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1

Dependence of time derivative of horizontal geomagnetic field on sunspot number and aa index  

NASA Astrophysics Data System (ADS)

This work investigated an interrelationship between the monthly means of time derivatives of horizontal geomagnetic field, d H/d t, sunspot number, R z , and aa index for the period of substorms (from -90 to -1800 nT) during the years 1990-2009. A total of 232 substorms were identified during the period of study. The time derivative of horizontal geomagnetic field, d H/d t, used as a proxy for geomagnetically induced current (GIC) exhibited high positive correlation with sunspot number (0.86) and aa index (0.8998). The obtained geomagnetic activity is in 92.665% explicable by the combined effect of sunspot number and aa index. The distribution of substorms as a function of years gives a strong support for the existence of geomagnetic activity increases, which implies that as the sunspot number increases the base level of geomagnetic activity increases too.

Falayi, Elijah O.; Rabiu, Babatunde A.

2013-02-01

2

Solar variability and climate change: Geomagnetic aa index and global surface temperature  

Microsoft Academic Search

During the past ?120 years, Earth's surface temperature is correlated with both decadal averages and solar cycle minimum values of the geomagnetic aa index. The correlation with aa minimum values suggests the existence of a long-term (low-frequency) component of solar irradiance that underlies the 11-year cyclic component. Extrapolating the aa-temperature correlations to Maunder Minimum geomagnetic conditions implies that solar forcing

E. W. Clivernd; V. Boriakoff; J. Feynman

1998-01-01

3

An extension of the geomagnetic activity index series aa for two solar cycles (1844–1868)  

Microsoft Academic Search

This paper deals with an extension of Mayaud's aa-index series (from 1868 to the present) for two solar cycles 1844–1868. The magnetic data sources are hourly declination readings at the Helsinki magnetic-meteorological observatory carried out in 1844–1880. The new data set provides a reliable and homogeneous series of declination for computations of equivalent aa–indices. For the time period 1868–1880 the

Heikki Nevanlinna; Eero Kataja

1993-01-01

4

Long-term biases in geomagnetic K and aa indices  

NASA Astrophysics Data System (ADS)

Analysis is made of the geomagnetic-activity aa index and its source K-index data from groups of ground-based observatories in Britain, and Australia, 1868.0-2009.0, solar cycles 11-23. The K data show persistent biases, especially for high (low) K-activity levels at British (Australian) observatories. From examination of multiple subsets of the K data we infer that the biases are not predominantly the result of changes in observatory location, localized induced magnetotelluric currents, changes in magnetometer technology, or the modernization of K-value estimation methods. Instead, the biases appear to be artifacts of the latitude-dependent scaling used to assign K values to particular local levels of geomagnetic activity. The biases are not effectively removed by weighting factors used to estimate aa. We show that long-term averages of the aa index, such as annual averages, are dominated by medium-level geomagnetic activity levels having K values of 3 and 4.

Love, J. J.

2011-08-01

5

Effects of station relocation in the aa index  

NASA Astrophysics Data System (ADS)

Earlier studies have shown that the long-term measure of geomagnetic activity, the aa index, is inhomogeneous and depicts an excessively large (about 12 nT) centennial increase. This has preliminarily been suggested to be due to possible station intercalibration problems in 1957 when the northern aa station was changed from Abinger to Hartland. In the present paper we show that the 3-hourly aa index time series is not uniform but includes systematic jump-like changes in the distribution of the various aa values with each change of stations in 1920, 1926, 1957, and 1980. We estimate how large a change to the aa index was caused by each particular aa value. We find that the changes to the aa index due to different ranges of activity are smooth and fairly similar for all jumps. In 1957 the largest aa values had, at the expense of more moderate aa values, a relatively larger contribution to the jump than in other station changes because the relative station coefficient was somewhat larger in 1957, leading to larger spreading and a higher average level of aa values. However, while this difference could cause a slight overestimate of the aa values, we find that the total changes in the aa index over jumps are in agreement, in both sign and magnitude, with the solar cycle variation. So it is unlikely that the excessive increase of the aa index would be due to erroneously estimated station coefficients.

Lukianova, R.; Alekseev, G.; Mursula, K.

2009-02-01

6

The geomagnetic index q - its persistence, predictability, and other pertinent properties. Environmental research papers  

SciTech Connect

The persistence and predictability of the geomagnetic index Q are demonstrated. The other important properties of this index are described. The immediate use and widespread utility of the results are indicated.

Reilly, A.E.

1978-09-18

7

Correcting the geomagnetic IHV index of the Eskdalemuir observatory  

NASA Astrophysics Data System (ADS)

We study here the recently proposed measure of local geomagnetic activity called the IHV (Inter-Hour Variability) index calculated for the Eskdalemuir (ESK) station. It was found earlier that the ESK IHV index depicts an artificial, step-like increase from 1931 to 1932. We show here that this increase is due to the fact that the values of the magnetic field components of the ESK observatory stored at the World Data Center are two-hour running averages of hourly data stored in ESK yearbooks. Two-hour averaging greatly reduces the variability of the data which leads to artificially small values of the IHV index in 1911-1931. We also study the effect of two-hour averaging upon hourly mean and spot values using 1-minute data available for recent years, and calculate the correction factors for the early years, taking into account the weak dependence of correction factors on solar activity. Using these correction factors, we correct the ESK IHV indices in 1912-1931, and revise the estimate of the centennial change based on them. The effect of correction is very significant: the centennial increase in the ESK IHV-raw (IHV-cor) index in 1912-2000 changes from 73.9% (134.4%) before correction to 10.3% (25.3%) thereafter, making the centennial increase at ESK quite similar to other mid-latitude stations. Obviously, earlier long-term studies based on ESK IHV values are affected by the correction and need to be revised. These results also strongly suggest that the ESK yearbook data should be digitized and the hourly ESK data at WDC should be replaced by them.

Martini, D.; Mursula, K.

2006-12-01

8

Geomagnetic-solar Activity Correlation Evolution  

Microsoft Academic Search

A study of the time evolution of solar (sunspot number-SSN) and geomagnetic (AA index) activity during the period 1868-1998 (annual averages) was made using Wavelet spectral analysis. As expected, wavelet maps have shown that the strongest signal in the SSN is the 11 years periodicity, while in the AA besides a period near 11 years, significant amplitudes are seen in

L. E. Vieira; N. R. Rigozo; E. Echer; D. J. Nordemann

2001-01-01

9

INTERPRETATION OF Kp INDEX AND M-REGION GEOMAGNETIC STORMS  

Microsoft Academic Search

It is argued that the traditional interpretation of the K\\/sub p\\/ index ; is no longer tenabie. The K\\/sub p\\/ index, generally taken to be a measure of the ; strength of the solar-wind flux, may be more acceptably interpreted as a measure ; of the time rate of change of the sum of plasma plus magnetic pressure acting on

A. J. Dessler; Fejer J. A

1963-01-01

10

Comparison of K-index Calculations between Several Geomagnetic Stations during IQDs and IDDs  

NASA Astrophysics Data System (ADS)

BOH magnetometer was installed at Mt. Bohyun in 2007 and has provided continuous dataset for 3-axis geomagnetic field over the South Korea. We have calculated real-time K-index based on BOH magnetic field data using well-known FMI method. Local K-index is calculated eight times a day, per every three hours. To calculate K-index, it is critical to get the Quiet Day Curve (QDC). For QDC calculation, we take the previous one month's average of H-component. In this paper, we compared four geomagnetic stations' magnetic field data over South Korea and Japan and K-indices of each stations; Bohyun, Gangneung, Jeju, and Kakioka for two years data, 2011-2012. To investigate the difference depending on the latitude, longitude and local time in more detail, we compare K-index on International Quiet Days (IQDs) and International Disturbed Days (IDDs). As a result, we report the correlation between local K-indices are higher than those between Kp and local K-indices, and the correlation is much better after sunset than after sunrise. As the geomagnetic activity becomes stronger, the correlation between the local K-indices and global Kp-index become higher.

Hwang, Junga; Kim, Hang-Pyo; Park, Young-Deuk

2013-09-01

11

Geomagnetic activity for northward interplanetary magnetic fields: Am index response  

SciTech Connect

The Am index is used to study the response of the magnetosphere to northward IMF. It is shown that most of the observed increase in activity can be explained by a correlation of the solar wind dynamic pressure with the IMF field strength such that the Am index varies only slightly with northward IMF strength when the solar wind dynamic pressure is held constant. There remains a smaller response of Am to solar wind velocity, which is usually attributed to a viscous interaction of the solar wind with the magnetosphere such as through the Kelvin-Helmholtz instability. The diurnal variation of Am during northward fields is also examined. A model invoking the Kelvin-Helmholtz instability on the flanks of the magnetopause have been used to predict the annual behavior of this diurnal variation. The predicted annual behavior is not found for northward IMF. The difference in diurnal variation from summer months to winter months, suggested to be caused solely by the Kelvin-Helmholtz instability, appears only for southward fields.

Scurry, L.; Russell, C.T. (Univ. of California, Los Angeles (USA))

1990-07-01

12

Forecasting the geomagnetic activity of the Dst index using multiscale radial basis function networks  

NASA Astrophysics Data System (ADS)

The Dst index is a key parameter which characterises the disturbance of the geomagnetic field in magnetic storms. Modelling of the Dst index is thus very important for the analysis of the geomagnetic field. A data-based modelling approach, aimed at obtaining efficient models from limited input-output observational data, provides a powerful tool for analysing and forecasting geomagnetic activities including the prediction of the Dst index. In this study, the process of the Dst index is treated to be a structure-unknown system, where the solar wind parameter ( VBs) and the solar wind dynamic pressure ( P) are the system inputs, and the Dst index is the system output. A novel multiscale RBF (MSRBF) network is introduced to represent such a two-input and single-output system, where the Dst index is related to the solar wind parameter and the dynamic pressure, via a hybrid network model consisting of two submodels: a linear part that reflects the linear relationship between the output and the inputs, and a nonlinear part that captures the effect of the interacting contribution of past observations of the inputs and the output, on the current output. The proposed MSRBF network can easily be converted into a linear-in-the-parameters form and the training of the linear network model can easily be implemented using a forward orthogonal regression (FOR) algorithm. One advantage of the new MSRBF network, compared with traditional single scale RBF networks, is that the new network is more flexible for describing complex nonlinear dynamical systems.

Wei, H. L.; Zhu, D. Q.; Billings, S. A.; Balikhin, M. A.

13

Connection of geomagnetic indexes SYM, ASYM with polar indexes AE (AU, AL) on different phases of a geomagnetic storm  

NASA Astrophysics Data System (ADS)

The research of connection of indexes SYM ASYM characterizing the ring current magnetic field with the indexes of auroral electrojets activity AE AU AL is carried out during the main phases and phases of recovery of some magnetic storms in 2000-2001 For the main phases of these magnetic storms the maximal correlation coefficients are between the arrays SYM and AU ASYM and AU ASYM and AL for phases of recovery between the arrays ASYM and AE ASYM and AL SYM and AE Thus the asymmetry of the ring current magnetic field is connected to the particular current systems parts of which are eastern and western electrojets during the whole magnetic storm The symmetrical part of the magnetic disturbance during development of the main phase of magnetic storm is connected to the current system part of which is eastern electrojet and during the storm recovery phase to the integral current activity in the whole oval of polar auroras The executed correlation analysis offers the scheme of equivalent current systems which is consistent with marked patterns in magnetic disturbance behavior Simultaneously with the correlation analysis when correlation was calculated with no temporary shift between studied values the analysis taking into consideration temporary delays in half an hour up to two hours between AE AU AL and indexes SYM ASYM was executed It showed that the development of the symmetrical part of the magnetic disturbance created by ring current lags behind development of western electrojet while its asymmetric part develops simultaneously

Barkhatov, N. A.; Levitin, A. E.; Tserkovniuk, O. M.

14

Indexing Anatomical Phrases in Neuro-Radiology Reports to the UMLS 2005AA  

PubMed Central

This work describes a methodology to index anatomical phrases to the 2005AA release of the Unified Medical Language System (UMLS). A phrase chunking tool based on Natural Language Processing (NLP) was developed to identify semantically coherent phrases within medical reports. Using this phrase chunker, a set of 2,551 unique anatomical phrases was extracted from brain radiology reports. These phrases were mapped to the 2005AA release of the UMLS using a vector space model. Precision for the task of indexing unique phrases was 0.87.

Bashyam, Vijayaraghavan; Taira, Ricky K.

2005-01-01

15

Correlation Between Ionospheric Electron Density Parameters and Geomagnetic Index Dst From Observations of FORMOSAT-3/COSMIC  

NASA Astrophysics Data System (ADS)

The FORMOSAT-3/COSMIC mission is composed of six identical micro-satellites launched on April 14, 2006 under a joint project between NSPO of Taiwan and NCAR of USA. This mission has provided the first satellite constellation for monitoring global weather using the Global Positioning System (GPS) radio occultation (RO) technique. Currently, there can be more than 2000 electron density profiles acquired per day covering a global range of the ionosphere from the altitude of 90km to 800km. Therefore, we adopt this advantage to statistically investigate the correlation between the ionospheric electron density parameters and geomagnetic disturbances based on analyzing the RO data from FS-3/COSMIC. NmF2 and TEC are the primary electron parameters studied; the geomagnetic index Dst at both quiet and storm time is the geomagnetic disturbance factor chosen to be compared with. We will present our statistical results on how NmF2 and TEC at different regions (by magnetic latitudes) and different time (by magnetic local time MLT) respond to the values of Dst and the temporal trend of Dst for both quiet and storm times. We have found that, in general, NmF2 and TEC increase as Dst decreases. These results can be applied to ionospheric and space weather forecasting in the future.

Wang, K.; Tam, S. W. Y.

2009-04-01

16

Forecasting geomagnetic activity indices using the Boyle index through artificial neural networks  

NASA Astrophysics Data System (ADS)

Adverse space weather conditions affect various sectors making both human lives and technologies highly susceptible. This dissertation introduces a new set of algorithms suitable for short term space weather forecasts with an enhanced lead-time and better accuracy in predicting Kp, Dst and the AE index over some leading models. Kp is a 3-hour averaged global geomagnetic activity index good for midlatitude regions. The Dst index, an hourly index calculated using four ground based magnetic field measurements near the equator, measures the energy of the Earth's ring current. The Auroral Electrojet indices or AE indices are hourly indices used to characterize the global geomagnetic activity in the auroral zone. Our algorithms can predict these indices purely from the solar wind data with lead times up to 6 hours. We have trained and tested an ANN (Artificial Neural Network) over a complete solar cycle to serve this purpose. Over the last couple of decades, ANNs have been successful for temporal prediction problems amongst other advanced non-linear techniques. Our ANN-based algorithms receive near-real-time inputs either from ACE (Advanced Composition Explorer), located at L1, and a handful of ground-based magnetometers or only from ACE. The Boyle potential, phi = 10-4 (vkm/sec)2+ 11.7BnT sin3 (theta/2) kV, or the Boyle Index (BI) is an empirically-derived formula that approximates the Earth's polar cap potential and is easily derivable in real time using the solar wind data from ACE. The logarithms of both 3-hour and 1-hour averages of the Boyle Index correlate well with the subsequent Kp, Dst and AE: Kp = 8.93 log 10 - 12.55. Dst = 0.355 - 6.48, and AE = 5.87 - 83.46. Inputs to our ANN models have greatly benefitted from the BI and its proven record as a forecasting parameter since its initiation in October, 2003. A preconditioning event tunes the magnetosphere to a specific state before an impending geomagnetic storm. The neural net not only improves the predictions but also helps the prediction by capturing the influence of preconditioning. Two of our models have been running in near-real-time forecast mode already, and the BI and Kp predictions can be obtained from http://space.rice.edu/ISTP/wind.html.

Balasubramanian, Ramkumar

2010-11-01

17

Superposed Epoch Analysis and Storm Statistics from 25 Years of the Global Geomagnetic Disturbance Index, USGS-Dst.  

National Technical Information Service (NTIS)

Statistics on geomagnetic storms with minima below -50 nanoTesla (nT) are compiled using a 25-year span of the 1-minute resolution disturbance index, U.S. Geological Survey Dst. A sudden commencement, main phase minimum, and time between the two has a mag...

J. L. Gannon

2012-01-01

18

Analysis of the geomagnetic activity of the Dst index and self-affine fractals using wavelet transforms  

NASA Astrophysics Data System (ADS)

The geomagnetic activity of the Dst index is analyzed using wavelet transforms and it is shown that the Dst index possesses properties associated with self-affine fractals. For example, the power spectral density obeys a power-law dependence on frequency, and therefore the Dst index can be viewed as a self-affine fractal dynamic process. In fact, the behaviour of the Dst index, with a Hurst exponent H?0.5 (power-law exponent ??2) at high frequency, is similar to that of Brownian motion. Therefore, the dynamical invariants of the Dst index may be described by a potential Brownian motion model. Characterization of the geomagnetic activity has been studied by analysing the geomagnetic field using a wavelet covariance technique. The wavelet covariance exponent provides a direct effective measure of the strength of persistence of the Dst index. One of the advantages of wavelet analysis is that many inherent problems encountered in Fourier transform methods, such as windowing and detrending, are not necessary.

Wei, H. L.; Billings, S. A.; Balikhin, M.

2004-06-01

19

Interplanetary magnetic field–geomagnetic field coupling and vertical variance index  

Microsoft Academic Search

The solar wind impacting at the geomagnetopause contains transient variations in the embedded interplanetary magnetic field (IMF). These disturbances are mirrored in the horizontal geomagnetic field measured at the Huancayo and Ascension Island stations. This investigation attempts to relate the microtemporal fluctuations in the IMF with the horizontal component of the geomagnetic field by means of a newly developed daily

A. Abraham; G. Renuka; L. Cherian

2010-01-01

20

Estimation of storm-time level of day-side wave geomagnetic activity using a new ULF index  

NASA Astrophysics Data System (ADS)

The level of wave geomagnetic activity in the morning and daytime sectors of auroral latitudes during strong magnetic storms with Dst min varying from -100 to -150 nT in 1995-2002 have been studied using a new ULF index of wave activity proposed in [Kozyreva et al., 2007]. It has been detected that daytime Pc5 pulsations (2-6 mHz) are most intense during the main phase of a magnetic storm rather than during the recovery phase as was considered previously. It has been indicated that morning geomagnetic pulsations during the substorm recovery phase mainly contribute to daytime wave activity. The appearance of individual intervals with the southward IMF B z component during the magnetic storm recovery phase results in increases in the ULF index values.

Kozyreva, O. V.; Kleimenova, N. G.

2008-08-01

21

Statistics of the largest geomagnetic storms per solar cycle (1844-1993)  

NASA Astrophysics Data System (ADS)

A previous application of extreme-value statistics to the first, second and third largest geomagnetic storms per solar cycle for nine solar cycles is extended to fourteen solar cycles (1844-1993). The intensity of a geomagnetic storm is measured by the magnitude of the daily aa index, rather than the half-daily aa index used previously. Values of the conventional aa index (1868-1993), supplemented by the Helsinki Ak index (1844-1880), provide an almost continuous, and largely homogeneous, daily measure of geomagnetic activity over an interval of 150 years. As in the earlier investigation, analytic expressions giving the probabilities of the three greatest storms (extreme values) per solar cycle, as continuous functions of storm magnitude (aa), are obtained by least-squares fitting of the observations to the appropriate theoretical extreme-value probability functions. These expressions are used to obtain the statistical characteristics of the extreme values; namely, the mode, median, mean, standard deviation and relative dispersion. Since the Ak index may not provide an entirely homogeneous extension of the aa index, the statistical analysis is performed separately for twelve solar cycles (1868-1993), as well as nine solar cycles (1868-1967). The results are utilized to determine the expected ranges of the extreme values as a function of the number of solar cycles. For fourteen solar cycles, the expected ranges of the daily aa index for the first, second and third largest geomagnetic storms per solar cycle decrease monotonically in magnitude, contrary to the situation for the half-daily aa index over nine solar cycles. The observed range of the first extreme daily aa index for fourteen solar cycles is 159-352 nT and for twelve solar cycles is 215-352 nT. In a group of 100 solar cycles the expected ranges are expanded to 137-539 and 177-511 nT, which represent increases of 108% and 144% in the respective ranges. Thus there is at least a 99% probability that the daily aa index will satisfy the condition aa<550 for the largest geomagnetic storm in the next 100 solar cycles. The statistical analysis is used to infer that remarkable conjugate auroral observations on the night of 16 September 1770, which were recorded during the first voyage of Captain Cook to Australia, occurred during an intense geomagnetic storm.

Willis, D. M.; Stevens, P. R.; Crothers, S. R.

1997-06-01

22

Secular variation of recurrent geomagnetic disturbance  

NASA Astrophysics Data System (ADS)

Analysis is made of the secular variation of the occurrence and recurrence statistics of magnetic storms and lower-levels of geomagnetic activity using K-index and aa-index data obtained from ground-based magnetic observatories, 1868.0-2009.0, solar cycles 11-23. Methods include parametric measures of correlation, autocorrelation, and conditional probability, and to accommodate calibration differences from data collected independently at different observatories, nonparametric measures of trend and correlation are used. Consistent signals can be interpreted in terms of solar-terrestrial interaction: (1) In rough correspondence to a general increase in sunspot number, over the past 142 years the occurrence and 27.0-d-recurrence of geomagnetic disturbance have both increased, but these changes are not simple linear trends. (2) The general increase in geomagnetic disturbance comes despite a slightly proportional decrease in 27.0-d recurrent geomagnetic disturbance. From this we infer that the role of high-speed streams as a driver of geomagnetic activity has slightly decreased in comparison to coronal-mass ejections. (3) Occasionally, geomagnetic disturbance shows 13.5-d recurrence, and there is even a hint of 9.0-d recurrence. From this we infer that the polarity of the heliodynamo can reverse via a variety of transitional routes, some of which exhibit more poloidal dipole symmetry than others. (4) The statistical relationship over the past 142 years between sunspot number, geomagnetic disturbance and geomagnetic recurrence is nonstationary. From this we infer that it is extremely challenging to backward extrapolate correlations involving modern data to understand the past historical evolution of the Sun. Likewise, it is extremely challenging to predict the number of future sunspot numbers, but there might be an opportunity to use nonstationary solar-terrestrial variables to test theories of coupling between the solar wind and the magnetosphere.

Love, J. J.

2011-12-01

23

Assessment of the auroral electrojet index performance under various geomagnetic conditions  

NASA Astrophysics Data System (ADS)

Saturation of the auroral electrojet (AE) index during storm times is a phenomenon that has been known but not fully understood. To address this puzzle, here we correlate the (provisional) AE index with net field-aligned current (Net-dB) index, which is a data product derived with magnetic field measurements from the Iridium satellite constellation (Anderson et al., 2010), with an assumption that AE is largely measuring convection driven by the field-aligned currents represented by the Net-dB index. The Net-dB index has a time resolution of ˜45 min and is currently available from February 18, 1999, to May 31, 2008. It is found that, for the entire data period, there is a good linear correlation (r=0.74) between the AE index, when averaging over the Net-dB index time grids, and the Net-dB index, suggesting that statistically ˜55% of the ionospheric Hall currents correlate with large scale convection as reflected in the field-aligned currents. It is also found that the correlation decreases during storm times, with a clear decreasing trend toward a more negative Sym-H. For large storms (Sym-H<-100 nT), the correlation becomes weak (r<0.4). Two correlation peaks are identified: a major peak (r=0.73) occurring at Sym-H>30 nT and a secondary peak (r=0.66) at Sym-H˜-50 to -30 nT. A further study shows that the variations of the AE-Net-dB correlation are associated with the location of the field-aligned currents into and out of the ionosphere relative to the ground magnetometer stations, as expected often but not demonstrated in the past.

Liou, K.; Takahashi, K.; Anderson, B. J.; Nose, M.; Iyemori, T.

2013-01-01

24

Solar Activates and its correlation with geomagnetic indices  

NASA Astrophysics Data System (ADS)

The data of last 3 cycles for aa-index and the Number SSCs indicate that there is a general trend for increasing of data. Geomagnetic storms have a good correlation with solar activity and solar radiation variability. Many proton events and Geomagnetic storms have occurred during solar cycles21, 22, and 23, and Halloween storms during Nov. 2003. Study of the geomagnetic storms these occurred in last three cycles, will give us a good indication of the climatic change and its behavior during 21st century. During the decline phase of the last 3 solar cycles, high energetic eruptive flares were recorded, and the appearance of the second peak on the decline phase of solar cycles.

Abdel Hady, A.

2009-04-01

25

Relationship between Solar Wind Speed, Earthward-Directed Coronal Mass Ejections, Geomagnetic Activity, and the Sunspot Cycle Using 12-Month Moving Averages.  

National Technical Information Service (NTIS)

For 1996 .2006 (cycle 23), 12-month moving averages of the aa geomagnetic index strongly correlate (r = 0.92) with 12-month moving averages of solar wind speed, and 12-month moving averages of the number of coronal mass ejections (CMEs) (halo and partial ...

D. H. Hathaway R. M. Wilson

2008-01-01

26

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

NASA Astrophysics Data System (ADS)

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 ? (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).

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

2012-09-01

27

Geomagnetism during solar cycle 23: Characteristics  

NASA Astrophysics Data System (ADS)

On the basis of more than 48 years of morphological analysis of yearly and monthly values of the sunspot number, the aa index, the solar wind speed and interplanetary magnetic field, we point out the particularities of geomagnetic activity during the period 1996-2009. We especially investigate the last cycle 23 and the long minimum which followed it. During this period, the lowest values of the yearly averaged IMF (3 nT) and yearly averaged solar wind speed (364 km/s) are recorded in 1996, and 2009 respectively. The year 2003 shows itself particular by recording the highest value of the averaged solar wind (568 km/s), associated to the highest value of the yearly averaged aa index (37 nT). We also find that observations during the year 2003 seem to be related to several coronal holes which are known to generate high-speed wind stream. From the long time (more than one century) study of solar variability, the present period is similar to the beginning of twentieth century. We especially present the morphological features of solar cycle 23 which is followed by a deep solar minimum.

Zerbo, Jean-Louis; Amory-Mazaudier, Christine; Ouattara, Frédéric

2013-05-01

28

Principles of major geomagnetic storms forecasting  

Microsoft Academic Search

According to NOAA Space Weather Scales, geomagnetic storms of scales G5 (3-hour index of geomagnetic activity Kp=9), G4 (Kp=8) and G3 (Kp=7) are dangerous for people technology and health (influence on power systems, on spacecraft operations, on HF radio-communications and others). To prevent these serious damages will be very important to forecast dangerous geomagnetic storms. In many papers it was

Alexander Zagnetko; David Applbaum; Lev Dorman; Lev Pustil'Nik; Abraham Sternlieb; Igor Zukerman

2010-01-01

29

On the Relationship between Solar Wind Speed, Earthward-Directed Coronal Mass Ejections, Geomagnetic Activity, and the Sunspot Cycle Using 12-Month Moving Averages  

NASA Astrophysics Data System (ADS)

For 1996 .2006 (cycle 23), 12-month moving averages of the aa geomagnetic index strongly correlate (r = 0.92) with 12-month moving averages of solar wind speed, and 12-month moving averages of the number of coronal mass ejections (CMEs) (halo and partial halo events) strongly correlate (r = 0.87) with 12-month moving averages of sunspot number. In particular, the minimum (15.8, September/October 1997) and maximum (38.0, August 2003) values of the aa geomagnetic index occur simultaneously with the minimum (376 km/s) and maximum (547 km/s) solar wind speeds, both being strongly correlated with the following recurrent component (due to high-speed streams). The large peak of aa geomagnetic activity in cycle 23, the largest on record, spans the interval late 2002 to mid 2004 and is associated with a decreased number of halo and partial halo CMEs, whereas the smaller secondary peak of early 2005 seems to be associated with a slight rebound in the number of halo and partial halo CMEs. Based on the observed aaM during the declining portion of cycle 23, RM for cycle 24 is predicted to be larger than average, being about 168+/-60 (the 90% prediction interval), whereas based on the expected aam for cycle 24 (greater than or equal to 14.6), RM for cycle 24 should measure greater than or equal to 118+/-30, yielding an overlap of about 128+/-20.

Wilson, Robert M.; Hathaway, David H.

2008-06-01

30

The presence of large sunspots near the central solar meridian at the times of major geomagnetic storms  

NASA Astrophysics Data System (ADS)

A further study is made of the validity of a technique developed by the authors to identify historical occurrences of intense geomagnetic storms, which is based on finding approximately coincident observations of sunspots and aurorae recorded in East Asian histories. Previously, the validity of this technique was corroborated using scientific observations of aurorae in Japan during the interval 1957-2004 and contemporaneous white-light images of the Sun obtained by the Royal Greenwich Observatory, the Big Bear Solar Observatory, the Debrecen Heliophysical Observatory, and the Solar and Heliospheric Observatory spacecraft. The present investigation utilises a list of major geomagnetic storms in the interval 1868-2008, which is based on the magnitude of the AA* magnetic index, and reconstructed solar images based on the sunspot observations acquired by the Royal Greenwich Observatory during the shorter interval 1874-1976. It is found that a sunspot large enough to be seen with the unaided eye by an "experienced" observer was located reasonably close to the central solar meridian for almost 90% of these major geomagnetic storms. Even an "average" observer would easily achieve a corresponding success rate of 70% and this success rate increases to about 80% if a minority of ambiguous situations are interpreted favourably. The use of information on major geomagnetic storms, rather than modern auroral observations from Japan, provides a less direct corroboration of the technique for identifying historical occurrences of intense geomagnetic storms, if only because major geomagnetic storms do not necessarily produce auroral displays over East Asia. Nevertheless, the present study provides further corroboration of the validity of the original technique for identifying intense geomagnetic storms. This additional corroboration of the original technique is important because early unaided-eye observations of sunspots and aurorae provide the only possible means of identifying individual geomagnetic storms during the greater part of the past two millennia.

Willis, D. M.; Henwood, R.; Stephenson, F. R.

2009-01-01

31

Long-Term Changes in the Annual and Diurnal Variations of Geomagnetic Indices  

NASA Astrophysics Data System (ADS)

Recent research by on the am geomagnetic data series, recording of which began in 1958, suggests that the Russell-McPherron (RM) effect is not responsible for the majority of annual and diurnal variations detected in geophysical indices, rather a so-called "equinoctial effect" is dominant. We demonstrate a simple conversion of the aa index (which, with only two antipodal stations, has difficulty resolving diurnal variations) into a proxy am index, allowing us to extend the analysis back to 1868. The case for the equinoctial effect becomes less compelling as we examine the earlier data. Additionally examination of in situ solar wind measurements shows that the RM effect is clearly visible in geophysical indices for slow solar wind but not for fast. Sargent's recurrence index is used to extend these results to the extended am index.

Finch, I.; Lockwood, M.

2003-04-01

32

Geomagnetic Storm Theory  

Microsoft Academic Search

A discussion of the two-gas theory of the transmission of geomagnetic disturb- ances through the atmosphere (to several earth radii) is extended, with the following results: (i) The central problem concerning the main phase of a geomagnetic storm is the mechanism of penetration of solar ions into the geomagnetic field. An explanation is given depending on a combination of a

J. H. Piddington

1960-01-01

33

Tropospheric vorticity responses to the solar magnetic sector structure and geomagnetic disturbances  

Microsoft Academic Search

The responses of the Vorticity Area Index (VAI) at 500 mb to large geomagnetic disturbances and to magnetic sector boundary crossings are evaluated for the periods 1947-57 and 1963-74, during which time the geomagnetic responses to sector structure were known to be distinctly different. Results indicate that the nature of the VAI response to geomagnetic disturbances is markedly similar between

A. D. Padgaonkar; B. R. Arora

1981-01-01

34

Tropospheric vorticity responses to the solar magnetic sector structure and geomagnetic disturbances  

Microsoft Academic Search

The responses of the Vorticity Area Index (VAI) at 500 mb to large geomagnetic disturbances and to magnetic sector boundary crossings are evaluated for the periods 1947–57 and 1963–74, during which time the geomagnetic response to sector structure were known to be distinctly different. Results indicate that the nature of the VAI response to geomagnetic disturbances is markedly similar between

A. D. Padgaonkar; B. R. Arora

1981-01-01

35

Finnish geomagnetically induced currents project  

SciTech Connect

This article is a summary of Results of the Finnish Project on Geomagnetically Induced Currents,'' published in Surveys in Geophysics 15:383-408, Kluwer Academic Publishers, Netherlands, 1994. IVO and FMI carried out a 1-year GIC project from June 1991 to May 1992. The time of the project was a little after the sunspot maximum, and the geomagnetic activity was high; there were 34 major or severe magnetic storm days (A[sub k] index at least 50). The main aim was to derive reliable statistics of the occurrences of GICs at different sites of the Finnish 400 and 220 kV power systems. Besides the practical engineering purpose, the project is also geophysically relevant by providing a GIC data set usable for large-scale investigations of auroral ionospheric-magnetospheric processes and of the earth's structure.

Vilianen, A.; Pirjola, R. (Finnish Meteorological Inst., Helsinki (Finland). Dept. of Geophysics)

1995-01-01

36

Predicting Solar Cycle 24 With Geomagnetic Precursors  

NASA Astrophysics Data System (ADS)

We describe using a geomagnetic precursor to predict the amplitude of the upcoming solar cycle. The amplitude prediction for Solar Cycle 24 is 65 +/- 20 in smoothed sunspot number, indicating a below-average amplitude for Solar Cycle 24. Four precursor peaks are seen in the decline of Solar Cycle 23. The earliest is the most prominent but coincides with large levels of non-recurrent geomagnetic activity associated with the Halloween storms. The second and third peaks are for smaller amplitudes and show that a weak cycle precursor closely following a period of strong solar activity may be difficult to resolve. A fourth peak, in early 2008, which has recurrent activity similar to precursors of earlier solar cycles and appears to be the ``true" precursor peak for Solar Cycle 24, predicts the smallest amplitude for Solar Cycle 24. Several effects contribute to the smaller prediction when compared to other geomagnetic precursor predictions. During Solar Cycle 23 the correlation between sunspot number and F10.7 shows that F10.7 is greater than the equivalent sunspot number over most of the cycle, implying the sunspot number underestimates the solar activity component. During 2003 the correlation between aa and Ap shows that aa is much greater than the value predicted from Ap, leading to an overestimate of the aa precursor for that year. But the most important effect is the lack of recurrent geomagnetic activity until 2008. We conclude that Solar Cycle 24 will be no stronger than average and could be much weaker than average.

Pesnell, W. Dean

2009-05-01

37

Introduction to Geomagnetic Fields  

NASA Astrophysics Data System (ADS)

Geomagnetic fields arise from a variety of electric current sources. The main, dipolar field results from currents in the Earth's outer core. Dynamo currents, driven by motion of the Earth's ionosphere, generate daily surface field variations, and the Sun's activity modifies the Earth's magnetosphere, producing storm currents on a global scale. Using a minimum of mathematics, and without sacrificing the depth of coverage, the author presents the geomagnetic source fields. Details of measurement methods and a thorough review of the societal impact and use of geomagnetic fields complete the main text. The book concludes with appendices that summarise the necessary background mathematics, provide a comprehensive list of geomagnetic information, and detail geomagnetic utility computer programs. With its refreshing presentation, Introduction to Geomagnetic Fields will appeal to graduate students and researchers seeking an understanding of these natural phenomena.

Campbell, Wallace H.

38

Introduction to geomagnetism  

SciTech Connect

This book examines a wide range of subjects in geomagnetism. It presents a brief introduction to physical principles of magnetism, and then focuses on the properties of the geomagnetic field as the sum of four interrelated phenomena: the main field, the local or crustal field, the external field, and the induced field. Additional topics, including paleomagnetism and magnetic methods in exploration, and the history of geomagnetism, are also discussed.

Parkinson, W.D.

1983-01-01

39

Long-term prediction of solar and geomagnetic activity daily time series using singular spectrum analysis and fuzzy descriptor models  

NASA Astrophysics Data System (ADS)

Of the various conditions that affect space weather, Sun-driven phenomena are the most dominant. Cyclic solar activity has a significant effect on the Earth, its climate, satellites, and space missions. In recent years, space weather hazards have become a major area of investigation, especially due to the advent of satellite technology. As such, the design of reliable alerting and warning systems is of utmost importance, and international collaboration is needed to develop accurate short-term and long-term prediction methodologies. Several methods have been proposed and implemented for the prediction of solar and geomagnetic activity indices, but problems in predicting the exact time and magnitude of such catastrophic events still remain. There are, however, descriptor systems that describe a wider class of systems, including physical models and non-dynamic constraints. It is well known that the descriptor system is much tighter than the state-space expression for representing real independent parametric perturbations. In addition, the fuzzy descriptor models as a generalization of the locally linear neurofuzzy models are general forms that can be trained by constructive intuitive learning algorithms. Here, we propose a combined model based on fuzzy descriptor models and singular spectrum analysis (SSA) (FD/SSA) to forecast a number of geomagnetic activity indices in a manner that optimizes a fuzzy descriptor model for each of the principal components obtained from singular spectrum analysis and recombines the predicted values so as to transform the geomagnetic activity time series into natural chaotic phenomena. The method has been applied to predict two solar and geomagnetic activity indices: geomagnetic aa and solar wind speed (SWS) of the solar wind index. The results demonstrate the higher power of the proposed method-- compared to other methods -- for predicting solar activity.

Mirmomeni, M.; Kamaliha, E.; Shafiee, M.; Lucas, C.

2009-09-01

40

Forecast of recurrent geomagnetic storms  

NASA Astrophysics Data System (ADS)

Long-term forecast of space weather allows in achieving a longer lead time for taking the necessary precautions against disturbances. Hence, there is a need for long-term forecasting of space weather. We studied the possibility for a long-term forecast of recurrent geomagnetic storms. Geomagnetic storms recur with an approximate 27-day period during the declining phase of a solar cycle. These disturbances are caused by the passage of corotating interaction regions, which are formed by interactions between the background slow-speed solar wind and high-speed solar wind streams from a coronal hole. In this study, we report on the performance of 27-day-ahead forecasts of the recurrent geomagnetic disturbances using Kp index. The methods of the forecasts are on the basis of persistence, autoregressive model, and categorical forecast using occurrence probability. The forecasts show better performance during the declining phase of a solar cycle than other phases. The categorical forecast shows the probability of detection (POD) more than 0.5 during the declining phase. Transition of the performance occurs sharply among the declining phases and other phases.

Watari, S.

2011-06-01

41

On exploring the local fractal properties of geomagnetic time series  

NASA Astrophysics Data System (ADS)

The purpose of this work is to present an alternative way to identify the short term geomagnetic field activity related to geomagnetic storms, using magnetograms instead of the processed Dst index. This approach takes into account the nonstationary properties of the data and allows to detect main events, such as Sudden Storm Commencement (SSC). Here, we investigate the spatial variation of the Hölderian regularity exponent (H) estimated from the Horizontal component of the transient external geomagnetic field recorded by the Intermagnet observatories. The analysis is performed on one minute sampling geomagnetic data recorded during quiet and disturbed days of the solar cycle 23. The results show that the H exponent can capture and categorize the main geomagnetic features contained in the signal. An abrupt change of H value marks the time of a storm onset, and the major singularities of the geomagnetic field temporal variations, such as SSC, are characterized by very low H values. Another important finding is that a significant correlation is noted between the horizontal component of the Earth's magnetic field and its estimated local regularity, whereas no clear relationship is drawn between these parameters. To conclude, the regularity exponent could be an efficient key indicator of geomagnetic activity and singularity detection. Keywords: geomagnetic activity, geomagnetic storm, regularity, Hölder exponent

Gaci, Said; Zaourar, Naima

2013-04-01

42

Long-term geomagnetic indices and their use in inferring solar wind parameters in the past  

NASA Astrophysics Data System (ADS)

We discuss three new geomagnetic indices [the Inter-Hour Variability ( IHV), the Inter-Diurnal Variability ( IDV), Svalgaard, L., Cliver, E.W. The IDV index: its derivation and use in inferring long-term variations of the interplanetary magnetic field strength. J. Geophys. Res. 110, A12103. doi:10.1029/2005JA011203, 2005; and the Polar Cap Potential ( PCP) index, Le Sager, P., Svalgaard, L. No increase of the interplanetary electric field since 1926. J. Geophys. Res. 109 (A7), A07106. doi:10.1029/2004JA010411, 2004], that are derivable from data available for a century or more. Each of these indices responds directly to either the solar wind magnetic field strength ( B) or to different combinations of B and the solar wind speed ( V). This over-determined system permits a reconstruction of these parameters for the past ˜150 years. The variation of yearly averages of B can be described as a constant value (4.6 nT) plus a component varying with the square root of the sunspot number. Because the latter seems to exhibit a ˜100 year Gleissberg cycle, B does as well. Since 1890, annual averages of V range from a low of ˜300 km/s in 1902 to 545 km/s in 2003. The IHV-index fords a way to check the calibration of other long-term geomagnetic indices. We find that the ap-index tracks the variation of IHV, back to 1932 but that the aa-index (extended back to 1844) is systematically too low (3-6 nT) before 1957, relative to modern values.

Svalgaard, L.; Cliver, E. W.

43

Modeling geomagnetically induced currents using geomagnetic indices and data  

Microsoft Academic Search

The possibilities of forecasting geomagnetically induced currents (GIC) in power transmission networks are dependent on the success in modeling these currents. To provide a valuable user-oriented forecast, modeling and proper evaluation of the models using GIC data is important. Many forecasts of geomagnetic storms are presented in terms of geomagnetic indices. Using the GIC data from measuring sites on three

L. Trichtchenko; D. H. Boteler

2004-01-01

44

Geomagnetic Indices Variations And Human Physiology  

NASA Astrophysics Data System (ADS)

A group of 86 volunteers was examined on each working day in autumn 2001 and in spring 2002. Systolic blood pressure (SBP), diastolic blood pressure (DBP) and heart rate (HR) were registered. Pulse pressure (PP) was calculated. Data about subjective psycho-physiological complaints (SPPC) were also gathered. Altogether 2799 recordings were obtained. ANOVA was employed to check the significance of influence of daily amplitude of H-component of local geomagnetic field, daily planetary Ap-index and hourly planetary Dst-index on the physiological parameters examined. Post hoc analysis was performed to elicit the significance of differences in the factors levels. Average values of SBP, DBP, PP and SPPC of the group were found to increase statistically significantly and biologically considerably with the increase of geomagnetic indices.

Dimitrova, S.

2007-12-01

45

Solar-geomagnetic activity influence on Earth's climate  

NASA Astrophysics Data System (ADS)

A long uninterrupted homogeneous data set on the annual mean Sea Surface Temperature (SST) anomaly records as a representative of the Earth's climatic parameter has been analyzed in conjunction with 158 year long time series on the annual sunspot indices, Rz and geomagnetic activity indices, aa for the period 1850-2007. The 11-year and 23-year overlapping means of global (?tg) as well as northern (?tn) and southern (?ts) hemispheric SST anomalies reveal significant positive correlation with both Rz and aa indices. Rz, aa and ?tg depict a similar trend in their long-term variation and both seem to be on increase after attaining a minimum in the early 20th century (˜1905). Whereas the results on the power spectrum analysis by the Multi-Taper Method (MTM) on ?tg, Rz and aa reveal periodicities of ˜79-80 years (Gleissberg's cycle) and ˜9-11 years (Schwabe solar cycle) consistent with earlier findings, MTM spectrum analysis also reveals fast cycles of 3-5 years. A period of ˜4.2 years in aa at 99% confidence level appears recorded in ?tg at ˜4.3 years at 90% confidence level. A period of ˜3.6-3.7 years at 99% confidence level found in ?tg is correlating with a similar periodic variation in sector structure of Interplanetary Magnetic Field (IMF). This fast cycle parallelism is new and is supportive of a possible link between the solar-modulated geomagnetic activity and Earth's climatic parameter i.e. SST.

Mufti, S.; Shah, G. N.

2011-08-01

46

Magnetospheric impulse response for many levels of geomagnetic activity  

Microsoft Academic Search

The temporal relationship between the solar wind and magnetospheric activity has been studied using 34 intervals of high time resolution IMP 8 solar wind data and the corresponding AL auroral activity index. The median value of the AL index for each interval were utilized to rank the intervals according to geomagnetic activity level. The linear prediction filtering technique was then

L. F. Bargatze; D. N. Baker; R. L. McPherron; Hones E. W. Jr

1985-01-01

47

Major geomagnetic storms and cosmic rays, 2. methods of CR using for forecasting  

Microsoft Academic Search

We present developing of methods (e.g., Dorman et al., 1995, 1999) to forecast on the basis of NM hourly on-line data (as well as on-line muon telescopes hourly data from different directions) geomagnetic storms of scales G5 (3-hour index of geomagnetic activity Kp=9), G4 (Kp=8) and G3 (Kp=7) (according to NOAA Space Weather Scales). These geomagnetic storms are dangerous for

A. V. Belov; L. I. Dorman; E. A. Eroshenko; R. T. Gushchina; N. Iucci; H. Mavromichalaki; L. A. Pustilnik; A. Sternlieb; G. Villoresi; V. G. Yanke; I. G. Zukerman

2001-01-01

48

Hydromagnetic Theory of Geomagnetic Storms  

Microsoft Academic Search

A hydromagnetic theory is presented which explains the average characteristics of geomagnetic storms. The magnetic storm is caused by a sudden increase in the intensity of the solar wind. Stresses are then set up in the geomagnetic field by the solar plasma impinging upon the geomagnetic field and becoming trapped in it. These stresses, which are propagated to the earth

A. J. Dessler; E. N. Parker

1959-01-01

49

Geomagnetic activity at the time of heliospheric current sheet crossings  

NASA Astrophysics Data System (ADS)

Geomagnetic activity during the three days preceding and following crossings of the heliospheric current sheet describing large-scale interplanetary magnetic field structure are examined. Superposed epoch analysis of geomagnetic activity as indicated by the AL index was carried out using the times of changes in the azimuthal angle of the interplanetary magnetic field as key dates. It is found that the expression obtained by Murayama (1979) relating geomagnetic activity to the southward component of the interplanetary magnetic field and the bulk solar wind velocity is valid for the AL index. Short-term variations of the AL index are further observed to be controlled by fluctuations in the southward interplanetary magnetic field component, while long term variations are controlled by the solar wind velocity.

Hakamada, K.

1980-09-01

50

A neural network based model for predicting large geomagnetic disturbances: a comparative analysis with ap and Dst geomagnetic indices.  

NASA Astrophysics Data System (ADS)

This paper presents the development of a a feed forward neural network model which can be used to predict large geomagnetic disturbances (Dst less than -100 nT).Only solar wind parameters were used as inputs to train the neural network. These inputs parameters are the solar wind particle number density (N), the interplanetary magnetic field (IMF) total average field (Bt) as well as the IMF Bz-component. The data used are the averaged hourly OMNI data comprising storm and quiet periods extracted from solar cycle 23: 1996-2006. An analysis of the prediction as performed on four large storms during both the solar maximum and the declining phase periods of solar 23 show an improved prediction performance of the ap geomagnetic index when compared to the predictions of od Dst reported in previous studies. Key words: Solar wind; geomagnetic storms; geomagnetic indices; neural networks.

Uwamahoro, Jean; McKinnell, Lee-Anne

51

On the high correlation between long-term averages of solar wind speed and geomagnetic activity  

Microsoft Academic Search

Six-month and yearly averages of solar wind speed from 1962 to 1975 are shown to be highly correlated with geomagnetic activity as measured by averages of the AP index. On the same time scale the correlation between the southward component of the interplanetary magnetic field and geomagnetic activity is poor. Previous studies with hourly averages give opposite results. The better

N. U. Crooker; J. Feynman; J. T. Gosling

1977-01-01

52

Introduction to Geomagnetic Fields  

NASA Astrophysics Data System (ADS)

Coincidentally, as I sat down in late October 2003 to read and review the second edition of Wallace H. Campbell's text, Introduction to Geomagnetic Fields, we received warnings from the news media of a massive solar flare and its possible effect on power supply systems and satellite communications. News programs briefly explained the source of Sun-Earth interactions. If you are interested in learning more about the physics of the connection between sun spots and power supply systems and their impact on orbiting satellites, I urge you to become acquainted with Campbell's book. It presents an interesting and informative explanation of the geomagnetic field and its applications to a wide variety of topics, including oil exploration, climate change, and fraudulent claims of the utility of magnetic fields for alleviating human pain. Geomagnetism, the study of the nature and processes of the Earth's magnetic fields and its application to the investigation of the Earth, its processes, and history, is a mature science with a well-developed theoretical foundation and a vast array of observations. It is discussed in varied detail in Earth physics books and most entry-level geoscience texts. The latter treatments largely are driven by the need to discuss paleomagnetism as an essential tool in studying plate tectonics. A more thorough explanation of geomagnetism is needed by many interested scientists in related fields and by laypersons. This is the objective of Campbell's book. It is particularly germane in view of a broad range of geomagnetic topics that are at the forefront of today's science, including environmental magnetism, so-called ``jerks'' observed in the Earth's magnetic field, the perplexing magnetic field of Mars, improved satellite magnetic field observations, and the increasing availability of high-quality continental magnetic anomaly maps, to name only a few.

Hinze, William J.

53

Observations of exosphere variations during geomagnetic storms  

NASA Astrophysics Data System (ADS)

dominant neutral constituent in Earth's upper exosphere, atomic hydrogen (H), resonantly scatters solar Lyman-alpha (121.567 nm) radiation, observed as the geocorona. We report here observations of an exospheric response to geomagnetic storms obtained using measurements of the geocorona by Lyman-alpha detectors on the Two Wide-angle Imaging Neutral-atom Spectrometers mission. We introduce a new parameter, NH, the number of H atoms in the spherical shell from a geocentric distance of 3 to 8 Earth radii, to quantitatively characterize in a simplified way global exospheric conditions. Five geomagnetic storms observed during three months in the second half of 2011 are accompanied by abrupt temporary increases, spikes, of NH from 6% to 17%, lasting not longer than a day. These increases seem to show some correlation with the minimum Dst index reached during the peak of each storm.

Bailey, J.; Gruntman, M.

2013-05-01

54

Report on Geomagnetic Observatory Operations, 1990.  

National Technical Information Service (NTIS)

Contents: A Report On Geomagnetic Observatory Operations, 1990; Tables--Geomagnetic Observatories in Operation During 1990, Annual Means Available (as of April 1990), Notes on Observatories (as of April 1990), Digital Geomagnetic Observatories, 1990; MAPS...

K. L. Svendsen W. M. Davis S. J. McLean H. Meyers

1992-01-01

55

On regional geomagnetic charts  

USGS Publications Warehouse

When regional geomagnetic charts for areas roughly the size of the US were compiled by hand, some large local anomalies were displayed in the isomagnetic lines. Since the late 1960s, when the compilation of charts using computers and mathematical models was started, most of the details available in the hand drawn regional charts have been lost. One exception to this is the Canadian magnetic declination chart for 1980. This chart was constructed using a 180 degrees spherical harmonic model. -from Author

Alldredge, L. R.

1987-01-01

56

An Introduction to Geomagnetism  

NSDL National Science Digital Library

This tutorial introduces students to geomagnetism, the Earth's magnetic field, and its changes through time and space. Topics include the properties of Earth's magnetic field, how it makes a compass work, and why Earth has a magnetic field. There is also discussion of magnetic reversals, a set of links to additional reading and resources, and a set of classroom activities on the basic properties of magnetic fields and Earth's changing magnetic field.

Odenwald, Sten

57

Resource Letter: G-1: Geomagnetism  

NASA Astrophysics Data System (ADS)

This Resource Letter provides a guide to the literature on the internally generated geomagnetic field. The topics covered include the origin of the geomagnetic field and the energy requirements and core properties necessary for its generation; a description of the geomagnetic field, including its spherical harmonic representation, and its rates of change, as well as models of the secular variation; observations of the field relevant to paleomagnetism and continental drift; information about magnetic anomalies in the oceans, sea floor spreading and plate tectonics; reversals of the geomagnetic field and magnetochronology.

Harrison, Christopher G. A.

2001-05-01

58

Geomagnetic survey and geomagnetic model research in China  

NASA Astrophysics Data System (ADS)

The geomagnetic survey at 135 stations in China were carried out in 2003. These stations are with better environmental condition and small magnetic field gradient (<5 nT/m). In the field survey, the geomagnetic declination D, the inclination I and the total intensity F were measured. Ashtech ProMark2 differential GPS (Global Positioning System) was used in measuring the azimuth, the longitude, the latitude and the elevation at these stations. The accuracy of the azimuth is 0.1´. The geomagnetic survey data were reduced using the data at geomagnetic observatories in China. The mean standard deviations of the geomagnetic reduced values are: <1.5 nT for F, <0.5´ for D and I. Using the geomagnetic data which include the data at 135 stations and 35 observatories in China, and the data at 38 IGRF (International Geomagnetic Reference Field) calculation points in China's adjacent regions, the Taylor polynomial model and the spherical cap harmonic model were calculated for the geomagnetic field in China. The truncation order of the Taylor polynomial model is 5, and its original point is at 36.0°N and 104.5°E. Based on the geomagnetic anomalous values and using the method of spherical cap harmonic (SCH) analysis , the SCH model of the geomagnetic anomalous field was derived. In the SCH model, the pole of the spherical cap is at 36.0°N and 104.5°E, and the half-angle is 30°, the truncation order K = 8 is determined according to the mean square deviation between the model calculation value and the observation value, the AIC (Akaike Information Criterion) and the distribution of geomagnetic field.

Gu, Z.; Zhan, Z.; Gao, J.; Han, W.; An, Z.; Yao, T.; Chen, B.

2006-06-01

59

Research Directed Toward the Collection, Reduction and Evaluation of Geomagnetic Field Data.  

National Technical Information Service (NTIS)

The operation of the Weston Geomagnetic Observatory is described. Brief descriptions are given of the Weston Index of magnetic activity, and of projects on the quiet day variation, telluric current and micropulsation recording. The support of the Air Forc...

J. F. Devane J. E. Hogan

1968-01-01

60

Sign Singularity in the Secular Acceleration of the Geomagnetic Field  

Microsoft Academic Search

We investigate the occurrence of sign singularity in the geomagnetic field secular acceleration. The results on the cancellation index kappa are compared with the results relative to experimental data from ordinary fluid and MHD turbulence, showing that a turbulent inhomogeneous cascading process occurs. The relevance of our results is pointed out and discussed in the context of fluid motions, acting

P. de Michelis; G. Consolini; A. Meloni

1998-01-01

61

Evolution of Solar and Geomagnetic Activity Indices, and Their Relationship: 1960 - 2001  

NASA Astrophysics Data System (ADS)

We employ annually averaged solar and geomagnetic activity indices for the period 1960 - 2001 to analyze the relationship between different measures of solar activity as well as the relationship between solar activity and various aspects of geomagnetic activity. In particular, to quantify the solar activity we use the sunspot number R s, group sunspot number R g, cumulative sunspot area Cum, solar radio flux F10.7, and interplanetary magnetic field strength IMF. For the geomagnetic activity we employ global indices Ap, Dst and Dcx, as well as the regional geomagnetic index RES, specifically estimated for the European region. In the paper we present the relative evolution of these indices and quantify the correlations between them. Variations have been found in: i) time lag between the solar and geomagnetic indices; ii) relative amplitude of the geomagnetic and solar activity peaks; iii) dual-peak distribution in some of solar and geomagnetic indices. The behavior of geomagnetic indices is correlated the best with IMF variations. Interestingly, among geomagnetic indices, RES shows the highest degree of correlation with solar indices.

Verbanac, G.; Mandea, M.; Vršnak, B.; Sentic, S.

2011-07-01

62

Major geomagnetic storms and cosmic rays, 1. search of features in CR what can be used for forecasting  

Microsoft Academic Search

According to NOAA Space Weather Scales, geomagnetic storms of scales G5 (3-hour index of geomagnetic activity Kp=9), G4 (Kp=8) and G3 (Kp=7) are dangerous for people technology and health (influence on power systems, on spacecraft operations, on HF radio-communications and others. To prevent these serious damages will be very important to forecast dangerous geomagnetic storms. In many papers it was

L. I. Dorman; H. Mavromichalaki; L. A. Pustilnik; A. Sternlieb; I. G. Zukerman

2001-01-01

63

NM-MT network and space dangerous phenomena, 2. Examples of cosmic ray using for forecasting of major geomagnetic storms  

Microsoft Academic Search

We present developing of methods (e.g., Dorman et al., 1995, 1999) for forecasting on the basis of neutron monitor hourly on-line data (as well as on-line muon telescopes hourly data from different directions) geomagnetic storms of scales G5 (3- hour index of geomagnetic activity Kp=9), G4 (Kp=8) and G3 (Kp=7) (according to NOAA Space Weather Scales). These geomagnetic storms are

A. Belov; L. Dorman; E. Eroshenko; N. Iucci; M. Parisi; L. Pustil Nik; A. Sternlieb; G. Villoresi; V. Yanke; I. Zukerman

2002-01-01

64

Geomagnetic Field During a Reversal.  

National Technical Information Service (NTIS)

By modifying the IGRF it is possible to learn what may happen to the geomagnetic field during a geomagnetic reversal. If the entire IGRF reverses then the declination and inclination only reverse when the field strength is zero. If only the dipole compone...

J. R. Heirtzler

2003-01-01

65

SEMIANNUAL VARIATION OF GEOMAGNETIC ACTIVITY  

Microsoft Academic Search

The semiannual variation in geomagnetic activity is well established in geomagnetic data Its explanation has remained elusive, however. We propose, simply, that it is caused by a semiannual variation in the effective southward component of the interplanetary field. The southward field arises because the interplanetary field is ordered in the solar equatorial coordinate system, whereas the interaction with the magnetosphere

C.T. Russell; R. L. McPherron

1973-01-01

66

Finnish Geomagnetically Induced Currents Project  

Microsoft Academic Search

This article is a summary of Results of the Finnish Project on Geomagnetically Induced Currents,'' published in Surveys in Geophysics 15:383-408, Kluwer Academic Publishers, Netherlands, 1994. IVO and FMI carried out a 1-year GIC project from June 1991 to May 1992. The time of the project was a little after the sunspot maximum, and the geomagnetic activity was high; there

A. Vilianen; R. Pirjola

1995-01-01

67

Resolving issues concerning Eskdalemuir geomagnetic hourly values  

NASA Astrophysics Data System (ADS)

The hourly values of the geomagnetic field from 1911 to 1931 derived from measurements made at Eskdalemuir observatory in the UK, and available online from the World Data Centre for Geomagnetism at http://www.wdc.bgs.ac.uk/, have now been corrected. Previously they were 2-point averaged and transformed from the original north, east and vertical down values in the tables in the observatory yearbooks. This paper documents the course of events from discovering the post-processing done to the data to the final resolution of the problem. As it was through the development of a new index, the Inter-Hour Variability index, that this post-processing came to light, we provide a revised series of this index for Eskdalemuir and compare it with that from another European observatory. Conclusions of studies concerning long-term magnetic field variability and inferred solar variability, whilst not necessarily consistent with one another, are not obviously invalidated by the incorrect hourly values from Eskdalemuir. This series of events illustrates the challenges that lie ahead in removing any remaining errors and inconsistencies in the data holdings of different World Data Centres.

MacMillan, S.; Clarke, E.

2011-02-01

68

Air showers and geomagnetic field  

NASA Astrophysics Data System (ADS)

The influence of the geomagnetic field on the development of air showers is studied. The well known International Geomagnetic Reference Field was included in the AIRES air shower simulation program as an auxiliary tool to allow the calculation of very accurate estimations of the geomagnetic field given the geographic coordinates, altitude above sea level and date of a given event. Our simulations indicate that the geomagnetic deflections significantly alter some shower observables such as, for example, the lateral distribution of muons in the case of events with large zenith angles (larger than 75°). On the other hand, such alterations seem to be unimportant for smaller zenith angles. Global observables such as the total number of particles or longitudinal development parameters do not present appreciable dependences on the geomagnetic deflections for all the cases that were studied.

Cillis, A.; Sciutto, S. J.

2000-03-01

69

British Geological Survey: Geomagnetism  

NSDL National Science Digital Library

The British Geological Survey illustrates its work monitoring the earth's magnetic field in the UK at this website. Users can learn about the six observatories located in the Atlantic and the UK. Using the Grid Magnetic Angle Calculator, visitors can determine the angle between the British National grid north and the magnetic north. The website features Mercator projects created with the World Magnetic Model, geomagnetic data for the academic community, space weather services for industry, and more. Students can find tutorials about the Earth's magnetic field, magnetic reversals, and magnetic storms.

70

USGS Geomagnetism Program Real-time Product Summary  

NASA Astrophysics Data System (ADS)

The USGS Geomagnetism Program operates magnetic observatories across the United States, providing high quality, near real-time magnetic field measurements. These data support operational tasks, and are used as near real-time drivers to space weather models and indices. This presentation describes the operational products being produced at the USGS, including 1-minute Dst, 1-minute K index, and local disturbance measurements. In addition, we present the USGS products under development, including hazard mapping, geomagnetic storm operational summaries, and ground level electric field estimates.

Gannon, J. L.; Love, J. J.; Finn, C. A.; Stewart, D. C.; McWhirter, E. A.

2011-12-01

71

Coupling function between solar wind parameters and geomagnetic indices  

Microsoft Academic Search

Results of past studies on the correlation of a function of solar wind parameters with a geomagnetic index are reviewed and examined to identify the most relevant coupling function among those hitherto proposed. For the AL index, three functions B(s)V, B(s)V-squared, and Akasofu's (1980) epsilon are compared, where B(s) is the southward component of the interplanetary magnetic field and V

Takashi Murayama

1982-01-01

72

Prepraring to Interpret: AA  

NSDL National Science Digital Library

Students will learn about Alcoholics Anonymous and prepare to interpret for a deaf member at a traditional AA meeting. Interpreting for Alcoholics Anonymous (AA) requires that the interpreter have an understanding of the purpose of the meetings, prepares adequately for frozen text and informal register that will be used, and has respect for the organization and its members. It can be a difficult, but rewarding assignment. Preparing to ...

2007-10-03

73

Proterozoic Geomagnetic Field Geometry  

NASA Astrophysics Data System (ADS)

Pre-Mesozoic continental reconstructions and paleoclimatic inferences from paleomagnetism rely critically upon the assumption of a time-averaged geocentric axial dipole (GAD) magnetic field. We have been testing the GAD assumption and localized non-dipole components in a different manner, by observing directional variations within the Matachewan, Mackenzie and Franklin dyke swarms. Large dyke swarms, commonly emplaced within a few million years, provide the necessary broad areal coverage to perform a test of global geomagnetic field geometry. Our analysis varies the quadrupole and octupole values of the generalized paleolatitude equation to determine a minimal angular dispersion and maximum precision of paleopoles from each dyke swarm. As a control, paleomagnetic data from the central Atlantic magmatic province (CAMP) show the sensitivities of our method to non-GAD contributions to the ancient geomagnetic field. Within the uncertainties, CAMP data are consistent with independent estimates of non-GAD contributions derived from global tectonic reconstructions (Torsvik & Van der Voo, 2002). Current results from the three Proterozoic dyke swarms all have best fits that are non-dipolar, but they differ in their optimal quadrupole/ octupole components. Treated together under the hypothesis of a static Proterozoic field geometry, the data allow a pure GAD geodynamo within the uncertainty of the method. Current results were performed using Fisherian statistics, but Bingham statistics will be included to account for the ellipticity of data.

Panzik, J. E.; Evans, D. A.

2011-12-01

74

Relationship between isolated sleep paralysis and geomagnetic influences: a case study.  

PubMed

This preliminary report, of a longitudinal study, looks at the relationship between geomagnetic activity and the incidence of isolated sleep paralysis over a 23.5-mo. period. The author, who has frequently and for the last 24 years experienced isolated sleep paralysis was the subject. In addition, incidence of lucid dreaming, vivid dreams, and total dream frequency were looked at with respect to geomagnetic activity. The data were in the form of dream-recall frequency recorded in a diary. These frequency data were correlated with geomagnetic activity k-index values obtained from two observatories. A significant correlation was obtained between periods of local geomagnetic activity and the incidence of isolated sleep paralysis. Specifically, periods of relatively quiet geomagnetic activity were significantly associated with an increased incidence of episodes. PMID:7478886

Conesa, J

1995-06-01

75

Lagged association between geomagnetic activity and diminished nocturnal pain thresholds in mice.  

PubMed

A wide variety of behaviors in several species has been statistically associated with the natural variations in geomagnetism. To examine whether changes in geomagnetic activity are associated with pain thresholds, adult mice were exposed to a hotplate paradigm once weekly for 52 weeks during the dark cycle. Planetary A index values from the previous 6 days of a given hotplate session were correlated with the mean response latency for subjects to the thermal stimulus. We found that hotplate latency was significantly (P < 0.05) and inversely correlated (rho = -0.25) with the daily geomagnetic intensity 3 days prior to testing. Therefore, if the geomagnetic activity was greater 3 days before a given hotplate trial, subjects tended to exhibit shorter response latencies, suggesting lower pain thresholds or less analgesia. These results are supported by related experimental findings and suggest that natural variations in geomagnetic intensity may influence nociceptive behaviors in mice. PMID:17657732

Galic, M A; Persinger, M A

2007-10-01

76

A space-based proxy for the Dst index  

Microsoft Academic Search

The Dst index was created to monitor and quantify disturbances in the inner magnetosphere using ground-based, magnetic field measurements. The phases and strengths of geomagnetic storms are usually defined by the evolution of Dst. The standard Dst database is computed and maintained at the World Data Center for Geomagnetism, Kyoto. We demonstrate that the Dst index can also be approximated

F. J. Rich; J. M. Bono; W. J. Burke; L. C. Gentile

2007-01-01

77

Quasi-Sinusoidal Geomagnetic Variations at Geomagnetic Midlatitude.  

National Technical Information Service (NTIS)

Three-component quasi-sinusoidal geomagnetic variations (micropulsations) at Concord, Massachusetts for a five month period have been reduced to hourly average amplitudes in six contiguous octave frequency bands covering the period range from 16 to 1024 s...

J. H. Frey W. L. Fischer

1972-01-01

78

Solar activity and human health at middle and low geomagnetic latitudes in Central America  

NASA Astrophysics Data System (ADS)

The study of the possible effect of solar variability on living organisms is one of the most controversial issues of present day science. It has been firstly and mainly carried on high latitudes, while at middle and low latitudes this study is rare. In the present review we focused on the work developed at middle and low geomagnetic latitudes of America. At these geomagnetic latitudes the groups consistently dedicated to this issue are mainly two, one in Cuba and the other in Mexico. The Cuban and Mexican studies show that at such latitudes there are biological consequences to the solar/geomagnetic activity, coinciding in four points: (1) the male population behave differently from the female population, (2) the most vulnerable age group to geomagnetic perturbations is that of ?65 years old, (3) there is a tendency for myocardial infarctions (death or occurrence) to increase one day after a geomagnetic Ap index large value or during the day of the associated Forbush decrease, and (4) the myocardial infarctions (death or occurrence) increase as the geomagnetic perturbation increases. Additionally, the Cuban group found seasonal periodicities from their data, and also that increases of female myocardial infarctions occurred before and after the day of the geomagnetic disturbance. The Mexican group found that the male sex is more vulnerable to geomagnetic perturbations and that the myocardial infarction deaths present the conspicuous cycle of ˜7 days.

Mendoza, Blanca; Sánchez de La Peña, Salvador

2010-08-01

79

AAS Career Services  

NASA Astrophysics Data System (ADS)

The American Astronomical Society provides substantial programs in the area of Career Services.Motivated by the Society's mission to enhance and share humanity's understanding of the Universe, the AAS provides a central resource for advertising positions, interviewing opportunities at its annual winter meeting and information, workshops and networks to enable astronomers to find employment.The programs of the Society in this area are overseen by an active committee on employment and the AAS Council itself.Additional resources that help characterize the field, its growth and facts about employment such as salaries and type of jobs available are regularly summarized and reported on by the American Institute of Physics.

Marvel, Kevin B.

2012-08-01

80

Cross-correlation of solar activity with seismicity and geomagnetic disturbances in Vrancea (Romania) source zone  

NASA Astrophysics Data System (ADS)

The paper brings together, in the same frame, the solar activity, the seismicity and the geomagnetic field behavior. Using statistical approaches, we try to find a degree of correlation between the three phenomena. On one part, the solar activity influences the geomagnetic field, giving rise to two types of variations: regular and irregular variations. Daily, seasonal and cyclic 11 years period are regular magnetic field variations and arise from current systems caused by regular and periodic solar radiation changes. These regular variations are composed with the irregular variations due to the irregular activity of the Sun. The magnetic activity indices (Ak, Kp, ap and so on) are designed to describe variation in the geomagnetic field caused by the irregular current systems produced by the multiple interactions between the solar wind, the magnetosphere and by the ionosphere itself. The sunspot number has its reflection in the regular 11 years cycle of the geomagnetic activity and the irregular solar currents (ap index) have the reflection in the irregular variations of the geomagnetic activity and is currently used for the identification of magnetic storms. Both are influencing the geomagnetic activity and records. Tectonic activity, on the other part, sometimes has its own signature on the geomagnetic field. The data used in this paper are obtained from the seismicity of Vrancea source zone (Romplus catalogue), the geomagnetic field recorded by the Romanian geomagnetic observatories (Muntele Rosu and Surlari NIEP and INTERMAGNET) and the global magnetic activity indices obtained from NOAA. The time span of more than 15 years of recordings is covering more than one solar cycle, giving us the opportunity to study the correlation during low and high solar activity periods. A special designed software is used for this study. It allows the visualization and analyzing long time intervals of records as seismicity, geomagnetic field and solar activity parameters.

Moldovan, Iren Adelina; Emilian Toader, Victorin; Otilia Placinta, Anica; Petruta Constantin, Angela; Popescu, Emilia

2013-04-01

81

Statistics of extreme geomagnetically induced current events  

NASA Astrophysics Data System (ADS)

In this work, space weather events associated with extreme geoelectric field and geomagnetically induced current (GIC) magnitudes are investigated. The geoelectric field and consequent GIC are computed using geomagnetic field recordings over an extended time period and ground conductivity and technological system configurations favorable for large GIC. The statistics are derived for both overall occurrence of the geoelectric field and geoelectric field occurrence conditioned by the state of the magnetosphere and the solar wind. It is shown that in high-latitude areas having resistive ground conductivity structures and in systems having characteristics favorable for large GIC, GIC amplitudes of about 200 A can be expected to occur 102-103 times (in 10-s values) per year while GIC of about 2000 A occur only 10-100 times in 100 years. On the basis of the Dst index and the solar wind electric field values derived by Siscoe et al. (2006) and Tsurutani et al. (2003), it is estimated by means of derived conditional probability distributions that although magnitudes of about 10 V/km are possible, the most probable value for the maximum magnitude of the geoelectric field during the Carrington event of 1-2 September 1859 is about 4 V/km. The usage of derived conditional probabilities in space weather applications is also discussed.

Pulkkinen, A.; Pirjola, R.; Viljanen, A.

2008-07-01

82

Severe geomagnetic storms and their sources on the sun  

NASA Astrophysics Data System (ADS)

A catalog of severe geomagnetic storms is compiled, using the Bartels index to define severity. Storms were coordinated with flare data selected according to rigorous rules. The duration of storm in eighths of a day, number of eighths during which the Kp index was 7- or more, the date, hour, and minute of sudden storm commencement (SSC) are stated. The distribution of storms in dependence on their duration is shown. It is found that for extremely intensive flares, which are responsible for severe geomagnetic storms mostly with SSC's, the average time elapsed between the beginning of the flare and the SSC is about 33.5 hrs. The association of severe storms with Type II and Type IV radio bursts is found to be indeterminate due to statistical insufficiencies, while the association of severe storms with Forbush decreases is found to be much more definite. Storms are also related to the longitudinal position of the source flare on the solar disk.

Krajcovic, S.; Krivsky, L.

1982-05-01

83

Secondary or Reactive AA Amyloidosis  

MedlinePLUS

Secondary AA Secondary amyloidosis is caused by a chronic infection or chronic inflammatory disease. The deposits in this type ... are made up of a protein called the AA protein. Medical or surgical treatment of the underlying ...

84

A Geomagnetic Reference Error Model  

NASA Astrophysics Data System (ADS)

The accuracy of geomagnetic field models, such as the International Geomagnetic Reference Field (IGRF) and the World Magnetic Model (WMM), has benefitted tremendously from the ongoing series of satellite magnetic missions. However, what do we mean by accuracy? When comparing a geomagnetic reference model with a magnetic field measurement (for example of an electronic compass), three contributions play a role: (1) The instrument error, which is not subject of this discussion, (2) the error of commission, namely the error of the model coefficients themselves in representing the geomagnetic main field, and (3) the error of omission, comprising contributions to the geomagnetic field which are not represented in the reference model. The latter can further be subdivided into the omission of the crustal field and the omission of the disturbance field. Several factors have a strong influence on these errors: The error of commission primarily depends on the time elapsed since the last update of the reference model. The omission error for the crustal field depends on altitude of the measurement, while the omission error for the disturbance field has a strong latitudinal dependence, peaking under the auroral electrojets. A further complication arises for the uncertainty in magnetic declination, which is directly dependent on the strength of the horizontal field. Here, we present an error model which takes all of these factors into account. This error model will be implemented as an online-calculator, providing the uncertainty of the magnetic elements at the entered location and time.

Maus, S.; Woods, A. J.; Nair, M. C.

2011-12-01

85

International Geomagnetic Reference Field-2000  

NASA Astrophysics Data System (ADS)

A group of geomagnetic field modellers associated with the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group 8, periodically examines various geomagnetic field representations from which the Earth's main field and its secular variation can be computed. They produce a set of coefficients to represent the main field at a particular epoch, usually every 5 years, and name it the International Geomagnetic Reference Field (IGRF). Also, if a previous IGRF is re-derived using new data not available at the time of its production and agreed upon when it is clear that no additional data are likely to emerge, it is called a Definitive Geomagnetic Reference Field (DGRF). For similar reasons, no DGRF model for 1995 has yet been adopted by the IAGA, Division V Working Group 8. Note that, when referring to these models, the designation “IGRF” refers to all available models, viewed collectively. If a particular model is intended, the reference must be specific; i.e., IGRF2000 or DGRF1990, rather than simply IGRF or DGRF

IAGA, Division V, Working Group 8,

86

Dependence of Inferred Magnetic Sector Structure Upon Geomagnetic and Solar Activity.  

National Technical Information Service (NTIS)

Inferred solar sector polarity given by the AC index of Svalgaard, has been intensively studied as a single time series and a time series correlated with geomagnetic and solar activity. Power auto-spectra of the AC index yield a highly significant harmoni...

P. F. Fougere

1973-01-01

87

On the Lunar Modulation of Geomagnetic Activity, 1884-1931 and 1932-1959.  

National Technical Information Service (NTIS)

The lunar modulation of geomagnetic activity for the years 1884-1959 is investigated by means of the magnetic character figure Ci. For the years 1932-1959, the Ci index gives a pattern very similar to that previously found with Kp index for 1932-1962. Thi...

B. Bell R. J. Defouw

1966-01-01

88

Secular trends in storm-level geomagnetic activity  

Microsoft Academic Search

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

J. J. Love

2011-01-01

89

Analysis of the three intense geomagnetic storm observed on july 20-31, 2004: solar, interplanetary and cosmic ray effects near the Earth  

Microsoft Academic Search

Geomagnetic storms are geomagnetic field disturbances caused by gusts in the solar wind injecting a substantial quantity of energy into the magnetosphere intensifying the ring current becoming strong enough to exceed some key threshold of the quantifying storm time Dst index In this work we analyze three intense geomagnetic storms Dst -100nT occurred in period of July 22nd 24th and

J. F. Savian; M. R. da Silva; A. Dal Lago; C. R. Braga; C. W. da Silva; L. C. Dos Santos; S. M. da Silva; K. Munakata; T. Kuwabara; N. J. Schuch

2006-01-01

90

Cosmic Ray Monitoring and Space Dangerous Phenomena, 1. Search of Features In Cosmic Rays What Can Be Used For Forecasting of Major Geomagnetic Storms  

Microsoft Academic Search

According to NOAA Space Weather Scales, geomagnetic storms of scales G5 (3- hour index of geomagnetic activity Kp=9), G4 (Kp=8) and G3 (Kp=7) are dangerous for people technology and health (influence on power systems, on spacecraft oper- ations, on HF radio-communications and others). To prevent these serious damages will be very important to forecast dangerous geomagnetic storms. In many papers

L. I. Dorman; L. A. Pustil'Nik; A. Sternlieb; I. G. Zukerman

2002-01-01

91

AAS Job Register  

NSDL National Science Digital Library

The Job Register of the American Astronomical Society has been updated for the month of November. It provides a list of current fellowships, postdoctoral, assistant, and faculty positions, for the current and previous months. At the Website, the user will also find additional resources such as descriptions of resume services, in the Editorial section; a Web Submission Form for posting jobs; and information on the AAS Job Center.

92

VARIATIONS OF GEOMAGNETIC ACTIVITY WITH LUNAR PHASE  

Microsoft Academic Search

An analysis of 31 years of Kdata suggests a variation of geomagnetic dis- turbance with lunar phase. A general increase in geomagnetic activity of about 4% begins after full moon and lasts for seven days. A general decrease in geomagnetic activity of about 4% is found for the seven days preceding full moon. A study of randomized data indicates that

Harold L. Stolov; A. G. W. Cameron

1964-01-01

93

Worldwide Geomagnetic Data Collection and Management  

Microsoft Academic Search

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

Mioara Mandea; Vladimir Papitashvili

2009-01-01

94

Geomagnetic activity influences the melatonin secretion at latitude 70 degrees N.  

PubMed

Factors other than light may affect variations in melatonin, including disturbances in the geomagnetic field. Such a possibility was tested in Alta, Norway, located at latitude 70 degrees N, where the aurora borealis is a result of large changes in the horizontal component (H) of the geomagnetic field. Geomagnetic disturbances are felt more strongly closer to the pole than at lower latitudes. Also noteworthy in Alta is the fact that the sun does not rise above the horizon for several weeks during the winter. To examine whether changes in geomagnetic activity influence the secretion of melatonin, saliva was collected from 25 healthy subjects in Alta several times during the day-night and at different times of the year. Single cosinor analyses yielded individual estimates of.the circadian amplitude and MESOR of melatonin. A 3-hour mean value for the local geomagnetic activity index, K, was used for approximately the same 24-hour span. A circadian rhythm was found to characterize both melatonin and K, the peak in K (23:24) preceding that of melatonin (06:08). During the span of investigation, a circannual variation also characterized both variables. Correlation analyses suggest that changes in geomagnetic activity had to be of a certain magnitude to affect the circadian amplitude of melatonin. If large enough (> 80 nT/3 h), changes in geomagnetic activity also significantly decreased salivary melatonin concentration. PMID:11774869

Weydahl, A; Sothern, R B; Cornélissen, G; Wetterberg, L

2001-01-01

95

What is a geomagnetic storm?  

SciTech Connect

The authors present a review of geomagnetic storm research. They examine the interaction of the solar wind with the magnetosphere. They argue that a storm results from the extended interaction of the solar wind/magnetosphere when a strong convection electric field is generated, which is able to perturb the ring current above some threshold level, triggering the event. They touch on interrelationships of the solar wind/magnetosphere/ionosphere as it bears on this problem, and offer ideas for continuing research directions to address the origin of geomagnetic storms.

Gonzales, W.D. [Instituto de Pesquisas Espaciais, Sao Paulo (Brazil); Joselyn, J.A. [National Oceanic and Space Administration, Boulder, CO (United States); Kamide, Y. [Nagoya Univ., Toyokawa (Japan)] [and others

1994-04-01

96

On the decadal to multi-decadal evolution and correlations of geomagnetic indices in relation to variations in solar activity  

NASA Astrophysics Data System (ADS)

Magnetic indices measure magnetic activity occurring over periods of time from minutes to hours, as recorded at geomagnetic observatories. They address in principle specific features of geomagnetic 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 ? (A-type) at decadal time scales. Pairs of indices (aa and Ap on one hand, Dst and ? on the other hand) display decade-long periods of high correlation interrupted by shorter periods of reduced correlation and even anti-correlation. Decadal variations of mutual correlation between A and B-type indices are governed by solar cycle evolution. Loss of correlation between geomagnetic indices coincides with loss of correlation between geomagnetic 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 geomagnetic indices will be briefly discussed.

Le Mouel, J.; Blanter, E.; Shnirman, M.; Courtillot, V.

2011-12-01

97

Johann von Lamont: A Pioneer in Geomagnetism  

NASA Astrophysics Data System (ADS)

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.

Soffel, Heinrich

2006-06-01

98

Computer Programming AAS  

NSDL National Science Digital Library

This one-page PDF document from the Jefferson Community and Technical College in Kentucky presents the course options and requirements for obtaining an AAS (Associate in Applied Science) degree in computer programming. General education, technical core, management, networking, and computer programming courses at the beginning, intermediate, and advanced levels are listed. This document would be helpful for anyone interested in procuring an entry-level computer programming position, or for information technology instructors at the high school and college levels engaged in curriculum development.

2009-09-24

99

No covariation between the geomagnetic activity and the incidence of acute myocardial infarction in the polar area of northern Sweden  

NASA Astrophysics Data System (ADS)

This study was undertaken to investigate whether there was any relation between the aurora borealis (measured as the geomagnetic activity) and the number of acute myocardial infarctions (AMI) in the northern, partly polar, area of Sweden. The AMI cases were collected from The Northern Sweden MONICA (multinational MONItoring of trends and determinants of CArdiovascular disease) AMI registry between 1985 and 1998, inclusive, and the information on the geomagnetic activity from continuous measurements at the Swedish Institute of Space Physics, Kiruna. In the analyses, both the relation between the individual AMI case and ambient geomagnetic activity, and the relation between the mean daily K index and the daily number of AMI cases were tested. We found no statistically significant relation between the number of fatal or non-fatal AMI cases, the number of sudden deaths or the number of patients with chest pain without myocardial damage, and geomagnetic activity. Our data do not support a relation between the geomagnetic activity and AMI.

Messner, T.; Häggström, I.; Sandahl, I.; Lundberg, V.

2002-02-01

100

NM-MT network and space dangerous phenomena, 1. Principles of major geomagnetic storms forecasting  

NASA Astrophysics Data System (ADS)

According to NOAA Space Weather Scales, geomagnetic storms of scales G5 (3- hour index of geomagnetic activity Kp=9), G4 (Kp=8) and G3 (Kp=7) are dangerous for people technology and health (influence on power systems, on spacecraft operations, on HF radio-communications and others). To prevent these serious damages will be very important to forecast dangerous geomagnetic storms. In many papers it was shown that in principle for this forecasting can be used data on CR intensity and CR anisotropy changing before SC of major geomagnetic storms accompanied by sufficient Forbush-decreases (e.g., Dorman et al., 1995, 1999). In this paper we consider over 100 major geomagnetic storms and for each case we analyze hourly data of many NM for 8 days with SC in the 4-st day of 8 days period (so before SC we have at least 3 full days). We- determine what part of major geomagnetic storms is accompanied CR intensity and CR anisotropy changing before SC, and what part of major geomagnetic storms does not show any features what can be used for forecasting. We estimate also how these parts depend from the index of geomagnetic activity Kp. This research is partly supported by the INTAS grant 00-0810. REFERENCES: Dorman L.I., et al. "Cosmic-ray forecasting features for big Forbush-decreases". Nuclear Physics B, 49A, 136-144 (1995). L.I.Dorman, et al, "Cosmic ray Forbush-decrease as indicators of space dangerous phenomenon and possible use of cosmic ray data for their prediction", Proc. of 26-th Intern. Cosmic Ray Conference, Salt Lake City, 6, 476-479 (1999).

Dorman, L.; Pustil Nik, L.; Sternlieb, A.; Zukerman, I.

101

A study of geomagnetic storms  

Microsoft Academic Search

The interplanetary energy flux is estimated on the basis of the Poynting flux and its variations with the rate of energy dissipation in terms of: (1) the ring-current particle injection, (2) Joule dissipation in the ionosphere, and (3) auroral particle injection for 15 major geomagnetic storms. A relationship, in terms of the angle between the interplanetary magnetic field vector and

Paul Perreault; S.-I. Akasofu

1978-01-01

102

What is a geomagnetic storm?  

Microsoft Academic Search

The authors present a review of geomagnetic storm research. They examine the interaction of the solar wind with the magnetosphere. They argue that a storm results from the extended interaction of the solar wind\\/magnetosphere when a strong convection electric field is generated, which is able to perturb the ring current above some threshold level, triggering the event. They touch on

W. D. Gonzales; J. A. Joselyn; Y. Kamide; H. W. Kroehl; G. Rostoker; B. T. Tsurutani; V. M. Vasyliunas

1994-01-01

103

Climate determinism or Geomagnetic determinism?  

NASA Astrophysics Data System (ADS)

A number of episodes of sharp geomagnetic field variations (in both intensity and direction), lasting on the order of a century, have been identified in archeomagnetic records from Western Eurasia and have been called "archeomagnetic jerks". These seem to correlate well with multi-decadal cooling episodes detected in the North Atlantic Ocean and Western Europe, suggesting a causal link between both phenomena. A possible mechanism could be a geomagnetic modulation of the cosmic ray flux that would control the nucleation rate of clouds. We wish to underline the remarkable coincidence between archeomagnetic jerks, cooling events in Western Europe and drought periods in tropical and sub-tropical regions of the northern hemisphere. The latter two can be interpreted in terms of global teleconnections among regional climates. It has been suggested that these climatic variations had caused major changes in the history of ancient civilizations, such as in Mesopotamia, which were critically dependent on water supply and particularly vulnerable to lower rainfall amounts. This is one of the foundations of "climate determinism". Our studies, which suggest a geomagnetic origin for at least some of the inferred climatic events, lead us to propose the idea of a "geomagnetic determinism" in the history of humanity.

Gallet, Y.; Genevey, A.; Le Goff, M.; Fluteau, F.; Courtillot, V.

2006-12-01

104

Reflection of the solar wind parameters in the CR geomagnetic cutoff rigidity before a strong magnetic storm in November 2003  

NASA Astrophysics Data System (ADS)

The time variations in the CR geomagnetic cutoff rigidity and their relation to the interplanetary parameters and the Dst index during a strong magnetic storm of November 18-24, 2003, have been analyzed. The Tsyganenko (Ts03) model of a strongly disturbed magnetosphere [Tsyganenko, 2002a, 2002b; Tsyganenko et al., 2003] have been used to calculate effective geomagnetic thresholds with the help of the method for tracing CR particle trajectories in the magnetospheric magnetic field. The geomagnetic thresholds have been calculated using the method of global spectrographic survey (GSS), based on the data from the global network of CR stations, and the results have been compared with the effective geomagnetic cutoff rigidities. The daily anisotropy of effective geomagnetic thresholds during the Dst variation minimum have been estimated. The relation of the theoretical and experimental geomagnetic thresholds, obtained using the GSS method, to the interplanetary parameters and Dst variation is analyzed. The Dst variations, IMF B z , and solar wind density are most clearly defined in the geomagnetic thresholds during this storm. The correlation between B y and experimental geomagnetic thresholds is higher than such a correlation between this parameter and theoretical thresholds by a factor 2-3, which suggests that a real dawn-dusk asymmetry during this storm was stronger than such an asymmetry represented by the Ts03 model.

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

2008-12-01

105

Semiannual Variation of Geomagnetic Activity: Protons or Photons?  

NASA Astrophysics Data System (ADS)

The cause(s) of the semiannual variation (SAV) of geomagnetic activity is a problem of long standard ( ˜100 years). The various mechanisms put forward can be divided into 'excitations' and 'modulations'. Using 45 years of the am-index, we show that the SAV is a modulation of existing activity. The modulation is a function of the angle between the Earth's dipole moment and either (1) the aberrated solar wind velocity and/or (2) the sun-Earth line, causing both time of year and time of day (UT) variations. Here we examine the correlation of geomagnetic activity with directions (1) and (2). Mechanisms involving interaction between the solar wind and the magnetopause would correlate best with direction (1). Mechanisms involving ionospheric conductance would correlate best with direction (2).

Svalgaard, L.; Schulz, M.; Cliver, E. W.

2004-12-01

106

Worldwide Geomagnetic Data Collection and Management  

NASA Astrophysics Data System (ADS)

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].

Mandea, Mioara; Papitashvili, Vladimir

2009-11-01

107

Research on Historical Records of Geomagnetic Storms  

NASA Astrophysics Data System (ADS)

In recent times, there has been keen interest in understanding Sun-Earth connection events, such as solar flares, CMEs and concomitant magnetic storms. Magnetic storms are the most dramatic and perhaps important component of space weather effects on Earth. Super-intense magnetic storms (defined here as those with Dst < -500 nT, where Dst stands for the disturbance storm time index that measures the strength of the magnetic storm) although relatively rare, have the largest societal and technological relevance. Such storms can cause life-threatening power outages, satellite damage, communication failures and navigational problems. However, the data for such magnetic storms is rather scarce. For example, only one super-intense magnetic storm has been recorded (Dst=-640 nT, March 13, 1989) during the space-age (since 1958), although such storms may have occurred many times in the last 160 years or so when the regular observatory network came into existence. Thus, research on historical geomagnetic storms can help to create a good data base for intense and super-intense magnetic storms. From the application of knowledge of interplanetary and solar causes of storms gained from the spaceage observations applied to the super-intense storm of September 1-2, 1859, it has been possible to deduce that an exceptionally fast (and intense) magnetic cloud was the interplanetary cause of this geomagnetic storm with a Dst -1760 nT, nearly 3 times as large as that of March 13, 1989 super-intense storm. The talk will focus on super-intense storms of September 1-2, 1859, and also discuss the results in the context of some recent intense storms.

Lakhina, G. S.; Alex, S.; Tsurutani, B. T.; Gonzalez, W. D.

108

Correlative comparison of geomagnetic storms and auroral substorms using geomagnetic indeces. Master's thesis  

SciTech Connect

Partial contents include the following: (1) Geomagnetic storm and substorm processes; (2) Magnetospheric structure; (3) Substorm processes; (4) Data description; (5) Geomagnetic indices; and (6) Data period and data sets.

Cade, W.B.

1993-06-01

109

Technical aspects and analysis of the cosmic ray modulation effects during geomagnetic storms  

NASA Astrophysics Data System (ADS)

Disturbances in the interplanetary space near the Earth are closely related to solar variability and its variety of eruptive phenomena, such as CMEs and CIRs. Many authors have shown that they are the interplanetary origin of geomagnetic storms. Such geomagnetic phenomena can cause damage to technological systems, both in space and on the ground. Structures ejected from the Sun can modulate high-energy cosmic rays that reach the Earth's Atmosphere. Ground based high-energy cosmic ray (muons) detectors can detect solar-related anisotropy effects. With suitable analysis, they can be used to observe signatures around 8 hours prior the disturbance arrival in the Earth's magnetosphere. A multidirectional high-energy > 50 GeV muon telescope was installed and is operational at the Southern Space Observatory - OES/CRS/CIE/INPE - MCT or SSO, as part of an international network which aims to study and forecast geomagnetic storms. Cosmic rays are also observed in a different energy range by Spaceship Earth, a neutron monitor network. The objective of this work is to present technical aspects of the SSO's muons telescope observations and to analyze the data related to geomagnetic storms. Comparison with the Spaceship Earth neutron monitor data is also presented. To identify and study interplanetary geoeffective structures we use plasma and magnetic field data from ACE spacecraft. Geomagnetic storms were identified using the Dst index. We show some cosmic ray (muons and neutrons) decreases associated with geomagnetic storms and its interplanetary origin.

Braga, Carlos Roberto; Schuch, Nelson Jorge; Martins da Silva, Samuel; Kemmerich, Níkolas; Vinicius Dias Silveira, Marcos; Deives Kummer, Fabricio; Dal Lago, Alisson; da Silva, Marlos; Munakata, Kazuoki; Kuwabara, Takao; Kato, Chihiro; Bieber, John W.; Francisco Savian, Jairo

110

Solar wind and IMF parameters associated with geomagnetic storms with Dst < - 50 nT  

NASA Astrophysics Data System (ADS)

A correlative study between the intensity of a geomagnetic storm (given by the Dst index) and the peak value reached by some solar wind parameters (velocity and density) and the southward component of the interplanetary magnetic field (IMF) is made. This study has been performed by using hourly values of the Dst index and measurements taken by the ACE spacecraft in the period 2000-2005, for which 72 geomagnetic storms were considered. It is confirmed that peak Dst is correlated to the maximum negative component Bz of the IMF better than the maxima of n and V (solar wind number density and speed, respectively). By considering all the storms, the correlation coefficient was found to be 0.88. If we consider the geomagnetic storms for which - 200 nT < peak Dst < - 60 nT, a lower correlation coefficient of 0.63 is obtained.

Mansilla, Gustavo A.

2008-10-01

111

Geomagnetic Field Frequently Asked Questions  

NSDL National Science Digital Library

At this site the question and answer format is used to provide information about the Earth's magnetic field. Frequently asked questions are linked to detailed answers. Along with standard questions about the magnetic poles and how a compass works, there are sections about geomagnetic models, Space Weather Scales and magnetic field reversals. Links lead to a site to download the latest model as well as sites for more detailed information.

2007-09-05

112

Research on earthquake prediction from geomagnetic pulsation  

Microsoft Academic Search

This paper has presented a research on the method of using digitized data of geomagnetic pulsation observation to predict\\u000a earthquakes and the research results. According to the theory of inductive magnetic effect, the observation of geomagnetic\\u000a pulsation events can detect the preseismic conductivity and structure anomalies of subsurface media more effectively than\\u000a the conventional geomagnetic observations, especially the short-impending anomalies

Jun-Cheng Zhou; Ke-Li Han; Pei-De Wang; Yue Lu

1995-01-01

113

Geomagnetic transmission of solar energetic protons during the geomagnetic disturbances of October 1989  

Microsoft Academic Search

We present orbit-averaged geomagnetic transmission measurements during the large solar energetic particle events of October 1989 using proton data from the NOAA-10 and GOES-7 satellites. We compare the measurements to geomagnetic transmission calculations determined by tracing particle trajectories through the combination of the International Geomagnetic Reference Field (IGRF) model and the 1989 Tsyganenko magnetospheric magnetic field model. We modify the

P. R. Boberg; A. J. Tylka; J. H. Adams; E. O. Flückiger; E. Kobel

1995-01-01

114

Geomagnetic transmission of solar energetic protons during the geomagnetic disturbances of October 1989  

Microsoft Academic Search

Orbit-averaged geomagnetic transmission measurements during the large solar energetic particle events of October 1989 are presented using proton data from the NOAA-10 and GOES-7 satellies. The measurements are compared to geomagnetic transmission calculations determined by tracing particle trajectories through the combination of the International Geomagnetic Reference Field (IGRF) model and the 1989 Tsyganenko magnetospheric magnetic field model. The effective 'ring

P. R. Boberg; A. J. Tylka; J. H. Adams Jr.; E. O. Flueckiger; E. Kobel

1995-01-01

115

International Geomagnetic Reference Field, 1991 revision  

NASA Astrophysics Data System (ADS)

The International Geomagnetic Reference Field (IGRF) is a series of mathematical models of the main geomagnetic field and its secular variations, with each model consisting of a set of spherical harmonic coefficients in a series expansion of the geomagnetic potential. Subsequent to the first IGRF 1965, five revisions have been adopted starting with IGRF 1975. This paper describes the fifth IGRF revision. A table is presented listing the spherical harmonic coefficients for all Definitive Geomagnetic Reference Field (DGRF) models (in which the term 'definitive' is used because the DGRF models are adopted only after it becomes unlikely that the data sets utilized will be further improved) and for IGRF 1990.

Langel, L. A.; Mundt, W.; Barraclough, D. R.; Barton, C. E.; Golovkov, V. P.; Hood, P. J.; Lowes, F. J.; Peddie, N. W.; Qi, Gui-Zhong; Quinn, J. M.

116

Effect of precipitating electrons on middle atmospheric ozone during enhanced geomagnetic activity  

NASA Astrophysics Data System (ADS)

We will investigate the solar influence on the destruction of middle atmospheric ozone by looking at ozone variations with respect to the Kp and Dst indices. A microwave radiometer developed at the British Antarctic Survey has provided 30-min temporal and 8-km vertical resolution ozone profiles between 30 and 80 km deep within the Antarctic vortex at Troll Station (72S, 2.5E, L=4.76). The Kp-index provides a measure of the geomagnetic depression at mid-latitudes occurring during enhanced geomagnetic activity, and the Dst-index indicates the geomagnetic depression at equator due to pronounced and prolonged geomagnetic activity. The number of precipitating electrons increases with increasing geomagnetic activity and thus these indices provide an indicator of the number of NO+ and HOx produced by these electrons in the upper atmosphere. The lifetime of HOx and its associated ozone destruction is short, whilst NO+ can form long-lived NOx, which will affect ozone over a wider temporal and spatial range due to transport. By doing a superposed epoch analysis of night-time ozone variations as a function of the Kp and Dst indices, we will present a statistical measure of the effect and efficiency of upper atmospheric NOx and HOx destruction of ozone.

Daae, Marianne; Kleinknecht, Nora H.; Espy, Patrick; Clilverd, Mark

117

Effect of a metallic core on transient geomagnetic induction  

NASA Astrophysics Data System (ADS)

Magnetic fields due to the magnetospheric ring current, together with their induced counterparts, must be correctly taken into account when modeling the geomagnetic field using modern observatory and satellite measurements. It is common practice to parameterize the induced field using a response function depending on a spherically symmetric electrical conductivity model of the solid Earth. We show that Earth's metallic core should be included in such conductivity models, which has not previously been the case. Abrupt changes in the amplitude of the ring current during geomagnetic storms excite a wide range of frequencies, some of which can induce electrical currents in the core. These currents decay very slowly because of the high conductivity of the core; the resulting induced field will therefore not be of zero mean even when averaged over many years. We present the results of time domain numerical simulations of induction that demonstrate the influence of a conducting core in an idealized experiment based on a synthetic geomagnetic storm. Moving to a more realistic scenario we show that taking 50 years of D_st(t) index as an input, an induced field I_st(t) with a mean value (when averaged over 10 years) of up to -1.5 nT is obtained. We conclude that transient induction in the metallic core caused by magnetospheric field variations must be included in accurate portrayals of the near-Earth magnetic environment.

Finlay, C. C.; Velimsky, J.

2011-12-01

118

Accelerated Approval (AA) for Oncology Drug Products:  

Center for Biologics Evaluation and Research (CBER)

Text VersionPage 1. 1 Accelerated Approval (AA) for Oncology Drug Products: ... 17 Trial Design – Initial AA • Trial design for initial accelerated approval (AA) ... More results from www.fda.gov/downloads/advisorycommittees/committeesmeetingmaterials

119

Robust estimation of geomagnetic transfer functions  

Microsoft Academic Search

It is shown, through an examination of residuals, that all of the statistical assumptions usually used in estimating transfer functions for geomagnetic induction data fail at periods from 5 min to several hours at geomagnetic midlatitudes. This failure can be traced to the finite spatial scale of many sources. In the past, workers have tried to deal with this problem

Gary D. Egbert; John R. Booker

1986-01-01

120

Croatian Geomagnetic Surveys 2004-2009  

Microsoft Academic Search

The setup and surveys of Croatian Geomagnetic Repeat Stations Network and the dense Croatian Geomagnetic Network for Field Mapping was presented. Regular and new field practices that include CROPOS coordinates determination and D-I-F Survey software utilization were described. Experiences encountered on the Adriatic volcanic island Jabuka, as well as on many terra rossa sights in Dalmatia and Istria, and the

Mario Brkic; Enio Jungwirth; Danijel Å. Ugar; Marko Pavasovic

2010-01-01

121

Electric utility industry experience with geomagnetic disturbances  

SciTech Connect

A geomagnetic disturbance (GMD) by its nature occurs globally and almost simultaneously. Severe geomagnetic storms cause problems for electric power systems. The vulnerability of electric power systems to such events has apparently increased during the last 10 to 20 years because power system transmission lines have become more interconnected and have increased in length and because power systems are now operated closer to their limits than in the past. In this report, the experience of electric utilities during geomagnetic storms is examined and analyzed. Measured data, effects on power system components, and power system impacts are considered. It has been found that electric power systems are susceptible to geomagnetically induced earth-surface potential gradients as small as few (2 to 3) volts per kilometer, corresponding to a storm of K-6 intensity over an area of high earth resistivity. The causes and effects are reasonably well understood, but additional research is needed to develop a better understanding of solar-induced geomagnetic storms and the responses of power systems to these types of storms. A better understanding of geomagnetic storms and the power systems` responses to GMDs is needed so that mitigation measures can be implemented that will make power systems less susceptible to severe geomagnetic disturbances. A GMD caused by a large high-altitude nuclear detonation is similar in many ways to that of solar-induced geomagnetic storms except that a nuclear-caused disturbance would be much more intense with a far shorter duration. 49 refs.

Barnes, P.R.; Rizy, D.T.; McConnell, B.W. [Oak Ridge National Lab., TN (United States); Taylor, E.R. Jr. [ABB Power Systems, Inc., Pittsburgh, PA (United States); Tesche, F.M.

1991-09-01

122

Electric utility industry experience with geomagnetic disturbances  

SciTech Connect

A geomagnetic disturbance (GMD) by its nature occurs globally and almost simultaneously. Severe geomagnetic storms cause problems for electric power systems. The vulnerability of electric power systems to such events has apparently increased during the last 10 to 20 years because power system transmission lines have become more interconnected and have increased in length and because power systems are now operated closer to their limits than in the past. In this report, the experience of electric utilities during geomagnetic storms is examined and analyzed. Measured data, effects on power system components, and power system impacts are considered. It has been found that electric power systems are susceptible to geomagnetically induced earth-surface potential gradients as small as few (2 to 3) volts per kilometer, corresponding to a storm of K-6 intensity over an area of high earth resistivity. The causes and effects are reasonably well understood, but additional research is needed to develop a better understanding of solar-induced geomagnetic storms and the responses of power systems to these types of storms. A better understanding of geomagnetic storms and the power systems' responses to GMDs is needed so that mitigation measures can be implemented that will make power systems less susceptible to severe geomagnetic disturbances. A GMD caused by a large high-altitude nuclear detonation is similar in many ways to that of solar-induced geomagnetic storms except that a nuclear-caused disturbance would be much more intense with a far shorter duration. 49 refs.

Barnes, P.R.; Rizy, D.T.; McConnell, B.W. (Oak Ridge National Lab., TN (United States)); Taylor, E.R. Jr. (ABB Power Systems, Inc., Pittsburgh, PA (United States)); Tesche, F.M.

1991-09-01

123

Geomagnetic westward drift using the correlation coefficient  

Microsoft Academic Search

An attempt is made to derive an estimate of geomagnetic westward drift from global models of the geomagnetic field, in order to determine whether a correlation can be found in the data. It is noted that the association with westward drift depends on the field pattern being fixed in the earth's outer core, as well as on its rotating at

B. M. Hodder

1983-01-01

124

Why utilities respect geomagnetically induced currents  

Microsoft Academic Search

It has been well known for more than 50 years that electric utilities in northern latitudes can have geomagnetically induced currents (GICs) flowing in their transmission lines and transformer ground points, and that these are caused by geomagnetic storms. Initially, these GICs were considered harmless and very little attention was paid to them. However, in the last 40 years it

Tom S. Molinski

2002-01-01

125

Geomagnetically induced currents during magnetic storms  

Microsoft Academic Search

The electric field which is induced by geomagnetic storms drives currents in technological systems, such as electric power transmission grids, oil and gas pipelines, telecommunication cables, and railway equipment. These geomagnetically induced currents (GIC) cause problems to the systems. In power grids, transformers may be saturated due to GIC resulting in harmful effects and possibly even to a collapse of

R. Pirjola

2000-01-01

126

Modeling geomagnetically induced currents in Hokkaido, Japan  

Microsoft Academic Search

In this paper a model for computing geomagnetically induced currents (GIC) from local geomagnetic field observations carried out in Hokkaido, Japan is constructed. The model is composed of system parameters mapping the horizontal geoelectric field to GIC and of 1D conductivity model. A rigorous model validation is used to show that the model reproduces the observed GIC with a very

A. Pulkkinen; R. Kataoka; S. Watari; M. Ichiki

2010-01-01

127

Statistics of extreme geomagnetically induced current events  

Microsoft Academic Search

In this work, space weather events associated with extreme geoelectric field and geomagnetically induced current (GIC) magnitudes are investigated. The geoelectric field and consequent GIC are computed using geomagnetic field recordings over an extended time period and ground conductivity and technological system configurations favorable for large GIC. The statistics are derived for both overall occurrence of the geoelectric field and

A. Pulkkinen; R. Pirjola; A. Viljanen

2008-01-01

128

Analysis of the October 3-7 2000 Geomagnetic Storm  

NASA Astrophysics Data System (ADS)

The 8 dimensional plasma physics model WINDMI is used to analyze the October 3-7, 2000 geomagnetic storm using solar wind input data from the ACE satellite. This period contains an extended interval of well-defined and quasi-periodic auroral activations called sawtooth oscillations, a phenomena whose relationship to substorm processes and to upstream solar wind drivers is still under debate. The model predicts both the occurrence of 8 auroral activations identified as sawtooth events during the 24 hour period on the 4th of October, and also an earlier multiple sawtooth interval on the 3rd of October, in agreement with the measured AL index. These intervals occur during steady but moderate solar wind IMF Bz values and the periodicity of the sawtooth events was not directly related to any periodic features in the upstream solar wind. The model also predicts the geomagnetic Dst index through the main and recovery phase of the storm. A genetic algorithm optimization routine was used to tune the parameters of the model to obtain a solution that has low ARV with respect to the AL index and also captures the eight substorms. Preliminary results of the analysis of the April 15-24 2002 storm are also presented.

Spencer, E.; Doxas, I.; Kozyra, J.

2005-10-01

129

Daily variation characteristics at polar geomagnetic observatories  

NASA Astrophysics Data System (ADS)

This paper is based on the statistical analysis of the diurnal variation as observed at six polar geomagnetic observatories, three in the Northern and three in the Southern hemisphere. Data are for 2006, a year of low geomagnetic activity. We compared the Italian observatory Mario Zucchelli Station (TNB; corrected geomagnetic latitude: 80.0°S), the French-Italian observatory Dome C (DMC; 88.9°S), the French observatory Dumont D'Urville (DRV; 80.4°S) and the three Canadian observatories, Resolute Bay (RES; 83.0°N), Cambridge Bay (CBB; 77.0°N) and Alert (ALE, 87.2°N). The aim of this work was to highlight analogies and differences in daily variation as observed at the different observatories during low geomagnetic activity year, also considering Interplanetary Magnetic Field conditions and geomagnetic indices.

Lepidi, S.; Cafarella, L.; Pietrolungo, M.; Di Mauro, D.

2011-08-01

130

Solar dynamo and geomagnetic activity  

NASA Astrophysics Data System (ADS)

The correlation between geomagnetic activity and the sunspot number in the 11-year solar cycle exhibits long-term variations due to the varying time lag between the sunspot-related and non-sunspot related geomagnetic activity, and the varying relative amplitude of the respective geomagnetic activity peaks. As the sunspot-related and non-sunspot related geomagnetic activity peaks are caused by different solar agents, related to the solar toroidal and poloidal fields, respectively, we use their variations to derive the parameters of the solar dynamo transforming the poloidal field into toroidal field and back. We find that in the last 12 cycles the solar surface meridional circulation varied between 5 and 20 m/s (averaged over latitude and over the sunspot cycle), the deep circulation varied between 2.5 and 5.5 m/s, and the diffusivity in the whole of the convection zone was ˜108 m2/s. In the last 12 cycles solar dynamo has been operating in moderately diffusion dominated regime in the bulk of the convection zone. This means that a part of the poloidal field generated at the surface is advected by the meridional circulation all the way to the poles, down to the tachocline and equatorward to sunspot latitudes, while another part is diffused directly to the tachocline at midlatitudes, “short-circuiting” the meridional circulation. The sunspot maximum is the superposition of the two surges of toroidal field generated by these two parts of the poloidal field, which is the explanation of the double peaks and the Gnevyshev gap in sunspot maximum. Near the tachocline, dynamo has been operating in diffusion dominated regime in which diffusion is more important than advection, so with increasing speed of the deep circulation the time for diffusive decay of the poloidal field decreases, and more toroidal field is generated leading to a higher sunspot maximum. During the Maunder minimum the dynamo was operating in advection dominated regime near the tachocline, with the transition from diffusion dominated to advection dominated regime caused by a sharp drop in the surface meridional circulation which is in general the most important factor modulating the amplitude of the sunspot cycle.

Georgieva, Katya; Kirov, Boian

2011-02-01

131

A method of calculation of vertical cutoff rigidity in the geomagnetic field  

NASA Astrophysics Data System (ADS)

On the basis of generalization of the results of extensive trajectory calculations for trial charged particles moving in the geomagnetic field the method of calculation of effective vertical cutoff rigidity, taking into account the values of K p -index and local time, is developed. The IGRF and Tsyganenko-89 models are used for the geomagnetic field. A comparison of the results of model simulations with the experimental data on penetration of charged particles into near-Earth space is made, and penetration functions for typical spacecraft orbits are calculated.

Nymmik, R. A.; Panasyuk, M. I.; Petrukhin, V. V.; Yushkov, B. Yu.

2009-06-01

132

Statistical comparison of interplanetary conditions causing intense geomagnetic storms (Dst ? -100 nT)  

NASA Astrophysics Data System (ADS)

It is well known that intense southward magnetic field and convection electric field (V × B) in the interplanetary medium are key parameters that control the magnitude of geomagnetic storms. By investigating the interplanetary conditions of 82 intense geomagnetic storms from 1998 to 2006, we have compared many different criteria of interplanetary conditions for the occurrence of the intense geomagnetic storms (Dst ? -100 nT). In order to examine if the magnetosphere always favors such interplanetary conditions for the occurrence of large geomagnetic storms, we applied these conditions to all the interplanetary data during the same period. For this study, we consider three types of interplanetary conditions as follows: Bz conditions, Ey conditions, and their combination. As a result, we present contingency tables between the number of events satisfying the condition and the number of observed geomagnetic storms. Then we obtain their statistical parameters for evaluation such as probability of detection yes, false alarm ratio, bias, and critical success index. From a comparison of these statistical parameters, we suggest that three conditions are promising candidates to trigger an intense storm: Bz ? -10 nT for >3 h, Ey ? 5 mV/m for >2 h, and Bz ? -15 nT or Ey ? 5 mV/m for >2 h. Also, we found that more than half of the “miss” events, when an intense storm occurs that was not expected, are associated with sheath field structures or corotating interacting regions. Our conditions can be used for not only the real-time forecast of geomagnetic storms but also the survey of interplanetary data to identify candidate events for producing intense geomagnetic storms.

Ji, Eun-Young; Moon, Y.-J.; Kim, K.-H.; Lee, D.-H.

2010-10-01

133

History of the geomagnetic field  

USGS Publications Warehouse

Direct measurements of the direction and strength of the earth's magnetic field have provided a knowledge of the field's form and behavior during the last few hundreds of years. For older times, however, it has been necessary to measure the magnetism of certain rocks to learn what the geomagnetic field was like. For example, when a lava flow solidifies (at temperatures near 1000??C) and cools through the Curie point of the magnetic minerals contained in it (around 500??C) it acquires a remanent magnetism that is (1) very weak, (2) very stablel, (3) paralle to the direction of the ambient geomagnetic field, and (4) proportional in intensity to the ambient field. Separating, by various analytical means, this magnetization from other 'unwanted' magnetizations has allowed paleomagnetists to study the historical and prehistorical behavior of the earth's field. It has been learned, for example, that the strength of the field was almost twice its present value 2000 years ago and that it has often completely reversed its polarity. Paleo-magnetists have also confirmed that most oceans are, geologically speaking, relatively new features, and that the continents have markedly changed their positions over the surface of the earth. ?? 1969 The American Institute of Physics.

Doell, R. R.

1969-01-01

134

Geomagnetic effects of high-density plasma with southward magnetic field in the interplanetary coronal mass ejection observed on May 2-3, 1998  

Microsoft Academic Search

This paper aims to clarify the effect of high-density plasma in interplanetary coronal mass ejection (ICME) observed during the May 2-3, 1998 geomagnetic storm. The examination is performed based on the estimation of Dst index, which is calculated with the observed solar wind parameters of the ICME. The estimated Dst index variation is compared with Dst index variation provided by

Haruka Adachi; Tohru Sakurai; Katsuhide Marubashi

2006-01-01

135

Solar and Interplanetary Causes of the Last Solar Cycle Deep Minimum in Geomagnetic Activity  

NASA Astrophysics Data System (ADS)

The recent solar cycle minimum (2008-2009) was extreme in several aspects, being the longest and deeper (low sunspot number) during the space era. Furthermore, the geomagnetic index ap showed its lowest value during the entire period of its record. The solar and interplanetary causes of this low geomagnetic activity were investigated. It was found that this period of minimum geomagnetic activity showed low values of interplanetary magnetic fields, solar wind speed, and the variance of the IMF Bz component. As a consequence, there was a minimum in energy transfer (epsilon parameter) from solar wind to the magnetosphere. The low IMF was caused by low solar magnetic fields, the low solar wind speed and low variances by the predominance of mid-latitude small coronal holes in this time of cycle, leading to solar wind streams from the edge of these holes to reach earth's orbit.

Echer, E.; Gonzalez, W. D.; Tsurutani, B.

2011-12-01

136

foF2 correlation studies with solar and geomagnetic indices for two equatorial stations  

NASA Astrophysics Data System (ADS)

The analysis of the contributions of solar and geomagnetic indices on the critical frequency of the ionospheric F2 layer (foF2)-, for different seasons and two Nigerian equatorial stations- Ibadan (Lat. 7.4°N, Long. 3.9°N) and Ilorin (Lat. 8.5°N, Long. 4.55°E)- are presented. The data set was randomly sampled across three solar cycles of periods of low, moderate and high solar activities. Solar indices used in this work are Coviten solar flux (F10.7 cm), daily solar radio flux (dF10.7), International Sunspot Number (ISSN), Smoothen Sunspot Number (SmSSN), and Sun Spot Number (SSN). The geomagnetic indices used are planetary indices Am, Aa, Ap, C9, Cp, and Kp. foF2 showed a non-linear trend with an average coefficient (R) of 0.70 across the various seasons. Regression lines for polynomials of degree n=1 to n=6 was fitted, for each data set. Am, Ap, Aa, SSN, ISSN, F10.7 cm, and dF10.7 with R values of 0.71,0.74,0.61,0.59,0.72,0.80, and 0.86, for the various geomagnetic and solar indices, had the highest contributions. We therefore advocate for SSN, ISSN, F10.7 cm, dF10.7 and Am, Ap or Aa in modeling foF2 for the African equatorial ionosphere. The results of this work are in line with the results of other works carried out at different equatorial stations.

Joshua, E. O.; Nzekwe, N. M.

2012-05-01

137

Evaluation of three predictors of geomagnetic activity  

SciTech Connect

Three functions, B/sub s/V, B/sub s/V/sup 2/, and B/sub s//sup 2/V where B/sub s/ is the southward component of the IMF and V, the solar wind speed, have been tested for their ability to predict geomagnetic activity as measured by the AL index. The data were selected from a period within 1 month of the June solstice for the years 1967--1974 inclusive, when AL apears to be most nearly a linear measure of magnetic activity. After correcting the index for processes not similar to substorms, separate comparisons of ..sigma..B/sup m//sub s/V/sup n/ with ..sigma..AL were made during isolated magnetic intervals so that the flux eroded from the forward magnetosphere could return, thus avoiding time delay estimates. Intervals during which there was evidence that the westward electrojet was displaced above or below the auroral observatory chain were eliminated. Under these carefully specified conditions, regression studies between AL and each of the three functions yield correlation coefficients of 0.97 for B/sub s/V/sup 2/, 0.92 for B/sub s/V, and 0.82 for B/sup 2//sub s/V. A study of the variation of each of three functions of the type ..sigma..AL/..sigma..B/sup m//sub s/V/sup n/ with B/sub s/ and with V has indicated that mapprox. =0.85 and n = 2. Some suggestions are offered to account for the diverse forms of the empirical prediction function used by various investigators.

Holzer, R.E.; Slavin, J.A.

1982-04-01

138

Major geomagnetic storms and cosmic rays, 1. search of features in CR what can be used for forecasting  

NASA Astrophysics Data System (ADS)

According to NOAA Space Weather Scales, geomagnetic storms of scales G5 (3-hour index of geomagnetic activity Kp=9), G4 (Kp=8) and G3 (Kp=7) are dangerous for people technology and health (influence on power systems, on spacecraft operations, on HF radio-communications and others. To prevent these serious damages will be very important to forecast dangerous geomagnetic storms. In many papers it was shown that in principle for this forecasting can be used data on CR intensity and CR anisotropy changing before SC of major geomagnetic storms accompanied by sufficient Forbush-decreases (e.g., Dorman et al., 1995, 1999). In this paper we consider over 100 major geomagnetic storms and for each case we analyze hourly data of many NM for 8 days with SC in the 4-st day of 8-days period (that before SC we have at least 3 full days). We determine what part of major geomagnetic storms is accompanied CR intensity and CR anisotropy changing before SC, and what part of major geomagnetic storms does not show any features what can be used for forecasting. We estimate also how these parts depend from the index of geomagnetic activity Kp. REFERNECES Yudakhin K.F., Bavassano B., Ptitsyna N.G., Tyasto M.I., "Cosmic-ray forecasting features for big Forbush-decreases". Nuclear Physics B, Vol. 49A, pp. 136-144. (1995). L.I.Dorman, N.Iucci, N.G.Ptitsyna, G.Villoresi, Cosmic ray Forbush-decrease as indicators of space dangerous phenomenon and possible use of cosmic ray data for their prediction , Proc. of 26-th Intern. Cosmic Ray Conference, Salt Lake City, Vol. 6, p. 476-479, (1999).

Dorman, L. I.; Mavromichalaki, H.; Pustilnik, L. A.; Sternlieb, A.; Zukerman, I. G.

2001-08-01

139

Geomagnetism Program Assessment and Planet Earth Initiative  

NASA Astrophysics Data System (ADS)

Congressman David Skaggs (D-Colo.) has requested an assessment by AGU of whether the U.S. geomagnetism program would be strengthened if the U.S. Geological Survey geomagnetic observatories program was transferred to the National Oceanic and Atmospheric Administration (NOAA). This assessment is needed by the end of January 1988The AGU Geomagnetism and Paleomagnetism Section and the Public Affairs Committee recommended that AGU do the study. A panel has been formed to develop a draft AGU position on this issue by early January for subsequent Council approval. The members of this panel will be

Eagleson, P. S.

140

Numerical Modeling of Auroral and Equatorial Electrojet Behavior during Geomagnetic Storm Sequence on September 9-14, 2005  

NASA Astrophysics Data System (ADS)

In Klimenko et al., 2006 the model of electric field and zonal current in the Earth's ionosphere has been presented. This model has been included into the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) developed in WD IZMIRAN (Namgaladze et al., 1988). The modified GSM TIP model has allowed to describe more correctly the behavior of electric field and different ionospheric parameters at low latitudes, and also to investigate the behavior of auroral and equatorial electrojets. In the given research we present the calculation results of behavior of auroral and equatorial electrojets during geomagnetic storm sequence on September 9-14, 2005. The calculations have been executed with use of the modified GSM TIP model. At that the model input parameters, such as the potential difference through polar caps, field-aligned currents of second region and particle precipitation fluxes and energy were set as function of AE-and Kp-indices of geomagnetic activity according to different empirical models Feshchenko and Maltsev, 2003; Zhang and Paxton, 2008 and morphological representations Cheng et al., 2008. Furthermore, at the storm sudden commencement phase we taken into account the shift of field-aligned currents of the second region into the lower latitudes as by Sojka et al., 1994 and 30 min. time delay of variations of the field-aligned currents of the second region relative to the variations of the potential drop through polar caps. Also, we taken into account the ionospheric effects of solar flares, which were taken place during the considered period. The calculation results are analyzed according to known morphological representations about auroral and equatorial electrojet behavior during geomagnetic storms. This study is supported by RFBR grant 08-05-00274. References Cheng Z.W., Shi J.K., Zhang T.L., Dunlop M. and Liu Z.X. Relationship between FAC at plasma sheet boundary layers and AE index during storms from August to October, 2001. Sci. China Ser. E-Tech. Sci., 2008, Vol. 51, No. 7, 842-848. Feshchenko E.Yu., Maltsev Yu.P. Relations of the polar cap voltage to the geophysical activity. Physics of Auroral Phenomena: XXVI Annual Seminar (February 25-28, 2003): Proc./PGI KSC RAS. Apatity, 2003, 59-61. Klimenko M.V., Klimenko V.V., Bryukhanov V.V. Numerical Simulation of the Electric Field and Zonal Current in the Earth's Ionosphere: The Dynamo Field and Equatorial Electrojet. Geomagn. Aeron. 2006, Vol. 46, No. 4, 457-466. Namgaladze A.A., Korenkov Yu.N., Klimenko V.V., Karpov I.V., Bessarab F.S., Surotkin V.A., Glushenko T.A., Naumova N.M. Global model of the thermosphere-ionosphere-protonosphere system. Pure and Applied Geophysics (PAGEOPH), 1988, Vol. 127, No. 2/3, 219-254. Sojka J.J., Schunk R.W., Denig W.F. Ionospheric response to the sustained high geomagnetic activity during the March '89 great storm. J. Geophys. Res., 1994, Vol. 99, No. A11, 21341-21352. Zhang Y., Paxton L.J. An empirical Kp-dependent global auroral model based on TIMED/GUVI FUV data. J. Atmos. Solar-Terr. Phys., 2008, Vol. 70, 1231-1242.

Klimenko, Maxim; Klimenko, Vladimir

141

S-transform view of geomagnetically induced currents during geomagnetic superstorms  

Microsoft Academic Search

Novel time-frequency analysis method S-transform capable of handling noisy non-stationary signals is applied to study the properties of geomagnetically induced current GIC fluctuations in the Finnish natural gas pipeline during geomagnetic superstorms New local time- and storm phase-dependent S-transform spectral properties of auroral region GIC fluctuations during geomagnetic superstorms are reported More specifically the S-transform spectra have two distinct regions

Antti Pulkkinen; Ryuho Kataoka

2006-01-01

142

An empirical model of ground-level geomagnetic perturbations  

NASA Astrophysics Data System (ADS)

A new empirical model for predicting ground-level geomagnetic perturbations has been developed. This model is based on global measurements of the magnetic field at multiple stations in the Northern Hemisphere collected over an 8 year period, along with the simultaneous measurements of the interplanetary magnetic field (IMF). Variations in ionospheric conductivity are implicitly contained in the measurements used in the model's construction, including the solar F10.7 index. Provided with the IMF, solar wind velocity, dipole tilt angle (for season), and F10.7 index, this model computes all three vector components of the magnetic perturbations at specified locations. The model results are consistent with the corresponding maps of the ionospheric electric potential. Interestingly, maps of the vertical component have patterns that resemble maps of the overhead, ionospheric field-aligned currents. Comparisons of model calculations with measurements at different locations show very good results, particularly at low frequencies. There are random variations at higher frequencies that are not reproduced well with the model, but they tend to occur in proportion to the predicted levels. This model could be useful for providing regional forecasts of geomagnetic activity with an approximately 1 h lead time.

Weimer, D. R.

2013-03-01

143

Geomagnetic cutoff rigidities and geomagnetic coordinates appropriate for the Carrington flare Epoch  

NASA Astrophysics Data System (ADS)

Using the trajectory-tracing technique for cosmic rays in the geomagnetic field, vertical cutoff rigidity values for a world grid have been determined for Epoch 1850. These values have been used to derive a world map of iso-rigidity contours that would have been appropriate for the era of the Carrington flare in September 1859. When comparing these iso-rigidity contours with those determined for Epoch 2000, large differences are found, particularly in the Atlantic Ocean region. Geomagnetic cutoff rigidity values and geomagnetic coordinates have been determined for selected mid and low latitude geographic locations for which aurora were sighted during the geomagnetic storms of late August and early September 1859 and compared with the values for those locations calculated for the year 2000. While the geomagnetic latitude differences are relatively small, there are major changes in the vertical cutoff rigidity values for these same locations over this 150-year period. The cutoff differences are attributed to a combination of: (1) the decreasing internal geomagnetic field over the last 150 years and (2) the westward drift of the major features of the geomagnetic field. The relatively small changes in geomagnetic latitude are attributed to the small change in the latitude of the north magnetic pole over this 150-year period. This study emphasizes that while geomagnetic cutoff values are essential for the analysis of high-energy solar proton events, they are not an appropriate parameter for evaluation of the equatorward extent of an auroral display.

Shea, M. A.; Smart, D. F.

2006-01-01

144

Magnetotactic Bacteria at the Geomagnetic Equator.  

National Technical Information Service (NTIS)

Magnetotactic bacteria are observed in freshwater and marine sediments of Fortaleza, Brazil, situated close to the geomagnetic equator. Both South-seeking and North-seeking bacteria are present in roughly equal numbers in the same samples. This observatio...

R. B. Frankel R. P. Blakemore F. F. T. Araujo D. M. S. Esquivel J. Danon

1981-01-01

145

A new way to study geomagnetic storms  

NASA Astrophysics Data System (ADS)

James Hutchinson and colleagues describe a novel radar technique to study geomagnetic storms: superposed latitude-time-velocity plots. This is a summary of the poster winning a Rishbeth Prize at the NAM/UKSP/MIST meeting in April.

Hutchinson, J. A.; Wright, D. M.; Milan, S. E.; Grocott, A.; Boakes, P. D.

2011-08-01

146

Geomagnetic storm characteristics under varied interplanetary conditions  

NASA Astrophysics Data System (ADS)

Solar cycle-23 witnessed many successive intense X-ray solar flares and coronal mass ejections (CME) during the peak activity period, as well as in the descending phase of the cycle. Some of these emissions had large solar energetic particle events associated with them. When such solar ejecta impact the Earth's magnetosphere, they cause large scale disturbances in the geomagnetic field known as geomagnetic storms. Large variability in the occurrence characteristics of geomagnetic storms is controlled ultimately by the solar activity. Thus the changes in the interplanetary conditions are distinctly seen in the low latitude geomagnetic records as each storm event differs from the other. Several intense storm events of solar cycle-23 are analyzed for assessing the role of interplanetary magnetic field components B_{y} (east-west) and B_{z} (north-south) in controlling the generation and development of various types of storms.

Rawat, R.; Alex, S.; Lakhina, G. S.

2007-12-01

147

Geomagnetic Observations at Memambetsu, Japan in 1971.  

National Technical Information Service (NTIS)

Results of geomagnetic observations carried out by Mema-betsu Magnetic Observatory are presented in tabular form. Data cover character of the magnetic disturbances, hourly values and associated mean values, and absolute values of magnetic elements.

1972-01-01

148

Effects of Starfish on Geomagnetically Trapped Protons.  

National Technical Information Service (NTIS)

Measurements of geomagnetically-trapped, 55 MeV protons made before and after the detonation of the STARFISH nuclear device revealed that at low altitudes the flux increased considerably after the STARFISH burst. Theoretical analyses presented in this rep...

J. B. Cladis G. T. Davidson W. E. Francis R. K. Jaggi G. H. Nakano

1969-01-01

149

On the seismogenic increase of the ratio of the ULF geomagnetic field components  

NASA Astrophysics Data System (ADS)

Following the paper by Fraser-Smith et al. (1990), many scientists have focused their research on the ULF geomagnetic field pulsations in the hope of finding possible anomalous signals caused by the seismic activity. Thereafter, many papers have reported ULF geomagnetic field polarization ratio increases which have been claimed to be related to the occurrence of moderate and strong earthquakes. Even if there is no firm evidence of correlation between the polarization ratio increase and seismic events, these publications maintain that these "anomalous" increases are without doubt precursors of pending earthquakes. Furthermore, several researchers suggest that these seismogenic signals may be considered a promising approach towards the possibility of developing short-term earthquake prediction capabilities based on electromagnetic precursory signatures. On the contrary, a part of the scientific community emphasizes the lack of validation of claimed seismogenic anomalies and doubt their association with the seismic activity. Since earthquake prediction is a very important topic of social importance, the authenticity of earthquake precursors needs to be carefully checked. The aim of this paper is to investigate the reliability of the ULF magnetic polarization ratio changes as an earthquakes' precursor. Several polarization ratio increases of the geomagnetic field, which previous researchers have claimed to have a seismogenic origin, are put into question by a qualitative investigation. The analysis takes into account both the temporal evolution of the geomagnetic field polarization ratio reported in previous papers, and the global geomagnetic activity behaviour. Running averages of the geomagnetic index Kp are plotted onto the original figures from previous publications. Moreover, further quantitative analyses are also reported. Here, nine cases are investigated which include 17 earthquakes. In seven cases it is shown that the suggested association between the geomagnetic field polarization ratio increases and the earthquake preparation process seems to be rather doubtful. More precisely, the claimed seismogenic polarization ratio increases are actually closely related to decreases in the geomagnetic activity level. Furthermore, the last two investigated cases seem to be doubtful as well, although a close correspondence between polarization ratio and geomagnetic activity cannot be unambiguously demonstrated.

Masci, Fabrizio

2011-07-01

150

Definition of new geomagnetic activity proxies and their use in thermosphere density modeling in the framework of the ATMOP project (invited)  

NASA Astrophysics Data System (ADS)

In the framework of the FP7 European program ATMOP (Advanced Thermosphere Modelling for Orbit Prediction), we present a test of new geomagnetic indices, that we propose to use in the new version of the semi empirical DTM thermosphere model. This new version of the DTM model will provide in quasi real time a precise air drag computation, necessary for accurate tracking of space objects in low earth orbit. To characterize the geomagnetic forcing in the upper atmosphere geomagnetic indices derived from ground based magnetic variation recordings are used. In the currently used semi-empirical density models (DTM, MSIS, JB2008) the geomagnetic forcing is characterized using the Km or Kp index with a 3 hour time resolution or the DST index with a 1 hour time resolution. We define new geomagnetic indices, based on ground based magnetic variations recorded in the am network observatories at sub-auroral latitudes to achieve a better temporal resolution (?m indices) or a better spatial representation of the local time dependency of the solar wind/magnetosphere interaction (am-MLT and ?m-MLT sector indices). This test will be carried out using CHAMP and GRACE densities (inferred from accelerometer data in the 370-490 km range) between years 2002-2006. Correlations between the variation of density and geomagnetic indices will give information on the geomagnetic indices to be used, taking into account constraints for an operational version of the DTM model.

El-Lemdani Mazouz, Farida; Menvielle, Michel; Lathuillère, Chantal; Marchaudon, Aurélie; Chamboudout, Aude; Bruinsma, Sean

2013-04-01

151

Midlatitude airglow variations during geomagnetic storms  

Microsoft Academic Search

In this paper, response to geomagnetic disturbances and geomagnetic storms in the mid-latitude airglow is considered. The 1997-2008 experimental observation data of the airglow over East-ern Siberia (52N, 103E) are used. Two types of disturbances in the 557.7 and 630 nm atomic oxygen emissions are analyzed. The first type is associated with onset of wavelike oscillations of the 557.7 and

Alexander Mikhalev; Alexander Beletsky; Liudmila Leonovich; Vitaly Leonovich; Jiyao Xu; Wei Yuan

2010-01-01

152

Solar cycle effects in near-Earth interplanetary parameters and geomagnetic activity  

NASA Astrophysics Data System (ADS)

Solar cycle effects are investigated in planetary geomagnetic activity from 27-day averages of several near-Earth OMNI parameters compared with equivalent Kp and Dst index averages for almost four decades (1964-2001). Some established trends in these parameters over solar cycles are confirmed; for example, it is concluded that changes in the magnitude (rather than in direction) constitute the primary solar cycle variation in the IMF. The solar cycle effects are also thoroughly studied from the northern polar cap magnetic activity index PCN (1975-2001), which is considered as an ``ionospheric gauge'' of the ``merging'' interplanetary electric field constantly applied to the geomagnetosphere; these results are compared with available studies of solar cycle effects in the auroral magnetic activity indices AL and AU. It is concluded that the 11-year solar activity cycle is clearly seen in all above-mentioned parameters and indices; however, the available time series are not long enough to confirm firmly the existing hypothesis of the increasing geomagnetic activity during last century. Our study also reveals that long-term changes in planetary geomagnetic activity are driven more actively by solar wind-magnetosphere coupling of an electrodynamic nature rather than by plasma transport into the magnetosphere. This suggests that ambient interplanetary ``electric'' environment (in which the Earth's magnetosphere is immersed over the solar cycles) may play a more significant role in causing changes in the frequency of geomagnetic storms and substorms than previously realized.

Papitashvili, V. O.; Papitashvili, N. E.; King, J. H.; Rasmussen, O.; Gromova, L. I.

2001-05-01

153

Geomagnetic disturbance effects on power systems  

SciTech Connect

In the northern hemisphere, the aurora borealis is visual evidence of simultaneous fluctuations in the earth's magnetic field (geomagnetic field). These geomagnetic disturbances (GMD's), or geomagnetic storms, can affect a number of man-made systems, including electric power systems. The GMD's are caused by the electromagnetic interaction of the solar wind plasma of protons and electrons with the geomagnetic field. These dynamic impulses in the solar wind are due to solar flares, coronal holes, and disappearing filaments, and reach the earth from one to six days after being emitted by a solar event. Instances of geomagnetic storms affecting telegraph systems were noted in England in 1846, and power system disturbances linked to GMD's were first reported in the United States in 1940. This Working Group report is a summary of the state of knowledge and research activity to the present time, and covers the GMD/Geomagnetically-induced currents (GIC) phenomena, transformer effects, the impact on generators, protective relay effects, and communication system effects. It also summarizes modeling and predicting GIC, measuring and monitoring GIC, mitigation methods, system operating guidelines during GMD's, and alerting and forecasting procedures and needs for the power industry.

Albertson, V.D.; Bozoki, B.; Feero, W.E.; Kappenman, J.G.; Larsen, E.V.; Nordell, D.E.; Ponder, J.; Prabhakara, F.S.; Thompson, K.; Walling, R.

1993-07-01

154

Space weather and dangerous phenomena on the Earth: principles of great geomagnetic storms forcasting by online cosmic ray data  

NASA Astrophysics Data System (ADS)

According to NOAA space weather scales, geomagnetic storms of scales G5 (3-h index of geomagnetic activity Kp=9), G4 (Kp=8) and G3 (Kp=7) are dangerous for satellites, aircrafts, and even for technology on the ground (influence on power systems, on spacecraft operations, on HF radio-communications and others). We show on the basis of statistical data, that these geomagnetic storms, mostly accompanied by cosmic ray (CR) Forbush-decreases, are also dangerous for people's health on spacecraft and on the ground (increasing the rate of myocardial infarctions, brain strokes and car accident road traumas). To prevent these serious damages it is very important to forecast dangerous geomagnetic storms. Here we consider the principles of using CR measurements for this aim: to forecast at least 10-15h before the sudden commencement of great geomagnetic storms accompanied by Forbush-decreases, by using neutron monitor muon telescope worldwide network online hourly data. We show that for this forecast one may use the following features of CR intensity variations connected with geomagnetic storms accompanied by Forbush-decreases: 1) CR pre-increase, 2) CR pre-decrease, 3) CR fluctuations, 4) change in the 3-D CR anisotropy.

Dorman, L. I.

2005-11-01

155

Large-scale lithospheric magnetic anomalies in Europe as revealed by recorded geomagnetic storms at the observatory network  

NASA Astrophysics Data System (ADS)

The magnetic field of the Earth, which extends in space as magnetosphere, is in permanent interaction with the solar electromagnetic, particle and magnetic flux outputs, i.e. the solar radiation, the solar wind, and, respectively, the heliospheric magnetic field. The variable current systems that develop as a result of these interactions create the so-called field of geomagnetic variations which, in turn, induces a response of the Earth's internal magnetic and conductive structures. In this study, the geomagnetic variations at storm timescales (minutes - days) provided by the network of European geomagnetic observatories have been used for modeling the magnetic structure of the European lithosphere. Large-scale magnetic structures in the lithosphere are evidenced by means of a magnetic induction model applied to geomagnetic observatory data recorded during several intense geomagnetic storm intervals (Dst<-200 nT) in the time period 2001-2005. The magnetic induction model assumes that the induced field is a linear combination of the components of the inducing field. As the inducing external source, the magnetic field of the ring current at each observatory location was used, inferred from the Dst geomagnetic index (minute). The lateral distribution of the lithosphere magnetic properties as described by the coefficients of the mentioned linear combination was derived and a comparison with distributions resulted in case of other variable sources (e.g. Sq) is discussed.

Dobrica, Venera; Demetrescu, Crisan

2013-04-01

156

Geomagnetic effects modelling for the PJM interconnection system. II. Geomagnetically induced current study results  

Microsoft Academic Search

The development of a computer program far calculation of geomagnetically induced current (GIC) and a GIC power system model for the Pennsylvania-New Jersey-Maryland Interconnection (PJM) is described. Results of GIC for three different ionospheric source configurations are shown. A new method is presented for estimating GIC in unmetered parts of the system based on a few measurements and precalculated geomagnetic

F. S. Prabhakara; L. N. Hannett; R. I. Ringlee; J. Z. Ponder

1992-01-01

157

Geomagnetically induced currents in the UK: geomagnetic variations and surface electric fields  

Microsoft Academic Search

The geomagnetically induced current (GIC) risk to the power transmission grid in the United Kingdom is discussed with reference to an example of a geomagnetic storm during which GICs were suspected of causing abnormal transformer behaviour. A simple measure of the power of the magnetic field variation, the hourly standard deviation (HSD) in the north or east horizontal component, is

D Beamish; T. D. G Clark; E Clarke; A. W. P Thomson

2002-01-01

158

Measurement of geomagnetic cutoff rigidities and particle fluxes below geomagnetic cutoff near Palestine, Texas  

Microsoft Academic Search

A high-statistics magnetic spectrometer measurement of the geomagnetic ; cutoff rigidity and related effects at Palestine, Texas is reported. The ; effective cutoffs observed are in agreement with computer-calculated cutoffs. ; Measured spectra of albedo and atmospheric secondary particles that come below ; geomagnetic cutoff are also reported. (auth);

C. R. Pennypacker; G. F. Smoot; A. Buffington; R. A. Muller; L. H. Smith

1973-01-01

159

Toward a standardized definition of geomagnetic sudden impulses and storm sudden commencements  

NASA Astrophysics Data System (ADS)

In an attempt to resolve some ambiguity in defining geomagnetic sudden impulses (Sis) and storm sudden commencements (SSCs) using the existing phenomenological definition (see, for example, Mayaud and Romana [1977]; Mayaud [1980]), Joselyn and Tsurutani [1990] recently constructed a scheme in which SSCs are a subset of Sis, depending on the magnitude of subsequent geomagnetic activity. For quantitative application, they have proposed that an SI be specified as a sharp change (at least 10 nT in 3 minutes or less) observed nearly simultaneously (within a few minutes) in either component of the horizontal magnetic field at globally spaced observatories near 20° geomagnetic latitude. In addition, SSCs are those Sis followed within 24 hours by an hourly Dst index of at least -50 nT. Because the Dst index is not readily available, the recommended provisional alternative indicators are a 3-hourly Kp index of 5 or more and a half-daily a a index of 60 or more. Joselyn and Tsurutani [1990] have recommended these new quantitative definitions of the two terms (Sis and SSCs) for open discussion.

Kamide, Y.; Joselyn, J. A.

160

Major geomagnetic storms and cosmic rays, 2. methods of CR using for forecasting  

NASA Astrophysics Data System (ADS)

We present developing of methods (e.g., Dorman et al., 1995, 1999) to forecast on the basis of NM hourly on-line data (as well as on-line muon telescopes hourly data from different directions) geomagnetic storms of scales G5 (3-hour index of geomagnetic activity Kp=9), G4 (Kp=8) and G3 (Kp=7) (according to NOAA Space Weather Scales). These geomagnetic storms are dangerous for people technology and health (influence on power systems, on spacecraft operations, on HF radio-communications and others). We show that for especially dangerous geomagnetic storms can be used global-spectrographic method if on-line will be available 35-40 NM and muon telescopes. In this case for each hour can be determined CR anisotropy vector, and the specifically behavior of this vector before SC of geomagnetic storms G5, G4 or G3 (according to NOAA Space Weather Scales) can be used as important factor for forecast. The second factor what can be used for SC forecast is specifically behavior of CR density (CR intensity) for about 30-15 hours before SC (caused mainly by galactic CR particles acceleration during interaction with shock wave moved from the Sun). We demonstrate developing methods on several examples of major geomagnetic storms. REFERENCES Dorman L.I., Villoresi G., Belov A.V., Eroshenko E.A., Iucci N., Yanke V.G., Yudakhin K.F., Bavassano B., Ptitsyna N.G., Tyasto M.I., "Cosmic-ray forecasting features for big Forbushdecreases". Nuclear Physics B, Vol. 49A, pp. 136(1995). L.I.Dorman, N.Iucci, N.G.Ptitsyna, G.Villoresi, 1999. Cosmic ray Forbush-decrease as indicators of space dangerous phenomenon and possible use of cosmic ray data for their prediction , Proc. of 26-th Intern. Cosmic Ray Conference, Salt Lake City, Vol. 6, p.

Belov, A. V.; Dorman, L. I.; Eroshenko, E. A.; Gushchina, R. T.; Iucci, N.; Mavromichalaki, H.; Pustilnik, L. A.; Sternlieb, A.; Villoresi, G.; Yanke, V. G.; Zukerman, I. G.

2001-08-01

161

Some results of geomagnetic storm events observed at the Brazilian Southern Space Observatory  

NASA Astrophysics Data System (ADS)

Space weather can be defined as the study of solar and interplanetary sources of geomagnetic storms. Coronal mass ejections (CMEs) are large plasma eruptions released from the Sun and they are one of the main solar-interplanetary structures causing the geomagnetic disturbances on Earth. Such events, also named (geomagnetic storms) are caused when there are changes in the plasma and magnetic field in the space that surrounds the Earth's magnetosphere. CME passages are known to be an important origin of such changes. The damage caused by geomagnetic storms are several, including loss of data from satellite, signal scintillation, interference on radar, telecommunications cable disruption, electricity grid disturbance and black-out electrical power. They are also responsible for the appearance of auroras. It is known that quantity of cosmic rays observed in each direction on Earth's surface is approximately unchanged on the time when there are no transient solar-interplanetary events. During disturbed periods, CME may shield cosmic rays, allowing terrestrial detectors to identify some signatures on the same period. Sometimes, these signatures can be identified prior to the occurence of the disturbance using a cosmic ray network around the Earth. With this purpose, a prototype detector of high-energy cosmic rays > 50 GeV, muons, was installed in the Brazilian Southern Space Observatory - SSO/CRS/CIE/INPE - MCT in 2001. It was composed of 2 layers of 4 detectors (2x2x2) with temporal resolution of one hour. The detector was upgraded in 2005 to 56 detectors (2x4x7) and temporal resolution of one minute. The expansion enabled a decrease of error from 0.16% to 0.06% in the counting of muons. The purpose of this paper is to discuss the expansion and to present results of the study of some geomagnetic storm events combining geomagnetic Dst index data, muon count rate data and data from the ACE satellite.

Kemmerich, Níkolas; Dal Lago, Alisson; Schuch, Nelson Jorge; Braga, Carlos Roberto; Deives Kummer, Fabricio; Vinicius Dias Silveira, Marcos; Munakata, Kazuoki; da Silva, Marlos; Martins da Silva, Samuel

162

Geomagnetic activity effects on semidiurnal winds in the lower thermosphere  

NASA Astrophysics Data System (ADS)

Steerable (L band) and fixed (UHF) radars were used in observing the incoherent scatter of E and F region ion drifts between July 1976 and November 1977. The wind measurements typically exhibited strong 12-hour oscillations with the eastward wind component reaching a maximum three hours ahead of the southward wind component. The results are seen as implying that the neutral winds are being dominated by semidiurnal tides. The geomagnetic activity dependence of the semidiurnal winds is arrived at by dividing the observations into quiet and disturbed periods on the basis of the Kp index. The winds during disturbed conditions were found to be significantly altered from the quiet time behavior, with the semidiurnal amplitudes reduced by 20 to 50 percent at the lowest altitudes and the altitude of maximum wind increased to be above 125 km. Under disturbed conditions, a decrease is also seen in the vertical wavelength. It is thought that some of these effects might derive from geomagnetic-activity induced changes in lower thermospheric temperature and density, which alter the dissipation of the upward-propagating tidal component.

Wand, R. H.

1983-11-01

163

The role of geomagnetic field configuration in EMIC wave generation  

NASA Astrophysics Data System (ADS)

Global configuration of the geomagnetic field plays an important role in magnetospheric dynamics. We study the effect of field configuration on electromagnetic ion-cyclotron (EMIC) wave growth with test particle simulations. As an initial study, we quantitatively examine the accuracy of several empirical geomagnetic field models widely in use. We study two years characterized by very different space weather conditions: 1996 and 2003. The year 1996, at solar minimum, exhibited many high-speed streams and a few co-rotating interaction regions, but was generally quiet. In contrast, 2003 included the "Halloween storm," one of the most intense geomagnetic storms on record caused by a coronal mass ejection. The performance of each model, as measured by prediction efficiency and skill score, is evaluated as a function of magnetospheric conditions (reflected by the geomagnetic index, Kp) and magnetic local time. We subsequently developed a new MHD/particle method to study electromagnetic ion-cyclotron (EMIC) wave growth in a realistic and dynamic magnetosphere. We simulate the phase space density dynamics of warm plasma particles in magnetospheric electromagnetic fields from the global Lyon-Fedder-Mobarry (LFM) MHD code and 3D test-particle trajectories. We use these results to compute temperature anisotropies and plasma densities. We then compute the convective EMIC wave growth rate using these macroscopic plasma quantities, and thus generate a spatiotemporal picture of the growth of these waves. We use our new MHD/particle method for studying EMIC wave growth to simulate a compression event observed on 29 June 2007 and compare the results with observations from ground observatories and spacecraft measurements. We then study the time evolution of various quantities to discern physical mechanisms leading to simulated wave growth. A fairly at simulated temperature profile in time suggested an absence of energizing processes during this event. This can be explained by two possible mechanisms: temperature anisotropy induced by drift shell splitting (DSS), and the bulk execution of unusual particle trajectories called Shabansky orbits. Finally, we used test particle simulations in a static analytic model field to study the two non-energizing processes. We show that Shabansky orbits executed in bulk provide a temperature anisotropy distinct from DSS-induced temperature anisotropy, and we discuss the two origins of this new physical mechanism for anisotropy generation.

McCollough, J. P.

164

Global-scale observations of ionospheric convection during geomagnetic storms  

NASA Astrophysics Data System (ADS)

The global effects on the ionosphere during periods of intense geomagnetic activity associated with geomagnetic storms are investigated using the Super Dual Auroral Radar Network (SuperDARN). The influence of the main and recovery phases of geomagnetic storms on ionospheric properties such as backscatter occurrence rates, velocity distributions, and convection patterns are presented. The evolution of magnetosphere and ionosphere parameters during the storms did not depend on the origin of the storm (e.g., a coronal mass ejection or a corotating interaction region). Instead, there was a continuum of response to the intensity of the driver. For example, we found a clear relationship between the most negative value of the southward component of the interplanetary magnetic field (IMF Bz) and the most negative value of the Sym-H index, which marks the end of the main phase of a storm. This is one of the first superposed epoch studies that analyzes the sunward/antisunward line-of-sight velocity as a function of magnetic local time for geomagnetic storms of various intensities. In the noon sector, before and during the main phase of the storms, the SuperDARN radars recorded faster antisunward ionospheric plasma drifts together with a significant increase in the number of ionospheric echoes. This is consistent with the expected increase in soft particle precipitation in the noon sector and with the reconnection electric field that occurs when the IMF Bz is strongly negative, as is the case during the main phase of storms. The SuperDARN echo occurrence in the noon sector returned to prestorm values early in the recovery phase. The overall response was similar in the midnight sector, except that the peak echo occurrence for the most intense storms was limited to a narrower time interval centered on the end of the main phase. There were reductions in the strong antisunward flows near local midnight observed during the main phase and early in the recovery phase, particularly for the intense storm class. Strong electric fields are applied in the nightside ionosphere during storms, and the decameter structures from which SuperDARN scatter are more easily produced. However, in regions of energetic auroral precipitation and after a long exposure to strong electric fields, there is often a reduction in SuperDARN echoes due to absorption or changes in radio wave propagation.

Gillies, D. M.; McWilliams, K. A.; St. Maurice, J.-P.; Milan, S. E.

2011-12-01

165

A realistic treatment of geomagnetic Cherenkov radiation from cosmic ray air showers  

NASA Astrophysics Data System (ADS)

We present a macroscopic calculation of coherent electro-magnetic radiation from air showers initiated by ultra-high energy cosmic rays, based on currents obtained from three-dimensional Monte Carlo simulations of air showers in a realistic geo-magnetic field. We discuss the importance of a correct treatment of the index of refraction in air, given by the law of Gladstone and Dale, which affects the pulses enormously for certain configurations, compared to a simplified treatment using a constant index. We predict in particular a geomagnetic Cherenkov radiation, which provides strong signals at high frequencies (GHz), for certain geometries together with "normal radiation" from the shower maximum, leading to a double peak structure in the frequency spectrum. We also provide some information about the numerical procedures referred to as EVA 1.0.

Werner, Klaus; de Vries, Krijn D.; Scholten, Olaf

2012-09-01

166

On the influence of DC railway noise on variation data from Belsk and Lviv geomagnetic observatories  

NASA Astrophysics Data System (ADS)

Geomagnetic variation data from the observatories in Belsk (BEL, Poland) and Lviv (LVV, Ukraine) significantly suffer from disturbances caused by direct current (DC) electric railways. The aim of this study is to quantify the impact of these disturbances on quantities derived from such data, as the K index of magnetic activity and the induction arrow used in the geomagnetic deep sounding method to indicate lateral contrasts of electric conductivity in the solid earth. Therefore, undisturbed data have been reconstructed by means of a frequency-domain transfer function that relates the horizontal magnetic field components of the observatory to the ones synchronously recorded at a noise-free reference station. The comparison of the K index derived from original and reconstructed data shows an increase of quiet time segments by 29% for LVV and by 14% for BEL due to our noise removal procedure. Furthermore, the distribution of the corrected K indices agrees well with the one from the Niemegk observatory in Germany.

Neska, Anne; Reda, Jan; Neska, Mariusz; Sumaruk, Yuri

2013-04-01

167

Predicting Large Geomagnetic Disturbances From The Inner Heliosphere: A Joint Helios 2 - Isee 3 Study For March 1979  

Microsoft Academic Search

We inquire into how much information content is lost in using interplanetary field and plasma parameters to predict the Dst index from monitors in the inner heliosphere (distance R < 1 AU) and displaced from the Sun-Earth line. To this end, we selected a period in March, 1979, during which 2 major geomagnetic storms (Dst < -100 nT) occurred. Data

C. J. Farrugia; V. K. Jordanova; D. B. Berdichevsky; I. G. Richardson; R. Schwenn; A. B. Galvin; R. P. Lepping

2002-01-01

168

Modeling of Ionosphere Effects of Geomagnetic Storm Sequence on September 9-14, 2005 in View of Solar Flares and Dependence of Model Input Parameters from AE-and Kp-indices  

NASA Astrophysics Data System (ADS)

Earlier by Klimenko et al., 2009 under carrying out the calculations of the ionospheric effects of storm sequence on September 9-14, 2005 the model input parameters (potential difference through polar caps, field-aligned currents of the second region and particle precipitation fluxes and energy) were set as function of Kp-index of geomagnetic activity. The analyses of obtained results show that the reasons of quantitative distinctions of calculation results and observations can be: the use of 3 hour Kp-index at the setting of time dependence of model input parameters; the dipole approach of geomagnetic field; the absence in model calculations the effects of the solar flares, which were taken place during the considered period. In the given study the model input parameters were set as function of AE-and Kp-indices of geomagnetic activity according to different empirical models and morphological representations Feshchenko and Maltsev, 2003; Cheng et al., 2008; Zhang and Paxton, 2008. At that, we taken into account the shift of field-aligned currents of the second region to the lower latitudes as by Sojka et al., 1994 and 30 min. time delay of variations of the field-aligned currents of second region relative to the variations of the potential difference through polar caps at the storm sudden commencement phase. Also we taken into account the ionospheric effects of solar flares. Calculation of ionospheric effects of storm sequence has been carried out with use of the Global Self-Consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP) developed in WD IZMIRAN (Nam-galadze et al., 1988). We carried out the comparison of calculation results with experimental data. This study is supported by RFBR grant 08-05-00274. References Cheng Z.W., Shi J.K., Zhang T.L., Dunlop M. and Liu Z.X. Relationship between FAC at plasma sheet boundary layers and AE index during storms from August to October, 2001. Sci. China Ser. E-Tech. Sci., 2008, Vol. 51, No. 7, 842-848. Feshchenko E.Yu., Maltsev Yu.P. Relations of the polar cap voltage to the geophysical activity. Physics of Auroral Phenomena: XXVI Annual Seminar (February 25-28, 2003): Proc./PGI KSC RAS. Apatity, 2003, 59-61. Klimenko M.V., Klimenko V.V., Ratovsky K.G., and Goncharenko L.P. Numerical modeling of ionospheric parameters during sequence of geomagnetic storms on September 9-14, 2005. Physics of Auroral Phenomena: XXXII Annual Seminar (March 3-6, 2009): Proc./PGI KSC RAS. Apatity, 2009, 162-165. Namgaladze A.A., Korenkov Yu.N., Klimenko V.V., Karpov I.V., Bessarab F.S., Surotkin V.A., Glushenko T.A., Naumova N.M. Global model of the thermosphere-ionosphere-protonosphere system. Pure and Applied Geophysics (PAGEOPH), 1988, Vol. 127, No. 2/3, 219-254. Sojka J.J., Schunk R.W., Denig W.F. Ionospheric response to the sustained high geomagnetic activity during the March '89 great storm. J. Geophys. Res., 1994, Vol. 99, No. A11, 21341-21352. Zhang Y., Paxton L.J. An empirical Kp-dependent global auroral model based on TIMED/GUVI FUV data. J. Atmos. Solar-Terr. Phys., 2008, Vol. 70, 1231-1242.

Klimenko, Maxim; Klimenko, Vladimir; Ratovsky, Konstantin; Goncharenko, Larisa

169

On the geomagnetic storm response and recovery timescales of the thermosphere  

NASA Astrophysics Data System (ADS)

The temperature of the Earth's thermosphere can be substantially increased during geomagnetic storms mainly due to high-latitude Joule heating induced by magnetospheric convection and auroral particle precipitation. The main cooling mechanism controlling the recovery of neutral temperature and density to geomagnetic activity is the infrared emission from nitric oxide (NO) emission at 5.3 micrometers. NO is produced by both solar and auroral activity, the first due to solar EUV and X-rays the second due to particle dissociation of N2, and has a typical lifetime of 12 to 24 hours in the mid and lower thermosphere. NO cooling in the thermosphere peaks between 150 and 200 km altitude. In this paper, a global, three-dimensional, time-dependent, non-linear coupled model of the thermosphere, ionosphere, plasmasphere, and electrodynamics (CTIPe) has been used to determine the response and recovery timescale of the upper atmosphere to geomagnetic activity. In these simulations, realistic NO storm increases are defined by the three-dimensional nitric oxide empirical model (NOEM) based on measurements from the Student Nitric Oxide Explorer (SNOE) scientific satellite. The F10.7 index is used to define solar EUV heating. The magnetospheric energy input into the system is characterized by the time variation of the solar wind velocity, the interplanetary magnetic field (IMF) magnitude and direction, and the auroral precipitation index derived from the TIROS/NOAA satellite observations. The solar wind parameters and auroral indices are used to define the magnetospheric convection electric field and auroral ionization/heating rates. The energy is subsequently lost from the system primarily by infrared radiation, particularly by NO cooling. The source is therefore the time integral of the electromagnetic energy input and the loss is radiative cooling. Together they combine to provide the characteristic response and recovery of the system to geomagnetic activity. Comparisons of the neutral density observed by the CHAMP satellite with predictions of CTIPe are presented for selected geomagnetic storm events.

Fedrizzi, M.; Fuller-Rowell, T. J.; Matsuo, T.; Codrescu, M. V.; Luehr, H.

2008-12-01

170

The Geomagnetic Field in the Archaean (Invited)  

NASA Astrophysics Data System (ADS)

The palaeomagnetic record provides a window into deep Earth processes occurring over timescales that can approach the age of the planet. A first-order description of geomagnetic secular variation may be obtained from the angular dispersion of virtual geomagnetic poles measured in fast-cooled igneous or sedimentary rocks. Such data can provide insights into the stability of the geodynamo for very old periods when no continuous sections are available to measure reversal frequency reliably. A study of geomagnetic palaeo-secular variation made using late Archean age rocks has suggested a much more stable field on average 2500 Myr ago than in the last few hundreds of Myr. It is speculated that the change between these two mean states resulted from processes linked to the secular evolution of the Earth’s deep interior. The enhanced stability of the geodynamo in the Archaean may have been linked to the smaller or absent inner core. Going back further into the Earth’s history, the evidence is mounting that a global geomagnetic field was already established at 3500 Myr, the age of the oldest rocks capable of preserving a palaeomagnetic signal. New results from rocks of this age from the Barberton Greenstone Belt in southern Africa will be presented. These data strengthen this claim further and even provide tentative evidence for geomagnetic polarity reversals occurring at this early stage of the planet’s history.

Biggin, A. J.; Langereis, C. G.; de Wit, M.

2010-12-01

171

Solar wind drivers of geomagnetic storms over more than four solar cycles  

NASA Astrophysics Data System (ADS)

Using a classification of near-Earth solar wind flows into corotating high-speed streams, slow interstream solar wind, and transients originating with coronal mass ejections at the Sun, we determine the drivers of geomagnetic storms of various sizes from 1964 to 2011 based on the Kp index, encompassing more than four solar cycles. We also briefly discuss storm occurrence rates since the beginning of Kp in 1932.

Richardson, Ian G.; Cane, Hilary V.

2013-06-01

172

The relationship between the recovery phase of geomagnetic storms and the magnetic clouds  

Microsoft Academic Search

Starting with our elliptical cross-section model for the study of the magnetic topology of magnetic clouds (MCs) in the interplanetary medium, we develop an analytical approach to the behavior of the Dst index at the recovery phase of a geomagnetic storm.Assuming an axially symmetric ring current, we estimate its physical parameters during that recovery phase of the storm-time. We compare

M. A. Hidalgo; I. R. Cantalapiedra; J. Sequeiros; C. Cid; T. Nieves-Chinchilla

2005-01-01

173

Great geomagnetic storms in 1841-1870 according to the data from the network of Russian geomagnetic observatories  

NASA Astrophysics Data System (ADS)

Great magnetic storms (geomagnetic index C9 is ?8 for St. Petersburg, which can correspond to Kp ? 8 or Dst < -200 nT), registered from 1841 to 1870 at the St. Petersburg, Yekaterinburg, Barnaul, Nerchinsk, Sitka, and Beijing (at the Russian embassy) observatories are analyzed. A catalog of intensive magnetic storms during this period, which includes solar cycles 9-11, has been compiled. The statistical characteristics of great magnetic storms during this historical period have been obtained. These results indicate that high solar activity played a decisive role in the generation of very intense magnetic storms during the considered period. These storms are characterized by only one peak in a solar cycle, which was registered in the years of the cycle minimum (or slightly earlier): the number of great geomagnetic storms near the solar activity maximum was twice as large as the number of such storms during less active periods. A maximum in September-October and an additional maximum in February are observed in the annual distribution of storms. In addition, the storm intensity inversely depends on the storm duration.

Ptitsyna, N. G.; Tyasto, M. I.; Khrapov, B. A.

2012-09-01

174

Forecasting ionospheric structure during the great geomagnetic storms  

Microsoft Academic Search

Characteristics of midlatitude ionospheric disturbances during several great geomagnetic storms have been investigated using data from the European geomagnetic observatories and ionospheric stations with the aim of developing the local forecasting models, as part of the prediction and retrospective ionospheric modeling over Europe project. Based on the analysis of the geomagnetic storms of February 6, 1986, and March 13, 1989,

L. R. Cander; S. J. Mihajlovic

1998-01-01

175

GEOMAGNETICALLY INDUCED CURRENTS IN THE SOUTHERN AFRICAN POWER NETWORK  

Microsoft Academic Search

SUMMARY Significant geomagnetic activity is expected during the next 3 years due to the current solar peak. Geomagnetic disturbances sometimes lead to a slowly varying current in transmission lines through grounded transformers called Geomagnetically Induced Currents (GICs). This phenomenon and the perturbations that it may cause were investigated. The existence of GICs in the Eskom MTS was modelled and subsequently

J Koen; C T Gaunt

176

Estimation of geomagnetically induced current levels from different input data  

Microsoft Academic Search

Pragmatic schemes for estimating geomagnetically induced current (GIC) values using different levels of knowledge about the physical quantities associated with the geomagnetic induction process are studied. The fundamental idea behind the proposed schemes is that as the knowledge about the detailed behavior of the relevant physical quantities decreases, the lack of knowledge is compensated by statistical characteristics of the geomagnetic

Antti Pulkkinen; Ari Viljanen; Risto Pirjola

2006-01-01

177

Estimation of geomagnetically induced current levels from different input data  

Microsoft Academic Search

Pragmatic schemes for estimating geomagnetically induced current GIC values using different levels of knowledge about the physical quantities associated with the geomagnetic induction process are studied The fundamental idea behind the proposed schemes is that as the knowledge about the detailed behavior of the relevant physical quantities decreases the lack of knowledge is compensated by statistical characteristics of the geomagnetic

Antti Pulkkinen; Ari Viljanen; Risto Pirjola

2006-01-01

178

Detecting Stochastic Behaviour and Scaling Laws in Time Series of Geomagnetic Daily Means  

NASA Astrophysics Data System (ADS)

We use advanced methods to extract quantitative time dynamics from geomagnetic signals. In particular we analyse daily geomagnetic time series measured at three stations in Norway. The dynamics of geomagnetic measurements has been investigated using autoregressive models. The procedure is based on two forecasting approaches: the global autoregressive approximation and the local autoregressive approximation. The first technique views the data as a realisation of a linear stochastic process, whereas the second considers them as a realisation of a deterministic process, supposedly non-linear. The comparison of the predictive skill of the two techniques is a strong test to discriminate between low-dimensional chaos and stochastic dynamics. Our findings suggest that the physical system governing the phenomena is characterised by a stochastic dynamics, and the process could be described by numerous degrees of freedom. We also investigated the kind of stochasticity of the geomagnetic signals, analysing the power spectrum density. We identify a power law P(ƒ) ƒ-?, with the scaling exponent ? which is a typical fingerprint of irregular processes. In this analysis we use the Higuchi method, which presents an interesting relationship between the fractal dimension D and the spectral power law scaling index ?.

Telesca, L.; Cuomo, V.; Lapenna, V.; Macchiato, M.; Serio, C.

179

Statistical Prediction of In Situ Hiss Amplitudes Using Solar Wind Data and Geomagnetic Indices  

NASA Astrophysics Data System (ADS)

Statistical Prediction of In Situ Hiss Amplitudes Using Solar Wind Data and Geomagnetic Indices Plasmaspheric hiss is a naturally-occurring electromagnetic wave which is often observed within the plasmasphere in the near-Earth magnetosphere. Hiss has been implicated as a major driving force for the loss of energetic electrons in the Earth's radiation belts. As such, radiation belt models require accurate estimates of hiss amplitudes in order to plausibly model the dynamics of the radiation belts. We present a novel and straightforward approach using solar wind parameters and geomagnetic indices to predict observed hiss amplitudes on the three inner-magnetospheric THEMIS probes. Our approach models hiss measurements as a first-order autoregressive process (to account for the high correlation between successive measurements), and predicts hiss amplitude using multiple regression on simultaneous solar wind parameters (e.g., dynamic pressure and IMF) and geomagnetic indices (e.g., AE and Dst). We present the performance of the model, evaluated using 10-fold cross validation. Global models such as this one have a great advantage over in situ measurements of hiss, as they are able to predict hiss amplitude over all space for any epoch where solar wind and geomagnetic index values are known.

Golden, D. I.; Spasojevic, M.; Li, W.; Nishimura, T.

2011-12-01

180

Jan Hospers's Key Contributions to Geomagnetism  

NASA Astrophysics Data System (ADS)

Although Bernard Brunhes in 1904 presented the first evidence that the geomagnetic field had once reversed in polarity [Laj et al., 2002], modern studies of reversals only began in the late 1940s with the work of Jan Hospers and Alexandre Roche [Opdyke and Channel, 1996]. Hospers also initiated modern studies of the time-averaged form of the geomagnetic field [Frankel, 1987]. His empirically based notion-that over several thousand years the geomagnetic field averaged to a geocentric axial dipole (GAD) that, as he and others showed, had recurrently reversed its polarity-allowed Creer et al. [1954] to trace the movement of the geographic pole (apparent polar wander path) relative to Britain and by geological extension, to Europe as well. This was the first such path based on paleomagnetic evidence, and it led in turn to the first successful physical test of continental drift [Irving, 1988].

Irving, Ted

2008-11-01

181

Do Gauss coefficients see the geomagnetic jerks  

NASA Astrophysics Data System (ADS)

Secular variation is defined as those changes in the geomagnetic field with a duration of order of decade and an origin in the Earth's magnetic field. Magnetic observations have revealed one of the main features of the secular variation, the geomagnetic jerks. These phenomena have been characterized using the data provided by the magnetic observatories. Here we present preliminary results of our study of jerks using geomagnetic field models. For long time period, the Jackson et al. (2000) model is used; for more recent period, models obtained from observatories data are analyzed. Wavelet analysis is applied to different Gauss coefficients (g10, g11, ...) series in order to find the existing singularities. These events are presented and discussed in correlation with previous studies.

Chambodut, A.; Mandea, M.; Hulot, G.

2003-04-01

182

The USGS Geomagnetism Program Observatory Network  

NASA Astrophysics Data System (ADS)

The mission of the U.S. Geological Survey's Geomagnetism Program is to monitor the Earth's magnetic field. Using ground-based observatories, the Program provides continuous records of magnetic field variations covering long timescales, ranging from seconds to over a century. The Program disseminates magnetic data to various governmental, academic, and private institutions; it conducts research into the nature of geomagnetic variations for purposes of scientific understanding and hazard mitigation. The Program is an integral part of the U.S. Government's National Space Weather Program. In this presentation, we summarize recent operational accomplishments of the USGS Geomagnetism Program, including the addition of a real-time one-second data product, development of quasi-definitive data from selected observatories, and improvements to the magnetic observatory network in Alaska.

Finn, C. A.

2011-12-01

183

Stratospheric Balloon Gradient Geomagnetic Measurements  

NASA Astrophysics Data System (ADS)

The study of the interior structure of the Earth and laws of its evolution is one of the most difficult problems of natural science. Among the geophysical fields the anomaly magnetic field is one of the most informational in questions of the Earth's crust structure. Many important parameters of an environment are expedient for measuring at lower altitudes, than satellite ones. So, one of the alternatives is stratospheric balloon survey. The balloon flight altitudes cover the range from 20 to 50 km. At such altitudes there are steady zone air flows due to which the balloon flight trajectories can be of any direction, including round-the-world (round-the-pole). One of the examples of such sounding system have been designed, developed and maintained at IZMIRAN during already about 20 years. This system consists of three instrumental con-tainers uniformly placed along a vertical 6 km line. System allows measuring a module and vertical gradient of the geomagnetic field along the whole flight trajectory and so one's name is -stratospheric balloon magnetic gradiometer (SMBG). The GPS-receivers, located in each instrumental container, fix the flight coordinates to within several tens meters. Data trans-mission is carried out by Globalstar satellite link. The obtained data are used in solving the problems of deep sounding of the Earth's crust magnetic structure -an extraction of magnetic anomalies, determination of a depth of bedding of magnetoactive rocks and others. The developed launching technology, deployment in flight, assembly, data processing, transfer and landing the containers with the equipment can be used for other similar problems of monitoring and sounding an environment. Useful flight weights of each instrumental container may be reaching 50 kg. More than ten testing flights (1986-2009) at stratospheric altitudes (20-30 km) have proven the reliability of this system.

Filippov, Sergey; Tsvetkov, Yury

184

Geomagnetically induced currents in power lines according to data on geomagnetic variations  

Microsoft Academic Search

The time derivative (d\\u000a H\\/dt) of the geomagnetic field horizontal component (H) for seven intervals of high geomagnetic activity in 2003–2005 has been calculated, based on the data of Alma-Ata, Novosibirsk,\\u000a and Irkutsk observatories, in order to estimate the probability of appearance of geomagnetically induced current (GIC), the\\u000a value of which is linearly dependent on d\\u000a H\\/dt, in power lines

V. V. Vodyannikov; G. I. Gordienko; S. A. Nechaev; O. I. Sokolova; S. Yu. Khomutov; A. F. Yakovets

2006-01-01

185

Constitutive behavior of as-cast AA1050, AA3104, and AA5182  

NASA Astrophysics Data System (ADS)

Recent thermomechanical modeling to calculate the stress field in industrially direct-chill (DC) cast-aluminum slabs has been successful, but lack of material data limits the accuracy of these calculations. Therefore, the constitutive behavior of three aluminum alloys (AA1050, AA3104, and AA5182) was determined in the as-cast condition using tensile tests at low strain rates and from room temperature to solidus temperature. The parameters of two constitutive equations, the extended Ludwik equation and a combination of the Sellars-Tegart equation with a hardening law, were determined. In order to study the effect of recovery, the constitutive behavior after prestraining at higher temperatures was also investigated. To evaluate the quantified constitutive equations, tensile tests were performed simulating the deformation and cooling history experienced by the material during casting. It is concluded that both constitutive equations perform well, but the combined hardening-Sellars-Tegart (HST) equation has temperature-independent parameters, which makes it easier to implement in a DC casting model. Further, the deformation history of the ingot should be taken into account for accurate stress calculations.

van Haaften, W. M.; Magnin, B.; Kool, W. H.; Katgerman, L.

2002-07-01

186

Toward a possible next geomagnetic transition?  

NASA Astrophysics Data System (ADS)

The geomagnetic field is subject to possible reversals or excursions of polarity during its temporal evolution. Considering that: (a) the typical average time between one reversal and the next (the so-called chron) is around 300 000 yr, (b) the last reversal occurred around 780 000 yr ago, (c) more excursions (rapid changes of polarity) can occur within the same chron and (d) the geomagnetic field dipole is currently decreasing, a possible imminent geomagnetic reversal or excursion would not be completely unexpected. In that case, such a phenomenon would represent one of the very few natural hazards which are really global. The South Atlantic Anomaly (SAA) is a great depression of the geomagnetic field at the Earth's surface, caused by a reverse magnetic flux in the terrestrial outer core. In analogy with critical point phenomena characterised by some cumulative quantity, we fit the surface extent of this anomaly over the last 400 yr with power or logarithmic functions in reverse time, also decorated by log-periodic oscillations, whose final singularity (a critical point tc) reveals a great change in the near future (2034 ± 3 yr), when the SAA area reaches almost a hemisphere. An interesting aspect that has been recently found is the possible direct connection between the SAA and the global mean sea level (GSL). That the GSL is somehow connected with SAA is also confirmed from the similar result when an analogous critical-like fit is performed over GSL: the corresponding critical point (2033 ± 11 yr) agrees, within the estimated errors, with the value found for SAA. From this result, we point out the intriguing conjecture that tc would be the time of no return, after which the geomagnetic field could fall into an irreversible process of a global geomagnetic transition that could be a reversal or excursion of polarity.

De Santis, A.; Qamili, E.; Wu, L.

2013-09-01

187

A.A., constructivism, and reflecting teams.  

PubMed

Numerous studies and clinical anecdotes reveal a relationship between attendance at A.A. meetings and/or degree of involvement in A.A. and maintenance of sobriety. Hypotheses as to how A.A. and/or the A.A. meeting is helpful to its members have ranged from a focus on factors common to all therapy groups, to aspects of A.A. "treatment" which are behavioral in nature. Presented here is another way of understanding A.A.'s effectiveness within the frame of more recent, constructivistic approaches to family therapy. In particular, the A.A. topic meeting is compared to the reflecting team concept of Tom Anderson. PMID:9440161

Nevels, B

1997-12-01

188

Geomagnetic sensor based on giant magnetoelectric effect  

NASA Astrophysics Data System (ADS)

Here, the authors report a new type of geomagnetic field sensor based on the giant magnetoelectric effect in Metglas/piezoelectric-fiber laminates that are wrapped with a coil. These sensors can measure quite precisely the value of both the Earth's magnetic field and its inclination. The geomagnetic field sensor does not require a dc magnetic bias and is driven by a 10 mA ac. Highly sensitive dc magnetic field variations of less than 10-9 T and angular inclinations of <=10-5 deg can be detected, potentially offering opportunities for a small global positioning device.

Zhai, Junyi; Dong, Shuxiang; Xing, Zengping; Li, Jiefang; Viehland, D.

2007-09-01

189

Possible associations between long term anomalous geomagnetic variations, Vrancea (Romania) intermediate depths earthquakes and the solar activity for the last 15 years  

NASA Astrophysics Data System (ADS)

Geomagnetic variations associated with earthquakes are widely accepted and several anomalous geomagnetic observations have been interpreted as a result of changing rock magnetic properties under varying tectonic stress (piezomagnetic effect). During the last 15 years of geomagnetic investigations conducted in Vrancea seismogenic zone, period covering more than a complete solar cycle, the solar-terrestrial perturbations have fluctuated from very low to very large values, providing the ideal medium to observe the correlation between the long and short term geomagnetic field perturbations, solar activity and earthquakes. The October 2004 intermediate depth earthquake (Mw=6.0) offered us the opportunity to investigate possible connections between the local geomagnetic field behavior and the occurrence of moderate magnitude Vrancea earthquakes. The comparison between the geomagnetic data obtained at a station inside the epicentral zone with other remote reference stations (outside the epicenter) considers an effective technique to detect the anomalous variation of a lithospheric origin. The working data are: (i) the geomagnetic field records made at Muntele Rosu Observatory (MLR), Surlari (SUA) and/or Tihany (THY) INTERMAGNET Observatories; (ii) the seismic data for Vrancea source zone; (iii) the daily geomagnetic index from NOAA/Space Weather. The one minute and daily averaged geomagnetic data were calculated at these stations for the whole period 1996-2011. The geomagnetic components: X, Y (horizontal North-South and East-West) and Z (vertical) and the normalized vertical component (Bz/Bx and Bz/By) were used in the data analysis processes and also in the comparison of the geomagnetic data between the selected stations. Our results indicate the presence of long term anomalous variations (weeks or months) in the geomagnetic components and in the magnetic impedance at MLR Observatory (close to the epicenter) and no magnetic modifications in the SUA and THY recordings (far from the epicenter) preceding the occurrence of earthquakes with Mw>4.0. Moreover, in the periods of anomalous behavior, the geomagnetic components recorded at MLR show no correlation with those recorded at the other two stations, as they do in the rest of the time. The observed anomalous variations may be explained as a result of the tectonic stress variations and the enhancement of the lithospheric conductivity in the Vrancea region during the preparation period of earthquakes.

Moldovan, I. A.; Moldovan, A. S.; Placinta, A. O.; Takla, E. M.; Constantin, A. P.; Popescu, E.

2012-04-01

190

Geomagnetic storms link to the mortality rate in the Smolyan region for the period 1988--2009  

NASA Astrophysics Data System (ADS)

We present correlations and trends of 10 parameters of annual mortality rate (1 to common mortality rate, 5 to cardiovascular reasons and 4 to "accidental" reasons (car accidents, suicides, infections)) with respect to 6 parameters of annual solar and geomagnetic activity (Wolf index, number of geomagnetic storms, duration of the storms, amplitude of the storms). During the period of observation, characterized by a 3-4-fold decrease of the mean geomagnetic activity (in terms of the number and the duration of the storms) and with a strong variations of the amplitude of the storms (about an almost constant mean values for the period), there is a 1.3-fold decrease in the urban population, a 1.5-fold increase of the common mortality rate, a 1.8-fold increase of the cardiovascular mortality rate and a 1.1-fold decrease of the "accidental" mortality rates. During the years 2003-2005 we observe about 2-fold temporary increase in the storm amplitudes. During the years 2007-2008, characterized by extremely low geomagnetic activity, we observe a surprising temporary increase of the common and the cardiovascular mortality rates 1.1 and 1.3-fold, respectively (Figures 1-4). We point out 3 main results. (1) The available data shows notable increase in the mortality rates while there is generally a decrease of the solar or geomagnetic activity during the studied period (Figures 5-9). We explain this anti-correlation with the domination of the increasing mortality rates as an effect of the advance in the mean age of the population (due to immigration of young people and decrease of new-borns), hiding an eventual display of the solar and geomagnetic influence on the mortality rates. Using this data we can not reveal influence of the long-time (10-20 years) change of the average solar and geomagnetic activity on the mortality rate. (2) Excluding the unusual years 2007 and 2008, we establish that with respect to the years with low geomagnetic activity (1993, 1995, 1996, 1999), in the years with high geomagnetic activity (2000, 2001, 2003-2005) the common and the cardiovascular mortality rates increase by at least 20% and at least 30%, respectively (Figures 10-13). (3) The time delay of the maximum of the common and the cardiovascular mortality rates in 2007-2008, about 3 years after the sharp maximum of the strong storms in 2003-2005, lead to suggestion that the influence of the storms on the mortality rates may manifest clearly itself some years later. Generally, our data shows that the geomagnetic storms increase notable the common and the cardiovascular mortality rates.

Simeonova, Siyka G. 1; Georgieva, Radostina C. 2; Dimitrova, Boryana H. 2; Slavcheva, Radka G. 2; Kerimova, Bojena P. 2; Georgiev, Tsvetan B. 34

191

Comment on "Possible association between anomalous geomagnetic variations and the Molise Earthquakes at Central Italy during 2002" by Takla et al. (2011)  

NASA Astrophysics Data System (ADS)

Takla et al. (2011) documented the observation of seismogenic precursory signals in the geomagnetic field components of L'Aquila station (LAQ) which occurred before the 2002 Molise earthquakes. Here, these claims are reviewed taking into account the geomagnetic index ?Kp time-series and by means of data coming from the Geomagnetic Observatory of L'Aquila where the LAQ station is located. This review shows that before the Molise earthquakes the anomalous behaviour of LAQ geomagnetic field components was actually caused by a possible thermal drift of the instrumentation. In conclusion there is no firm relation between the earthquakes occurrence and the observed magnetic anomalous signatures documented by Takla et al. (2011).

Masci, Fabrizio

2012-08-01

192

The Management of AAS Meetings  

NASA Astrophysics Data System (ADS)

The American Astronomical Society organizes the largest astronomical conferences in the world. This article describes the way we organize our own conferences, the content of our meetings and how it is developed and provides some tips for successfully organizing scientific conferences generally, both financially and scientifically. Organizing meetings is difficult and requires specialized skills and experience. It is often best to have scientists focus on organizing the scientific aspects of conferences while leaving the logistical and financial aspects to professional meeting organizers. The AAS provides these services for its own meetings, the meetings of its Divisions and to others on a case-by-case basis.

Marvel, Kevin B.

2013-01-01

193

The Effect of Helio-Geomagnetic Activity on the Proceedings in the Emergency Department of Two Greek Hospitals  

NASA Astrophysics Data System (ADS)

Study of the solar and geomagnetic activity influence on the emergency proceedings in Greece, for selected months of solar cycle 23 and especially for the year 2005 is presented. We examined the time association between the magnetic storms (Dst geomagnetic index), daily numbers of solar flares and Coronal Mass Ejections (CMEs) with the emergency proceedings. The sample of about 30000 cases from two Greek hospitals (The General Hospital of the town of Lamia and The General Hospital of the town of Veria) analyzed according to diagnoses. The cardiological, neurological, accidents (multitrauma and burns) and oncological patients as well as in partially pathological/surgical patients showed an increase during periods of high helio-geomagnetic activity. In order to strengthen this result, more data need to be collected and analyzed.

Preka-Papadema, P.; Moussas, X.; Noula, M.; Katranitsa, H.; Theodoropoulou, A.; Katsavrias, Ch.; Vasiliou, Ch.; Kontogeorgou, E.; Tsaliki, S.-M.; Kailas, K.; Papadima, Th.

2010-01-01

194

Laboratory Astrophysics Division of The AAS (LAD)  

NASA Astrophysics Data System (ADS)

The purpose of the Laboratory Astrophysics Division (LAD) is to advance our understanding of the Universe through the promotion of fundamental theoretical and experimental research into the underlying processes that drive the Cosmos. LAD represents all areas of astrophysics and planetary sciences. The first new AAS Division in more than 30 years, the LAD traces its history back to the recommendation from the scientific community via the White Paper from the 2006 NASA-sponsored Laboratory Astrophysics Workshop. This recommendation was endorsed by the Astronomy and Astrophysics Advisory Committee (AAAC), which advises the National Science Foundation (NSF), the National Aeronautics and Space Administration (NASA), and the U.S. Department of Energy (DOE) on selected issues within the fields of astronomy and astrophysics that are of mutual interest and concern to the agencies. In January 2007, at the 209th AAS meeting, the AAS Council set up a Steering Committee to formulate Bylaws for a Working Group on Laboratory Astrophysics (WGLA). The AAS Council formally established the WGLA with a five-year mandate in May 2007, at the 210th AAS meeting. From 2008 through 2012, the WGLA annually sponsored Meetings in-a-Meeting at the AAS Summer Meetings. In May 2011, at the 218th AAS meeting, the AAS Council voted to convert the WGLA, at the end of its mandate, into a Division of the AAS and requested draft Bylaws from the Steering Committee. In January 2012, at the 219th AAS Meeting, the AAS Council formally approved the Bylaws and the creation of the LAD. The inaugural gathering and the first business meeting of the LAD were held at the 220th AAS meeting in Anchorage in June 2012. You can learn more about LAD by visiting its website at http://lad.aas.org/ and by subscribing to its mailing list.

Salama, Farid; Drake, R. P.; Federman, S. R.; Haxton, W. C.; Savin, D. W.

2012-10-01

195

Geomagnetic activity indicators for geomagnetically induced current studies in South Africa  

NASA Astrophysics Data System (ADS)

Intense geomagnetic activity is known to give rise to large geomagnetically induced currents (GICs) in power transmission grids. Recordings of geomagnetic activity provide an efficient and economical way for power transmission system operators to assess GIC risks in retrospective studies. This study investigates local geomagnetic indicators (i.e., hourly peak value, hourly range indicator and hourly standard deviation) in order to determine their usefulness for understanding the drivers of GICs in the South African power network. Results show that the GICs have a higher correlation with the geomagnetic indicators derived from the East-West component of the horizontal geomagnetic field, than the indicators derived from the North-South component of the horizontal field. This directional dependence corresponds very well with the North-South orientation of the power lines feeding the power transformers at the South African Grassridge electrical substation GIC site. It therefore follows that, the geoelectric field driving the GICs at Grassridge is North-South oriented. Further, it is shown that the hourly range indicator has a higher correlation with the GICs than the hourly standard deviation for this particular network configuration.

Ngwira, Chigomezyo M.; McKinnell, Lee-Anne; Cilliers, Pierre J.

2011-08-01

196

Cosmic Ray Monitoring and Space Dangerous Phenomena, 1. Search of Features In Cosmic Rays What Can Be Used For Forecasting of Major Geomagnetic Storms  

NASA Astrophysics Data System (ADS)

According to NOAA Space Weather Scales, geomagnetic storms of scales G5 (3- hour index of geomagnetic activity Kp=9), G4 (Kp=8) and G3 (Kp=7) are dangerous for people technology and health (influence on power systems, on spacecraft oper- ations, on HF radio-communications and others). To prevent these serious damages will be very important to forecast dangerous geomagnetic storms. In many papers it was shown that in principle for this forecasting can be used data on CR intensity and CR anisotropy changing before SC of major geomagnetic storms accompanied by sufficient Forbush-decreases (e.g., Dorman et al., 1995, 1999). In this paper we con- sider over 100 major geomagnetic storms and for each case we analyze hourly data of many NM for 8 days with SC in the 4-st day of 8-days period (that before SC we have at least 3 full days). We determine what part of major geomagnetic storms is accompanied CR intensity and CR anisotropy changing before SC, and what part of major geomagnetic storms does not show any features what can be used for forecast- ing. We estimate also how these parts depend from the index of geomagnetic activ- ity Kp. REFERENCES: Dorman L.I., et al. "Cosmic-ray forecasting features for big Forbush-decreases". Nuclear Physics B, Vol. 49A, pp. 136-144. (1995). L.I.Dorman, et al, "Cosmic ray Forbush-decrease as indicators of space dangerous phenomenon and possible use of cosmic ray data for their prediction", Proc. of 26-th Intern. Cos- mic Ray Conference, Salt Lake City, Vol. 6, p. 476-479, (1999).

Dorman, L. I.; Pustil'Nik, L. A.; Sternlieb, A.; Zukerman, I. G.

197

Intense geomagnetic storms and causative interplanetary conditions  

NASA Astrophysics Data System (ADS)

Active sun is characterized by large and powerful emissions triggered by the twisting and shearing of solar magnetic field lines Orientation of the coronal ejecta and the structure and direction of interplanetary parameters play a dominant role in the formulation and development of intense geomagnetic storms Digital magnetic observations at low latitude locations are worth considering for understanding and interpreting the varied dynamics of intense geomagnetic storms Variations in the Horizontal and Declination components of geomagnetic field that are attributed to the varying interplanetary conditions are discussed for a set of intense storm events occurred in the current solar cycle Differing response of geomagnetic field to the interplanetary shocks driven by fast halo coronal mass ejections fast solar wind streams from the coronal hole regions and the dynamic pressure pulses associated with these mechanisms will be projected Contribution from the solar wind plasma and interplanetary magnetic field for these events are discussed in relation to the quantum of energy transfer from the solar wind into the earth s magnetosphere

Rawat, R.; Alex, S.; Lakhina, G. S.

198

Geomagnetic referencing in the arctic environment  

USGS Publications Warehouse

Geomagnetic referencing is becoming an increasingly attractive alternative to north-seeking gyroscopic surveys to achieve the precise wellbore positioning essential for success in today's complex drilling programs. However, the greater magnitude of variations in the geomagnetic environment at higher latitudes makes the application of geomagnetic referencing in those areas more challenging. Precise, real-time data on those variations from relatively nearby magnetic observatories can be crucial to achieving the required accuracy, but constructing and operating an observatory in these often harsh environments poses a number of significant challenges. Operational since March 2010, the Deadhorse Magnetic Observatory (DED), located in Deadhorse, Alaska, was created through collaboration between the United States Geological Survey (USGS) and a leading oilfield services supply company. DED was designed to produce real-time geomagnetic data at the required level of accuracy, and to do so reliably under the extreme temperatures and harsh weather conditions often experienced in the area. The observatory will serve a number of key scientific communities as well as the oilfield drilling industry, and has already played a vital role in the success of several commercial ventures in the area, providing essential, accurate data while offering significant cost and time savings, compared with traditional surveying techniques.

Podjono, Benny; Beck, Nathan; Buchanan, Andrew; Brink, Jason; Longo, Joseph; Finn, Carol A.; Worthington, E. William

2011-01-01

199

Geomagnetic referencing in the arctic environment  

USGS Publications Warehouse

Geomagnetic referencing is becoming an increasingly attractive alternative to north-seeking gyroscopic surveys to achieve the precise wellbore positioning essential for success in today's complex drilling programs. However, the greater magnitude of variations in the geomagnetic environment at higher latitudes makes the application of geomagnetic referencing in those areas more challenging. Precise, real-time data on those variations from relatively nearby magnetic observatories can be crucial to achieving the required accuracy, but constructing and operating an observatory in these often harsh environments poses a number of significant challenges. Operational since March 2010, the Deadhorse Magnetic Observatory (DED), located in Deadhorse, Alaska, was created through collaboration between the United States Geological Survey (USGS) and a leading oilfield services supply company. DED was designed to produce real-time geomagnetic data at the required level of accuracy, and to do so reliably under the extreme temperatures and harsh weather conditions often experienced in the area. The observatory will serve a number of key scientific communities as well as the oilfield drilling industry, and has already played a vital role in the success of several commercial ventures in the area, providing essential, accurate data while offering significant cost and time savings, compared with traditional surveying techniques. Copyright 2011, Society of Petroleum Engineers.

Poedjono, B.; Beck, N.; Buchanan, A.; Brink, J.; Longo, J.; Finn, C. A.; Worthington, E. W.

2011-01-01

200

Elliptical magnetic clouds and geomagnetic storms  

Microsoft Academic Search

Magnetic clouds are simple phenomena which modulate the interplanetary space and they are a subset of Interplanetary Coronal Mass Ejections. Due to the sustained orientation of their magnetic fields south- and northwards, they can influence the Earth's magnetosphere and may give rise to geomagnetic storms. Since such storms are dominant factors of space weather predictions, magnetic clouds are an important

I. Antoniadou; A. Geranios; M. Vandas; M. Panagopoulou; O. Zacharopoulou; O. Malandraki

2008-01-01

201

Geomagnetic effects on atmospheric Cerenkov images  

Microsoft Academic Search

Atmospheric Cerenkov telescopes are used to detect electromagnetic showers from primary -rays of energy ~300 GeV up to 10 TeV and to discriminate these from cascades due to hadrons using the Cerenkov images. The geomagnetic field affects the development of showers and is shown to diffuse and distort the images. When the component of the field normal to the shower

P. M. Chadwick; K. Lyons; T. J. L. McComb; K. J. Orford; J. L. Osborne; S. M. Rayner; I. D. Roberts; S. E. Shaw; K. E. Turver

1999-01-01

202

Helio-geomagnetic influence in cardiological cases  

NASA Astrophysics Data System (ADS)

The effects of the energetic phenomena of the Sun, flares and coronal mass ejections (CMEs) on the Earth's ionosphere-magnetosphere, through the solar wind, are the sources of the geomagnetic disturbances and storms collectively known as Space Weather. The research on the influence of Space Weather on biological and physiological systems is open. In this work we study the Space Weather impact on Acute Coronary Syndromes (ACS) distinguishing between ST-segment elevation acute coronary syndromes (STE-ACS) and non-ST-segment elevation acute coronary syndromes (NSTE-ACS) cases. We compare detailed patient records from the 2nd Cardiologic Department of the General Hospital of Nicaea (Piraeus, Greece) with characteristics of geomagnetic storms (DST), solar wind speed and statistics of flares and CMEs which cover the entire solar cycle 23 (1997-2007). Our results indicate a relationship of ACS to helio-geomagnetic activity as the maximum of the ACS cases follows closely the maximum of the solar cycle. Furthermore, within very active periods, the ratio NSTE-ACS to STE-ACS, which is almost constant during periods of low to medium activity, changes favouring the NSTE-ACS. Most of the ACS cases exhibit a high degree of association with the recovery phase of the geomagnetic storms; a smaller, yet significant, part was found associated with periods of fast solar wind without a storm.

Katsavrias, Ch.; Preka-Papadema, P.; Moussas, X.; Apostolou, Th.; Theodoropoulou, A.; Papadima, Th.

2013-01-01

203

Rotor heating effects from geomagnetic induced currents  

Microsoft Academic Search

The heating effects at the end-ring connection areas of the rotor due to the harmonic current generation of a saturating unit transformer from geomagnetic induced currents (GIC) on the transmission system have been calculated from observed data and from EMTP studies sponsored by the Electric Power Research Institute. These calculations show that damage may occur during strong GIC storm activity.

W. B. Gish; W. E. Feero; G. D. Rockefeller

1994-01-01

204

Geomagnetically Induced Current Effects on Transformers  

Microsoft Academic Search

Geomagnetically induced currents (GIC) can cause saturation of the magnetic circuit of transformers in a power system. This saturation can increase the Mvar absorption of the transformers leading to voltage control problems, generate significant harmonic currents and cause heating of the internal components of the transformer itself, leading to gas relay alarm\\/operation as well as possible damage. This paper sets

P. R. Price

2002-01-01

205

Geomagnetically induced current effects on transformers  

Microsoft Academic Search

Geomagnetically induced currents (GICs) can cause saturation of the magnetic circuit of transformers in a power system. This saturation can increase the MVAr absorption of the transformers, leading to voltage-control problems, generating significant harmonic currents, and cause heating of the internal components of the transformer itself, leading to gas relay alarm\\/operation as well as possible damage. This paper sets out

Philip R. Price

2002-01-01

206

No covariation between the geomagnetic activity and the incidence of acute myocardial infarction in the polar area of northern Sweden.  

PubMed

This study was undertaken to investigate whether there was any relation between the aurora borealis (measured as the geomagnetic activity) and the number of acute myocardial infarctions (AMI) in the northern, partly polar, area of Sweden. The AMI cases were collected from The Northern Sweden MONICA (multinational MONItoring of trends and determinants of CArdiovascular disease) AMI registry between 1985 and 1998, inclusive, and the information on the geomagnetic activity from continuous measurements at the Swedish Institute of Space Physics, Kiruna. In the analyses, both the relation between the individual AMI case and ambient geomagnetic activity, and the relation between the mean daily K index and the daily number of AMI cases were tested. We found no statistically significant relation between the number of fatal or non-fatal AMI cases, the number of sudden deaths or the number of patients with chest pain without myocardial damage, and geomagnetic activity. Our data do not support a relation between the geomagnetic activity and AMI. PMID:12135204

Messner, T; Häggström, I; Sandahl, I; Lundberg, V

2002-05-01

207

Comparison of polar cap electron density enhancement due to solar illumination and geomagnetic activity as measured by IMAGE/RPI  

NASA Astrophysics Data System (ADS)

Polar cap electron density (Ne) measurements made between the years 2000 - 2005 by the radio plasma imager (RPI) on board the IMAGE spacecraft are used to study the density enhancements resulting from changes in solar illumination and geomagnetic activity level. This study covers a geocentric distance, R = 1.4 - 5.0 RE and the polar cap is defined by an empirical boundary model that takes into account the dynamic nature of the location and size of the polar cap. The average polar cap electron density profile depends on geomagnetic activity level e.g., measured by the Kp index and solar illumination (solar zenith angle) at the footprints of the geomagnetic field lines. Our analysis of RPI Ne data shows that increase in geomagnetic activity leads to an enhancement in Ne. This enhancement in Ne is found to increase with altitude. At geocentric distance of R = 4.5 RE, an increase in the geomagnetic activity level from Kp < 2 to ~5 results in an Ne increase by a factor of ~5. On the other hand, a strong solar illumination control of Ne at lower altitudes, and not at higher is observed. At geocentric distance of ~ 2 RE, the average Ne is larger on the sunlit side than on the dark side by a factor of 3 - 4 both for quiet and disturbed conditions. At geocentric distance of about 2.5 RE the effects of these two factors on Ne appear to be comparable. Similar to previous polar cap density models, a functional representation of RPI Ne that takes the form of a power law is proposed. While in the previous Ne functional representations the power index is a constant, the power index in our representation of Ne distribution is found to correlate with (and hence is a function of) the Kp index and the solar zenith angle (SZA).

Nsumei, P.; Reinisch, B.; Song, P.; Tu, J.; Huang, X.

2007-12-01

208

Ionospheric Behaviors Over Korea Peninsula During the Super Geomagnetic Storm Using GPS Measurements  

NASA Astrophysics Data System (ADS)

The super-geomagnetic storms called 2003 Halloween event globally occurred during the period of 29 through 31 which are the following days when the solar flares of X18 class exploded on 28 October 2003. The S4 index from GPS signal strength and the peak electron density (NmF2) from GPS tomography method are analyzed according to the date. The occurrences of the cycle slip and scintillation in the GPS signals are 1,094 and 1,387 on 28 and 29 October, respectively and these values are higher than 604 and 897 on 30 and 31 October. These mean the ionospheric disturbances are not always generated by the period of geomagnetic storm. Therefore, GPS S4 index is useful to monitor the ionospheric disturbances. Behaviors of ionospheric electron density estimated from GPS tomography method are analyzed with the date. At UT = 18 hr, the maximum NmF2 is shown on 28 October. It agrees with NmF2 variation measured from Anyang ionosonde, and the GPS signal are better condition on 30 and 31 October than 28 October. In conclusion, GPS signal condition is relation with geomagnetic activities, and depend upon the variation of the electron density. We will study the long-term data to examine the relationship between the GPS signal quality and the electron density as the further works.

Chung, Jong-Kyun; Choi, Byung-Kyu; Baek, Jungho; Jee, Geonhwa; Cho, Jungho

2009-12-01

209

Long-term changes in indices of geomagnetic activity at the auroral station Sodankylä  

NASA Astrophysics Data System (ADS)

Here we compare the traditional analog measure of geomagnetic activity, Ak, with the more recent digital indices of IHV and Ah based on hourly mean data, and their derivatives at the auroral station Sodankylä. By this selection of indices we study the effects of (i) analog vs. digital technique, and (ii) full local-time vs. local night-time coverage on quantifying local geomagnetic activity. We find that all other indices are stronger than Ak during the low-activity cycles 15-16 suggesting an excess of very low scalings in Ak at this time. The full-day indices consistently depict stronger correlation with the interplanetary magnetic field strength, while the night-time indices have higher correlation with solar wind speed. The Ak index correlates better with the digital indices of full-day coverage than with any night-time index. However, Ak depicts somewhat higher activity levels than the digital full-day indices in the declining phase of the solar cycle, indicating that, due to their different sampling rates, the latter indices are less sensitive to high-frequency variations driven by the Alfvén waves in high-speed streams. On the other hand, the night-time indices have an even stronger response to solar wind speed than Ak. The results strongly indicate that at auroral latitudes, geomagnetic indices with different local time coverage reflect different current systems, which, by an appropriate choice of indices, allows studying the century-scale dynamics of these currents separately.

Martini, D.; Mursula, K.; Ulich, T.; Pandey, V. S.; Kim, K.-H.; Lee, D.-H.

2012-09-01

210

Studies of ionospheric variations during geomagnetic activities at the low-latitude station, Ile-Ife, Nigeria  

NASA Astrophysics Data System (ADS)

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 geomagnetic activity period (when Dst is from -40 to 0 nT) and during geomagnetic storm events (with Dst about -100 nT). Seasonal variations 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 geomagnetic 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 geomagnetic 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.

Ariyibi, Emmanuel A.; Joshua, Emanuel O.; Rabiu, Babatunde A.

2013-02-01

211

OI 630.0 nm Night Airglow Observations during the Geomagnetic Storm on November 20, 2003 at Kolhapur (P43)  

NASA Astrophysics Data System (ADS)

sharma_ashokkumar@yahoo.com The ground based photometric observations of OI 630 nm emission line have been carried out from Kolhapur station (Geog. Lat.16.8?N, Geo. Long 74.2?E), India during the period of the largest geomagnetic storm of the solar cycle 23 which occurred on 20 November 2003, with minimum Dst index 472 nT occurring around mid-night hours. We observed that on 19 November 2003 which was geomagnetically quiet day, the airglow activity of OI 630 nm emission was subdued and it was decreasing monotonically. However, on the night of November 20, 2003 the enhancement is observed during geomagnetic storm due to the increased electron density at the altitude of the F region which is related to the downward transport of electron from the plasmasphere to the F-region. Airglow intensity at OI 630.0 nm showed increase around midnight on November 21, 2003 but comparatively on a smaller scale. On this night the DST index was about 100 nT. This implies that the effect of the geomagnetic storm persisted on that night also. These observations have been explained by the penetration magnetospheric electric field to the low latitude region and the subsequent modulation of meridional wind during the magnetic disturbance at night.

Sharma, A. K.; et al.

2006-11-01

212

Trapping of strangelets in the geomagnetic field  

NASA Astrophysics Data System (ADS)

Strangelets arriving from the interstellar medium are an interesting target for experiments searching for evidence of this hypothetical state of hadronic matter. We entertain the possibility of a trapped strangelet population, quite analogous to ordinary nuclei and electron belts. For a population of strangelets to be trapped by the geomagnetic field, these incoming particles would have to fulfill certain conditions, namely, having magnetic rigidities above the geomagnetic cutoff and below a certain threshold for adiabatic motion to hold. We show in this work that, for fully ionized strangelets, there is a narrow window for stable trapping. An estimate of the stationary population is presented and the dominant loss mechanisms discussed. It is shown that the population would be substantially enhanced with respect to the interstellar medium flux (up to 2 orders of magnitude) due to quasistable trapping.

Paulucci, L.; Horvath, J. E.; Medina-Tanco, G. A.

2008-02-01

213

Evaluation of Geomagnetic Activity in the MAD Frequency Band (.04 to 0.6 Hz).  

National Technical Information Service (NTIS)

After defining geomagnetic noise as it applies to MAD, the geomagnetic indices currently used by the fleet to predict MAD geomagnetic noise are reviewed to determine their actual applicability. The current indices are determined to be insufficient, method...

J. M. Schweiger

1982-01-01

214

Radiation Belt's Reaction to Geomagnetic Storms  

NASA Video Gallery

From October to December 2003, the radiation belts swelled and shrank in response to geomagnetic storms as particles entered and escaped the belts. At one point, 3 radiation belts are detected. Under the wave of energetic particles from the Halloween 2003 solar storm events, the Earth's radiation belts underwent significant changes in structure. This visualization is constructed using daily-averaged particle flux data from the SAMPEX satellite installed in a simple dipole model for the Earth's magnetic field.

Holly Zell

2012-01-18

215

An Absence of Equatorial Scintillation Activity Prior to Large Geomagnetic Storms  

NASA Astrophysics Data System (ADS)

A recent study has established a technique for forecasting the occurrence or non-occurrence of equatorial scintillation activity after sunset by observing the virtual height of the bottom-side F layer (h’F) from a ground-based digital sounder on the magnetic equator. As measured by the UHF S4 Index at Ancon, Peru, there exists a “threshold” in h’F at 1930 local time (h’Fthr) above which scintillation activity is likely to occur and below which scintillation activity is unlikely to occur. This h’Fthr value increases linearly with increasing F10.7 cm flux values. For an F10.7 cm value of 70, h’Fthr = 260 km and for F10.7 cm flux = 180; h’Fthr= 400 km. Several days prior to large geomagnetic storms, the F10.7 cm flux values begin increasing from their nominally quiet values to much greater values. For example, prior to the October, 2003 Halloween storm (Oct. 5 - 17), F10.7 cm flux was about 100 and beginning on Oct. 19, the F10.7 values began increasing to a value of 298 on the 26th, just prior to the Halloween storm period. The consequence of this increase is to increase the h’Fthr values such that the day-to-day h’F (1930 LT) values begin falling below the h’Fthr values and scintillation activity decreases as measured by the S4 Index at Ancon, Peru SCIntillation Network Decision Aid (SCINDA) site. We present results prior to the Halloween, 2003 geomagnetic storm and the October-November, 2001 geomagnetic storm that support this argument. We compare the average F10.7 cm fluxes, h’Fthr, h’F (1930 LT), and scintillation S4 Index values for the “quiet” period where the F10.7 values are relatively constant with the same averages over the period where F10.7 cm flux is increasing prior to the geomagnetic storms. We find that the average Total Hourly Mean S4 (THMS4) value just prior to the Halloween geomagnetic storm is 50% lower than the average THMS4 value for the “quiet” period. The possibilities for global verification of these results are discussed.

Anderson, D. N.; Redmon, R. J.

2009-12-01

216

A new approach to geomagnetic matching navigation  

NASA Astrophysics Data System (ADS)

A new method of global optimal matching theory based on linear drawing of geomagnetic filed is proposed and researched. Navigation system based on the geomagnetic field has no accumulated error, and it is not influenced by weather, terrain and other factors as it is passive. Thus, geomagnetic navigation has good potentials to be an assistant method for other navigation systems such as inertial navigation system. The matching navigation method avoids the disadvantages of Kalman filter because it makes use of a set of relative information. In the literatures, the forming principle of linear drawing is discussed. A necessary global optimal matching technique is researched because matching a linear drawing with a standard planar chart results in infinite instances and the previous mismatch will affect the following process. Correlation method is applied in the matching process for its simpleness. Genetic simulated annealing algorithm is applied in the optimal researching process for its rapid convergence and global optimization. Mathematical simulations are carried out to verify the correctness and efficiency of the new solution. The results are listed in the end, which prove the rightness of the methods proposed in this paper.

Ge, Zhi-lei; Zhou, Jun

2007-11-01

217

Solar Energetic Particle Events and Geomagnetic Storms  

NASA Astrophysics Data System (ADS)

lakhina@iigs.iigm.res.in The solar energetic particle (SEP) events are the energetic outbursts as a result of acceleration and heating of solar plasma during solar flares and coronal mass ejections (CMEs). The SEP events are characterized by abrupt enhancements in the proton flux in the energy range of keVs to MeVs as measured by spacecraft at 1 AU. On impacting the earth's magnetosphere, the SEP events can lead to a sudden disturbance of the earth's magnetic field, known as Geomagnetic storms. In the present study, the effects of some strong SEP events of the present solar cycle on various magnetic storm processes are investigated by using the Solar flare and CME data from GOES-8 and SOHO, interplanetary plasma and magnetic field data from ACE and Wind, and the ground magnetic field data from Alibag and Tirunelveli magnetic observatories. The main focus will be to highlight the low latitude geomagnetic signatures produced by these SEP events. The SEP events with the persistence of high level of proton flux after the shock are found to be associated with intense magnetic storms. The role of SEP events in the prediction of intense geomagnetic storms will be discussed.

Lakhina, G. S.; Rawat, R.; Alex, S.

2006-11-01

218

Study of the recovery phase of the extreme geomagnetic storms from 1859 to 1989  

NASA Astrophysics Data System (ADS)

The Dst index is used as a proxy of energy ring current content. In a storm event, the enhancement of the current appears as a depression of the index. To know in advance the minimum value that will reach the index and the time in which it will happen are usually the main aims in the forecasting scheme. However, the knowledge of the time remaining for the magnetosphere to reach again quiet time, or at least 'non-dangerous time' is an important input for many technological systems. These predictions are even more relevant for severe geomagnetic storms. In a previous study, we analyzed the recovery phase of intense geomagnetic storms (Dst ? - 100 nT) in the period 1963-2003 [Aguado et al., 2010]. The results obtained showed that the decay of the Dst index follows a hyperbolic law, which recovery time depends linearly on the intensity of the storm. Now, we study the recovery phase of the largest storms even recorded [Tsurutani et al., 2003]. These events provide an extraordinary opportunity for two goals: (1) to validate the hyperbolic model for disturbances at terrestrial surface as severe as the Carrington event, or that related to the Hydro-Quebec blackout, and (2) to check if the linear relationship between the recovery time and the intensity of the storm still remains.

Saiz, Elena; Cid, Consuelo; Palacios, Judith; Aguado, Jesus; Cerrato, Yolanda; Guerrero, Antonio

2013-04-01

219

NM-MT network and space dangerous phenomena, 2. Examples of cosmic ray using for forecasting of major geomagnetic storms  

NASA Astrophysics Data System (ADS)

We present developing of methods (e.g., Dorman et al., 1995, 1999) for forecasting on the basis of neutron monitor hourly on-line data (as well as on-line muon telescopes hourly data from different directions) geomagnetic storms of scales G5 (3- hour index of geomagnetic activity Kp=9), G4 (Kp=8) and G3 (Kp=7) (according to NOAA Space Weather Scales). These geomagnetic storms are dangerous for people technology and health (influence on power systems, on spacecraft operations, on HF radio-communications and others). We show that for especially dangerous geomagnetic storms can be used global-spectrographic method if on-line will be available 35-40 NM and muon telescopes. In this case for each hour can be determined CR anisotropy vector, and the specifically behavior of this vector before SC of geomagnetic storms G5, G4 or G3 (according to NOAA Space Weather Scales) can be used as important factor for forecast. The second factor what can be used for SC forecast is specifically behavior of CR density (CR intensity) for about 30-15 hours before SC (caused mainly by galactic CR particles acceleration during interaction with shock wave moved from the Sun). The third factor is effect of cosmic ray pre-decreasing, caused by magnetic connection of the Earth with the region behind the shock wave. We demonstrate developing methods on several examples of major geomagnetic storms. This research is partly supported by the INTAS grant 00-0810. REFERENCES: Dorman L.I., et al. "Cosmic-ray forecasting features for big Forbush-decreases". Nuclear Physics B, 49A, 136-144 (1995). L.I.Dorman, et al, "Cosmic ray Forbush-decrease as indicators of space dangerous phenomenon and possible use of cosmic ray data for their prediction", Proc. of 26-th Intern. Cosmic Ray Conference, Salt Lake City, 6, 476-479 (1999).

Belov, A.; Dorman, L.; Eroshenko, E.; Iucci, N.; Parisi, M.; Pustil Nik, L.; Sternlieb, A.; Villoresi, G.; Yanke, V.; Zukerman, I.

220

Earth-ionosphere transmission line model for an impulsive geomagnetic disturbance at the dayside geomagnetic equator  

NASA Astrophysics Data System (ADS)

The near instantaneous onset of a geomagnetic impulse such as the preliminary reverse impulse (PRI) of the geomagnetic sudden commencement at high latitude and at the dayside geomagnetic equator has been explained by means of the TM0 mode waves in the Earth-ionosphere waveguide (Kikuchi and Araki, J. Atmosph. Terrest. Phys., 41, 927-936, 1979). There is, on the other hand, a time lag of the order of 10 sec in the peak amplitude of the magnetic impulse at the dayside equator. To explain these two temporal aspects, we examine transmission of the TM0 mode in a finite-length Earth-ionosphere transmission line composed of a finitely conducting ionosphere and the perfectly conducting Earth, with a fixed electric potential at one end and null potential at the other end of the transmission line, corresponding to the foot of a field-aligned current on the dawn- or dusk-side in the polar cap and middle point on the noon-midnight meridian at low latitude, respectively. Successive transmission and reflection in the bounded transmission line lead to that the ionospheric currents start to grow instantaneously, but reach a steady state with a relaxation time proportional to the length of the transmission line and the ionospheric conductivity. The relaxation time is of the order of 10 sec when we give high conductivity applicable to the equatorial ionosphere, which matches the observed time lag in the peak amplitude of the equatorial geomagnetic impulse. Consequently, the TM0 mode in the finite-length Earth-ionosphere transmission line explains both the instantaneous onset and time lag in the peak amplitude of the geomagnetic impulse at the dayside geomagnetic equator.

Kikuchi, T.

2004-12-01

221

Geomagnetic effects modelling for the PJM interconnection system. Part 2; Geomagnetically induced current study results  

SciTech Connect

The development of a computer program for calculation of geomagnetically induced current (GIC) and a GIC power system model for the Pennsylvania-New Jersey-Maryland Interconnection is described in this paper. Results of GIC for three different ionospheric source configurations are shown. A new method is presented for estimating GIC in unmetered parts of the system based on a few measurements and precalculated geomagnetic disturbance conditions. The use of an interactive, menu driven GIC program to study mitigation concepts including the effects of line outages, line series capacitors, transformer neutral blocking resistors and transformer neutral blocking capacitors is also presented.

Prabhakara, F.S.; Hannett, L.N.; Ringlee, R.J. (Power Technologies, Inc., Schenectady, NY (United States)); Ponder, J.Z. (PJM Interconnection, Norristown, PA (US))

1992-05-01

222

Bacillus thuringiensis subsp. israelensis Cyt1Aa synergizes Cry11Aa toxin by functioning as a membrane-bound receptor  

PubMed Central

Bacillus thuringiensis subsp. israelensis produces crystal proteins, Cry (4Aa, 4Ba, 10Aa, and 11Aa) and Cyt (1Aa and 2Ba) proteins, toxic to mosquito vectors of human diseases. Cyt1Aa overcomes insect resistance to Cry11Aa and Cry4 toxins and synergizes the toxicity of these toxins. However, the molecular mechanism of synergism remains unsolved. Here, we provide evidence that Cyt1Aa functions as a receptor of Cry11Aa. Sequential-binding analysis of Cyt1Aa and Cry11Aa revealed that Cyt1Aa binding to Aedes aegypti brush border membrane vesicles enhanced the binding of biotinylated-Cry11Aa. The Cyt1Aa- and Cry11Aa-binding epitopes were mapped by means of the yeast two-hybrid system, peptide arrays, and heterologous competition assays with synthetic peptides. Two exposed regions in Cyt1Aa, loop ?6-?E and part of ?7, bind Cry11Aa. On the other side, Cry11Aa binds Cyt1Aa proteins by means of domain II-loop ?8 and ?-4, which are also involved in midgut receptor interaction. Characterization of single-point mutations in Cry11Aa and Cyt1Aa revealed key Cry11Aa (S259 and E266) and Cyt1Aa (K198, E204 and K225) residues involved in the interaction of both proteins and in synergism. Additionally, a Cyt1Aa loop ?6-?E mutant (K198A) with enhanced synergism to Cry11Aa was isolated. Data provided here strongly indicates that Cyt1Aa synergizes or suppresses resistance to Cry11Aa toxin by functioning as a membrane-bound receptor. Bacillus thuringiensis subsp. israelensis is a highly effective pathogenic bacterium because it produces a toxin and also its functional receptor, promoting toxin binding to the target membrane and causing toxicity.

Perez, Claudia; Fernandez, Luisa E.; Sun, Jianguang; Folch, Jorge Luis; Gill, Sarjeet S.; Soberon, Mario; Bravo, Alejandra

2005-01-01

223

Side effects of AAS abuse: an overview.  

PubMed

Anabolic - androgenic steroids (AAS) were originally developed to promote growth of skeletal muscle. AAS abuse is commonly associated with bodybuilders, weightlifters, and other athletes. The issue of AAS toxicity is not yet completely understood since the adverse effects outline a varied scenario with side effects reported affecting many organs and systems in humans. The true incidence of AAS related medical problems is not known, due to several drawbacks in human studies. The entity of side effects depends on the sex, the dose, the duration of treatment, whether they are taken during exercise training or under sedentary conditions, and the susceptibility of the individuals themselves to androgen exposure partly depending on genetic factors. Both the acute and the chronic effects can lead to toxicity, but generally the serious and even fatal effects depend on the time and the duration of AAS administration. A limitation of human studies is represented by the fact that information about the intake of steroids are, generally, self reported and it is hardly possible to assess the exact dosage. AAS are often used in combination with other dugs or substances, so it is difficult to separate their toxic effects from those caused by the other drugs abused. Hence experimental studies conducted on animal models are mandatory to investigate the mechanisms underlying to AAS toxicity and the organ alterations due to these substances. Finally, clinicians should be aware of the complex and varied pattern of toxicity so as to be able to perform correct diagnoses and treatments. PMID:21443513

Turillazzi, E; Perilli, G; Di Paolo, M; Neri, M; Riezzo, I; Fineschi, V

2011-05-01

224

Wave dynamics in the geomagnetic tail  

NASA Astrophysics Data System (ADS)

The Geomagnetic tail is the region of the earth's magnetosphere stretched by the solar wind away from the Sun. The stretched Geomagnetic tail acts as a huge magnetic energy reservoir powering a variety of processes, for instance the substorm and the aurora, which affect the entire magnetosphere. This thesis presents analyses of the wave dynamics of the geomagnetic tail at the spatial scale from the Magnetohydrodynamics (MHD) to the ion gyroradius and the temporal scale from the ion gyro-period to many gyro-periods. The results provide new insights into the energy flow process in the magnetotail reconnection. In addition, the implication of these results sheds light on the energy transport from the geomagnetic tail to the aurora zone. The bidirectional out owing ion jet is a diagnostic signal of magnetic reconnection. We present a Cluster spacecraft study of the intense surface waves in the earthward and tailward reconnection outflow jets in the geomagnetic tail. The four Cluster spacecraft are used to determine quantitatively the scale size and phase velocity of waves with spacecraft frequencies from 3 x 10-2 Hz to 1 Hz and spatial scales ranging from much larger (x50) than to comparable to the H+ gyroradius scale. The wave phase velocity relative to the spacecraft frame is directed mainly in the equatorial plane and it tracks the variation in the direction of the jet's velocity projection perpendicular to the magnetic field lying in the xy-gse plane. The surface waves are phase standing in the flow normal to the plasma sheet boundary, but partially or entirely convected by the flow in the plane of the plasma sheet (xy-gse). The surface wave is consistent with a Kelvin Helmholtz instability driven by the gradient in the normal direction of the component of the reconnection ion jet velocity perpendicular to magnetic field. E/B ratios provide evidence that dispersive Alfven waves are excited at small scales. Analysis of electric and magnetic field data shows that the wave perturbations are associated with strong Alfvenic Poynting flux radiated away from the reconnection region toward Earth along the geomagnetic field. The mapped values (to 100 km altitude) of Poynting flux (100ergs/cm2s) and longitudinal scales (10-100 km) of the waves suggest that the observed waves and their motions are an important boundary condition in determining both the energetics of the aurora and their complex motions in the night sky. The Harris current sheet is a good approximation of the Geomagnetic Tail configuration. We present a theoretical analysis of the linear Alfven eigenmode dynamics of a Harris current sheet. The implication of this theory in the context of magnetic reconnection is not presented. Alfven eigenmodes are confined by the Harris current sheet in the same way that quantum mechanical waves are confined by the tanh2 potential. Although the Alfven eigenmodes are confined in the current layer, their dynamics is interrelated with the global-scale information of the current sheet. The linear dynamics of the Harris current sheet is described as a eigenmode-source coupling process, during which magnetic energy can be converted into plasma energy and the first-order magnetic configuration of the Harris sheet alters.

Dai, Lei

225

Enhancement of solar wind low-energy energetic particles as precursor of geomagnetic disturbance in operational geomagnetic forecast  

NASA Astrophysics Data System (ADS)

A study of the relationship between solar wind low-energy energetic particles using data from the Electron, Proton, and Alpha Monitor (EPAM) onboard the Advanced Compositional Explorer spacecraft (ACE) and geomagnetic activity using data from Canadian magnetic observatories in Canada's polar cap, auroral zone, and subauroral zone was carried out for a period spanning 1997-2005. Full halo coronal mass ejections (CMEs) were used to gauge the initial particle enhancements and the subsequent geomagnetic activity. It was found that maximum geomagnetic activity is related to maximum particle enhancements in a non-linear fashion. Quadratic fit of the data results in expressions that can be easily used in an operational space weather setting to forecast geomagnetic disturbance quantitatively. A superposed epoch analysis shows increase in particle flux level starts hours before geomagnetic activity attains its peak, affirming the precursory nature of EPAM particles for the impending geomagnetic impact of CME. This can supplement the decision process in formulating geomagnetic warning after the launch of CME from the Sun but before the arrival of shock at Earth. The empirical relationships between solar wind low-energy energetic particles and geomagnetic activity revealed in this statistical study can be easily codified, and thus utilized in operational space weather forecast to appraise the geoeffectiveness of the CME and to provide a quantitative forecast for maximum geomagnetic activity in Canada's polar cap, auroral zone, and subauroral zone after the occurrence of a CME.

Lam, H.-L.

2009-05-01

226

Statistical analyses of influence of solar and geomagnetic activities on car accident events.  

PubMed

Statistical analyses of the influence of Solar and geomagnetic activity, sector structure of the interplanetary magnetic field and galactic cosmic ray Forbush effects on car accident events in Poland for the period of 1990-1999 have been carried out. Using auto-correlation, cross-correlation, spectral analyses and superposition epochs methods it has been shown that there are separate periods when car accident events have direct correlation with Ap index of the geomagnetic activity, sector structure of the interplanetary magnetic field and Forbush decreases of galactic cosmic rays. Nevertheless, the single-valued direct correlation is not possible to reveal for the whole period of 1990-1999. Periodicity of 7 days and its second harmonic (3.5 days) has been reliably revealed in the car accident events data in Poland for the each year of the period 1990-1999. It is shown that the maximum car accident events take place in Poland on Friday and practically does not depend on the level of solar and geomagnetic activities. PMID:11803971

Alania, M V; Gil, A; Wieliczuk, R

2001-01-01

227

Geomagnetic storm effects in the ionospheric E- and F-regions  

NASA Astrophysics Data System (ADS)

Ground-based ionosonde data obtained at Alma-Ata station [?=43.25°N, ?=76.92°E, ?=33.47°N, L=1.44) were analysed to study the ionospheric responses of nine intense (Kp?8, Dst<-100 nT) geomagnetic storms with storm sudden commencement (ssc). The collected data show that the ionospheric responses to the geomagnetic storms are highly complex and variable; however, negative ionospheric disturbances are a common feature of the responses. The occurrence of normal night E2-, E-, F1- and auroral type r (retardation) sporadic Es-layers, which are unusual for Alma-Ata, was observed during most active phase in the Dst index. Employing the International Reference Ionosphere (IRI), the night-time E region electron density Ne was estimated for “quiet” conditions on the epochs of the storm time periods. A direct comparison of the “quiet” and “storm” electron density in the 110-200 km altitude range shows a significant storm-induced increase in Ne that reaches a factor of approximately 10 at the 110 km altitude. The interaction of precipitating energetic neutralised ring current particles with the upper atmosphere during geomagnetic disturbances is assumed to be a possible explanation for the observed night events at this latitude sector.

Gordienko, G. I.; Vodyannikov, V. V.; Yakovets, A. F.

2011-08-01

228

Dependence of neutral temperatures in the lower thermosphere on geomagnetic activity  

NASA Astrophysics Data System (ADS)

The neutral temperature (Tn) in the lower thermosphere has been measured using high-resolution (0.13 nm) N2 Lyman-Birge-Hopfield (LBH) band emissions, taken from the High-Resolution Ionospheric and Thermospheric Spectrograph (HITS) instrument aboard the Advanced Research and Global Observation Satellite (ARGOS). Tn in the lower thermosphere (below ˜200 km) has been examined for 12 days in 2000 and 2001. During geomagnetically quiet conditions, the observed HITS temperatures (THITS) as a function of latitude and calculations using the NRLMSISE-00 model are in good agreement. During periods with geomagnetic disturbances, the model temperatures are unable to match the spatial and temporal variations exhibited by the measurements. An analysis of HITS temperatures and measurements of the auroral electrojet index AL indicates that THITS changes typically follow variations in AL obtained between 13 and 18.5 hours earlier. On average, the time delay is 16 hours and 25 min earlier (correlation coefficient of 0.55), yielding the following empirical formula between Tn and AL changes: ?Tn[K] = 2.1 × ?AL[nT]. Also, the agreement between measured (HITS) and modeled (NRLMSISE-00) Tn values has been investigated for 8 days with similar geomagnetic conditions, yielding a correlation coefficient of 0.75 between the THITS-TMSIS agreement and the previously measured AL.

Aksnes, A.; Eastes, R.; Budzien, S.; Dymond, K.

2007-06-01

229

Geophysical variables and behavior: C. Increased geomagnetic activity on days of commercial air crashes attributed to computer or pilot error but not mechanical failure.  

PubMed

Global geomagnetic activity (aa values) for the days of crashes of airplanes and for each of the three days before and after the crashes were compared for 373 events (years 1940 through 2002) attributed to unknown factors, mechanical errors, electronic/computer failures or pilot errors. Interactions between days and classifications of the crashes were due to the significantly greater geomagnetic activity on the days of crashes attributed to pilot or computer error but not to mechanical or unknown factors. Successive temporal analyses indicated that the elevated activity on the days of crashes attributed to pilot error have not changed over time, but there was an increase in those attributed to electronic errors after 1965. No more than 9% of the variance in geomagnetic activity on the days of the crashes was associated with the type of crash. These results are consistent with our hypothesis that some factor or factors associated with relative increases in geomagnetic activity may affect complex electronic systems composed of either silica (computer) or carbon (brain) aggregates. PMID:15291208

Fournier, N M; Persinger, M A

2004-06-01

230

Low-latitude geomagnetic signatures during major solar energetic particle events of solar cycle-23  

NASA Astrophysics Data System (ADS)

The frequency of occurrence of disruptive transient processes in the Sun is enhanced during the high solar activity periods. Solar cycle-23 evidenced major geomagnetic storm events and intense solar energetic particle (SEP) events. The SEP events are the energetic outbursts as a result of acceleration of heliospheric particles by solar flares and coronal mass ejections (CMEs). The present work focuses on the geomagnetic variations at equatorial and low-latitude stations during the four major SEP events of 14 July 2000, 8 November 2000, 24 September 2001 and 4 November 2001. These events have been reported to be of discernible magnitude following intense X-ray flares and halo coronal mass ejections. Low-latitude geomagnetic records evidenced an intense main phase development subsequent to the shock impact on the Earth's magnetosphere. Satellite observations show proton-flux enhancements associated with solar flares for all events. Correlation analysis is also carried out to bring out the correspondence between the polar cap magnetic field perturbations, AE index and the variations of low-latitude magnetic field. The results presented in the current study elucidate the varying storm development processes, and the geomagnetic field response to the plasma and interplanetary magnetic field conditions for the energetic events. An important inference drawn from the current study is the close correspondence between the persistence of a high level of proton flux after the shock in some events and the ensuing intense magnetic storm. Another interesting result is the role of the pre-shock southward IMF Bz duration in generating a strong main phase.

Rawat, R.; Alex, S.; Lakhina, G. S.

2006-12-01

231

The effect of precipitating particles on middle atmospheric night time ozone during enhanced geomagnetic activity  

NASA Astrophysics Data System (ADS)

We have investigated the effect of precipitating particles on middle atmospheric ozone during a moderate geomagnetic storm in July 2009. It is expected that the number of precipitating particles increases with increasing geomagnetic activity, and that these precipitated particles will subsequently enhance the production of nitrosonium (NO+) and odd hydrogen (HOx) in the upper atmosphere. The lifetime of HOx and its associated ozone (O3) destruction is short, whilst NO+ can form long-lived odd nitrogen during times of high geomagnetic activity, (NOx), which can affect ozone over a longer time span, and hence a wider spatial range due to transport. We use the National Oceanic and Atmospheric Administration (NOAA) satellite data to identify and analyze the particles that precipitated over Antarctica during the moderate geomagnetic storm. To analyze the subsequent nitric oxide (NO) enhancement and O3 depletion we use a microwave radiometer stationed at Troll, Antarctica (72°S, 2.5°E, L=4.76). This microwave radiometer operating at 250 GHz gives high temporal and vertical resolution of the NO and O3 column. The Atmospheric Radiation Transfer Simulator (ARTS) and QPack have been employed to perform the inversions of the spectra. During the July storm that reached -79 nT on the Dst index, we observe radiation-belt particle precipitation over Troll, an NO increase, and a direct O3 depletion of 30% between 60 and 80 km altitude. This O3 depletion lasted for 9 days, and its centroid descended to 55 km altitude at a vertical velocity of 1-3 m/s. This work shows that moderate storms, which are common-place and occur even during solar minimum, can cause a significant and direct effect in the middle atmospheric ozone distribution.

Daae, M.; Espy, P. J.; Newnham, D.; Kleinknecht, N.; Clilverd, M.

2010-12-01

232

Some data about the relationship between ths human state and external perturbations of geomagnetic field  

NASA Astrophysics Data System (ADS)

The influence of solar activity changes and related to them geomagnetic field variations on human health is confirmed in a lot of publications but the investigations in this area are still sporadic and incomplete because of the fact that it is difficult to separate the geomagnetic influence from the environmental factor complex, which influence the human life activity. That is why we have studied the influence of changes in geomagnetic activity on human physiological, psycho-physiological parameters and behavioural reactions. In this article we looked for influence of changes in GMA on the systolic and diastolic blood pressure and pulse-rate. We examined 54 volunteers. 26 persons of them had some cardio-vascular or blood pressure disturbances. The registrations were performed every day at one and the same time for each person during the period 1.10 - 10.11.2001. Four-way analysis of variance (MANOVA method) with factors: GMA, day, sex and cardiovascular pathology was performed. GMA was divided into four levels according to the Kp- and Ap-index values. The days examined were divided into six levels in relation to the day with increased GMA. Factor "cardiovascular pathology" was divided into two levels: healthy subjects and subjects that had some cardio -vascular or blood pressure disturbances. When we employed four-way analysis of variance, the influence of some of the factors on the physiological parameters examined turned out to be statistically significant at p<0.05. Our investigations indicate that most of the persons examined irrespectively to their status could be sensitive to the geomagnetic disturbances.

Dimitrova, S.; Stoilova, I.; Yanev, T.

233

Contribution of wind, conductivity, and geomagnetic main field to the variation in the geomagnetic Sq field  

NASA Astrophysics Data System (ADS)

variation in the geomagnetic Sq field and the cause of the variation were examined. The amplitude of the geomagnetic Y component (Sq(Y)) in equinox was averaged for each year and adopted as a proxy of the Sq field. Sq(Y) was combined with the ionospheric conductivity estimated by the International Reference Ionosphere model to determine the dynamo electric field and neutral wind velocity by using the geomagnetic main field strength. It was found that the solar activity dependence of the Sq field could be almost completely attributed to the conductivity variation, and neutral winds tend to decrease when the solar activity increases. Although the long-term variation in the dynamo field differed among observatories, these differences were mostly attributed to the locality of the geomagnetic secular variation, whereas the variations in neutral wind amplitude were nearly the same in all regions. On the other hand, no clear long-term variation in neutral wind was detected other than that by solar activity.

Takeda, Masahiko

2013-07-01

234

April 2000 Geomagnetic Storm: Ionospheric Drivers of Large Geomagnetically Induced Currents  

Microsoft Academic Search

Geomagnetically induced currents (GIC) flowing in technological systems on the ground are a manifestation of space weather. Due to the proximity of very dynamic ionospheric current systems, GIC are of special interest at high latitudes where they are known to cause harm e.g. for normal operation of power transmission systems and buried pipelines. Despite numerous studies on GIC, there still

A. Pulkkinen; T. Pulkkinen; A. Thomson; E. Clarke; A. McKay; A. Viljanen

2002-01-01

235

April 2000 geomagnetic storm: ionospheric drivers of large geomagnetically induced currents  

Microsoft Academic Search

Geomagnetically induced currents (GIC) flowing in technological systems on the ground are a direct manifestation of space weather. Due to the proximity of very dynamic ionospheric current systems, GIC are of special interest at high latitudes, where they have been known to cause problems, for example, for normal operation of power transmission systems and buried pipelines. The basic physics underlying

A. Pulkkinen; A. Thomson; E. Clarke; A. McKay

2003-01-01

236

Geomagnetic effects modelling for the PJM interconnection system. Part 2; Geomagnetically induced current study results  

Microsoft Academic Search

The development of a computer program for calculation of geomagnetically induced current (GIC) and a GIC power system model for the Pennsylvania-New Jersey-Maryland Interconnection is described in this paper. Results of GIC for three different ionospheric source configurations are shown. A new method is presented for estimating GIC in unmetered parts of the system based on a few measurements and

F. S. Prabhakara; L. N. Hannett; R. J. Ringlee; J. Z. Ponder

1992-01-01

237

AA amyloidosis in vaccinated growing chickens.  

PubMed

Systemic amyloid-A (AA) amyloidosis in birds occurs most frequently in waterfowl such as Pekin ducks. In chickens, AA amyloidosis is observed as amyloid arthropathy. Outbreaks of systemic amyloidosis in flocks of layers are known to be induced by repeated inflammatory stimulation, such as those resulting from multiple vaccinations with oil-emulsified bacterins. Outbreaks of fatal AA amyloidosis were observed in growing chickens in a large scale poultry farm within 3 weeks of vaccination with multiple co-administered vaccines. This study documents the histopathological changes in tissues from these birds. Amyloid deposits were also observed at a high rate in the tissues of apparently healthy chickens. Vaccination should therefore be considered as a potential risk factor for the development of AA amyloidosis in poultry. PMID:23570943

Murakami, T; Inoshima, Y; Sakamoto, E; Fukushi, H; Sakai, H; Yanai, T; Ishiguro, N

2013-04-06

238

Advantages and limitations of spherical harmonic analyses of geomagnetic data  

NASA Astrophysics Data System (ADS)

The separation of external and internal geomagnetic variation fields using spherical harmonic data analysis is discussed. Examples obtained from geomagnetic data from 40 stations are presented. A large number of high order spherical harmonic terms is needed to approximate satisfactorily the latitudinal field distribution with sharp gradients in the auroral and equatorial regions.

Matsushita, S.

239

On the vulnerability of electric power to geomagnetic storms  

Microsoft Academic Search

Geomagnetic storms associated with sunspot and solar flare activity can disturb communications and disrupt electric power. A severe geomagnetic storm could cause a major blackout with an economic impact of several billion dollars. The vulnerability of electric power systems in the northeast United States will likely increase during the 1990's due to the trend of wheeling large amounts of power

P. R. Barnes; J. W. Van Dyke

1990-01-01

240

Geomagnetic storms: Potential economic impacts on electric utilities  

Microsoft Academic Search

Geomagnetic storms associated with sunspot and solar flare activity can disturb communications and disrupt electric power. A very severe geomagnetic storm could cause a major blackout with an economic impact of several billion dollars. The vulnerability of electric power systems in the northeast United States will likely increase during the 1990s because of the trend of transmitting large amounts of

P. R. Barnes; J. W. Vandyke

1991-01-01

241

Geomagnetic storm effects on the earth's ozone layer  

Microsoft Academic Search

The study of the response of the terrestrial environment to the different forms of solar activity is a relevant task. Geomagnetic perturbations arise from the solar wind\\/magnetospheric coupling and major magnetic storms are caused by intense, long duration Southward interplanetary magnetic fields. This paper addresses reader's attention on possible effects induced by geomagnetic storms on the Earth's ozone layer by

M. Storini

2001-01-01

242

Solar wind density influence on geomagnetic storm intensity  

Microsoft Academic Search

Solar wind density has been argued to have a strong effect on geomagnetic storms. Elevated solar wind density tends to occur in time intervals when the solar wind electric field is large. This complicates the analysis required to identify a solar wind density influence because the solar wind electric field is the dominant driver of geomagnetic storms. Statistical studies have

R. S. Weigel

2010-01-01

243

Using the moon to probe the geomagnetic tail lobe plasma  

Microsoft Academic Search

We have detected the presence of plasma in the lobes of the geomagnetic tail from observations of magnetic induction in the moon forced by time variations of the earth's magnetotail lobe field. The magnitude of the moon's tangential electromagnetic transfer function when the moon is in the lobes of the geomagnetic tail is less than that when the moon is

G. Schubert; C. P. Sonett; B. F. Smith; D. S. Colburn; K. Schwartz

1975-01-01

244

Effects of Geomagnetically-Induced Currents on HVDC Converter Operation  

Microsoft Academic Search

Electrons and protons emitted by a solar flare can be captured by the Earth's magnetic field. The resulting transient in the geomagnetic field can produce quasi-dc currents in electric power systems. These geomagnetically-induced currents (GIC) in excess of 100 amps have been measured in the transformer neutral leads. With the practice of using EHV and UHV lines for transmitting ac

N. Mohan; V. D. Albertson; T. J. Speak; K. G. Kappenman; M. P. Bahrman

1982-01-01

245

Real-Time Simulation of Geomagnetically Induced Currents  

Microsoft Academic Search

To monitor the impact of geomagnetic disturbances on a power network a system has been developed to provide real-time simulations of the geomagnetically induced currents flowing in a power system. The Real- Time GIC Simulator uses real-time magnetic data from a magnetic observatory. This is combined with a model of the earth conductivity structure to determine the electric field produced

D. H. Boteler; L. Trichtchenko; R. Pirjola; J. Parmelee; S. Souksaly; A. Foss; L. Marti

2007-01-01

246

Prediction of geomagnetically induced currents in power transmission systems  

Microsoft Academic Search

Geomagnetically induced currents (GIC) in technological systems are a manifestation of space weather at the Earth's surface. In power systems GIC cause saturation of transformers, which may even result in a collapse of the whole system and in damage of transformers. Predictions of GIC could help power systems operate smoothly through large geomagnetic disturbances. In physical modelling the key quantity

Risto Pirjola; David Boteler; Ari Viljanen; Olaf Amm

2000-01-01

247

Power flow studies in the presence of geomagnetically induced currents  

Microsoft Academic Search

Embedding the modeling and simulation of geomagnetically induced currents, GIC, into power flow simulation software allows the study of sensitivity and transient stability of the North American bulk power system under the distress of a geomagnetic storm. Modeling the interaction between the auroral electrojets and the Earth's atmosphere is a crucial step in determining the geoelectric field induced by the

Trevor R. Hutchins; Thomas J. Overbye

2012-01-01

248

Ionospheric and Geomagnetic Activity Investigated Using Oblique Sounding Comparisons With an HF Radio Propagation Model  

NASA Astrophysics Data System (ADS)

Oblique HF sounder paths over ~2000km have been operating between New Zealand and Australia for a number of years. The maximum observed frequencies (MOF) are compared with predictions from the climatological HF radio skywave propagation model used by IPS. Variations from predicted median (MUF),lower (OWF) and upper decile frequencies may be interpreted in terms of ionospheric and geomagnetic activity and the effectiveness of parameterisation of ionospheric support for HF by the T-index examined. Closely spaced multiple paths provide opportunities to investigate small scale F2 layer structures.

Neudegg, D.; Layoun, M.; Hutchinson, S.

2008-12-01

249

Dipole axially symmetric, external field components in the analysis of the geomagnetic field  

NASA Astrophysics Data System (ADS)

Correction equations are developed to account for the time-varying part of dipole axially symmetric external fields in the analysis of the geomagnetic field using the D(st) index. These equations are applied to the inclination value obtained from the Project Magnet data for 1957-1966. The results suggest that a steady part of the field exists which cannot be accounted for by D(st) corrections. This residual field is estimated, assuming that it is axially symmetric. The steady field calculated in this way has an equatorial value of about 40 nT.

Kawasaki, K.; Cain, J. C.; Peters, R. D.

250

The Changing Shape of the AAS  

NASA Astrophysics Data System (ADS)

What is the astronomical workforce like? Where do astronomers work? How old are they? How permanent are their jobs? As we move into a period of increased uncertainty in federal funding for science it is important to know the answers to these questions. There are four sources of information for answers: 1. Information from the AAS membership database. 2. A survey of the AAS membership. 3. Surveys of samples of the AAS membership by AIP. 4. Information from the NRC and NSF. We have gender and age data from 1. A survey of the AAS membershWe will have age and gender data from 1. We will complete and analyze a new membersip survey shortly. The latest AIP data is from 1994. They will do a new sample in 1996. Much of the NRC data is aggregated with physics, and that does not give information about astronomers. Nevertheless, we do have some interesting information. The ages and genders of AAS members are available for 1972, 1990 and 1995. The time sequence provides an interesting look at the AAS. For instance, from 1990 to 1995 the number of women in each 5-year age group below the the age of 65 increased. Contrary to popular perception, women are not leaving the Society as they get older. However, the number of men actually decreased in each age group above the age of 35. This and other interesting trends will be discussed.

Boyce, P. B.

1995-12-01

251

Stress corrosion cracking susceptibility of friction stir welded AA7075–AA6056 dissimilar joint  

Microsoft Academic Search

Two aluminium alloys, AA7075 and AA6056, were friction stir welded, with the AA7075 alloy placed on the advancing side of the welding tool. Microstructural observations revealed the development of a recrystallised fine-grained weld nugget, with two different grain sizes, resulting from the two different base materials. Slow strain rate tensile (SSRT) tests in air have shown that the weld nugget

P. Bala Srinivasan; W. Dietzel; R. Zettler; J. F. dos Santos; V. Sivan

2005-01-01

252

Geomagnetically Induced Currents: Progress and Issues  

NASA Astrophysics Data System (ADS)

Geomagnetically induced currents (GIC) are a hazard to conducting networks such as high-voltage power and pipeline grids. GIC have been known for decades to affect power systems at higher latitudes (e.g. Europe and North America), although more recently GIC have also been found to affect power networks at middle and lower latitudes. Mitigating the effects of GIC remains an issue for the power and pipeline industries and for governments concerned with the societal and economic implications. To understand, e.g. to model and predict, GIC in conducting grids needs expertise drawn from electrical engineering, geophysics and space weather science - a truly multi-disciplinary undertaking. In terms of geophysics and space physics, issues such as Earth structure (e.g. 3D versus 1D mantle and lithospheric conductivity structure), ocean/continent conductivity contrasts, ionospheric current systems and their variability and Sun-Earth magnetic interactions are all relevant. The start of solar cycle 24 provides an opportune time to consider the status of GIC research and to assess what new studies are required in geophysical modelling and in hazard analysis. What do we need to improve on to better specify/predict GIC flowing in power grids, from ‘up-stream' observations of coronal mass ejections through to geomagnetic field measurements made during magnetic storms? In this invited review we will consider aspects of a) Measurement: how do we measure GIC in grids; b) Analysis: how do measured GIC relate to geophysical and space physics data; c) Modelling: what methods exist for modelling GIC, again in relation to other data, and how accurate are models; and d) Prediction: how predictable are GIC and what are the implications for, e.g., the power industry and national governments. We will review the more recent developments in GIC and related geomagnetism and space weather science. We will outline what issues are widely believed to now be understood and what issues remain to be addressed. Throughout, the relationship between GIC studies and geomagnetism science in general will be stressed. Issues around providing GIC-related services to industry will also be mentioned and a proposed study of GIC in the pan-European high-voltage power grid will be described.

Thomson, Alan

2010-05-01

253

Geographical localisation of the geomagnetic secular variation  

NASA Astrophysics Data System (ADS)

Directly observed changes in Earth's magnetic field occur most prominently at low latitudes beneath the Atlantic hemisphere, while the Pacific is comparatively quiet. This striking hemispheric asymmetry in geomagnetic secular variation is a consequence of the geographical localisation of intense, westward moving, magnetic flux patches at the core surface. Despite its successes in explaining the main morphological properties of Earth's magnetic field, self-consistent numerical modelling of the geodynamo has so far failed to reproduce this field variation pattern. Furthermore its magnetohydrodynamic origin, an essential pre-requisite for predicting the field evolution over the future decades, has been unclear. In this presentation we report on results obtained with numerical dynamos where we modify the treatment of mechanical boundary conditions, and impose heterogeneous thermochemical boundary control from either, or both, the inner-core boundary and the core-mantle boundary. In addition to presenting an Earth-like magnetic field morphology, these new numerical models also reproduce the morphology and localization of geomagnetic secular variation. In our models, the conservation of the angular momentum in the coupled inner-core / outer core / mantle system (the inner core and the mantle being held together by gravitational coupling) creates a westward columnar gyre circling around the inner core, which localises the secular variation in a narrow latitudinal band. An additional heterogeneous thermochemical boundary control distorts this gyre (the strongest distortion being obtained with inner core heterogeneous control) and localises the field changes in a hemispherical longitudinal sector. The two effects combine to recreate the observed localisation of geomagnetic secular variation in both longitude and latitude as a reult of a westward, columnar, eccentric gyre that penetrates throughout the outer core in a manner reminiscent of recent flow inversions. We also characterise the azimuthal drift of magnetic field structures using a Radon transform method, and find overall agreement between the model and geomagnetic data previously processed in the same way. Our results suggest that conservation of angular momentum and heterogeneous thermochemical boundary control in the coupled inner core / outer core / mantle system are central to understanding how Earth's magnetic field currently evolves.

Aubert, Julien; Finlay, Christopher; Fournier, Alexandre

2013-04-01

254

Advanced Theory of Deep Geomagnetic Sounding  

NASA Astrophysics Data System (ADS)

Advanced Theory of Deep Geomagnetic Sounding is a specialized treatise that covers recent work, mostly from the Soviet Union, on the theory, analysis, and interpretation of natural source electromagnetic induction processes in complex geological structures, with an emphasis on subsurface conductive anomalies. The scope of the book is limited, as suggested by the title, and the authors stress the application of electromagnetic principles to the study of regional geology and deep earth structure rather than surface exploration. The book is clearly aimed at the practicing specialist rather than the graduate student attempting to learn about the broader field of electromagnetic geophysics.

Chave, Alan D.

255

Homocysteine induced cardiovascular events: a consequence of long term anabolic-androgenic steroid (AAS) abuse  

PubMed Central

Objectives The long term effects (>20?years) of anabolic?androgenic steroid (AAS) use on plasma concentrations of homocysteine (HCY), folate, testosterone, sex hormone binding globulin (SHBG), free androgen index, urea, creatinine, haematocrit (HCT), vitamin B12, and urinary testosterone/epitestosterone (T/E) ratio, were examined in a cohort of self?prescribing bodybuilders. Methods Subjects (n?=?40) were divided into four distinct groups: (1) AAS users still using AAS (SU; n?=?10); (2) AAS users abstinent from AAS administration for 3?months (SA; n?=?10); (3) non?drug using bodybuilding controls (BC; n?=?10); and (4) sedentary male controls (SC; n?=?10). Results HCY levels were significantly higher in SU compared with BC and SC (p<0.01), and with SA (p<0.05). Fat free mass was significantly higher in both groups of AAS users (p<0.01). Daily energy intake (kJ) and daily protein intake (g/day) were significantly higher in SU and SA (p<0.05) compared with BC and SC, but were unlikely to be responsible for the observed HCY increases. HCT concentrations were significantly higher in the SU group (p<0.01). A significant linear inverse relationship was observed in the SU group between SHBG and HCY (r?=??0.828, p<0.01), indicating a possible influence of the sex hormones in determining HCY levels. Conclusions With mounting evidence linking AAS to adverse effects on some clotting factors, the significantly higher levels of HCY and HCT observed in the SU group suggest long term AAS users have increased risk of future thromboembolic events.

Graham, M R; Grace, F M; Boobier, W; Hullin, D; Kicman, A; Cowan, D; Davies, B; Baker, J S

2006-01-01

256

Development of Geomagnetic Data Assimilation Framework: the Challenges and Progress  

NASA Astrophysics Data System (ADS)

The scientific significance of assimilating surface geomagnetic observations into numerical geodynamo models is most obvious for the improvements that can be made to the models: observations can be used to constrain and identify appropriate dynamics for numerical modeling, and to create a dynamically consistent estimate of the state of the Earth's core. This estimate is an essential component needed in order to predict Earth's magnetic environment changes. Supported by NASA and NSF, research groups in NASA GSFC, UMBC and Harvard University are working together to establish a framework for geomagnetic data assimilation. Geomagnetic data assimilation faces new challenges in geomagnetism and geodynamo studies, because the work must necessarily bring together numerical modeling and surface observations, using an assimilation algorithm. These challenges include the differences between the parameter domains used in numerical dynamo modeling and that appropriate for the Earth's core. Also, surface observations can only provide a record on part of the poloidal magnetic field over a fraction of magnetic free decay time of the Earth's core. But foremost, we need an appropriate assimilation algorithm that will allow us to gain insight on model errors and the impact of observations on the physical quantities in the Earth's core. Our current effort involves three main projects: (1) synthetic geomagnetic data assimilation using model generated 'data', aiming at understanding the impact of parameter differences on geomagnetic data assimilation; (2) ensemble error covariance estimation, obtaining insight on how the corrections to the poloidal magnetic field at the core-mantle boundary (CMB) are correlated with other physical quantities; (3) geomagnetic data assimilation tests using real surface geomagnetic records (spectral coefficients from ufm and comprehensive field models) and an optimal interpolation scheme, to examine how numerical dynamo solutions are changed by the surface observations on time scales of several hundred years. These efforts lead to the development of the first geomagnetic data assimilation framework, which includes the three major components: geomagnetic field modeling, geodynamo modeling and data assimilation.

Kuang, W.; Tangborn, A.; Sun, Z.; Liu, D.; Jiang, W.; Sabaka, T.; Bloxham, J.

2005-12-01

257

Surface electric fields and geomagnetically induced currents in the Scottish Power grid during the 30 October 2003 geomagnetic storm  

Microsoft Academic Search

A surface electric field model is used to estimate the UK surface E field during the 30 October 2003 severe geomagnetic storm. This model is coupled with a power grid model to determine the flow of geomagnetically induced currents (GIC) through the Scottish part of the UK grid. Model data are compared with GIC measurements at four sites in the

Alan W. P. Thomson; Allan J. McKay; Ellen Clarke; Sarah J. Reay

2005-01-01

258

Geomagnetically induced currents in the New Zealand power network  

NASA Astrophysics Data System (ADS)

Adverse space weather conditions have been shown to be directly responsible for faults within power networks at high latitudes. A number of studies have also shown space weather to impact power networks at lower latitudes, although most of these studies show increases in GIC activity within networks not directly related to hardware faults. This study examines a GIC event that occurred in New Zealand's South Island power network on 6th November 2001. A transformer failure that occurred during this day is shown to be associated with a change in the solar wind dynamic pressure of nearly 20 nPa. Measurements of GICs recorded on the neutral lines of transformers across the Transpower network during this event show good correlation with a GIC-index, a proxy for the geoelectric field that drives GIC. Comparison of this event with GIC activity observed in the Transpower network during large space weather storms such as the "2003 Halloween storm," suggests that solar wind shocks and associated geomagnetic sudden impulse (SI) events may be as hazardous to middle latitude power networks as GIC activity occurring during the main phase of large storms. Further, this study suggests that the latitudinal dependence of the impacts of SI events on power systems differs from that observed during large main phase storms. This study also highlights the importance of operating procedures for large space weather events, even at middle latitude locations.

Marshall, R. A.; Dalzell, M.; Waters, C. L.; Goldthorpe, P.; Smith, E. A.

2012-08-01

259

The dynamic response of geomagnetic sudden commencement to tectonic zone and large earthquakes in China  

Microsoft Academic Search

Based on the skin effect of EM waves, geomagnetic storm variations can be used to study the subsurface tectonic structure and faulting to have information of penetration view of the earth's interior. We collected geomagnetic storm report data for 8 years 2000-2007 from 35 geomagnetic stations in China and calculated the amplitude of the vertical component of geomagnetic storm sudden

X. Zeng; J. Zheng; Z. Wang; Y. Lin

2009-01-01

260

Magnetic Flux Transport and Pressure Variations at Magnetotail Plasma Flow Bursts during Geomagnetically Quiet Times  

NASA Astrophysics Data System (ADS)

The fast plasma flows in the geomagnetotail are observed during both geomagnetically active and quiet times. However, it has been unclear about the fundamental difference in the plasma fast flows between at two different geomagnetic conditions, that is, the generation mechanism of, and pictures of the energy transport and balance at the fast plasma flows. Magnetic reconnection in the magnetotail has been believed as one of the most possible mechanisms to generate the fast plasma flows regardless of the geomagnetic conditions. Recently, Nowada et al. [2012], however, demonstrated that the magnetotail magnetic reconnection does not always contribute to the generation of the fast plasma flows at geomagnetically quiet times based on the THEMIS measurements. It is very important to reveal how the energy transport and balance in the magnetotail in association with these plasma fast flows are on obtaining a clue to elucidate an essential difference in the plasma fast flows between during active and quiet geomagnetic conditions. Based on three events of the magnetotail plasma flow bursts, which are transient fast plasma flows with the durations between 1 and 2 minutes, during geomagnetically quiet times, observed by THEMIS, we examined detailed variations of the electric field as a proxy of the flux transport aspect, and associated pressure. The main characteristics of these events are shown as follows; 1) the GSM-X component of the plasma velocity (Vx) was higher than 300 km/s 2) associated parallel (V//) and perpendicular (V?) velocities to the local magnetic field line were higher than 200 km/s 3) the flow bursts were observed during which AL and AU indices were lower than 40 nT, and simultaneous Kp index range was between -1 and 1. For almost events, the parallel (E//) and perpendicular (E?) components of the electric field to the local magnetic field line were much stronger than the dawn-dusk electric field component (Ey). This result implies that a larger amount of the magnetic flux was transported into the parallel and perpendicular directions to the local magnetic field line than the dawn-dusk direction at the flow bursts. However, in the Ey component, the contribution from the dawn-to-dusk electric field (VxBz) was much greater than that from the dusk-to-dawn component (VzBx). Furthermore, for two events, significant reduction of the plasma pressure, and enhancement of the north-south magnetic field component (Bz) were observed at/near the flow bursts. Simultaneous total pressure was well-balanced, indicating that the magnetotail during the plasma flow bursts was in the state of equilibrium. Based on these results, "bubble" might play a crucial role for generating the plasma flow bursts at geomagnetically quiet times. Reference: Nowada, M., S. -Y. Fu, G. K. Parks, Z. -Y. Pu, V. Angelopoulos, C. W. Carlson, H. -U. Auster (2012), Plasma flow bursts in the magnetotail during geomagnetically quiet times 2: Relation to the magnetic reconnection and substorm process, to be submitted to Journal of Geophysical Research -Space Physics-. Corresponding Author : Motoharu Nowada nowada@pku.edu.cn

Nowada, M.; Fu, S.-Y.; Parks, G. K.; Pu, Z.-Y.; Angelopoulos, V.; Carlson, C. W.; Auster, H.-U.

2012-04-01

261

Geomagnetic Core Field Secular Variation Models  

NASA Astrophysics Data System (ADS)

We analyse models describing time changes of the Earth's core magnetic field (secular variation) covering the historical period (several centuries) and the more recent satellite era (previous decade), and we illustrate how both the information contained in the data and the a priori information (regularisation) affect the result of the ill-posed geomagnetic inverse problem. We show how data quality, frequency and selection procedures govern part of the temporal changes in the secular variation norms and spectra, which are sometimes difficult to dissociate from true changes of the core state. We highlight the difficulty of resolving the time variability of the high degree secular variation coefficients (i.e. the secular acceleration), arising for instance from the challenge to properly separate sources of internal and of external origin. In addition, the regularisation process may also result in artificial changes in the model norms and spectra. Model users should keep in mind that such features can be mis-interpreted as the signature of physical mechanisms (e.g. diffusion). Finally, we present perspectives concerning core field modelling: imposing dynamical constraints (e.g. by means of data assimilation) reduces the non-uniqueness of the geomagnetic inverse problem.

Gillet, N.; Lesur, V.; Olsen, N.

2010-08-01

262

Nonlinear time series analysis of geomagnetic pulsations  

NASA Astrophysics Data System (ADS)

A detailed nonlinear time series analysis has been made of two daytime geomagnetic pulsation events being recorded at L'Aquila (Italy, L ? 1.6) and Niemegk (Germany, L ? 2.3). Grassberger and Procaccia algorithm has been used to investigate the dimensionality of physical processes. Surrogate data test and self affinity (fractal) test have been used to exclude coloured noise with power law spectra. Largest Lyapunow exponents have been estimated using the methods of Wolf et al. The problems of embedding, stability of estimations, spurious correlations and nonlinear noise reduction have also been discussed. The main conclusions of this work, which include some new results on the geomagnetic pulsations, are (1) that the April 26, 1991 event, represented by two observatory time series LAQ1 and NGK1 is probably due to incoherent waves; no finite correlation dimension was found in this case, and (2) that the June 18, 1991 event represented by observatory time series LAQ2 and NGK2, is due to low dimensional nonlinear dynamics, which include deterministic chaos with correlation dimension D2(NGK2) = 2.25 ± 0.05 and D2(NDK2) = 2.02 ± 0.03, and with positive Lyapunov exponents ?max (LAQ2) = 0.055 ± 0.003 bits/s and ?max (NGK2) = 0.052 ± 0.003 bits/s; the predictability time in both cases is ? 13 s.

Vörös, Z.; Verö, J.; Kristek, J.

263

Continental scale modelling of geomagnetically induced currents  

NASA Astrophysics Data System (ADS)

The EURISGIC project (European Risk from Geomagnetically Induced Currents) aims at deriving statistics of geomagnetically induced currents (GIC) in the European high-voltage power grids. Such a continent-wide system of more than 1500 substations and transmission lines requires updates of the previous modelling, which has dealt with national grids in fairly small geographic areas. We present here how GIC modelling can be conveniently performed on a spherical surface with minor changes in the previous technique. We derive the exact formulation to calculate geovoltages on the surface of a sphere and show its practical approximation in a fast vectorised form. Using the model of the old Finnish power grid and a much larger prototype model of European high-voltage power grids, we validate the new technique by comparing it to the old one. We also compare model results to measured data in the following cases: geoelectric field at the Nagycenk observatory, Hungary; GIC at a Russian transformer; GIC along the Finnish natural gas pipeline. In all cases, the new method works reasonably well.

Viljanen, Ari; Pirjola, Risto; Wik, Magnus; Ádám, Antal; Prácser, Ernö; Sakharov, Yaroslav; Katkalov, Juri

2012-09-01

264

Localized modeling of regional geomagnetic field attributes  

NASA Astrophysics Data System (ADS)

Geomagnetic features have been modeled by spherical harmonics. However, this global approach is best applied where the data are uniformly distributed over the globe. Satellite observations meet this requirement, but unequally distributed data cannot be easily adopted in global modeling. A spherical cap analysis has been used as an alternative in regional modeling for geopotential fields and recently this technique was well updated by Thebault et al. (2006) and Thebault (2008). In this study, we introduce a localized analysis technique that has been effectively used to model satellite gravity data for small cap regions of the Earth and Moon (Han et al.,2008; Han, 2009). The orthogonality of basis functions is valid in the area of interest so that the spectral properties are maintained with a considerably fewer number of coefficients that are basically transformed spherical harmonic coefficients. These so-called, Slepian functions (eigenvectors) also have been used as multitapers to model signals over windowed areas of the globe as well as the 2-D Fourier plane. As an application, we consider the regional secular variations since the year of 1590 from the geomagnetic Gauss coefficients of the gufm1 model (Jackson et al.2000), over South America and Antarctica.

Kim, H.; von Frese, R. R.

2009-12-01

265

Geomagnetic excursions reflect an aborted polarity state  

NASA Astrophysics Data System (ADS)

Geomagnetic excursions represent short episodes of a few thousand years at most during which the field considerably exceeds its normal range of variability during a polarity state. Paleomagnetic records have now been obtained with extremely high temporal resolution which have improved our knowledge of these short events. We have compiled the most detailed records of excursions that had occurred during the Brunhes and Matuyama chrons. We show that virtual geomagnetic poles (VGPs) of at least one record of each event are able to reach the opposite polarity. In the next step, we have computed different simulations of excursions during which the dipole progressively vanishes before growing back without reversing. This scenario produces very few reversed directions which are only visible at some latitudes. We infer that it is impossible to reach the ratio of reversed to intermediate VGPs present in the paleomagnetic records if the excursions were not associated with a short period of reversed dipole field. Therefore, excursions should be regarded as two successive reversals bracketing an aborted polarity interval. We propose that the same underlying mechanisms prevail in both situations (excursions or reversals) and that below a certain strength the field reaches an unstable position which preludes either the achievement of a reversal or its return to the former polarity.

Valet, Jean-Pierre; Plenier, Guillaume; Herrero-Bervera, E.

2008-10-01

266

AA2618 and AA7075 alloys superplastic transition in isothermal hot-deformation tests  

Microsoft Academic Search

This work deals with the isothermal deformation behaviour of two aluminium alloys, AA2618 and AA7075. These materials were integrated by mechanical tests, differential thermal analysis (DTA), and metallographic examination. Stress–relaxation and compression tests confirmed that both alloys exhibit a superplastic behaviour, characterised by a large elongation before failure and at low flow stress. Ranges of temperature and strain rate, at

C. Testani; F. M. Ielpo; E. Alunni

2000-01-01

267

A new versatile method for modelling geomagnetic induction in pipelines  

NASA Astrophysics Data System (ADS)

Geomagnetic induction drives telluric currents in pipelines and creates fluctuations in pipe-to-soil potentials (PSP) that interfere with pipeline surveys and create conditions where corrosion is more likely to occur. To understand the process of geomagnetic induction and determine the severity and location of troublesome effects requires the ability to model geomagnetic induction in realistic pipeline networks. Previous modelling work, based on transmission line theory, has provided some insights into the process but has to be customized for each situation. This paper presents a new versatile modelling technique that can be easily applied to any pipeline network. The essential part of the new method is the development of an equivalent-pi circuit for geomagnetic induction in a pipeline section. A complex pipeline network can then be represented as a set of equivalent-pi circuits that are combined to form a nodal admittance network comprising connections between nodes and to ground from each node. The nodal admittance matrix method is then used to determine the voltages everywhere in the pipeline system. Sample results are presented for geomagnetic induction in an example pipeline. It is shown how the modelling results can be combined with electric fields calculated from geomagnetic observatory data to determine the PSP variations that occur during geomagnetic disturbances.

Boteler, D. H.

2013-04-01

268

Geomagnetic jerks as chaotic fluctuations of the Earth's magnetic field  

NASA Astrophysics Data System (ADS)

The geomagnetic field is chaotic and can be characterized by a mean exponential time scale < ? > after which it is no longer predictable. It is also ergodic, so time analyses can substitute the more difficult phase space analyses. Taking advantage of these two properties of the Earth's magnetic field, a scheme of processing global geomagnetic models in time is presented, to estimate fluctuations of the time scale ?. Here considering that the capability to predict the geomagnetic field is reduced over periods of geomagnetic jerks, we propose a method to detect these events over a long time span. This approach considers that epochs characterized by relative minima of fluctuations in time scale ?, i.e., those periods when a geomagnetic field is less predictable, are possible jerk occurrence dates. We analyze the last 400 years of the geomagnetic field (covered by the Gufm1 model) to detect minima of fluctuations, i.e., epochs characterized by low values of the time scale. Most of the well known jerks are confirmed through this method and a few others have been suggested. Finally, we also identify some short periods when the field is less chaotic (more predictable) than usual, naming these periods as steady state geomagnetic regime, to underline their opposite behavior with respect to jerks.

Qamili, E.; de Santis, A.; Isac, A.; Mandea, M.; Duka, B.; Simonyan, A.

2013-04-01

269

Generation of 100-year geomagnetically induced current scenarios  

NASA Astrophysics Data System (ADS)

A series of 100-year extreme geoelectric field and geomagnetically induced current (GIC) scenarios are explored by taking into account the key geophysical factors associated with the geomagnetic induction process. More specifically, we derive explicit geoelectric field temporal profiles as a function of ground conductivity structures and geomagnetic latitudes. We also demonstrate how the extreme geoelectric field scenarios can be mapped into GIC. Generated statistics indicate 20 V/km and 5 V/km 100-year maximum 10-s geoelectric field amplitudes at high-latitude locations with poorly conducting and well-conducting ground structures, respectively. We show that there is an indication that geoelectric field magnitudes may experience a dramatic drop across a boundary at about 40°-60° of geomagnetic latitude. We identify this as a threshold at about 50° of geomagnetic latitude. The sub-threshold geoelectric field magnitudes are about an order of magnitude smaller than those at super-threshold geomagnetic latitudes. Further analyses are required to confirm the existence and location of the possible latitude threshold. The computed extreme GIC scenarios can be used in further engineering analyses that are needed to quantify the geomagnetic storm impact on conductor systems such as high-voltage power transmission systems. To facilitate further work on the topic, the digital data for generated geoelectric field scenarios are made publicly available.

Pulkkinen, A.; Bernabeu, E.; Eichner, J.; Beggan, C.; Thomson, A. W. P.

2012-04-01

270

MAXIMUM CORONAL MASS EJECTION SPEED AS AN INDICATOR OF SOLAR AND GEOMAGNETIC ACTIVITIES  

SciTech Connect

We investigate the relationship between the monthly averaged maximal speeds of coronal mass ejections (CMEs), international sunspot number (ISSN), and the geomagnetic Dst and Ap indices covering the 1996-2008 time interval (solar cycle 23). Our new findings are as follows. (1) There is a noteworthy relationship between monthly averaged maximum CME speeds and sunspot numbers, Ap and Dst indices. Various peculiarities in the monthly Dst index are correlated better with the fine structures in the CME speed profile than that in the ISSN data. (2) Unlike the sunspot numbers, the CME speed index does not exhibit a double peak maximum. Instead, the CME speed profile peaks during the declining phase of solar cycle 23. Similar to the Ap index, both CME speed and the Dst indices lag behind the sunspot numbers by several months. (3) The CME number shows a double peak similar to that seen in the sunspot numbers. The CME occurrence rate remained very high even near the minimum of the solar cycle 23, when both the sunspot number and the CME average maximum speed were reaching their minimum values. (4) A well-defined peak of the Ap index between 2002 May and 2004 August was co-temporal with the excess of the mid-latitude coronal holes during solar cycle 23. The above findings suggest that the CME speed index may be a useful indicator of both solar and geomagnetic activities. It may have advantages over the sunspot numbers, because it better reflects the intensity of Earth-directed solar eruptions.

Kilcik, A.; Yurchyshyn, V. B.; Abramenko, V.; Goode, P. R. [Big Bear Solar Observatory, Big Bear City, CA 92314 (United States); Gopalswamy, N. [NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Ozguc, A. [Kandilli Observatory and Earthquake Research Institute, Bogazici University, 34684 Istanbul (Turkey); Rozelot, J. P. [Nice University, OCA-Fizeau Dpt. Av. Copernic, 06130 Grasse (France)

2011-01-20

271

Geomagnetic storms: Potential economic impacts on electric utilities  

NASA Astrophysics Data System (ADS)

Geomagnetic storms associated with sunspot and solar flare activity can disturb communications and disrupt electric power. A very severe geomagnetic storm could cause a major blackout with an economic impact of several billion dollars. The vulnerability of electric power systems in the northeast United States will likely increase during the 1990s because of the trend of transmitting large amounts of power over long distance to meet the electricity demands of this region. A comprehensive research program and a warning satellite to monitor the solar wind are needed to enhance the reliability of electric power systems under the influence of geomagnetic storms.

Barnes, P. R.; Vandyke, J. W.

1991-03-01

272

Geomagnetic cutoff rigidities and geomagnetic coordinates appropriate for the Carrington flare Epoch  

Microsoft Academic Search

Using the trajectory-tracing technique for cosmic rays in the geomagnetic field, vertical cutoff rigidity values for a world grid have been determined for Epoch 1850. These values have been used to derive a world map of iso-rigidity contours that would have been appropriate for the era of the Carrington flare in September 1859. When comparing these iso-rigidity contours with those

M. A. Shea; D. F. Smart

2006-01-01

273

Oxygen Isotopic Stratigraphy and Geomagnetic Field Intensity  

NASA Astrophysics Data System (ADS)

Nick Shackleton intellectual leadership in isotope stratigraphy had profound implications for paleoclimatology and paleoceanography. What is not so well enough known is that Nick contributed also to significant advances in studies of variations of the Earth's magnetic field. The first link between the two disciplines was certainly the paper that he produced with Neil Opdyke in 1973. About twenty years later Nick Shackleton obtained a very detailed isotope stratigraphy after analyzing the oxygen isotopes of bulk sediment of two cores from the Somali basin characterized by high resolution records of relative paleointensity for the past 140 kyr. This stratigraphy allowed us to correlate these two records with other independent data from the Mediterranean sea and to propose that the signal which was recorded at the two locations was global and thus of geomagnetic origin. The fast growing database made possible a stacking of the results for the past 200 ka and then for the past 800 kyr. The resulting curve was constructed from 33 paleointensity records and Shackleton's isotopic records were essential in many cases. Indeed without high resolution stratigraphy much information could not be retrieved due to uncertainties in correlating different records. The results revealed the very variable character of the field with large 20 to 60 kyr oscillations and changes in amplitude that can exceed a factor of five, but no apparent periodicity. Short periods of very low intensity occur at more or less regular intervals (roughly every 100 kyr) and correspond with geomagnetic excursions. The next step was to obtain a much longer record that would document the field changes across reversals and during entire polarity intervals. The opportunity was met during ODP Leg 138 with the recovery of beautifully magnetized sequences that covered at least 4 Myr of geomagnetic history. Nick was responsible for correlating sedimentary columns taken at each site. He performed a tremendeous task by orbitally tuning the density variations for thousands of meters of sediment. This allowed us to correlate the paleointensity signals from several holes and to produce the first long dataset with a very accurate time-depth control. Very recently the accumulation of data made it possible to stack records from different oceans for the past 2 Myr and to extract features of field intensity which add significant constraints to the modelling of the geodynamo. Alternatively this curve can be used as a stratigraphic reference, similarly to isotopes records.

Meynadier, L.; Valet, J.

2004-12-01

274

Chronomics, neuroendocrine feedsidewards and the recording and consulting of nowcasts--forecasts of geomagnetics.  

PubMed

A multi-center four-hourly sampling of many tissues for 7 days (00:00 on April 5-20:00 to April 11, 2004), on rats standardized for 1 month in two rooms on antiphasic lighting regimens happened to start on the day after the second extremum of a moderate double magnetic storm gauged by the planetary geomagnetic Kp index (which at each extremum reached 6.3 international [arbitrary] units) and by an equatorial index Dst falling to -112 and -81 nT, respectively, the latter on the first day of the sampling. Neuroendocrine chronomes (specifically circadian time structures) differed during magnetically affected and quiet days. The circadian melatonin rhythm had a lower MESOR and lower circadian amplitude and tended to advance in acrophase, while the MESOR and amplitude of the hypothalamic circadian melatonin rhythm were higher during the days with the storm. The circadian parameters of circulating corticosterone were more labile during the days including the storm than during the last three quiet days. Feedsidewards within the pineal-hypothalamic-adrenocortical network constitute a mechanism underlying physiological and probably also pathological associations of the brain and heart with magnetic storms. Investigators in many fields can gain from at least recording calendar dates in any publication so that freely available information on geomagnetic, solar and other physical environmental activity can be looked up. In planning studies and before starting, one may gain from consulting forecasts and the highly reliable nowcasts, respectively. PMID:16275503

Jozsa, R; Halberg, F; Cornélissen, G; Zeman, M; Kazsaki, J; Csernus, V; Katinas, G S; Wendt, H W; Schwartzkopff, O; Stebelova, K; Dulkova, K; Chibisov, S M; Engebretson, M; Pan, W; Bubenik, G A; Nagy, G; Herold, M; Hardeland, R; Hüther, G; Pöggeler, B; Tarquini, R; Perfetto, F; Salti, R; Olah, A; Csokas, N; Delmore, P; Otsuka, K; Bakken, E E; Allen, J; Amory-Mazaudin, C

2005-10-01

275

Chronomics, neuroendocrine feedsidewards and the recording and consulting of nowcasts--forecasts of geomagnetics  

PubMed Central

A multi-center four-hourly sampling of many tissues for 7 days (00:00 on April 5–20:00 to April 11, 2004), on rats standardized for 1 month in two rooms on antiphasic lighting regimens happened to start on the day after the second extremum of a moderate double magnetic storm gauged by the planetary geomagnetic Kp index (which at each extremum reached 6.3 international [arbitrary] units) and by an equatorial index Dst falling to ?112 and?81 nT, respectively, the latter on the first day of the sampling. Neuroendocrine chronomes (specifically circadian time structures) differed during magnetically affected and quiet days. The circadian melatonin rhythm had a lower MESOR and lower circadian amplitude and tended to advance in acrophase, while the MESOR and amplitude of the hypothalamic circadian melatonin rhythm were higher during the days with the storm. The circadian parameters of circulating corticosterone were more labile during the days including the storm than during the last three quiet days. Feedsidewards within the pineal-hypothalamic-adrenocortical network constitute a mechanism underlying physiological and probably also pathological associations of the brain and heart with magnetic storms. Investigators in many fields can gain from at least recording calendar dates in any publication so that freely available information on geomagnetic, solar and other physical environmental activity can be looked up. In planning studies and before starting, one may gain from consulting forecasts and the highly reliable nowcasts, respectively.

Jozsa, R.; Halberg, F.; Cornelissen, G.; Zeman, M.; Kazsaki, J.; Csernus, V.; Katinas, G.S.; Wendt, H.W.; Schwartzkopff, O.; Stebelova, K.; Dulkova, K.; Chibisov, S.M.; Engebretson, M.; Pan, W.; Bubenik, G.A.; Nagy, G.; Herold, M.; Hardeland, R.; Huther, G.; Poggeler, B.; Tarquini, R.; Perfetto, F.; Salti, R.; Olah, A.; Csokas, N.; Delmore, P.; Otsuka, K.; Bakken, E.E.; Allen, J.; Amory-Mazaudin, C.

2008-01-01

276

Do ambient electromagnetic fields affect behaviour? A demonstration of the relationship between geomagnetic storm activity and suicide.  

PubMed

The relationship between ambient electromagnetic fields and human mood and behaviour is of great public health interest. The relationship between Ap indices of geomagnetic storm activity and national suicide statistics for Australia from 1968 to 2002 was studied. Ap index data was normalised so as to be globally uniform and gave a measure of storm activity for each day. A geomagnetic storm event was defined as a day in which the Ap index was equal to or exceeded 100 nT. Suicide data was a national tally of daily male and female death figures where suicide had been documented as the cause of death. A total of 51 845 males and 16 327 females were included. The average number of suicides was greatest in spring for males and females, and lowest in autumn for males and summer for females. Suicide amongst females increased significantly in autumn during concurrent periods of geomagnetic storm activity (P = .01). This pattern was not observed in males (P = .16). This suggests that perturbations in ambient electromagnetic field activity impact behaviour in a clinically meaningful manner. The study furthermore raises issues regarding other sources of stray electromagnetic fields and their effect on mental health. PMID:16304696

Berk, Michael; Dodd, Seetal; Henry, Margaret

2006-02-01

277

A Multiscale Power Spectrum for Geomagnetic Modeling  

NASA Astrophysics Data System (ADS)

Degree Variances are a frequently used tool to analyze the internal geomagnetic field. They describe the contribution of a spherical harmonic degree n to the mean square value of the magnetic field b. In this talk we want to introduce multiscale variances that can be interpreted as the influence of a scale-dependent region on the mean square value of b. The foundation for their definition is an expansion of the magnetic field in terms of spatially localizing wavelets. In this sense the multiscale variances form a spatially-oriented counterpart to the frequency-oriented degree variances. We investigate the corresponding multiscale power spectrum for the MF7 model and the CHAOS-4 model as well as for different continental and oceanic regions. The multiscale variances reflect the expected weaker power of the crustal field over oceanic regions and show differences between the MF7 model and the CHAOS-4 model at higher scales.

Gerhards, Christian

2013-04-01

278

Geomagnetic Effect Caused by 1908 Tunguska Event  

NASA Astrophysics Data System (ADS)

The analysis of the magnetograms of Irkutsk observatory on the 30th June 1908 showed that the explosion of Tunguska bolide was accompanied by variations of the Earth’s magnetic field, which were being continued for several hours [1]. Irkutsk geophysical observatory is located approximately in 950 km to the southeast from the point of Tunguska explosion and it was nearest point, where the continuous recording of the components of the geomagnetic field was in progress. We suppose that it was caused by magnetic field of the current system, generated in the E-layer of ionosphere by gas dynamical flow after the Tunguska explosion [2]. Plunging through the atmosphere, cosmic body forms a hot rarefied channel behind it; the hydrostatic equilibrium of pressure in the channel becomes broken. The particles of the body vapor and atmospheric air, involved in the motion, lift along this channel upward (so-called plume). In the rarefied layers of the atmosphere they move along the ballistic trajectories in the gravitational field. While falling down gas loses its kinetic energy in dense layers of the atmosphere, which is converted into thermal energy. Then the reflected shock wave is formed. The gas heated in it rises up and all these processes repeat. The effects of heating and ionization of gas at height of 100 km, caused by the oscillations in the atmosphere, can lead to a distortion of the existing current system in ionosphere and generation of new ones. Since the Tunguska body had an oblique trajectory, the plume was ejected in the direction opposite to motion of Tunguska body and provided ionized region at the distance about 700 km from the epicenter at time moment 400 seconds after explosion. Gas dynamical simulation and estimates of the plume parameters have been fulfilled to calculate conductivity profiles and the electric field. Magnetic field of the induced current system has been obtained by the numerical simulation of Maxwell’s equations. Analysis of calculation results of this current system shows that an unique azimuth of trajectory of the body exists, for which the variations of all three components of the geomagnetic field do not contradict to the observation data. This azimuth is equal to 306 degrees, while other estimates are in the range of 290-344 degrees. This idea of the atmospheric plume ejected along the trajectory and ionization in the upper atmosphere, caused by the following atmospheric oscillations, could explain the geomagnetic effect both in general and locally in Irkutsk observatory: the time delay and the variations of all magnetic field components. Binding of simulation results of observation data also allows us to select the unique trajectory azimuth for Tunguska body. References: [1] Ivanov K.G. The Geomagnetic phenomena, which were being observed on the Irkutsk magnetic observatory, following the explosion of the Tunguska meteorite //Meteoritika. 1961. Iss. XXI. P.46-49 (in Russian). [2] Losseva T., Merkin V., Nemtchinov I. Estimations of the Aeronomical and Electromagnetic Disturbances in the E-layer of the Ionosphere, caused by Tunguska Event // AGU Fall Meeting. 1999. SA32A-09.

Losseva, T. V.; Kuzmicheva, M. Y.

2010-12-01

279

Evidence of transmission of polar electric fields to the low latitude at times of geomagnetic sudden commencements  

NASA Astrophysics Data System (ADS)

HF Doppler measurements of geomagnetic sudden commencements (sc) are presented to demonstrate the transmission of the polar electric field responsible for the preliminary reverse impulse (PRI) to a low latitude. The data were gathered in Japan with the geomagnetic latitude of the apex of the HF signal propagation path at about 25 deg. The Doppler frequency deviations (DFD) for the observed PRIs were equivalent to those previously determined for high latitudes. The negative value for the nighttime deviation was caused by a dusk-to-dawn polar electric field that caused the PRI, which were associated with a worldwide increase in the AE index. The conclusion is that the electric field generated in the magnetosphere at the onset of an sc is transmitted to low latitudes via the polar ionosphere by means of hydromagnetic waves. The DFDs started simultaneously at high and low latitudes during the day, indicating that the westward electric field is transmitted directly from the magnetosphere by compressional hydromagnetic waves.

Kikuchi, T.

1986-03-01

280

Statistical relations among substorm occurrence, geomagnetic pulsations and particle precipitation pulsations as seen at Indian Antarctic station Maitri  

NASA Astrophysics Data System (ADS)

Substorms at the auroral latitudes trigger a peculiar dynamics where a sharp depression in the AL index is observed along with an abrupt absorption in the cosmic noise due to ionospheric disturbances caused by high electron precipitation. However, such abrupt absorption may not always be seen during a substorm. Maitri (70°45' S, 11°45'E, geographic; 66°S, 53°21E, geomagnetic) is considered to be located at sub-auroral latitude and behaves as an auroral station during disturbed period. India has recently installed an Imaging Riometer at this sub auroral location. Using the data of cosmic noise intensity from Imaging riometer and the simultaneous magnetic field variation from digital flux gate magnetometer (DFM), a statistical study was performed in corroboration with the prevailing interplanetary conditions. Pi2 geomagnetic pulsations often accompanied by pulsations in particle precipitation flux have been thoroughly analyzed. Diurnal and seasonal patterns of such events were also statistically examined.

Behera, Jayanta Kumar; Singh, Anand Kumar; Pathan, B. M.; Sinha, Ashwini Kumar; Rawat, Rahul

2012-07-01

281

Auroral Zone E-Region Electron Density Geomagnetic Storm Enhancements Predicted by the Empirical STORM-E Model  

NASA Astrophysics Data System (ADS)

Auroral nighttime infrared emission observed by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument onboard the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite is used to develop an empirical model of geomagnetic storm enhancements to E-region electron densities. The empirical model is called STORM-E. The proxy for characterizing the E-region response to geomagnetic forcing is NO+(v) volume emission rates (VER) derived from the TIMED/SABER 4.3 um channel limb radiance measurements. The storm-time response of the NO+(v) 4.3 um VER is most sensitive to auroral particle precipitation. A statistical database of storm-time to climatological quiet-time ratios of SABER-observed NO+(v) 4.3 um VER are fit to widely available geomagnetic indices using the theoretical framework of linear impulse-response theory. The STORM-E model provides a dynamic storm-time correction factor to adjust a known quiescent E-region electron density peak concentration for geomagnetic enhancements due to auroral particle precipitation. In this paper, the development of the E-region electron density storm-time correction factor is described. The STORM-E storm-time correction factor is fit to a single geomagnetic index. There are four versions of the STORM-E model. Each version is fit to one of the following indices: HP-, AE-, Ap-, or Dst. High-latitude incoherent scatter radar (ISR) E-region electron density measurements are compared to STORM-E predictions for various geomagnetic storm periods during solar cycle 23. These comparisons show that STORM-E significantly improves the prediction of E-region electron density enhancements due to auroral particle precipitation, in comparison to the nominal International Reference Ionosphere (IRI) model or to the quiet-time baseline electron density concentrations measured by ISR. The version of the STORM-E model based on the fit to the Ap-index is now incorporated into the 2012 release of the IRI.

Mertens, Christopher; Bilitza, Dieter; Xu, Xiaojing

2012-07-01

282

Was the Ancient Geomagnetic Field Dipolar?  

NASA Astrophysics Data System (ADS)

One of the most useful assumptions in paleomagnetism is that the time-averaged geomagnetic field is closely approximated by a geocentric axial dipole (GAD). This has been found to be true for at least the last 5 million years with the largest non-GAD contribution to the spherical harmonic expansion generally being of the order of 5%. For the more ancient past, it is difficult to test the GAD (or any other field) hypothesis owing to plate motions, rock deformation and accumulating problems of overprinting. Although most paleomagnetic studies make the implicit assumption of a GAD field, several recent studies have called the essential GAD nature of the ancient field into question and have suggested large (up to 20%) contributions of the axial octupolar term to the geocentric axial dipole in the spherical harmonic expansion even in the Cenozoic. In this paper, we develop a new statistical model for the geomagnetic field to diagnose directional dispersion resulting from sedimentary inclination error, a widespread process that plausibly explains many of the observed discrepancies from the GAD field hypothesis. We also present a methodology to correct the resulting persistent shallow bias. Application of this technique to one of the few published studies from the Cenozoic of Asia with adequate data shows that the reported discrepancies from a GAD field in this region are most probably due to sedimentary inclination error rather than a non-GAD field geometry or undetected crustal shortening. Although non-GAD fields cannot in general be strongly rejected (actually, only GAD is a well posed and testable, i.e., refutable, hypothesis), the principle of least astonishment requires us to consider plausible geological mechanisms such as sedimentary inclination error as the cause of persistent shallow bias prior to the very ``expensive" option of throwing out the GAD hypothesis.

Tauxe, L.; Kent, D. V.

2003-12-01

283

[Biphasic response of the human nervous system to geomagnetic storms studied by EEG].  

PubMed

In two subjects: a male phlegmatic, 56, and a female melancholic, 22, the EEG was recorded at resting. The EEG patterns were juxtaposed with the geomagnetic activity index Ar and the solar activity index SF, as well as between themselves. The results revealed qualitatively similar biphasic responses: a generalised diminishing of the EEG spatial synchronisation and, on the next day, a generalised augmentation of the phenomenon, as compared with a prolonged quiet period. A general unspecific stress response is supposed to underlie the aforementioned dynamics, whereas a reduced cortical tone during a magnetic storm and an enhanced one after its cessation correspond to the two phases observed. Specifics of responses in both subjects corresponded to their individual profiles of interhemisphere asymmetry. PMID:11386154

Belov, D P; Getmanenko, O V; Kiselev, B V

2001-03-01

284

On the terms of geomagnetic daily variation in Antarctica  

NASA Astrophysics Data System (ADS)

The target of this work is to investigate the nature of magnetic perturbations produced by ionospheric and magnetospheric currents as recorded at high-latitude geomagnetic stations. In particular, we investigate the effects of these currents on geomagnetic data recorded in Antarctica. To this purpose we apply a mathematical method, known as Natural Orthogonal Composition, to analyze the magnetic field disturbances along the three geomagnetic field components (X, Y and Z) recorded at Mario Zucchelli Station (IAGA code TNB; geographic coordinates: 74.7° S, 164.1° E) from 1995 to 1998. Using this type of analysis, we characterize the dominant modes of the geomagnetic field daily variability through a set of empirical orthogonal functions (EOFs). While such mathematically independent EOFs do not necessarily represent physically independent modes of variability, we find that some of them are actually related to well known current patterns located at high latitudes.

de Michelis, P.; Tozzi, R.; Meloni, A.

2009-06-01

285

Corrosion rates of buried pipelines caused by geomagnetic storms  

SciTech Connect

Telluric effects associated with geomagnetic field variations caused currents to flow in buried pipelines, which present a continuing problem for monitoring cathodic protection. Protection methods involving the application of a noncorrosive coating with cathodic protection should present the circulation of erratic currents. Nevertheless, often these currents cannot be compensated. During days of high geomagnetic activity, an excess of current that cannot be drained circulates along the pipe. This effect has a strong dependence on the electrical resistivity of the host soil, produces a strong current channeling along the pipes, and increases the risk of corrosion. A method was proposed to quantify the corrosion effects over the pipelines, assuming the geomagnetic field as the external source responsible for the erratic currents. Nondisturbed fields and geomagnetic storms were modeled and pipeline currents were calculated as a function of the characteristics of the soils and pipe sizes using a numerical code previously developed.

Osella, A.; Favetto, A.; Lopez, E.

1999-07-01

286

Interplanetary Magnetic Sector Polarity Inferred from Polar Geomagnetic Field Observations.  

National Technical Information Service (NTIS)

In order to infer the interplanetary sector polarity from observations at Thule and Godhavn abs In order to infer the interplanetary sector polarity from polar geomagnetic field diurnal variations, measurements were carried out at Godhavn and Thule (Denma...

E. Friis-christensen K. Lassen J. M. Wilcox W. Gonzalez D. S. Colburn

1971-01-01

287

The Association Between ULF Geomagnetic Fluctuations and Doppler Ionospheric Observations.  

National Technical Information Service (NTIS)

Published studies of ionospheric motions directly associated with geomagnetic variations have postulated three different models of the mechanism by which the interaction occurs. All the models predict relative amplitudes which agree with the observations ...

H. J. Duffus G. M. Boyd

1967-01-01

288

Notes on the Optics of Geomagnetic Recording Systems.  

National Technical Information Service (NTIS)

A survey is made of the optics in classical geomagnetic instruments using photographic recording to judge the importance which different imperfections may have for the quality of the recordings. Included in the survey are variometer lenses and mirrors, cy...

E. K. Lauridsen

1974-01-01

289

A model of geomagnetic secular variation for 1980-1983  

USGS Publications Warehouse

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.

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

1987-01-01

290

Geomagnetic Storm Forecasting Advances for the Electric Power Industry  

NASA Astrophysics Data System (ADS)

Geomagnetic disturbances may impact the operational reliability of electric power systems due to electromagnetic coupling from the geomagnetic environment causing Geomagnetically-induced currents (GIC) that disrupt operations of the large-scale infrastructure of modern power grids. These geomagnetic disturbances can be geographically widespread and can have rapid onsets, threatening the reliability of operations within a matter of minutes. Operators of critical infrastructures, such as electric power grids around the world, have been undertaking efforts to assess their vulnerability to these environments and incorporating continuous forecast models of the space environment into their operational control facilities. Significant advances have been made in understanding this interaction and in efforts to forecast and model the environment for power grid infrastructure operators. This presentation will provide a summary and overview of GIC forecasting and modeling advances.

Kappenman, J. G.

2002-05-01

291

Geomagnetically induced currents: The ultimate threat to system security  

Microsoft Academic Search

The effects - better expressed, the threats - of Geomagnetically Induced Currents (GICs) are now reasonably well known. GICs are supposed to be caused by electrically charged particles ejected from the Sun. These particles create ionospheric currents that \\

L. M. V. Pinto; J. Szczupak; M. A. Drummond; L. H. Macedo; L. M. Barreto

2005-01-01

292

Geomagnetic variation anomalies in north-western Italy  

Microsoft Academic Search

A preliminary geomagnetic variation data analysis has been made in the Piedmont-Ligurian area in north-western Italy. Data were collected by means of two instruments: an Askania portable variograph and a LaCour fixed station operated in the Roburent geomagnetic observatory. The portable variograph has been moved to several locations in north-western Italy. Parkinson vectors were drawn for 8, 20 and 60

Emanuele Bozzo; Antonio Meloni

1989-01-01

293

Detection and characterization of geomagnetic pulsations using HF ionospheric heating  

SciTech Connect

This paper describes the geomagnetic pulsations observed in the high-latitude ionosphere during an experiment dealing with the ionospheric generation of ELF/VLF EM waves in June and October 1987. There was clear evidence of geomagnetic pulsations intermixed with the ELF/VLF signals in both the magnitude and phase data. A simple simulation model is introduced to facilitate the interpretation of the data, and a procedure for characterizing the pulsation is described. 5 refs.

Lee, H.S.; Ferraro, A.J.; Olson, J.V. (Pennsylvania State Univ., University Park (USA) Alaska Univ., Fairbanks (USA))

1990-12-01

294

Behaviour of geomagnetic variations across the western ukraine  

Microsoft Academic Search

Since 1967, the staff of the Geophysical Institute of the Ukrainian Academy of Sciences and of affiliated organization in Lvov have been making observations of the geomagnetic field components across the territories of the Ukrainian Carpathians and the Volyno-Podolian plate. The field equipment IZMIRAN-4 and MEVS orientated in the geomagnetic co-ordinate system were used in recording the time variations of

I. M. Logvinov; S. N. Kulik; T. K. Burakhovich; A. I. Bilinskij; F. I. Sedova

1991-01-01

295

Characterization of electron beam welded AA2024  

Microsoft Academic Search

For aerospace manufacturing, the perseverance for improving performance (high strength to density ratio) and reducing weight and costs has motivated consideration of welding techniques applicable to aluminum alloys. During fusion welding of aluminum alloy (AA) 2024, the avoidance of defects (e.g., porosity, oxides, solidification cracking, undercutting) and the optimization of the microstructure-property characteristics are of critical concern. In this work,

P. Wanjara; M. Brochu

2010-01-01

296

Geomagnetic storm environments and effects on electrical systems  

SciTech Connect

This paper briefly reviews the behavior of the earth's magnetic field during a geomagnetic storm. Temporal variations of the B-field on the earths surface can induce an electric field in the earth, and this E-field will induce currents to flow in long, grounded conductors. Previous experience with geomagnetic storms indicates that such geomagnetically-induced currents can cause damage to power system components, and at times, can cause power blackouts. This paper presents some recently measured geomagnetic field variations, and illustrates how the induced electric field can be calculated, assuming a simple model of the imperfectly conducting earth. This calculation may be performed either in the time or in the frequency domain. Approximations to the time dependence of the geomagnetic field permit an analytical evaluation of the corresponding E-field in the earth, and this results in a simple expression for the transient Enfield. A knowledge of this Enfield is important in understanding the effects of geomagnetic storms on the power system, and in devising protection methods.

Tesche, F.M. (Tesche (F.M.), Dallas, TX (United States)); Barnes, P.R. (Oak Ridge National Lab., TN (United States))

1992-01-01

297

Geomagnetic storm environments and effects on electrical systems  

SciTech Connect

This paper briefly reviews the behavior of the earth`s magnetic field during a geomagnetic storm. Temporal variations of the B-field on the earths surface can induce an electric field in the earth, and this E-field will induce currents to flow in long, grounded conductors. Previous experience with geomagnetic storms indicates that such geomagnetically-induced currents can cause damage to power system components, and at times, can cause power blackouts. This paper presents some recently measured geomagnetic field variations, and illustrates how the induced electric field can be calculated, assuming a simple model of the imperfectly conducting earth. This calculation may be performed either in the time or in the frequency domain. Approximations to the time dependence of the geomagnetic field permit an analytical evaluation of the corresponding E-field in the earth, and this results in a simple expression for the transient Enfield. A knowledge of this Enfield is important in understanding the effects of geomagnetic storms on the power system, and in devising protection methods.

Tesche, F.M. [Tesche (F.M.), Dallas, TX (United States); Barnes, P.R. [Oak Ridge National Lab., TN (United States)

1992-11-01

298

Results of geomagnetic observations in Central Africa by Portuguese explorers during 1877 1885  

NASA Astrophysics Data System (ADS)

In this short contribution, geomagnetic measurements in Central Africa made by Capelo and Ivens - two Portuguese explorers - during the years 1877 and 1885 are provided. We show the scarce number of geomagnetic observation in Africa compiled until now. These Portuguese explorers performed a considerable amount of measurements of geomagnetic declination (44 measurements), inclination (50) and horizontal component (50) of the geomagnetic field. We compared the results attained by these keen observers with those derived from the global geomagnetic model by Jackson et al. [Jackson, A., Jonkers, A.,Walker, M., 2000. Four centuries of geomagnetic secular variation from historical records. Philos. Trans. R. Soc. Lond. 358, 957-990].

Vaquero, José M.; Trigo, Ricardo M.

2006-08-01

299

Statistical study of interplanetary condition effect on geomagnetic storms  

NASA Astrophysics Data System (ADS)

Based on the archive OMNI data for the period 1976-2000 an analysis has been made of 798 geomagnetic storms with D st < -50 nT and their interplanetary sources-large-scale types of the solar wind: CIR (145 magnetic storms), Sheath (96), magnetic clouds MC (62), and Ejecta (161). The remaining 334 magnetic storms have no well-defined sources. For the analysis, we applied the double method of superposed epoch analysis in which the instants of the magnetic storm beginning and minimum of D st index are taken as reference times. The well-known fact that, independent of the interplanetary source type, the magnetic storm begins in 1-2 h after a southward turn of the IMF ( B z < 0) and both the end of the main phase of a storm and the beginning of its recovery phase are observed in 1-2 h after disappearance of the southward component of the IMF is confirmed. Also confirmed is the result obtained previously that the most efficient generation of magnetic storms is observed for Sheath before MC. On the average parameters B z and E y slightly vary between the beginning and end of the main phase of storms (minimum of D st and D {/st *} indices), while D st and D {/st *} indices decrease monotonically proportionally to integral of B z and E y over time. Such a behavior of the indices indicates that the used double method of superposed epoch analysis can be successfully applied in order to study dynamics of the parameters on the main phase of magnetic storms having different duration.

Yermolaev, Yu. I.; Lodkina, I. G.; Nikolaeva, N. S.; Yermolaev, M. Yu.

2010-12-01

300

The influence of manmade noise and geomagnetic fluctuations on seismo-magnetic signatures  

NASA Astrophysics Data System (ADS)

In the frame of the South European Geomagnetic Array (SEGMA) chain we investigate the magnetic background with the scientific goal to identify and characterise seismo-magnetic signals. Therefore it is mandatory to differentiate between exogenic (atmospheric / ionospheric / magnetospheric) and endogenic (lithospheric) sources of magnetic variations together with instrumental behaviour. The SEGMA chain consists of five stations spread over mid- and south Europe, data are continuously provided for the last 10 years. The experience has shown that the signal-to-noise ratio of the individual stations depends both on location and time where manmade noise sources have to be considered carefully. Beside the local environments at the SEGMA stations we are considering several geomagnetic indices, e.g. AP-, KP- and DST index. In addition to various geomagnetic signals the possible seismic part of the variations has to be characterised. Reliable results are achieved through the multi-station SEGMA approach in combination with alternative datasets, e.g. from seismic and electromagnetic networks. Earthquake magnitude and distance to the sensors are the most important parameters, the ground conductivity profile is whenever possible, i.e. reliable measurements are available, considered. Long term observations and station comparisons have shown the quality figure of each SEGMA station. The S/N of the L'Aquila station (Italy) was sufficiently high to detect magnetic variations related to the L'Aquila magnitude M=6.3 earthquake, April 6, 2009. In comparison no seismic signals were detected on the other SEGMA stations. We conclude that possible seismic signals can be detected with the SEGMA multi-station network approach if the environmental conditions can be characterised.

Prattes, G.; Schwingenschuh, K.; Eichelberger, H. U.; Magnes, W.; Berghofer, G.; Stachel, M.; Besser, B.; Wolbang, D.; Vellante, M.; Villante, U.; Nenovski, P.

2012-04-01

301

Spherical cap harmonic analysis of geomagnetic secular variation over Canada 1960-1983  

NASA Astrophysics Data System (ADS)

The new technique of spherical cap harmonic anaylsis has enabled a model of secular variation to be constructed that applies to an area of over 30 million square kilometers and a time interval of over 20 years. This technique is a regional analog of the ordinary method of spherical harmonic analysis and ensures that the curl and divergence of the secular variation vector are zero. By making each harmonic coefficient a polynomial in time, the model provides both spatial and temporal continuity. The secular variation data, from 1960 to 1983, comprise 1227 first central differences of annual mean values from 24 observatories in Canada, United States, Greenland, and Iceland, and 939 first central differences from 138 Canadian and American repeat stations, divided by their respective time intervals. The secular variation model includes terms up to spatial index 4 and temporal degree 2. Although such a model allows for 75 coefficients, only 39 were found to be statistically significant. The temporal behavior of the model at observatories and repeat stations is compared on time plots to that of the secular variation data itself. The scatter about the regression model, or standard error of estimate, was 11.8 nT/yr. The model is required both to update aeromagnetic survey data for producing Canadian geomagnetic main field charts at 1985.0 and to provide annual change information for the extrapolation of those charts up to 1990. The average secular variations derived from the Definitive (DGRF) and Provisional (PGRF) International Geomagnetic Reference Fields agree well with the model, but the average secular variation for 1980-1985 from the predictive International Geomagnetic Reference Field (IGRF) does not.

Haines, G. V.

1985-12-01

302

[Vulnerability to atmospheric and geomagnetic factors of the body functions in healthy male dwellers of the Russian North].  

PubMed

In April 2009 through to November 2011, a Mars-500 satellite study of Russian Northerners (Syktyvkar citizens) was performed using the standard ECOSAN-2007 procedure evaluating the atmospheric and geomagnetic susceptibility of the main body functional parameters. Seventeen essentially healthy men at the age of 25 to 46 years were investigated. Statistical data treatment included correlation and single-factor analysis of variance. Comparison of the number of statistical correlations of the sum of all functional parameters for participants showed that most often they were sensitive to atmospheric pressure, temperature, relative humidity and oxygen partial pressure (29-35 %), and geomagnetic activity (28 %). Dependence of the functional parameters on the rate of temperature and pressure change was weak and comparable with random coincidence (11 %). Among the hemodynamic parameters, systolic pressure was particularly sensitive to space and terrestrial weather variations (29 %); sensitivity of heart rate and diastolic pressure were determined in 25 % and 21 % of participants, respectively. Among the heart rate variability parameters (HRV) the largest number of statistically reliable correlations was determined for the centralization index (32 %) and high-frequency HRV spectrum (31 %); index of the regulatory systems activity was least dependable (19 %). Life index, maximal breath-holding and Ckibinskaya's cardiorespiratory index are also susceptible. Individual responses of the functional parameters to terrestrial and space weather changes varied with partidpants which points to the necessity of individual approach to evaluation of person's reactions to environmental changes. PMID:23814894

Markov, A L; Zenchenko, T A; Solonin, Iu G; Bo?ko, E R

303

The correlation of the geomagnetic anomalies recorded at Muntele Rosu (Romania) Seismic Observatory with earthquake occurrence and solar magnetic storms (2000 - 2009)  

NASA Astrophysics Data System (ADS)

The paper is based on geomagnetic records made at Muntele Rosu Observatory (Romania), during the time interval from 2000 to date. The working data are represented by the geomagnetic field as recorded at Muntele Rosu Observatory and manual corrected emphasizing the missing data and by the seismic data, taken from the seismic bulletins of the National Institute for Earth Physics, for Vrancea source zone. First of all, in this paper we want to correct some conclusions given by previous studies that have associated magnetic anomalies due to the missing data or to the solar magnetic storms with the occurrence of Vrancea intermediate depth earthquakes, in the period 2000-2005. Because the investigated period is of 5 years, covering almost half of a complete solar cycle, the solar-terrestrial perturbations have fluctuated from extremely small values to extremely large values, providing a very good medium to observe the correlation of magnetic signals with solar perturbations. In order to discriminate local and global phenomena, the local geomagnetic data are compared with data provided by the INTERMAGNET Project, from 2 stations located outside the epicentral region, considered as reference stations (Surlari-SUA, Romania and Tihany-THY-Hungaria) and with the global geomagnetic indexes. The largest intermediate depth earthquake occurred in this time interval had the moment magnitude Mw=6.3 (2004) and the largest crustal event had the moment magnitude Mw=4.4 (2008) offering us the opportunity to investigate possible connections between the geomagnetic field behavior and the local crustal and sub crustal seismicity. That's why in the present paper we will also analyze these events and the corresponding geomagnetic anomalies.

Moldovan, Iren-Adelina; Otilia Placinta, Anca; Petruta Constantin, Angela; Septimiu Moldovan, Adrian

2010-05-01

304

Results of Russian geomagnetic observatories in the 19th century: magnetic activity, 1841-1862  

NASA Astrophysics Data System (ADS)

Hourly (spot readings) magnetic data (H- and D-components) were digitized from Russian yearbook tables for the years 1850-1862 from four observatories. The pdf pictures for digitization were taken by a normal digital camera. The database obtained consists of about 900 000 single data points. The time series of hourly magnetic values reveal slow secular variations (declination only) as well as transient and regular geomagnetic variations of external origin. The quality and homogeneity of the data is satisfactory. Daily Ak-indices were calculated using the index algorithm that has been earlier applied to 19th century data from Helsinki (Finland) as well as modern magnetic observatory recordings. The activity index series derived from the Russian data is consistent with earlier activity index series for 1850-1862. The digitized index data series derived in this study was extended back to 1841 by including magnetic C9 activity index data available from a Russian observatory (St. Petersburg). Magnetic data rescued here is well suitable for various reconstructions for studies of the long-term variation of the space weather in the 19th century.

Nevanlinna, H.; Häkkinen, L.

2010-04-01

305

7 CFR 51.596 - U.S. Grade AA.  

Code of Federal Regulations, 2013 CFR

...INSPECTION ACT FRESH FRUITS, VEGETABLES AND OTHER PRODUCTS 1,2 (INSPECTION, CERTIFICATION, AND STANDARDS) United States Consumer Standards for Celery Stalks Grades § 51.596 U.S. Grade AA. U.S. Grade AA shall...

2013-01-01

306

Validation Studies of the Active Australia Survey (AAS)  

Cancer.gov

Validation Studies of the Active Australia Survey (AAS) Heesch et al. 2011 See reference #124 Methods Relation between The Active Australia Survey (AAS) daily walking minutes and total physical activity (PA) minutes (walking, moderate-intensity PA and

307

Discrete Scale Invariance in Geomagnetic Data  

NASA Astrophysics Data System (ADS)

The geomagnetic field has recently been shown to exhibit scale-invariant features, most notably in terms of power laws, e.g., in power spectra and ranked intervals between dipole reversals. However, these scaling laws are merely a first approximation, leaving substantial residuals unexplained. With the aid of a novel technique (in principle applicable to any time series of sufficient length), additional information may be extracted that quantifies the characteristic scales of the studied process, that is, the preferred size(s) of the most important fluctuations and their associated timings. This so-called discrete scale invariance (DSI) betrays its presence by a logperiodic modulation of the underlying power law, and can be detected through a bootstrapping approach. Given an observed gamut of fluctuations over a studied period, a set of linearly incremental thresholds of absolute change is first defined, and the associated intervals between successive exceedances recorded, to be ranked by size on a log-log scale (thus yielding as many new datasets as there are thresholds). To all sets satisfying certain basic quality criteria, a power law fit is performed (negative gradient), and its residuals (unequally spaced on a log-scale) subjected to Lomb spectral analysis, which exploits this uneven spread. If a significant, coherent modulation is found, matrix inversion will yield the remaining wave parameters, and the associated topmost scaling stratum can then be identified as the highest point where the modulation intersects the power law from below. This level is stored with the set's (log-scaled) threshold, contributing to a meta-dataset that associates these preferred timings with their fluctuation threshold. After additional quality control of this set, a new power law fit is performed (positive gradient), and its residuals subjected to Lomb analysis and inversion. The resulting wave parameters yield the preferred scaling levels of the original observable and the associated timings. An additional feature of this approach is its potential predictive power above and below the observed range. Three independent geomagnetic datasets were examined to look for signatures of discrete scale invariance: the sequence of dipole reversal intervals from the Mesozoic to the present day (161-0 Ma, Gradstein & Ogg 1996); fluctuations in relative intensity over the last 2 Ma (SINT2000 dipole excursions, Valet, Meynadier & Guyodo 2005); and secular variation as captured by the historical field map gufm1 (1590-1990 A.D., Jackson, Jonkers & Walker 2000). Not only does each set exhibit significant DSI, but the recorded characteristic scales of both reversals and secular variation (individually) are quite well predicted by each of the other two datasets.

Jonkers, A.

2005-12-01

308

Immigration Index  

NSDL National Science Digital Library

Striving to become the "immigration resource directory on the net," the Immigration Index is a newly launched Website dedicated to news and information about immigration worldwide. Along with breaking headlines from a variety of news sources about immigration-related issues such as asylum, migration, trafficking and women, and much more, the site contains a fully annotated collection of links to immigration materials all around the World Wide Web. Only a month old, some of the categories in the Index's hierarchy still need some filling in. In time, however, the Immigration Index promises to become an invaluable resource for interested parties.

309

High Speed Stream Properties and Related Geomagnetic Activity During the Whole Heliosphere Interval (WHI): 20 March to 16 April 2008  

NASA Astrophysics Data System (ADS)

We study the interplanetary features and concomitant geomagnetic activity of the two high-speed streams (HSSs) selected by the Whole Heliosphere Interval (WHI) campaign participants: 20 March to 16 April 2008 in Carrington rotation (CR) 2068. This interval was chosen to perform a comprehensive study of HSSs and their geoeffectiveness during this “deep” solar minimum. The two HSSs within the interval were characterized by fast solar-wind speeds (peak values > 600 km s-1) containing large-amplitude Alfvénic fluctuations, as is typical of HSSs during normal solar minima. However, the interplanetary magnetic field (IMF) magnitude [ B o] was exceptionally low (?3 - 5 nT) during these HSSs, leading to lower than usual IMF B z values. The first HSS (HSS1) had favorable IMF polarity for geomagnetic activity (negative during northern Spring). The average AE and Dst for the HSS1 proper (HSS1P) were + 258 nT and - 21 nT, respectively. The second HSS (HSS2) had a positive sector IMF polarity, one that is less favorable for geomagnetic activity. The AE and Dst index averages were + 188 nT and - 7 nT, both lower than corresponding numbers for the first event, as expected. The HSS1P geomagnetic activity is comparable to, and the HSS2P geomagnetic activity lower than, corresponding observations for the previous minimum (1996). Both events’ geomagnetic activities are lower than HSS events previously studied in the declining phase (in 2003). In general, V sw was faster for the HSSs in 2008 compared to 1996. The southward IMF B z was lower in the former. The product of these two parameters [ V sw and IMF B z ] comprises the solar-wind electric field, which is most directly associated with the energy input into the magnetosphere during the HSS intervals. Thus the combined effects led to the solar wind energy input in 2008 being slightly less than that in 1996. A detailed analysis of magnetic-field variances and Alfvénicity is performed to explore the characteristics of Alfvén waves (a central element in the geoeffectiveness of HSSs) during the WHI. The B z variances in the proto-CIR (PCIR) were ? 30 nT2 and < 10 nT2 in the high speed streams proper.

Echer, E.; Tsurutani, B. T.; Gonzalez, W. D.; Kozyra, J. U.

2011-12-01

310

UK Index  

NSDL National Science Digital Library

The UK Index provides a searchable index of resources in or about the United Kingdom. The Quick Reference section offers links to News Resources in the UK such as the BBC, weather information, UK record charts, and UK related USENET newsgroups. The Foreign & Commonwealth Office provides good advice for travelers. The search engine allows the selection of categories such as arts or business to restrict the search to pages included in one category or a combination of categories.

311

The Effectiveness of the AAS REU Program  

NASA Astrophysics Data System (ADS)

In an attempt to address the particular needs of astronomy faculty and undergraduate students, in 1991 the Education Office of the American Astronomical Society approached the National Science Foundation with a unique proposal for funding through the Research Experiences for Undergraduates program. The goals of the AAS program were to "slow the hemorrhage of students out of science...", extend the REU program to non-NSF-funded scientists, to reach under-represented women and minority students particularly in small educational institutions, and to encourage research scientists there to mentor students. As this grant has now expired, the AAS has surveyed the 44 mentors and their students to assess the program's effect on the mentor and the mentor's career; the educational institution; and the student's education and career choices. More than half the mentors responded by the abstract deadline. The program clearly had an effect upon the individuals involved. The greatest effect (in 85% of the cases) was to develop more interest in the mentor's research project both among the students and among the mentor's faculty colleagues. The mentors rated the grant to be a medium or strong factor in their student's decision to pursue graduate study, which 90% of them did. All but one of the AAS-REU students attended an AAS meeting and 3/4 of those gave a paper on their project research. Over 90% of the mentors felt that the research experience strongly promoted a greater interest in science, a greater understanding of science and a desire to continue in science. According to the mentors, this was a very positive and beneficial program for the students as well as for themselves.

Hemenway, M. K.; Boyce, P. B.; Milkey, R. W.

1996-05-01

312

Thermospheric neutral wind response to geomagnetic storms  

NASA Astrophysics Data System (ADS)

The CISM Coupled Magnetosphere-Ionosphere-Thermosphere (CMIT) model, which includes two-way coupling between the Thermosphere/Ionosphere Nested Grid (TING) Model and the Lyon-Fedder-Mobarry (LFM) global magnetosphere MHD code, is run to investigate the near Earth space weather response to the 12-15 May 1997 geomagnetic storm. In this paper we will focus on the high and middle latitudes thermospheric wind variations during the storm. Two major processes change the storm time neutral wind circulation: an enhanced ion drag effect that forces the neutrals to follow the expanded ion convective drift, and an intensified Joule heating effect that increases the high latitude pressure gradient and thus changes the global wind pattern. We will discuss temporal and spatial evolutions of neutral wind changes after the storm commencement, and the time cadence of neutral wind recovery after the storm. Of particular interest to this study is a jet of neutral winds that occurs in the middle latitudes during the storm.

Wang, W.; Burns, A. G.; Wiltberger, M.; Solomon, S. C.; Killeen, T. L.; Lyon, J. G.; Goodrich, C.

2005-05-01

313

Periodic substorm activity in the geomagnetic tail  

SciTech Connect

On 19 May 1978 an anusual series of events is observed with the Quadrispherical LEPEDEA on board the ISEE-1 satellite in the Earth's geomagnetic tail. For 13 hours periodic bursts of both ions and electrons are seen in all the particle detectors on the spacecraft. On this day periodic activity is also seen on the ground, where multiple intensifications of the electrojets are observed. At the same time the latitudinal component of the interplanetary magnetic field shows a number of strong southward deflections. It is concluded that an extended period of substorm activity is occurring, which causes repeated thinnings and recoveries of the plasma sheet. These are detected by ISEE, which is situated in the plasma sheet boundary layer, as periodic dropouts and reappearances of the plasma. Comparisons of the observations at ISEE with those at IMP-8, which for a time is engulfed by the plasma sheet, indicate that the activity is relatively localized in spatial extent. For this series of events it is clear that a global approach to magnetospheric dynamics, e.g., reconnection, is inappropriate.

Huang, C.Y.; Eastman, T.E.; Frank, L.A.; Williams, D.J.

1983-01-01

314

Geomagnetic secular variation over Spain 1970-1988 by means of spherical cap harmonic analysis  

NASA Astrophysics Data System (ADS)

A spherical cap harmonic analysis was applied to Spain and neighbouring areas, covering a region with a cap halfangle of 16°. The technique, due to Haines, has allowed us to obtain a model of secular variation (SV) for a time interval of 18 years reduced to the epoch 1987.5. The total number of selected data points was 1581 provided from ten observatories and 60 repeat stations. The SV model has a maximum spatial index of four and temporal degree of two. The coefficients were tested and the statistically non-significant terms removed. Another model covering a smaller region with greater density of data has been developed and both results compared. The average secular variations derived from the definitive geomagnetic reference field (DGRF) and the international geomagnetic reference field (IGRF) were compared with these models and maps plotting the calculated first field derivatives are presented. The integration of the final model will serve to update satellite data in order to produce a regional main field model.

Garcia, A.; Torta, J. M.; Curto, J. J.; Sanclement, E.

1991-08-01

315

Dependence of neutral temperatures in the lower thermosphere on geomagnetic activity  

NASA Astrophysics Data System (ADS)

The neutral temperature Tn in the Earth's lower thermosphere is important to understand the atmospheric conditions. Tn responds to changes in solar irradiance and geomagnetic activity, meaning the atmospheric density and composition may vary strongly in time and space. Unfortunately, there have been few direct measurements of Tn at altitudes between 150 and 200 km. Recently, a new technique has been used to provide the neutral temperature, using measurements of N2 Lyman-Birge-Hopfield (LBH) band emissions from the High-resolution Ionospheric and Thermospheric Spectrograph (HITS) instrument on the Advanced Research and Global Observation Satellite (ARGOS). By fitting the high resolution N2 LBH band profiles, Tn in the lower thermosphere can be retrieved. In this presentation we examine the latitudinal and temporal variations in the temperatures as observed by HITS for 10 days in 2000 and 2001. The observed temperature changes follow variations in geomagnetic activity. Also, we find a good (poor) match during quiet (active) conditions between Tn from HITS and model calculations using the NRLMSISE-00 code. The agreement found reveals an almost linear relationship with the AL-index, yielding a correlation coefficient of 0.87.

Aksnes, A.; Eastes, R.; Budzien, S.; Dymond, K.

2006-12-01

316

Ising Phase in AA Stacked Bilayer Graphene  

NASA Astrophysics Data System (ADS)

AA stacked bilayer graphene bears a close resemblance to biased, double layer graphene (in which a strong barrier separates the two layers), with layer bonding and anti-bonding states of the AA system playing the roles of layer states in the double layer system. The latter has a U(1) symmetry which can break, to form a condensed exciton groundstate. The AA system however has only Ising symmetry. In this presentation we analyze the possibility that electron-electron interactions break this to open a gap in the energy spectrum. We find that, in the mean field approximation, the ground state has a charge density wave character, with the charge modulation of each layer out of phase. We calculate the gap and the mean field critical temperature as a function of the strength of the Coulomb interaction, taking screening into account self-consistently with the calculation of the gap. We also analyze the transition between ordered and thermally disordered phases based on a continuum model, and find that the transition is controlled by an effective U(1) stiffness. We argue that in the limit of zero layer separation, for which the full U(1) symmetry of the Hamiltonian is restored, the Ising transition continuously goes into a Kosterlitz-Thouless transition.

Fertig, Herbert; Brey, Luis

2013-03-01

317

Introducing the AAS Astronomy Ambassadors Program  

NASA Astrophysics Data System (ADS)

Newly established by the American Astronomical Society (AAS), the Astronomy Ambassadors program is designed to support early-career AAS members with training in resources and techniques for effective outreach to students and/or the public. A pilot Astronomy Ambassadors workshop will be held at the January 2013 AAS meeting. Workshop participants will learn to communicate effectively with public and school audiences; find outreach opportunities and establish ongoing partnerships with local schools, science centers, museums, parks, and/or community centers; reach audiences with personal stories, hands-on activities, and jargon-free language; identify strategies and techniques to improve their presentation skills; gain access to a menu of outreach resources that work in a variety of settings; and become part of an active community of astronomers who do outreach. Applications are welcome from advanced undergraduates (those doing research and committed to continuing in astronomy), graduate students, and postdocs and new faculty in their first two years after receipt of the PhD. We especially encourage applications from members of groups that are presently underrepresented in science.

Gurton, S.; Fienberg, R. T.; Fraknoi, A.; Prather, E. E.

2013-04-01

318

Corrosion mechanism of laser-melted AA 2014 and AA 2024 alloys  

NASA Astrophysics Data System (ADS)

The corrosion performance of laser-melted AA 2014-T6 and AA 2024-T351 alloys, using a 2 kW CW CO 2 laser, has been examined to gain insight into the factors influencing pitting corrosion resistance. Examination of laser-melted surfaces in terms of microstructure and phase analysis was performed using scanning electron microscopy (SEM), with associated elemental analysis by energy dispersive X-ray (EDX) spectroscopy, electron probe microanalysis (EPMA) and X-ray diffraction (XRD). Pitting corrosion resistance was evaluated using potentiodynamic anodic polarisation in 1 M NaCl solution. The work revealed that there was an improvement of pitting corrosion resistance for the laser-melted AA 2014-T6 alloy, but no improvement for AA 2024-T351 alloy. It indicated that the refinement of the microstructure, per se, with finer intermetallic particles, did not play an important role in corrosion performance. More importantly, the extension of copper solubility in the ?-Al matrix, leading to an increased corrosion potential, was considered to be the key factor responsible for the corrosion behaviours of the laser-melted aluminium alloys. For the AA 2014-T6 alloy, due to the cathodic nature of the Al 2Cu phase relative to the ?-Al solution, the rise of corrosion potential of the ?-Al solution reduced the galvanic coupling between the Al 2Cu and ?-Al matrix. As a result, the driving force for pitting corrosion in the ?-Al solution was reduced. For the AA 2024-T351 alloy, due to the anodic nature of the Al 2CuMg phase relative to the ?-Al solution, the driving force for pit initiation at the Al 2CuMg phase was enhanced. Therefore, the laser melting promoted the pitting corrosion of the AA 2024-T351 alloy.

Liu, Z.; Chong, P. H.; Butt, A. N.; Skeldon, P.; Thompson, G. E.

2005-07-01

319

Geomagnetic signatures during the intense geomagnetic storms of 29 October and 20 November 2003  

NASA Astrophysics Data System (ADS)

Solar cycle 23 in its declining phase witnessed the most pronounced space weather events during October November 2003. A series of powerful solar flares and associated geoeffective Coronal Mass Ejections (CMEs) travelling at ˜2000 km/s drove shock fronts that impacted the Earth's magnetic field consecutively on 29 and 30 October, resulting in intense geomagnetic disturbances during 29 31 October. Another intense geomagnetic storm activity occurred during 20 21 November, resulting from a solar flare that had an associated geoeffective CME travelling at a speed of ˜1100 km/s. Digital ground magnetic field measurements from the equatorial and low-latitude locations in the Indian longitude zone, in conjuction with the interplanetary solar wind and magnetic filed parameters, are used to study the characteristics of these storms. Maximum magnitude of the total magnetospheric energy injected into the magnetosphere during the mainphase of the three major storm amounts to approximately 4.5×1013, 3.6×1013, 2.8×1013 W. Another salient feature brought out is the close correspondence between the magnitude of the peak of the southward component of the interplanetary magnetic field Bz and the strength of the storm intensity as inferred from the Dst and low-latitude digital magnetic records.

Alex, S.; Mukherjee, S.; Lakhina, G. S.

2006-04-01

320

Transitional geomagnetic impulse hypothesis: Geomagnetic fact or rock-magnetic artifact?  

NASA Astrophysics Data System (ADS)

A striking feature of the Steens Mountain (Oregon) geomagnetic polarity reversal is the two (maybe three) extremely rapid field directional changes (6 degrees per day) proposed to account for unusual behavior in direction of remanent magnetization in a single lava flow. Each of these very fast field changes, or impulses, is associated with a large directional gap (some 90°) in the record. In order to check the spatial reproducibility of the paleomagnetic signal over distances up to several kilometers, we have carried out a paleomagnetic investigation of two new sections (B and F) in the Steens summit region which cover the second and the third directional gap. The main result is the description of two new directions, which are located between the pre second and post second impulse directions. These findings weigh against the hypothesis that the geomagnetic field cause the unusual intraflow fluctuations, which now appears to be more ad hoc as an explanation of the paleomagnetic data. However, the alternative baking hypothesis remains also ad hoc since we have to assume variable rock magnetic properties that we have not yet been able to detect within the flows at the original section Steens A and D 1.5 km to the north. In addition, new results for 22 transitional and normal lava flows in section B are presented that correlate well with earlier results from section A.

Camps, Pierre; Coe, Robert S.; PréVot, Michel

1999-08-01

321

Some Geomagnetic and Ionospheric Effects in Antarctica Prior to Storm Sudden Commencements.  

National Technical Information Service (NTIS)

Ionospheric height changes, blackout conditions, and geomagnetic activity for Antarctica in the relatively quiet times (geomagnetically) before storm sudden commencements are investigated. The principal results give evidence for 24-hourly periodicities in...

G. G. Bowman

1966-01-01

322

77 FR 22312 - Geomagnetic Disturbances to the Bulk-Power System; Notice of Technical Conference  

Federal Register 2010, 2011, 2012, 2013

...System as affected by geomagnetic disturbances. The conference will explore the risks and impacts from geomagnetically induced currents to transformers and other equipment on the Bulk-Power System, as well as, options for addressing...

2012-04-13

323

77 FR 24952 - Staff Technical Conference on Geomagnetic Disturbances to the Bulk-Power System; Technical...  

Federal Register 2010, 2011, 2012, 2013

...System as affected by geomagnetic disturbances. The conference will explore the risks and impacts from geomagnetically induced currents to transformers and other equipment on the Bulk-Power System, as well as, options for addressing...

2012-04-26

324

The AAS Visiting Professor Programs: Three Anniversaries  

NASA Astrophysics Data System (ADS)

The AAS Program of Visiting Professors was started in 1958 with three astronomers as lecturers. They were Paul Merrill (Mt. Wilson and Palomar Observatories), Seth Nicholson (Mt. Wilson and Palomar Observatories) and Harlow Shapley (Harvard College Observatory). The program was run by a Committee on Visiting Professors from 1958 through 1963. The program was funded by grants from the National Science Foundation. The Executive Officer of the AAS, Paul Routley headed the program from the 1963 - 64 academic year through the 1968 - 69 academic year. Larry Fredrick headed the program for 1969 - 70 and then Hank Gurin headed it through 1973 -74, the last year of the program. At the end of this summer meeting, the combined Visiting Professors Program and the Shapley Program will be starting their 47th year. The Shapley Visiting Lectureships in Astronomy Program was started in the 1974 - 75 academic year under the leadership of Hank Gurin. The original funding came from the Perkin Fund and a three year grant from the Research Corporation. In 1975 the Shapley Endowment fund was set up to help pay the expenses of the program. In 1976 there was support from the Slipher fund which lasted through the 1978 - 79 academic year. From 1979 to the present the program is financed by the Shapley Endowment Fund and by the contributions made by institutions which host the visits. In the fall of 1998 the fee that Institutions pay to the AAS in support of their Shapley visits was reduced from 300 to 250 to make it easier for them to apply for visits. Members of the AAS have made contributions to the program over the years and we are very appreciative of this support. In 1974 there were 42 lecturers in the program, of whom four are still active giving lectures (George Carruthers, Larry Fredrick, Arlo Landolt and Davis Philip). After the summer meeting, the Shapley Program will be embarking on its 30th year. Now there are 82 astronomers in the program and we get from 40 to 60 requests a year. Shapley visits have been made to Canadian institutions since 1976 and to Mexican institutions since 1998. After the summer meeting it will be the start of the 10th year of my directing the program. On May 26 there will be a Shapley Dinner at Dyer Observatory in Nashville for the Shapley lecturers who are attending the AAS meeting and we will celebrate these three anniversaries.

Philip, A. G. Davis

2003-05-01

325

A predicted geomagnetic field model for epoch 1990.0  

NASA Astrophysics Data System (ADS)

An epoch 1990.0 geomagnetic field model will be produced by the Naval Oceanographic Office (NAVOCEANO) using magnetic field measurements from the recently launched (April 1990) Polar Orbiting Geomagnetic Survey satellite for part of the input data. To aid in the production and evaluation of this model, NAVOCEANO requested that the Naval Oceanographic and Atmospheric Research Laboratory (NOARL) develop a predicted field model for 1990.0. A predicted model of the geomagnetic field for epoch 1990.0 has been developed. The model is based on the Definitive Geomagnetic Reference Field (DGRF) model for 1980.0 updated to 1990.0 by use of a secular variation model for 1980.0 developed at NOARL. The NOARL secular variation model is based upon annual means of vector geomagnetic field components from 73 magnetic observatories for years 1976.5 through 1983.5. The predicted model is of spherical harmonic degree and order 10. The rms error of the predicted model is estimated to be 200 nT relative to an accurate degree 10 field model for epoch 1990.0. Peak errors relative to an accurate model are estimated to be 500 nT for vector field error magnitude and +/-350, +250, and +/-500 nT for north, east, and vertical field components errors, respectively. If the DGRF model for 1980.0 were used without updating to represent the degree 10 field for 1990.0, estimated errors would be about four times as large.

McLeod, Malcolm G.

1993-01-01

326

Geomagnetically induced currents in a power grid of northeastern Spain  

NASA Astrophysics Data System (ADS)

Using the geomagnetic records of Ebro geomagnetic observatory and taking the plane wave assumption for the external current source and a homogeneous Earth conductivity, a prediction of the effects of the geomagnetic activity on the Catalonian (northeastern Spain) power transmission system has been developed. Although the area is located at midlatitudes, determination of the geoelectric field on the occasion of the largest geomagnetic storms during the last solar cycles indicates amplitudes that are higher than those recorded in southern Africa, where some transformer failures on large transmission systems have been reported. A DC network model of the grid has been constructed, and the geomagnetically induced current (GIC) flows in the power network have been calculated for such extreme events using the electric field at Ebro as a regional proxy. In addition, GICs have been measured at one transformer neutral earthing of the power grid, so that there the accuracy of the model has been assessed. Although the agreement is quite satisfactory, results indicate that better knowledge of the ground conductivity structure is needed. This represents the first attempt to study and measure GICs in southern European power grids, a region considered to have low GIC-risk up to the present.

Torta, J. Miquel; Serrano, LluíS.; Regué, J. Ramon; SáNchez, Albert M.; RoldáN, Elionor

2012-06-01

327

High cycle fatigue of AA6082 and AA6063 aluminum extrusions  

NASA Astrophysics Data System (ADS)

The high cycle fatigue behavior of hollow extruded AA6082 and AA6063 aluminum extrusions has been studied. Hollow extruded aluminum profiles can be processed into intricate shapes, and may be suitable replacements for fatigue critical automotive applications requiring reduced weight. There are several features inherent in hollow aluminum extrusions, such as seam welds, charge welds, microstructural variations and die lines. The effects of such extrusion variables on high cycle fatigue properties were studied by taking specimens from an actual car bumper extrusion. It appears that extrusion die lines create large anisotropy differences in fatigue properties, while welds themselves have little effect on fatigue lives. Removal of die lines greatly increased fatigue properties of AA6082 specimens taken transverse to the extrusion direction. Without die lines, anisotropy in fatigue properties between AA6082 specimens taken longitudinal and transverse to the extrusion direction, was significantly reduced, and properties associated with the orientation of the microstructure appears to be isotropic. A fibrous microstructure for AA6082 specimens showed great improvements in fatigue behavior. The effects of elevated temperatures and exposure of specimens to NaCl solutions was also studied. Exposure to the salt solution greatly reduced the fatigue lives of specimens, while elevated temperatures showed more moderate reductions in fatigue lives.

Nanninga, Nicholas E.

328

The solar and geomagnetic inputs into the JB2008 thermospheric density model for use by CIRA08 and ISO 14222  

NASA Astrophysics Data System (ADS)

Solar and geomagnetic indices are described for use in the Jacchia-Bowman 2008 thermospheric density model (JB2008). There are four solar and two geomagnetic indices used by JB2008. The F10.7, S10.7, M10.7, and Y10.7 solar indices are formed using the JB2006 methodology and they map energy from specific solar irradiance sources to major thermospheric layers. Energy that is deposited to the lower thermosphere and mesopause (85-100 km) is now provided. These solar proxies and indices are compliant with the ISO International Standard 21348 for determining solar irradiances. Reference values of the solar indices and proxies for short-term, intermediate-term, solar cycle, and 25-year periods from solar cycle 23 examples are provided for users who want reference values for planning and tests. The ap geomagnetic and Dst ring current indices are used in a two-index formulation that captures both low/unsettled activity and substorms/storms to represent changes to the neutral thermospheric densities as a result of high-latitude Joule heating and charged particle precipitation. The storm effects change the rate of exospheric temperature change, dTc, which affects satellite orbits. Reference values for ap, Dst, and dTc are provided using an example storm of November 20-21, 2003 for users who want reference values for planning and tests. Use of these solar, geomagnetic, and ring current indices in the JB2008 model produces significant improvements in empirical thermospheric density modeling. JB2008 provides standard deviations of approximately 9-10 percent at 400 km, which is a significant decrease from 16 percent 1-sigma uncertainty previously obtained using the Jacchia 70 model.

Tobiska, W. Kent

329

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)

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 effect, which may also have contributed to anomalies in the secular variation. The remarkable changes in the total intensity of the geomagnetic field observed on five profiles indicate the piezomagnetic and/or electrokinetic effect or, both these mechanisms seem to be operative for the secular variation anomalies in the seismoactive zone of NSL.

Waghmare, S. Y.

2009-12-01

330

Statistical comparison of interplanetary conditions causing intense geomagnetic storms (Dst ? ?100 nT)  

Microsoft Academic Search

It is well known that intense southward magnetic field and convection electric field (V × B) in the interplanetary medium are key parameters that control the magnitude of geomagnetic storms. By investigating the interplanetary conditions of 82 intense geomagnetic storms from 1998 to 2006, we have compared many different criteria of interplanetary conditions for the occurrence of the intense geomagnetic

Eun-Young Ji; Y.-J. Moon; K.-H. Kim; D.-H. Lee

2010-01-01

331

IMPROVED CALCULATION OF GEOMAGNETICALLY INDUCED CURRENTS IN POWER NETWORKS IN LOW-LATITUDE REGIONS  

Microsoft Academic Search

Previous calculations of geomagnetically induced currents (GICs) in Southern Africa assumed a plane wave model for the ionospheric current that induces low frequency GICs in power transmission networks. Recent work shows it is insufficient to use the geomagnetic data from only one observatory to represent the whole region. An ionospheric elementary current interpolation method using data from three geomagnetic observatories

E. H. Bernhardi; T. A. Tjimbandi; P. J. Cilliers; C. T. Gaunt

332

Stratospheric warmings and the geomagnetic lunar tide: 1958-2007  

NASA Astrophysics Data System (ADS)

A quantitative comparison of the geomagnetic lunar tide and lower stratospheric parameters (zonal mean air temperature T and zonal mean zonal wind U) is carried out for the period 1958-2007. The correlation between the amplitude of the geomagnetic lunar tide at an equatorial station, Addis Ababa, and the lower stratospheric parameters from the National Centers for Environmental Prediction-National Center for Atmospheric Research (NCEP-NCAR) reanalysis is examined. It is found that the lunar tidal amplitude tends to be positively and negatively correlated with the stratospheric T and U, respectively, in high latitudes of the Northern Hemisphere during December and January. High correlations are observed in approximately 70% of stratospheric sudden warming (SSW) events. The results suggest that variability of the geomagnetic lunar tide during the northern winter is closely linked with dynamical changes in the lower stratospheric parameters associated with SSWs.

Yamazaki, Y.; Richmond, A. D.; Yumoto, K.

2012-04-01

333

22' MAX China Meridian Chain of Geomagnetic and Aeronomic Observatories.  

NASA Astrophysics Data System (ADS)

The 22' MAX China Meridian Chain of Geomagnetic and Aeronomic Observatories is briefly introduced. The purpose of this chain is to provide the ground-based data for studying (1) the coupling between the solar wind, magnetosphere, ionosphere and neutral atmosphere, (2) the behaviour and the role of the mid-low latitude ionosphere and magnetosphere in the energy coupling processes, (3) large-scale magnetospheric-ionospheric current systems at mid-low latitudes during various solar-terrestrial events, (4) geomagnetic micropulsations at mid-low latitudes and their generation, propagation and related plasma instabilities, (5) whistler and VLF emission and related wave-partical interaction, (6) the geomagnetic main field, in particular, the East Asia anomaly.

Xu, Wen-Yao

1989-10-01

334

Fifty years of progress in geomagnetic cutoff rigidity determinations  

NASA Astrophysics Data System (ADS)

This paper is a review of the progress made in geomagnetic cutoff rigidity calculations over the past 50 years. Determinations of cosmic ray trajectories, and hence cutoff rigidities, using digital computers began in 1956 and progressed slowly until 1962 when McCracken developed an efficient computer program to determine cosmic ray trajectories in a high degree simulation of the geomagnetic field. The application of this cosmic ray trajectory technique was limited by the available computer power. As computers became faster it was possible to determine vertical cutoff rigidity values for cosmic ray stations and coarse world grids; however, the computational effort required was formidable for the computers of the 1960s. Since most cosmic ray experiments were conducted on the surface of the Earth, the vertical cutoff rigidity was adopted as a standard reference value. The effective cutoff value derived from trajectory calculations appeared to be adequate for ordering cosmic ray data from latitude surveys. As the geomagnetic field evolution became more apparent, it was found necessary to update the world grid of cutoff rigidity values using more accurate descriptions of the geomagnetic field. In the 1970s and 1980s it became possible to do experimental verification of the accuracy of these cosmic ray cutoff determinations and also to design experiments based on these cutoff rigidity calculations. The extensive trajectory calculations done in conjunction with the HEAO-3 satellite and a comparison between these experimental measurements and the trajectory calculations verified the Störmer theory prediction regarding angular cutoff variations and also confirmed that the structure of the first order penumbra is very stable and could be used for isotope separation. Contemporary work in improving cutoff rigidities seems to be concentrating on utilizing improved magnetospheric models in an effort to determine more accurate geomagnetic cutoff values. When using geomagnetic cutoff rigidity values to predict the cosmic radiation access to spacecraft for a satisfactory computation of the radiation dose, both the particle transmission though the cosmic ray penumbra and angular cutoffs must be considered.

Smart, D. F.; Shea, M. A.

2009-11-01

335

Observed effects of a geomagnetic storm on an RTK positioning network at high latitudes  

NASA Astrophysics Data System (ADS)

At high latitudes, above 60° N, in the vicinity of the auroral oval, the ionosphere frequently experiences disturbed conditions that impact GNSS-based services. The Norwegian Mapping Authority (NMA) is operating a national real-time kinematic (RTK) positioning network and an ionosphere monitoring software. This paper presents the ionospheric observations during a geomagnetic storm, and the observed consequences for the positioning service. Significant disruptions that can be clearly related to the ionospheric disturbances were observed. They tend to occur in roughly longitudinal bands, which is expected for disturbances caused by the particle and energy precipitation in the auroral oval. The position error is found to increase exponentially with increasing rate of TEC index (ROTI). The disturbances are compared to auroral electrojet measurements and results from an operational auroral oval forecasting model. The disturbances are found to be strongly related to auroral electrojet currents.

Jacobsen, Knut Stanley; Schäfer, Sebastian

2012-08-01

336

INDEXING MECHANISM  

DOEpatents

A device is presented for loading and unloading fuel elements containing material fissionable by neutrons of thermal energy. The device comprises a combination of mechanical features Including a base, a lever pivotally attached to the base, an Indexing plate on the base parallel to the plane of lever rotation and having a plurality of apertures, the apertures being disposed In rows, each aperture having a keyway, an Index pin movably disposed to the plane of lever rotation and having a plurality of apertures, the apertures being disposed in rows, each aperture having a keyway, an index pin movably disposed on the lever normal to the plane rotation, a key on the pin, a sleeve on the lever spaced from and parallel to the index pin, a pair of pulleys and a cable disposed between them, an open collar rotatably attached to the sleeve and linked to one of the pulleys, a pin extending from the collar, and a bearing movably mounted in the sleeve and having at least two longitudinal grooves in the outside surface.

Kock, L.J.

1959-09-22

337

Geomagnetic intensity variation during the last 4000 years  

NASA Astrophysics Data System (ADS)

Thellier-type determinations of the ancient geomagnetic intensity are reported for a large number of samples from Greece, comprising ancient pottery and other archaeologically dated forms of baked clay. Comparison is made with results for other parts of the world of about the same latitude: the Near East, China and the western U.S.A. These data indicate that, in the time-range studied, variation of the geomagnetic dipole moment is unlikely to have been the dominant influence; it is suggested that the westward drift of a non-dipole disturbance could have been responsible.

Aitken, Martin J.; Allsop, Adrian L.; Bussell, Gillian D.; Winter, Mona B.

1989-07-01

338

Secular Variations of the Geomagnetic Field in Europe  

NASA Astrophysics Data System (ADS)

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 probably caused by data errors, which may have different sources. Their existence cannot be explained by now. Therefore the MagNetE project should be continued.

Sas-Uhrynowski, A.; Welker, E.

2009-09-01

339

GEOMAGNETIC REVERSALS DRIVEN BY ABRUPT SEA LEVEL CHANGES  

SciTech Connect

Changes in the moment of inertia of the earth, brought about by the redistribution of ocean water from the tropics to ice at high latitudes, couple energy from the spin of the earth into convection in the liquid core. This mechanism may help provide the driving energy for the earth's dynamo. Sufficiently rapid ocean level changes can disrupt the dynamo, resulting (in half of the cases) in a geomagnetic field reversal. The model can account for the previously mysterious correlation reported between geomagnetic reversals and mass extinctions.

Muller, R.A.; Morris, D.E.

1986-10-01

340

Abnormal scintigraphic evolution in AA hepatic amyloidosis  

SciTech Connect

A patient with AA amyloidosis secondary to ankylosing spondylitis showed intense liver uptake of Tc-99m MDP on bone imaging. The biopsy showed hepatic amyloid deposition. A repeat bone scan with Tc-99m MDP 1 year later was negative, although the clinical signs and liver function tests of the patient had not changed. A mechanism might exist, other than the affinity of amyloid to calcium, which would explain the extraosseous uptake of pyrophosphates and diphosphonates in organs and soft tissues affected by systemic amyloidosis.

Lomena, F.; Rosello, R.; Pons, F.; Grau, M.; Garcia, A.; Catafau, A.; Setoain, J.

1988-03-01

341

Impact resistance of AA6005 panels  

NASA Astrophysics Data System (ADS)

The interest regarding use of extruded aluminium panels as lightweight protective structures is cmrently increasing. Even so, there are few experimental and computational investigations considering such structures. This paper presents some perforation tests on AA6005-T6 aluminium panels impacted by ogival-nose steel projectiles, where special emphasis was paid to the determination of the ballistic limit. Moreover, a material test programme including high strain rate tests using a split-Hopkinson tension bar was carried out in order to calibrate the Johnson-Cook constitutive model. Results from numerical analyses with LS-DYNA are finally included.

Clausen, A. H.; Borvik, T.; Hopperstad, O. S.; Langseth, M.

2003-09-01

342

Cu(II)-catalyzed reactions in ternary [Cu(AA)(AA - H)]+ complexes (AA = Gly, Ala, Val, Leu, Ile, t-Leu, Phe).  

PubMed

The unimolecular chemistry of [Cu(II)AA(AA - H)](+) complexes, composed of an intact and a deprotonated amino acid (AA) ligand, have been probed in the gas phase by tandem and multistage mass spectrometry in an electrospray ionization quadrupole ion trap mass spectrometer. The amino acids examined include Gly, Ala, Val, Leu, Ile, t-Leu and Phe. Upon collisionally-activated dissociation (CAD), the [Cu(II)AA(AA - H)](+) complexes undergo decarboxylation with simultaneous reduction of Cu(II) to Cu(I); during this process, a radical site is created at the alpha-carbon of the decarboxylated ligand (H(2)N(1) - (*)C(alpha)H - C(beta)H(2) - R; R = side chain substituent). The radical site is able to move along the backbone of the decarboxylated amino acid to form two new radicals (HN(1)(*) - C(alpha)H(2) - C(beta)H(2) - R and H(2)N(1) - C(alpha)H(2) - (*)C(beta)H - R). From the complexes of Gly and t-Leu, only C(alpha) and N(1) radicals can be formed. The whole radical ligand can be lost to form [Cu(I)AA](+) from these three isomeric radicals. Alternatively, further radical induced dissociations can take place along the backbone of the decarboxylated amino acid ligand to yield [Cu(II)AA(AA - 2H - CO(2))](+), [Cu(I)AA((*)NH(2))](+), [Cu(I)AA(HN = C(alpha)H(2))](+), or [Cu(I)AA(H(2)N - C(alpha)H = C(beta)H - R'](+) (R' = partial side chain substituent). The sodiated copper complexes, [Cu(II)(AA - H + Na)(AA - H)](+), show the same fragmentation patterns as their non-sodiated counterparts; sodium ion is retained on the intact amino acid ligand and is not involved in the CAD pathways. The amino groups of both AA units, the carbonyl group of the intact amino acid, and the deprotonated hydroxyl oxygen coordinate Cu(II) in square-planar fashion. Ab initio calculations indicate that the metal ion facilitates hydrogen atom shuttling between the N(1), C(alpha) and C(beta) atoms of the decarboxylated amino acid ligand. The dissociations of the decarboxylated radical ions unveil important insight about the so far largely unknown intrinsic chemistry of alpha-amino acid and peptide radicals, which are implicated as intermediates in numerous pathogenic biological processes. PMID:19423917

Wang, Ping; Ohanessian, Gilles; Wesdemiotis, Chrys

2009-01-01

343

First results from the first Croatian geomagnetic observatory  

NASA Astrophysics Data System (ADS)

The first Croatian geomagnetic observatory was established in the area of the Nature Park Lonjsko Polje, after a century of sporadic efforts originating from the proposals of Andrija Mohorovicic. The location was chosen after exhaustive surveys of possible sites. It is located far enough from sources of civilization noise, and was found to be an area without magnetic anomalies and with a low field gradient. The construction of the observatory buildings was completed in the autumn of 2011. The furnishing and installation of instruments and test measurements were completed by the beginning of summer 2012, ever since we have continuous recordings of the geomagnetic elements. In the beginning of December 2012 the fluxgate magnetometer LEMI-035 (H,D,Z orientation) has been installed under the framework of the PLASMON project in cooperation with the Tihany Observatory (Hungary). Permanent data of high quality from our observatory will contribute to the monitoring of the Earth's magnetic field on the regional and global levels, thus enabling further development of geomagnetism in Croatia through collaboration with scientists from the other countries, participation in the international projects, eventual membership in the International Real-time Magnetic Observatory Network (INTERMAGNET), etc. The field elements for the epoch 2012,75 and the baselines are presented together with highlights of some recorded geomagnetic events so far. Furthermore, the comparison between the variation data recorded by the dIdD and the fluxgate LEMI-035 magnetometer is presented.

Mandic, Igor; Herak, Davorka; Heilig, Balazs

2013-04-01

344

Eects of geomagnetic storms on the ionosphere and atmosphere  

Microsoft Academic Search

A geomagnetic storm is a complex process: its various features act at dierent heights. In the F2 layer the midlatitude eect is basically an ionospheric response to storm-induced changes in the neutral atmosphere, which are primarily a consequence of a strong Joule heating in the auroral thermosphere. At lower heights the role of ionization and photochemical processes increases due to

A. D. Danilov; J. Lastovicka

2001-01-01

345

Attitude Control of Small Scientific Satellite Using Geomagnetism  

Microsoft Academic Search

Geomagnetism was used to control the attitude of the small scientific satellite at low altitude in sun-synchronous orbit. First, we analyzed the telemetry data. The rotation state of the satellite can be known from the magnitude and variations of the magnetic field which is measured from the 3 axis magnetometer. In axisymmetric case, it is possible to control the attitude

Sung-Koo Bae; Jae-Ho Seok; Kyu-Hong Choi

1991-01-01

346

Disambiguating Robot Positioning Using Laser and Geomagnetic Signatures  

Microsoft Academic Search

This article proposes a technique for position disambiguating of mobile robots using laser and geomagnetic signatures in indoor terrains. Referring to the geo- magnetic signature, magnetic field disturbances are used as unique recognition signa- tures. First, we gather information about the magnetic heading and the laser mapping as our robot traverses a path between start and goal points of the

Ashraf Aboshosha; Andreas Zell

2004-01-01

347

Influence of local geomagnetic storms on arterial blood pressure.  

PubMed

This study attempts to assess the influence of local geomagnetic storms at middle latitudes on some human physiological parameters. The blood pressure (bp), heart rate and general well-being of 86 volunteers were measured, the latter by means of a standardised questionnaire, on work days in autumn, 2001 (1 Oct to 9 Nov), and in spring, 2002 (8 April to 28 May). These timespans were chosen as periods of maximal expected geomagnetic activity (GMA). Altogether, 2799 recordings were obtained and analysed. A four factor analysis of variance (MANOVA) was employed to check the significance of the influence of four factors (local GMA level; sequence of the days of measurements covering up to 3 days before and after geomagnetic storms; sex and the presence of medication) on the physiological parameters under consideration. Post hoc analysis was performed to elicit the significance of differences in the factors' levels. Arterial bp was found to increase with the increase of the GMA level, and systolic and diastolic bp were found to increase significantly from the day before till the second day after the geomagnetic storm. These effects were present irrespective of sex and medication. PMID:15300726

Dimitrova, S; Stoilova, I; Cholakov, I

2004-09-01

348

Observations of geomagnetically induced currents in the Australian power network  

NASA Astrophysics Data System (ADS)

such as pipelines and power networks at low-middle latitude regions have historically been considered relatively immune to geomagnetically induced currents (GICs). Over the past decade there have been an increasing number of investigations into the impact of GICs in long grounded conductors at these latitudes. The Australian region power network spans thousands of kilometers from low to middle latitudes. The approaching maximum of solar cycle 24 and recent findings of studies into power networks located at similar latitudes have stimulated the Australian power industry to better understand this phenomenon in their region. As a result, a pilot study to compare space weather activity with in situ GIC monitors at strategic locations within the power network was initiated. This paper provides some results from the first of these operational GIC monitors during a modest geomagnetic storm, showing the first observational evidence of space weather well correlated with GICs measured in the Australian power network. Transformer neutral currents show a high degree of similarity with the geoelectric field derived from the closest available geomagnetic observatory. Current maxima of 4-5 amperes were observed in association with geoelectric field values of ~0.06-0.07 volts per kilometer. This paper also discusses the GIC measurements obtained during this storm in terms of the space weather drivers and the considerably larger geoelectric field values anticipated during larger geomagnetic storms.

Marshall, R. A.; Gorniak, H.; van der Walt, T.; Waters, C. L.; Sciffer, M. D.; Miller, M.; Dalzell, M.; Daly, T.; Pouferis, G.; Hesse, G.; Wilkinson, P.

2013-01-01

349

Development of Geomagnetic Data Assimilation Framework: the Challenges and Progress  

Microsoft Academic Search

The scientific significance of assimilating surface geomagnetic observations into numerical geodynamo models is most obvious for the improvements that can be made to the models: observations can be used to constrain and identify appropriate dynamics for numerical modeling, and to create a dynamically consistent estimate of the state of the Earth's core. This estimate is an essential component needed in

W. Kuang; A. Tangborn; Z. Sun; D. Liu; W. Jiang; T. Sabaka; J. Bloxham

2005-01-01

350

New insights on geomagnetic storms from observations and modeling  

SciTech Connect

Understanding the response at Earth of the Sun's varying energy output and forecasting geomagnetic activity is of central interest to space science, since intense geomagnetic storms may cause severe damages on technological systems and affect communications. Episodes of southward (Bzgeomagnetic conditions are associated either with coronal mass ejections (CMEs) and possess long and continuous negative IMF Bz excursions, or with high speed solar wind streams (HSS) whose geoeffectiveness is due to IMF Bz profiles fluctuating about zero with various amplitudes and duration. We show examples of ring current simulations during two geomagnetic storms representative of each interplanetary condition with our kinetic ring current atmosphere interactions model (RAM), and investigate the mechanisms responsible for trapping particles and for causing their loss. We find that periods of increased magnetospheric convection coinciding with enhancements of plasma sheet density are needed for strong ring current buildup. During the HSS-driven storm the convection potential is highly variable and causes small sporadic injections into the ring current. The long period of enhanced convection during the CME-driven storm causes a continuous ring current injection penetrating to lower L shells and stronger ring current buildup.

Jordanova, Vania K [Los Alamos National Laboratory

2009-01-01

351

Response of the thermosphere and ionosphere to geomagnetic storms  

Microsoft Academic Search

Four numerical simulations have been performed, at equinox, using a coupled thermosphere-ionosphere model, to illustrate the response of the upper atmosphere to geomagnetic storms. The storms are characterized by an increase in magnetospheric energy input at high latitude for a 12-hour period; each storm commences at a different universal time (UT). The initial response at high latitude is that Joule

T. J. Fuller-Rowell; M. V. Codrescu; R. J. Moffett; S. Quegan

1994-01-01

352

Multivariate analysis of geomagnetic array data. I - The response space  

Microsoft Academic Search

An approach for multiple-station analysis of geomagnetic array data is developed, based on the observation that the observable electromagnetic fields at the earth's surface (the response space) can be approximated by spaces of very low dimension. This method is compared with transfer function methods. A statistical model using the method is demonstrated with a small five-station magnetotelluric array. The method

Gary D. Egbert; John R. Booker

1989-01-01

353

DIRECT OBSERVATIONS OF THERMOSPHERIC WINDS DURING GEOMAGNETIC STORMS  

Microsoft Academic Search

Direct measurements of thermospheric winds were made during two geomagnetic storms. Winds were detected (a) in the stable auroral red arc of October 31 to November 1, 1968, and (b) during the aurora .of May 14-15, 1969. In both storms the measured winds were from the north and persisted throughout the night with a velocity between 250 and 400 m

P. B. Hays; R. G. Roble

1971-01-01

354

Surface electric fields for North America during historical geomagnetic storms  

NASA Astrophysics Data System (ADS)

To better understand the impact of geomagnetic disturbances on the electric grid, we recreate surface electric fields from two historical geomagnetic storms—the 1989 "Quebec" storm and the 2003 "Halloween" storms. Using the Spherical Elementary Current Systems method, we interpolate sparsely distributed magnetometer data across North America. We find good agreement between the measured and interpolated data, with larger RMS deviations at higher latitudes corresponding to larger magnetic field variations. The interpolated magnetic field data are combined with surface impedances for 25 unique physiographic regions from the United States Geological Survey and literature to estimate the horizontal, orthogonal surface electric fields in 1 min time steps. The induced horizontal electric field strongly depends on the local surface impedance, resulting in surprisingly strong electric field amplitudes along the Atlantic and Gulf Coast. The relative peak electric field amplitude of each physiographic region, normalized to the value in the Interior Plains region, varies by a factor of 2 for different input magnetic field time series. The order of peak electric field amplitudes (largest to smallest), however, does not depend much on the input. These results suggest that regions at lower magnetic latitudes with high ground resistivities are also at risk from the effect of geomagnetically induced currents. The historical electric field time series are useful for estimating the flow of the induced currents through long transmission lines to study power flow and grid stability during geomagnetic disturbances.

Wei, Lisa H.; Homeier, Nicole; Gannon, Jennifer L.

2013-08-01

355

Solar Activity, Different Geomagnetic Activity Levels and Acute Myocardial Infarction  

NASA Astrophysics Data System (ADS)

Results on revealing a possible relationship between solar activity (SA) and geomagnetic activity (GMA) and acute myocardial infarction (AMI) morbidity are presented. Studies were based on medical data covering the period from 1.12.1995 to 31.12.2004 and concerned daily distribution of patients with AMI diagnose (in total 1192 cases) from Sofia region on the day of admission at the hospital. Analysis of variance (ANOVA) was applied to check the significance of GMA intensity effect and the type of geomagnetic storms, those caused by Magnetic Clouds (MC) and by High Speed Solar Wind Streams (HSSWS), on AMI morbidity. Relevant correlation coefficients were calculated. Results revealed statistically significant positive correlation between considered GMA indices and AMI. ANOVA revealed that AMI number was signifi- cantly increased from the day before (-1st) till the day after (+1st) geomagnetic storms with different intensities. Geomagnetic storms caused by MC were related to significant increase of AMI number in comparison with the storms caused by HSSWS. There was a trend for such different effects even on -1st and +1st day.

Dimitrova, Svetla; Jordanova, Malina; Stoilova, Irina; Taseva, Tatiana; Maslarov, Dimitar

356

Model simulation of thermospheric response to recurrent geomagnetic forcing  

Microsoft Academic Search

We assess model capability in simulating thermospheric response to recurrent geomagnetic forcing driven by modulations in the solar wind speed and the interplanetary magnetic field. Neutral density and nitric oxide (NO) cooling rates are simulated for the declining phase of solar cycle 23. The simulated results are compared to neutral density derived from satellite drag and to NO cooling measured

Liying Qian; Stanley C. Solomon; Martin G. Mlynczak

2010-01-01

357

Ionospheric Effects of Geomagnetic Storms on GNSS based Systems  

Microsoft Academic Search

It is known that ionosphere is the effective indicator of the space weather state. Severe ionospheric perturbations can seriously degrade the performance of Global Navigation Satellite Systems (GNSS). During geomagnetic storms the ionospheric gradients are essentially increased in compare with quiet conditions. Strong ionospheric gradients can caused the deterioration of GPS positioning. In the given report it is presented the

Irk Shagimuratov; Andrzej Krankowski; Irina Zakharenkova; Ivan Karpov; Galina Yakimova

2010-01-01

358

Surface electric fields for North America during historical geomagnetic storms  

USGS Publications Warehouse

To better understand the impact of geomagnetic disturbances on the electric grid, we recreate surface electric fields from two historical geomagnetic storms—the 1989 “Quebec” storm and the 2003 “Halloween” storms. Using the Spherical Elementary Current Systems method, we interpolate sparsely distributed magnetometer data across North America. We find good agreement between the measured and interpolated data, with larger RMS deviations at higher latitudes corresponding to larger magnetic field variations. The interpolated magnetic field data are combined with surface impedances for 25 unique physiographic regions from the United States Geological Survey and literature to estimate the horizontal, orthogonal surface electric fields in 1 min time steps. The induced horizontal electric field strongly depends on the local surface impedance, resulting in surprisingly strong electric field amplitudes along the Atlantic and Gulf Coast. The relative peak electric field amplitude of each physiographic region, normalized to the value in the Interior Plains region, varies by a factor of 2 for different input magnetic field time series. The order of peak electric field amplitudes (largest to smallest), however, does not depend much on the input. These results suggest that regions at lower magnetic latitudes with high ground resistivities are also at risk from the effect of geomagnetically induced currents. The historical electric field time series are useful for estimating the flow of the induced currents through long transmission lines to study power flow and grid stability during geomagnetic disturbances.

Wei, Lisa H.; Homeier, Nichole; Gannon, Jennifer L.

2013-01-01

359

Possible helio-geomagnetic activity influence on cardiological cases  

Microsoft Academic Search

Eruptive solar events as flares and coronal mass ejections (CMEs) occur during solar activ-ity periods. Energetic particles, fast solar wind plasma and electromagnetic radiation pass through interplanetary space, arrive on Earth's ionosphere-magnetosphere and produce various disturbances. It is well known the negative influence of geomagnetic substorms on the human technological applications on geospace. During the last 25 years, many studies

Christos Katsavrias

2010-01-01

360

Geomagnetic effects on the performance of atmospheric Cerenkov telescopes  

Microsoft Academic Search

We have reported the results of the interaction between the geomagnetic field and the development of atmospheric electron cascades as manifested by the distortion of the atmospheric Cerenkov signal. We will summarize these effects and describe our initial attempt to remove this distortion for those cases where the cascade develops perpendicular to a strong (>0.35 G) field and so enhance

P. M. Chadwick; K. Lyons; T. J. L. McComb; K. J. Orford; J. L. Osborne; S. M. Rayner; S. E. Shaw; K. E. Turver

2000-01-01

361

An empirical model of the quiet daily geomagnetic field variation  

USGS Publications Warehouse

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.

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

362

Sharks can detect changes in the geomagnetic field  

Microsoft Academic Search

We used behavioural conditioning to demonstrate that sharks can detect changes in the geomagnetic field. Captive sharks were conditioned by pairing activation of an artificial magnetic field with presentation of food over a target. Conditioned sharks subsequently con- verged on the target when the artificial magnetic field was activated but no food reward was presented thereby demonstrating that they were

Carl G. Meyer; Kim N. Holland; Yannis P. Papastamatiou

2005-01-01

363

Spatial Distribution of Energetic Electrons in the Geomagnetic Tail.  

National Technical Information Service (NTIS)

Counting rates from a solid-state detector in the experiment of Fan, Gloeckler, and Simpson on the IMP 1 satellite have been analyzed to investigate the spatial distribution of electrons with energies > 30 kev in the geomagnetic tail and in the magnetoshe...

T. Murayama

1966-01-01

364

Shape of the Geomagnetic Field Solar Wind Boundary  

Microsoft Academic Search

The shape of the boundary of the geomagnetic field in a solar wind has been calculated by a self-consistent method in which, in first order, approximate magnetic fields are used to calculate a boundary surface. The electric currents in this boundary produce mag- netic fields, which can be calculated once the first surface is known. These are added to the

Gilbert D. Mead; David B. Beard

1964-01-01

365

Recent progress in estimating uncertainty in geomagnetic field modeling  

Microsoft Academic Search

Recent work pertaining to estimating error and accuracies in geomagnetic field modeling is reviewed from a unified viewpoint and illustrated with examples. The formulation of a finite dimensional approximation to the underlying infinite dimensional problem is developed. Central to the formulation is an inner product and norm in the solution space through which a priori information can be brought to

R. A. Langel

1991-01-01

366

Continuous global geomagnetic field models for the past 3000 years  

Microsoft Academic Search

Several global geomagnetic field models exist for recent decades, but due to limited data availability models for several centuries to millennia are rare. We present a continuous spherical harmonic model for almost 3 millennia from 1000 b.c. to 1800 a.d., based on a dataset of directional archaeo- and paleomagnetic data and axial dipole constraints. The model, named Continuous Archaeomagnetic and

Monika Korte; Catherine Constable

2003-01-01

367

A history of the early recording of geomagnetic variations  

Microsoft Academic Search

As pulsations and circulating currents are caused by solar activity, a short survey is given of how to recognise solar influences on terrestrial magnetism, and particularly the hypotheses of Balfour Stewart and the two treatises of Arthur Schuster about the daily variations. In meteorology and geomagnetism, photographic self-registering equipment was developed in Greenwich and Kew; E. Mascart and M. Eschenhagen

Wilfried Schröder; Karl-Heinrich Wiederkehr

2000-01-01

368

Particle acceleration from reconnection in the geomagnetic tail  

SciTech Connect

Acceleration of charged particles in the near geomagnetic tail, associated with a dynamic magnetic reconnection process, was investigated by a combined effort of data analysis, using Los Alamos data from geosynchronous orbit, MHD modeling of the dynamic evolution of the magnetotail, and test particle tracing in the electric and magnetic fields obtained from the MHD simulation.

Birn, J.; Borovsky, J.E.; Thomsen, M.F.; McComas, D.J.; Reeves, G.D.; Belian, R.D. [Los Alamos National Lab., NM (United States); Hesse, M. [National Aeronautics and Space Administration, Greenbelt, MD (United States). Goddard Space Flight Center; Schindler, K. [Ruhr-Univ., Bochum (Germany)

1997-08-01

369

Geomagnetically Induced Currents in European High-Voltage Power Systems  

Microsoft Academic Search

Geomagnetically induced currents (GIC) in power systems are a ground manifestation of space weather arising from solar activity. Most of the research on GIC done in Europe so far refers to Scandinavian power grids. A power outage due to GIC occurred in southern Sweden in October 2003. The principal reason that similar GIC problems as in Sweden have not occurred

Risto J. Pirjola; David H. Boteler

2006-01-01

370

Geomagnetic storms and their impact on power systems  

SciTech Connect

This article examines the lessons learned for solar cycle 22 and the application of these to solar cycle 23. The topics of the article include a review of the characteristics of the current solar cycle, the power system reliability threat, geomagnetically induced currents (GIC) as the cause of transformer failures, and magnetic storm forecast improvements.

Kappenman, J.G. [Minnesota Power, Duluth, MN (United States)

1996-05-01

371

Geomagnetically induced currents in the Southern African electricity transmission network  

Microsoft Academic Search

This report describes the findings of the extended investigation into the existence and effects of geomagnetically induced currents (GICs) on the Southern African network. This would also apply to any other network at mid-latitude. The transmission network was modelled and the GICs calculated for major storms at various substations. Thereafter equipment was installed at two substations to monitor the performance

Jacko Koen; Trevor Gaunt

2003-01-01

372

A geomagnetically induced current warning system: model development and validation  

Microsoft Academic Search

Geomagnetically Induced Currents (GIC), which can flow in technological systems at the Earth's surface, are a consequence of magnetic storms and Space Weather. A well-documented practical problem for the power transmission industry is that GIC can affect the lifetime and performance of transformers within the power grid. Operational mitigation is widely considered to be one of the best strategies to

A. McKay; E. Clarke; S. Reay; A. Thomson

2004-01-01

373

Modeling geomagnetically induced currents during different ionospheric situations  

Microsoft Academic Search

We use several realistic three-dimensional models of ionospheric currents to calculate geomagnetically induced currents (GIC) in the Finnish high-voltage power system. Of special interest are events during which the magnetic field changes rapidly and GIC are large. The geoelectric field driving GIC is determined with the complex image method, which is a fast and accurate tool for taking into account

Ari Viljanen; Olaf Amm; Risto Pirjola

1999-01-01

374

Geomagnetically induced currents: Present knowledge and future research  

Microsoft Academic Search

The knowledge base regarding the production of geomagnetically induced currents (GIC) in power systems is briefly reviewed. The relationship between electric and magnetic fields for a layered earth is derived and used to calculate the electric fields produced in Quebec during the March 13, 1989, magnetic disturbance. Factors influencing the distribution of GIC throughout a system are also examined. The

D. H. Boteler

1994-01-01

375

Geomagnetic storm environments and effects on electrical systems.  

National Technical Information Service (NTIS)

This paper briefly reviews the behavior of the earth's magnetic field during a geomagnetic storm. Temporal variations of the B-field on the earths surface can induce an electric field in the earth, and this E-field will induce currents to flow in long, gr...

F. M. Tesche P. R. Barnes

1992-01-01

376

Wear behaviour of AA6061 aluminium alloy and its composites  

Microsoft Academic Search

This study investigates the wear resistance of four AA6061 MMCs together with the monolithic AA6061 alloy, all in the T6 condition, using a pin-on-disc test. In addition to the widely studied 20 vol.% Saffil MMCs, the present investigation considered a hybrid of 11% Saffil + 20% SiCP and a high volume fraction SiCP MMC, AA6061 + 60% SiCP. The wear

A. B. Gurcan; T. N. Baker

1995-01-01

377

Physical Meaning of the Equinoctial Effect for Seasonal Variation of Geomagnetic Activity  

NASA Astrophysics Data System (ADS)

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 variation 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 variation of geomagnetic 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 equinoctial epochs, if VxVx for each point at solstices are reduced to VxVx sin (c) where c is the geomagnetic colatitude of the sub-solar point. This finding indicates that the emergence of the geomagnetic disturbance is regulated by the component of the solar wind velocity perpendicular to the dipole axis of the geomagnetic field. The magnitude of the perpendicular velocity component varies seasonally even if the solar wind velocity remains constant. This appears to be the long-missed key factor causing the equinoctial effect. It is interesting to note that both the RM and equinoctial effects are related to seasonal changes in the efficiency of solar wind - magnetosphere coupling caused by changes in the geometric configuration between the sun and the geomagnetic dipole field, one in relation to Bs of the IMF, and the other in relation to the component of solar wind velocity perpendicular to the dipole axis.

Yoshida, A.

2008-12-01

378

PDGF receptor-? modulates metanephric mesenchyme chemotaxis induced by PDGF AA  

PubMed Central

PDGF B chain or PDGF receptor (PDGFR)-?-deficient (?/?) mice lack mesangial cells. To study responses of ?- and ?-receptor activation to PDGF ligands, metanephric mesenchymal cells (MMCs) were established from embryonic day E11.5 wild-type (+/+) and ?/? mouse embryos. PDGF BB stimulated cell migration in +/+ cells, whereas PDGF AA did not. Conversely, PDGF AA was chemotactic for ?/? MMCs. The mechanism by which PDGFR-? inhibited AA-induced migration was investigated. PDGF BB, but not PDGF AA, increased intracellular Ca2+ and the production of reactive oxygen species (ROS) in +/+ cells. Transfection of ?/? MMCs with the wild-type ?-receptor restored cell migration and ROS generation in response to PDGF BB and inhibited AA-induced migration. Inhibition of Ca2+ signaling facilitated PDGF AA-induced chemotaxis in the wild-type cells. The antioxidant N-acetyl-l-cysteine (NAC) or the NADPH oxidase inhibitor diphenyleneiodonium (DPI) abolished the BB-induced increase in intracellular Ca2+ concentration, suggesting that ROS act as upstream mediators of Ca2+ in suppressing PDGF AA-induced migration. These data indicate that ROS and Ca2+ generated by active PDGFR-? play an essential role in suppressing PDGF AA-induced migration in +/+ MMCs. During kidney development, PDGFR ?-mediated ROS generation and Ca2+ influx suppress PDGF AA-induced chemotaxis in metanephric mesenchyme.

Ricono, Jill M.; Wagner, Brent; Gorin, Yves; Arar, Mazen; Kazlauskas, Andrius; Choudhury, Goutam Ghosh; Abboud, Hanna E.

2009-01-01

379

Geomagnetic Storms and Acute Myocardial Infarctions Morbidity in Middle Latitudes  

NASA Astrophysics Data System (ADS)

Results of collaborative studies on revealing a possible relationship between solar activity (SA) and geomagnetic activity (GMA) and pre-hospital acute myocardial infarction (AMI) morbidity are presented. Studies were based on medical data from Bulgaria and Azerbaijan. Bulgarian data, covering the period from 01.12.1995 to 31.12.2004, concerned daily distribution of number of patients with AMI diagnose (in total 1192 cases) from Sofia Region on the day of admission at the hospital. Azerbaijani data contained 4479 pre-hospital AMI incidence cases for the period 01.01.2003-31.12.2005 and were collected from 21 emergency and first medical aid stations in Grand Baku Area (including Absheron Economical Region with several millions of inhabitants). Data were "cleaned" as much as possible from social and other factors and were subjected to medical and mathematical/statistical analysis. Medical analysis showed reliability of the used data. Method of ANalysis Of VAriance (ANOVA) was applied to check the significance of GMA intensity effect and the type of geomagnetic storms - those caused by magnetic clouds (MC) and by high speed solar wind streams (HSSWS) - on AMI incidences. Relevant correlation coefficients were calculated. Results were outlined for both considered data. Results obtained for the Sofia data showed statistically significant positive correlation between considered GMA indices and AMI occurrence. ANOVA revealed that AMI incidence number was significantly increased from the day before till the day after geomagnetic storms with different intensities. Geomagnetic storms caused by MC were related to significant increase of AMI number in comparison with the storms caused by HSSWS. There was a trend for such different effects even on -1st and +1st day for the period 1995-2004. Results obtained for the Baku data revealed trends similar to those obtained for Sofia data. AMI morbidity increment was observed on the days with higher GMA intensity and after these days as well as on the days of geomagnetic storms caused by MC and after these days.

Dimitrova, S.; Babayev, E. S.; Mustafa, F. R.; Stoilova, I.; Taseva, T.; Georgieva, K.

2009-12-01

380

Unusual declining phase of solar cycle 23: Weak semi-annual variations of auroral hemispheric power and geomagnetic activity  

NASA Astrophysics Data System (ADS)

Seasonal variations of geomagnetic activity during the declining phase of solar cycle 23 (SC23-D, 2002-2007) have been studied using auroral hemispheric power (HP), solar wind and interplanetary magnetic field (IMF) data and the Kp index. The well known semi-annual variations of geomagnetic activity, with peaks occurring during equinoxes, were virtually absent during SC23-D. This makes SC23-D markedly different from previous solar cycles which had clear semi-annual variations. In SC23-D, both Kp and HP had unusual peaks around the December solstice (in years 2003, 2004 and 2006) and August (in years 2004 and 2005), instead of at the equinoxes. These peaks appeared to be associated with solar wind/IMF and the consequent merging electric field peaks in the same periods. Furthermore, the absolute values and relative changes of the Kp index were much smaller in SC23-D than in other solar cycles. The very weak dynamic pressure and southward IMF in SC23-D might also limit the regular modulation effects that contribute to the occurrence of peaks in equinoxes.

Luan, Xiaoli; Wang, Wenbin; Burns, Alan G.; Solomon, Stanley C.; Zhang, Yongliang; Paxton, Larry J.

2009-11-01

381

Effects on the geomagnetic tail at 60 R\\/subE\\/ of the geomagnetic storm of April 9, 1971  

Microsoft Academic Search

A geomagnetic stonn beginning with a sc occurred on April 9, 1971. ; During the storm the charged particle lunar environment experiment at the Apollo ; 14 site, the solar wind spectrometer experiment at the Apollo 12 site, and the ; Ames magnetometers on Explorer 35 took data in the magnetosheath, at the ; magnetopause, in the plasma sheet, and

William J. Burke; Frederick J. Rich; David L. Reasoner; David S. Colburn; Bruce E. Goldstein

1973-01-01

382

Hot tearing studies in AA5182  

NASA Astrophysics Data System (ADS)

One of the major problems during direct chill (DC) casting is hot tearing. These tears initiate during solidification of the alloy and may run through the entire ingot. To study the hot tearing mechanism, tensile tests were carried out in semisolid state and at low strain rates, and crack propagation was studied in situ by scanning electron microscopy (SEM). These experimentally induced cracks were compared with hot tears developed in an AA5182 ingot during a casting trial in an industrial research facility. Similarities in the microstructure of the tensile test specimens and the hot tears indicate that hot tearing can be simulated by performing tensile tests at semisolid temperatures. The experimental data were compared with existing hot tearing models and it was concluded that the latter are restricted to relatively high liquid fractions because they do not take into account the existence of solid bridges in the crack.

van Haaften, W. M.; Kool, W. H.; Katgerman, L.

2002-10-01

383

Geomagnetic field intensity and inclination records from the Hawaiian long basaltic cores: geomagnetic implications  

NASA Astrophysics Data System (ADS)

In the long basaltic cores drilled in the Big Island of Hawaii, the sub-horizontal orientation of the flows and their regular accumulation with time, which makes the continuity in time almost comparable with sediments, provides an excellent opportunity to obtain a detailed record of the absolute intensity and inclination of the geomagnetic field from a sequence of lava flows. Here, we report new paleointensity (Thellier and Thellier) and inclination determinations obtained from the analysis of 370 samples from 130 flows in the subaerial part of HSDP2. These new results are combined with previous results obtained from the other long basaltic cores in Hawaii (HSDP1, SOH4 and SOH1) all selected using a set of stringent paleointensity selection criteria (PICRIT-03). In a first step the Sharp and Renne age model was used for correlation of the records. In a second step correlation was refined using some characteristic features of the paleomagnetic records themselves (HSDP 1 and HSDP 2 in particular), which led to a slight modification of the Sharp and Renne age model. The age model was further improved by correlation with the sedimentary SINT-800 record. The results are consistent between these independent records, over the different time intervals where they overlap. This allows construction of the first accurate lava record of absolute intensity and inclination at Hawaii which overlap for almost 75% of this time interval these different records overlap, the results are very consistent and allow to construct an accurate lava record of absolute geomagnetic field intensity and inclination at Hawaii for the last 420 kyr based on at least two independent records over almost. The VADM undergoes large oscillations between about 3 and 16 10^22 A.m*2 with an average values of about 8 10^22 A m^2. When the values corresponding to recognized excursional periods are omitted, the inclination is on the average 29.6°, i.e. about 6° shallower than the GAD value. These results will be compared with the prediction of dynamo solutions based on lower mantle seismic tomography of Davies et al.(2008)

Laj, C. E.; Kissel, C.; Davies, C.; Gubbins, D.

2009-12-01

384

Real-time Neural Network predictions of geomagnetic activity indices  

NASA Astrophysics Data System (ADS)

The Boyle potential or the Boyle Index (BI), ? (kV)=10-4 (V/(km/s))2 + 11.7 (B/nT) sin3(?/2), is an empirically-derived formula that can characterize the Earth's polar cap potential, which is readily derivable in real time using the solar wind data from ACE (Advanced Composition Explorer). The BI has a simplistic form that utilizes a non-magnetic "viscous" and a magnetic "merging" component to characterize the magnetospheric behavior in response to the solar wind. We have investigated its correlation with two of conventional geomagnetic activity indices in Kp and the AE index. We have shown that the logarithms of both 3-hr and 1-hr averages of the BI correlate well with the subsequent Kp: Kp = 8.93 log10(BI) - 12.55 along with 1-hr BI correlating with the subsequent log10(AE): log10(AE) = 1.78 log10(BI) - 3.6. We have developed a new set of algorithms based on Artificial Neural Networks (ANNs) suitable for short term space weather forecasts with an enhanced lead-time and better accuracy in predicting Kp and AE over some leading models; the algorithms omit the time history of its targets to utilize only the solar wind data. Inputs to our ANN models benefit from the BI and its proven record as a forecasting parameter since its initiation in October, 2003. We have also performed time-sensitivity tests using cross-correlation analysis to demonstrate that our models are as efficient as those that incorporates the time history of the target indices in their inputs. Our algorithms can predict the upcoming full 3-hr Kp, purely from the solar wind data and achieve a linear correlation coefficient of 0.840, which means that it predicts the upcoming Kp value on average to within 1.3 step, which is approximately the resolution of the real-time Kp estimate. Our success in predicting Kp during a recent unexpected event (22 July ’09) is shown in the figure. Also, when predicting an equivalent "one hour Kp'', the correlation coefficient is 0.86, meaning on average a prediction within 0.99 step. Our model is also successful in predicting AE in its original 1-hr cadence format to achieve a linear correlation of 0.83. Our real-time AE prediction model is currently being developed. However, live results of the BI plot and Kp prediction can be obtained from http://space.rice.edu/ISTP/wind.htmlspacalrt system will receive email alerts whenever the value of the predicted Kp reaches 6 or higher, or when the 10-minute BI exceeds 200 kV.

Bala, R.; Reiff, P. H.

2009-12-01

385

A statistical study of low latitude F region irregularities at Brazilian longitudinal sector response to geomagnetic storms during post-sunset hours in solar cycle 23  

NASA Astrophysics Data System (ADS)

Effects of intense geomagnetic storms (Dst index < -100) to low latitude F region irregularities in the post-sunset hours are statistically studied by the total electron content (TEC) phase fluctuation observations obtained from the ground-based global positioning system (GPS) receivers in the Brazilian longitude sector during a 7.5-year period of 1 April 1998-31 October 2005. Results show that the low latitude irregularities are significantly suppressed during the main and recovery phases of the intense geomagnetic storms in the months (September-March) that normally have high irregularity activity. In contrast, the post-sunset triggering signatures are pronounced in the low irregularity activity season (April-August) during storms. To further understand the storm-produced behaviors in the low latitude F region irregularity in the post-sunset hours, the relationship between the intensity of GPS phase fluctuations and the occurrence time of the of IMF Bz turnings is examined and discussed.

Sun, Y. Y.; Liu, J. Y.; Lin, C. H.

2012-03-01

386

Dissimilar friction stir welds in AA5083-AA6082. Part II: Process parameter effects on microstructure  

NASA Astrophysics Data System (ADS)

The aim of this study is to explore the bounds of the so-called processing window, within which good-quality welds can be produced, for the friction stir welding of AA5083 to AA6082 using a systematic set of rotation and traverse speeds. The first paper in this series examined the thermal and macroscopic aspects. In this paper, several microstructurally related characteristics, including hardness, grain size, and precipitate distribution, have been examined in greater detail. The observed variations are correlated and contrasted with the observed and predicted thermal distributions. In addition, the thermal model developed in part I has been coupled to hardness models based on classical isothermal aging studies for each alloy to predict the hardness variations across the welds.

Peel, M. J.; Steuwer, A.; Withers, P. J.

2006-07-01

387

Satellite and ground-based observations of auroral energy deposition and the effects on thermospheric composition during large geomagnetic storms: 1. Great geomagnetic storm of 20 November 2003  

Microsoft Academic Search

This report describes thermospheric composition and particle precipitation changes that occurred during the period of the great geomagnetic storm of 20–21 November 2003, an event that was associated with the passage of a magnetic cloud past the Earth. These changes are compared to those observed during geomagnetic activity on 17 November 2003 and during the intervening quieter period. The data

J. H. Hecht; T. Mulligan; D. J. Strickland; A. J. Kochenash; Y. Murayama; Y.-M. Tanaka; D. S. Evans; M. G. Conde; E. F. Donovan; F. J. Rich; D. Morrison

2008-01-01

388

Glycoxidative modification of AA amyloid deposits in renal tissue  

Microsoft Academic Search

lar matrix components. Glycoxidative modification may have a functional link to AA amyloid deposition Background. Ne-carboxymethyllysine (CML) is a prod- uct of the oxidative modification of glycated proteins, in renal tissues. which damages proteins with ageing, diabetes, uraemia and Alzheimer's disease. In contrast, pyrraline is one Keywords: AA amyloid; CML; extracellular matrix; of the advanced glycation end products, which is

Noriko Uesugi; Noriyuki Sakata; Ryoji Nagai; Tadashi Jono; Seikoh Horiuchi; Shigeo Takebayashi

2000-01-01

389

Tree-stem diameter fluctuates with the lunar tides and perhaps with geomagnetic activity.  

PubMed

Our initial objective has been to examine the suggestion of Zürcher et al. (Nature 392:665–666, 1998) that the naturally occurring variations in stem diameter of two experimental trees of Picea alba were related to near simultaneous variations in the lunisolar tidal acceleration. The relationship was positive: Lunar peaks were roughly synchronous with stem diameter peaks. To extend the investigation of this putative relationship, additional data on stem diameter variations from six other tree species were gathered from published literature. Sixteen sets of data were analysed retrospectively using graphical representations as well as cosinor analysis, statistical cross-correlation and cross-spectral analysis, together with estimated values of the lunisolar tidal acceleration corresponding to the sites, dates and times of collection of the biological data. Positive relationships were revealed between the daily variations of stem diameter and the variations of the lunisolar tidal acceleration. Although this relationship could be mediated by a 24.8-h lunar rhythm, the presence of a solar rhythm of 24.0 h could not be ruled out. Studies of transpiration in two of the observed trees indicated that although this variable was not linked to stem diameter variation, it might also be subject to lunisolar gravitational regulation. In three cases, the geomagnetic Thule index showed a weak but reciprocal relationship with stem diameter variation, as well as a positive relationship with the lunisolar tidal force. In conclusion, it seems that lunar gravity alone could influence stem diameter variation and that, under certain circumstances, additional regulation may come from the geomagnetic flux. PMID:20393759

Barlow, Peter W; Mikulecký, Miroslav; St?eštík, Jaroslav

2010-11-01

390

The cytochrome P450 2AA gene cluster in zebrafish (Danio rerio): Expression of CYP2AA1 and CYP2AA2 and response to phenobarbital-type inducers.  

PubMed

The cytochrome P450 (CYP) 2 gene family is the largest and most diverse CYP gene family in vertebrates. In zebrafish, we have identified 10 genes in a new subfamily, CYP2AA, which does not show orthology to any human or other mammalian CYP genes. Here we report evolutionary and structural relationships of the 10 CYP2AA genes and expression of the first two genes, CYP2AA1 and CYP2AA2. Parsimony reconstruction of the tandem duplication pattern for the CYP2AA cluster suggests that CYP2AA1, CYP2AA2 and CYP2AA3 likely arose in the earlier duplication events and thus are most diverged in function from the other CYP2AAs. On the other hand, CYP2AA8 and CYP2AA9 are genes that arose in the latest duplication event, implying functional similarity between these two CYPs. A molecular model of CYP2AA1 showing the sequence conservation across the CYP2AA cluster reveals that the regions with the highest variability within the cluster map onto CYP2AA1 near the substrate access channels, suggesting differing substrate specificities. Zebrafish CYP2AA1 transcript was expressed predominantly in the intestine, while CYP2AA2 was most highly expressed in the kidney, suggesting differing roles in physiology. In the liver CYP2AA2 expression but not that of CYP2AA1, was increased by 1,4-bis [2-(3,5-dichloropyridyloxy)] benzene (TCPOBOP) and, to a lesser extent, by phenobarbital (PB). In contrast, pregnenolone 16?-carbonitrile (PCN) increased CYP2AA1 expression, but not CYP2AA2 in the liver. The results identify a CYP2 subfamily in zebrafish that includes genes apparently induced by PB-type chemicals and PXR agonists, the first concrete in vivo evidence for a PB-type response in fish. PMID:23726801

Kubota, Akira; Bainy, Afonso C D; Woodin, Bruce R; Goldstone, Jared V; Stegeman, John J

2013-05-29

391

The Cry48Aa-Cry49Aa binary toxin from Bacillus sphaericus exhibits highly restricted target specificity  

PubMed Central

The Cry48Aa/Cry49Aa binary toxin of Bacillus sphaericus was recently discovered by its ability to kill Culex quinquefasciatus mosquito larvae through a novel interaction between its two components. We have investigated the target specificity of this toxin and show it to be non-toxic to coleopteran, lepidopteran and other dipteran insects, including closely related Aedes and Anopheles mosquitoes. This represents an unusually restricted target range for crystal toxins from either B. sphaericus or Bacillus thuringiensis. Gut extracts from Culex and Aedes larvae show differential processing of the Cry48Aa protein, with the location of cleavage sites in Culex reflecting those previously shown for the activation of Cry4 toxins in mosquitoes. Pre-activation of Cry48Aa/Cry49Aa with Culex extracts, however, fails to induce toxicity to Aedes larvae. Co-administration of Cry49Aa with Cry4Aa gives higher than predicted toxicity, perhaps suggesting weak synergism against Culex larvae between Cry49Aa and other three-domain Cry toxins.

Jones, Gareth W; Wirth, Margaret C; Monnerat, Rose G; Berry, Colin

2008-01-01

392

Neutral wind spectra at the auroral zone mesopause Geomagnetic effect?  

NASA Astrophysics Data System (ADS)

Neutral winds at 86 km obtained by the mesosphere-stratosphere-troposphere (MST) radar at Poker Flat, Alaska during June and July of 1980-1982 have been spectrally analyzed for evidence of changes in the neutral wind spectrum related to geomagnetic activity. Average zonal and meridional power spectra were found to be constant from year to year at periods shorter than about eight hours. The high-frequency portion of the gravity wave regime appears quite constant with no apparent correlation with local electrojet activity. Qualitative differences in the average power spectra for geomagnetically active and quiet periods at low frequencies are apparent, especially in the meridional component. The low-frequency regime is dominated by diurnal and semi-diurnal fluctuations whose amplitude is quite variable.

Johnson, R. M.; Luhmann, J. G.

1985-02-01

393

A new regard about Surlari National Geomagnetic Observatory  

NASA Astrophysics Data System (ADS)

Geomagnetic field study in Romanian stations has started with irregular measurements in late XIXth century. In 1943, the foundation of Surlari National Geomagnetic Observatory (SNGO) marks the beginning of a new era in the systematic study of geomagnetic field by a continuous registration of its variations and by carrying out standard absolute measurements in a fundamental station. The location of the observatory meets the highest exigencies, being situated in physical-geological conditions of a uniform local field, at a reasonably long distance from human activities. Its laboratories observe strict conditions of non-magnetism, ensuring the possibility of absolute standard measurements (national magnetic standards) for all the units in the country, civil or military, which are endowed with equipment based on geomagnetic metrology. These basic conditions have allowed the observatory to become by developing its initial preoccupations a centre of complex geomagnetic research, constantly involved in national and international issues, promoting new themes in our country and bringing significant contributions. During the last two decades, infrastructure and equipment used in monitoring geomagnetic field at European and planetary level have experienced a remarkable development. New registering techniques have allowed a complete to automate of data acquisition, and sampling step and their precision increased by two classes of size. Systems of transmitting these data in real time to world collecting centres have resulted in the possibility of approaching globalize studies, suitable for following some phenomena at planetary scale. At the same time, a significant development in the procedures of processing primary data has been registered, based on standardized programmes. The new stage of this fundamental research, largely applicable in various fields, is also marked by the simultaneous observation of space-time distribution of terrestrial electromagnetic field by means of stations set on satellites circling on orbits around the Earth. In Romania, fundamental research in this field have developed within a special unit SNGO, which has followed ever since its foundation two main objectives: a permanent observation of planetary magnetic field within a world net of observatories, and rendering evident some local disturbances connected, through electromagnetic induction, to the geological structure of our country's territory. Since 1998, Romanian researchers have been allowed to take part in the largest international scientific cooperation programme in the field INTERMAGNET. Last year in SNGO was made modernize of infrastructure, techniques, apparatus and informatics system suitable for acquisition, procession and interpretation of data for a continuous and systematic study of Earth electromagnetic field. After geomagnetic field and telluric field analysis of external components (daily, semi-daily, continuous and non-continuous pulsations, disturbances magnetic storms, seismic-electric signals, etc), as well as of internal components correlated with geodynamic activity and events with natural risk. Correlative phenomenological interpretation of the results obtained by SNGO with the ones obtained by other geomagnetic observatories in the INTERMAGNET network, as well as to the possibility of separating causes at local, regional and planetary scale.

Asimopolos, Laurentiu; Asimopolos, Natalia-Silvia; Pestina, Agata-Monica

2010-05-01

394

On the Terms of Geomagnetic Daily Variation in Antarctica  

NASA Astrophysics Data System (ADS)

The nature of magnetic perturbations produced by ionospheric and magnetospheric currents recorded in Antarctica, is here investigated. A mathematical method, known as Natural Orthogonal Composition, is applied to analyze the magnetic field disturbances along the three geomagnetic field components (X, Y and Z) measured at Mario Zucchelli Station (IAGA code TNB; geographic coordinates: 74.7°S, 164.1°E) from 1995 to 1998. This type of analysis allows characterizing the dominant modes of the geomagnetic field daily variability through a set of empirical orthogonal functions (EOFs). Even though such mathematically independent EOFs do not necessarily represent physically independent modes of variability, results show that some of them are actually related to well known current patterns located at high latitudes.

Tozzi, R.; de Michelis, P.; Meloni, A.

2009-12-01

395

Inferring interplanetary magnetic field polarities from geomagnetic variations  

NASA Astrophysics Data System (ADS)

In this paper, we propose a modified procedure to infer the interplanetary magnetic field (IMF) polarities from geomagnetic observations. It allows to identify the polarity back to 1905. As previous techniques it is based on the well-known Svalgaard-Mansurov effect. We have improved the quality and accuracy of polarity inference compared with the previous results of Svalgaard (1975) and Vennerstroem et al. (2001) by adding new geomagnetic stations and extracting carefully diurnal curve. The data demonstrates an excess of one of the two IMF sectors within equinoxes (Rosenberg-Coleman rule) evidencing polar field reversals at least for the last eight solar cycles. We also found a predominance of the two-sector structure in late of descending phase of solar cycle 16.

Vokhmyanin, M. V.; Ponyavin, D. I.

2012-06-01

396

Effects of geomagnetically-induced currents on HVDC converter operation  

SciTech Connect

Electrons and protons emitted by a solar flare can be captured by the Earth's magnetic field. The resulting transient in the geomagnetic field can produce quasi-dc currents in electric power systems. These geomagnetically-induced currents (GIC) in excess of 100 amps have been measured in the transformer neutral leads. With the practice of using EHV and UHV lines for transmitting ac power over long distances and because the systems are more solidly grounded, the problems posed by GIC have become more severe. This paper presents the consequences of transformer halfcycle saturation on the operation of HVDC converter terminals. A detailed computer simulation of the Square Butte HVDC system reveals that the large values of GIC can cause enough distortion in the ac system voltage at the inverter end to prevent normal system operation. Moreover, the amount of harmonics generated could overload the ac as well as the dc-side filters.

Mohan, N.; Albertson, V.D.; Bahrman, M.P.; Kappenman, K.G.; Speak, T.J.

1982-11-01

397

European Project to Improve Models of Geomagnetically Induced Currents  

NASA Astrophysics Data System (ADS)

Geomagnetically induced currents (GICs) from solar storms pose a risk to the operation of power transmission grids in Europe and across the globe. The European Risk from Geomagnetically Induced Currents (EURISGIC) project, which began in March 2011 and is supported by the Seventh Framework Programme of the European Union, seeks to mitigate this natural hazard by developing European capabilities for GIC forecasting and warning. Recent well-recognized GIC events were the province-wide blackout in Quebec, Canada, in March 1989 and the blackout in the city of Malmö, in southern Sweden, during the Halloween storm of October 2003. The progressive integration of interconnected and geographically wide power transmission grids is obviously increasing the GIC risk. Hence, there is a need for greater scientific understanding of phenomena in the solar-terrestrial environment that lead to GICs and for the development of systems that facilitate GIC modeling, forecasting, and mitigation.

Viljanen, Ari

2011-07-01

398

Analysis of transformer overheating due to geomagnetically induced currents  

SciTech Connect

Two transformers in the east coast where igneous rock zone prevails had experienced adverse effects of geomagnetically induced current (GIC) during the intense geomagnetic storm with K-9 factor. Both of these transformers exhibited dramatically different GIC effects. One transformer exhibited significant discoloration of tank paint along with a sudden increase in combustible gases. The other failed due to excessive heating in windings. This paper describes the analyses performed to explain the behavior of these two transformers. For this purpose, a rigorous method has been developed and successfully applied to a number of shell-form transformers. The method provides information on: resulting magnitude and wave-shape of exciting current; losses, loss distribution, and temperature rise in windings and tank; and permissible GIC level criterion versus applied load.

Girgis, R.S.; Ko, C.D. (ABB Power T and D Co., Muncie, IN (US)); Scott, D.J. (Westinghouse, STC, Pittsburgh, PA (US))

1991-01-01

399

Steady induction effects in geomagnetism. Part 1C: Geomagnetic estimation of steady surficial core motions: Application to the definitive geomagnetic reference field models  

NASA Astrophysics Data System (ADS)

In the source-free mantle/frozen-flux core magnetic earth model, the non-linear inverse steady motional induction problem was solved using the method presented in Part 1B. How that method was applied to estimate steady, broad-scale fluid velocity fields near the top of Earth's core that induce the secular change indicated by the Definitive Geomagnetic Reference Field (DGRF) models from 1945 to 1980 are described. Special attention is given to the derivation of weight matrices for the DGRF models because the weights determine the apparent significance of the residual secular change. The derived weight matrices also enable estimation of the secular change signal-to-noise ratio characterizing the DGRF models. Two types of weights were derived in 1987-88: radial field weights for fitting the evolution of the broad-scale portion of the radial geomagnetic field component at Earth's surface implied by the DGRF's, and general weights for fitting the evolution of the broad-scale portion of the scalar potential specified by these models. The difference is non-trivial because not all the geomagnetic data represented by the DGRF's constrain the radial field component. For radial field weights (or general weights), a quantitatively acceptable explication of broad-scale secular change relative to the 1980 Magsat epoch must account for 99.94271 percent (or 99.98784 percent) of the total weighted variance accumulated therein. Tolerable normalized root-mean-square weighted residuals of 2.394 percent (or 1.103 percent) are less than the 7 percent errors expected in the source-free mantle/frozen-flux core approximation.

Voorhies, Coerte V.

1993-10-01

400

Variations in cosmic ray cutoff rigidities during the great geomagnetic storm of November 2004  

NASA Astrophysics Data System (ADS)

A very strong interplanetary and magnetospheric disturbance observed on 7-13 November 2004 can be regarded as one of the strongest events during the entire period of space observations. In this paper we report on the studies of cosmic ray cutoff rigidity variations during 7-13 November 2004 showing how storm conditions can affect the direct cosmic ray access to the inner magnetosphere. Effective cutoff rigidities have been calculated for selected points on the ground by tracing trajectories of cosmic ray particles through the magnetospheric magnetic field of the "storm-oriented" Tsyganenko 2003 model. Cutoff rigidity variations have also been determined by the spectrographic global survey method on the basis of experimental data of the neutron monitor network. Relations between the calculated and experimental cutoff rigidities and the geomagnetic Dst-index and interplanetary parameters have been investigated. Correlation coefficients between the cutoff rigidities obtained by the trajectory tracing method and the spectrographic global survey method have been found to be in the limits 0.76-0.89 for all stations except the low-latitude station Tokyo (0.35). The most pronounced correlation has been revealed between the cutoff rigidities that exhibited a very large variation of ˜1-1.5 GV during the magnetic storm and the Dst index.

Tyasto, M. I.; Danilova, O. A.; Ptitsyna, N. G.; Sdobnov, V. E.

2013-04-01

401

Temporal fluctuations of the geomagnetic field affect pigeons' entire homing flight.  

PubMed

Tracks of pigeons, recorded with the help of GPS-receivers from two sites 30 km north and south of the Frankfurt loft, were analyzed in view of an influence of irregular fluctuations of the geomagnetic field. The data obtained were correlated with indices characterizing different aspects of these fluctuations. We found the best correlations with the index quantifying the average amplitude of the magnetic disturbance, and with an index that quantifies the average variability of the magnetic field on the day of release: stronger and more variable fluctuations lead to a counter-clockwise shift of the mean headings during the initial phase at the release site and the following departure phase, but not during the final homing phase leading to the loft. The steadiness of flight was not affected during the initial phase; however, during the later parts of the homing flight, stronger fluctuations, as well as higher variability in the magnetic field led to a marked decrease in steadiness. This continuing effect of magnetic fluctuations indicates that magnetic factors not only affect the beginning, but remain an integral part of the pigeons' navigational processes during the entire homing flight. PMID:21451981

Schiffner, Ingo; Wiltschko, Roswitha

2011-03-31

402

Mirror and Azimuthal Drift Frequencies for Geomagnetically Trapped Particles  

Microsoft Academic Search

For charged particles trapped in the geomagnetic field, the frequencies of the mirror oscillationsoand the azimuthal driftoa are defined as appropriate averages over the helieM motion around the field lines and the mirror motion between reflection points in the two mag- netic hemispheres. These integrals foro, and oa are evaluated numerically. Results are tabulated, illustrated, and represented by approximate anMytieM

D. A. Hamlin; R. Karplus; R. C. Vik; K. M. Watson

1961-01-01

403

Macroscopic model of geomagnetic-radiation from air showers  

NASA Astrophysics Data System (ADS)

We have developed a macroscopic description of coherent electro-magnetic radiation from air showers initiated by ultra-high energy cosmic rays in the presence of the geomagnetic field. This description offers a simple and direct insight in the relation between the properties of the air shower and the time-structure of the radio pulse. As we show, the structure of the pulse is a direct reflection of the important length scales in the shower.

Scholten, Olaf; Werner, Klaus

2009-06-01

404

The flywheel effect: Ionospheric currents after a geomagnetic storm  

Microsoft Academic Search

In the period following a geomagnetic storm the high-latitude, magnetospheric-driven convection pattern is normally weak. However, the neutral circulation, set up by ion-neutral momentum coupling during the main phase of the storm, may continue for several hours after the storm has ended. This persistent neutral circulation has the potential to drive Hall currents for some hours. In this paper the

W. Deng; T. L. Killeen; A. G. Burns; R. G. Roble

1991-01-01

405

Dinamics of particles and plasma movement during geomagnetic storms  

Microsoft Academic Search

Movement of moving boundaries of energetic particles (electrons with E=0.04-2.0 MeV), thermal plasma and low -frequency emission during a number of geomagnetic storms in the Earth magnetosphere and ionosphere are concidered. The data from a number of satellites Kosmos-900, Intercosmos-19, and Ohzora are used. In the main phase of a storm boundaries of particles, plasma and waves move mostly towards

G. Gdalevich; Y. Mineev

2002-01-01

406

Geomagnetic Effects on the Performance of Atmospheric Cerenkov Telescopes  

Microsoft Academic Search

Atmospheric Cerenkov telescopes are used to detect electromagnetic showers\\u000afrom primary gamma rays of energy > 300 GeV and to discriminate these from\\u000acascades due to hadrons using the shape and orientation of the Cerenkov images.\\u000aThe geomagnetic field affects the development of showers and diffuses and\\u000adistorts the images. When the component of the field normal to the shower

P. M. Chadwick; K. Lyons; T. J. L. McComb; K. J. Orford; J. L. Osborne; S. M. Rayner; S. E. Shaw; K. E. Turver

1999-01-01

407

Geomagnetic Measurements on Heavy Primary Cosmic Radiation near the Equator  

Microsoft Academic Search

The azimuthal angular distribution of primary cosmic radiation with charges Z>=6 has been measured near the geomagnetic equator (at Guam) in horizontal emulsions with known orientation relative to the earth. The observed distribution is well described by using the centered-dipole approximation to the earth's surface magnetic field (north pole at 79°N and 70°W) if the effect of the solid earth

Robert E. Danielson

1959-01-01

408

Geomagnetic Instability Time Scale 2008 (GITS-08) and dynamo processes  

Microsoft Academic Search

During the past 2.6 million years Earth's outer core geodynamo has produced at least 18 geomagnetic excursions and 5 full polarity reversals. This record has been compiled from terrestrial volcanic rocks, including mainly basaltic lava flow sequences, but also two silicic ash beds, that have been analyzed using modern paleomagnetic techniques and dated using the 40Ar\\/39Ar method. Several brief periods

B. S. Singer; K. A. Hoffman

2008-01-01

409

22' MAX China Meridian Chain of Geomagnetic and Aeronomic Observatories  

Microsoft Academic Search

The 22' MAX China Meridian Chain of Geomagnetic and Aeronomic Observatories is briefly introduced. The purpose of this chain is to provide the ground-based data for studying (1) the coupling between the solar wind, magnetosphere, ionosphere and neutral atmosphere, (2) the behaviour and the role of the mid-low latitude ionosphere and magnetosphere in the energy coupling processes, (3) large-scale magnetospheric-ionospheric

Wen-Yao Xu

1989-01-01

410

Possible Cosmic Ray Using for Forecasting of Major Geomagnetic Storms, Accompanied by Forbush-Effects  

Microsoft Academic Search

We present developing of methods for forecasting on the basis of NM hourly on-line data geomagnetic storms accompanied by Forbush-effects. These geomagnetic storms are dangerous for technology (influence on power systems, on spacecraft operations, on HF radio-communications and others) and people health. We show that for esp ecially dangerous geomagnetic storms can be used global-sp ectrographic method if on-line will

L. I. Dorman; A. V. Belov; E. A. Eroshenko; L. A. Pustil'Nik; A. Sternlieb; V. G. Yanke; I. G. Zukerman

2003-01-01

411

Cosmic Ray Monitoring and Space Dangerous Phenomena, 2. Methods of Cosmic Ray Using For Forecasting of Major Geomagnetic Storms  

NASA Astrophysics Data System (ADS)

We present developing of methods (e.g., Dorman et al., 1995, 1999) for forecasting on the basis of neutron monitor hourly on-line data (as well as on-line muon tele- scopes hourly data from different directions) geomagnetic storms of scales G5 (3- hour index of geomagnetic activity Kp=9), G4 (Kp=8) and G3 (Kp=7) (according to NOAA Space Weather Scales). These geomagnetic storms are dangerous for peo- ple technology and health (influence on power systems, on spacecraft operations, on HF radio-communications and others). We show that for especially dangerous geo- magnetic storms can be used global-spectrographic method if on-line will be avail- able 35-40 NM and muon telescopes. In this case for each hour can be determined CR anisotropy vector, and the specifically behavior of this vector before SC of ge- omagnetic storms G5, G4 or G3 (according to NOAA Space Weather Scales) can be used as important factor for forecast. The second factor what can be used for SC forecast is specifically behavior of CR density (CR intensity) for about 30-15 hours before SC (caused mainly by galactic CR particles acceleration during interaction with shock wave moved from the Sun). The third factor is effect of cosmic ray pre- decreasing, caused by magnetic connection of the Earth with the region behind the shock wave. We demonstrate developing methods on several examples of major ge- omagnetic storms. REFERENCES: Dorman L.I., et al. "Cosmic-ray forecasting fea- tures for big Forbush-decreases". Nuclear Physics B, Vol. 49A, pp. 136-144. (1995). L.I.Dorman, et al, "Cosmic ray Forbush-decrease as indicators of space dangerous phenomenon and possible use of cosmic ray data for their prediction", Proc. of 26-th Intern. Cosmic Ray Conference, Salt Lake City, Vol. 6, p. 476-479, (1999).

Belov, A. V.; Dorman, L. I.; Eroshenko, E. A.; Iucci, N.; Mavromichalaki, H.; Pustil'Nik, L. A.; Sternlieb, A.; Villoresi, G.; Yanke, V. G.; Zukerman, I. G.

412

Characterization of AA size lithium rechargeable cells  

NASA Astrophysics Data System (ADS)

Testing of AA size rechargeable cells for underwater vehicle and other naval applications is complete for AT&T's lithium/niobium triselenide (Li/NbSe3) and Moli Energy's lithium/molybdenum disulfide (Li/MoS2) and in progress on Moli Energy's lithium/manganese dioxide (Li/MnO2) and W. R. Grace's lithium/titanium disulfide (Li/TiS2). Cell cycling was performed at various discharge rates, temperatures, and depths of discharge. At 25 C and 1 mA/cm2 (roughly the C/4 rate), delivered energy densities were about 40 Wh/lb for NbSe3, TiS2, and MnO2 and 22 Wh/lb for MoS2. Under the same conditions, nickel/cadmium (Ni/Cd) cells deliver only 10 Wh/lb. However Ni/Cd cycles much longer and the lithium cells are far more vulnerable than Ni/Cd to performance loss in low temperature, high discharge rate cycling. The NbSe3 data and the (limited) TiS2 data indicate that these cells tend to accept excessive charge which is often associated with lithium dendrite shorting and considered potentially hazardous. At 1 mA/cm2 and 25 C, discharge plateaus ranged from 2.9 V for MnO2 to 1.8 V for MoS2.

Murphy, T. C.; Cason-Smith, D. M.; James, S. D.; Smith, P. H.

413

Characterization of spent AA household alkaline batteries.  

PubMed

The aim of this work is identification of the structural components of actual domestic spent alkaline AA batteries, as well as quantification of some of their characteristics. Weight, humidity, ash content, zinc and zinc oxide on anode, manganese on cathode and other metals, potassium hydroxide on the internal components and heating values for papers, anode and cathode were determined in several batteries. As expected, cathode, anode and the steel can container are the main contributors to the 23.5 g average weight of the batteries. Cathode is also the major contributor to the positive heating value of the batteries as well as to the heavy metals content. Mercury was detected in very low levels in these mercury-free batteries. Zinc and zinc oxide amounts in the anodes are highly variable. Results obtained were compared to information on alkaline batteries in the literature from 1993 to 1995; and a positive evolution in their manufacture is readily apparent. Data from the producer of batteries shows some small discrepancies relative to the results of this experimental work. PMID:15964181

Almeida, Manuel F; Xará, Susana M; Delgado, Julanda; Costa, Carlos A

2005-06-16

414

Polar cap electron density distribution from IMAGE radio plasma imager measurements: Empirical model with the effects of solar illumination and geomagnetic activity  

NASA Astrophysics Data System (ADS)

We present a statistical study of the relative importance of solar illumination and geomagnetic activity dependences of the electron density (Ne) distribution in the polar cap magnetosphere based on 5 years of electron density measurements made by the radio plasma imager (RPI) on board the IMAGE spacecraft. This study covers a geocentric distance of R = 1.4-5.0 RE, and the polar cap is defined by an empirical boundary model that takes into account the dynamic nature of the location and size of the polar cap. The RPI Ne data show that the electron density distribution within the polar cap depends on the geocentric distance, R, geomagnetic activity level, e.g., measured by the Kp index, and solar illumination (solar zenith angle) at the footprints of the geomagnetic field lines. Our analysis of RPI Ne data shows that although an increase in geomagnetic activity leads to an enhanced Ne, the enhancement is found to be altitude-dependent such that it is most pronounced at higher altitudes and less significant at lower altitudes. At geocentric distance of R = 4.5 RE, an increase in the geomagnetic activity level from Kp < 2 to ˜5 results in an Ne increase by a factor of ˜5. On the other hand, the observations show a strong solar illumination control of Ne at lower altitudes and not at higher. RPI Ne data show that at geocentric distance of about 2 RE in the polar cap, the average Ne is larger on the sunlit side than on the darkside by a factor of 3-4 for both quiet and disturbed conditions. At geocentric distance of R ? 2.5 RE the effects of these two factors on Ne appear to be comparable. Similar to previous polar cap density models, the new empirical model of Ne developed in this study takes the form of a power law. While in the previous Ne functional representations the power index is a constant, the power index in our representation of Ne distribution is a function of Kp and solar zenith angle.

Nsumei, Patrick A.; Reinisch, Bodo W.; Song, Paul; Tu, Jiannan; Huang, Xueqin

2008-01-01

415

Midlatitude cooling caused by geomagnetic field minimum during polarity reversal.  

PubMed

The climatic effects of cloud formation induced by galactic cosmic rays (CRs) has recently become a topic of much discussion. The CR-cloud connection suggests that variations in geomagnetic field intensity could change climate through modulation of CR flux. This hypothesis, however, is not well-tested using robust geological evidence. Here we present paleoclimate and paleoenvironment records of five interglacial periods that include two geomagnetic polarity reversals. Marine oxygen isotope stages 19 and 31 contain both anomalous cooling intervals during the sea-level highstands and the Matuyama-Brunhes and Lower Jaramillo reversals, respectively. This contrasts strongly with the typical interglacial climate that has the temperature maximum at the sea-level peak. The cooling occurred when the field intensity dropped to <40% of its present value, for which we estimate >40% increase in CR flux. The climate warmed rapidly when field intensity recovered. We suggest that geomagnetic field intensity can influence global climate through the modulation of CR flux. PMID:23297205

Kitaba, Ikuko; Hyodo, Masayuki; Katoh, Shigehiro; Dettman, David L; Sato, Hiroshi

2013-01-07

416

Archaeomagnetic Dating in Europe Using a Global Geomagnetic Field Model  

NASA Astrophysics Data System (ADS)

Using up-to-date archaeomagnetic data from Europe and CALS7K.2 as an apriori model, we produce a global geomagnetic field model to be used for archaeomagnetic dating in Europe. More details on the modelling process will be presented elsewhere (in session GP12, abstract: Geophysical insights from archaeomagnetic dating). Here we apply the global geomagnetic field model to a series of test cases from both recently published data and unpublished data to demonstrate its application to archaeomagnetic dating. We compare the results produced using our model with those from the spherical cap harmonic model, SCHA.DIF.3K (Pavón-Carrasco et al., 2009), the global geomagnetic field model, ARCH3K.1 (Korte et al., 2009) and those produced using the palaeosecular variation curves generated using Bayesian statistics (Lanos, 2004). We include examples which emphasise the importance of using three component data (declination, inclination and intensity) to produce an improved archaeomagnetic date. In addition to the careful selection of an appropriate model for archaeomagnetic dating, the choice of errors on the model curves is vital for providing archaeologists with an age range of possible dates. We discuss how best to constrain the errors on the model curves and alternative ways to the mathematical method of Lanos (2004) for producing an archaeomagnetic date for archaeologists.

Lodge, A.; Suttie, N.; Holme, R.; Shaw, J.; Hill, M. J.; Linford, P.

2009-12-01

417

Recent developments in the global geomagnetic observatory network  

NASA Astrophysics Data System (ADS)

Magnetic observatories provide precise and continuous measurements of geomagnetic variations over time scales ranging from one second to more than a century. They have been an essential observational infrastructure for geomagnetic research for about 170 years. A large fraction of magnetic observatories belong to INTERMAGNET (International Real-time Magnetic Observatory Network), a global network founded in the late 1980s which now includes about 115 observatories in 45 countries. INTERMAGNET magnetic observatories comply with strict data quality and timeliness standards and distribute their data through an integrated data information system. Recent years have seen a rapid expansion of the global network: new observatories have been installed in remote locations, such as oceanic islands (St Helena, Easter Island, Tristan da Cunha) or Antarctica (Dome C); ancient observatories have been upgraded to international standards (for example in China and Siberia). This has been prompted by the need to have a more geographically homogeneous network. In parallel, new data products (one second data and quasi-definitive data) are being made available, addressing a wide variety of research needs, and real timeliness is being improved for operational purposes such as space weather monitoring and forecasting. This presentation will provide an overview of these recent developments, focusing on those most relevant to the geomagnetic modeling community, and discuss their expected scientific benefits.

Chulliat, A.

2011-12-01

418

Geomagnetic storm effect on low-latitude total electron content  

NASA Astrophysics Data System (ADS)

During geomagnetically disturbed conditions electrodynamic coupling between high and lowlatitude ionosphere dominates the ionospheric behavior at low latitudes. The interplanetary electric field coupled to low-latitude ionosphere plays a significant role in low-latitude Total Electron Content (TEC) variation during geomagnetic storms. In the present paper, TEC observations using GPS satellites from a chain of GPS receivers extending from the magnetic equator to the crest of the Equatorial Ionization Anomaly (EIA) and beyond, in the Indian region during three storm periods in May 2005, a low solar activity period, are used to bring out for the first time, the TEC behavior during storms over such a wide geographical region. The EIA development is found to be strongly modulated by the storm-time electric field. The double main phase moderate geomagnetic storm on 8 May 2005 causes an enhancement and poleward movement of EIA crest on 9 and 10 May, which recovers to normal values on 11 May, in accordance with the storm evolution. Similar analysis for the strong storm of 15 May and weak storm of 20 May are also presented. The reasons for the observed differences in the TEC behavior between these storms are discussed in detail in terms of the physical processes.

Bagiya, Mala; Thampi, Smitha; Aggarwal, Malini; Ravindran, Sudha; Joshi, H. P.; Iyer, K. N.; G, Manju; Sridharan, R.

419

Response of ionosphere to strong geomagnetic storm: observation and modelling  

NASA Astrophysics Data System (ADS)

This paper presents the results derived from investigating the ionospheric response in middle and auroral latitudes to a strong geomagnetic storm on September 25, 1998. Our analysis of the behavior of the ionosphere was based on using the measurements from a network of ionospheric stations located in the region of Siberia and the Far East. According to the latitudinal location, the stations under consideration can be divided into three groups: auroral, subauroral, and mid-latitude stations. Data from some of European stations were used in the comparison. The numerical model for ionosphere-plasmasphere coupling that was developed at the ISTP SB RAS, was used to interpret the observational data. By analyzing the data, it was possible to identify the following regularities and differences. Intense negative disturbances during the main phase of the September 25 geomagnetic storm were observed at all stations under investigation. The main differences were marked both during the initial phase and in the recovery phase of the geomagnetic storm. The ionospheric response during the initial phase is determined primarily by the local time of geomagnetic storm onset and the latitude of station. The longitude effect of ionospheric disturbances was observed during the recovery phase. A theoretical analysis of the processes controlling the mid-latitude ionospheric response to the geomagnetic storm showed a good agreement of modeling results and measurements, as well as made it possible to ascertain the crucial role of the neutral composition variations in the ionospheric parameter variations observed. At auroral and subauroral stations the electron density variability during the storm is much more pronounced. According to results of analysis of the ionospheric plasma convection trajectories, this variability is caused by the combined effect of convection and energetic electron precipitation. Neutral thermospheric composition disturbances exert some influence on the electron density background level in this range of latitudes. The reversal of sign of the disturbance, when moving eastward from the west, during the storm recovery phase is difficult to explain by the local time effect. One possible reason could be the wave phenomena in the thermosphere, and local changes in the neutral wind system.

Pirog, P.; Polekh, P.; Tashchilin, T.; Romanova, R.; Zherebtsov, Z.

420

A database of synthetic observations for geomagnetic data assimilation practice  

NASA Astrophysics Data System (ADS)

Data assimilation aims at producing an optimal estimate of the state of the dynamical system one is interested in by combining two sources of information : physical laws (in the form of a numerical model) and observations. A mandatory step during the development of a data assimilation framework involves a validation phase using synthetic data. In this well-controlled environment, the true dynamical trajectory of the system is known (it results from the integration of the numerical model), and it is used to generate synthetic observations. Those are subsequently used to assess the efficacy, and to highlight possible shortcomings, of the chosen methodology. Data assimilation has recently come to the fore in geomagnetism (e.g. Fournier et al., 2010), a surge motivated by our increased ability to observe the geomagnetic field (thanks to dedicated satellite missions), and by the concurrent progress in the numerical description of core dynamics. Open questions are related to the type of physical models one should resort to, and to the choice of a suitable algorithm, able to integrate the highly heterogeneous geomagnetic record at our disposal, and to deal with the non-linearities of the problem at hand (e.g. Aubert & Fournier, 2011; Fournier et al., 2011). Here we report on the construction of a database of synthetic observations meant at reproducing the heterogeneity of the geomagnetic record (in terms of temporal and spatial coverage). This database relies on two dynamical trajectories: a long-term dynamical trajectory (spanning the equivalent of the past few millenia) computed from a three-dimensional, convection-driven, dynamo model, able to represent accurately the long-term variability of the geomagnetic field a short-term dynamical trajectory (spanning the equivalent of a few decades), computed from a high-resolution three-dimensional model, able to represent interannual to decadal core processes (e.g. Gillet et al., 2011), and whose basic state is determined from the long-term trajectory. These two trajectories are used to generate synthetic observations representative of the current archeomagnetic, historical, observatory and satellite catalogs. For each catalog, we add realistic contributions from other sources (crust, external fields) and noise to the observations, with levels and properties expected for each. We also complement the archeomagnetic, historical and observatory catalog with a corresponding perfect catalog (in terms of the uniformity of the coverage), and with a catalog containing the Gauss coefficients describing the magnetic field at the surface of the Earth (with an arbitrary level of truncation).

Fournier, A.; Aubert, J.; Thebault, E.; Schaeffer, N.

2012-04-01