in the equatorial region than the tangentially geostrophic flow. We then analyze the residuals between observed <span class="hlt">secular</span> <span class="hlt">variation</span> and its predictions from the flow. We note larger residuals for the tangentially geostrophic flow, where strong radial <span class="hlt">secular</span> <span class="hlt">variation</span> and a weak radial field are observed. Although diffusive effects cannot be ruled out as a potential source of the mismatch, we attribute the larger residuals to be caused by a flawed estimation of the poloidal flow. We also seek to relate temporal changes in the fluid flow to the <span class="hlt">geomagnetic</span> jerk which occurred at the beginning of 2003. It is found that this <span class="hlt">geomagnetic</span> jerk coincides with <span class="hlt">variations</span> in the zonal flow components of both flow types, suggesting a possible link to torsional oscillations. However, we argue that other</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMGP23A1282S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMGP23A1282S"><span>Late Quaternary paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span>, relative paleointensity, and environmental magnetism from Cascade Lake, Brooks Range, Arctic Alaska</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Steen, D. P.; Kaufman, D. S.; Stoner, J. S.; Reilly, B. T.</p> <p>2015-12-01</p> <p>Two sediment cores from Cascade Lake (68.38°N, 154.60°W), Arctic Alaska were selected for paleomagnetic analysis to compare 14C age control with paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> (PSV) and relative paleointensity (RPI) age control derived from field models and other local sedimentary records. Rock magnetic experiments were performed to quantify variability in magnetic properties and to infer sediment sourcing during the late Quaternary. U-channels were studied through AF demagnetization of the natural remanent magnetization, and laboratory-induced magnetizations including anhysteretic remanent magnetization (ARM) acquisition, ARM demagnetization, and isothermal remanent magnetization (IRM). Maximum angular deviation values average <2°, indicating a strong, well-defined characteristic remanent magnetization dominated by a low-coercivity component that increases up core. Average inclinations are within 4° of the expected geocentric axial dipole, and major inclination features can be correlated across the two cores. Correlation of inclination changes with the Burial Lake record, 200 km to the west (Dorfman, 2013, unpub. thesis), indicates that the Cascade Lake sedimentary sequence overlying the basal diamicton likely spans at least 16 ka. Cascade Lake sediments may be suitable for RPI estimation using the ARM or IRM as a normalizer, following a more detailed examination of magnetic properties. A systematic offset between the Cascade Lake 14C chronology and PSV and RPI chronologies wiggle-matched to field models suggests a hard-water effect of ~1000 yr, although we cannot rule out the possibility that at least some of the age offset represents a post-depositional remanent magnetization lock-in effect at Cascade Lake. S-ratios (IRM0.3T/SIRM) and ARM-ratios (ARM/SIRM) show a sharp decrease in low-coercivity material across the transition from clastic sediments to organic-rich sediments, followed by an increase in the concentration of fine-grained magnetic material and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeoJI.209..587L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoJI.209..587L"><span>Long-term palaeomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> and excursions from the western Equatorial Pacific Ocean (MIS2-4)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lund, Steve; Schwartz, Martha; Stott, Lowell</p> <p>2017-05-01</p> <p>New palaeomagnetic results are presented for the Pleistocene (MIS2-4) portion of deep-sea core MD98-2181 (MD81; Devao Gulf, Philippine Islands). MD81 is the highest resolution (∼50 cm ky-1) palaeomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> (PSV) record for ∼12-70 ka ever recovered from equatorial latitudes (±15°). Magnetic studies indicate that MD81 has a stable natural remanence with directional uncertainties (MAD angles) typically less than 3°. We have also recovered a relative palaeointensity estimate from these sediments based on normalization to isothermal remanence. We have correlated our relative palaeointensity record with high-resolution relative palaeointensity records from the North Atlantic Ocean. The MD81 ages are always within ±500 yr of the North Atlantic records over the entire core. We also correlate our PSV record with another published PSV record from Indonesia (MD34). We are able to correlate 25 inclination features, 25 declination features and 24 relative palaeointensity features between MD81 and MD34. We identify three intervals of 'anomalous' directions in the cores (based on >2σ deviation from mean directions). One of these intervals contains true excursional directions and is dated to ∼40.5 ka. We associate this interval with the Laschamp Excursion. We also note two other intervals that have anomalous directions, but no true excursional directions. These intervals occur around ∼34.5 and ∼61.5 ka and we associate them with the Mono Lake Excursion (∼33.5-34.5 ka) in western USA and the Norwegian-Greenland Sea Excursion (∼61 ± 2 ka) in the North Atlantic Ocean. We view our 'anomalous' PSV in the three intervals to be truly anomalous even though most directions are not truly excursional. We think that it is time to reconsider the definition of what is 'anomalous' PSV or excursions. To do that we need good-quality PSV records from several regions that have reproducible records of normal PSV, excursional waveforms and relative palaeointensity</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920019389&hterms=electromagnetic+effects&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Delectromagnetic%2Beffects','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920019389&hterms=electromagnetic+effects&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Delectromagnetic%2Beffects"><span>Magnetic and Electromagnetic Induction Effects in the Annual Means of <span class="hlt">Geomagnetic</span> Elements</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Demetrescu, Crisan; Andreescu, Maria</p> <p>1992-01-01</p> <p>The solar-cycle related (SC) <span class="hlt">variation</span> in the annual means of the horizontal and vertical components of the <span class="hlt">geomagnetic</span> field at European observatories is used to infer information on the magnetic and electric properties of the interior, characteristic of the observatory location, by identifying and analyzing the magnetic induction component and respectively the electromagnetic induction component of the SC <span class="hlt">variation</span>. The obtained results and the method can be used to better constrain the anomaly bias in main field modelling and to improve the reliability of <span class="hlt">secular</span> <span class="hlt">variation</span> models beyond the time interval covered by data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920019389&hterms=electromagnetic+induction&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Delectromagnetic%2Binduction','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920019389&hterms=electromagnetic+induction&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Delectromagnetic%2Binduction"><span>Magnetic and Electromagnetic Induction Effects in the Annual Means of <span class="hlt">Geomagnetic</span> Elements</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Demetrescu, Crisan; Andreescu, Maria</p> <p>1992-01-01</p> <p>The solar-cycle related (SC) <span class="hlt">variation</span> in the annual means of the horizontal and vertical components of the <span class="hlt">geomagnetic</span> field at European observatories is used to infer information on the magnetic and electric properties of the interior, characteristic of the observatory location, by identifying and analyzing the magnetic induction component and respectively the electromagnetic induction component of the SC <span class="hlt">variation</span>. The obtained results and the method can be used to better constrain the anomaly bias in main field modelling and to improve the reliability of <span class="hlt">secular</span> <span class="hlt">variation</span> models beyond the time interval covered by data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007JGRA..11210111S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007JGRA..11210111S"><span>Interhourly variability index of <span class="hlt">geomagnetic</span> activity and its use in deriving the long-term <span class="hlt">variation</span> of solar wind speed</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Svalgaard, Leif; Cliver, Edward W.</p> <p>2007-10-01</p> <p>We describe the detailed derivation of the interhourly variability (IHV) index of <span class="hlt">geomagnetic</span> activity. The IHV index for a given <span class="hlt">geomagnetic</span> element is mechanically derived from hourly values or means as the sum of the unsigned differences between adjacent hours over a 7-hour interval centered on local midnight. The index is derived separately for stations in both hemispheres within six longitude sectors spanning the Earth using only local night hours. It is intended as a long-term index and available data allows derivation of the index back well into the 19th century. On a timescale of a 27-day Bartels rotation, IHV averages for stations with corrected <span class="hlt">geomagnetic</span> latitude less than 55° are strongly correlated with midlatitude range indices (R2 = 0.96 for the am index since 1959; R2 = 0.95 for the aa index since 1980). We find that observed yearly averages of aa before the year 1957 are ˜3 nT too small compared to values calculated from IHV using the regression constants based on 1980-2004. We interpret this discrepancy as an indication that the calibration of the aa index is in error before 1957. There is no systematic discrepancy between observed and similarly calculated ap values back to 1932. Bartels rotation averages of IHV are also strongly correlated with solar wind parameters (R2 = 0.79 with BV2). On a timescale of a year combining the IHV index (giving BV2 with R2 = 0.93) and the recently developed interdiurnal variability (IDV) index (giving interplanetary magnetic field magnitude, B, with R2 = 0.74) allows determination of solar wind speed, V, from 1890 to present. Over the ˜120-year series, the yearly mean solar wind speed varied from a low (inferred) of 303 km/s in 1902 to a high (observed) value of 545 km/s in 2003. The calculated yearly values of the product BV using B and V separately derived from IDV and IHV agree quantitatively with (completely independent) BV values derived from the amplitude of the diurnal <span class="hlt">variation</span> of the horizontal</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AdSpR..53.1246A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AdSpR..53.1246A"><span>Seasonal <span class="hlt">variations</span> of GPS derived TEC at three different latitudes of the southern hemisphere during <span class="hlt">geomagnetic</span> storms</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Adebiyi, S. J.; Adimula, I. A.; Oladipo, O. A.</p> <p>2014-04-01</p> <p>Data from the archive of the International GNSS Services (IGS) were used to study the seasonal <span class="hlt">variations</span> of Total Electron Content (TEC) over three stations located at different latitudes in the southern hemisphere during the <span class="hlt">geomagnetic</span> storms of 11 January, 6 April, 8 June, and 13 October 2000, representing storms that occurred in summer, autumn equinox, winter and spring equinox, respectively. The percentage TEC deviation with respect to reference values differs substantially from season to season. A strong seasonal anomaly and clear equinoctial asymmetry in TEC response to the storms were observed. Weak and short-lived positive TEC deviations as well as strong and long-lasting negative trends were observed in summer storm during the main and recovery phases respectively over the high and low latitudes whereas in winter storm, the highest positive TEC deviations was recorded during the main phase over the entire latitudes. TEC enhancement dominated all the stations during the autumn (March) equinox storm while TEC depletion was majorly observed during the spring (September) equinox. All these <span class="hlt">variations</span> find their explanations in the thermospheric composition change and circulation. Future work with direct or modeled measurement of atomic Oxygen to molecular Nitrogen ratio (O/N2), large number of storms and other possible factors such as <span class="hlt">variations</span> in storm’s intensity and local time dependence of the storm onset is expected to validate the observations in this study.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009GeoJI.178.1273S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009GeoJI.178.1273S"><span>An electromagnetic sounding experiment in Germany using the vertical gradient of <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> observed in a deep borehole</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schmucker, Ulrich; Spitzer, Klaus; Steveling, Erich</p> <p>2009-09-01</p> <p>We have recorded for 13 d, <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> simultaneously on the Earth's surface and in a borehole at 832 m depth straight below, with a sampling rate of 1 Hz. In addition, geoelectric <span class="hlt">variations</span> were observed at the same site near Bad Königshofen in Frankonia, Germany. The penetrated moderately conductive Triassic sediments lie above highly resistive Permian deposits. A presumably crystalline basement begins at 1500-1900 m depth. The purpose of the experiment is to determine the skin effect of <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> and to derive from it the equivalent to the magnetotelluric (MT) surface impedance, using the vertical gradient (VG) method of electromagnetic (EM) sounding. In this way, we were able to reproduce all four elements of the MT impedance tensor, except for an unexplained but consistent downward shift of VG phases against MT phases by roughly 15° for the two off-diagonal elements. Hence, our tensor evaluation goes beyond the common practice, to express the skin effect by a single VG transfer function in response to a layered structure. The otherwise good agreement of VG and MT results implies that at our test site, the MT impedance tensor is largely distortion-free and that, for example, its pronounced anisotropy should be regarded as a genuine characteristic of the EM response for a laterally non-uniform or possibly anisotropic deep structure. The drilling site lies within the range of a widespread induction anomaly. We have observed the resulting <span class="hlt">variations</span> of the vertical magnetic component at the surface and in the borehole and found them to be identical. The thus established absence of a skin effect for the vertical component allows us to treat the sedimentary layer down to the depth of the borehole instrument as a thin sheet, and the pertinent thin-sheet approximation for EM induction forms the basis of our analysis. We have derived the required estimate of conductance from the skin effect of horizontal components, noting that this estimate</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016E%26PSL.442...80B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016E%26PSL.442...80B"><span>High-intensity <span class="hlt">geomagnetic</span> field 'spike' observed at ca. 3000 cal BP in Texas, USA</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bourne, Mark D.; Feinberg, Joshua M.; Stafford, Thomas W.; Waters, Michael R.; Lundelius, Ernest; Forman, Steven L.</p> <p>2016-05-01</p> <p>By observing the fluctuations in direction and intensity of the Earth's magnetic field through time, we increase our understanding of the fluid motions of the Earth's outer core that sustain the <span class="hlt">geomagnetic</span> field, the geodynamo. Recent archaeomagnetic studies in the Near East have found extremely rapid increases - 'spikes' - in <span class="hlt">geomagnetic</span> field intensity at ca. 3000 yr cal BP. These observations have proved problematic for our current understanding of core-flow. However, until now, these <span class="hlt">geomagnetic</span> spikes had not been observed outside of the Near East, where they have been preserved in metallurgical slag and fired, mud brick walls. We present a new, fully oriented, <span class="hlt">geomagnetic</span> <span class="hlt">secular</span> <span class="hlt">variation</span> and relative palaeointensity (RPI) record for the last 17,000 yr from Hall's Cave, Texas, whose complete, >3.8 m thick sedimentary sequence spans from the present to 16 , 850 ± 110 RC yr BP (Modern to 20,600 cal BP). Within the stable, cool climate of the cave, pedogenic and bioturbation processes are negligible to non-existent, thereby limiting post-depositional physical and geochemical alteration of the magnetic record. The sub-aerial and subterranean setting of the sedimentary sequence in Hall's Cave enabled us to collect oriented palaeomagnetic cubes from a previously excavated stratigraphic section. The palaeomagnetic samples yielded high-quality vectors. An age model for the sequence, determined using 15 AMS 14C-dates on individual bones from microvertebrates, was combined with the palaeomagnetic data to construct a <span class="hlt">secular</span> <span class="hlt">variation</span> record. The record is in broad agreement with predictions by Holocene field models for the site's location. However, starting ca. 3000 yr ago, the RPI data indicate an almost four-fold increase in <span class="hlt">geomagnetic</span> field intensity lasting several hundred years. This record presents well-dated evidence, obtained using conventional techniques, for the existence of a <span class="hlt">geomagnetic</span> intensity spike in North America that is contemporaneous with the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JASS...30..101O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JASS...30..101O"><span><span class="hlt">Variation</span> of Solar, Interplanetary and <span class="hlt">Geomagnetic</span> Parameters during Solar Cycles 21-24</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Oh, Suyeon; Kim, Bogyeong</p> <p>2013-06-01</p> <p>The length of solar cycle 23 has been prolonged up to about 13 years. Many studies have speculated that the solar cycle 23/24 minimum will indicate the onset of a grand minimum of solar activity, such as the Maunder Minimum. We check the trends of solar (sunspot number, solar magnetic fields, total solar irradiance, solar radio flux, and frequency of solar X-ray flare), interplanetary (interplanetary magnetic field, solar wind and galactic cosmic ray intensity), and <span class="hlt">geomagnetic</span> (Ap index) parameters (SIG parameters) during solar cycles 21-24. Most SIG parameters during the period of the solar cycle 23/24 minimum have remarkably low values. Since the 1970s, the space environment has been monitored by ground observatories and satellites. Such prevalently low values of SIG parameters have never been seen. We suggest that these unprecedented conditions of SIG parameters originate from the weakened solar magnetic fields. Meanwhile, the deep 23/24 solar cycle minimum might be the portent of a grand minimum in which the global mean temperature of the lower atmosphere is as low as in the period of Dalton or Maunder minimum.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016FrEaS...4...71B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016FrEaS...4...71B"><span>Investigating dynamical complexity of <span class="hlt">geomagnetic</span> jerks using various entropy measures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Balasis, Georgios; Potirakis, Stelios; Mandea, Mioara</p> <p>2016-06-01</p> <p>Recently, many novel concepts originated in dynamical systems or information theory have been developed, partly motivated by specific research questions linked to geosciences, and found a variety of different applications. This continuously extending toolbox of nonlinear time series analysis highlights the importance of the dynamical complexity to understand the behavior of the complex Earth's system and its components. Here, we propose to apply such new approaches, mainly a series of entropy methods to the time series of the <span class="hlt">geomagnetic</span> field. Two datasets provided by Chambon la Foret (France) and Niemegk (Germany) observatories are considered for analysis to detect dynamical complexity changes associated with <span class="hlt">geomagnetic</span> jerks, the abrupt changes in the second temporal derivative of the Earth's magnetic field. The results clearly demonstrate the ability of Shannon and Tsallis entropies as well as Fisher information to detect events in a regional manner having identified complexities lower than the background in time intervals when <span class="hlt">geomagnetic</span> jerks have already been reported in the literature. Additionally, these information measures are directly applicable to the original data without having to derive the <span class="hlt">secular</span> <span class="hlt">variation</span> or acceleration from the observatory monthly means. The strength of the proposed analysis to reveal dynamical complexity features associated with <span class="hlt">geomagnetic</span> jerks can be utilized for analyzing not only ground measurements, but also satellite data, as those provided by the current magnetic field mission of Swarm.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20630526','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20630526"><span>Growth <span class="hlt">variation</span>, final height and <span class="hlt">secular</span> trend. Proceedings of the 17th Aschauer Soiree, 7th November 2009.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hermanussen, M; Godina, E; Rühli, F J; Blaha, P; Boldsen, J L; van Buuren, S; MacIntyre, M; Assmann, C; Ghosh, A; de Stefano, G F; Sonkin, V D; Tresguerres, J A F; Meigen, C; Scheffler, C; Geiger, C; Lieberman, L S</p> <p>2010-08-01</p> <p>Growth and body height have always been topics interesting to the public. In particular, the stupendous increase of some 15-19cm in final adult height during the last 150 years in most European countries (the "<span class="hlt">secular</span> trend"), the concomitant changes in body and head proportions, the tendency towards early onset of sexual maturation, the changes in the age when final height is being reached, and the very recent trend in body mass index, have generated much scientific literature. The marked plasticity of growth in height and weight over time causes problems. Child growth references differ between nations, they tend to quickly become out of date, and raise a number of questions regarding fitting methods, effects caused by selective drop-out, etc. New findings contradict common beliefs about the primary importance of nutritional and health related factors for <span class="hlt">secular</span> changes in growth. There appears to be a broad age span from mid-childhood to early adolescence that is characterised by a peculiar insusceptibility. Environmental factors that are known to influence growth during this age span appear to have only little or no impact on final height. Major re-arrangements in height occur at an age when puberty has almost been completed and final height has almost been reached, implying that factors, which drive the <span class="hlt">secular</span> trend in height, are limited to early childhood and late adolescence.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JGRB..120.8012P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JGRB..120.8012P"><span>Time-correlated patterns from spherical harmonic expansions: Application to <span class="hlt">geomagnetism</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pais, M. A.; Alberto, P.; Pinheiro, F. J. G.</p> <p>2015-12-01</p> <p>We use empirical orthogonal function analysis (EOFA) directly on sets of Schmidt spherical harmonic (SH) coefficients modeling the internal <span class="hlt">geomagnetic</span> field or its time derivatives at different epochs. We show how to properly use the method such that the application of EOFA to either spatial or spectral domains leads to the same results, bypassing the need to work on snapshots of field charts synthesized from SHs. In case a spatial grid is required, we point out which is the best grid to use. We apply the method to the CM4 <span class="hlt">geomagnetic</span> field model to illustrate the differences in EOFA modes obtained with and without corrections. Once the corrected main modes of <span class="hlt">secular</span> acceleration (SA) have been singled out, we retrieve previous results showing that the 1969, 1978, and 1991 <span class="hlt">geomagnetic</span> field acceleration jumps have the same spatial pattern. A new finding in this study is that the same spatial pattern is present in principal modes of <span class="hlt">secular</span> <span class="hlt">variation</span> which, once inverted, may provide the flow responsible for the jerk sequence. Another finding is the unveiling of a different spatial structure common to a second group of jerks with SA pulses around 1985 and 1996, displaying a localization very similar to SA pulses identified in 2006 and 2009 using recent satellite data. Finally, if properly handled, the EOFA can be directly applied to a grid of data values of the <span class="hlt">geomagnetic</span> field in order to produce SH models of decorrelated modes which may help to separate different sources of the field.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA......210B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA......210B"><span>Restoration project of <span class="hlt">geomagnetic</span> survey in Latvia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Burlakovs, J.; Lembere, I.</p> <p>2003-04-01</p> <p>THE RESTORATION PROJECT OF <span class="hlt">GEOMAGNETIC</span> SURVEY IN LATVIA J. Burlakovs, I. Lembere State Land Service of Latvia, Geodesy Board juris.burlakovs@gp.vzd.gov.lv / Fax: +371-7612736 The aim of <span class="hlt">geomagnetic</span> survey measurements is to study the <span class="hlt">geomagnetic</span> field at global, regional as well as local scales. To determine <span class="hlt">secular</span> changes of the <span class="hlt">geomagnetic</span> field it is very important to do a lot of regular field work. Recalculation and comparison of measured data for corrections must be made using the observatory or magnetic station data collected nearby the investigated area in the real-time. Field <span class="hlt">geomagnetic</span> survey measurements in Latvia have not been made since 1991. The State Land Service of Latvia, the Geodesy Board plans to restart such kind of measurements in Latvia. The repeat station network must be renewed, regular magnetic declination, inclination and total field intensity data must be gathered, compared with the observatory data and <span class="hlt">secular</span> changes of the <span class="hlt">geomagnetic</span> field discovered. It is also possible to do regional correlations for data to determine future trends of the <span class="hlt">geomagnetic</span> field changes. The detection of <span class="hlt">geomagnetic</span> anomalies and the reason of the existence of those at particular territories could be made. Such kind of measurements demands the highest accuracy and therefore is necessary to cooperate with <span class="hlt">geomagnetic</span> research network groups in neighbouring areas - Estonia, Finland and Poland, where permanent magnetic stations are situated. One permanent magnetic station also could be established in Latvia to do permanent recordings of <span class="hlt">geomagnetic</span> field components, which give the possibility to do regional corrections for separate measurement recordings in the field. <span class="hlt">Geomagnetic</span> field studies are important for cartography, navigational and military needs, also it is possible to use this information together with geological and geophysical data to create and specify the geological model for the territory. In future Latvia must participate within the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28163989','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28163989"><span>Authigenic (10)Be/(9)Be ratio signatures of the cosmogenic nuclide production linked to <span class="hlt">geomagnetic</span> dipole moment <span class="hlt">variation</span> since the Brunhes/Matuyama boundary.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Simon, Quentin; Thouveny, Nicolas; Bourlès, Didier L; Valet, Jean-Pierre; Bassinot, Franck; Ménabréaz, Lucie; Guillou, Valéry; Choy, Sandrine; Beaufort, Luc</p> <p>2016-11-01</p> <p><span class="hlt">Geomagnetic</span> dipole moment <span class="hlt">variations</span> associated with polarity reversals and excursions are expressed by large changes of the cosmogenic nuclide beryllium-10 ((10)Be) production rates. Authigenic (10)Be/(9)Be ratios (proxy of atmospheric (10)Be production) from oceanic cores therefore complete the classical information derived from relative paleointensity (RPI) records. This study presents new authigenic (10)Be/(9)Be ratio results obtained from cores MD05-2920 and MD05-2930 collected in the west equatorial Pacific Ocean. Be ratios from cores MD05-2920, MD05-2930 and MD90-0961 have been stacked and averaged. <span class="hlt">Variations</span> of the authigenic (10)Be/(9)Be ratio are analyzed and compared with the <span class="hlt">geomagnetic</span> dipole low series reported from global RPI stacks. The largest (10)Be overproduction episodes are related to dipole field collapses (below a threshold of 2 × 10(22) Am(2)) associated with the Brunhes/Matuyama reversal, the Laschamp (41 ka) excursion, and the Iceland Basin event (190 ka). Other significant (10)Be production peaks are correlated to <span class="hlt">geomagnetic</span> excursions reported in literature. The record was then calibrated by using absolute dipole moment values drawn from the Geomagia and Pint paleointensity value databases. The (10)Be-derived <span class="hlt">geomagnetic</span> dipole moment record, independent from sedimentary paleomagnetic data, covers the Brunhes-Matuyama transition and the whole Brunhes Chron. It provides new and complementary data on the amplitude and timing of millennial-scale <span class="hlt">geomagnetic</span> dipole moment <span class="hlt">variations</span> and particularly on dipole moment collapses triggering polarity instabilities.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5256419','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5256419"><span>Authigenic 10Be/9Be ratio signatures of the cosmogenic nuclide production linked to <span class="hlt">geomagnetic</span> dipole moment <span class="hlt">variation</span> since the Brunhes/Matuyama boundary</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Thouveny, Nicolas; Bourlès, Didier L.; Valet, Jean‐Pierre; Bassinot, Franck; Ménabréaz, Lucie; Guillou, Valéry; Choy, Sandrine; Beaufort, Luc</p> <p>2016-01-01</p> <p>Abstract <span class="hlt">Geomagnetic</span> dipole moment <span class="hlt">variations</span> associated with polarity reversals and excursions are expressed by large changes of the cosmogenic nuclide beryllium‐10 (10Be) production rates. Authigenic 10Be/9Be ratios (proxy of atmospheric 10Be production) from oceanic cores therefore complete the classical information derived from relative paleointensity (RPI) records. This study presents new authigenic 10Be/9Be ratio results obtained from cores MD05‐2920 and MD05‐2930 collected in the west equatorial Pacific Ocean. Be ratios from cores MD05‐2920, MD05‐2930 and MD90‐0961 have been stacked and averaged. <span class="hlt">Variations</span> of the authigenic 10Be/9Be ratio are analyzed and compared with the <span class="hlt">geomagnetic</span> dipole low series reported from global RPI stacks. The largest 10Be overproduction episodes are related to dipole field collapses (below a threshold of 2 × 1022 Am2) associated with the Brunhes/Matuyama reversal, the Laschamp (41 ka) excursion, and the Iceland Basin event (190 ka). Other significant 10Be production peaks are correlated to <span class="hlt">geomagnetic</span> excursions reported in literature. The record was then calibrated by using absolute dipole moment values drawn from the Geomagia and Pint paleointensity value databases. The 10Be‐derived <span class="hlt">geomagnetic</span> dipole moment record, independent from sedimentary paleomagnetic data, covers the Brunhes‐Matuyama transition and the whole Brunhes Chron. It provides new and complementary data on the amplitude and timing of millennial‐scale <span class="hlt">geomagnetic</span> dipole moment <span class="hlt">variations</span> and particularly on dipole moment collapses triggering polarity instabilities. PMID:28163989</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..12.7385B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..12.7385B"><span>Explanation of observable <span class="hlt">secular</span> <span class="hlt">variations</span> of gravity and alternative methods of determination of drift of the center of mass of the Earth</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Barkin, Yury</p> <p>2010-05-01</p> <p>The summary. On the basis of geodynamic model of the forced relative displacement of the centers of mass of the core and the mantle of the Earth the <span class="hlt">secular</span> <span class="hlt">variations</span> of a gravity and heights of some gravimetry stations on a surface of the Earth have ben studied. At the account of <span class="hlt">secular</span> drift of the center of mass of the Earth which on our geodynamic model is caused by the unidirectional drift of the core of the Earth relatively to the mantle, the full explanation is given to observable <span class="hlt">secular</span> <span class="hlt">variations</span> of a gravity at stations Ny-Alesund (Norway), Churchill (Canada), Medicine (Italy), Sayowa (Antarctica), Strastburg (France), Membach (Belgium), Wuhan (China) and Metsahovi (Finland). Two new methods of determination of <span class="hlt">secular</span> drift of the center of mass of the Earth, alternative to classical method of a space geodesy are offered: 1) on the basis of gravimetry data about <span class="hlt">secular</span> trends of a gravity at the stations located on all basic regions of the Earth; 2) on the basis of the comparative analysis of altimetry and coastal data about <span class="hlt">secular</span> changes of sea level also in basic regions of ocean. 1. <span class="hlt">Secular</span> drift of the center of mass of the core and the center of mass of the Earth. A <span class="hlt">secular</span> drift of the center of mass of the Earth to the North relatively to special center O on an axis of rotation of the Earth for which the coefficient of third zonal harmonic J3' = 0, has been predicted in the author work [1]. A drift in a direction to a geographical point (pole P) 70°0 N and 104°3 E has been established for the first time theoretically - as a result of the analysis of the global directed redistribution of masses of the Earth, explaining the observed <span class="hlt">secular</span> drift of the pole of an axis of rotation of the Earth and not tidal acceleration of its axial rotation [2]. In [1] velocity of drift it has been estimated in 1-2 cm/yr. For specified center O the figure of a planet is as though deprived of pure-shaped form (J3' = 0). And in this sense the point O can be</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ngmdb.usgs.gov/Prodesc/proddesc_81154.htm','USGSPUBS'); return false;" href="http://ngmdb.usgs.gov/Prodesc/proddesc_81154.htm"><span>The International <span class="hlt">Geomagnetic</span> Reference Field, 2005</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Rukstales, Kenneth S.; Love, Jeffrey J.</p> <p>2007-01-01</p> <p>This is a set of five world charts showing the declination, inclination, horizontal intensity, vertical component, and total intensity of the Earth's magnetic field at mean sea level at the beginning of 2005. The charts are based on the International <span class="hlt">Geomagnetic</span> Reference Field (IGRF) main model for 2005 and <span class="hlt">secular</span> change model for 2005-2010. The IGRF is referenced to the World Geodetic System 1984 ellipsoid. Additional information about the USGS <span class="hlt">geomagnetism</span> program is available at: http://geomag.usgs.gov/</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGRA..121.7183P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGRA..121.7183P"><span><span class="hlt">Geomagnetic</span> control of the midlatitude foF1 and foF2 long-term <span class="hlt">variations</span>: Recent observations in Europe</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Perrone, L.; Mikhailov, A. V.</p> <p>2016-07-01</p> <p>A new very simple method, allowing an easy control, has been applied to extract long-term (11 year) δfoF2 11y and δfoF1 11y <span class="hlt">variations</span> from June foF2 and foF1 monthly median observations at European Slough/Chilton and Juliusruh stations, including recent data until 2015. The aim of the analysis was to check the validity of the <span class="hlt">geomagnetic</span> control of foF2 and foF1 long-term <span class="hlt">variations</span> in the 21st century with the main accent on the period including the last deep solar minimum in 2008-2009. The <span class="hlt">geomagnetic</span> control was shown to be valid. Moreover, the dependence on <span class="hlt">geomagnetic</span> activity has become more pronounced and explicit after 1990. A simultaneous analysis of foF2 and foF1 long-term <span class="hlt">variations</span> improves the reliability of the obtained conclusions and helps understand the physical mechanism of these <span class="hlt">variations</span>. Due to common neutral composition and the similarity of photochemical processes noontime foF2 and foF1 demonstrate similar long-term <span class="hlt">variations</span>: the correlation coefficient between δfoF2 11y and δfoF1 11y is 0.834 at Slough/Chilton and 0.884 at Juliusruh with the 99% confidence level according to Fisher's F criterion. Midnight long-term δfoF2 11y <span class="hlt">variations</span> also manifest a pronounced dependence on Ap11y which may be interpreted in the framework of the <span class="hlt">geomagnetic</span> control concept.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFMGP51B0761Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFMGP51B0761Y"><span><span class="hlt">Geomagnetic</span> field <span class="hlt">variations</span> during the last 400 kyr in the western equatorial Pacific: Paleointensity-inclination correlation revisited</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yamazaki, T.; Kanamatsu, T.; Mizuno, S.; Hokanishi, N.; Gaffar, E. Z.</p> <p>2008-12-01</p> <p>A paleomagnetic study was conducted on four piston cores newly obtained from the West Caroline Basin in the western equatorial Pacific in order to investigate <span class="hlt">variations</span> in paleointensity and inclination during the last 400 kyr. An inclination-intensity correlation was previously reported in this region using giant piston cores, but the quality of the paleomagnetic data of the younger end, the last ca. 300 kyr, was needed to be checked because the upper part of the giant piston cores could suffer from perturbation by oversampling. Age control is based on the oxygen-isotope ratios for one core and inter-core correlation using relative paleointensity for other cores. The mean inclinations of the four cores show negative inclination anomalies ranging from -5.2 to -11.2 degree. The western equatorial Pacific is documented as a region of a large negative inclination anomalies, and the observed values are comparable to those expected from the time-averaged field (TAF) models [Johnson and Constable, 1997; Hatakeyama and Kono, 2002]. Stacked curves of paleointensity and inclination were constructed from the four cores. It was confirmed that <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> on the order of 10 to 100 kyrs occur in inclination as well as paleointensity. A cross-correlation analysis showed that significant in-phase correlation occurs between intensity and inclination for periods longer than about 25 kyr, and power spectra of both paleointensity and inclination <span class="hlt">variations</span> have peaks at ~100 kyr periods. The regional paleointensity stack with higher resolution than the Sint-800 stack [Guyodo and Valet, 1999] should be useful for paleointensity-assisted chronostratigraphy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008Ge%26Ae..48..408N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008Ge%26Ae..48..408N"><span><span class="hlt">Variations</span> in the <span class="hlt">geomagnetic</span> field strength in the 5th 3rd centuries BC in the eastern Mediterranean (according to narrowly dated ceramics)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nachasova, I. E.; Burakov, K. S.; Il'Ina, T. A.</p> <p>2008-06-01</p> <p>The magnetization of ceramics from the eastern Mediterranean dated within a short period (mostly shorter than ±20 years) has been studied, which made it possible to specify the <span class="hlt">geomagnetic</span> field <span class="hlt">variations</span> on the time interval 5th 3rd centuries BC. The 11-year time series of the <span class="hlt">geomagnetic</span> field strength values has been constructed. The field strength changes have been considered, which indicated that the centennial <span class="hlt">variation</span> with a characteristic time of ˜130 years (according to the obtained data) is observed on this time interval as well as during the last two millennia. The ceramic material from the Mayskaya Gora archeological site (Taman), the preparation succession of which was established based on the shape of pottery but the problem of absolute dating was not solved, has been dated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014IzAOP..50..736Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014IzAOP..50..736Z"><span>Synchronization of human heart-rate indicators and <span class="hlt">geomagnetic</span> field <span class="hlt">variations</span> in the frequency range of 0.5-3.0 mHz</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zenchenko, T. A.; Medvedeva, A. A.; Khorseva, N. I.; Breus, T. K.</p> <p>2014-12-01</p> <p>Fifty-seven experiments have been conducted to monitor the minute indicators of heart rate at rest in 38 practically healthy individuals (9 men and 29 women) from 18 to 58 years old. The duration of each observation period is 60 to 200 min. We have measured the heart rate and the minute-averaged cardiac section durations reflecting the passage of electrical excitation over different parts of myocardium. A comparison of the dynamics of minute values of these physiological parameters with <span class="hlt">variations</span> of the X and Z components of the <span class="hlt">geomagnetic</span> field has shown that two-thirds of experiments revealed the synchronization of oscillations in the heart rate and <span class="hlt">variations</span> in the components of the <span class="hlt">geomagnetic</span> field. We have revealed both the matching of the observed periods of oscillations ranging between 4 and 30 min and an approximate synchronicity in the times of their appearance and disappearance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/7061389','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/7061389"><span>Structure in the <span class="hlt">secular</span> <span class="hlt">variation</span> of seawater sup 87 Sr/ sup 86 Sr for the Ivorian/Chadian (Osagean, Lower Carboniferous)</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Douthit, T.L.; Hanson, G.N.; Meyers, W.J. )</p> <p>1990-05-01</p> <p>The <span class="hlt">secular</span> <span class="hlt">variations</span> of {sup 87}Sr/{sup 86}Sr in seawater for the Ivorian/Chadian, (equivalent to the Osagean, Lower Carboniferous) were determined through detailed analysis of well-preserved marine cements from the Waulsortian facies of Ireland. The results indicate that marine cements have utility in characterizing marine paleochemistries. Marine cements were judged pristine on the basis of nonluminescent character and stable isotopic composition comparable to previous estimates of Mississippian marine calcite. Analysis of the marine cements yielded {sup 87}Sr/{sup 86}Sr ratios lower than previously reported values for the Ivorian/Chadian. Error resulting from chronostratigraphic correlation between different geographic areas was avoided by restricting the sample set to a single 1,406-ft-long core (core P-1). The P-1 core is estimated to represent a minimum of 8.7 m.y. of continuous Waulsortian Limestone deposition. The {sup 87}Sr/{sup 86}Sr ratios of 11 nonluminescent cements document a non-monotonic <span class="hlt">variation</span> in seawater {sup 87}Sr/{sup 86}Sr along the length of the core. {sup 87}Sr/{sup 86}Sr ranges from a high of 0.707908 in the early Ivorian to a low of about 0.707650 in the late Ivorian and middle Chadian with an early Chadian maximum at 0.707800 (all data are adjusted to a value of 0.710140 for SRM 987). The indicated maximum rate of change in seawater {sup 87}Sr/{sup 86}Sr is {minus}0.00011/Ma, comparable in magnitude to Tertiary values. The <span class="hlt">secular</span> <span class="hlt">variation</span> curve of seawater {sup 87}Sr/{sup 86}Sr for the Ivorian/Chadian has previously been thought to decrease monotonically with decreasing age. These data suggest that the seawater {sup 87}Sr/{sup 86}Sr <span class="hlt">variation</span> over this interval may be sinusoidal in nature and emphasize the importance of well-characterized intraformational isotopic base lines.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMGP41B..02L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMGP41B..02L"><span>High-resolution paleomagnetic <span class="hlt">secular</span> <span class="hlt">variations</span> and relative paleointensity since the Late Pleistocene in southern South America</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lise-Pronovost, A.; St-Onge, G.; Gogorza, C. G.; Haberzettl, T.; Kliem, P.; Francus, P.; Zolitschka, B.</p> <p>2012-12-01</p> <p>High-resolution paleomagnetic records from the Southern Hemisphere are largely under-represented relative to the Northern Hemisphere. Here we present a high-resolution u-channel-based full vector (inclination, declination and relative paleointensity) paleomagnetic reconstruction since 51.2 ka cal BP from the maar lake Laguna Potrok Aike in Southern Patagonia (52°S, 70°W) in order to 1) document the variability of the <span class="hlt">geomagnetic</span> field in an area of the world where observations are scarce and 2) compare this new record with other high-resolution records and stacks from around the globe in order to assess the <span class="hlt">geomagnetic</span> field behavior in the Southern Hemisphere. The long sedimentary sequence was recovered in 2008 in the framework of the International Continental scientific Drilling Program (ICDP) Potrok Aike maar lake Sediment Archive Drilling prOject (PASADO) and the radiocarbon-based chronology indicates an average sedimentation rate of 89 cm/ka for the last 51.2 ka. Detailed rock-magnetic analyses reveal that the magnetic assemblage is dominated by pseudo single domain magnetite, which is optimal for paleomagnetic reconstructions, and that the sediment fulfills the common criteria for high-quality paleomagnetic archives. The new high-resolution record from Laguna Potrok Aike is compared with the available records from the mid- to high-latitude of the Southern Hemisphere, as well as with reference records and stacks from the Northern Hemisphere, revealing consistent millennial-scale variability, the Laschamp and possibly the Mono Lake <span class="hlt">geomagnetic</span> excursions. Interestingly, the regional and global comparisons reveal a directional swing and sharp minimum in intensity at 46 ka cal BP which appears to be mainly observed in the Southern Hemisphere and could likely be used as a new chronostratigraphic marker. In addition, a direction swing at 20 ka cal BP could be associated with the Hilina Pali excursion, recorded with details in Hawaiian lava flows. Finally, these</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMGP34A..04I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMGP34A..04I"><span>Time scale of FAC <span class="hlt">variations</span> estimated by SWARM and a comparison with ground based <span class="hlt">geomagnetic</span> and micro-barometric observations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Iyemori, T.; Nakanishi, K.; Aoyama, T.; Luhr, H.; Odagi, Y.; Yokoyama, Y.; Iguchi, M.; Sugitani, S.; Hashiguchi, H.; Utsugi, M.; Ono, T.; Sanoo, Y.</p> <p>2015-12-01</p> <p>The low altitude magnetic satellites such as Oersted, CHAMP or SWARM observed small scale magnetic fluctuations having period about 10 to 30 sec along their orbits in middle or low latitudes. The amplitude is usually less than a few nT and they were observed almost always on the dayside. Most of them are interpreted as the spatial structure of small scale FACs probably generated by atmospheric gravity waves (Nakanishi et al., 2014). From a statistical analysis of correlation coefficients between a pair of the SWARM satellites, Iyemori et al. (2015) estimated the temporal scale of FAC <span class="hlt">variation</span> to be roughly about 200 secs for meridional magnetic components and about 340 secs for longitudinal, i.e., east-west component. Based on a spectral analysis of ground <span class="hlt">geomagnetic</span> and micro-barometric observations, we found that the spectral peaks with similar periods, i.e., 200sec or 320-350sec tend to appear statistically. This tendency supports the idea that the source of the FACs is mainly the acoustic mode of gravity waves. We discuss the characteristics of the power spectra, in particular, those of micro-barometric observations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016cosp...41E.979K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016cosp...41E.979K"><span>The <span class="hlt">variations</span> of ionosphere critical frequency of E layer over the equatorial <span class="hlt">geomagnetic</span> region in Southeast Asia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kenpankho, Prasert; Ishii, Mamoru; Supnithi, Pornchai</p> <p>2016-07-01</p> <p>We investigate the values of the critical frequency of the ionospheric E layer, foE, obtained at Chumphon ionospheric observatory station, Thailand. For a declining phase of the solar cycle 23 during the year 2005-2008 and an inclining phase of the solar cycle 24 during the year 2009-2013, the foE data have been used to investigate the foE <span class="hlt">variations</span> over the equatorial <span class="hlt">geomagnetic</span> region in Southeast Asia. A comparison between the observation data and International Reference Ionosphere (IRI) 2012 model has also been investigated and studied. The results show that the foE obtained from IRI 2012 model underestimates foE from Chumphon station especially during the period of 7-11 am and after 6 pm for each day and all seasons. As the results combining with the previous investigations, we suggest that the underestimation of ionospheric foE by IRI 2012 model is helpful for the correction and improvement of IRI model in an equatorial Asia region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19800042198&hterms=fallout&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dfallout','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19800042198&hterms=fallout&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dfallout"><span>Seasonal and <span class="hlt">secular</span> <span class="hlt">variation</span> of wind streaks on Mars - An analysis of Mariner 9 and Viking data</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Thomas, P.; Veverka, J.</p> <p>1979-01-01</p> <p>Viking orbiter observations extending over 1 Martian year have been used in conjunction with Mariner 9 data obtained in 1971-1972 to study the seasonal and <span class="hlt">secular</span> behavior of several kinds of wind streaks. Most bright streaks, inferred to consist of dust storm fallout in the lees of obstacles, have changed very little in form or orientation over a period of 3 Martian years. Some are extremely stable and have experienced no effective eolian action over the 3 years. A few bright streaks changed rapidly during global dust storms; these streaks are located in areas subject to both global and topographic winds. Viking images have shown for the first time that dark, erosional streaks are stable from the time of their formation after major dust storms until the onset of the next episode of major storm activity. Available evidence shows that the large, dark streaks in Oxia Palus consist of material deflated from dune fields within the associated craters. These streaks lengthened <span class="hlt">secularly</span> since 1972; changes appear to occur episodically during southern summer. The great majority of all streaks reflect winds during the period from late southern spring to early southern fall, although some changes occur throughout the year. The global pattern of wind streaks and the variability of the streaks thus depend strongly upon the current south-north asymmetry of seasons on Mars.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009E%26PSL.284..132G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009E%26PSL.284..132G"><span>Evidence for rapid <span class="hlt">geomagnetic</span> field intensity <span class="hlt">variations</span> in Western Europe over the past 800 years from new French archeointensity data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Genevey, Agnès; Gallet, Yves; Rosen, Jean; Le Goff, Maxime</p> <p>2009-06-01</p> <p>The number of reliable archeointensity determinations obtained from Western Europe for the past millennium remains limited. Moreover, the large scatter between different datasets available is puzzling. The present study analyzed 31 new groups of baked clay (ceramic or brick) fragments sampled in France (29 groups) and in Belgium (2 groups). These groups contain several fragments collected from different artefacts and are precisely dated principally from historical constraints between the XIIIth and the XIXth centuries. Additionally, we re-evaluated 14 intensity values that we previously obtained from the same time period. The fragments were analyzed using two different thermal methods: (1) the "in field-zero field" (IZ) or the IZZI version of the classical Thellier and Thellier method and (2) the Triaxe protocol that involves high-temperature magnetization measurements. Data were corrected for the anisotropy of thermoremanent magnetization (TRM) and the dependence of TRM acquisition on the cooling rate was taken into account in the different protocols. Archeointensity data obtained on twin specimens sampled from the same fragment and using both experimental techniques generally show a good agreement (i.e. within 5%) at the fragment and at the site level. All retained site-level averaged intensity results (43 of 45 groups) have standard deviations of less than 5 µT. Furthermore, groups of approximately the same age have very consistent archeointensity. Altogether, the data presented herein recover a detailed and smoothed <span class="hlt">geomagnetic</span> field intensity <span class="hlt">variation</span> curve characterized by two peaks in intensity, the first during the second half of the XIVth century and the second around AD 1600, followed by a significant decreasing trend in intensity during most the XVIIth and XVIIIth centuries. This evolution does not satisfactorily fit with the expected intensity values for France derived from <span class="hlt">geomagnetic</span> field models relying on a different evolution of the axial dipole</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1912314H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1912314H"><span><span class="hlt">Geomagnetic</span> Diurnal <span class="hlt">Variations</span> - Analysis in Space and Time Associated with the 2011 off the Pacific Coast of Tohoku Earthquake (Mw9.0)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hattori, Katsumi; Han, Peng</p> <p>2017-04-01</p> <p>Recent studies have reported unusual behaviors of <span class="hlt">geomagnetic</span> diurnal <span class="hlt">variation</span> (GDV) in the vertical component prior to the 2011 off the Pacific coast of Tohoku earthquake (Mw 9.0). To make a better understanding of this phenomenon, time-spatial analysis of GDV has been applied in this study. <span class="hlt">Geomagnetic</span> data of long term observations at 17 stations in Japan have been analyzed using the same method in Han et al. 2015. Ratios of diurnal <span class="hlt">variation</span> range between the target station and the reference station KAK have been computed. After removing seasonal <span class="hlt">variations</span> revealed by wavelet transform analysis, the 15-day mean values of the ratios in the vertical component shows a clear anomaly exceeding the statistical threshold about 2 months before the mega event in both ESA and MIZ stations in the Tohoku Region. Similar results could not be found in other regions of Japan. Spatial distributions of the ratios show a good agreement between the location of the anomalies and the epicenter of Mw 9.0 earthquake. These time-spatial results seem to be consistent with independent results obtained from other observations such as radon density, seismicity, and GPS displacements, which suggest the <span class="hlt">geomagnetic</span> data might be useful in earthquake monitoring and disaster mitigation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013QSRv...71...91P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013QSRv...71...91P"><span>High-resolution paleomagnetic <span class="hlt">secular</span> <span class="hlt">variations</span> and relative paleointensity since the Late Pleistocene in southern South America</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>PASADO Science Team Lisé-Pronovost, Agathe; St-Onge, Guillaume; Gogorza, Claudia; Haberzettl, Torsten; Preda, Michel; Kliem, Pierre; Francus, Pierre; Zolitschka, Bernd</p> <p>2013-07-01</p> <p>Paleomagnetic inclination, declination and relative paleointensity were reconstructed from the sediments of Laguna Potrok Aike in the framework of the International Continental scientific Drilling Program (ICDP) Potrok Aike maar lake Sediment Archive Drilling prOject (PASADO). Here we present the u-channel-based full vector paleomagnetic field reconstruction since 51.2 ka cal BP. The relative paleointensity proxy (RPI) was built by normalising the natural remanent magnetisation with the anhysteretic remanent magnetisation using the average ratio at 4 demagnetisation steps part of the ChRM interval (NRM/ARM10-40 mT). A grain size influence on the RPI was removed using a correction based on the linear relationship between the RPI and the median destructive field of the natural remanent magnetisation (MDFNRM). The new record is compared with other lacustrine and marine records and stacks from the mid- to high-latitudes of the Southern Hemisphere, revealing consistent millennial-scale variability, the identification of the Laschamp and possibly the Mono Lake <span class="hlt">geomagnetic</span> excursions, and a direction swing possibly associated to the Hilina Pali excursion at 20 ka cal BP. Nonetheless, a global-scale comparison with other high-resolution records located on the opposite side of the Earth and with various dipole field references hint at a different behaviour of the <span class="hlt">geomagnetic</span> field around southern South America at 46 ka cal BP.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMGP41B..01S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMGP41B..01S"><span>Holocene <span class="hlt">Geomagnetic</span> Change in the Northern North Atlantic</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stoner, J. S.; Channell, J. E.; Mazaud, A.; Xuan, C.; Strano, S. E.; Olafsdottir, S.; Jennings, A. E.</p> <p>2012-12-01</p> <p>High-resolution and well-dated paleomagnetic records constrain the <span class="hlt">geomagnetism</span> of the Holocene North Atlantic. These records comprise ultra-high resolution sediment records from lakes (Haukadalsvatn, Iceland) and from continental margins (MD99-2269, N Iceland shelf; MD99-2322, E. Greenland), and from high accumulating (>50 cm/kyr) deep-sea sediments from the Eirik Drift, Labrador Sea (IODP Site U1305). Similarities among these directional paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> (PSV) records from very different environments imply that the records provide robust reconstructions of the paleo-<span class="hlt">geomagnetic</span> field. Assuming that the age of magnetization is best defined by PSV in the highest sedimentation rate (>200 cm /kyr) records, allows us to place northern North Atlantic PSV and relative paleointensity (RPI) into a regional context. Northern North Atlantic PSV and RPI are more consistent with European than North American records, and the evolution of virtual <span class="hlt">geomagnetic</span> poles (VGP) are temporally and longitudinally similar too global reconstructions, though with much larger latitudinal <span class="hlt">variations</span>. The largest deviation from a geocentric axial dipole, in contrast to the usual assumption, is observed during times of highest field intensities in the North Atlantic and globally, while the highest rates of VGP change are associated with North Atlantic field intensity lows. These observations are consistent with the hypothesis that PSV results from temporal oscillations of flux concentrations (lobes) at a few recurrent locations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EP%26S...69..112F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EP%26S...69..112F"><span><span class="hlt">Geomagnetically</span> conjugate observations of ionospheric and thermospheric <span class="hlt">variations</span> accompanied by a midnight brightness wave at low latitudes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fukushima, D.; Shiokawa, K.; Otsuka, Y.; Kubota, M.; Yokoyama, T.; Nishioka, M.; Komonjinda, S.; Yatini, C. Y.</p> <p>2017-08-01</p> <p>We conducted <span class="hlt">geomagnetically</span> conjugate observations of 630-nm airglow for a midnight brightness wave (MBW) at Kototabang, Indonesia [<span class="hlt">geomagnetic</span> latitude (MLAT): 10.0°S], and Chiang Mai, Thailand (MLAT: 8.9°N), which are <span class="hlt">geomagnetically</span> conjugate points at low latitudes. An airglow enhancement that was considered to be an MBW was observed in OI (630-nm) airglow images at Kototabang around local midnight from 2240 to 2430 LT on February 7, 2011. This MBW propagated south-southwestward, which is <span class="hlt">geomagnetically</span> poleward, at a velocity of 290 m/s. However, a similar wave was not observed in the 630-nm airglow images at Chiang Mai. This is the first evidence of an MBW that does not have <span class="hlt">geomagnetic</span> conjugacy, which also implies generation of MBW only in one side of the hemisphere from the equator. We simultaneously observed thermospheric neutral winds observed by a co-located Fabry-Perot interferometer at Kototabang. The observed meridional winds turned from northward (<span class="hlt">geomagnetically</span> equatorward) to southward (<span class="hlt">geomagnetically</span> poleward) just before the wave was observed. This indicates that the observed MBW was generated by the poleward winds which push ionospheric plasma down along <span class="hlt">geomagnetic</span> field lines, thereby increasing the 630-nm airglow intensity. The bottomside ionospheric heights observed by ionosondes rapidly decreased at Kototabang and slightly increased at Chiang Mai. We suggest that the polarization electric field inside the observed MBW is projected to the northern hemisphere, causing the small height increase observed at Chiang Mai. This implies that electromagnetic coupling between hemispheres can occur even though the original disturbance is caused purely by the neutral wind.[Figure not available: see fulltext.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70016888','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70016888"><span>Evaluation of models proposed for the 1991 revision of the International <span class="hlt">Geomagnetic</span> Reference Field</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Peddie, N.W.</p> <p>1992-01-01</p> <p>The 1991 revision of the International <span class="hlt">Geomagnetic</span> Reference Field (IGRF) comprises a definitive main-field model for 1985.0, a main-field model for 1990.0, and a forecast <span class="hlt">secular-variation</span> model for the period 1990-1995. The five 1985.0 main-field models and five 1990.0 main-field models that were proposed have been evaluated by comparing them with one another, with magnetic observatory data, and with Project MAGNET aerial survey data. The comparisons indicate that the main-field models proposed by IZMIRAN, and the <span class="hlt">secular-variation</span> model proposed jointly by the British Geological Survey and the US Naval Oceanographic Office, should be assigned relatively lower weight in the derivation of the new IGRF models. -Author</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AdSpR..40.1941B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AdSpR..40.1941B"><span>Effects of <span class="hlt">geomagnetic</span> activity <span class="hlt">variations</span> on the physiological and psychological state of functionally healthy humans: Some results of Azerbaijani studies</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Babayev, Elchin S.; Allahverdiyeva, Aysel A.</p> <p></p> <p>There are collaborative and cross-disciplinary space weather studies in the Azerbaijan National Academy of Sciences conducted with purposes of revealing possible effects of solar, <span class="hlt">geomagnetic</span> and cosmic ray variability on certain technological, biological and ecological systems. This paper describes some results of the experimental studies of influence of the periodical and aperiodical changes of <span class="hlt">geomagnetic</span> activity upon human brain, human health and psycho-emotional state. It also covers the conclusions of studies on influence of violent solar events and severe <span class="hlt">geomagnetic</span> storms of the solar cycle 23 on the mentioned systems in middle-latitude location. It is experimentally established that weak and moderate <span class="hlt">geomagnetic</span> storms do not cause significant changes in the brain's bioelectrical activity and exert only stimulating influence while severe disturbances of <span class="hlt">geomagnetic</span> conditions cause negative influence, seriously disintegrate brain's functionality, activate braking processes and amplify the negative emotional background of an individual. It is concluded that <span class="hlt">geomagnetic</span> disturbances affect mainly emotional and vegetative spheres of human beings while characteristics reflecting personality properties do not undergo significant changes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA100156','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA100156"><span>Data Acquisition System for Use in the Study of <span class="hlt">Geomagnetic</span> <span class="hlt">Variations</span>.</span></a></p> <p><a target="_blank" href="http://www.dtic.mil/">DTIC Science & Technology</a></p> <p></p> <p>1980-12-01</p> <p><span class="hlt">VARIATION</span>, LONG TERM T2% 3 START/STOP PERIOD Z5/26 x 10 SEC START/STOP DISTANCE @ READ WRITE SPEED 0.300/0.405 INCHES @ SEARCH REWIND SPEED 2.97/3.42...defined as the period from applica- tion of the state (either forward or reverse) command to when >95% of final long term speed is reached, exclusive of...their functions would be extremely long and beyond the scope of this thesis. Only those aspects specifically related to this design will be discussed. A</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUSMGP71A..06M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUSMGP71A..06M"><span>Intensity <span class="hlt">variation</span> of the <span class="hlt">geomagnetic</span> field in Mesoamerica during the last 3500 years</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Morales, J.; Gogichaisvili, A.</p> <p>2009-05-01</p> <p>After Nagata's and Bucha's pioneering works in Mesoamerica in the 60th's and 70th's a gap in archeointensity studies in the region seems to be opened, in spite of the abundant well known archeological vestiges available in Mexico. Aimed to improve the insipient reference curve for Mesoamerica, and to contribute to the global intensity database, we present latest archeointensity determinations obtained from oldest Western Mesoamerican archaeological deposits, as well as from pre-Columbian Central and Eastern Mexican archaeological sites. Although still not enough in number to define a <span class="hlt">variation</span> curve for the region, they outline a tendency that differs to that of model predictions based on previous data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003GeoJI.152..392B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003GeoJI.152..392B"><span>Analysis of long-term <span class="hlt">variations</span> in the <span class="hlt">geomagnetic</span> poloidal field intensity and evaluation of their relationship with global geodynamics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Biggin, A. J.; Thomas, D. N.</p> <p>2003-02-01</p> <p>The 1167 published cooling unit (CU) palaeointensity estimates contained in the 400-10 Ma portion of the PINT global database were rigorously filtered according to accurate age determinations, palaeodirectional reliability, recognition of polarity and the method of palaeointensity acquisition. The remaining 865 estimates (group 1) were further filtered to ensure self-consistency, reducing the data set to 425 estimates (group 2). Group 1 and 2 data were clustered into temporally and/or spatially distinct rock suites (RS) enabling each part of the record to be assessed for potential biasing by overrepresentation of palaeosecular <span class="hlt">variation</span> (PSV). The record was segmented according to the distribution of the data, rather than using arbitrary time windows, to ensure quasi-consistent behaviour within each segment. Differences between these segments clearly indicate that a significant long-timescale (107 and 108 yr) <span class="hlt">variation</span> of the mean <span class="hlt">geomagnetic</span> poloidal field intensity (GPFI) occurred during the 400-10 Ma period and hence that changing lowermost mantle conditions affect the capacity of the geodynamo to generate a poloidal field. Both the mean dipole moment and its standard deviation appear to be a function of the range of values each CU may adopt at one particular time. This range is itself controlled by the <span class="hlt">variation</span> of the maximum limit of dipole moment, while the value of the minimum limit remains relatively constant. Tentative support is provided for the recent suggestion that PSV may have been reduced during the Cretaceous normal superchron (CNS), though more data are needed in the range 120-60 Ma to confirm this. No conclusive evidence was found to support the suggestion that the GPFI record may be biased towards low or high values by palaeointensity determinations obtained using methods that do not adopt pTRM checks. Indeed, offsets caused by unreliable data in well-represented parts of the record are likely to be random and cancel one another out. When GPFI</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AdSpR..58.1208F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AdSpR..58.1208F"><span>Storm-time <span class="hlt">variation</span> of the horizontal and vertical components of the <span class="hlt">geomagnetic</span> fields and rate of induction at different latitudes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Falayi, E. O.; Oyebanjo, O. A.; Omotosho, T. V.; Okusanya, A. A.</p> <p>2016-10-01</p> <p>The paper presents the hourly mean <span class="hlt">variation</span> of horizontal (H) and vertical (Z) components of the <span class="hlt">geomagnetic</span> field and the rate of induction ΔH/ΔZ at different latitudes during magnetic storm of 20 March 2001 and 1 October 2001. The results of the analysis revealed that at high latitude stations greater than 60°, the reduction in ΔH component was noticed after the noon time while other stations less than 60° experienced reduction of H in the morning time during the <span class="hlt">geomagnetic</span> storm. Large amplitude of ΔH and ΔZ were exhibited during the daytime over the equatorial zone, the amplitude decreases from mid latitudes to the dip equator during the nighttime. The daytime enhancement of ΔH at AAE, BAN and MBO suggest the presence of a strong eastward directed current which comes under the influence of electrojet. There were strong positive and negative correlations between ring current (DR) and horizontal component of the magnetic field ΔH. The effect of rate of induction is more significant at high latitudes than lower latitudes, during the <span class="hlt">geomagnetic</span> storm. More enhancement in rate of induction occurred at nighttime than daytime. This result may be from other sources other than the ionosphere that is magnetospheric process significantly contributes toward the <span class="hlt">variation</span> of induction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeoJI.208.1740F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoJI.208.1740F"><span>Palaeo- and rock magnetic investigations on Late Quaternary sediments from low latitudes. I: <span class="hlt">geomagnetic</span> palaeosecular <span class="hlt">variation</span> and relative palaeointensity records from the Tobago Basin, Southeast Caribbean</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Frank, Ute; Nowaczyk, Norbert R.; Frederichs, Thomas; Korte, Monika</p> <p>2017-03-01</p> <p>Detailed palaeo- and rock magnetic investigations were carried out on two sediment cores from the Tobago Basin, Eastern Caribbean. The 2.8 m long profiles span the last 15 kyr, according to accelerator mass spectrometry 14C dates. Global climatic <span class="hlt">variations</span> marking the transition from the Pleistocene into the Holocene are clearly reflected in the rock magnetic parameters. Their <span class="hlt">variations</span> reflect the contribution of the coarse-grained fraction to the bulk composition. However, fine-grained Ti-magnetite particles carry a fairly stable magnetization in sediments deposited in the last 10 kyr. Comparison of stacked directional records of characteristic remanent magnetization inclination and declination, with data obtained from <span class="hlt">geomagnetic</span> field models revealed distinct similarities for most intervals and add to the knowledge about the variability of the <span class="hlt">geomagnetic</span> field in this area poorly covered by experimental data. A stacked record of relative palaeointensity was also established, using anhysteretic remanent magnetization as normalization parameter. Thus, the intensity of the <span class="hlt">geomagnetic</span> field was steadily decreasing in the Caribbean between 9 and 0 ka, a trend that does not fit to relative paleointensity records available from Northern Hemisphere stacks but matches other low-latitude records and the South Atlantic Palaeointensity Stack.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PEPI..262..101H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PEPI..262..101H"><span>Paleomagnetism and 40Ar/39Ar geochronology of the Plio-Pleistocene Boring Volcanic Field: Implications for the <span class="hlt">geomagnetic</span> polarity time scale and paleosecular <span class="hlt">variation</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hagstrum, Jonathan T.; Fleck, Robert J.; Evarts, Russell C.; Calvert, Andrew T.</p> <p>2017-01-01</p> <p>Paleomagnetic directions and 40Ar/39Ar ages have been determined for samples of lava flows from the same outcrops, where possible, for 84 eruptive units ranging in age from 3200 ka to 60 ka within the Boring Volcanic Field (BVF) of the Pacific Northwest, USA. This study expands upon our previous results for the BVF, and compares the combined results with the current <span class="hlt">geomagnetic</span> polarity time scale (GPTS). Lava flows with transitional directions were found within the BVF at the Matuyama-Brunhes and Jaramillo-Matuyama polarity boundaries, and replicate ages corresponding to these and other boundaries have been newly ascertained. Although the BVF data generally agree with GPTS chronozone boundaries, they indicate that onset of the Gauss-Matuyama transition and Olduvai subchron occurred significantly earlier than given in the current time scale calibration. Additional comparisons show that the BVF results are consistent with recent statistical models of <span class="hlt">geomagnetic</span> paleosecular <span class="hlt">variation</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMGP53A3748G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMGP53A3748G"><span><span class="hlt">Geomagnetic</span> Paleosecular <span class="hlt">Variation</span> and Tectonic Correction for the Past 12 Ma in Baja California, Mexico</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Garcia-Amador, B. I.; Alva-Valdivia, L. M.; Canon-Tapia, E.</p> <p>2014-12-01</p> <p>During the last 30 years, study of Paleosecular <span class="hlt">Variation</span> (PSV) has been analyzed within specific timescales (e.g. 0-5 Ma; 5-22.5 Ma; etc.), considering the main criteria <span class="hlt">variation</span> in directions of paleomagnetic data due to displacement of tectonic plates, and the scarcity of spatial and temporal distribution of rock outcrops, we propose using the previous geological and geophysical studies comprising the tectonic displacement of Baja California for the last 12 Ma, a method (working in space and time) to precise the PSV of our paleomagnetic sites (assuming a thermoremanent magnetization). We completed two paleomagnetic rock field sampling works: Loreto-Santa Rosalia-Punta Abreojos (between 26° and 27.4° N), with 156 cores from 16 sites; and San Borja and Jaraguay volcanic fields (between 28° and 30° N), with 230 cores from 27 sites. These sites are mainly volcanic rocks (andesite-basalt) with radiometric ages previously reported. We selected those younger than 12 Ma age without effect of rotation or flattening within the peninsula. Rock magnetic experiments were done to characterize the magnetic carrier of the remanence, such as susceptibility vs. low and high temperature, hysteresis, FORC, Koenigsberger ratio determination and directional analysis. Our results suggest that in most of the cases (80%) we have a contribution of TM0 to TM20, and magnetic domain of PSD + SP. In addition to our data, we gathered all paleomagnetic works in volcanic rocks younger than 12 Ma along Baja California. For the PSV, we calculated the angular standard deviation (SB) of the VGPs with respect to its mean average and also to the geographic axis. Both results were compared with the calculation of the SB once the correction of paleomagnetic sites based on the tectonic displacement was applied. Finally, all results (with and without correction) were compared with Model G and TK03.GAD, finding that data of the SB with tectonic correction are the best fit models, suggesting a</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010cosp...38.2135R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010cosp...38.2135R"><span>Long periods (1 -10 mHz) <span class="hlt">geomagnetic</span> pulsations <span class="hlt">variation</span> with solar cycle in South Atlantic Magnetic Anomaly</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rigon Silva, Willian; Schuch, Nelson Jorge; Guimarães Dutra, Severino Luiz; Babulal Trivedi, Nalin; Claudir da Silva, Andirlei; Souza Savian, Fernando; Ronan Coelho Stekel, Tardelli; de Siqueira, Josemar; Espindola Antunes, Cassio</p> <p></p> <p>The occurrence and intensity of the <span class="hlt">geomagnetic</span> pulsations Pc-5 (2-7 mHz) and its relationship with the solar cycle in the South Atlantic Magnetic Anomaly -SAMA is presented. The study of <span class="hlt">geomagnetic</span> pulsations is important to help the understanding of the physical processes that occurs in the magnetosphere region and help to predict <span class="hlt">geomagnetic</span> storms. The fluxgate mag-netometers H, D and Z, three axis <span class="hlt">geomagnetic</span> field data from the Southern Space Observatory -SSO/CRS/INPE -MCT, São Martinho da Serra (29.42° S, 53.87° W, 480m a.s.l.), RS, Brasil, a were analyzed and correlated with the solar wind parameters (speed, density and temperature) from the ACE and SOHO satellites. A digital filtering to enhance the 2-7 mHz <span class="hlt">geomagnetic</span> pulsations was used. Five quiet days and five perturbed days in the solar minimum and in the solar maximum were selected for this analysis. The days were chosen based on the IAGA definition and on the Bartels Musical Diagrams (Kp index) for 2001 (solar maximum) and 2008 (solar minimum). The biggest Pc-5 amplitude averages differences between the H-component is 78,35 nT for the perturbed days and 1,60nT for the quiet days during the solar maximum. For perturbed days the average amplitude during the solar minimum is 8,32 nT, confirming a direct solar cycle influence in the <span class="hlt">geomagnetic</span> pulsations intensity for long periods.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010BGeo....7.2795R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010BGeo....7.2795R"><span>Review: geological and experimental evidence for <span class="hlt">secular</span> <span class="hlt">variation</span> in seawater Mg/Ca (calcite-aragonite seas) and its effects on marine biological calcification</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ries, J. B.</p> <p>2010-09-01</p> <p>Synchronized transitions in the polymorph mineralogy of the major reef-building and sediment-producing calcareous marine organisms and abiotic CaCO3 precipitates (ooids, marine cements) throughout Phanerozoic time are believed to have been caused by tectonically induced <span class="hlt">variations</span> in the Mg/Ca ratio of seawater (molar Mg/Ca>2="aragonite seas", <2="calcite seas"). Here, I assess the geological evidence in support of <span class="hlt">secular</span> <span class="hlt">variation</span> in seawater Mg/Ca and its effects on marine calcifiers, and review a series of recent experiments that investigate the effects of seawater Mg/Ca (1.0-5.2) on extant representatives of calcifying taxa that have experienced <span class="hlt">variations</span> in this ionic ratio of seawater throughout the geologic past. <span class="hlt">Secular</span> <span class="hlt">variation</span> in seawater Mg/Ca is supported by synchronized <span class="hlt">secular</span> <span class="hlt">variations</span> in (1) the ionic composition of fluid inclusions in primary marine halite, (2) the mineralogies of late stage marine evaporites, abiogenic carbonates, and reef- and sediment-forming marine calcifiers, (3) the Mg/Ca ratios of fossil echinoderms, molluscs, rugose corals, and abiogenic carbonates, (4) global rates of tectonism that drive the exchange of Mg2+ and Ca2+ along zones of ocean crust production, and (5) additional proxies of seawater Mg/Ca including Sr/Mg ratios of abiogenic carbonates, Sr/Ca ratios of biogenic carbonates, and Br concentrations in marine halite. Laboratory experiments have revealed that aragonite-secreting bryopsidalean algae and scleractinian corals and calcite-secreting coccolithophores exhibit higher rates of calcification and growth in experimental seawaters formulated with seawater Mg/Ca ratios that favor their skeletal mineral. These results support the assertion that seawater Mg/Ca played an important role in determining which hypercalcifying marine organisms were the major reef-builders and sediment-producers throughout Earth history. The observation that primary production increased along with calcification within the bryopsidalean</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/circ/1995/1109/report.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/circ/1995/1109/report.pdf"><span><span class="hlt">Geomagnetism</span> applications</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Campbell, Wallace H.</p> <p>1995-01-01</p> <p>The social uses of <span class="hlt">geomagnetism</span> include the physics of the space environment, satellite damage, pipeline corrosion, electric power-grid failure, communication interference, global positioning disruption, mineral-resource detection, interpretation of the Earth's formation and structure, navigation, weather, and magnetoreception in organisms. The need for continuing observations of the <span class="hlt">geomagnetic</span> field, together with careful archiving of these records and mechanisms for dissemination of these data, is emphasized.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002EGSGA..27.1318K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002EGSGA..27.1318K"><span>Experience of <span class="hlt">Geomagnetic</span> Investigations For Studying Earthquake Precursors</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kuznetsova, V.; Maksymchuk, V.; Gorodisky, Yu.</p> <p></p> <p>We present the results of <span class="hlt">geomagnetic</span> investigasions of studying earthquake precur- sors and peculiarities of modern geodynamic processes in the territory of the seis- moactive part of Ukrainian Carpathians - Transcarpathian Trough. The observations were carried out using high precision proton magnetometers with sensitivity of 0.1 nT and mean square error of mean daily values of dF being within abs(0.6-0.9) nT. The component magneto-<span class="hlt">variational</span> digital station and analog station were in opera- tion. The results obtained are as folows: 1. <span class="hlt">Secular</span> <span class="hlt">variation</span> (SV) peculiarities have been studied for the period of 1990-1995 using the data of European observatories and regime <span class="hlt">geomagnetic</span> stations. 2. Using profile observation results the zone (8 MSR) of <span class="hlt">geomagnetic</span> field anomalous temporal changes upto 5-7 nT per year has been mapped; this zone is connected with the zone of seismoactive Transcarpathian fault. 3. A series of anomalous effects has been separated on the base of continuous F-observations held at 4 regime <span class="hlt">geomagnetic</span> stations during the period of 1990-1999. Episodical anomalous of precursor type and bay-like form; they are characterized by duration from 30 days to 3-4 months, intensity of 1.5-3 nT and are correlated with lo- cal earthquakes with M=2-4. Long-term (upto 130 days) anomalies with amplitude of 1.5-2.5 nT; they are observed in spring time and therefore considered to be seasonal. Long-term quasilinear trend field changes of possible tectonic origin. 4. Investigation of peculiarities of temporal changes of Wiese Vector components for the 10 years shows that there exists correlation between these changes and local seismisity regime.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040021386','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040021386"><span>Narrow Scale Flow and a Weak Field by the Top of Earth's Core: Evidence from Orsted, Magsat and <span class="hlt">Secular</span> <span class="hlt">Variation</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Voorhies, Coerte V.</p> <p>2004-01-01</p> <p>As Earth's main magnetic field weakens, our magnetic shield against the onslaught of the solar wind thins. And the field strength needed to fend off battering by solar coronal mass ejections is decreasing, just when the delicate complexity of modem, vulnerable, electro-technological systems is increasing at an unprecedented rate. Recently, a working group of distinguished scientist from across the nation has asked NASA's Solid Earth and Natural Hazards program a key question: What are the dynamics of Earth s magnetic field and its interactions with the Earth system? Paleomagnetic studies of crustal rocks magnetized in the geologic past reveal that polarity reversals have occurred many times during Earth s history. Networked super-computer simulations of core field and flow, including effects of gravitational, pressure, rotational Coriolis, magnetic and viscous forces, suggest how this might happen in detail. And space-based measurements of the real, time-varying magnetic field help constrain estimates of the speed and direction of fluid iron flowing near the top of the core and enable tests of some hypotheses about such flow. Now scientists at NASA s Goddard Space Flight Center have developed and applied methods to test the hypotheses of narrow scale flow and of a dynamically weak magnetic field near the top of Earth s core. Using two completely different methods, C. V. Voorhies has shown these hypotheses lead to specific theoretical forms for the "spectrum" of Earth s main magnetic field and the spectrum of its rate of change. Much as solar physicists use a prism to separate sunlight into its spectrum, from long wavelength red to short wavelength blue light, geophysicists use a digital prism, spherical harmonic analysis, to separate the measured <span class="hlt">geomagnetic</span> field into its spectrum, from long to short wavelength fields. They do this for the rate of change of the field as well.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002EGSGA..27.3969T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002EGSGA..27.3969T"><span>A 350 Kyr Record of <span class="hlt">Geomagnetic</span> Paleosecular <span class="hlt">Variation</span> and Excursions From Giant Sedimentary Cores Collected Off Portugal.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Thouveny, N.; Moreno, E.; Carcaillet, J.; Bourles, D.</p> <p></p> <p>Sedimentary cores collected off the Iberian margin (between 37° and 40° lat N) by the french R.V. Marion Dufresne containing sequences of clays and carbonaceous clays deposited between 2000 and 3200 m depth, have been studied for rock- magnetic and paleomagnetic purposes. Cubic discrete specimens and Uchannel were subsampled from 4 giant (30 to 35 m long) piston cores (MD952039, -2040 and - 2042) and from 3 shorter (5 to 15 m long ) gravity cores (MD99-2334K, MD012440G and MD01-2441). NRM measurements were performed on a 2G cryogenic magnetometer (type 760R) before and after an upgrade from large (120 mm) to small (45 mm) diameter and from RF to DC SQUIDS. Main carriers of the natural remanent magnetization have been identified by SEM coupled with a semi- quantitative chemical probe, as titano-magnetites in the size range 0.1-10 mm. The removal of a soft viscous overp rint leaves a stable single component interpreted as the characteristic remanence acquired through (p)DRM processes. Detailed intercore correlation of susceptibility peaks leads to the construction of a composite sequence dated by radiocarbon and by correlation of delta O-18 profiles with the SPECMAP chronology. A continuous record of paleosecular <span class="hlt">variation</span> of the direction and relative paleointensity through the last 350 ka (i.e. since isotopic stage 10) is obtained. The major paleomagnetic excursions known from this interval, i.e. Laschamp (ca 40 ka BP), Blake ( 105-120 ka BP), Jamaica (ca 180 ka BP) and Levantine (ca 290 ka BP).are described as anomalies of the direction of the stable magnetization, accompanied by large and lasting drops of relative paleointensity (NRM/ARM; NRM/SIRM). A cosmonuclide Be-10 record (see contribution by Carcaillet et al.) obtained for the same time-interval from the same cores further confirms the link between the drastic reduction of the <span class="hlt">geomagnetic</span> dipole moment and departures from the near axial dipole configuration. Slight shifts between the paleomagnetic and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GPC...113...91I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GPC...113...91I"><span>Combined palaeomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> and petrophysical records to time-constrain geological and hazardous events: An example from the eastern Tyrrhenian Sea over the last 120 ka</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Iorio, Marina; Liddicoat, Joseph; Budillon, Francesca; Incoronato, Alberto; Coe, Robert S.; Insinga, Donatella D.; Cassata, William S.; Lubritto, Carmine; Angelino, Antimo; Tamburrino, Stella</p> <p>2014-02-01</p> <p>Long-term change of Earth's magnetic field (palaeomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span>, PSV) during much of the last approximately 120 ka was recorded in cored sediment from the slope margin of the eastern Tyrrhenian Sea. The PSV record has been correlated to master curves of global palaeomagnetic field intensity and PSV records for western Europe. Tephrochronology and radiometric dating (14C and 40Ar/39Ar) have also been used to constrain the age of the PSV record. The combination of the new data with prior PSV and petrophysical data from the area provides a chronological framework for geological events such as large-scale submarine slumps, stratigraphic gaps and short-term changes in deposition rate on the continental margin. These latter changes are linked to the combined action of relative sea-level oscillations, climate events, and consequent <span class="hlt">variations</span> in land exposure through time. Moreover, new data concerning the thickness and dispersal of Campanian Plain pyroclastic deposits in the marine setting enable volcanic-hazard evaluation. Finally, a pyroclastic deposit (tephra X-6) found offshore in the Southern Campanian marine environment was 40Ar/39Ar dated for the first time at 108.9 ± 1.8 ka BP.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70014206','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70014206"><span>Assessment of models proposed for the 1985 revision of the international <span class="hlt">geomagnetic</span> reference field</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Peddie, N.W.; Zunde, A.K.</p> <p>1987-01-01</p> <p><span class="hlt">Geomagnetic</span> measurements from land, marine and aerial surveys conducted in the years 1945-1964 were used to test the 14 models proposed as additions, for that period, to the series of definitive <span class="hlt">geomagnetic</span> reference field (DGRF) models. Overall, NASA's 'SFAS' models and the BGS (British Geological Survey) models agree best with these data. Comparisons of the two proposed definitive main-field models for 1980.0, with each other and with the existing IGRF 1980 main-field model, show mostly close agreement, with the greatest absolute differences (several tens of nanotesla) occurring in the region of Antarctica. Comparison of the the three proposed forecast <span class="hlt">secular-variation</span> models for 1985-1990 with estimates of recent rates of change at 148 magnetic observatories shows that the IZMIRAN (U.S.S.R.) and USGS models are in closest agreement with these data. ?? 1987.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JAESc.129...13H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JAESc.129...13H"><span>Spatiotemporal characteristics of the <span class="hlt">geomagnetic</span> diurnal <span class="hlt">variation</span> anomalies prior to the 2011 Tohoku earthquake (Mw 9.0) and the possible coupling of multiple pre-earthquake phenomena</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Han, Peng; Hattori, Katsumi; Huang, Qinghua; Hirooka, Shinji; Yoshino, Chie</p> <p>2016-11-01</p> <p>Xu et al. (2013) and Han et al. (2015) have reported unusual behaviors of <span class="hlt">geomagnetic</span> diurnal <span class="hlt">variation</span> (GDV) in the vertical component prior to the 2011 off the Pacific coast of Tohoku earthquake (Mw 9.0). To make a better understanding of this phenomenon, temporal-spatial analyses of GDV have been applied in this study. <span class="hlt">Geomagnetic</span> data of long-term observations at 17 stations in Japan have been analyzed using the same method in Han et al. (2015). Ratios of diurnal <span class="hlt">variation</span> range between the reference station KAK and the target stations have been computed. After removing seasonal <span class="hlt">variations</span>, the 15-day backward running mean values of the ratios in the vertical component shows a clear anomaly exceeding the statistical threshold about 2 months before the mega event at both ESA and MIZ stations in the Tohoku Region. Locations of anomalies in spatial distribution show a good correlation with the epicenter of the Mw 9.0 earthquake. These spatiotemporal results are consistent with those obtained from other independent observations such as groundwater level and GPS displacements. The coupling of multiple pre-earthquake phenomena may help to understand the preparation process of a mega earthquake in the subduction zone.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EP%26S...67...71G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EP%26S...67...71G"><span>Stochastic forecasting of the <span class="hlt">geomagnetic</span> field from the COV-OBS.x1 <span class="hlt">geomagnetic</span> field model, and candidate models for IGRF-12</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gillet, Nicolas; Barrois, Olivier; Finlay, Christopher C.</p> <p>2015-05-01</p> <p>We present the <span class="hlt">geomagnetic</span> field model COV-OBS.x1, covering 1840 to 2020, from which have been derived candidate models for the IGRF-12. Towards the most recent epochs, it is primarily constrained by first differences of observatory annual means and measurements from the Oersted, Champ, and Swarm satellite missions. Stochastic information derived from the temporal spectra of <span class="hlt">geomagnetic</span> series is used to construct the a priori model covariance matrix that complements the constraint brought by the data. This approach makes it possible the use of a posteriori model errors, for instance, to measure the `observations' uncertainties in data assimilation schemes for the study of the outer core dynamics. We also present and illustrate a stochastic algorithm designed to forecast the <span class="hlt">geomagnetic</span> field. The radial field at the outer core surface is advected by core motions governed by an auto-regressive process of order 1. This particular choice is motivated by the slope observed for the power spectral density of <span class="hlt">geomagnetic</span> series. Accounting for time-correlated model errors (subgrid processes associated with the unresolved magnetic field) is made possible thanks to the use of an augmented state ensemble Kalman filter algorithm. We show that the envelope of forecasts includes the observed <span class="hlt">secular</span> <span class="hlt">variation</span> of the <span class="hlt">geomagnetic</span> field over 5-year intervals, even in the case of rapid changes. In a purpose of testing hypotheses about the core dynamics, this prototype method could be implemented to build the `state zero' of the ability to forecast the <span class="hlt">geomagnetic</span> field, by measuring what can be predicted when no deterministic physics is incorporated into the dynamical model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AdSpR..45..940M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AdSpR..45..940M"><span>Effects of <span class="hlt">geomagnetic</span> activity and atmospheric power <span class="hlt">variations</span> on quantitative measures of brain activity: Replication of the Azerbaijani studies</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mulligan, Bryce P.; Hunter, Mathew D.; Persinger, Michael A.</p> <p>2010-04-01</p> <p>This study replicates and extends the observations by Babayev and Allahveriyeva that changes in right hemispheric electroencephalographic activity are correlated with increases in <span class="hlt">geomagnetic</span> activity. During the <span class="hlt">geomagnetically</span> quiet interface between solar cycle 23 and 24 quantitative electroencephalographic (QEEG) measurements were completed for normal young adults in three separate experiments involving about 120 samples over 1.5 years. The most consistent, moderate strength correlations occurred for the changes in power within the gamma and theta ranges over the right frontal lobe. Real-time measures of atmospheric power obtained from polar orbiting satellites showed similar effects. The preferential involvement of the right frontal lobe and the regions subject to its inhibition with environmental energetic changes are consistent with the behavioural correlations historically associated with these conditions. They include increased incidence of emotional lability, erroneous reconstruction of experiences, social confrontations, and unusual perceptions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004PEPI..146..333K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004PEPI..146..333K"><span>Material circulation model including chemical differentiation within the mantle and <span class="hlt">secular</span> <span class="hlt">variation</span> of temperature and composition of the mantle</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Komiya, Tsuyoshi</p> <p>2004-08-01</p> <p> indicates that the upper mantle had higher FeO content (10 wt.%), and that the FeO content was constant until early Proterozoic, and then decreased. Segregation of iron grains from subducted oceanic crust during slab penetration into the lower mantle is plausible to decrease the FeO content in the mantle. If the produced metallic iron sinks and accumulates on the core, the metallic iron layer would be about 57 km thick. The potential mantle temperature of the upper mantle was about 1480 °C in the Archean and was hotter by ca. 150-200 °C than the modern mantle. The temperature decreased not monotonously but episodically. In addition, recent ultra-high pressure experiments presumed chemical differentiation within the mantle, dehydration or slab melting of subducted oceanic crust beneath a subduction zone, segregation of iron grains from slab materials during slab penetration [Science 273 (1996) 1522], and partial melting of subducted oceanic crust on the core-mantle boundary [Phys. Earth Planet. Inter. (2002)]. This work proposes a global material circulation model, which includes three chemical differentiations within the mantle and the <span class="hlt">secular</span> change of temperature and composition of the mantle.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70014204','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70014204"><span>The <span class="hlt">geomagnetic</span> jerk of 1969 and the DGRFs</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Thompson, D.; Cain, J.C.</p> <p>1987-01-01</p> <p>Cubic spline fits to the DGRF/IGRF series indicate agreement with other analyses showing the 1969-1970 magnetic jerk in the h ??12 and g ??02 <span class="hlt">secular</span> change coefficients, and agreement that the h ??11 term showed no sharp change. The <span class="hlt">variation</span> of the g ??01 term is out of phase with other analyses indicating a likely error in its representation in the 1965-1975 interval. We recommend that future derivations of the 'definitive' <span class="hlt">geomagnetic</span> reference models take into consideration the times of impulses or jerks so as to not be bound to a standard 5 year interval, and otherwise to make more considered analyses before adopting sets of coefficients. ?? 1987.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110012874','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110012874"><span>Effect of Cross-Correlation on <span class="hlt">Geomagnetic</span> Forecast Accuracies</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kuang, Weijia; Wei, Zigang; Tangborn, Andrew</p> <p>2011-01-01</p> <p>Surface <span class="hlt">geomagnetic</span> observation can determine up to degree L = 14 time-varying spherical harmonic coefficients of the poloidal magnetic field. Assimilation of these coefficients to numerical dynamo simulation could help us understand better the dynamical processes in the Earth's outer core, and to provide more accurate forecast of <span class="hlt">geomagnetic</span> <span class="hlt">secular</span> <span class="hlt">variations</span> (SV). In our previous assimilation studies, only the poloidal magnetic field in the core is corrected by the observations in the analysis. Unobservable core state variables (the toroidal magnetic field and the core velocity field) are corrected via the dynamical equations of the geodynamo. Our assimilation experiments show that the assimilated core state converges near the CMB, implying that the dynamo state is strongly constrained by surface <span class="hlt">geomagnetic</span> observations, and is pulled closer to the truth by the data. We are now carrying out an ensemble of assimilation runs with 1000 years of <span class="hlt">geomagnetic</span> and archeo/paleo magnetic record. In these runs the cross correlation between the toroidal and the poloidal magnetic fields is incorporated into the analysis. This correlation is derived from the physical boundary conditions of the toroidal field at the core-mantle boundary (CMB). The assimilation results are then compared with those of the ensemble runs without the cross-correlation, aiming at understanding two fundamental issues: the effect of the crosscorrelation on (1) the convergence of the core state, and (2) the SV prediction accuracies. The constrained dynamo solutions will provide valuable insights on interpreting the observed SV, e.g. the near-equator magnetic flux patches, the core-mantle interactions, and possibly other geodynamic observables.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PEPI..266...39T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PEPI..266...39T"><span>Relating the South Atlantic Anomaly and <span class="hlt">geomagnetic</span> flux patches</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Terra-Nova, Filipe; Amit, Hagay; Hartmann, Gelvam A.; Trindade, Ricardo I. F.; Pinheiro, Katia J.</p> <p>2017-05-01</p> <p>The South Atlantic Anomaly (SAA) is a region of weak <span class="hlt">geomagnetic</span> field intensity at the Earth's surface, which is commonly attributed to reversed flux patches (RFPs) on the core-mantle boundary (CMB). While the SAA is clearly affected by the reversed flux region below the South Atlantic, we show that the relation between the intensity minimum at Earth's surface and RFPs is not straightforward. We map a field-dependent intensity kernel (Constable, 2007a) to study the relation between the radial <span class="hlt">geomagnetic</span> field at the CMB and the field intensity at Earth's surface. Synthetic tests highlight the role of specific patches (reversed and normal) in determining the location of the surface intensity minimum and demonstrate that the SAA can indeed be explained by a few intense patches. We show that the level of axial dipolarity of the field determines the stability of the relation between the SAA minimum and RFPs. The present position of the SAA minimum is determined by the interplay among several robust <span class="hlt">geomagnetic</span> flux patches at the CMB. The longitude of the SAA minimum appears near the longitude of the Patagonia RFP due to the low-latitude normal flux patches (NFPs) near Africa and mid-Atlantic which diminish the effect of the Africa RFPs. The latitude of the SAA minimum is lower than the Patagonia RFP latitude due to the South Pacific high-latitude NFP and the axial dipole effect. The motion of the SAA minimum is explained by the motions and changes in intensity of these robust <span class="hlt">geomagnetic</span> flux patches. Simple <span class="hlt">secular</span> <span class="hlt">variation</span> (SV) scenarios suggest that while the SAA path can be explained by advection, its intensity decrease requires magnetic diffusion. In addition these SV scenarios provide some speculative predictions for the SAA.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EurSS..45..119D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EurSS..45..119D"><span>Dynamics of the properties of steppe paleosols of the Sarmatian time (2nd century BC-4th century AD) in relation to <span class="hlt">secular</span> <span class="hlt">variations</span> in climatic humidity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Demkin, V. A.; Zolotareva, B. N.; Demkina, T. S.; Khomutova, T. E.; Kashirskaya, N. N.; El'Tsov, M. V.; Udal'Tsov, S. N.</p> <p>2012-02-01</p> <p>Paleosols buried under kurgans of the Early (2nd-1st centuries BC), Middle (1st-2nd centuries AD) and Late (2nd-IV centuries AD) Sarmatian epochs were studied in dry steppes and desert steppes of the Lower Volga region (the Privolzhskaya and Ergeni Uplands and the Caspian Lowland). It was found that temporal <span class="hlt">variations</span> in the morphological, chemical, microbiological, and magnetic properties of the paleosols in the interval of 2200-1600 BP were characterized by the cyclic pattern related to <span class="hlt">secular</span> dynamics of climatic humidity with changes in the mean annual precipitation of ±30-50 mm. These climate changes did not transform chestnut paleosols and paleosolonetzes at the type or subtype taxonomic levels. However, they led to certain changes in the humus, carbonate, and salt profiles of the soils; in the character of solonetzic horizon B1; and in the state of microbial communities. According to these data, the Sarmatian time was characterized by alternation of micropluvial and microarid stages lasting fro about 100-200 years. In particular, the stages of humidization were observed in the 1st century BC-1st century AD and in the 4th century AD; the most arid conditions were observed in the second half of the 2nd and the first half of the 3rd century AD.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950004618','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950004618"><span>Measurements of the vertical profile, diurnal <span class="hlt">variation</span>, and <span class="hlt">secular</span> change of ClO in the stratosphere over Thule, Greenland, February-March, 1992</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Dezafra, Robert L.; Emmons, Louisa K.; Reeves, John M.; Shindell, Drew T.</p> <p>1994-01-01</p> <p>We report observations of stratospheric chlorine monoxide over the altitude range approx. 16 to 50 km at Thule, Greenland from Feb. 8 to Mar. 24, 1992. A new, more sensitive ground-based mm-wave spectrometer was employed for these measurements, similar in principle to that used earlier for the discovery of low altitude ClO in the Antarctic springtime. In this report, we discuss different aspects of vertical distribution, <span class="hlt">secular</span> trends, and diurnal <span class="hlt">variation</span> of ClO in the Arctic stratosphere, based on a preliminary analysis of our Thule data. We see no evidence for large (approx. 1.2-1.5 ppb) amounts of ClO in the lower stratosphere at any time during February or March, in agreement with UARS-MLS findings for this period, and in marked contrast to findings reported for the Arctic in January. We have some evidence for small enhancements (approx. 0.2-0.5 ppb) in the 18-30 km range in late February-early March, which might be associated with volcanic aerosol, rather than PSC, processing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..15.1949S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..15.1949S"><span><span class="hlt">Variations</span> in the <span class="hlt">geomagnetic</span> and gravitational background associated with two strong earthquakes of the May 2012 sequence in the Po Valley Plain (Italy).</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Straser, Valentino</p> <p>2013-04-01</p> <p>Reawakening of seismic activity in the Emilian Po Valley Plain (Italy) resulted in 2,492 earthquakes over five and a half months: 2,270 with M<3, 189 with a magnitude from 3.0<= M <4.0, 27 con 4.0<= M <5.0, and 7 M>= 7. The mainshock was recorded during the night of 20 May 2012, at 04:03:52 Italian time (02:03:52 UTC) with epicentre in Finale Emilia, at a depth of 6.3km, by the Italian National Institute of Geophysics and Vulcanology (INGV). A long sequence of telluric shocks occurred in the same seismic district in the areas between the provinces of Modena, Ferrara, Mantua, Reggio Emilia, Bologna and Rovigo. In addition to the general devastation plus damage to civil and industrial buildings and the historical heritage, the earthquakes resulted in a total of 27 victims. Concomitant with the two strongest quakes, recorded on 20 and 29 May 2012, respectively, as in the case of others, <span class="hlt">variations</span> were noted in the <span class="hlt">geomagnetic</span> background by the LTPA monitoring station in Rome (Italy). The <span class="hlt">geomagnetic</span> background <span class="hlt">variations</span> were associated with the appearance of radio-anomalies in a frequency range from 0.1 to 3.0Hz, as well as gravimetric <span class="hlt">variations</span> found around 60km from the epicentre. The peak accelerations, detected in correspondence with the strongest shocks on 20 and 29 May 2012, were respectively 0.31g and 0.29g. The appearance of the radio-anomalies coincided, from a temporal point of view, with average gravimetric <span class="hlt">variations</span> of approximately 30µGal around the epicentre areas, concurrent with the mainshock. In this study, both the appearance of radio-anomalies and the gravitational <span class="hlt">variations</span> recorded before strong earthquakes were related to the dynamics of the fault and a progressive reduction in granulometry in the core of the fracture, until the point of dislocation was reached. The intense friction in the fault and the damping factors produced before the shock are hypothesized as being proportional to the number of radio-anomalies measured. The radio</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19740019238','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19740019238"><span>Dynamic techniques for studies of <span class="hlt">secular</span> <span class="hlt">variations</span> in position from ranging to satellites. [using laser range measurements</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Smith, D. E.; Kolenkiewicz, R.; Agreen, R. W.; Dunn, P. J.</p> <p>1974-01-01</p> <p>Satellite laser range measurements were applied to the study of latitude <span class="hlt">variation</span> arising from polar motion, and the solid-earth and ocean tidal distortion of the earth's gravity field. Experiments involving two laser tracking stations were conducted. The relative location of one station with respect to the other was determined by performing simultaneous range measurements to a satellite from two stations several hundred kilometers apart. The application of this technique to the San Andreas Fault Experiment in California is discussed. Future capabilities of spacecraft equipped with laser retroreflectors include: (1) determination of the product of the earth's mass and gravitational constant; (2) measurement of crustal and tectonic motions; (3) determination of the elastic response of the solid-earth tidal forces; (4) measurement of the amplitudes and phase of certain components of the ocean tides; and (5) self-monitoring of the latitude and height <span class="hlt">variations</span> of the tracking station.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.4088A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.4088A"><span>Geodynamo simulations: tools to understand and forecast the <span class="hlt">geomagnetic</span> field evolution</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Aubert, Julien</p> <p>2016-04-01</p> <p>The past two decades have seen an extensive development of numerical geodynamo simulations as tools to understand the mechanisms through which the magnetic field of internal origin of our planet is generated. Though these are still run at parameter regimes far from that of the Earth's core, the similarity of their output with the various observables of the field, <span class="hlt">secular</span> <span class="hlt">variation</span>, and underlying core flows has strengthened the prospect to use these simulations as analysis and forecasting tools for the <span class="hlt">geomagnetic</span> field evolution. In this presentation, I will report on recent progress in <span class="hlt">geomagnetic</span> data assimilation, an emerging discipline which blends together the high-quality satellite data such as these obtained by the Swarm mission, and state-of-the art numerical geodynamo simulation with an Earth-like output. The outcome of data assimilation is an estimate of the internal geodynamo structure, which sheds light into the mechanisms currently responsible for the <span class="hlt">geomagnetic</span> dipole decay and the extension of the South Atlantic <span class="hlt">geomagnetic</span> anomaly. Starting from such estimates obtained at present, ensemble-based techniques akin to those used in meteorology can help to estimate how the present field will evolve in the future. For the next century, our operational forecasts predict a further dipole decay of about 1 microtesla at Earth's surface, together with a similar deepening and a westward motion of the South Atlantic anomaly.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1988NCimC..11..353M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1988NCimC..11..353M"><span>Solar, <span class="hlt">geomagnetic</span> and seismic activity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mazzarella, A.; Palumbo, A.</p> <p>1988-08-01</p> <p>An 11-yr modulation of large Italian earthquakes has been successfully identified and found to be positively linked to sunspot activity. The seismic activity appears to be modulated by the 11-yr sunspot cycle through the coherent <span class="hlt">variation</span> of <span class="hlt">geomagnetic</span> activity. It is proposed that the two phenomena are linked by the influence of a magnetostriction process on stresses in the crust. An implication of this model is that <span class="hlt">geomagnetic</span> storms may directly trigger large earthquakes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA165131','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA165131"><span><span class="hlt">Geomagnetic</span> Disturbances.</span></a></p> <p><a target="_blank" href="http://www.dtic.mil/">DTIC Science & Technology</a></p> <p></p> <p>1986-01-01</p> <p>Sheeley, Jr., and J.T. Hoeksema. Lund University, Lund , Sweden, August 1983 (Invited Talks): "The Structure of the Heliospheric Current Sheet: 1976...Society, San Franciso, California, January 13-16, 1980: "<span class="hlt">Geomagnetic</span> Activity and Hale Sector Boundaries," Henrik Lundstedt. "Solar Oscillations with</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19830057379&hterms=coefficient+variation&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dcoefficient%2Bvariation','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19830057379&hterms=coefficient+variation&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dcoefficient%2Bvariation"><span><span class="hlt">Secular</span> <span class="hlt">variation</span> of earth's gravitational harmonic J2 coefficient from Lageos and nontidal acceleration of earth rotation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Yoder, C. F.; Williams, J. G.; Dickey, J. O.; Schutz, B. E.; Eanes, R. J.; Tapley, B. D.</p> <p>1983-01-01</p> <p>Analysis of 5.5 years of Lageos satellite range data reveal significant residual nodal signatures: an acceleration and annual and semiannual periods. These signatures primarily reflect <span class="hlt">variations</span> in the zonal gravitational harmonic J2 coefficient and hence the polar moment of inertia. The implied decrease of J2 = -3 x 10 to the -11th/yr is consistent with both historical observations of the nontidal acceleration of the earth's rotation and models of viscous rebound of the solid earth from the decrease in load due to the last deglaciation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19810028804&hterms=contamination+soils&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dcontamination%2Bsoils','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19810028804&hterms=contamination+soils&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dcontamination%2Bsoils"><span>Evidence for a <span class="hlt">secular</span> <span class="hlt">variation</span> in the C-13/C-12 ratio of carbon implanted in lunar soils</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Becker, R. H.</p> <p>1980-01-01</p> <p>A curve of delta(C-13) vs delta(N-15) for lunar soils and breccias shows that the previously recorded 30% change in delta(N-15) is associated with a change in delta(C-13). The correlation represents concurrent changes in the isotope ratios of both elements at their source, and does not result from maturation effects or nonselective sample contamination. A computation of the relative production rates of C-13 and N-15 shows that spallation reactions in the sun could produce the observed ratio of the delta(C-13) to delta (N-15) <span class="hlt">variations</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMGP23A1286S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMGP23A1286S"><span>Authigenic 10Be/9Be Ratio Signatures of the Cosmogenic Nuclide Production Linked to <span class="hlt">Geomagnetic</span> Dipole Moment <span class="hlt">Variation</span> During and Since the Brunhes/Matuyama Boundary</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Simon, Q.; Thouveny, N.; Bourles, D. L.; Ménabréaz, L.; Valet, J. P.; Valery, G.; Choy, S.</p> <p>2015-12-01</p> <p>The atmospheric production rate of cosmogenic nuclides is linked to the <span class="hlt">geomagnetic</span> dipole moment (GDM) by a non-linear inverse relationship. Large amplitude GDM <span class="hlt">variations</span> associated with reversals and excursions can potentially be reconstructed using time <span class="hlt">variation</span> of the cosmogenic beryllium-10 (10Be) production recorded in ocean sediments. Downcore profiles of authigenic 10Be/9Be ratios (proxy of atmospheric 10Be production) in oceanic cores provide independent and additional records of the evolution of the <span class="hlt">geomagnetic</span> intensity and complete previous information derived from relative paleointensity (RPI). Here are presented new authigenic 10Be/9Be results obtained from cores MD05-2920 and from the top of core MD05-2930 collected in the West Equatorial Pacific Ocean. Completing data of Ménabréaz et al. (2012, 2014), these results provide the first continuous 10Be production rate sedimentary record covering the last 800 ka. Along these cores, authigenic 10Be/9Be ratio peaks are recorded - within methodological errors - at the stratigraphic level of RPI lows. High-resolution chronologies (δ18O-derived) lead to interpret these peaks as successive global 10Be overproduction events triggered by <span class="hlt">geomagnetic</span> dipole lows present in the PISO-1500 and Sint-2000 stacks. The largest amplitude 10Be production enhancement is synchronous to the very large decrease of the dipole field associated with the last polarity reversal (772 ka). It is consistent in shape and duration with the peak recorded in core MD90-0961 from the Maldive area (Indian Ocean) (Valet et al. 2014). Two significant 10Be production enhancements are coeval with the Laschamp (41 ka) and Icelandic basin (190 ka) excursions, while 10Be production peaks of lower amplitude correlate to other recognized excursions such as the Blake (120 ka), Pringle-Falls (215 ka), Portuguese Margin (290 ka), Big Lost (540 ka) among others. This study provides new data on the amplitude and timing of dipole field <span class="hlt">variations</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMGP41E..02L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMGP41E..02L"><span>A Comparison of Paleomagnetic <span class="hlt">Secular</span> <span class="hlt">Variation</span> during MIS 7-10 between the Bering Sea (IODP Ex. 323) and North Atlantic Ocean (ODP Leg 172): Implications for the space/time pattern of field and environmental variability (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lund, S.; Okada, M.; Acton, G.; Clement, B. M.; Stoner, J. S.; Platzman, E. S.</p> <p>2013-12-01</p> <p>Detailed records of Brunhes paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> (PSV) during Marine Isotope Stages (MIS) 7-10 have been recovered from four IODP Ex. 323 sites in the Bering Sea (U1339, U1343-U1345) and four ODP Leg 172 sites from the subtropical North Atlantic Ocean (1060-1063). Reproducible records of PSV (both directions and paleointensity) have been recovered from three or more holes at each site and correlated among the four independent sites in each region. These PSV records provide an unprecedented database for considering patterns of long-term <span class="hlt">secular</span> <span class="hlt">variation</span> and evidence for excursional field behavior on a larger than individual regional scale. We will present reproducible evidence for sustained long-term <span class="hlt">secular</span> <span class="hlt">variation</span> in each region and assess the extent to which they may be interrelated. We have identified the times of magnetic field excursions 7α, 7β, 8α, 9α, and 9β in the Atlantic records and correlated those times to the Bering Sea records. There are no true excursions in the Bering Sea at those times, but several of these intervals mark the most anomalous field behavior in the Bering Sea during MIS 7-10. In both regions, the PSV also serves as a high-resolution chronostratigraphic tool for regional correlation of environmental variability. Both regions show clear, reproducible evidence among the sites for synchronous millennial-scale environmental variability that has not been diagnosed previously.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..1212546L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..1212546L"><span>Dating Lake Tahoe (CA/NV) and Mono Lake (CA) sediment using palaeomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> as a chronology for late Pleistocene palaeoclimate in the U.S. Great Basin</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liddicoat, Joseph</p> <p>2010-05-01</p> <p>In 1976, six meters of graded and varved sediment were recovered in three piston cores from Lake Tahoe, CA/NV, and used for palaeomagnetic and sedimentologic investigations (Palmer et al., 1979; Denham, 1981). The long-term changes (<span class="hlt">secular</span> <span class="hlt">variation</span>) in the Lake Tahoe palaeomagnetic record were compared to <span class="hlt">secular</span> <span class="hlt">variation</span> in exposed lacustrine sediment of the Wilson Creek Formation (Lajoie, 1993) in the Mono Basin, CA, (Denham and Cox, 1971), 100 km away. During the more than 30 years since the coring was done in Lake Tahoe, the record of palaeomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> in the Mono Basin and elsewhere in the Great Basin has been refined (Liddicoat and Coe, 1979; Lund et al., 1988, Liddicoat and Coe, 1997; Liddicoat and Coe, 1998; Benson et al., 1998; Negrini and Davis, 1992; Kent et al., 2002; Zimmerman et al., 2006) to allow a reexamination of the palaeomagnetic directions and environmental magnetic record in the Lake Tahoe cores and the age of those sediments. Inferences are also possible about the sedimentological importance during the recording of the palaeomagnetic field at Lake Tahoe and possibly in the Mono Basin, and the age of the Lake Tahoe sediment recovered, which postdates the Mono Lake Excursion. The age of the Mono Lake Excursion and Wilson Creek Formation is relevant to investigations of Late Pleistocene palaeoclimate reconstructions for the U.S. Great Basin (Zimmerman et al., 2006).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1983EOSTr..64..484F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1983EOSTr..64..484F"><span><span class="hlt">Geomagnetism</span> and paleomagnetism 1979-1983</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fuller, M.</p> <p></p> <p>My function, in writing these notes, is to bring you up to date in <span class="hlt">Geomagnetism</span> and Paleomagnetism, in as painless a manner as possible—without tears, as the French language texts for tourists used to promise. In writing this account of progress in the past quadrennium, I must first acknowledge that it is a personal and subjective viewpoint;; another reporter would surely emphasize other developments. Yet, there is some virture in writing of things, about which one knows something, so I leave to future reporters the task of redresssing the balance in matters covered.At the outset, one very sad event must be recorded. On April 3, 1981, Sir Edward Bullard died. His published work alone marks him as one of the leaders of <span class="hlt">geomagnetism</span> in our times. Yet his contribution was much greater; many an American geophysicist, as well as a whole generation of British colleagues, have felt the benefit of his perceptive advice on their research. To those who saw him in the last few months of his life, his courage in the face of his illness was a remarkable example of fortitude. It is by now well known that the definitive paper, which he wrote with Malin, on <span class="hlt">secular</span> <span class="hlt">variation</span> at London, was only completed immediately before his death. The transmittal letter had been typed, but death prevented him from signing it. Bullard returned in this final paper to a topic to which he had contributed much. In it, he notes the role of Halley, who first described the phenomenon of westward drift, to which Bullard gave a new numerical precision, two and a half centuries later. I seem to remember Bullard saying in a lecture years ago that, while the Newtons of this world seem other than mortal, Halley was a scientist whose life and acheivements could encourage one's own efforts. Bullard, like Halley, inspires and encourages us.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28636777','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28636777"><span>Biological effects related to <span class="hlt">geomagnetic</span> activity and possible mechanisms.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Krylov, Viacheslav V</p> <p>2017-06-21</p> <p>This review presents contemporary data on the biological effects of <span class="hlt">geomagnetic</span> activity. Correlations between <span class="hlt">geomagnetic</span> indices and biological parameters and experimental studies that used simulated <span class="hlt">geomagnetic</span> storms to detect possible responses of organisms to these events in nature are discussed. Possible mechanisms by which <span class="hlt">geomagnetic</span> activity influences organisms are also considered. Special attention is paid to the idea that <span class="hlt">geomagnetic</span> activity is perceived by organisms as a disruption of diurnal <span class="hlt">geomagnetic</span> <span class="hlt">variation</span>. This <span class="hlt">variation</span>, in turn, is viewed by way of a secondary zeitgeber for biological circadian rhythms. Additionally, we discuss the utility of cryptochrome as a biological detector of <span class="hlt">geomagnetic</span> storms. The possible involvement of melatonin and protein coding by the CG8198 gene in the biological effects of <span class="hlt">geomagnetic</span> activity are discussed. Perspectives for studying mechanisms by which <span class="hlt">geomagnetic</span> storms affect organisms are suggested. Bioelectromagnetics. 2017;9999:1-14. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016STP.....2c..33L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016STP.....2c..33L"><span><span class="hlt">Geomagnetic</span> effects caused by rocket exhaust jets</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lipko, Yuriy; Pashinin, Aleksandr; Khakhinov, Vitaliy; Rahmatulin, Ravil</p> <p>2016-09-01</p> <p>In the space experiment Radar-Progress, we have made 33 series of measurements of <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> during ignitions of engines of Progress cargo spacecraft in low Earth orbit. We used magneto-measuring complexes, installed at observatories of the Institute of Solar-Terrestrial Physics of Siberian Branch of the Russian Academy of Sciences, and magnetotelluric equipment of a mobile complex. We assumed that engine running can cause <span class="hlt">geomagnetic</span> disturbances in flux tubes crossed by the spacecraft. When analyzing experimental data, we took into account space weather factors: solar wind parameters, total daily mid-latitude <span class="hlt">geomagnetic</span> activity index Kp, <span class="hlt">geomagnetic</span> auroral electrojet index AE, global <span class="hlt">geomagnetic</span> activity. The empirical data we obtained indicate that 18 of the 33 series showed <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> in various time ranges.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AdSpR..50.1310A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AdSpR..50.1310A"><span>Temporal <span class="hlt">variation</span> of the arterial pressure in healthy young people and its relation to <span class="hlt">geomagnetic</span> activity in Mexico</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Azcárate, T.; Mendoza, B.; Sánchez de la Peña, S.; Martínez, J. L.</p> <p>2012-11-01</p> <p>We present a study of the temporal behavior of the systolic (SBP) and diastolic (DBP) blood pressure for a sample of 51 normotensive, healthy volunteers, 18 men and 33 women with an average age of 19 years old in Mexico City, Mexico, during April and May, 2008. We divided the data by sex along the circadian rhythm. Three <span class="hlt">geomagnetic</span> storms occurred during the studied time-span. The strongest one, a moderate storm, is attributed to a coronal hole border that reached the Earth. The ANOVA test applied to the strongest storm showed that even though we are dealing with a moderate <span class="hlt">geomagnetic</span> storm, there are statistically significant responses of the blood pressure. The superposed epoch analysis during a three-day window around the strongest storm shows that on average the largest changes occurred for the SBP. Moreover, the SBP largest increases occurred two days before and one day after this storm, and women are the most sensitive group as they present larger SBP and DBP average changes than men. Finally, given the small size of the sample, we cannot generalize our results.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GGG....17..538S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GGG....17..538S"><span>Plio-Pleistocene paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> and time-averaged field: Ruiz-Tolima volcanic chain, Colombia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sánchez-Duque, A.; Mejia, V.; Opdyke, N. D.; Huang, K.; Rosales-Rivera, A.</p> <p>2016-02-01</p> <p>Paleomagnetic results obtained from 47 Plio-Pleistocene volcanic flows from the Ruiz-Tolima Volcanic Chain (Colombia) are presented. The mean direction of magnetization among these flows, which comprise normal (n = 43) and reversed (n = 4) polarities, is Dec = 1.8°, Inc = 3.2°, α95 = 5.0°, and κ = 18.4. This direction of magnetization coincides with GAD plus a small persistent axial quadrupolar component (around 5%) at the site-average latitude (4.93°). This agreement is robust after applying several selection criteria (α95 < 10º α95 < 5.5º polarities: normal, reversed, and tentatively transitional). The data are in agreement with Model G proposed by McElhinny and McFadden (1997) and the fit is improved when sites tentatively identified as transitional (two that otherwise have normal polarity) are excluded from the calculations. Compliance observed with the above mentioned time-averaged field and paleosecular <span class="hlt">variation</span> models, is also observed for many recent similar studies from low latitudes, with the exception of results from Galapagos Islands that coincide with GAD and tend to be near sided.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19880040223&hterms=fashion+trend&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dfashion%2Btrend','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19880040223&hterms=fashion+trend&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dfashion%2Btrend"><span>A model for solar constant <span class="hlt">secular</span> changes</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Schatten, Kenneth H.</p> <p>1988-01-01</p> <p>In this paper, contrast models for solar active region and global photospheric features are used to reproduce the observed Active Cavity Radiometer and Earth Radiation Budget <span class="hlt">secular</span> trends in reasonably good fashion. A prediction for the next decade of solar constant <span class="hlt">variations</span> is made using the model. <span class="hlt">Secular</span> trends in the solar constant obtained from the present model support the view that the Maunder Minimum may be related to the Little Ice Age of the 17th century.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JGRA..122.4571S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JGRA..122.4571S"><span>Solar and lunar tidal variabilities in GPS-TEC and <span class="hlt">geomagnetic</span> field <span class="hlt">variations</span>: Seasonal as well as during the sudden stratospheric warming of 2010</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sridharan, S.</p> <p>2017-04-01</p> <p>The Global Positioning System (GPS) deduced total electron content (TEC) data at 15°N (<span class="hlt">geomagnetic</span>), which is the northern crest region of equatorial ionization anomaly, are used to study solar and lunar tidal variabilities during the years 2008 and 2009 and also during the 2009-2010 winter, when a major sudden stratospheric warming (SSW) event has occurred. The diurnal and semidiurnal tidal amplitudes show semiannual <span class="hlt">variation</span> with maximum amplitudes during February-March and September-November, whereas terdiurnal tide is larger during April-September. They show significant longitudinal variability with larger (smaller) amplitudes over 250°E-150°E (200°E-250°E). Lunar semidiurnal tidal amplitudes show sporadic enhancements during northern winter months and negligible amplitudes during northern summer months. They also show notable longitudinal variabilities. The solar migrating tides DW1 and SW2 show semiannual <span class="hlt">variation</span> with larger amplitudes during spring equinox months, whereas TW3 maximizes during northern summer. DW2 shows larger amplitudes during summer months. During the SSW, except TW3, the migrating tides DW1 and SW2 show considerable enhancements. Among solar nonmigrating tides, SW1, TW2, and DS0 show larger enhancements. Solar tides in TEC and equatorial electrojet strength over Tirunelveli vary with the time scale of 60 days during October 2009-March 2010 similar to ozone mass mixing ratio at 10 hPa, and this confirms the vital role of ozone in tidal variabilities in ionospheric parameters. Lunar tidal amplitudes in changes in horizontal component of <span class="hlt">geomagnetic</span> field (ΔH) are larger over Tirunelveli, a station near dip equator. Solar semidiurnal tides in ΔH have larger amplitudes than lunar tides over polar stations, Mawson and Godhavn.<abstract type="synopsis"><title type="main">Plain Language SummaryIn this paper, the <span class="hlt">variations</span> of solar and lunar tides in a few ionospheric parameters during the years 2008 and 2009 and during a disturbed</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.458..120L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.458..120L"><span>A full-vector paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> record (PSV) from Pyramid Lake (Nevada) from 47-17 ka: Evidence for the successive Mono Lake and Laschamp Excursions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lund, S.; Benson, L.; Negrini, R.; Liddicoat, J.; Mensing, S.</p> <p>2017-01-01</p> <p>We have carried out a paleomagnetic study of late-Pleistocene Pyramid Lake core PLC08-1 (1680 cm). Our goals were to develop a full-vector paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> (PSV) record for the core, establish a paleomagnetic chronostratigraphy for the lake based on correlation of the PSV record to other dated PSV records in the region, compare that chronostratigraphy with previously developed radiocarbon and ash chronologies, and search for evidence of the Mono Lake Excursion and Laschamp Excursion. We have recovered a full-vector PSV record (inclination, declination, relative paleointensity) for the interval 47 ka to 17 ka. Twenty radiocarbon dates and four dated ashes provided a chronostratigraphic framework for this record. We have also used the link between our PSV and other dated PSV records to develop an independent PSV chronostratigraphy for the core. The PSV chronostratigraphy is not significantly different from that estimated by the radiocarbon and ash chronologies. We note the existence of two intervals of anomalous paleomagnetic directions. The younger interval, centered at 34.1 ± 0.4 ka, has the characteristic vector component features of the Mono Lake Excursion. The older interval, centered at 40.9 ± 0.5 ka, has the characteristic paleomagnetic signature of the Laschamp Excursion. This is the first time both intervals of excursional behavior have been found in the same sediment record from the western USA. Our new PSV record also corroborates previous estimates of the Mono Lake Excursion directional field behavior (Liddicoat and Coe, 1979) and age (Benson et al., 2003).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013seg..book.....F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013seg..book.....F"><span><span class="hlt">Secular</span> Evolution of Galaxies</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Falcón-Barroso, Jesús; Knapen, Johan H.</p> <p>2013-10-01</p> <p>Preface; 1. <span class="hlt">Secular</span> evolution in disk galaxies John Kormendy; 2. Galaxy morphology Ronald J. Buta; 3. Dynamics of <span class="hlt">secular</span> evolution James Binney; 4. Bars and <span class="hlt">secular</span> evolution in disk galaxies: theoretical input E. Athanassoula; 5. Stellar populations Reynier F. Peletier; 6. Star formation rate indicators Daniela Calzetti; 7. The evolving interstellar medium Jacqueline van Gorkom; 8. Evolution of star formation and gas Nick Z. Scoville; 9. Cosmological evolution of galaxies Isaac Shlosman.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014SGeo...35.1123G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014SGeo...35.1123G"><span>Survey of <span class="hlt">Geomagnetic</span> Observations Made in the Northern Sector of Russia and New Methods for Analysing Them</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gvishiani, Alexei; Lukianova, Renata; Soloviev, Anatoly; Khokhlov, Andrei</p> <p>2014-09-01</p> <p>An overview of the <span class="hlt">geomagnetic</span> observations made in the northern part of Russia is presented from a historical perspective. Several stations were deployed on the territory of the former Soviet Union during the International Geophysical Year, 1957-1958, with the active participation and guidance of the Interagency Geophysical Committee which is inherited by the Geophysical Center of the Russian Academy of Sciences (GC RAS). In the 1990s, the majority of these stations, especially those in the remoter regions, were closed. Nowadays, the <span class="hlt">geomagnetic</span> network, including the observatories of the INTERMAGNET program, has been restored. Examples of high-latitude <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> in the Russian longitudinal sector are shown, and maps and trends of the <span class="hlt">secular</span> <span class="hlt">variation</span> over the territory of Russia presented. Particular attention is paid to the automated processing of data and to the analysis methods used. To process the growing amount of high-resolution <span class="hlt">geomagnetic</span> data, sophisticated mathematical methods based on the fuzzy logic approach and new discrete mathematical analysis algorithms have been developed. The formal methods and algorithms for recognizing both artificial and natural disturbances in the magnetograms are described.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014Ap%26SS.350..459G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014Ap%26SS.350..459G"><span>Study of simultaneous presence of DD and PP electric fields during the <span class="hlt">geomagnetic</span> storm of November 7-8, 2004 and resultant TEC <span class="hlt">variation</span> over the Indian Region</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Galav, P.; Sharma, Shweta; Rao, S. S.; Veenadhari, B.; Nagatsuma, T.; Pandey, R.</p> <p>2014-04-01</p> <p>During very intense <span class="hlt">geomagnetic</span> storm of November 7-8, 2004 simultaneous presence of storm time disturbance dynamo and eastward and westward directed prompt penetration electric fields inferred from the ground based magnetometer data in the 75∘ E sector is presented. Magnetometer observations show that, on the whole, average Δ H <span class="hlt">variation</span> on 8 November remains below the night time level compared to its quiet day <span class="hlt">variation</span>. A number of upward and downward excursions have been observed between 0130 UT and 0800 UT in the Δ H <span class="hlt">variation</span> on 8 November. These excursions in Δ H have been attributed to the episodes of eastward and westward prompt penetrating electric fields. Ionospheric response in the equatorial ionization anomaly region along 75∘ E has also been studied using the total electron content data recorded at five GPS stations, namely Udaipur, Bengaluru (IISC), Hyderabad (HYDE), Maldives (MALD) and Diego Garcia (DGAR). Observation of markedly suppressed EIA, in conjunction with Δ H <span class="hlt">variation</span> which was m negative during the daytime on 8 November, indicates the presence of an external field of opposite polarity (the disturbance dynamo electric field) that either undermined, or overshadowed the daytime ambient (eastward) electric field to the extent that the equatorial plasma fountain could not become effective.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMGC43B0718F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMGC43B0718F"><span>The influence of El-Niño Southern Oscillation and Pacific Decadal Oscillation on <span class="hlt">secular</span> rainfall <span class="hlt">variations</span> in Hawai'i</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Frazier, A. G.; Elison Timm, O.; Giambelluca, T. W.</p> <p>2014-12-01</p> <p>Large-scale teleconnections, particularly the El-Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO), have a strong influence on rainfall patterns in Hawai'i. Over the last century, we have observed statistically significant declines in rainfall across the state, and it is unknown whether these declines are due to changes in these natural large-scale <span class="hlt">variations</span> in climate, or whether these downward trends can be explained by anthropogenic effects. To better aid managers and decision-makers, it is important to understand what is driving current trends. Here we use an empirical approach to study long-term trends in a geographically complex region and diverse climate. Using a time series of month-year rainfall maps for Hawai'i starting in January 1920 at 250 m resolution, an empirical orthogonal function (EOF) analysis was performed to study the spatiotemporal <span class="hlt">variations</span> and trend patterns. We further correlate the leading spatial and temporal components with ENSO and PDO indices, linear trends, and <span class="hlt">secular</span> trends. More of the variability is contained in the first component in the winter (December-January-February) than in the summer (June-July-August), especially in the northern islands (Kaua'i and O'ahu) suggesting that natural climate variability has a stronger effect on the spatiotemporal rainfall patterns during the winter season than the summer season. Currently, independent efforts to downscale future climate projections for Hawai'i have produced different future outlooks for rainfall. In the absence of adequately designed control experiments with regional climate models, we propose evaluating differences between observed and projected trend patterns as an alternative criterion for measuring the significance and plausibility of future climate change projections. Our results show the difficulties of separating anthropogenic and natural rainfall trends, e.g., identifying spatial (and seasonal) patterns of the trends that are different from</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMGP12A..02S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMGP12A..02S"><span>Northern hemisphere mid-latitude <span class="hlt">geomagnetic</span> anomaly revealed from Levantine Archaeomagnetic Compilation (LAC).</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shaar, R.; Tauxe, L.; Agnon, A.; Ben-Yosef, E.; Hassul, E.</p> <p>2015-12-01</p> <p>The rich archaeological heritage of Israel and nearby Levantine countries provides a unique opportunity for archaeomagnetic investigation in high resolution. Here we present a summary of our ongoing effort to reconstruct <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> of the past several millennia in the Levant at decadal to millennial resolution. This effort at the Southern Levant, namely the "Levantine Archaeomagnetic Compilation" (LAC), presently consists of data from over 650 well-dated archaeological objects including pottery, slag, ovens, and furnaces. In this talk we review the methodological challenges in achieving a robust master <span class="hlt">secular</span> <span class="hlt">variation</span> curve with realistic error estimations from a large number of different datasets. We present the current status of the compilation, including the southern and western Levant LAC data (Israel, Cyprus, and Jordan) and other published north-eastern Levant data (Syria and southern Turkey), and outline the main findings emerging from these data. The main feature apparent from the new compilation is an extraordinary intensity high that developed over the Levant region during the first two millennia BCE. The climax of this event is a double peak intensity maximum starting at ca. 1000 BCE and ending at ca. 735 BCE, accompanied with at least two events of <span class="hlt">geomagnetic</span> spikes. Paleomagnetic directions from this period demonstrate anomalies of up to 20 degrees far from the averaged GAD field. This leads us to postulate that the maximum in the intensity is a manifestation of an intense mid-latitude local positive <span class="hlt">geomagnetic</span> anomaly that persisted for over two centuries.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/15864403','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/15864403"><span>Correlations of life-span <span class="hlt">variation</span> parameters in 128 successive generations of Drosophila melanogaster with changes in atmospheric pressure and <span class="hlt">geomagnetic</span> activity.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Izmaylov, D M; Obukhova, L K; Konradov, A A</p> <p>2005-05-01</p> <p>Correlations between the parameters of life-span (LS) distribution of Drosophila melanogaster, including mean LS (MLS) and the time of 10 and 90% population mortality, and some geophysical parameters that are usually beyond the control of researchers dealing with laboratory cultures, including atmospheric pressure, solar activity indices (Wolf's sunspot numbers and 2,800-MHz radio flux), and <span class="hlt">geomagnetic</span> activity (planetary index, K(p)), were studied. Geophysical data were obtained from free-access official web sites of the National Oceanic & Atmospheric Administration of the US Department of Commerce and the Institute of Terrestrial Magnetism and Radiowave Propagation of the Russian Academy of Sciences. The geophysical parameters were calculated only for the period corresponding to 10 days of preimaginal development of the flies from egg to imago. Canonical correlation analysis, calculation of the non-parametric Spearman rank-order correlation coefficients, and graphical data analysis were used. Highly significant correlations between parameters of LS distribution in males and females and environmental factors, such as the atmospheric pressure on the 4th and 5th day of development and <span class="hlt">geomagnetic</span> activity indices (K(p)) on the 6th and 10th day of development were found, with correlation coefficients varying from 0.31 to 0.37 (P<0.02). Assuming a causal relationship between geophysical factors and LS, it may be hypothesized that energetically weak environmental factors determine the formation of LS oscillatory dynamics in laboratory populations. The possible mechanisms underlying the contribution of these environmental factors to the LS <span class="hlt">variation</span> in successive generations are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006GeCoA..70..891R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006GeCoA..70..891R"><span>Mg fractionation in crustose coralline algae: Geochemical, biological, and sedimentological implications of <span class="hlt">secular</span> <span class="hlt">variation</span> in the Mg/Ca ratio of seawater</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ries, Justin B.</p> <p>2006-02-01</p> <p> Mg incorporation. Therefore, the Mg/Ca ratio of well-preserved fossils of crustose coralline algae, when corrected for the effect of seawater temperature, may be an archive of oceanic Mg/Ca throughout the Phanerozoic. Magnesium fractionation algorithms that model algal skeletal Mg/Ca as a function of seawater Mg/Ca and temperature are presented herein. The results of this study support the empirical fossil evidence that <span class="hlt">secular</span> <span class="hlt">variation</span> of oceanic Mg/Ca has caused the mineralogy and skeletal chemistry of many calcifying marine organisms to change significantly over geologic time.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012QSRv...42...43L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012QSRv...42...43L"><span>Using an independent geochronology based on palaeomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> (PSV) and atmospheric Pb deposition to date Baltic Sea sediments and infer 14C reservoir age</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lougheed, Bryan C.; Snowball, Ian; Moros, Matthias; Kabel, Karoline; Muscheler, Raimund; Virtasalo, Joonas J.; Wacker, Lukas</p> <p>2012-05-01</p> <p>Dating of sediment cores from the Baltic Sea has proven to be difficult due to uncertainties surrounding the 14C reservoir age and a scarcity of macrofossils suitable for dating. Here we present the results of multiple dating methods carried out on cores in the Gotland Deep area of the Baltic Sea. Particular emphasis is placed on the Littorina stage (8 ka ago to the present) of the Baltic Sea and possible changes in the 14C reservoir age of our dated samples. Three geochronological methods are used. Firstly, palaeomagnetic <span class="hlt">secular</span> <span class="hlt">variations</span> (PSV) are reconstructed, whereby ages are transferred to PSV features through comparison with varved lake sediment based PSV records. Secondly, lead (Pb) content and stable isotope analysis are used to identify past peaks in anthropogenic atmospheric Pb pollution. Lastly, 14C determinations were carried out on benthic foraminifera (Elphidium spec.) samples from the brackish Littorina stage of the Baltic Sea. Determinations carried out on smaller samples (as low as 4 μg C) employed an experimental, state-of-the-art method involving the direct measurement of CO2 from samples by a gas ion source without the need for a graphitisation step - the first time this method has been performed on foraminifera in an applied study. The PSV chronology, based on the uppermost Littorina stage sediments, produced ten age constraints between 6.29 and 1.29 cal ka BP, and the Pb depositional analysis produced two age constraints associated with the Medieval pollution peak. Analysis of PSV data shows that adequate directional data can be derived from both the present Littorina saline phase muds and Baltic Ice Lake stage varved glacial sediments. Ferrimagnetic iron sulphides, most likely authigenic greigite (Fe3S4), present in the intermediate Ancylus Lake freshwater stage sediments acquire a gyroremanent magnetisation during static alternating field (AF) demagnetisation, preventing the identification of a primary natural remanent magnetisation for</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016QSRv..144...16L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016QSRv..144...16L"><span>Full-vector paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> records from latest quaternary sediments of Lake Malawi (10.0°S, 34.3°E)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lund, Steve; Platzman, Ellen; Johnson, Tom</p> <p>2016-07-01</p> <p>We have conducted a paleomagnetic study of Late Quaternary sediments from Lake Malawi, East Africa, in order to develop a high-resolution record of paleomagnetic <span class="hlt">secular</span> <span class="hlt">variation</span> (PSV). This study has recovered PSV records from two cores (3P, 6P) in northern Lake Malawi (10.0°S, 34.3°E). The PSV appears to be recorded in fine-grained detrital magnetite/titanomagnetite grains. Detailed af demagnetization of the natural remanence (NRM) shows that a distinctive characteristic remanence (ChRM) is demagnetized from ∼20 to 80 mT, which decreases simply toward the origin. The resulting directional PSV records for 3P and 6P are easily correlatable with 29 distinct inclination features and 29 declination features. The statistical character of the PSV in both cores is consistent with Holocene PSV noted at other Holocene equatorial sites. Radiocarbon dating of the cores is based on 18 independent radiocarbon dates and four dated stratigraphic horizons that can be correlated into each core. The final directional PSV time series cover the last 24,000 years with an average sediment accumulation rate of ∼30 cm/kyr. We have also developed a relative paleointensity estimate for these PSV records based on normalizing the NRM (after 20 mT af demagnetization) by the SIRM (after 20 mT af demagnetization). Changing sedimentation patterns complicate any attempt to develop a single paleointensity record for the entire core lengths. We have developed a relative paleointensity record for the last 6000 years that has 14 correlatable features including 5 notable peaks in intensity. Three of these peaks are synchronous with paleointensity highs farther north in SE Europe/SW Asia/Egypt but two of the peaks are at times of low paleointensity farther north. We interpret this to indicate that Lake Malawi (10°S) is at least partly under the influence of a different flux-regeneration region of the outer-core dynamo. A relative paleointensity record was also developed for ∼11,000-24,000 YBP</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AAS...21340613B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AAS...21340613B"><span><span class="hlt">Secular</span> Acceleration of Barnard's Star</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bartlett, Jennifer L.; Ianna, P. A.</p> <p>2009-01-01</p> <p>Barnard's Star should have significant <span class="hlt">secular</span> acceleration because it lies close to the Sun and has the highest known proper motion along with a large radial velocity. It will pass within about 1.4 pc in another 9,750 years. <span class="hlt">Secular</span> changes in proper motion and radial velocity are essentially the Coriolis and centrifugal accelerations, respectively, arising from use of a rotating coordinate system defined by the Sun-star radius vector. Although stellar space velocities measured with respect to the Sun are essentially constant, these perspective effects arise with changing distance and viewing angle. Hipparcos-2 plus Nidever et al. (2002) predict a perspective change in the proper motion of 1.285±0.006 mas yr-2 for Barnard's Star. Recent analysis of 900+ photographic plates between 1968 and 1998 with the 26.25-in (0.67-m) McCormick refractor detected a <span class="hlt">secular</span> acceleration of 1.25±0.04 mas yr-2, which agrees with the predicted value within the measurement errors. Earlier, Benedict et al. (1999) measured its <span class="hlt">secular</span> acceleration to be 1.2±0.2 mas yr-2 using 3 years of HST FGS observations. Similarly, a perspective change in radial velocity of 4.50±0.01 m s-1 yr-1 can be predicted for Barnard's Star. Kürster et al. (2003) detected <span class="hlt">variations</span> in their observations of it that are largely attributable to <span class="hlt">secular</span> acceleration along the line of sight with some contribution from stellar activity. Although <span class="hlt">secular</span> acceleration effects have been limited for past studies of stellar motions, they can be significant for observations extending over decades or for high-precision measurements required to detect extrasolar planets. Future studies will need to consider this factor for the nearest stars and for those with large proper motions or radial velocities. NSF grant AST 98-20711; Litton Marine Systems; Peninsula Community Foundation Levinson Fund; UVa Governor's Fellowship, Dean's F&A Fellowship, and Graduate School of Arts and Sciences; and, US Naval Observatory</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMGP23A1277C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMGP23A1277C"><span>New Archaeointensity Result from Middle-Eastern China and Its Constraints on the <span class="hlt">Variation</span> of the <span class="hlt">Geomagnetic</span> Field during the last 6 kyr</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cai, S.; Jin, G.; Deng, C.; Tauxe, L.; Qin, H.; Pan, Y.; Zhu, R.</p> <p>2015-12-01</p> <p>Archaeomagnetic study is an effective way to understand the <span class="hlt">variation</span> of the <span class="hlt">geomagnetic</span> field over periods of hundreds to thousands of years. We have carried out archaeointensity studies on archaeological artifacts, including pottery fragments, bricks and baked clay, collected from several sites covering the middle to eastern part of China spanning the past ~6 kyr. We designed detailed rock magnetic and archaeointensity experiments in this study. Rock magnetic results indicate that the main magnetic carriers of these samples are stable magnetite or titanomagnetite with mainly fine particles of SD and SP. About 40% of the specimens in the paleointensity experiment pass the strict selection criteria and are considered to record robust intensity values. The virtual axial dipole moments (VADMs) of our sites range from ~2.5×1022 to ~15.8×1022 Am2. We record three low intensity values with VADMs of less than 3×1022 Am2, two of them comparable to the one reported by Cai et al. (2015) at ~3000 BCE while the other one comparable to those reported by Cai et al. (2014) at ~2200 BCE, which supply further evidence for the existence of 'DIPs' (decreases in paleoinetnsity) in China during the period of ~3000-2000 BCE. A high intensity value of ~16×1022 Am2 is recorded by our new data at ~1300 BCE, which may represent a new spike at this time period. The low and high values recorded by our new data update the six-fold <span class="hlt">variation</span> between ~2200 BCE and ~1300 BCE discussed in Cai et al. (2014) to eight-fold, which may indicate a stronger geodynamic process during this period. Our new data are generally in good agreement with the published data in China, Japan and Korea at similar time periods, except the extreme low and high values discussed above, which will improve the Eastern Asian model greatly. The new data together with the published data suggest severe fluctuation of the <span class="hlt">geomagnetic</span> field in Eastern Asia during the last 6 kyr. Vast quantities of reliable data are needed to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..1914014M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..1914014M"><span>Electrical conductivity structure of the mantle derived from inversion of <span class="hlt">geomagnetic</span> observatory data: implications for lateral <span class="hlt">variations</span> in temperature, composition and water content.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Munch, Federico; Grayver, Alexander; Khan, Amir; Kuvshinov, Alexey</p> <p>2017-04-01</p> <p>As most of Earth's interior remains geochemically unsampled, geophysical techniques based on seismology, geodesy, gravimetry, and electromagnetic studies play prominent roles because of their ability to sense structure at depth. Although seismic tomography maps show a variety of structures, separating thermal and compositional contributions from seismic velocities alone still remains a challenging task. Alternatively, as electrical conductivity is sensitive to temperature, chemical composition, oxygen fugacity, water content, and the presence of melt, it can serve for determining chemistry, mineralogy, and physical structure of the deep mantle. In this work we estimate and invert local C-responses (period range 3-100 days) for a number of worldwide <span class="hlt">geomagnetic</span> observatories to map lateral <span class="hlt">variations</span> of electrical conductivity in Earth's mantle (400-1600 km depth). The obtained conductivity profiles are interpreted in terms of basalt fraction in a basalt-harzburgite mixture, temperature structure, and water content <span class="hlt">variations</span>. Interpretation is based on a self-consistent thermodynamic calculation of mineral phase equilibria, electrical conductivity databases, and probabilistic inverse methods.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007IzPSE..43..819G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007IzPSE..43..819G"><span>Wavelet analysis of paleomagnetic data: 1. Characteristic average times (5 10 kyr) of <span class="hlt">variations</span> in the <span class="hlt">geomagnetic</span> field during and immediately before and after the Early Jaramillo reversal (Western Turkmenistan)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gurarii, G. Z.; Aleksyutin, M. V.; Ataev, N.</p> <p>2007-10-01</p> <p>Joint wavelet analysis of complete and downsampled series of paleomagnetic and petromagnetic characteristics of rocks in the Matuyama-Jaramillo transitional zone in the Adzhidere section is used to extract paleomagnetic data whose <span class="hlt">variations</span> are associated with the <span class="hlt">geomagnetic</span> field alone and data correlating with <span class="hlt">variations</span> in petromagnetic parameters. It supposed that this correlation can be caused by an external factor affecting weak <span class="hlt">variations</span> in the magnetic field and climatic changes reflected in the composition and amount of the ferromagnetic fraction in rocks. Preliminary data are obtained for the characteristic times of field <span class="hlt">variations</span> at the time of accumulation of rocks in the transitional zone.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/7302560','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/7302560"><span>Geochemistry of Cambro-Ordovician Arbuckle limestone, Oklahoma: Implications for diagenetic. delta. sup 18 O alteration and <span class="hlt">secular</span>. delta. sup 13 C and sup 87 Sr/ sup 86 Sr <span class="hlt">variation</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Gao, Guoqiu; Land, L.S. )</p> <p>1991-10-01</p> <p>Isotopic analyses of 227 limestone samples from the Cambro-Ordovician Arbuckle Group, Oklahoma, document slow <span class="hlt">secular</span> changes in the chemistry of the limestones. From late Cambrian to early Ordovician, the {delta}{sup 18}O values of the limestones increase from {minus}10{per thousand} to {minus}7{per thousand} (PDB); {delta}{sup 13}C values decrease from 0{per thousand} to {minus}2{per thousand} (PDB); and {sup 87}Sr/{sup 86}Sr ratios decrease from 0.7091 to 0.7088. The light {delta}{sup 18}O values suggest that all Arbuckle limestones underwent diagenetic alteration, probably caused by meteoric water recharged during the development of the overlying, pre-middle Ordovician unconformity. The gradual {delta}{sup 18}O increase from late Cambrian to early Ordovician reflects reduced {sup 18}O depletion with decreasing burial temperature during alteration, although the presence of additional primary <span class="hlt">secular</span> {delta}{sup 18}O <span class="hlt">variation</span> cannot be ruled out. The {delta}{sup 13}C and {sup 87}Sr/{sup 86}Sr <span class="hlt">variations</span>, in accord with {delta}{sup 13}C and {sup 87}Sr/{sup 86}Sr <span class="hlt">variations</span> in the literature, represent primary <span class="hlt">secular</span> <span class="hlt">variations</span>. The <span class="hlt">variations</span> indicate that the {delta}{sup 13}C value and {sup 87}Sr/{sup 86}Sr ratio of early Paleozoic surface seawater decreased from late Cambrian to early Ordovician. The {delta}{sup 13}C <span class="hlt">variation</span> during this time period seems to correlate with sea-level <span class="hlt">variation</span>. Specifically, during sea-level fall, an increase in the rate of oxidation of organic matter caused {sup 13}C depletion of inorganic bicarbonate in seawater. As a result, early Ordovician carbonates, probably deposited during the regression stage of the latest Precambrian to latest early Ordovician cycle, became {sup 13}C depleted, relative to late Cambrian carbonates. The decrease of seawater {sup 87}Sr/{sup 86}Sr ratio from late Cambrian to early Ordovician may have resulted from decreased riverine Sr input caused by decreased rate of continental weathering.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998PCE....23..703L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998PCE....23..703L"><span>Keith's early work in <span class="hlt">geomagnetism</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lowes, F. J.</p> <p></p> <p>This paper describes how Runcorn was started on his geophysical career by a chance combination of circumstances, when in 1947 he was given the job of measuring the <span class="hlt">variation</span> of the <span class="hlt">geomagnetic</span> field with depth inside the Earth, down British coal mines. It then shows how his interest in the semi-conduction of the lower mantle led to attempts to detect DC earth currents, at first again in mines, but later using discarded trans-Pacific telegraph cables. It ends by briefly discussing the “fifth force” measurements he instigated, which, though not a <span class="hlt">geomagnetic</span> problem, had many similarities with the original mine experiments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19730030036&hterms=Mead&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DMead%2BG.','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19730030036&hterms=Mead&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DMead%2BG."><span><span class="hlt">Geomagnetic</span> response to solar activity.</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mead, G. D.</p> <p>1972-01-01</p> <p>The relationship between solar activity and <span class="hlt">geomagnetic</span> <span class="hlt">variations</span> is discussed in the light of spacecraft data obtained during the last decade. The effects of centers of solar activity responsible for producing <span class="hlt">geomagnetic</span> activity on earth are believed to be transmitted through the solar wind, and there is usually a delay of two or three days before the onset of magnetic activity. Attempts to make a one-to-one correspondence between specific solar events and specific magnetic storms, however, are usually unsuccessful, because of the complex and indirect processes linking the two phenomena. Normally, only statistical tendencies can be shown.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998GeoRL..25.1011J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998GeoRL..25.1011J"><span>Persistently anomalous Pacific <span class="hlt">geomagnetic</span> fields</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Johnson, Catherine L.; Constable, Catherine G.</p> <p></p> <p>A new average <span class="hlt">geomagnetic</span> field model for the past 3kyr (ALS3K) helps bridge a large temporal sampling gap between historical models and more traditional paleomagnetic studies spanning the last 5 Myr. A quasi-static feature seen historically in the central Pacific has the opposite sign in ALS3K; its structure is similar to, but of larger amplitude than, that in the time-averaged <span class="hlt">geomagnetic</span> field for the last 5 Myr. Anomalous <span class="hlt">geomagnetic</span> fields exist beneath the Pacific over timescales ranging from 10²-106 years. It is unlikely that bias over such long time scales arises from electromagnetic screening, but conceivable that the Lorentz force is influenced by long wavelength thermal <span class="hlt">variations</span> and/or localized regions of increased electrical conductivity (associated with compositional anomalies and possibly partial melt). This is consistent with recent seismic observations of the lower mantle.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013IzPSE..49..130G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013IzPSE..49..130G"><span>Wavelet analysis of paleomagnetic data: 5. Early Jaramillo reversal and main characteristic times in the interval from 3 to 70 ka in the <span class="hlt">variations</span> of the elements of <span class="hlt">geomagnetic</span> field (Western Turkmenia)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gurarii, G. Z.</p> <p>2013-01-01</p> <p>The data on the <span class="hlt">variations</span> in the elements of the <span class="hlt">geomagnetic</span> field with the characteristic times of 3-70 ka during the 180-ka interval that includes the final stage of the Matuyama chron, the Jaramillo subchron, and the Early Jaramillo reversal are presented. A series of particular features are revealed in the <span class="hlt">variations</span>. It is shown that such detailed characteristics of the <span class="hlt">variations</span>, which might be critical for identifying the causes of the reversals, can only be derived by thorough investigation of the sedimentary rocks that were accumulated during very long time intervals (many hundreds of years) and slowly cooling intrusions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMSA44A..05R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMSA44A..05R"><span><span class="hlt">Variation</span> of Plasmaspheric (90-4000 km) Field-aligned Electron Density and Ion Composition as a Function of <span class="hlt">Geomagnetic</span> Storm Activity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Reddy, A.; Sonwalkar, V. S.</p> <p>2015-12-01</p> <p>Whistler mode (WM) radio sounding from IMAGE has led to the first measurements of plasmaspheric field-aligned electron density and ion composition as a function of <span class="hlt">geomagnetic</span> storm activity during Aug-Sep 2005, a period that included several successive <span class="hlt">geomagnetic</span> storms of varying strength. The plasmapause was located at L~2.4 during the onset and main phases of the storms. On the dayside, as a function of storm activity we found in general the following results: (1) The electron density, relative ion concentrations, and O+/H+ transition height had different temporal behavior. (2) Electron density in the first 1-2 days of the storm increased followed by a decrease in the recovery phase. (3) αH+ decreased during the onset, main and early recovery phase, and then it increased; αO+ increased in the early recovery phase, and then it decreased; αHe+ in general increased in the onset or main phase and decreased in the recovery phase. (4) O+/H+ transition height increased by ~200-300 km during the onset, main and early recovery phase. (5) When successive storms occurred in less than a day's span, the latter storms had little or no effect on the electron density and ion composition. On the nightside, WM sounding data was sparse. In the case of one moderate storm, we found that 3 days after the storm, electron density at F2 peak and relative ion concentrations (at all altitudes) were comparable to those before the storm, whereas electron density above O+/H+ transition height decreased. WM sounding results for the dayside and nightside were in agreement with measurements from CHAMP (350 km) and DMSP (850 km). WM sounding measurements coupled with physics-based models (e.g. SAMI2) will allow: (a) investigation of the role of thermospheric winds, dynamo and storm time electric fields in causing the <span class="hlt">variations</span> in electron and ion densities, and (b) testing of current theories and validating physics-based models of the thermosphere-ionosphere-magnetosphere coupling.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19870035698&hterms=Earth+core&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DEarth%2Bcore','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19870035698&hterms=Earth+core&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DEarth%2Bcore"><span>Steady flows at the top of earth's core derived from <span class="hlt">geomagnetic</span> field models</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Voorhies, Coerte V.</p> <p>1986-01-01</p> <p>Select models of the main <span class="hlt">geomagnetic</span> field and its <span class="hlt">secular</span> <span class="hlt">variation</span> are extrapolated to the base of an insulating mantle and used to estimate the adjacent fluid motion of a perfectly conducting outer core. The assumption of steady motion provides formally unique solutions and is tested along with that of no upwelling. The hypothesis of no upwelling is found to be substantially worse than that of steady motion. Although the actual motion is not thought to be steady, the large-scale <span class="hlt">secular</span> <span class="hlt">variation</span> at the top of the core can be adequately described by a large-scale, combined toroidal-poloidal circulation which is steady for intervals of at least a decade or two. The derived flows include a bulk westward drift but are complicated by superimposed jets, gyres, and surface divergence indicative of vigorous vertical motion at depth. The circulation pattern and key global properties including rms speed, upwelling, and westward drift are found to be fairly insensitive to <span class="hlt">variations</span> in modeling parameters.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1987AnGeo...5..429T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1987AnGeo...5..429T"><span>Simulation of ionospheric electric fields and <span class="hlt">geomagnetic</span> field <span class="hlt">variation</span> by the ionospheric dynamo for different solar activity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Takeda, Masahico; Yamada, Yuji</p>