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1

Power grid disturbances and polar cap index during geomagnetic storms  

NASA Astrophysics Data System (ADS)

The strong geomagnetic storm in the evening of 30 October 2003 caused high-voltage power grid disturbances in Sweden that expanded to produce hour-long power line outage in Malmö located in the southern part of the country. This was not a unique situation. The geomagnetic storm on 13 March 1989 caused extensive disruptions of high-voltage power circuits especially in the Province of Quebec, Canada, but also to a lesser degree in Scandinavia. Similar events have occurred earlier, among others, during the great storms of 13-14 July 1982 and 8-9 February 1986. These high-voltage power grid disturbances were related to impulsive magnetic variations accompanying extraordinarily intense substorm events. The events were preceded by lengthy intervals of unusually high values of the Polar Cap (PC) index caused by enhanced transpolar ionospheric convection. The transpolar convection transports magnetic flux from the dayside to nightside which causes equatorward displacements of the region of auroral activity enabling the substorms to hit vital power grids. During the 30 October 2003 event the intense solar proton radiation disabled the ACE satellite observations widely used to provide forecast of magnetic storm events. Hence in this case the alarmingly high PC index could provide useful warning of the storm as a back-up of the missing ACE-based forecast. In further cases, monitoring the PC index level could provide supplementary storm warnings to the benefit of power grid operators.

Stauning, Peter

2013-06-01

2

Homogenization of the historical records of geomagnetic field components and geomagnetic K-index of the Magnetic Observatory of Coimbra  

NASA Astrophysics Data System (ADS)

The Coimbra Magnetic Observatory (COI) (Portugal) has a long history of observation of the geomagnetic field, spanning almost 150 years. Measurements of the geomagnetic field components started in 1866 and include the observations of all components: horizontal (H), downward vertical (Z), northward (X), eastward (Y), total field magnitude (F), inclination (I) and declination (D). These long instrumental geomagnetic records provide very important information about variability of measured parameters, their trends and cycles, and can be used to improve our knowledge on the sources that drive variations of the geomagnetic field: liquid core dynamics (internal) and solar forcing (external). However, during the long life of the Coimbra observatory, some inevitable changes in station location, instrument's park and electromagnetic environment took place. These changes affected the quality of the data causing breaks and jumps in the series. Clearly, these inhomogeneities, typically of shift-like (step-like) or trend-like, have to be corrected or, at least, minimized in order for the data to be used in scientific studies or to be submitted to international databases. The homogenization of the monthly and annual averages of geomagnetic field components has been done using visual and statistical tests (e.g. standard normal homogeneity test), allowing to estimate not only the level of inhomogeneity of the studied series, but also to detect the highly probable homogeneity break points. These have been compared with the metadata, reference series from the nearest geomagnetic stations and geomagnetic field models (e.g. CM4 and CHAOS3) in order to find and to set up the indispensable correction factors. Similar methods have been applied to the homogenization of the local geomagnetic K-index series (from 1952 to 2012). As a result, the homogenized geomagnetic monthly and annual averages of the series measured in COI are considered to be essentially free of artificial shifts and ready to be used by the scientific community.

Morozova, Anna; Ribeiro, Paulo; Pais, M. Alexandra

2013-04-01

3

Relationship Between the Magnetic Flux of Solar Eruptions and the Ap Index of Geomagnetic Storms  

NASA Astrophysics Data System (ADS)

Solar coronal mass ejections (CMEs) are main drivers of the most powerful non-recurrent geomagnetic storms. In the extreme-ultraviolet range, CMEs are accompanied by bright post-eruption arcades and dark dimmings. The analysis of events of the Solar Cycle 23 (Chertok et al., 2013, Solar Phys. 282, 175) revealed that the summarized unsigned magnetic flux in the arcades and dimming regions at the photospheric level, $\\Phi$, is significantly related to the intensity (Dst index) of geomagnetic storms. This provides the basis for the earliest diagnosis of geoefficiency of solar eruptions. In the present article, using the same data set, we find that a noticeable correlation exists also between the eruptive magnetic flux, $\\Phi$, and another geomagnetic index, Ap. As the magnetic flux increases from tens to $\\approx 500$ (in units of $10^{20}$ Mx), the geomagnetic storm intensity measured by the 3-hour Ap index, enhances in average from Ap $\\approx 50$ to a formally maximum value of 400 (in units of 2 nT). The established relationship shows that in fact the real value of the Ap index is not limited and during the most severe magnetic storms may significantly exceed 400.

Chertok, I. M.; Abunina, M. A.; Abunin, A. A.; Belov, A. V.; Grechnev, V. V.

2014-11-01

4

Solar wind and geomagnetism: toward a standard classification of geomagnetic activity from 1868 to 2009  

NASA Astrophysics Data System (ADS)

We examined solar activity with a large series of geomagnetic data from 1868 to 2009. We have revisited the geomagnetic activity classification scheme of Legrand and Simon (1989) and improve their scheme by lowering the minimum Aa index value for shock and recurrent activity from 40 to 20 nT. This improved scheme allows us to clearly classify about 80% of the geomagnetic activity in this time period instead of only 60% for the previous Legrand and Simon classification.

Zerbo, J. L.; Amory Mazaudier, C.; Ouattara, F.; Richardson, J. D.

2012-02-01

5

Relationship between the Magnetic Flux of Solar Eruptions and the Ap Index of Geomagnetic Storms  

E-print Network

Solar coronal mass ejections (CMEs) are main drivers of the most powerful non-recurrent geomagnetic storms. In the extreme-ultraviolet range, CMEs are accompanied by bright post-eruption arcades and dark dimmings. The analysis of events of the Solar Cycle 23 (Chertok et al., 2013, Solar Phys. 282, 175) revealed that the summarized unsigned magnetic flux in the arcades and dimming regions at the photospheric level, Phi, is significantly related to the intensity (Dst index) of geomagnetic storms. This provides the basis for the earliest diagnosis of geoefficiency of solar eruptions. In the present article, using the same data set, we find that a noticeable correlation exists also between the eruptive magnetic flux, Phi, and another geomagnetic index, Ap. As the magnetic flux increases from tens to approx. 500 (in units of 10^{20} Mx), the geomagnetic storm intensity measured by the 3-hour Ap index, enhances in average from Ap approx. 50 to a formally maximum value of 400 (in units of 2 nT). The established rela...

Chertok, I M; Abunin, A A; Belov, A V; Grechnev, V V

2014-01-01

6

Forecasting geomagnetic sctivity of Dst index using radial basis function networks  

NASA Astrophysics Data System (ADS)

The magnetosphere can be considered as a complex input-output system For such a system the solar wind plays the role of the input and the geomagnetic indices can be considered as outputs The Dst index is used to measure the disturbance of the geomagnetic field in the magnetic storms Numerous studies of correlations between the solar wind parameters and magnetospheric disturbances show that the product of the solar wind velocity V and the southward component of the magnetic field quantified by Bs represents the input that can be considered as the input to the magnetosphere This multiplied input will be denoted by VB s Many approaches have been proposed to analyse the Dst and other geomagnetic activity indices Input-output observational data-based modelling approaches provides a powerful tool for forecasting geomagnetic activities for example the prediction of the Dst index Radial basis function RBF networks as a special class of single hidden-layer feedforward neural networks have been proved to be universal approximators One advantage of RBF networks compared with multi-layer perceptrons MLP is that the linearly weighted structure of RBF networks where parameters in the units of the hidden layer can often be pre-fixed can be easily trained with a fast speed without involving nonlinear optimization Another advantage of RBF networks compared with other basis function networks is that each basis function in the hidden units is a nonlinear mapping which maps a multivariable input to a

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

7

Changes in fractal properties of geomagnetic indexes as possible magnetic storms precursors  

E-print Network

Records of Dst, Kp and Sym-H indexes are analyzed looking for evidences of possible precursors for magnetic storms. To accomplish this task the main magnetic storms were located and some periods immediately before storms and some periods well before them studied. Statistical properties of both types of periods were then compared. In particular, were compared the slopes of the power laws that have been found for the distributions of indexes values. A systematic deviation was found between both distributions for the Kp index. It was no so for Dst and Sym-H indexes. For the three indexes it was found a correlation between slopes and the corresponding storm intensity, which could serve as a probabilistic approach to magnetic storms forecasting. The data for the analysis was obtained at the World Data Centre for Geomagnetism at Kyoto.

Dias, V H A; Papa, A R R; Dias, Vitor H. A.; Franco, Jorge O. O.; Papa, Andres R. R.

2006-01-01

8

The correlation between solar and geomagnetic activity - Part 1: Two-term decomposition of geomagnetic activity  

NASA Astrophysics Data System (ADS)

By analyzing the logarithmic relationship between geomagnetic activity as represented by the annual aa index and solar magnetic field activity as represented by the annual sunspot number (Rz) during the period 1844-2010, aa is shown to lie in between two lines defined solely by Rz. Two ways can be used to decompose the aa index into two components. One is decomposing aa into the sum of the baseline (aab) and the remainder (aau) with a null correlation. Another is dividing the top-line (aat) into the sum of aa and the remainder (aad) with a null correlation. The first decomposition is similar to the traditional one. The second decomposition implies a nonlinear relationship of aa with Rz (aat) and a decay process (aad). Therefore, aat=aa+aad=aab+aau+aad: (i) aat is related to the solar energy potential of generating geomagnetic activity (associated with Rz); (ii) aab is related to transient phenomena; (iii) aau is related to recurrent phenomena; and (iv) aad is related to the energy loss in the transmission from solar surface to the magnetosphere and ionosphere that failed to generate geomagnetic activity.

Du, Z. L.

2011-08-01

9

Trend and abrupt changes in long-term geomagnetic indices  

NASA Astrophysics Data System (ADS)

Advanced statistical methods are employed to analyze three long-term time series of geomagnetic activity indices (aa, IHV, and IDV) together with sunspot number (Rz) to examine whether or not the aa index can realistically represent long-term variations of geomagnetic activity. We make use of a decomposition method called STL, which is a time domain filtering procedure that decomposes a time series into trend, cyclic, and residual components using nonparametric regression. A Bayesian change point analysis is also applied to the geomagnetic indices, as well as to sunspot number, to detect abrupt changes that may be caused by either instrumental changes, calibration errors, or sudden changes in solar activity. Our analysis shows that all three long-term geomagnetic indices share a similar centennial-scale variation that resembles the long-term trend of sunspot number Rz. The amplitude ratio between the centennial-scale variation and 11-year cycle of aa and IHV are closely comparable. Overall, our analysis suggests that the majority of the changes in the aa index are controlled by solar activity. Instrumental change or site relocation has only a limited effect on the long-term trend of aa. This is in good agreement with those previous studies which have shown aa to be a reliable long-term index.

Lu, Hua; Li, Yun; Clilverd, Mark A.; Jarvis, Martin J.

2012-05-01

10

GPS phase scintillation and proxy index at high latitudes during a moderate geomagnetic storm  

NASA Astrophysics Data System (ADS)

The amplitude and phase scintillation indices are customarily obtained by specialised GPS Ionospheric Scintillation and TEC Monitors (GISTMs) from L1 signal recorded at the rate of 50 Hz. The scintillation indices S4 and ?? are stored in real time from an array of high-rate scintillation receivers of the Canadian High Arctic Ionospheric Network (CHAIN). Ionospheric phase scintillation was observed at high latitudes during a moderate geomagnetic storm (Dst = -61 nT) that was caused by a moderate solar wind plasma stream compounded with the impact of two coronal mass ejections. The most intense phase scintillation (?? ~ 1 rad) occurred in the cusp and the polar cap where it was co-located with a strong ionospheric convection, an extended tongue of ionisation and dense polar cap patches that were observed with ionosondes and HF radars. At sub-auroral latitudes, a sub-auroral polarisation stream that was observed by mid-latitude radars was associated with weak scintillation (defined arbitrarily as ?? < 0.5 rad). In the auroral zone, moderate scintillation coincided with auroral breakups observed by an all-sky imager, a riometer and a magnetometer in Yellowknife. To overcome the limited geographic coverage by GISTMs other GNSS data sampled at 1 Hz can be used to obtain scintillation proxy indices. In this study, a phase scintillation proxy index (delta phase rate, DPR) is obtained from 1-Hz data from CHAIN and other GPS receivers. The 50-Hz and 1-Hz phase scintillation indices are correlated. The percentage occurrences of ?? > 0.1 rad and DPR > 2 mm s-1, both mapped as a function of magnetic latitude and magnetic local time, are very similar.

Prikryl, P.; Ghoddousi-Fard, R.; Kunduri, B. S. R.; Thomas, E. G.; Coster, A. J.; Jayachandran, P. T.; Spanswick, E.; Danskin, D. W.

2013-05-01

11

Statistical Technique for Intermediate and Long-Range Estimation of 13-Month Smoothed Solar Flux and Geomagnetic Index  

NASA Technical Reports Server (NTRS)

This report documents the Marshall Space Flight Center (MSFC) 13-month smoothed solar flux (F(sub 10.7)) and geomagnetic index (A(sub p)) intermediate (months) and long-range (years) statistical estimation technique, referred to as the MSFC Lagrangian Linear Regression Technique (MLLRT). Estimates of future solar activity are needed as updated input to upper atmosphere density models used for satellite and spacecraft orbital lifetime predictions. An assessment of the MLLRT computer program's products is provided for 5-year periods from the date estimates were made. This was accomplished for a number of past solar cycles.

Niehuss, K. O.; Euler, H. C., Jr.; Vaughan, W. W.

1996-01-01

12

Schizophrenia and season of birth: relationship to geomagnetic storms.  

PubMed

An excess pattern of winter and spring birth, of those later diagnosed as schizophrenic, has been clearly identified in most Northern Hemisphere samples with none or lesser variation in Equatorial or Southern Hemisphere samples. Pregnancy and birth complications, seasonal variations in light, weather, temperature, nutrition, toxins, body chemistry and gene expression have all been hypothesized as possible causes. In this study, the hypothesis was tested that seasonal variation in the geomagnetic field of the earth primarily as a result of geomagnetic storms (GMS) at crucial periods in intrauterine brain development, during months 2 to 7 of gestation could affect the later rate of development of schizophrenia. The biological plausibility of this hypothesis is also briefly reviewed. A sample of eight representative published studies of schizophrenic monthly birth variation were compared with averaged geomagnetic disturbance using two global indices (AA*) and (aa). Three samples showed a significant negative correlation to both geomagnetic indices, a further three a significant negative correlation to one of the geomagnetic indices, one showed no significant correlation to either index and one showed a significant positive correlation to one index. It is suggested that these findings are all consistent with the hypothesis and that geomagnetic disturbance or factors associated with this disturbance should be further investigated in birth seasonality studies. PMID:14693348

Kay, Ronald W

2004-01-01

13

Assessing the validity of station location assumptions made in the calculation of the geomagnetic disturbance index, Dst  

USGS Publications Warehouse

In this paper, the effects of the assumptions made in the calculation of the Dst index with regard to longitude sampling, hemisphere bias, and latitude correction are explored. The insights gained from this study will allow operational users to better understand the local implications of the Dst index and will lead to future index formulations that are more physically motivated. We recompute the index using 12 longitudinally spaced low-latitude stations, including the traditional 4 (in Honolulu, Kakioka, San Juan, and Hermanus), and compare it to the standard United States Geological Survey definitive Dst. We look at the hemisphere balance by comparing stations at equal geomagnetic latitudes in the Northern and Southern hemispheres. We further separate the 12-station time series into two hemispheric indices and find that there are measurable differences in the traditional Dst formulation due to the undersampling of the Southern Hemisphere in comparison with the Northern Hemisphere. To analyze the effect of latitude correction, we plot latitudinal variation in a disturbance observed during the year 2005 using two separate longitudinal observatory chains. We separate these by activity level and find that while the traditional cosine form fits the latitudinal distributions well for low levels of activity, at higher levels of disturbance the cosine form does not fit the observed variation. This suggests that the traditional latitude scaling is insufficient during active times. The effect of the Northern Hemisphere bias and the inadequate latitude scaling is such that the standard correction underestimates the true disturbance by 10–30 nT for storms of main phase magnitude deviation greater than 150 nT in the traditional Dst index.

Gannon, Jennifer

2012-01-01

14

Coincident 1.3-year periodicities in the ap geomagnetic index and the solar wind  

E-print Network

to the one-hour resolution of the space- craft data used, it should be a better index for the purposes Center for Space Research, Massachusetts Institute of Technology, Cambridge, Massachusetts A. Szabo Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, Maryland J. D

Richardson, John

15

Solar-Terrestrial Coupling Evidenced by Periodic Behavior in Geomagnetic Indexes and the Infrared Energy Budget of the Thermosphere  

NASA Technical Reports Server (NTRS)

We examine time series of the daily global power (W) radiated by carbon dioxide (at 15 microns) and by nitric oxide (at 5.3 microns) from the Earth s thermosphere between 100 km and 200 km altitude. Also examined is a time series of the daily absorbed solar ultraviolet power in the same altitude region in the wavelength span 0 to 175 nm. The infrared data are derived from the SABER instrument and the solar data are derived from the SEE instrument, both on the NASA TIMED satellite. The time series cover nearly 5 years from 2002 through 2006. The infrared and solar time series exhibit a decrease in radiated and absorbed power consistent with the declining phase of the current 11-year solar cycle. The infrared time series also exhibits high frequency variations that are not evident in the solar power time series. Spectral analysis shows a statistically significant 9-day periodicity in the infrared data but not in the solar data. A very strong 9-day periodicity is also found to exist in the time series of daily A(sub p) and K(sub p) geomagnetic indexes. These 9-day periodicities are linked to the recurrence of coronal holes on the Sun. These results demonstrate a direct coupling between the upper atmosphere of the Sun and the infrared energy budget of the thermosphere.

Mlynczak, Martin G.; Martin-Torres, F. Javier; Mertens, Christopher J.; Marshall, B. Thomas; Thompson, R. Earl; Kozyra, Janet U.; Remsberg, Ellis E.; Gordley, Larry L.; Russell, James M.; Woods, Thomas

2008-01-01

16

AGU: Journal of Geophysical Research geomagnetic ionosphere currents  

E-print Network

fits are shown along-side scatter plots of individual measurements in corrected geomagnetic apexAGU: Journal of Geophysical Research Keywords geomagnetic ionosphere currents Index Terms Ionosphere: Polar cap ionosphere Ionosphere: Current systems Geomagnetism and Paleomagnetism: Rapid time

Michigan, University of

17

Did Open Solar Magnetic Field Increase during the last 100 Years: A Reanalysis of Geomagnetic Activity  

NASA Astrophysics Data System (ADS)

One of the most interesting and important questions in solar-terrestrial physics is whether the magnetic activity of the Sun has greatly increased during the last 100 years. A significant increase in solar magnetic activity is indicated by the well known fact that the average amplitude of sunspot cycles during the latter part of the 20th century is higher than in the beginning. The increasing sunspot activity leads, in a model presented by Solanki et al. (2000), to a corresponding centennial increase of the total and open (heliospheric) solar magnetic fields. The heliospheric magnetic field is a major driver of cosmic ray modulation and geomagnetic activity. Lockwood et al. (1999) used the geo-magnetic aa index to show that the interplanetary magnetic field has more than doubled during the last 100 years. Also, Usoskin et al. (2003) used long-term measurements of cosmogenic isotopes produced by cosmic rays to show that the average sunspot activity since 1940s is higher than during the last 1000 years. Despite the versatility and reason-able uniformity of these results, serious concern has recently been raised on the long-term consistency of the aa index and, thereby, on the centennial rise of solar magnetic activity. As an alternative to the aa index, Svalgaard et al. (2003) introduced introduced a new IHV index as a more reliable and more homogeneous measure of long-term geomag-netic activity, finding no significant increase during the last 100 years. Here we reanalyse the longest series of geomagnetic observations from a number of stations in order to find out whether or not there is reliable evidence for a centennial increase of geomagnetic activity and, therby, of solar magnetic field.

Mursula, K.; Martini, D.; Karinen, A.

18

On the long-term evolution of the PC index  

NASA Astrophysics Data System (ADS)

A number of geomagnetic indices have been designed to describe the evolution of various current systems developing in the magnetosphere and ionosphere as a consequence of the interaction of the solar wind and heliospheric magnetic field. The Polar Cap (PC) index, a proxy for the electric field and convection in the polar ionosphere, has been only recently introduced (1980). We attempt here to reconstruct the PC index back to 1870, based on a correlation comparison of several geomagnetic indices (aa, AE, Dst, PC) that show common long-term behaviour, characterised by solar activity signature at Hale and Gleissberg cycles time scales.

Demetrescu, C.; Dobrica, V.

2012-04-01

19

On the statistics of El Nino occurrences and the relationship of El Nino to volcanic and solar/geomagnetic activity  

NASA Technical Reports Server (NTRS)

El Nino is conventionally defined as an anomalous and persistent warming of the waters off the coasts of Ecuador and Peru in the eastern equatorial Pacific, having onset usually in Southern Hemispheric summer/fall. Some of the statistical aspects of El Nino occurrences are examined, especially as they relate to the normal distribution and to possible associations with volcanic, solar, and geomagnetic activity. With regard to the very strong El Nino of 1982 to 1983, it is noted that, although it may very well be related to the 1982 eruptions of El Chichon, the event occurred essentially on time (with respect to the past behavior of elapsed times between successive El Nino events; a moderate-to-stronger El Nino was expected during the interval 1978 to 1982, assuming that El Nino occurrences are normally distributed, having a mean elapsed time between successive onsets of 4 years and a standard deviation of 2 years and a last known occurrence in 1976). Also, although not widely recognized, the whole of 1982 was a record year for geomagnetic activity (based on the aa geomagnetic index, with the aa index registering an all time high in February 1982), perhaps, important for determining a possible trigger for this and other El Nino events. A major feature is an extensive bibliography (325 entries) on El Nino and volcanic-solar-geomagnetic effects on climate. Also, included is a tabular listing of the 94 major volcanic eruptions of 1835 to 1986.

Wilson, Robert M.

1989-01-01

20

Presumed rising trend of solar magnetic flux and old geomagnetic data sets  

NASA Astrophysics Data System (ADS)

In this paper we show the results of thorough correlative analysis of different geomagnetic and solar indices calculated from the data registered since 1841 to the present in order to verify the conclusions of Loockwood et al (1999) that the total magnetic flux leaving the Sun has risen by a factor of 2,3 since 1901and increased by 40% from 1964 until 1996. The last result has been negated by Kotov and Kotova (2001) and Stozkov (2002), the earlier result of Loockwood is based on behaviour of annual means of aa index which showed an approximately linear rise in geomagnetic levels between about 1900 and sixties. It was firstly noticed by Mayaud (1972), who showed also the same trend in Ci index series. In this period smoothed sunspot number attained from cycle to cycle, but with relatively stable minimum value. Ponyavin (2001) has pointed out that the annual means of the data of planetary C9 index from 1890 to the present and C9 derived from Petersburg magnetic data (Zosimovic, 1981) dd not show such increase as aa index. aa has been derived from magnetograms of 2 nearly antipodal stations (Greenwich, 1868-1925 and Melbourne 1868-1919, Abinger, 1926-1956 and Toolangui, 1920-1979, Hartland, 1957 - until present, and Canberra, 1980- until present). As it is seen from the paper the quality of aa index in the early period till 15 solar cycle is not so good as indices obtained from one northern hemisphere observatory (A_k at Helsinki and C9 at Petersburg). The mean level of this indices in the time interval from 1841 to 1964 have been approximately constant. A_k obtained from Sodankyla has been slightly drift between 1914 and fifties. The quality of geomagnetic indices during the last solar cycles from 16 to 19 is much better than during an earlier time. hus, the suggestions about the rising of the total solar magnetic flux derived from the behavior of aa index is questionable and ought to be discussed and collated with of other old registrations.

Kobylinski, Z.; Izdebska, J.

2003-04-01

21

Association of a planetary tidal effect with the time variation of the ~13.5 day component of geomagnetic activity  

E-print Network

We show that there is a previously unreported quad-annual variation in the ~13.5 day component of the aa index of geomagnetic activity. We derive a model based on the planetary tidal effect at the solar surface due to Mercury and Jupiter that, when combined with an equinoctial response of the magnetosphere, predicts the times of occurrence of predominantly quad-annual variation or predominantly semi-annual variation in the ~13.5 day component of the aa index. In support of the model we show that, during years when the quad-annual variation in the ~13.5 day component of aa index is predominant there is a large component at the 88 day periodicity of Mercury in the ~13.5 day component of solar wind speed. As further support for the model we establish that significant peaks in the aa index spectrum are due to an 88 day modulation of 27 day period solar activity. The model also predicts the occurrence of planetary tidal effect maximum in anti-phase with solar cycle maximums around 1970 and we show this is consiste...

Edmonds, I R

2014-01-01

22

On the Relationship Between Global Land-Ocean Temperature and Various Descriptors of Solar-Geomagnetic Activity and Climate  

NASA Technical Reports Server (NTRS)

Examined are sunspot cycle- (SC-) length averages of the annual January-December values of the Global Land-Ocean Temperature Index () in relation to SC-length averages of annual values of various descriptors of solar-geomagnetic activity and climate, incorporating lags of 0-5 yr. For the overall interval SC12-SC23, the is inferred to correlate best against the parameter <aa(I:SSN)> incorporating lag = 5 yr, where the parameter <aa(I:SSN)> refers to the resultant aa value having removed that portion of the annual aa average value due to the yearly variation of sunspot number (SSN). The inferred correlation between the and <aa(I:SSN)> is statistically important at confidence level cl > 99.9%, having a coefficient of linear correlation r = 0.865 and standard error of estimate se = 0.149 degC. Excluding the most recent cycles SC22 and SC23, the inferred correlation is stronger, having r = 0.969 and se = 0.048 degC. With respect to the overall trend in the , which has been upwards towards warmer temperatures since SC12 (1878-1888), solar-geomagnetic activity parameters are now trending downwards (since SC19). For SC20-SC23, in contrast, comparison of the against SC-length averages of the annual value of the Mauna Loa carbon dioxide () index is found to be highly statistically important (cl >> 99.9%), having r = 0.9994 and se = 0.012 degC for lag = 2 yr. On the basis of the inferred preferential linear correlation between the and , the current ongoing SC24 is inferred to have warmer than was seen in SC23 (i.e., >0.526 degC), probably in excess of 0.68 degC (relative to the 1951-1980 base period).

Wilson, Robert M.

2014-01-01

23

A Quantitative Model of Geomagnetic Activity  

Microsoft Academic Search

A quantitative model of geomagnetic activity is developed and utilized to investigate the causes of the diurnal, seasonal, and IMF sector variations in the AL index records. This auroral index was chosen for study because of its high sensitivity to the strength of the westward electrojet and, hence, magnetospheric substorm activity. After the introduction of corrections for processes not related

Robert E. Holzer; James A. Slavin

1982-01-01

24

Canadian National Geomagnetism Program  

NSDL National Science Digital Library

The Canadian National Geomagnetism Program provides excellent resources for keeping track of the Earth's ever-changing magnetic field throughout Canada. The information here covers "time-scales ranging from seconds to decades." Data include short- and long-term magnetic activity forecasts, and plots of one-minute variations of the geomagnetic field. Also, an in-depth geomagnetic hazards section discusses effects of magnetic storms on power systems, pipelines, and communication cables.

25

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

26

On the causes of geomagnetic activity  

NASA Technical Reports Server (NTRS)

The causes of geomagnetic activity are studied both theoretically in terms of the reconnection model and empirically using the am-index and interplanetary solar wind parameters. It is found that two separate mechanisms supply energy to the magnetosphere. One mechanism depends critically on the magnitude and direction of the interplanetary magnetic field. Both depend strongly on solar wind speed.

Svalgaard, L.

1975-01-01

27

Reconstruction of Geomagnetic activity and near-Earth interplanetary conditions over the past 167 years.  

NASA Astrophysics Data System (ADS)

Records of geomagnetic activity have previously been used to reconstruct the conditions in near-Earth space, such as the interplanetary magnetic field (IMF), solar wind speed (Vsw) and open solar flux (OSF). Reliable geomagnetic activity records exist back until the mid-1800's, and these data provide one of the few means of inferring variations in the conditions in near-Earth space before the advent of the space age. However, there are challenges in using geomagnetic activity records to reconstruct interplanetary conditions. In particular it is necessary to ensure, as best as is possible, the homogeneity and reliability of any geomagnetic indices used. This becomes increasingly difficult further back in history, as both the quality of the data and the number of observing stations decreases. A new geomagnetic activity index, the IDV(1D) index, is presented, which is designed to be as homogeneous in its construction as possible (Lockwood et al. 2013a). This is achieved by only combining data that, by virtue of the locations of the source observatories used, have similar responses to solar wind and IMF variations. IDV(1d) employs many of the principles of the IDV index (Svalgaard and Cliver (2010)), inspired by the u index of Bartels (1932). The index uses interdiurnal variation data from Helsinki for 1845- 1890 and 1893-1896 and from Eskdalemuir from 1911 to the present. The gaps are filled using data from the Potsdam (1891-1892 and 1897-1907) and the nearby Seddin observatories (1908-1910) and intercalibration achieved using the Potsdam-Seddin sequence. The index is compared with independent, early data from European-sector stations, as well as the composite u index and the IDV index. Agreement is found to be extremely good in most cases. IDV(1D) does not suffer from the poor homogeneity of the IDV index, and is more highly correlated with the IMF, consequently it yields a more reliable reconstruction (Lockwood et al 2013b). For completeness, we use 4 different combinations of the IDV(1D), IDV, aa and IHV geomagnetic indices to reconstruct the near-Earth IMF, Vsw, and the OSF from 1845 to 2013. Although each of the different indices is constructed using different data and algorithms the results are very similar and consistent for all 4 combinations of parameters. The OSF variation derived is shown to be very similar indeed to that obtained using the method of Lockwood et al. (1999). This reaffirms one of the key findings from Lockwood et al. (1999), that the OSF approximately doubled over the period 1902-1955. Furthermore, this reconstruction shows that the OSF in the minima of solar cycle 23 and rise phase of solar cycle 24 is the lowest in approximately 100 years, being comparable to levels last experienced in solar cycle 14 (1902-1913).

Lockwood, Mike; Nevanlinna, Heikki; Barnard, Luke; Owens, Mat; Harrison, Giles; Rouillard, Alexis; Scott, Chris; Vokhmyanin, Mikhail; Ponyavin, Dmitri; Sokolov, Sergey

2014-05-01

28

Major geomagnetic storm due to solar activity (2006-2013).  

NASA Astrophysics Data System (ADS)

Major geomagnetic storm due to solar activity (2006-2013). Bhupendra Kumar Tiwari Department of Physics, A.P.S.University, Rewa(M.P.) Email: - btiwtari70@yahoo.com mobile 09424981974 Abstract- The geospace environment is dominated by disturbances created by the sun, it is observed that coronal mass ejection (CME) and solar flare events are the causal link to solar activity that produces geomagnetic storm (GMS).CMEs are large scale magneto-plasma structures that erupt from the sun and propagate through the interplanetary medium with speeds ranging from only a few km/s to as large as 4000 km/s. When the interplanetary magnetic field associated with CMEs impinges upon the earth’s magnetosphere and reconnect occur geomagnetic storm. Based on the observation from SOHO/LASCO spacecraft for solar activity and WDC for geomagnetism Kyoto for geomagnetic storm events are characterized by the disturbance storm time (Dst) index during the period 2006-2013. We consider here only intense geomagnetic storm Dst <-100nT, are 12 during 2006-2013.Geomagnetic storm with maximum Dst< -155nT occurred on Dec15, 2006 associated with halo CME with Kp-index 8+ and also verify that halo CME is the main cause to produce large geomagnetic storms.

Tiwari, Bhupendra Kumar

29

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 all types of observed precursor effects in CR what can be used for forecasting of great geomagnetic storms and possible mechanisms of these precursor effects origin. 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 pre-diction", Proc. of 26-th Intern. Cosmic Ray Conference, Salt Lake City, 6, 476-479 (1999).

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

30

Corrected geomagnetic pole coordinates  

Microsoft Academic Search

A new method for the accurate calculation of the corrected geomagnetic pole coordinates is developed. The results are compared with those obtained by previous methods, and maximum divergence was found to be approximately 1-deg.

Iu. L. Sverdlov; T. N. Khorkova

1982-01-01

31

The normal geomagnetic field  

NASA Astrophysics Data System (ADS)

Data on the normal geomagnetic field (NGF) and its gradients on the earth's surface and at different heights are examined. Methods for plotting the NMG for the USSR and other countries are developed, and mathematical approximations of the geomagnetic field are presented. The nature of the NGF is analyzed on the basis of geophysical, geological, and geochemical data, as well as data on the internal structure of the earth.

Pochtarev, V. I.

32

On correlations between the North Atlantic Oscillation, geopotential heights, and geomagnetic activity  

Microsoft Academic Search

We investigate correlations between geomagnetic activity indices, the North Atlantic Oscillation (NAO), and stratospheric geopotential heights. It is shown that the correlation between the geomagnetic index Ap and the NAO index is high and significant since about 1970, that it is significant during winter only, that it was not significant before about 1970, and that the correlations are dominated by

Peter Thejll; Bo Christiansen

2003-01-01

33

Dependence of geosynchronous relativistic electron enhancements on geomagnetic parameters  

E-print Network

Relativistic electron fluxes observed in geosynchronous orbit by GOES-8 in 1997 to 2000 were considered as a complex function of geomagnetic indices PC, Kp, and Dst as well as parameters of the magnetosphere size, subsolar Rs and terminator Rf magnetopause distances. A geosynchronous relativistic electron enhancement (GREE) is determined as daily maximal electron flux exceeding the upper root mean square deviation (RMSD) threshold of about 1500 (cm2s sr)-1. Comparison analysis of the GREE dynamics and geomagnetic conditions on the rising phase of current solar cycle revealed suppression of the relativistic electron enhancements by substantially increased strong geomagnetic activity in the solar maximum. Statistical consideration of a relationship between the GREEs and the geomagnetic parameters showed that the most important parameters controlling the geosynchronous relativistic electron enhancements were 4-day averaged Kp index, PC index and magnetopause termination distance Rf delayed respectively on 3 and ...

Dmitriev, A V

2014-01-01

34

Modelling the geomagnetic field  

NASA Astrophysics Data System (ADS)

A review is presented of the manner in which models of the geomagnetic field are produced. The data on which spherical harmonic models of the main geomagnetic field and its secular variation are used by scientists and engineers studying the earth's interior, its ionosphere and magnetosphere, must be of the highest quality and must be distributed as homogeneously as possible worldwide. As the quality of a model is dependent on the quality of the data on which it is based, sources of data for secular-variation and for main-field modeling are discussed in detail. The methods presently utilized for producing spherical harmonic models are described and some estimates of the accuracies of some recent geomagnetic field models are given.

Barraclough, D. R.

35

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

36

Conjugate Event Study of Geomagnetic ULF Pulsations with Wavelet-based Indices  

NASA Astrophysics Data System (ADS)

The interactions between the solar wind and geomagnetic field produce a variety of space weather phenomena, which can impact the advanced technology systems of modern society including, for example, power systems, communication systems, and navigation systems. One type of phenomena is the geomagnetic ULF pulsation observed by ground-based or in-situ satellite measurements. Here, we describe a wavelet-based index and apply it to study the geomagnetic ULF pulsations observed in Antarctica and Greenland magnetometer arrays. The wavelet indices computed from these data show spectrum, correlation, and magnitudes information regarding the geomagnetic pulsations. The results show that the geomagnetic field at conjugate locations responds differently according to the frequency of pulsations. The index is effective for identification of the pulsation events and measures important characteristics of the pulsations. It could be a useful tool for the purpose of monitoring geomagnetic pulsations.

Xu, Z.; Clauer, C. R.; Kim, H.; Weimer, D. R.; Cai, X.

2013-12-01

37

Bayesian inference in geomagnetism  

Microsoft Academic Search

The inverse problem in empirical geomagnetic modeling is investigated, with critical examination of recently published studies. Particular attention is given to the use of Bayesian inference (BI) to select the damping parameter lambda in the uniqueness portion of the inverse problem. The mathematical bases of BI and stochastic inversion are explored, with consideration of bound-softening problems and resolution in linear

George E. Backus

1988-01-01

38

Foundations of Geomagnetism  

NASA Astrophysics Data System (ADS)

The study of the magnetic field of the Earth, or geomagnetism, is one of the oldest lines of scientific enquiry. Indeed, it has often been said that William Gilbert's De Magnete, published in 1600 and predating Isaac Newton's Principia by 87 years, can claim to be the first true scientific textbook; his study was essentially the first of academic rather than practical interest.What then, we may ask, has been accomplished in the nearly 400 intervening years up to the publication of Foundations of Geomagnetism? In short, a wealth of observational evidence, considerable physical understanding, and a great deal of mathematical apparatus have accrued, placing the subject on a much surer footing.The latter two categories are described in considerable detail, and with attendant rigor, in this book. The sphericity of the Earth means that a frequent theme in the book is the solution of the partial differential equations of electrodynamics in a spherical geometry.

Jackson, Andy

39

On extreme geomagnetic storms  

NASA Astrophysics Data System (ADS)

Extreme geomagnetic storms are considered as one of the major natural hazards for technology-dependent society. Geomagnetic field disturbances can disrupt the operation of critical infrastructures relying on space-based assets, and can also result in terrestrial effects, such as the Quebec electrical disruption in 1989. Forecasting potential hazards is a matter of high priority, but considering large flares as the only criterion for early-warning systems has demonstrated to release a large amount of false alarms and misses. Moreover, the quantification of the severity of the geomagnetic disturbance at the terrestrial surface using indices as Dst cannot be considered as the best approach to give account of the damage in utilities. High temporal resolution local indices come out as a possible solution to this issue, as disturbances recorded at the terrestrial surface differ largely both in latitude and longitude. The recovery phase of extreme storms presents also some peculiar features which make it different from other less intense storms. This paper goes through all these issues related to extreme storms by analysing a few events, highlighting the March 1989 storm, related to the Quebec blackout, and the October 2003 event, when several transformers burnt out in South Africa.

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

2014-10-01

40

The national geomagnetic initiative  

NASA Technical Reports Server (NTRS)

The Earth's magnetic field, through its variability over a spectrum of spatial and temporal scales, contains fundamental information on the solid Earth and geospace environment (the latter comprising the atmosphere, ionosphere, and magnetosphere). Integrated studies of the geomagnetic field have the potential to address a wide range of important processes in the deep mantle and core, asthenosphere, lithosphere, oceans, and the solar-terrestrial environment. These studies have direct applications to important societal problems, including resource assessment and exploration, natural hazard mitigation, safe navigation, and the maintenance and survivability of communications and power systems on the ground and in space. Studies of the Earth's magnetic field are supported by a variety of federal and state agencies as well as by private industry. Both basic and applied research is presently supported by several federal agencies, including the National Science Foundation (NSF), U.S. Geological Survey (USGS), U.S. Department of Energy (DOE), National Oceanic and Atmospheric Administration (NOAA), National Aeronautics and Space Administration (NASA), and U.S. Department of Defense (DOD) (through the Navy, Air Force, and Defense Mapping Agency). Although each agency has a unique, well-defined mission in geomagnetic studies, many areas of interest overlap. For example, NASA, the Navy, and USGS collaborate closely in the development of main field reference models. NASA, NSF, and the Air Force collaborate in space physics. These interagency linkages need to be strengthened. Over the past decade, new opportunities for fundamental advances in geomagnetic research have emerged as a result of three factors: well-posed, first-order scientific questions; increased interrelation of research activities dealing with geomagnetic phenomena; and recent developments in technology. These new opportunities can be exploited through a national geomagnetic initiative to define objectives and encourage coordination of efforts among federal and state agencies, academic institutions, and industry to systematically characterize the spatial and temporal behavior of the Earth's magnetic field on local, regional, and global scales in order to understand the physical processes in the solid earth and geospace environment, and to apply this understanding to a variety of scientific problems and to technical and societal needs.

1993-01-01

41

Centennial increase in geomagnetic activity: Latitudinal differences and global estimates  

Microsoft Academic Search

We study here the centennial change in geomagnetic activity using the newly proposed Inter-Hour Variability (IHV) index. We correct the earlier estimates of the centennial increase by taking into account the effect of the change of the sampling of the magnetic field from one sample per hour to hourly means in the first years of the previous century. Since the

K. Mursula; D. Martini

2006-01-01

42

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

43

Sources of Geomagnetic Activity during Nearly Three Solar Cycles (1972-2000)  

NASA Technical Reports Server (NTRS)

We examine the contributions of the principal solar wind components (corotating highspeed streams, slow solar wind, and transient structures, i.e., interplanetary coronal mass ejections (CMEs), shocks, and postshock flows) to averages of the aa geomagnetic index and the interplanetary magnetic field (IMF) strength in 1972-2000 during nearly three solar cycles. A prime motivation is to understand the influence of solar cycle variations in solar wind structure on long-term (e.g., approximately annual) averages of these parameters. We show that high-speed streams account for approximately two-thirds of long-term aa averages at solar minimum, while at solar maximum, structures associated with transients make the largest contribution (approx. 50%), though contributions from streams and slow solar wind continue to be present. Similarly, high-speed streams are the principal contributor (approx. 55%) to solar minimum averages of the IMF, while transient-related structures are the leading contributor (approx. 40%) at solar maximum. These differences between solar maximum and minimum reflect the changing structure of the near-ecliptic solar wind during the solar cycle. For minimum periods, the Earth is embedded in high-speed streams approx. 55% of the time versus approx. 35% for slow solar wind and approx. 10% for CME-associated structures, while at solar maximum, typical percentages are as follows: high-speed streams approx. 35%, slow solar wind approx. 30%, and CME-associated approx. 35%. These compositions show little cycle-to-cycle variation, at least for the interval considered in this paper. Despite the change in the occurrences of different types of solar wind over the solar cycle (and less significant changes from cycle to cycle), overall, variations in the averages of the aa index and IMF closely follow those in corotating streams. Considering solar cycle averages, we show that high-speed streams account for approx. 44%, approx. 48%, and approx. 40% of the solar wind composition, aa, and the IMF strength, respectively, with corresponding figures of approx. 22%, approx. 32%, and approx. 25% for CME-related structures, and approx. 33%, approx. 19%, and approx. 33% for slow solar wind.

Richardson, I. G.; Cane, H. V.; Cliver, E. W.; White, Nicholas E. (Technical Monitor)

2002-01-01

44

Air Showers and Geomagnetic Field  

E-print Network

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 calculating 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 alter significantly some shower observables like, for example, the lateral distribution of muons in the case of events with large zenith angles (larger than 75 degrees). On the other hand, such alterations seem not to be important for smaller zenith angles. Global observables like total numbers of particles or longitudinal development parameters do not present appreciable dependences on the geomagnetic deflections for all the cases that were studied.

A. Cillis; S. J. Sciutto

1999-07-31

45

Ionospheric redistribution during geomagnetic storms  

NASA Astrophysics Data System (ADS)

The abundance of plasma in the daytime ionosphere is often seen to grow greatly during geomagnetic storms. Recent reports suggest that the magnitude of the plasma density enhancement depends on the UT of storm onset. This possibility is investigated over a 7year period using global maps of ionospheric total electron content (TEC) produced at the Jet Propulsion Laboratory. The analysis confirms that the American sector exhibits, on average, larger storm time enhancement in ionospheric plasma content, up to 50% in the afternoon middle-latitude region and 30% in the vicinity of the high-latitude auroral cusp, with largest effect in the Southern Hemisphere. We investigate whether this effect is related to the magnitude of the causative magnetic storms. Using the same advanced Dst index employed to sort the TEC maps into quiet and active (Dst<-100 nT) sets, we find variation in storm strength that corresponds closely to the TEC variation but follows it by 3-6h. For this and other reasons detailed in this report, we conclude that the UT-dependent peak in storm time TEC is likely not related to the magnitude of external storm time forcing but more likely attributable to phenomena such as the low magnetic field in the South American region. The large Dst variation suggests a possible system-level effect of the observed variation in ionospheric storm response on the measured strength of the terrestrial ring current, possibly connected through UT-dependent modulation of ion outflow.

Immel, T. J.; Mannucci, A. J.

2013-12-01

46

Longitude dependent response of the GPS derived ionospheric ROTI to geomagnetic storms  

NASA Astrophysics Data System (ADS)

The local time dependent effects of geomagnetic storm on the ionospheric TEC and Rate of change of TEC Index (ROTI) are studied here using the GPS data for four different low latitude stations: Ogaswara, Japan (24.29 °N, 153.91 °E; Geomagnetic: 17.21 °N, 136.16 °W); Surat, India (21.16 °N, 72.78 °E; Geomagnetic: 12.88 °N, 146.91 °E); Bogota, Colombia (4.64 °N, -74.09 °E; Geomagnetic: 14.42 °N, 1.67 °W); and Kokee park Waimea, Hawaii, US (22.12 °N, -159.67 °E; Geomagnetic: 22.13 °N, 91.19 °W). The solar wind velocity and geomagnetic indices: Dst, Kp and IMF Bz are utilized to validate the geomagnetic storms registered during the years 2011 and 2012. Using the GPS based TEC data and computed values of ROTI, the storm induced ionospheric irregularities generation and inhibition has been studied for all stations. The present study suggests that, the F-region irregularities of a scale length of few kilometers over the magnetic equator are locally affected by geomagnetic storms. This study also shows a good agreement (70-84 %) with the Aaron's criteria (Aarons, Radio Sci., 26:1131-1149, 1991; Biktash, Ann. Geophys., 19:731-739, 2004) as significant absence and enhancement of ROTI was found to be influenced by the local time of the negative peak of Dst index association.

Tanna, H. J.; Pathak, K. N.

2014-08-01

47

Bayesian inference in geomagnetism  

NASA Technical Reports Server (NTRS)

The inverse problem in empirical geomagnetic modeling is investigated, with critical examination of recently published studies. Particular attention is given to the use of Bayesian inference (BI) to select the damping parameter lambda in the uniqueness portion of the inverse problem. The mathematical bases of BI and stochastic inversion are explored, with consideration of bound-softening problems and resolution in linear Gaussian BI. The problem of estimating the radial magnetic field B(r) at the earth core-mantle boundary from surface and satellite measurements is then analyzed in detail, with specific attention to the selection of lambda in the studies of Gubbins (1983) and Gubbins and Bloxham (1985). It is argued that the selection method is inappropriate and leads to lambda values much larger than those that would result if a reasonable bound on the heat flow at the CMB were assumed.

Backus, George E.

1988-01-01

48

Bracing for the geomagnetic storms  

SciTech Connect

The authors discuss the impact of geomagnetic storms on utility transmission networks. The effects of a recent storm on the Hydro-Quebec transmission system are described in detail. Research into geomagnetic disturbance prediction is discussed. In coming months, geomagnetic field activity will be high as it builds toward a peak, the 22nd since reliable records of the phenomenon began in the mid-1700s. The peaks come in roughly 11-year cycles, and the next is expected later this year or early in 1991. The solar activity has so far risen at one of the fastest rates ever recorded, and solar forecasters expect cycle 22 to have unusually high activity levels.

Kappenman, J.G. (Minnesota Power, Duluth, MN (US)); Albertson, V.D. (Univ. of Minnesota, Dept. of Electrical Engineering, Minneapolis, MN (US))

1990-03-01

49

High latitude TEC fluctuations and irregularity oval during geomagnetic storms  

NASA Astrophysics Data System (ADS)

GPS measurements obtained by the global IGS network were used to study the occurrence of TEC fluctuations in the northern and southern high-latitude ionosphere during severe geomagnetic storms. In the northern hemisphere, GPS stations located higher than 55N Corrected Geomagnetic Latitude (CGL) at different longitudes were selected. In the southern hemisphere, Antarctic permanent GPS stations were used. Dual-frequency GPS measurements for individual satellite passes served as raw data. As a measure of fluctuation activity the rate of TEC (ROT) was used, and the fluctuation intensity was evaluated using the ROTI index. Using daily GPS measurements from all selected stations, images of the spatial and temporal behavior of TEC fluctuations were formed (in Corrected Geomagnetic Coordinates-CGC and geomagnetic local time-GLT). Similarly to the auroral oval, these images demonstrate an irregularity oval. The occurrence of the irregularity oval relates to the auroral oval, cusp and polar cap. During a storm, the intensity of TEC fluctuations essentially increased. The irregularity oval expands equatorward with an increase of magnetic activity. The study showed that the existing high-latitude GPS stations can provide a permanent monitoring tool for the irregularity oval in near real-time. In this paper, the features of the development of phase fluctuations at the geomagnetic conjugate points, and inter-hemispheric differences and similarities during winter and summer conditions, are discussed.

Shagimuratov, I. I.; Krankowski, A.; Ephishov, I.; Cherniak, Yu.; Wielgosz, P.; Zakharenkova, I.

2012-06-01

50

[Can solar/geomagnetic activity restrict the occurrence of some shellfish poisoning outbreaks? The example of PSP caused by Gymnodinium catenatum at the Atlantic Portuguese coast].  

PubMed

Cyclic outbreaks of accumulation of paralytic shellfish poisoning (PSP) toxins in mussels attributed to Gymnodinium catenatum blooms displayed several of the highest inter-annual maxima coincidental with minima of the 11-year solar sunspot number (SSN) cycle. The monthly distribution of PSP was associated with low levels of the solar radio flux, a more quantitative approach than SSN for fluctuations in solar activity. A comparison between monthly distribution of PSP and other common biotoxins (okadaic acid (OA), dinophysistoxin-2 (DTX2) and amnesic shellfish poisoning (ASP) toxins) demonstrated that only PSP was significantly associated with low levels of radio flux (p < 0.01). PSP occurrence suggests a prior decline in solar activity could be required to act as a trigger, in a similar manner to a photoperiodic signal. The seasonal frequency increased towards autumn during the study period, which might be related to the progressive atmospheric cut-off of deleterious radiation associated with the seasonal change in solar declination, and might play an additional role in seasonal signal-triggering. PSP distribution was also associated with low levels of the geomagnetic index Aa. A comparison between monthly distribution of PSP and other common biotoxins, also demonstrated that only PSP was significantly associated with low levels of the Aa index (p < 0.01). In some years of SSN minima no significant PSP-outbreaks in mussels were detected. This was attributed to a steady rise in geomagnetic activity that could disrupt the triggering signal. Global distribution patterns show that hotspots for G. catenatum blooms are regions with deficient crustal magnetic anomalies. In addition to the variable magnetic field mostly of solar origin, static fields related to magnetized rocks in the crust and upper mantle might play a role in restricting worldwide geographic distribution. PMID:24455892

Vale, P

2013-01-01

51

Probing Geomagnetic Jerks combining Geomagnetic and Earth Rotation Observations (Invited)  

NASA Astrophysics Data System (ADS)

Geomagnetic jerks, first observed in the late 1970s, are the most rapid variations in the observed geomagnetic field that are believed to be of internal origin. Their occurence has been correlated with a number of different geophysical phenomena. Here we consider simultaneous features in variations in Earth's length of day. Recently, we have provided a simple description of non-atmospheric variations in length of day (LOD), consisting of 3 components: a slowly varying decadal trend, a 5.9-year oscillation, and occasional sudden jumps. Both of the shorter period parts of this correlate with geomagnetic jerks, with peaks in the LOD oscillation being contemporaneous with well-known jerk occurances (for example in 1969, 1972, 1978 and 1982), and jumps in the LOD fitting a jerk observed in satellite data in 2003.5. The simultaneous observation of these two features constrains Earth structure, in particular limiting the electric conductivity of the deep mantle. However, the nature of the LOD changes also may change the paradigm for the study of jerk timings. it is customarily assumed that the jerks represent features in the geomagnetic field that are continuous in the secular variation, but discontinuous in its derivative, the secular acceleration. However, a jump in LOD suggested by the modelling of the data would correspond also to a jump in SV, thus invalidating standard methods for temporal location of a jerk (which will consider the intersection of best-fit straight lines to the secular variation before and after). Olsen and Mandea have localised a jerk in satellite virtual observatory data using flow modelling; this seems the most promising method to investigate whether jerks could have discontinuous secular variation. We apply similar methods to time series of virtual geomagnetic obseratories from satellite data to further explore geomagnetic jerks and their rotational links in the geomagnetic satellite era.

Holme, R. T.; de Viron, O.

2013-12-01

52

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

53

a Millennium of Geomagnetism  

NASA Astrophysics Data System (ADS)

The history of geomagnetism began around the year 1000 with the discovery in China of the magnetic compass. Methodical studies of the Earth's field started in 1600 with William Gilbert's De Magnete [Gilbert, 1600] and continued with the work of (among others) Edmond Halley, Charles Augustin de Coulomb, Carl Friedrich Gauss, and Edward Sabine. The discovery of electromagnetism by Hans Christian Oersted and André-Marie Ampére led Michael Faraday to the notion of fluid dynamos, and the observation of sunspot magnetism by George Ellery Hale led Sir Joseph Larmor in 1919 to the idea that such dynamos could sustain themselves naturally in convecting conducting fluids. From that came modern dynamo theory, of both the solar and terrestrial magnetic fields. Paleomagnetic studies revealed that the Earth's dipole had undergone reversals in the distant past, and these became the critical evidence in establishing plate tectonics. Finally, the recent availability of scientific spacecraft has demonstrated the intricacy of the Earth's distant magnetic field, as well as the existence of magnetic fields associated with other planets and with satellites in our solar system.

Stern, David P.

2002-11-01

54

Croatian Geomagnetic Surveys 2004-2009  

NASA Astrophysics Data System (ADS)

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 influence of artificial noises, were investigated. The reduced geomagnetic field of 2007.5 and its annual variation for the territory of Croatia was presented. Keywords: geomagnetic repeat station network, geomagnetic network for field mapping, geomagnetic surveys.

Brki?, Mario; Jungwirth, Enio; Ugar, Danijel Å.; Pavasovi?, Marko

2010-05-01

55

An interplanetary scintillation activity index  

Microsoft Academic Search

Using interplanetary scintillation (IPS) data obtained from the Cambridge 81.5 MHz array, an activity index is developed in which it is possible to identify (1) discrete structures, most likely relating to transient density enhancements, and (2) periodic activity, relating to corotating interplanetary structure. Significant, yet weak correlations are found between the index and geomagnetic activity. Results suggest that the pursuit

R. A. Harrison; M. A. Hapgood; V. Moore; E. A. Lucek

1992-01-01

56

Different geomagnetic indices as an indicator for geo-effective solar storms and human physiological state  

NASA Astrophysics Data System (ADS)

A group of 86 healthy volunteers were examined on each working day during periods of high solar activity. Data about systolic and diastolic blood pressure, pulse pressure, heart rate and subjective psycho-physiological complaints were gathered. MANOVA was employed to check the significance of the influence of three factors on the physiological parameters. The factors were as follows: (1) geomagnetic activity estimated by daily amplitude of H-component of the local geomagnetic field, Ap- and Dst-index; (2) gender; and (3) the presence of medication. Average values of systolic, diastolic blood pressure, pulse pressure and subjective complaints of the group were found to increase significantly with geomagnetic activity increment.

Dimitrova, Svetla

2008-02-01

57

Kuramoto Model of Nonlinear Coupled Oscillators as a Way for Understanding Phase Synchronization: Application to Solar and Geomagnetic Indices  

NASA Astrophysics Data System (ADS)

We apply a Kuramoto model of nonlinear coupled oscillators to the simulation of slow variations of the phase difference between sunspot number [ R I ] and geomagnetic indices [aa and ?]. The Kuramoto model is described for the particular case of two oscillators connected by symmetric coupling with quasi-stationary behavior, and its properties are investigated. By solving an inverse problem, we reconstruct the evolution of the couplings between pairs of indices [ R I and aa, R I and ?, aa and ?], and interpret these in terms of the physics of the solar dynamo. The de-correlation between R I and geomagnetic indices found in Solar Cycle 20 by Le Mouël et al. ( J. Geophys. Res. 117, A09103, 2012) is successfully reproduced by the Kuramoto model and corresponds to the alternation of the leading oscillator. Application of the Kuramoto model to the cross-correlations [ C( R I , ?) and C(aa, ?)] for ?-indices computed in eight geomagnetic stations shows the latitudinal dependence of the mean phase difference. We discuss these results in terms of the solar-wind contribution to local geomagnetic indices [ ?].

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

2014-11-01

58

What causes geomagnetic activity during sunspot minimum?  

NASA Astrophysics Data System (ADS)

Since the beginning of the geomagnetic measurements, the variations in the geomagnetic field have been related to solar activity. It is now known that big sporadic (non-recurrent) geomagnetic storms are caused by coronal mass ejections. The coronal mass ejections are related to the solar toroidal field whose manifestation are sunspots, so during sunspot maximum there is also a maximum in geomagnetic activity. Another source of geomagnetic activity are the coronal holes - open unipolar magnetic field areas from which the high speed solar wind emanates. Disturbances caused by high speed solar wind are maximum during the sunspots declining phase, which leads to two geomagnetic activity maxima in the 11-year sunspot cycle. In sunspot minimum, even during long periods without sunspots and without low-latitude coronal holes, geomagnetic disturbances are still observed. In the present work we analyze the geomagnetic activity during sunspot minimum, its sources and the reasons for its cyclic variations.

Kirov, Boian; Obridko, Vladimir; Asenovski, Simeon

59

Short-period geomagnetic secular variation  

Microsoft Academic Search

In this paper, the main problems of the theory of the short period geomagnetic secular variation are described. An approximate analytical representation of the observational data on both the geomagnetic field variations and the associated variations in the length of the day, the kinematics of the generation of geomagnetic variations in the skin layer at the core-mantle boundary, and the

S. I. Braginskii

1984-01-01

60

On statistical relationship of solar, geomagnetic and human activities.  

PubMed

Data of galactic cosmic rays, solar and geomagnetic activities and solar wind parameters on the one side and car accident events (CAE) in Poland on the other have been analyzed in order to reveal the statistical relationships among them for the period of 1990-2001. Cross correlation and cross spectrum of the galactic cosmic ray intensity, the solar wind (SW) velocity, Kp index of geomagnetic activity and CAE in Poland have been carried out. It is shown that in some epochs of the above-mentioned period there is found a reliable relationship between CAE and solar and geomagnetic activities parameters in the range of the different periodicities, especially, 7 days. The periodicity of 7 days revealed in the data of the CAE has the maximum on Friday without any exception for the minimum and maximum epochs of solar activity. However, the periodicity of 7 days is reliably revealed in other parameters characterizing galactic cosmic rays, SW, solar and geomagnetic activities, especially for the minimum epoch of solar activity. The periodicity of 3.5 days found in the series of CAE data more or less can be completely ascribed to the social effects, while the periodicity of 7 days can be ascribed to the social effect or/to the processes on the Sun, in the interplanetary space and in the Earth's magnetosphere and atmosphere. PMID:15880899

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

2004-01-01

61

Solar sources, interplanetary causes and space weather consequences of `multiple-dip' geomagnetic storms  

NASA Astrophysics Data System (ADS)

Study of geomagnetic storms of varying intensity has been useful to understand, (a) the physics of interplanetary plasma and field interaction with the geo-magnetosphere (b) the structure and dynamics of interplanetary structures responsible for them, (c) the physical mechanism playing important role in producing geomagnetic storms, and (d) their space weather consequences. Most of the early studies have been confined to the study of the classical geomagnetic storms with well defined time profile; a sharp decrease in Dst geomagnetic index within a day and slow recovery in about a week time or so. However, with the availability of high resolution solar/interplanetary data, it has now become possible to study the solar sources and interplanetary causes of geomagnetic storms with complex structures; one of them is the so called ‘multiple-dip’ storm. We have identified a number of such events in high resolution geomagnetic data, and analyzed them for understanding their solar and interplanetary causes. In addition, we utilized simultaneous geomagnetic and interplanetary plasma/field data to study the physical phenomena during their development. We also discuss the space weather consequences of such complex events.

Aslam, O. P. M.; Badruddin, B.

62

GPS study of ionospheric variability during geomagnetic storms at crest of equatorial region  

NASA Astrophysics Data System (ADS)

The dual frequency Global Positioning System (GPS) receivers provide an opportunity to de-termine Total Electron Content (TEC) over the crest of equatorial ionization anomaly region Bhopal by taking advantage of the dispersive nature of the ionospheric medium. The TEC values observed for eight geomagnetic storms of the period 2004-2005 is used in this paper to discuss the behaviour of ionospheric total electron content (TEC) during geomagnetically dis-turbed periods. Variation of TEC is studied in correlation with the geomagnetic index Dst and southward component of interplanetary magnetic field Bz. The main purpose of this study is to know how TEC varies from its average values with geomagnetic storms. The TEC variability is found to vary between 49

Gwal, Anurag; Sarkar, Shivalika; Gwal, Ashok Kumar

63

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

64

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

65

Solar wind and geomagnetism: toward a standard classification of geomagnetic activity from 1868 to 2009  

E-print Network

We examined solar activity with a large series of geomagnetic data from 1868 to 2009. We have revisited the geomagnetic activity classification scheme of Legrand and Simon (1989) and improve their scheme by lowering the ...

Zerbo, J. L.

66

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

67

Statistical properties of geomagnetic measurements as possible precursors for magnetic storms  

Microsoft Academic Search

Records of geomagnetic measurements have been analyzed looking for evidences of possible precursors for magnetic storms. With this objective, the main magnetic storms in the period 1998-2002 have been located in Dst index record. Periods immediately before storms and periods well before them were studied by applying a method recently introduced in the literature. Statistical properties of both types of

Andres R. R. Papa; Lilian P. Sosman

2006-01-01

68

Drift shell splitting by internal geomagnetic multipoles  

Microsoft Academic Search

Computations on an 80-coefficient model of the earth's field illustrate the 'topography' of the magnetic equatorial surface (on which B ß VB - 0) and the geometry of the drift shells of geomagnetically trapped particles. Individual terms in the spherical harmonic expansion (offset dipole coordinates) of the geomagnetic scalar potential V(r, O, v,) are either even or odd in cos

J. G. Roederer; H. H. Hilton; Michael Schulz

1973-01-01

69

[Severe trauma rate during planet geomagnetic storms].  

PubMed

The growth of the diurnal frequency of appearance of heavy traumas during planetary geomagnetic storms is shown and statistically justified. No effect of short-term geomagnetic disturbances of natural and technogenic nature on the occurrence of acute mental and cardiovascular pathologies was detected on the basis of diurnal data. PMID:11605399

Kuleshova, V P; Pulinets, S A

2001-01-01

70

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

71

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

72

Predicting ground electric field due to geomagnetic disturbances  

NASA Astrophysics Data System (ADS)

Electric field induced in the ground by geomagnetic disturbances drives currents in the power transmission grids, telecommunication lines or buried pipelines. These currents, known as Geomagnetically Induced Currents (GIC) are known to cause service disruptions. This effect is maximal at high latitudes due to the presence of strong polar electrojet currents. However both observations and models show that GIC caused by ring current intensifications also pose a risk at low- and mid-latitude locations, where majority of systems vulnerable to GIC are installed. A technique to model geoelectric field induced by the magnetospheric currents in a 3D conductivity model of the Earth is presented by Püthe & Kuvshinov (2013). We extend this work by predicting the induced geoelectric field solely based on Disturbance storm time index (Dst), a measure of ring current activity. Two major components of this effort are 1) Pre-computed 3D electromagnetic response of the ground to a unit magnetopsheric (P01) source and 2) Forecasted Dst data (Temerin & Li, 2002; 2006) from Advanced Composition Explorer (ACE) satellite at the L1 Lagrange point. Depending on the solar wind speed, the Dst forecasts are available approximately 1 hour in advance. The pre-computed response function for a site is multiplied by the Dst data in frequency domain to obtain predicted electric field for that location. Validating our approach, the predicted geoelectric field compares favorably with observed data from an ocean bottom electromagnetic array in the Pacific Ocean during the geomagnetic storm of April 2000. We also compare data from USArray magnetotelluric stations operational during the geomagnetic storm of October 2011. In this case, the results are site specific, with varying degrees of model fit. This indicates the influence of local surface conductivity inhomogeneities on the observed geoelectric data. Averaging data from adjacent stations seems to improve the fit with the prediction.

Nair, M. C.; Püthe, C.; Kuvshinov, A. V.

2013-12-01

73

An improved geomagnetic data selection algorithm for global geomagnetic field modelling  

NASA Astrophysics Data System (ADS)

A spherical harmonic degrees 60, global internal field model is described (called BGS/G/L/0706). This model includes a degree 15 core and piecewise-linear secular variation model and is derived from quiet-time Ørsted and CHAMP satellite data sampled between 2001.0 and 2005.0. For the satellite data selection, a wide range of geomagnetic index and other data selection filters have been used to best isolate suitably quiet magnetospheric and ionospheric conditions. Only a relatively simple, degree one spherical harmonic, external field model is then required. It is found that a new `Vector Magnetic Disturbance' index (VMD), the existing longitude sector A indices, the auroral zone index IE, and the polar cap index PC are better than Kp and Dst at rejecting rapidly varying external field signals at low, middle, auroral and polar latitudes. The model quality is further enhanced by filling spatial and temporal gaps in the quiet data selection with a second selection containing slightly more disturbed data. It is shown that VMD provides a better parametrization than Dst of the large-scale, rapidly changing, external field. The lithospheric field model between degrees 16 and 50 is robust and displays good coherence with other recently published models for this epoch. BGS/G/L/0706 also shows crustal anomalies consistent with other studies, although agreement is poorer in the southern polar cap. Intermodel coherency reduces above about degree 40, most likely due to incompletely filtered signals from polar ionospheric currents and auroral field aligned currents. The absence of the PC index for the southern hemisphere for 2003 onwards is a particular concern.

Thomson, Alan W. P.; Lesur, Vincent

2007-06-01

74

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

75

Geomagnetic storm intensity forecast caused by magnetic clouds of solar wind  

NASA Astrophysics Data System (ADS)

Method of short-term forecast intensity of geomagnetic storms, expected by effect Solar wind magnetic clouds in the Earth's magnetosphere is developed. The method is based calculation of the magnetic field clouds distribution, suitable to the Earth, the initial satellite measurements therein components of the interplanetary magnetic field in the solar ecliptic coordinate system. Conclusion about the magnetic storm intensity is expected on the basis of analysis of the dynamics of the reduced magnetic field Bz component clouds and established communication intensity of geomagnetic storms on Dst-index values and Bz component of the interplanetary magnetic field vector.

Barkhatov, N. A.; Levitin, A. E.; Revunova, E. A.

2014-11-01

76

Section AA Pre2004 Fire, Section AA 2009, Section AA, South ...  

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

Section A-A Pre-2004 Fire, Section A-A 2009, Section A-A, South Elevation - Boston & Maine Railroad, Berlin Branch Bridge #148.81, Formerly spanning Moose Brook at former Boston & Maine Railroad, Gorham, Coos County, NH

77

Minimax confidence intervals in geomagnetism  

NASA Technical Reports Server (NTRS)

The present paper uses theory of Donoho (1989) to find lower bounds on the lengths of optimally short fixed-length confidence intervals (minimax confidence intervals) for Gauss coefficients of the field of degree 1-12 using the heat flow constraint. The bounds on optimal minimax intervals are about 40 percent shorter than Backus' intervals: no procedure for producing fixed-length confidence intervals, linear or nonlinear, can give intervals shorter than about 60 percent the length of Backus' in this problem. While both methods rigorously account for the fact that core field models are infinite-dimensional, the application of the techniques to the geomagnetic problem involves approximations and counterfactual assumptions about the data errors, and so these results are likely to be extremely optimistic estimates of the actual uncertainty in Gauss coefficients.

Stark, Philip B.

1992-01-01

78

Geomagnetic activity: Dependence on solar wind parameters  

NASA Technical Reports Server (NTRS)

Current ideas about the interaction between the solar wind and the earth's magnetosphere are reviewed. The solar wind dynamic pressure as well as the influx of interplanetary magnetic field lines are both important for the generation of geomagnetic activity. The influence of the geometry of the situation as well as the variability of the interplanetary magnetic field are both found to be important factors. Semi-annual and universal time variations are discussed as well as the 22-year cycle in geomagnetic activity. All three are found to be explainable by the varying geometry of the interaction. Long term changes in geomagnetic activity are examined.

Svalgaard, L.

1977-01-01

79

Geomagnetic activity and local modulations of cosmic rays circa 1 GV  

NASA Technical Reports Server (NTRS)

Solar-sector synchronous modulations of the particulate cosmic radiation reaching the earth's atmosphere have been studied using low altitude satellite and surface data. The flux in the broad maximum of the galactic cosmic ray differential spectrum (near GV rigidity) exhibits an intermittent north-south asymmetry (NSA) in mid and high geomagnetic latitudes. During the 1964 and 1965 years of sunspot minimum, this modulation had a negative rigidity dependence and strong correlations with geomagnetic disturbance index (ap) and interplanetary magnetic field direction. Taken together with other features, this ap dependence is consistent with the hypothesis that reconnection of the interplanetary and geomagnetic fields should produce a local NSA independent of much larger scale NSAs associated with cosmic ray gradients in the heliosphere. This finding is also consistent with suggestions that solar activity influence on atmospheric processes may be mediated by the resulting modulations of upper tropospheric ionization.

Ely, J. T. A.; Huang, T. C.

1987-01-01

80

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

81

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

82

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

83

Geomagnetic field effects of the Chelyabinsk meteoroid  

NASA Astrophysics Data System (ADS)

An analysis was conducted of time variations in geomagnetic field components on the day of the Chelyabinsk meteorite event (February 15, 2013) and on control days (February 12 and 16, 2013). The analysis uses the data collected by magnetic observatories in Novosibirsk, Almaty, Kyiv, and Lviv. The distance R from the explosion site to the observatories varies in the range 1200-2700 km. The flyby and explosion of the Chelyabinsk cosmic body is found to have been accompanied by variations mainly in the horizontal component of the geomagnetic field. The variations are quasi-periodic with a period of 30-40 min, an amplitude of 0.5-2 nT for R ? 2700-1200 km, respectively, and a duration of 2-3 h. The horizontal velocity of the geomagnetic field disturbances is close to 260-370 m/s. A theoretical model of wave disturbances is proposed. According to the model, wave disturbances in the geomagnetic field are caused (a) by the motion of the gravity wave generated in the atmosphere by the falling space body and (b) by traveling ionospheric disturbances, which modulate the ionospheric current at dynamo altitudes. The calculated amplitudes of the wave disturbances are 0.6-1.8 nT for R ? 2700-1200 km, respectively. The estimates are in good agreement with the observational data. Disturbances in the geomagnetic field level (geomagnetic pulsations) in the period range 1-1000 s are negligible (less than 1 nT).

Chernogor, L. F.

2014-09-01

84

Synchronization of heart rate indices of human and Pc5 pulsations in the geomagnetic quiet conditions  

NASA Astrophysics Data System (ADS)

Geomagnetic pulsations with duration of the period over 150 seconds (Pc5-6) are present in the magnetosphere almost constantly. Unlike other types of geomagnetic pulsations, they are characterized by high amplitudes reaching in auroral latitudes 30-100 nT, and even 300 - 600 nT in time of significant geomagnetic disturbances [1]. To date, it is generally accepted that the classic morning and afternoon Pc5 pulsations in the magnetosphere are toroidal Alfven resonance vibrations of the geomagnetic field lines [2, 3]. It was revealed that the basic oscillation periods, presented in heart rate variability of healthy subjects, in conditions of rest, at each time point substantially coincide with the periods of oscillation of the X-vector components of the geomagnetic field in the frequency range of Pc5-6 pulsations. Synchronization effect was observed in approximately 60% of cases [4]. The above statement is based on the results of more than 100 experiments (recording time from 60 to 200 min), conducted in the period 2011-2013 in various research groups [4]. In total, 37 volunteers in the age range 18-65 yrs took part in the experiments. Experiments were performed in Pushchino and Khimki (Moscow region), Arkhangelsk, Tomsk, Sofia (Bulgaria), as well as at the station Starorusskaya (Leningrad region). The geomagnetic data were obtained from INTERMAGNET network (http://ottawa.intermagnet.org/Welcom_e.php). From a biophysical point of view, the observed effects of timing fluctuations of heart rate of healthy subjects with the oscillations of the magnetic induction vector of the GMF could be an effective tool for solving one of the most actual problems in heliobiophysics, namely the identification of specific physiological mechanisms of biosystems response to low-intensity variations external factors. 1. Pilipenko V.A., Kleimenova N.G., Kozyreva O.V., Yumoto K., Bitterly G. Geomagnetism and aeronomy, 1997, V. 37, ?.3, P. 64-76 2. Chen L. and Hasegawa A. J.Geophys. Res. 1974. Vol.79,P.1024-1032 3. Southwood D.J. Planet. Space Sci. 1974. Vol.22, P.483-491. 4.Zenchenko T.A., Medvedeva A.A., Khorseva N.I., Breus T.K. // Geophysical Processes and Biosphere. 2013. V. 12. ? 4. P. 73-84

Zenchenko, Tatiana

85

Relationship Between Human Physiological Parameters And Geomagnetic Variations Of Solar Origin  

NASA Astrophysics Data System (ADS)

This study attempts to assess the influence of increased geomagnetic activity on some human physiological parameters. The blood pressure, heart rate and general well-being of 86 volunteers were measured (the latter by means of a standardized questionnaire) on work days in autumn 2001 (01/10 to 09/11) and in spring 2002 (08/04 to 28/05). These periods were chosen because of maximal expected geomagnetic activity. Altogether, 2799 recordings were obtained and analysed. MANOVA was employed to check the significance of the influence of three factors on the physiological parameters under consideration. The three factors were the following: 1) planetary geomagnetic activity level estimated by Ap-index and divided into five levels; 2) gender - males and females; 3) blood pressure degree - persons in the group examined were divided into hypotensive, normotensive and hypertensive. Post hoc analysis was performed to elicit the significance of differences in the factors' levels. The average arterial blood pressure of the group was found to increase significantly with the increase of geomagnetic activity level. The average increment of systolic and diastolic blood pressure reached 9%, which deserves attention from a medical point of view. This effect was present irrespectively of gender. Results obtained suppose that hypertensive persons have the highest sensitivity and the hypotensive persons have the lowest sensitivity of the arterial blood pressure to increase of geomagnetic activity. The results did not show significant changes in the heart rate. The percentage of the persons who reported subjective psycho-physiological complaints was also found to increase significantly with the geomagnetic activity increase. During severe geomagnetic storms 30% of the persons examined reported subjective complaints and the highest sensitivity was revealed for the hypertensive females. The results obtained add further evidence that blood pressure seems to be affected by geomagnetic variations of solar origin. The examinations and analyses performed show that space weather prediction may be utilized for the purpose of pharmacological and regime measures to limit the adverse physiological reactions to geomagnetic storms.

Dimitrova, S.

86

Geomagnetic substorm association of plasmoids  

NASA Technical Reports Server (NTRS)

The relationship of geomagnetic substorms and plasmoids is examined by determining the correlation of the 366 plasmoids identified by Moldwin and Hughes (1992) with ground auroral zone magnetograms and geosynchronous particle data signatures of substorm onsets. Over 84 percent of the plasmoid events occurred between 5 and 60 min after the substorm onsets. We also find near one-to-one correlation between large isolated substorm signatures in the near-earth region and signatures consistent with a passing plasmoid in the distant tail. However, there does not appear to be an absolute correspondence of every substorm onset to a plasmoid signature in the deep tail especially for periods of prolonged disturbance that have multiple substorm onsets. A correlation of interplanetary magnetic field Bz south with plasmoid observations was also found. The locations of the near- and far-earth reconnection sites are estimated using the time of flight of the plasmoids from substorm onset to their observation at ISEE 3. The estimates of the near- and far-earth reconnection sites are highly variable and range from 10 to 140 R(E).

Moldwin, Mark B.; Hughes, W. J.

1993-01-01

87

On Geomagnetism and Paleomagnetism I  

NASA Technical Reports Server (NTRS)

A partial description of Earth's broad scale, core-source magnetic field has been developed and tested three ways. The description features an expected, or mean, spatial magnetic power spectrum that is approximately inversely proportional to horizontal wavenumber atop Earth's core. This multipole spectrum describes a magnetic energy range; it is not steep enough for Gubbins' magnetic dissipation range. Temporal variations of core multipole powers about mean values are to be expected and are described statistically, via trial probability distribution functions, instead of deterministically, via trial solution of closed transport equations. The distributions considered here are closed and neither require nor prohibit magnetic isotropy. The description is therefore applicable to, and tested against, both dipole and low degree non-dipole fields. In Part 1, a physical basis for an expectation spectrum is developed and checked. The description is then combined with main field models of twentieth century satellite and surface geomagnetic field measurements to make testable predictions of the radius of Earth's core. The predicted core radius is 0.7% above the 3480 km seismological value. Partial descriptions of other planetary dipole fields are noted.

Voorhies, Coerte V.

2000-01-01

88

Geomagnetic Field Modeling with DMSP  

NASA Astrophysics Data System (ADS)

The Defense Meteorological Satellite Program (DMSP) launches and maintains a network of satellites to monitor the meteorological, oceanographic, and solar-terrestrial physics environments. In the past decade, geomagnetic field modelers have focused much attention on magnetic measurements from missions such as CHAMP, Oersted and SAC-C. With the completion of the CHAMP mission in 2010, there have been limited satellite-based vector and scalar magnetic field measurements available for main field modeling. In this study, we investigate the feasibility of using the Special Sensor Magnetometer (SSM) instrument onboard DMSP for main field modeling. These vector field measurements are calibrated to compute instrument timing shifts, scale factors, offsets, and non-orthogonalities in the fluxgate magnetometer cores. Euler angles are then computed to determine the orientation of the vector magnetometer with respect to a local coordinate system. We fit a degree 12 main field model to the dataset and compare with similar models such as the World Magnetic Model (WMM) and IGRF. Initial results indicate that the DMSP dataset will be a valuable source for main field modeling for the years between CHAMP and the upcoming Swarm mission.

Alken, P.; Redmon, R. J.; Rich, F. J.; Maus, S.; Luhr, H.

2013-12-01

89

Relationship between human physiological parameters and geomagnetic variations of solar origin  

NASA Astrophysics Data System (ADS)

Results presented concern influence of increased geomagnetic activity on some human physiological parameters. The blood pressure and heart rate of 86 volunteers were measured on working days in autumn 2001 (01/10 09/11) and in spring 2002 (08/04 28/05). These periods were chosen because of maximal expected geomagnetic activity. Altogether 2799 recordings were obtained and analysed. Questionnaire information about subjective psycho-physiological complaints was also gathered. MANOVA was employed to check the significance of the influence of three factors on the physiological parameters under consideration. The factors were the following: (1) planetary geomagnetic activity level estimated by Ap-index and divided into five levels; (2) gender males and females; (3) blood pressure degree persons in the group examined were divided into hypotensive, normotensive and hypertensive. Post hoc analysis was performed to elicit the significance of differences in the factors’ levels. The average arterial blood pressure of the group was found to increase significantly with the increase of geomagnetic activity level. The average increment of systolic and diastolic blood pressure of the group examined reached 9%. This effect was present irrespectively of gender. Results obtained suppose that hypertensive persons have the highest sensitivity and the hypotensive persons have the lowest sensitivity of the arterial blood pressure to increase of geomagnetic activity. The results did not show significant changes in the heart rate. The percentage of the persons who reported subjective psycho-physiological complaints was also found to increase significantly with the geomagnetic activity increase and the highest sensitivity was revealed for the hypertensive females.

Dimitrova, S.

90

UV aurora mapping in corrected geomagnetic coordinates  

NASA Astrophysics Data System (ADS)

Ultraviolet images obtained by the USAF Geophysics Lab's Polar Bear satellite were subjected to geometric and photometric correction and used to map the UV aurora intensity in the north polar region. Radiation was measured at 135.6 and 159.6 nanometers. The work mainly comprised statistical processing of the aurora data, mapped on the corrected geomagnetic coordinate system, with a fixed direction relative to the sun. This enabled about 40 pictures to be processed in a common coordinate system. The statistical processing included computation of the mean aurora intensity and frequency of appearance. The images were separated into 5 groups according to the level of geomagnetic disturbance prevailing at the time of image reception. The final result was a statistical mapping of the UV aurora as a function of the geomagnetic disturbance level. The main conclusions are: (1) the UV aurora is distributed in an oval shape about the geomagnetic pole; (2) the radiation intensity and spatial distribution depend on the geomagnetic disturbance level, the dependence resembles that of the visible aurora; and (3) there is a general correspondence to the Feldstein ovals. The most important deviation detected was 5-degree poleward on the day side.

Rabitz, Arnoldo

1989-10-01

91

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

92

International Geomagnetic Reference Field: the third generation.  

USGS Publications Warehouse

In August 1981 the International Association of Geomagnetism and Aeronomy revised the International Geomagnetic Reference Field (IGRF). It is the second revision since the inception of the IGRF in 1968. The revision extends the earlier series of IGRF models from 1980 to 1985, introduces a new series of definitive models for 1965-1976, and defines a provisional reference field for 1975- 1980. The revision consists of: 1) a model of the main geomagnetic field at 1980.0, not continuous with the earlier series of IGRF models together with a forecast model of the secular variation of the main field during 1980-1985; 2) definitive models of the main field at 1965.0, 1970.0, and 1975.0, with linear interpolation of the model coefficients specified for intervening dates; and 3) a provisional reference field for 1975-1980, defined as the linear interpolation of the 1975 and 1980 main-field models.-from Author

Peddie, N. W.

1982-01-01

93

Magnetospheric mapping with quantitative geomagnetic field models  

NASA Technical Reports Server (NTRS)

The Mead-Fairfield geomagnetic field models were used to trace field lines between the outer magnetosphere and the earth's surface. The results are presented in terms of ground latitude and local time contours projected to the equatorial plane and into the geomagnetic tail. With these contours various observations can be mapped along field lines between high and low altitudes. Low altitudes observations of the polar cap boundary, the polar cusp, the energetic electron trapping boundary and the sunward convection region are projected to the equatorial plane and compared with the results of the model and with each other. The results provide quantitative support to the earlier suggestions that the trapping boundary is associated with the last closed field line in the sunward hemisphere, the polar cusp is associated with the region of the last closed field line, and the polar cap projects to the geomagnetic tail and has a low latitude boundary corresponding to the last closed field line.

Fairfield, D. H.; Mead, G. D.

1973-01-01

94

An introduction to quiet daily geomagnetic fields  

USGS Publications Warehouse

On days that are quiet with respect to solar-terrestrial activity phenomena, the geomagnetic field has variations, tens of gamma in size, with major spectral components at about 24, 12, 8, and 6 hr in period. These quiet daily field variations are primarily due to the dynamo currents flowing in the E region of the earth's ionosphere, are driven by the global thermotidal wind systems, and are dependent upon the local tensor conductivity and main geomagnetic field vector. The highlights of the behavior and interpretation of these quiet field changes, from their discovery in 1634 until the present, are discussed as an introduction to the special journal issue on Quiet Daily Geomagnetic Fields. ?? 1989 Birkha??user Verlag.

Campbell, W. H.

1989-01-01

95

Relationship Between Global Land-Ocean Temperature and Various Descriptors of Solar-Geomagnetic Activity and Climate.  

National Technical Information Service (NTIS)

Examined are sunspot cycle- (SC-) length averages of the annual January-December values of the Global Land-Ocean Temperature Index () in relation to SC-length averages of annual values of various descriptors of solar-geomagnetic activity and climat...

R. M. Wilson

2014-01-01

96

INFLUENCE OF INTERPLANETARY MAGNETIC FIELD AND PLASMA ON GEOMAGNETIC ACTIVITY DURING QUIET-SUN CONDITIONS  

Microsoft Academic Search

Observations by the IMP 1 satellite of the interplanetary magnetic field and plasma have been compared with the 3-hour geomagnetic activity index K. The average Kis approximately a linear function of the interplanetary field magnitude B in gammas (i -- (0.33 =k 0.02)B =k 0.2). It appears significant that this relation betweenand field magnitude passes through the origin, whereas the

John M. Wilcox; Kenneth H. Schatten; Norman F. Ness

1967-01-01

97

Interplanetary Origin of Geomagnetic Activity in the Declining Phase of the Solar Cycle  

Microsoft Academic Search

Interplanetary magnetic field (IMF) and plasma data are contpared with ground-based geomagnetic Dsr and AE indices to determine the causes of magnetic storms, substor-(ns, and quiet during the descending phase of the solar cycle. In this paper we focus pJ imarily on 1974 when the AZ index is anomalously high (~ = 283 nT). This year is characterized by the

Bruce T. Tsurutani; Walter D. Gonzalez; Alicia L. C. Gonzalez; Frances Tang; John K. Arballo; Masaki Okada

1995-01-01

98

Statistical properties of geomagnetic measurements as possible precursors for magnetic storms  

Microsoft Academic Search

Records of geomagnetic measurements have been analyzed looking for evidences\\u000aof possible precursors for magnetic storms. With this objective, the main\\u000amagnetic storms in the period 1998-2002 have been located in Dst index record.\\u000aPeriods immediately before storms and periods well before them were studied by\\u000aapplying a method recently introduced in the literature. Statistical properties\\u000aof both types of

Andres R. R. Papa; Lilian P. Sosman

2006-01-01

99

Predicting geomagnetic storms from solar-wind data using time-delay neural networks  

Microsoft Academic Search

We have used time-delay feed-forward neural networks to compute the geomagnetic-activity index Dst one hour ahead from a temporal sequence of solar-wind data. The input data include solar-wind density n, velocity V and the southward component Bz of the interplanetary magnetic field. Dst is not included in the input data. The networks implement an explicit functional relationship between the solar

H. Gleisner; H. Lundstedt; P. Wintoft

1996-01-01

100

Satellite Data for Geomagnetic Field Modeling  

NASA Technical Reports Server (NTRS)

Satellite measurements of the geomagnetic fields began with the launch of Sputnik 3 in May of 1958 and have continued sporadically. Spacecraft making significant contributions to main field geomagnetism will be reviewed and the characteristics of their data discussed, including coverage, accuracy, resolution and data availability. Of particular interest are Vanguard 3; Cosmos 49, Ogo's -2, -4, and -6; Magsat; DE-2; and POGS. Spacecraft make measurements on a moving platfrom above the ionosphere as opposed to measurements from fixed observatories and surveys, both below the ionosphere. Possible future missions, such as Aristoteles and GOS are reviewed.

Langel, R. A.; Baldwin, R. T.

1992-01-01

101

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

102

Empirical STORM-E model: II. Geomagnetic corrections to nighttime ionospheric E-region electron densities  

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 and will be incorporated into the 2012 release of the International Reference Ionosphere (IRI). 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 ?m channel limb radiance measurements. The storm-time response of the NO+(v) 4.3 ?m 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 ?m 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 nighttime quiescent E-region electron density peak concentration for geomagnetic enhancements due to auroral particle precipitation. Part I of this series gives a detailed description of the algorithms and methodologies used to derive NO+(v) VER from SABER 4.3 ?m limb emission measurements. In this paper, Part II of the series, 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, which are currently independent of magnetic local time. 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 IRI model or to the quiet-time baseline electron density concentrations measured by ISR. The STORM-E/ISR comparisons indicate that the STORM-E fits to the Ap-, AE-, and HP-indices are comparable in both absolute accuracy and relative dynamical response. Contrarily, the Dst-index does not appear to be a suitable input driver to parameterize the E-region electron density response to geomagnetic activity.

Mertens, Christopher J.; Xu, Xiaojing; Bilitza, Dieter; Mlynczak, Martin G.; Russell, James M.

2013-02-01

103

ULF geomagnetic pulsations in the southern polar cap: Simultaneous measurements near the cusp and the geomagnetic pole  

Microsoft Academic Search

During November 2003, a 1-week test campaign of ULF geomagnetic field measurements was conducted at the new Italian\\/French base of Concordia (Dome C, Antarctic plateau), close to the geomagnetic pole, at a corrected geomagnetic latitude of ?89°S. An analysis of these measurements is presented, together with a comparison with simultaneous measurements conducted at the Italian “Mario Zucchelli” base, at Terra

M. De Lauretis; P. Francia; M. Vellante; A. Piancatelli; U. Villante; D. Di Memmo

2005-01-01

104

Modeling System Earth During Geomagnetic Polarity Transitions  

NASA Astrophysics Data System (ADS)

During a geomagnetic polarity transition, the configuration and strength of the Earth's geomagnetic field can differ very much from the current state. This has consequences not only for the large-scale current systems, but also for the distribution of high-energy particle precipitation into the middle atmosphere, and therefore, for the composition of the middle atmosphere during and after large energetic particle events. Observations of the Earth's magnetic field during the last century show an increase of variability and a decrease of magnetic field strength. It has been argued that this might imply that a new polarity transition of the Earth's magnetic field is preparing to occur. This work is a multi-institutional collaboration aiming at modeling the magnetosphere during polarity transitions, the resulting energetic particle fluxes, and their effect on the middle atmospheric ozone concentration. We use MHD simulations and parametric modeling of the paleomagnetosphere to determine the geomagnetic field configuration for different transition scenarios. Particle orbits are traced and the resulting particle fluxes are used as input parameters in Monte-Carlo simulations of the mesospheric and stratospheric energy deposition and ionization. The effects on the composition of the middle atmosphere are investigated by means of a two-dimensional photochemistry and transport model. Although these models describe very different physical processes, links can be established through well-defined interfaces, and the chain of models allows us to study the global consequences of geomagnetic field reversals on system Earth.

Sinnhuber, M.; Zieger, B.; Vogt, J.; Stadelmann, A.; Kuenzi, K. F.; Kallenrode, M.; Heber, B.; Glassmeier, K.; Burrows, J. P.

2003-12-01

105

Corrected geomagnetic coordinates for Epoch 1980  

Microsoft Academic Search

A new set of corrected geomagnetic coordinates have been calculated. They are based on the field model IGRF-1980 for Epoch 1980. They differ from the earlier coordinates based on IGRF-1965 model by about one degree in latitude in the auroral oval region and a few degrees in longitude in certain areas.

G. Gustafsson

1984-01-01

106

Corrected geomagnetic coordinates for Epoch 1980  

NASA Astrophysics Data System (ADS)

A new set of corrected geomagnetic coordinates have been calculated. They are based on the field model IGRF-1980 for Epoch 1980. They differ from the earlier coordinates based on IGRF-1965 model by about one degree in latitude in the auroral oval region and a few degrees in longitude in certain areas.

Gustafsson, G.

107

UV aurora mapping in corrected geomagnetic coordinates  

Microsoft Academic Search

Ultraviolet images obtained by the USAF Geophysics Lab's Polar Bear satellite were subjected to geometric and photometric correction and used to map the UV aurora intensity in the north polar region. Radiation was measured at 135.6 and 159.6 nanometers. The work mainly comprised statistical processing of the aurora data, mapped on the corrected geomagnetic coordinate system, with a fixed direction

Arnoldo Rabitz

1989-01-01

108

Space radiation enhancement linked to geomagnetic disturbances.  

PubMed

Space radiation dosimetry measurements have been made on board the Space Shuttle. A newly developed active detector called "Real-time Radiation Monitoring Device (RRMD)" was used (Doke et al., 1995; Hayashi et al., 1995). The RRMD results indicate that low Linear Energy Transfer (LET) particles steadily penetrate around the South Atlantic Anomaly (SAA) without clear enhancement of dose equivalent and some daily periodic enhancements of dose equivalent due to high LET particles are seen at the lower geomagnetic cutoff regions (Doke et al., 1996). We also have been analyzing the space weather during the experiment, and found that the anomalous high-energy particle enhancement was linked to geomagnetic disturbance due to the high speed solar wind from a coronal hole. Additional analysis and other experiments are necessary for clarification of these phenomena. If a penetration of high-energy particles into the low altitude occurs by common geomagnetic disturbances, the prediction of geomagnetic activity becomes more important in the next Space Station's era. PMID:11541771

Tomita, F; Den, M; Doke, T; Hayashi, T; Nagaoka, T; Kato, M

1997-12-01

109

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

110

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

111

Modelling of geomagnetic induction in pipelines  

NASA Astrophysics Data System (ADS)

Geomagnetic field variations induce telluric currents in pipelines, which modify the electrochemical conditions at the pipe/soil interface, possibly contributing to corrosion of the pipeline steel. Modelling of geomagnetic induction in pipelines can be accomplished by combining several techniques. Starting with geomagnetic field data, the geoelectric fields in the absence of the pipeline were calculated using the surface impedance derived from a layered-Earth conductivity model. The influence of the pipeline on the electric fields was then examined using an infinitely long cylinder (ILC) model. Pipe-to-soil potentials produced by the electric field induced in the pipeline were calculated using a distributed source transmission line (DSTL) model. The geomagnetic induction process is frequency dependent; therefore, the calculations are best performed in the frequency domain, using a Fourier transform to go from the original time domain magnetic data, and an inverse Fourier transform at the end of the process, to obtain the pipe-to-soil potential variation in the time domain. Examples of the model calculations are presented and compared to observations made on a long pipeline in the auroral zone.

Trichtchenko, L.; Boteler, D. H.

2002-07-01

112

Power lines and the geomagnetic field  

SciTech Connect

The metric of prime interest in power line epidemiological studies has been AC magnetic intensity. To consider also possible geomagnetic involvement, the orientation of a long straight power line is examined relative to a uniform geomagnetic field (GMF) with dip angle {alpha}. An expression is derived for the component of the total GMF that is parallel, at an elevation {beta}, to the circular magnetic field that surrounds the line. This component is a function of the angles {alpha} and {beta}, the total geomagnetic intensity B{sub T}, and the angle {theta} between the axis of the power line and magnetic north. Plotting these geomagnetic parameters for known leukemia residences allows one to test for possible ion cyclotron resonance or other GMF interactions. This approach, in principle, is an easy addition to existing or planned studies, because residential access is not required to obtain local values for {alpha}, {beta}, {theta}, and B{sub T}. The authors recommend including these parameters in the design of epidemiological studies examining power line fields and childhood leukemia.

Liboff, A.R. [Oakland Univ., Rochester, MI (United States). Dept. of Physics; McLeod, B.R. [Montana State Univ., Bozeman, MT (United States). Dept. of Electrical Engineering

1995-09-01

113

An assessment study of the wavelet-based index of magnetic storm activity (WISA) and its comparison to the Dst index  

E-print Network

of magnetic storm activity (WISA) and its comparison to the Dst index Zhonghua Xu a,Ã?, Lie Zhu a , Jan Sojka: Geomagnetic indices Ring current Magnetic storms Wavelet transform a b s t r a c t A wavelet-based index. Wavelet-based index of magnetic storm activity. Journal of Geophysical Research 111, A09215, doi:10

Kokoszka, Piotr

114

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

115

Surface electromagnetic impedance and geomagnetic activity: results of long term observation  

NASA Astrophysics Data System (ADS)

The magnetotelluric (MT) method is one of the most useful geophysical tool to discover even the deep subsurface structures. The target function of the MT data processing is the surface electromagnetic (EM) impedance. In case of practical MT exploration the surface EM impedance is computed based on a simplification related to the nature of the ionospheric source of the surface EM signals. Assuming that the ionospheric current systems result in homogeneous surface electromagnetic variations, the uncertainty of the computed surface electromagnetic impedance tensor depends only the duration of the EM observation. However the surface EM field can only be approached by plane waves in certain time periods and besides given uncertainty. The EM impedance may be sensitive to magnetospheric and -indirectly- interplanetary circumstances and solar activity. Four years continuous observation of telluric and surface geomagnetic components allowed to perform a representative survey to discover if geomagnetic activity has any effect on observed EM impedance tensor. Geomagnetic indices (Dst, ULF-index, ASY-H, SYM-H) have been used to classify dates according to geomagnetic activity. Processing to estimate the mean surface EM impedance tensor has been performed in each dataset, each class separately. The sensitivity and the characteristics of the answer of the EM impedance tensor to the geomagnetic disturbances seems to be definite. This presentation aims to briefly summarize the preliminary results of our study based on the unique dataset of the Széchenyi István Geophysical Obsevatory (Intermagnet code:NCK). In addition, pointing out the limitations of the routine way of practical MT data processing and interpretation is an important duty of this study. This study was supported by the TAMOP-4.2.2.C-11/1/KONV-2012-0015 (Earth-system) project sponsored by the EU and European Social Foundation.

Lemperger, István; Menvielle, Menvielle; Wesztergom, Viktor; Bencze, Pál; Szendr?i, Judit; Novák, Attila; Kis, Árpád; Szalai, Sándor

2014-05-01

116

Geomagnetic storms and transient depressions in cosmic rays due to coronal mass ejections and corotating interaction regions: A comparative study  

NASA Astrophysics Data System (ADS)

We study selected geomagnetic storms and transient depressions (Forbush decreases) in cosmic ray intensity. We use ground-based neutron monitors as a measure of cosmic ray intensity. Geomagnetic index Dst is used as a measure of level of geomagnetic activity. We identify coronal mass ejections (CMEs) and high-speed streams from coronal holes on the solar surface and corresponding structures evolved in the interplanetary space e.g. shock/sheath regions, interplanetary counterpart of CMEs (ICMEs) and corotating interaction regions (CIRs), responsible for these phenomenon e.g. geomagnetic storms (GS) and Forbush decrease (FD) in cosmic ray intensity. An ICME or CIR that is strongly geo-effective is not necessarily effective in producing large depressions in cosmic ray intensity. It is therefore, important to study solar wind plasma/field parameters during the passage of such structures and identify the solar/interplanetary parameters of major importance and physical mechanism responsible for GS and FDs. This has been attempted by detailed study of the observed differences in geomagnetic and cosmic-ray response to same solar sources. Space weather implication of this study is also discussed.

Kumar, Anand; Badruddin, B.

117

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

118

Cosmic Rays during Intense Geomagnetic Conditions and their Solar / Interplanetary features  

NASA Astrophysics Data System (ADS)

In this study we discuss the behavior of cosmic rays during the phase of highly intense or ultra intense geomagnetic storms, as shocks driven by energetic coronal mass ejections (CME’s) and other interplanetary (IP) transients are mainly responsible for initiating large and intense geomagnetic storms. Observational results indicate that galactic cosmic rays (CR) coming from deep surface interact with these abnormal solar and IP conditions and suffer modulation effects. In this paper a systematic study has been performed to analyze the CRI variation during super storms i.e. very intense geomagnetic storms with Dst index ? -300 nT. The neutron monitor data of three stations Oulu (Rc = 0.77 GV), Climax (Rc = 2.97 GV) and Huancayo (Rc = 13.01 GV) well distributed over different latitudes and hourly values of IMF parameters derived from satellite observations near Earth IP medium from OMNI Data base is used for the period spanning over solar cycles 20, 21, 22 and 23. It is found that AP and AE indices show rise before the forward turnings of IMF, while the Dst index shows a classic storm time decrease. The analysis indicates that the magnitude of all the responses depends on BZ component of IMF being well correlated with solar maximum and minimum periods. Transient decrease in cosmic ray intensity with slow recovery is observed during the storm phase duration.

Kaushik, Subhash Chandra

119

Historical variation of the geomagnetic axial dipole  

NASA Astrophysics Data System (ADS)

The geomagnetic axial dipole (hereinafter denoted g10) is the largest component of our planet's magnetic field. Its magnitude determines the morphology of solar-terrestrial electrical current systems and it is the most fundamental diagnostic property of the core-generated geodynamo. Elucidating past and future variations of g10(t) is consequently of central importance in geomagnetism. Previous historical geomagnetic field models, such as gufm1 of Jackson et al. [Jackson, A., Jonkers, A.R.T., Walker, M.R., 2000. Four centuries of geomagnetic secular variation from historical records. Philos. Trans. R. Soc. Lond. A 358, 957-990], used direct observations to constrain g10(t) only after 1840 A.D.; before this time a crude linear extrapolation of the post-1840 A.D. rate of change (15 nT/year) was employed. In this contribution I construct historical field models with g10(t) instead constrained from 1590 A.D. to 1840 A.D. by an archaeointensity dataset compiled by Korte et al. [Korte, M., Genevey, A., Constable, C.G., Frank, U., Schnepp, E., 2005. Continuous geomagnetic field models for the past 7 millennia. 1. A new global data compilation. Geochem. Geophys. Geosyst. 6, doi:10.1029/2004GC000800]. A range of possible linear models of the form g10(t)=g10(1840)+?(t-1840) are first explored; ?=2.74±42.32 nT/year is found to explain the archaeointensity dataset with maximum likelihood, consistent with the recent findings of Gubbins et al. [Gubbins, D., Jones, A.L., Finlay, C.C., 2006. Fall in Earth's magnetic field is erratic. Science 312, 900-902]. Relaxing the linear constraint in an effort to find more physically plausible models, I find it is necessary to artificially increase the weight given to the archaeointensity data in order to obtain acceptable models. Despite satisfactorily explaining both the historical and archaeointensity data, and possessing reasonable spatial and temporal complexity, such free evolution models perform worse than the simpler linearly constrained models when tested against the independent dataset of Gallet et al. [Gallet, Y., Genevey, A., Fluteau, F., 2005. Does Earth's magnetic field secular variation control centennial climate change? Earth Plan. Sci. Lett. 236, 159-173]. Bayesian model comparison techniques indicate that a model ( gufm1-g10c) involving no change in g10(t) between 1590 A.D. and 1840 A.D. is most probable given the presently available data and current modelling techniques. I propose that this new, empirically derived, constraint on the evolution of the geomagnetic axial dipole be incorporated into the next generation of historical field models.

Finlay, Christopher C.

2008-09-01

120

Environmental and geomagnetic factors in relation to self-destructive ideation and behaviour  

NASA Astrophysics Data System (ADS)

Besides the individual factors such as the reaction to conflicts, several exogenous factors environmental and social may exert a pathogenic influence on suicidal behavior, suicide attempts and complete suicide on predisposed individuals. In the turn of the century many reports accord for the seasonality of suicides, which seems to have a bimodal distribution with a major peak around the spring-summer (April-May) and a second minor in autumn. On the other hand, the seasonal variation of environmental factors (daylight, sunlight duration, weather, temperature, air pressure, humidity, geomagnetism, solar activity, etc), of biological factors (melatonin, serotonin, serotonin precursors, etc) as also of sociological factors (ethnic events, major holidays, weekends etc) possibly influences the seasonal pattern of self-destructive behavior. Bimodal seasonal variation is also reported for biochemical parameters (L-tryptophan, serotonin, endorphin I fraction) that matches seasonal pattern in the prevalence of violent suicide in the total population and also in the incidence of the affective disorders. The aim of this study is to investigate the relation of environmental factors expressed by the Discomfort Index (DI) and geomagnetic factors expressed by the geomagnetic field Index DST in relation to suicidal behavior. The total number (4803) of patients recorded in the Ambulance of a Phychiatric Hospital (Eginition) throughout 1994 was used along with the records of 2750 patients of the year 1989. The Index DI is a function of dry and wet-bulb temperature. DST is probably one of the geomagnetic indices that expresses and monitors with the greatest accuracy the equatorial ring current variations. Our results show that there is a seasonal variation of suicidal behavior (Fourier analysis) with a major peak during summer (July) and a minor one during spring. A difference in the occurrence of the peaks was observed among genders. A relation of self-destructive behavior and the daily changes of the geomagnetic index DST was found. This was significant with a latency of three days. As reported in the literature, serotonin, which is involved in the presence of suicide, was found to be magnetosensitive with a latency of three days. The contextual influence of the above factors in suicidal behavior will be discussed.

Bergiannaki, J. D.; Psarros, C.; Nastos, P. Th.; Paparigopoulos, T.; Paliatsos, A. G.; Tritakis, V. P.; Stefanis, C. N.

2001-09-01

121

The calculation of corrected geomagnetic coordinates in the high latitude region  

Microsoft Academic Search

Because the real geomagnetic field in Space, especially during geomagnetic perturbations has very complex spatial distribution, we had to use adjusted geomagnetic coordinates. The calculation of these coordinates is connected with the correct calculation of field lines inclusive the internal IGRF (International Geomagnetic Reference Field) and external geomagnetic field. Tables of such coordinates are somewhat incorrect as they do not

Leonid Alperovich; Anatoly Levitin; Lyudmila Gromova; Lyudmila Dremukhina

2008-01-01

122

Geomagnetic and Solar Indices Data at NGDC  

NASA Astrophysics Data System (ADS)

The National Geophysical Data Center, Solar and Terrestrial Physics Indices program is a central repository for global indices derived at numerous organizations around the world. These datasets are used by customers to drive models, evaluate the solar and geomagnetic environment, and to understand space climate. Our goal is to obtain and disseminate this data in a timely and accurate manner, and to provide the short term McNish-Lincoln sunspot number prediction. NGDC is in partnership with the NOAA Space Weather Prediction Center (SWPC), University Center for Atmospheric Sciences (UCAR), the Potsdam Helmholtz Center (GFZ), the Solar Indices Data Center (SIDC), the World Data Center for Geomagnetism Kyoto and many other organizations. The large number of available indices and the complexity in how they are derived makes understanding the data one of the biggest challenges for the users of indices. Our data services include expertise in our indices and related datasets to provide feedback and analysis for our global customer base.

Mabie, J. J.

2012-12-01

123

MAGSAT for geomagnetic studies over Indian region  

NASA Technical Reports Server (NTRS)

Progress in the preparation of software for converting data tapes produced on an IBM system to data readable on a DEC-10 system, in the creation of awareness of the utility of MAGSAT data among users in India, and in making computer programs supplied by NASA operational on the DEC-10 system is reported. Papers presented to Indian users, at the IAGA fourth scientific assembly, at a symposium on interdisciplinary approaches to geomagnetism, and a paper published in Science Today are included.

Rastogi, R. G.; Bhargava, B. N.; Singh, B. P.; Rao, D. R. K.; Rangarajan, G. K.; Rajaram, R.; Roy, M.; Arora, B. R.; Seth, A. (principal investigators)

1981-01-01

124

Centennial to millennial geomagnetic secular variation  

Microsoft Academic Search

A time-varying spherical harmonic model of the palaeomagnetic field for 0-7 ka is used to investigate large-scale global geomagnetic secular variation on centennial to millennial scales. We study dipole moment evolution over the past 7 kyr, and estimate its rate of change using the Gauss coefficients of degree 1 (dipole coefficients) from the CALS7K.2 field model and by two alternative

M. Korte; C. G. Constable

2006-01-01

125

NOAA Plans for Geomagnetic Storm Observations  

NASA Astrophysics Data System (ADS)

For many years, NOAA has issued geomagnetic storm watches and warnings based on coronal mass ejection (CME) imagery and in-situ solar wind measurements from research satellites. The NOAA Satellite and Information Service (NESDIS) recognizes the importance of this service to protecting technological infrastructure including power grids, polar air travel, and satellite navigation, so is actively planning to replace these assets to ensure their continued availability. NOAA, NASA, and the US Air Force are working on launching the first operational solar wind mission in 2014, the Deep Space Climate Observatory (DSCOVR), to follow NASA's Advanced Composition Explorer (ACE) in making solar wind measurements at the sun-Earth L1 for 15-60 minute geomagnetic storm warning. For continuing operations after the DSCOVR mission, one technology NOAA is looking at is solar sails that could greatly improve the lead time of geomagnetic storm warnings by stationkeeping closer to the sun than L1. We are working with NASA and private industry on the Sunjammer solar sail demonstration mission to test making solar wind measurements from a solar sail in the sun-Earth L1 region. NOAA uses CME imagery from the NASA/ESA Solar and Heliospheric Observatory (SOHO) and the NASA Solar Terrestrial Relations Observatory (STEREO) satellites to issue 1-3 day geomagnetic storm watches. For the future, NOAA worked with the Naval Research Laboratory (NRL) to develop a Compact Coronagraph (CCOR) through Phase A, and is studying ways to complete instrument development and test fly it for use in the future.

Diedrich, B. L.; Biesecker, D. A.; Mulligan, P.; Simpson, M.

2012-12-01

126

Visualization of geomagnetic field for education and outreach  

NASA Astrophysics Data System (ADS)

Since April 2007 in the project "MAGE" (Mapping Applications to Geomagnetic Environments) we publish tools for visualization of the geomagnetic field on the web. Now five kinds of the geomagnetic field flucuation (from observations and paleomagnetic results) and geodynamo models are freely downloadable from our website, http://mage-p.org/. Access the webpage, download the KML files and open them from Google Earth, then you can experience changing geomagnetic field lines and observations, inclinations, declination, field strength and others, on the Earth's surface. One of our actions in the project is preparation of the documentations of the geomagnetic field and its fluctuations for education and outreach. Especially in Japan, there are poor treatments in the education during elementary and high schools, and the expository writing of the geomagnetic field and concerned articles are also scarce. Moreover, we provide the movie files and stereoscopic visions for the user experiences of the 3D images.

Hatakeyama, T.

2010-12-01

127

Geomagnetic Field Response at Southern and Northern Hemisphere  

NASA Astrophysics Data System (ADS)

Geomagnetic Field Response at Southern and Northern Hemisphere Babita Chandel, Shailendra Saini, Sneha Yadav,S.K.Vijay and A.K.Gwal Space Science Laboratory, Department of Physics, Barkatullah University, Bhopal-462026, India ABSTRACT: This paper represents the geomagnetic field response at Southern Hemisphere (MAITRI) and Northern Hemisphere (TROMSO). The Indian Antarctic Station MAITRI is located at geomagnetic Long. (66.030, 53.210) where as TROMSO is at geomagnetic Long. (66.030, 53.210). We studied the behaviour of geomagnetic field with respect to geomagnetic storms at both the stations TROMSO and MAITRI. It was observed that at Southern Hemisphere there is more variation in winter as compared to the summer season, where as in Northern Hemisphere the variations are more in summer as compared to winter. As in the Northern hemisphere the magnetospheric plasma is strongly turbulized in summer and in Southern hemisphere the magentospheric plasma is strongly turbulized in winter.

Chandel, Babita

128

Geomagnetic Earthquake Precursors Improvement Formulation on the basis of SKO (Skopje) and PAG (Intermagnet) Geomagnetic Data  

E-print Network

In this paper we show that the simple analysis of the local geomagnetic field behaviour can serve as reliable imminent precursor for regional seismic activity increasing. As the first step the problem was investigated using one- component Dubna fluxgate magnetometer. The result of 2001-2004 Sofia monitoring confirmed many old papers for connection between Earth tide (Sun- Moon tides as earthquakes trigger) and jump (Geomagnetic quake) of daily averaged one minute standart deviation of the geomagnetic field. The second step (2004-present), which included analisys of three-component Danish fluxgate magnetometer data, worked in Skopje Seismological observatory, confirmed the first step result. The analysis of INTERMAGNET data stations around which was happened stronger earthquakes also confirmed our result. The distribution of time difference between the times of such earthquakes and local daily averaged tide vector movement for impending tide extreme confirms our estimate that the increasing seismicity is reali...

Mavrodiev, Strachimir Chterev

2012-01-01

129

Geomagnetic effects on cosmic ray propagation for different conditions  

NASA Astrophysics Data System (ADS)

The geomagnetic field (Bgeo ) sets a lower cutoff rigidity (Rc ) to the entry of cosmic particles to Earth which depends on the geomagnetic activity. From numerical simulations of the trajectory of a proton (performed with the MAGCOS code) in the Bgeo , we use backtracking to analyze particles arriving at the Auger Observatory location. We determine the asymptotic trajectories and the values of Rc in different incidence directions. Simulations were done using several models of Bgeo that emulate different geomagnetic conditions.

Masías-Meza, Jimmy J.; Bertou, Xavier; Dasso, Sergio

2012-07-01

130

Multifractal analysis of low-latitude geomagnetic fluctuations  

Microsoft Academic Search

The technique of large deviation multifractal spectrum has shown that the high-latitude (77.5° N, 69.2° W) geomagnetic fluctuations can be described from direct dissipation process or loading-unloading regimes of the solar wind-magnetosphere coupling. In this paper, we analyze the H-component of low-latitude (22.4° S, 43.6° W) geomagnetic field variability observed during the month of July 2000 at the Geomagnetic Observatory,

M. J. A. Bolzan; R. R. Rosa; Y. Sahai

2009-01-01

131

Magnetospheric geomagnetic coordinates for space physics data presentation and visualization  

NASA Astrophysics Data System (ADS)

Corrected geomagnetic coordinates, which account for the multipolar geomagnetic field, are frequently used to organize the ionospheric-altitude data. However, realistic organization of data measured simultaneously in the magnetosphere and ionosphere in a some sort of magnetic coordinate system requires a combination of the high-altitude external magnetic fields and the multipolar low-altitude field. Such combinations have been non-existent in the past. A new magnetospheric geomagnetic coordinate system is introduced providing such a combination.

Papitashvili, V. O.; Papitashvili, N. E.; King, J. H.

1997-09-01

132

Some topics and historical episodes in geomagnetism and aeronomy  

SciTech Connect

The author provides historical perspective on work in the area of geomagnetism and aeronomy. He discusses early ideas discussed in the literature, work by Birkelund on current flows, ideas on the curl-freeness of the geomagnetic fields, studies of auroral records recorded by man, studies of magnetic storms, geomagnetic field measurements, and of late the wealth of satellite information of the magnetosphere and solar wind effects.

Fukushima, N. [Univ. of Tokyo (Japan)

1994-10-01

133

Geomagnetic activity, humidity, temperature and headache: is there any correlation?  

PubMed

Meterological factors influence several biological functions. Geomagnetic activity (GMA) can be considered a trigger factor of migraine attacks. We studied the possible relationship between 40 migraine patients and some meteorological factors: humidity, temperature and geomagnetic activity in particular. All frequency changes of geomagnetic activity, temperature and humidity values are recorded daily. The study was performed from March to June 1988 over a geographically small area in order to avoid climatic and environmental influences. Our results indicate a significant correlation between geomagnetic activity and migraine attack frequency. Controversial opinions concerning the modalities of data collection and the possible relationships between environment and headache raise the need of further studies. PMID:8132439

De Matteis, G; Vellante, M; Marrelli, A; Villante, U; Santalucia, P; Tuzi, P; Prencipe, M

1994-01-01

134

Coronal mass ejections and geomagnetic storms: Seasonal variations  

SciTech Connect

The well-established semiannual geomagnetic cycle, with peak activity near the equinoxes, has been attributed to the angle between the solar rotation axis and the geomagnetic dipole, which modulates the GSM Bz component in the interplanetary magnetic field (MF). This effect is predicted to be accentuated in the shocked plasma ahead of fast coronal mass ejections (CMESs); its relevance to the internal fields of the ejecta is unclear. CMEs, particularly fast events driving interplanetary shocks, are the cause of almost all large geomagnetic storms near solar maximum. We use a set of CMEs identified by ISEE-3 observations of bidirectional electron streaming, plus IMF and geomagnetic data, to investigate the semiannual geomagnetic variation and its relation to CMEs. We find that the geomagnetic effectiveness of CMEs and post-shock solar wind is well-ordered by speed and by the southward component of the IMF in GSM coordinates, as well as by preexisting geomagnetic conditions. The post-shock seasonal effect, with geomagnetic effectiveness maximizing near April 5 for negative GSEQ By and near October 5 for positive GSEQ By, is identifiable in shock and shock/CME events, but not for CME events without leading shocks. When used to complement the more fundamental causal parameter of CME speed, the seasonal effect appears to have value for prediction of geomagnetic storms.

Phillips, J.L.; Gosling, J.T.; McComas, D.J.

1992-07-01

135

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

Microsoft Academic Search

Recent thermomechanical modeling to calculate the stress field in industrially direct-chill (DC) cast-aluminum slabs has been\\u000a successful, but lack of material data limits the accuracy of these calculations. Therefore, the constitutive behavior of three\\u000a aluminum alloys (AA1050, AA3104, and AA5182) was determined in the as-cast condition using tensile tests at low strain rates\\u000a and from room temperature to solidus temperature.

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

2002-01-01

136

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

137

Non-linear relation of heart rate variability during exercise recovery with local geomagnetic activity.  

PubMed

Heart rate variability (HRV) during 30 minute's recovery from a 30-minute exercise was established for 6 healthy men 23-30 years old. The exercise-recovery schedule was performed at 8 circadian stages over 11 days for each subject and analyzed over consecutive 5-minute segments. The local K index for the time of the recovery was recorded as a variable for geomagnetic activity. Pooling all HRV values across the different times into recovery, the relation of HRV to local K is found to be non-linear. A quadratic model fitted to the pooled HRV values is statistically significant. The present study indicates that during recovery from exercise, the effect of geomagnetic disturbances on HRV is non-linear. A non-linear relation of HRV with respect to geomagnetic activity deserves further work to determine whether it can account for discrepant findings of an effect of magnetic storms on the incidence of myocardial infarctions, for which a decreased HRV is a predictor. PMID:12653183

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

2002-01-01

138

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

USGS Publications Warehouse

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

Peddie, N. W.

1992-01-01

139

Solar activity, magnetic clouds, and geomagnetic storms  

NASA Technical Reports Server (NTRS)

Associational aspects of magnetic clouds and solar activity, and of magnetic clouds and geomagentic storms are described. For example, recent research has shown associations to exist between the launch of magnetic clouds directed Earthward from the Sun and, in particular, two forms of solar activity: flare-related, type II metric radio bursts and disappearing filaments (prominences). Furthermore, recent research has shown an association to exist between the onset of magnetic clouds on Earth and the initiation of geomagnetic storms. Based on these findings, STIP Intervals XV-XIX are examined for possible occurrences of Earthward-directed magnetic clouds.

Wilson, Robert M.

1987-01-01

140

Geomagnetic effects on atmospheric Cerenkov images  

E-print Network

Atmospheric Cerenkov telescopes are used to detect electromagnetic showers from primary gamma rays of energy ~300 GeV - ~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 axis is sufficiently large (> 0.4 G) the performance of gamma ray telescopes may be affected, although corrections should be possible.

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

1999-04-07

141

A geomagnetic field based positioning technique for underground mines  

Microsoft Academic Search

A geomagnetic field based positioning technique is proposed for underground mining environments. The proposed technique utilizes the anomalies of the geomagnetic field present in underground environments. The main source of the magnetic anomalies is the complex distribution of metallic minerals such as iron ore. The distribution of metallic minerals produces unique spatial magnetic patterns in underground mines which can be

Janne Haverinen; Anssi Kemppainen

2011-01-01

142

The use of geomagnetic field models in magnetic surveys  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

143

The role of geomagnetic field configuration in EMIC wave generation  

Microsoft Academic Search

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

J. P. McCollough

2010-01-01

144

Empirical analytic transformations between geographic and corrected geomagnetic coordinates  

NASA Technical Reports Server (NTRS)

Based upon a mathematical model of contours of constant corrected geomagnetic latitude in a polar projection of geographic coordinates, analytic equations are developed for converting geographic coordinates to corrected geomagnetic coordinates and vice versa. The equations were programmed for use on a small computer. This treatment is restricted to the Northern Hemisphere.

Comfort, R. H.

1970-01-01

145

Optical distortion due to geomagnetism in quantitative angiography  

Microsoft Academic Search

Modern X-ray systems exhibit distortion effects due to the influence of the geomagnetic field on the electron rays inside the image intensifier. In parallel orientation of the image intensifier axis to the geomagnetic field, a characteristic S-shaped distortion arises. This distortion can produce errors in the evaluation of angiograms. Miscalculations may arise in determination of the spatial orientation of the

U. Solzbach; H. Wollschlager; A. Zeiher; H. Just

1988-01-01

146

Predictability of large geomagnetic disturbances based on solar wind conditions  

Microsoft Academic Search

We test the ability of a data-derived model of geomagnetic activity, originally optimized to have a high prediction efficiency (PE), for its ability to predict only large geomagnetic disturbances. Correlation-based metrics, such as prediction efficiency, are often used as a measure of model performance. This metric puts equal weight on prediction of both large and small measurements. However, for space

Robert S. Weigel; Daniel N. Baker; E. Joshua Rigler; Dimitris Vassiliadis

2004-01-01

147

Plasma and Magnetic Field Correlations Between Spacecraft During Geomagnetic Storms  

E-print Network

Plasma and Magnetic Field Correlations Between Spacecraft During Geomagnetic Storms S. Jurac and J and By is about 0.9 during severe geo- magnetic storms. The perpendicular scale-length of plasma and magnetic geomagnetic storms. 2 #12;1. INTRODUCTION Simultaneous monitoring of the solar wind plasma and magnetic

Richardson, John

148

Search for correlation between geomagnetic disturbances and mortality  

NASA Technical Reports Server (NTRS)

Statistical evaluation of death rates in the U.S.A. from heart diseases or stroke did not show any correlation with measured geomagnetic pulsations and thus do not support a claimed relationship between geomagnetic activity and mortality rates to low frequency fluctuations of the earth's magnetic field.

Lipa, B. J.; Barnes, C. W.; Sturrock, P. A.; Feinleib, M.; Rogot, E.

1975-01-01

149

CIRES/NGDC Research Associate Geomagnetism Scientific Team Lead  

E-print Network

's global Earth Magnetic Anomaly Grid (EMAG) Participate in calibration, validation and data analysis-doctoral researchers and students in NGDC's geomagnetism team. Requirements PhD in geophysics, planetary physics knowledge of geomagnetism and/or planetary magnetism, geophysics, data analysis, mathematical statistics

Colorado at Boulder, University of

150

On claimed ULF seismogenic fractal signatures in the geomagnetic field  

Microsoft Academic Search

During the last ten years, fractal analysis of ultra low frequency (ULF) geomagnetic field components has been proposed as one of the most promising tools to highlight magnetic precursory signals possibly generated by the preparation processes of earthquakes. Several papers claim seismogenic changes in the fractal features of the geomagnetic field some months before earthquakes occur. The target of the

Fabrizio Masci

2010-01-01

151

Gravitational dynamos and the low-frequency geomagnetic secular variation  

E-print Network

Gravitational dynamos and the low-frequency geomagnetic secular variation P. Olson* Department-sustaining numerical dynamos are used to infer the sources of low-frequency secular variation of the geomagnetic field number. Chaotic gravitational dynamos have large-amplitude dipole secular variation with maximum power

Olson, Peter L.

152

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

153

Season Variation of Ionosphere Effects of geomagnetic Storms at different Latitudes of East Asia  

NASA Astrophysics Data System (ADS)

The most important factors governing the variations of the ionosphere at the time of the geomagnetic storm include a change in electron composition and the circulation system of neutral wind, which depends substantially on the season. Besides, the difference of the geographic and magnetic coordinates complicates the picture of disturbances and leads to a longitudinal dependence of ionospheric effects of geomagnetic storms. We analyzed the state of the ionosphere using the data from a network of ionosondes and digisondes located in the longitudinal sector of 90-130°E. This region is of interest because the difference between the geographic and magnetic coordinates there is the largest, and formation of a large-scale structure proceeds at the more high geographic latitudes where ionization very depends from season. We investigated the variations of F2-layer critical frequencies, ionospheric altitudes and the ionospheric disturbance index DfoF2. The average a few quiet days variations of foF2, hF and hmF2 were used as the undisturbed level. We considered geomagnetic storms of a different intensity evolving from May, 2003 till January, 2004. During this period there were marked ten storms, which could be divided into the different season. The prolonged negative disturbances at high and middle latitudes were typical for the summer geomagnetic storms during all disturbed period. The increase of foF2 with a subsequent abrupt decrease of foF2 occurred in the evening after the Dst-index had reached its minimum value. At magnetic latitudes lower 30° the disturbances were mainly positive. The tendency of the disturbance variations maintained in the winter and in the autumn. However at high latitudes the intensive positive disturbances caused by precipitation of auroral fluxes were observed in the evening and night. The received variety of disturbances in different seasons is determined primarily by the illumination conditions of ionosphere and the local time of geomagnetic storm onset. The presented experimental results can be used to testing and the correction of empirical models. This work was done with financial support of the Russian Foundation for Basic Research (grant 02-05-39002).

Pirog, O. M.; Polekh, N. M.; Ratovsky, K. G.; Zherebtsov, G. A.; Smirnov, V. F.; Shi, J. K.; Wang, X.

154

Solar and Interplanetary Disturbances Causing Moderate Geomagnetic Storms  

NASA Astrophysics Data System (ADS)

The effect of solar and interplanetary disturbances on geomagnetospheric conditions leading to one hundred twenty one moderate geomagnetic storms (MGSs) with planetary index, Ap ? 20 and horizontal component of earth's magnetic field, H ? 250? have been investigated using solar geophysical data (SGD), solar wind plasma (SWP) and interplanetary magnetic field (IMF) data during the period 1978-99. It is observed statistically that 64%, 36%, MGSs have occurred during maximum and minimum phase of solar cycle 21st and 22nd respectively. Further, it is observed that H?, X-ray solar flares and active prominences and disapp earing filaments (APDFs) have occurred within lower helio latitude region associated with larger number of MGSs. No significant correlation between the intensity of GMSs and importance of H?, X-ray solar flares have been observed. Maximum number of MGSs are associated with solar flares of lower importance of solar flare faint (SF). The lower importance in association with some specific characteristics i.e. location, region, duration of occurrence of event may also cause MGSs. The correlation coefficient between MGSs and sunspot numbers (SSNs) using Karl Pearson method, has been obtained 0.37 during 1978-99.

Pratap Yadav, Mahendra; Kumar, Santosh

2003-07-01

155

Tsallis statistic applied to geomagnetic field reversals  

NASA Astrophysics Data System (ADS)

The data analysis shows that the paleomagnetic Earth's magnetic field reversed its polarity, several times, suddenly and disorderly in the last 160 million years. Recent work on data analysis, theoretical modeling and experimental dynamos have expanded the knowledge on the geomagnetic field. However, some fundamental questions related to polarity transitions remain unanswered: the physical mechanism that gives rise to reversals and the statistical distribution of inter-reversals times, are still open issues. In this paper we focus on the statistical distribution of the intervals between reversals. Several contributions indicated that a distribution that fits the data geomagnetic distribution was Poisson process with a rate constant or variable. Recent studies have ruled out this possibility. In the case of large time intervals, studies indicate power laws as possible distributions. Recently Tsallis distribution was pointed as a possible alternative to previous proposals. This work performed statistical tests to prove and find the best parameters of Tsallis distribution that fits the data. As a result of this study, we analyzed the correlation of the time intervals of the same polarity to show the presence of memory effects on the mechanism that generates reversals.

Barbosa, C.; Papa, A. R.

2013-05-01

156

The science of geomagnetically induced currents  

NASA Astrophysics Data System (ADS)

Geomagnetically induced currents (GIC) phenomenon impacting long conductor systems on the ground can be considered as the end link of chain of complex physical processes comprising the Sun-Earth system. In this paper I briefly review the current status of our understanding of the physics of GIC and novel applications enabled by the new understanding. More specifically, I will demonstrate how we can follow the chain of physical processes from the solar corona down to the upper mantle of the Earth and to GIC. Further, I will show how state-of-the-art models enable predictive modeling of the entire chain of complex processes. The potential for severe societal consequences has been driving recent increasing interest in extreme GIC events. I will show how we have addressed the issue by generating 100-year GIC event scenarios. These scenarios are of substantial power grid industry interest and have been fed directly into further engineering analyses. I will review the results of our of 100-year geomagnetically induced current scenarios work and discuss some of the future directions in the field.

Pulkkinen, A.

2012-12-01

157

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

158

Imaging core flow from geomagnetic secular variation: Consequences for core-mantle interactions and geomagnetic dipole moment changes  

E-print Network

Imaging core flow from geomagnetic secular variation: Consequences for core-mantle interactions-mantle boundary is inferred from ge- omagnetic secular variation data, assuming frozen magnetic flux, tangential geomagnetic secular variation be- tween 1895-1985 to isolate the time-average and time-dependent parts

Amit, Hagay

159

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

160

Ionospheric, protonospheric and total electron content in quiet geomagnetic conditions and during geomagnetic storm  

NASA Astrophysics Data System (ADS)

This report presents the results of studies the ionospheric, plasmaspheric and total electron content during recent minimum of solar activity in quiet geomagnetic condition and for geomagnetic storm on 26 September 2011. A comparison of the calculation results obtained using the GSM TIP model, with observational data of the mid- and high-latitude ionospheric sounding stations, as well as estimation of the plasmaspheric reservoir contribution into the total electron content obtained from GPS TEC measurements, COSMIC radio-occultation experiment and incoherent scatter radars were presented. The particular attention is given to the global distribution of the O+/H+ transition height in order to determine the top and low boundary for ionospheric and protonospheric electron content, respectively. This work was supported by Grant of Russian President ???-4866.2014.5, ?14-05-00578, and Program 22 RAS.

Nosikov, Igor; Klimenko, Maxim; Klimenko, Vladimir

161

The Microjet of AA Tau  

Microsoft Academic Search

The microjet of AA Tau A.W. Cox (Atholton High School, Columbia MD), G.M. Hilton (SSAI and GSFC), G.M. Williger (JHU and U. Louisville), C.A. Grady (Eureka Scientific and GSFC) B.Woodgate (NASA's GSFC) AA Tau is a classical T Tauri star with a spatially resolved disk viewed at approximately 70 degrees from pole-on. Photo-polarimetric variability of the star has been interpreted

A. W. Cox; G. M. Hilton; G. M. Williger; C. A. Grady; B. Woodgate

2005-01-01

162

Is motivation influenced by geomagnetic activity?  

PubMed

To eventually build a scientific bridge to religion by examining whether non-photic, non-thermic solar effects may influence (religious) motivation, invaluable yearly world wide data on activities from 1950 to 1999 by Jehovah's Witnesses on behalf of their church were analyzed chronobiologically. The time structure (chronome) of these archives, insofar as it is able to be evaluated in yearly means for up to half a century, was assessed. Least squares spectra in a frequency range from one cycle in 42 to one in 2.1 years of data on the average number of hours per month spent in work for the church, available from 103 different geographic locations, as well as grand totals also including other sites, revealed a large peak at one cycle in about 21 years. The non-linear least squares fit of a model consisting of a linear trend and a cosine curve with a trial period of 21.0 years, numerically approximating that of the Hale cycle, validated the about 21.0-year component in about 70% of the data series, with the non-overlap of zero by the 95% confidence interval of the amplitude estimate. Estimates of MESOR (midline-estimating statistic of rhythm, a rhythm (or chronome) adjusted mean), amplitude and period were further regressed with geomagnetic latitude. The period estimate did not depend on geomagnetic latitude. The about 21.0-year amplitude tends to be larger at low and middle than at higher latitudes and the resolution of the about 21.0-year cycle, gauged by the width of 95% confidence intervals for the period and amplitude, is higher (the 95% confidence intervals are statistically significantly smaller) at higher than at lower latitudes. Near-matches of periods in solar activity and human motivation hint that the former may influence the latter, while the dependence on latitude constitutes evidence that geomagnetic activity may affect certain brain areas involved in motivation, just as it was earlier found that it is associated with effects on the electrocardiogram and anthropometry. PMID:12653182

Starbuck, S; Cornélissen, G; Halberg, F

2002-01-01

163

Cutoff latitudes of solar protons during geomagnetic storms observed by NOAA/POES multi-satellites  

NASA Astrophysics Data System (ADS)

Solar energetic particles are injected into the Earth s magnetosphere but do not reach the inner magnetosphere connected to the low-latitudes by the field lines based on the well-known St o rmer theorem Geomagnetic cutoff rigidity and cutoff latitudes of energetic particles have been investigated in the past studies and are reported to be controlled by the geomagnetic activities Obayashi 1961 Fl u ckiger et al 1990 Leske et al 2001 Smart and Shea 2001 2005 Birch et al 2005 etc The polar orbiting NOAA POES satellites N15 N16 N17 and newly N18 have observed particles in a wide range of local time at altitudes of about 850 km The onboard radiation monitors detect solar energetic protons 16 - 500 MeV We have analyzed the combined data from the three or four satellites with time resolution of 1 5 hours which is near the orbital period of about 100 min in order to investigate local time dependences The observations show that the cutoff latitudes L -values of solar protons change accompanying with the phases of geomagnetic storms with local time dependence In particular during the big November 2004 storms with the minimum Dst of -380 nT the cutoff latitude in the nightside sector was about 5 degrees lower than those in the dayside sector The cutoff L -values averaged for all local time regions were correlated with variation of the Kp index better than the Dst index This fact indicates that the cutoff latitudes of 16 MeV protons are due to the magnetospheric structure affected by magnetospheric

Asai, K. T.; Nagatsuma, T.; Shimazu, H.; Hori, T.; Kitamura, K.; Miyoshi, Y.

164

Corrosion resistance in FSW and in MIG welding techniques of AA6XXX  

Microsoft Academic Search

A comparison of the corrosion resistance of AA6060T5 and AA6082T6 jointed surfaces via Friction Stir Welding (FSW) and Metal Inert Gas (MIG), respectively, is reported. The test was conducted putting the welded and polished samples in an acid salt solution. The corrosion resistance was detected via morphological analysis of the surface. The attack was localized (pitting), an index referred to

Stefano Maggiolino; Chiara Schmid

2008-01-01

165

Spatial power spectra of the crustal geomagnetic field and core geomagnetic field  

NASA Technical Reports Server (NTRS)

Equations providing numerical values of the geomagnetic field spherical harmonic spatial power spectrum as defined by Lowes (1966, 1974) are obtained and this power spectrum is related to various other power spectra. Equations relating the spherical harmonic spatial power spectrum to average great circle power spectra for components of the vector magnetic field in the radial direction, along the great circle track and perpendicular to the first two directions are derived under the assumption that the sources of the field are internal. A statistical model for the crustal and core geomagnetic fields is proposed and used to derive equations for the expected main and crustal spherical harmonic power spectra. The model equations are then compared with observations to determine a scale factor which is then used to obtain an estimate for the core radius and a great circle power spectrum for the field component perpendicular to the great circle and radial directions which are in good agreement with observations. The predicted spherical harmonic power spectrum for the crustal field is found to be consistent with POGO satellite and aircraft data. Other possible models for the crustal and core geomagnetic fields are also briefly considered.

Mcleod, M. G.; Coleman, P. J., Jr.

1980-01-01

166

Protection against lightning on the geomagnetic observatory  

NASA Astrophysics Data System (ADS)

The Sinji Vrh Geomagnetic Observatory was built on the brow of the mountain Gora, above Ajdovš?ina, and all over Europe one may hardly find an area which is more often struck by lightning than this south-western part of Slovenia. When the humid air masses of a storm front hit the edge of Gora, they rise up more than 1000 m in a very short time, and this causes the additional electrical charge of stormy clouds. The reliability of operations performed in the every building of observatory could be increased by understanding the formation of lightning in the thunderstorm cloud, the application of already proven methods of protection against a strike of lightning and against its secondary effects. To reach this goal the following groups of experts have to co-operate: the experts in the field of protection against lightening phenomenon, the constructors and manufacturers of equipment and the observatory managers.

?op, R.; Milev, G.; Deželjin, D.; Kosma?, J.

2014-04-01

167

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

168

Protection against lightning at a geomagnetic observatory  

NASA Astrophysics Data System (ADS)

The Sinji Vrh Geomagnetic Observatory was built on the brow of Gora, the mountain above Ajdovš?ina, which is a part of Trnovo plateau, and all over Europe one can hardly find an area which is more often struck by lightning than this southwestern part of Slovenia. When the humid air masses of a storm front hit the edge of Gora, they rise up more than 1000 m in a very short time, and this causes an additional electrical charge of stormy clouds. The reliability of operations performed in every section of the observatory could be increased by understanding the formation of lightning in a thunderstorm cloud and the application of already-proven methods of protection against a stroke of lightning and against its secondary effects. To reach this goal the following groups of experts have to cooperate: experts in the field of protection against lightning, constructors and manufacturers of equipment and observatory managers.

?op, R.; Milev, G.; Deželjin, D.; Kosma?, J.

2014-08-01

169

Initial geomagnetic field model from MAGSAT  

NASA Technical Reports Server (NTRS)

Magsat data from magnetically quiet days were used to derive a thirteenth degree and order spherical harmonic geomagnetic field model, MGST(3/80). The model utilized both scalar and vector data and fit that data with standard deviations of 8, 52, 55 and 97 nT for the scalar magnitude, B sub r, B sub theta and B sub phi respectively. When compared with earlier models, the Earth's dipole moment continues to decrease at a rate of about 26 nT/year. Evaluation of earlier models with Magsat data shows that the scalar field at the Magsat epoch is best predicted by the POGO(2/72) model but that the AWC/75 and IGS/75 are better for predicting vector fields.

Langel, R. A.; Estes, R. H.; Mead, G. D.; Fabiano, E. B.; Lancaster, E. R.

1980-01-01

170

Search for correlation between geomagnetic disturbances and mortality  

NASA Technical Reports Server (NTRS)

A search is conducted for a possible correlation between solar activity and myocardial infarction and stroke in the United States. A statistical analysis is performed using data on geomagnetic activity and the daily U.S. mortality due to coronary heart disease and stroke for the years 1962 through 1966. None of the results are found to yield any evidence of a correlation. It is concluded that correlations claimed by Soviet workers between geomagnetic activity and the incidence of various human diseases are probably not statistically significant or probably are not due to a causal relation between geomagnetic activity and disease.

Lipa, B. J.; Sturrock, P. A.; Rogot, F.

1976-01-01

171

On the vulnerability of electric power to geomagnetic storms  

SciTech Connect

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 over long distances 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. 7 refs., 1 fig., 1 tab.

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

1990-05-01

172

Geomagnetic storms: Potential economic impacts on electric utilities  

SciTech Connect

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. 7 refs., 2 figs., 1 tab.

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

1991-03-20

173

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

174

Responses of the lower thermospheric temperature to the 9 day and 13.5 day oscillations of recurrent geomagnetic activity  

NASA Astrophysics Data System (ADS)

of the lower thermospheric temperature to the 9 day and 13.5 day oscillations of recurrent geomagnetic activity and solar EUV radiation have been investigated using neutral temperature data observed by the TIMED/SABER (Thermosphere Ionosphere Mesosphere Energetics and Dynamics/Sounding of the Atmosphere using Broadband Emission Radiometry) instrument and numerical experiments by the NCAR-TIME-GCM (National Center for Atmospheric Research-thermosphere-ionosphere-mesosphere electrodynamics-general circulation model). The TIMED/SABER data analyzed were for the period from 2002 to 2007 during the declining phase of solar cycle 23. The observations show that the zonal mean temperature in the lower thermosphere oscillated with periods of near 9 and 13.5 days in the height range of 100-120 km. These oscillations were more strongly correlated with the recurrent geomagnetic activity than with the solar EUV variability of the same periods. The 9 day and 13.5 day oscillations of lower thermospheric temperature had greater amplitudes at high latitudes than at low latitudes; they also had larger amplitudes at higher altitudes, and the oscillations could penetrate down to ~105 km, depending on the strength of the recurrent geomagnetic activity for a particular time period. The data further show that the periodic responses of the lower thermospheric temperature to recurrent geomagnetic activity were different in the two hemispheres. In addition, numerical experiments have been carried out using the NCAR-TIME-GCM to investigate the causal relationship between the temperature oscillations and the geomagnetic activity and solar EUV variations of the same periods. Model simulations showed the same periodic oscillations as those seen in the observations when the real geomagnetic activity index, Kp, was used to drive the model. These numerical results show that recurrent geomagnetic activity is the main cause of the 9 day and 13.5 day variations in the lower thermosphere temperature, and the contribution from solar EUV variations is minor. Furthermore, we also found that consecutive coronal mass ejection events could cause long-duration enhancements in the lower thermospheric temperature that strengthen the 9 day and 13.5 day signals, and this kind of phenomenon mostly occurred between 2002 and 2005 during the declining phase of solar cycle 23.

Jiang, Guoying; Wang, Wenbin; Xu, Jiyao; Yue, Jia; Burns, Alan G.; Lei, Jiuhou; Mlynczak, Martin G.; Rusell, James M.

2014-06-01

175

Global Mean Total Electron Content Behavior in Periods of High Geomagnetic Activity  

NASA Astrophysics Data System (ADS)

The 24-hour global mean Total Electron Content (TEC) varies significantly on periods as short as two to three days. Analyses of ground based GPS receiver measurements, CHAMP satellite GPS receiver measurements, and Jason-1 altimeter measurements yield consistent pictures of highly structured changes in the global mean TEC. In particular, we have focused on three time periods of high geomagnetic activity: October through November, 2003, November, 2004, and May through June, 2005. During these time periods, rapid changes in the global mean TEC appear related to disturbances in the DST index, changes in the solar wind speed, and spikes in the solar wind density. Comparison of CHAMP data (measurements of TEC above approximately 400 kilometers altitude) and ground based data reveals a correlation between the DST index and the proportion of TEC that is below CHAMP. This correlation suggests that DST related global enhancements are most significant above 400 kilometers.

Fienberg, A. T.; Coster, A. J.; Zhang, S.

2011-12-01

176

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

177

Solar activity and geomagnetic storms: The first 40 years  

SciTech Connect

This article is the first of a series of three that traces the evolution of present understanding of the relationship between solar and geomagnetic activity from the mid-19tb century to the present era.

Cliver, E.W.

1994-12-06

178

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

179

Spatial and temporal power spectra of the geomagnetic field  

SciTech Connect

This report explores the statistical properties of the geomagnetic field. This research tries to determine the gaussian coefficient covariance from magnetic field measurements of spatial and temporal power spectra and give a theoretical explanation for the nature of these covariances.

McLeod, M.G. [Naval Research Lab., Stennis Space Center, MS (United States)] [Naval Research Lab., Stennis Space Center, MS (United States)

1996-02-10

180

Magnetospheric geomagnetic coordinates for space physics data presentation and visualization  

Microsoft Academic Search

Corrected geomagnetic coordinates, which account for the multipolar geomagnetic field, are frequently used to organize the ionospheric-altitude data. However, realistic organization of data measured simultaneously in the magnetosphere and ionosphere in a some sort of magnetic coordinate system requires a combination of the high-altitude external magnetic fields and the multipolar low-altitude field. Such combinations have been non-existent in the past.

V. O. Papitashvili; N. E. Papitashvili; J. H. King

1997-01-01

181

Geomagnetic Links to Climate Change and Orbital Cycles  

NASA Astrophysics Data System (ADS)

Years of speculation, newly recognized mechanisms for interactions, and a sparse but expanding number of observations support some form of link between geomagnetic field variability and climate change and/or orbital cycles. Early paleomagnetic observations only hinted at the links and failed to withstand scrutiny for a number of reasons including poor data quality, poor age control, poor resolution of short-term geomagnetic directional variability over sufficiently long time periods, and a reliance on relative paleointensity records. Even though Milankovitch periodicities have been observed in the latter, proving that these are not influenced by climatically induced lithologic changes rather than by geomagnetic field variability is difficult. At this point, the speculation has been more interesting that the evidence has been convincing. New long continuous records of short-term paleomagnetic directional variability that span the past 1 m.y., however, show intriguing correlations of geomagnetic excursions with precession cycles and with deglacials. The changes in directions for these excursions are too large to be attributed to lithologic variations nor can they be attributed to local sedimentary or tectonic processes as the excursion are observed regionally or globally. Although such correlations might have been regarded as fortuitous in the past, age constraints have improved significantly by obtaining stable isotope records or other climate proxies directly from the same stratigraphic sections as the geomagnetic records. Furthermore, speculation about mechanisms for geomagnetic links to climate and orbital cycles have been succeeded by climate studies that have found that cloud formation is associated with the amount of cosmogenic radiation, which is largely controlled by the geomagnetic field. Similarly, precession had been disregarded as a driving force for the geodynamo, but recent modeling shows that such conclusions were premature. Thus, causal relationships between geomagnetic field variability, climate change, and orbital cycles are not unexpected nor are they unobserved.

Acton, G.

2006-12-01

182

On the digital geomagnetic observatory at Lunping, Taiwan  

Microsoft Academic Search

A permanent Lunping Observatory was established by the author in 1965 at Lunping (25°00' N; 121°10' E), Taiwan. A set of Ruska magnetographs, a proton precession magnetometer and a GSI 1st Order Precession Magnetometer have been used to measure the hourly mean values of the geomagnetic three components, H, Z, D, and to determine the three hourly geomagnetic K indices

Yinn-Nien Huang

1990-01-01

183

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

184

A Windshear Hazard Index  

NASA Technical Reports Server (NTRS)

An aircraft exposed to hazardous low-level windshear may suffer a critical loss of airspeed and altitude, thus endangering its ability to remain airborne. In order to characterize this hazard, a nondimensional index was developed based oil aerodynamic principals and understanding of windshear phenomena, 'This paper reviews the development and application of the Bowles F-tactor. which is now used by onboard sensors for the detection of hazardous windshear. It was developed and tested during NASA/I:AA's airborne windshear program and is now required for FAA certification of onboard radar windshear detection systems. Reviewed in this paper are: 1) definition of windshear and description of atmospheric phenomena that may cause hazardous windshear. 2) derivation and discussion of the F-factor. 3) development of the F-factor hazard threshold, 4) its testing during field deployments, and 5) its use in accident reconstructions,

Proctor, Fred H.; Hinton, David A.; Bowles, Roland L.

2000-01-01

185

Multifractal analysis of low-latitude geomagnetic fluctuations  

NASA Astrophysics Data System (ADS)

The technique of large deviation multifractal spectrum has shown that the high-latitude (77.5° N, 69.2° W) geomagnetic fluctuations can be described from direct dissipation process or loading-unloading regimes of the solar wind-magnetosphere coupling. In this paper, we analyze the H-component of low-latitude (22.4° S, 43.6° W) geomagnetic field variability observed during the month of July 2000 at the Geomagnetic Observatory, Vassouras, RJ, Brazil. The variability pattern during this period is a mixture of quiet and disturbed days including the Bastille Day intense geomagnetic storm on 15 July. Due to the complexity of this data, we pursue a detailed analysis of the geomagnetic fluctuations in different time scales including a multifractal approach using the singular power spectrum deviations obtained from the wavelet transform modulus maxima (WTMM). The results suggest, as observed from high-latitude data, the occurrence of low-latitude multifractal processes driving the intermittent coupling between the solar wind-magnetosphere and geomagnetic field variations. On finer scales possible physical mechanisms in the context of nonlinear magnetosphere response are discussed.

Bolzan, M. J. A.; Rosa, R. R.; Sahai, Y.

2009-02-01

186

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

187

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

188

Frequency-modulated solar rotational periodicity of geomagnetic indices  

NASA Astrophysics Data System (ADS)

Many attempts have been made to search for various timescales in the power spectrum of geomagnetic indices so that common periodicities in the solar activity and geomagnetic activity indices are identified. The spectral behavior of geomagnetic activity parameters may also provide invaluable information about physical processes involved. In this study we attempt to demonstrate that the frequency modulation associated with a long-term variation may cause extra sidelobes around the principal peak with a periodicity of ˜ 27 d in the observed power spectrum of geomagnetic activity indices, and/or may even split the peak into two adjacent peaks. We employ a straightforward model of an oscillation frequency-modulated by an arbitrary agent to consider the solar rotational periodicity of geomagnetic indices. As a result, we have found that the peak with the periodicity of ˜ 27 d in the observed power spectrum of geomagnetic indices seems likely frequency-modulated by the amount of 0.0026 d-1 which corresponds to a ˜ 1 yr period. We thus suggest that the fundamental period of the periodic perturbative agent is much longer than a year according to our analysis. Finally, we conclude by discussing the implications of what we have found.

Chang, Heon-Young

2014-10-01

189

Frequency-modulated solar rotational periodicity of geomagnetic indices  

NASA Astrophysics Data System (ADS)

Many attempts have been made to search for various timescales in the power spectrum of geomagnetic indices so that common periodicities in the solar activity and geomagnetic activity indices are identified. The spectral behavior of geomagnetic activity parameters may also provide invaluable information about physical processes involved. In this study we attempt to demonstrate that the frequency modulation associated with a long-term variation may cause extra sidelobes around the principal peak with a periodicity of ˜ 27 d in the observed power spectrum of geomagnetic activity indices, and/or may even split the peak into two adjacent peaks. We employ a straightforward model of an oscillation frequency-modulated by an arbitrary agent to consider the solar rotational periodicity of geomagnetic indices. As a result, we have found that the peak with the periodicity of ˜ 27 d in the observed power spectrum of geomagnetic indices seems likely frequency-modulated by the amount of 0.0026 d-1 which corresponds to a ˜ 1 yr period. We thus suggest that the fundamental period of the periodic perturbative agent is much longer than a year according to our analysis. Finally, we conclude by discussing the implications of what we have found.

Chang, Heon-Young

2014-09-01

190

Some properties of the Svalgaard A/C index. [of polar cap magnetic variations  

NASA Technical Reports Server (NTRS)

Several properties of the A/C index of polar cap variations introduced by L. Svalgaard in 1972 have been found to vary with time. In the presatellite era, C days, as measured by the Ap index, are almost twice as geomagnetically active as A days, while in the modern epoch they have essentially identical activity. Prior to 1962 there were over 40% more A days than C days per year, while during the modern epoch there are essentially equal numbers of A days and C days. In view of this strong bias to assigning a 'toward' classification on geomagnetically active days it is recommended that the Svalgaard A/C classification not be used in studies of geomagnetic activity. It is also recommended that a full and thorough documentation of the index be prepared and/or that others undertake to compile such a classification separately.

Russell, C. T.; Burton, R. K.; Mcpherron, R. L.

1975-01-01

191

A Quaternary Geomagnetic Instability Time Scale  

NASA Astrophysics Data System (ADS)

Reversals and excursions of Earth's geomagnetic field create marker horizons that are readily detected in sedimentary and volcanic rocks worldwide. An accurate and precise chronology of these geomagnetic field instabilities is fundamental to understanding several aspects of Quaternary climate, dynamo processes, and surface processes. For example, stratigraphic correlation between marine sediment and polar ice records of climate change across the cryospheres benefits from a highly resolved record of reversals and excursions. The temporal patterns of dynamo behavior may reflect physical interactions between the molten outer core and the solid inner core or lowermost mantle. These interactions may control reversal frequency and shape the weak magnetic fields that arise during successive dynamo instabilities. Moreover, weakening of the axial dipole during reversals and excursions enhances the production of cosmogenic isotopes that are used in sediment and ice core stratigraphy and surface exposure dating. The Geomagnetic Instability Time Scale (GITS) is based on the direct dating of transitional polarity states recorded by lava flows using the 40Ar/39Ar method, in parallel with astrochronologic age models of marine sediments in which O isotope and magnetic records have been obtained. A review of data from Quaternary lava flows and sediments yields a GITS comprising 10 polarity reversals and 27 excursions during the past 2.6 million years. Nine of the ten reversals bounding chrons and subchrons are associated with 40Ar/39Ar ages of transitionally-magnetized lava flows. The tenth, the Guass-Matuyama chron boundary, is tightly bracketed by 40Ar/39Ar dated ash deposits. Of the 27 well-documented excursions, 14 occurred during the Matuyama chron and 13 during the Brunhes chron; 19 have been dated directly using the 40Ar/39Ar method on transitionally-magnetized volcanic rocks and form the backbone of the GITS. Excursions are clearly not the rare phenomena once thought. Rather, during the Quaternary period, they occur nearly three times as often as full polarity reversals. I will address analytical issues, including the size and consistency of system blanks, that have led to the recognition of minor (1%) discrepencies between the 40Ar/39Ar age for a particular reversal or excursion and the best astrochronologic estimates from ODP sediment cores. For example, re-analysis of lava flows from Haleakala volcano, Maui that record in detail the Matuyama-Brunhes polarity reversal have been undertaken with blanks an order of magntitude smaller and more stable than was common a decade ago. Using the modern astrochronologic calibration of 28.201 Ma for the age of the Fish Canyon sanidine standard, results thus far yield an 40Ar/39Ar age of 772 × 11 ka for the reversal that is identical to the most precise and accurate astrochronologic age of 773 × 2 ka for this reversal from ODP cores. Similarly, new dating of sanidine in the Cerro Santa Rosa I rhyolite dome, New Mexico reveals an age of 932 × 5 ka for the excursion it records, in perfect agreement with astrochronologically dated ODP core records. Work underway aims at refining the 40Ar/39Ar ages that underpin the entire GITS by further eliminating the bias between the radioisotopic and astrochronologically determined ages for several reversals and excursions.

Singer, B. S.

2013-12-01

192

The response of GPS TEC to the sequence of September 2011 geomagnetic storms  

NASA Astrophysics Data System (ADS)

The behavior of total electron content (TEC) over European region was analyzed for the sequence of geomagnetic storms in September 2011. Three geomagnetic storms with similar magnitude and different time of occurrence took place during 3 week period. The sudden beginning of the first storm took place at 14 UT on September 09, 2011. Dst index was sharply changed from 0 to 17 nT and drop to -63 nT. The second storm occurred on September 17, 2011 at the moment of 9 UT, the Dst index changed from 30 nT to -58 nT. The third event began on September 26, 2011 at 16 UT, minimal Dst index was equal to -103 nT in 11 hours after beginning. GPS TEC estimates were calculated with using data of European GNSS network. The spatial-temporal dynamics of TEC was analyzed on the base of constructed regional TEC maps and diurnal TEC variations over selected GNSS stations spaced along meridian of 20°E between latitudes of 70°-30°N. The ionosphere's response for September 9-10, 2011 geomagnetic storm was mainly negative; the average TEC depression was about 30% at daytime over European mid-latitude stations. The short positive splash in TEC variations was observed at evening September 9 in several hours after the storm's beginning. The distinguishing feature of September 17 storm was the strong positive effect which occurred on day-time over Europe region. The enhancement of TEC reached the factor of 1.7-2.0. Maximal effect was observed at high latitudes and slowly decreased to low latitudes. The duration of positive ionospheric effect was about 4-5 h. At high latitude stations of Kiruna (Sweden) TEC reached 30 TECU in compare with undisturbed level of 13-15 TECU. The maximal TEC enhancement was rather short-term and continued only 1.0-1.5 hour. The surge of TEC enhancement was moved from north to south, the delay between Kiruna and Noto (Sicilia) stations was 120-150 min. The ionospheric storm occurred on September 27, 2011 was the strongest one in the considered period. The ionospheric depression (up to 60%) corresponds to the main phase of storm with minimal value of Dst index equal to -103 nT. The development of the negative ionospheric storm had classical character. In this report we discuss the physical process in ionosphere and magnetosphere accompanied considered events and effects.

Shagimuratov, I.; Krankowski, A.; Cherniak, Iu.; Zakharenkova, I.; Yakimova, G.; Koltunenko, L.

2012-04-01

193

Spatial power spectra of the crustal geomagnetic field and core geomagnetic field  

NASA Astrophysics Data System (ADS)

Lowes (1966, 1974) has introduced the function Rn defined by Rn =(n + 1) ?m=0? [(gmn)2 + (hmn)2] where gnm and hnm are the coefficients of a spherical harmonic expansion of the scalar potential of the geomagnetic field at the Earth's surface. The mean squared value of the magnetic field B = -?V on a sphere of radius r > ? is given by =?n=1? Rn(a//r)2n=4 where a is the Earth's radius. We refer to Rn as the spherical harmonic spatial power spectrum of the geomagnetic field. In this paper it is shown that Rn = RMn = RCn where the components RnM due to the main (or core) field and RnC due to the crustal field are given approximately by RMn = [(n =1)//(n + 2)](1.142 × 109)(0.288n ?2 RCn = [(n =1){[1 - exp(-n/290)]//(n/290)} 0.52 ?2 where I? = 1 nT. The two components are approximately equal for n = 15. Lowes has given equations for the core and crustal field spectra. His equation for the crustal field spectrum is significantly different from the one given here. The equation given in this paper is in better agreement with data obtained on the POGO spacecraft and with data for the crustal field given by Alldredge et al. (1963). The equations for the main and crustal geomagnetic field spectra are consistent with data for the core field given by Peddie and Fabiano (1976) and data for the crustal field given by Alldredge et al. The equations are based on a statistical model that makes use of the principle of equipartition of energy and predicts the shape of both the crustal and core spectra. The model also predicts the core radius accurately. The numerical values given by the equations are not strongly dependent on the model. Equations relating average great circle power spectra of the geomagnetic field components to Rn are derived. The three field components are in the radial direction, along the great circle track, and perpendicular to the first two. These equations can, in principle, be inverted to compute the Rn for celestial bodies from average great circle power spectra of the magnetic field components.

McLeod, Malcolm G.; Coleman, Paul J.

1980-08-01

194

Investigation of a strong positive ionospheric storm during geomagnetic disturbances occurred in the Brazilian sector  

NASA Astrophysics Data System (ADS)

In this paper, we have investigated the responses of the ionospheric F region at equatorial and low latitude regions in the Brazilian sector during the super geomagnetic storm on 15-16 May 2005. The geomagnetic storm reached a minimum Dst of -263 nT at 0900 UT on 15 May. In this paper, we present vertical total electron content (vTEC) and phase fluctuations (in TECU/min) from Global Positioning System (GPS) observations obtained at Belém (BELE), Brasília (BRAZ), Presidente Prudente (UEPP), and Porto Alegre (POAL), Brazil, during the period 14-17 May 2005. Also, we present ionospheric parameters h'F, hpF2, and foF2, using the Canadian Advanced Digital Ionosonde (CADI) obtained at Palmas (PAL) and São José dos Campos (SJC), Brazil, for the same period. The super geomagnetic storm has fast decrease in the Dst index soon after SSC at 0239 UT on 15 May. It is a good possibility of prompt penetration of electric field of magnetospheric origin resulting in uplifting of the F region. The vTEC observations show a trough at BELE and a crest above UEPP, soon after SSC, indicating strengthening of nighttime equatorial anomaly. During the daytime on 15 and 16 May, in the recovery phase, the variations in foF2 at SJC and the vTEC observations, particularly at BRAZ, UEPP, and POAL, show large positive ionospheric storm. There is ESF on the all nights at PAL, in the post-midnight (UT) sector, and phase fluctuations only on the night of 14-15 May at BRAZ, after the SSC. No phase fluctuations are observed at the equatorial station BELE and low latitude stations (BRAZ, UEPP, and POAL) at all other times. This indicates that the plasma bubbles are generated and confined on this magnetically disturbed night only up to the low magnetic latitude and drifted possibly to west.

de Abreu, A. J.; Sahai, Y.; Fagundes, P. R.; de Jesus, R.; Bittencourt, J. A.; Pillat, V. G.

2012-12-01

195

Equatorial airglow and the ionospheric geomagnetic anomaly  

NASA Astrophysics Data System (ADS)

Ogo 4 observations of the O I (6300-A) emissions have revealed a global pattern hitherto undetected from the ground-based observations. It is seen that the postsunset emission of O I (6300 A) in October 1967 is very asymmetrical with respect to the geomagnetic equator in certain longitude regions and shows poor correlation with the electron density measured simultaneously from the same spacecraft. This asymmetry is less marked in the UV airglow, O I (1356 A), which appears to vary as the square of the maximum electron density in the F region. The horizon scan data of the 6300-A airglow reveal that the latitudinal asymmetry is associated with asymmetry in the height of the O I (6300-A) emission and hence with the altitude of the F2 peak. From the correlative studies of the airglow and the ionospheric measurements the mechanisms for the UV and the 6300-A emissions are discussed in terms of the processes involving radiative and dissociative recombination. Theoretical expressions are developed relating the airglow data to the ionospheric parameters, and it is shown that the agreement between observed and calculated emission rates is well within the uncertainty of the measurements.

Chandra, S.; Reed, E. I.; Troy, B. E., Jr.; Blamont, Jacques E.

196

The Livingston Island Geomagnetic and Ionospheric Observatory  

NASA Astrophysics Data System (ADS)

The Ebre Observatory Institute manages a geophysical observatory installed at the Spanish Antarctic Station (SAS) Juan Carlos I. It was set up in 1995 and it has been updated yearly by our team throughout several projects carried out since then. Nowadays, it hosts a magnetic station providing 1-second data of the 3 components (X, Y, Z) and the total force (F) during the entire year, and an ionospheric station providing vertical and oblique data during austral summer. This observatory has provided long data series of high scientific value from this remote region of the Earth. They have been used to improve the knowledge of the climate and weather behavior of the geomagnetic field and ionosphere in the area, and to model and expand the capacity of data transmission. This contribution aims to present a brief review of the instruments installed at SAS, the research results obtained from their data, and the developing activities under the current project. Finally, future perspectives are outlined with regard to adapting our geophysical observatory to the evolving needs of observatory practice.

Altadill, David; Marsal, Santiago; Blanch, Estefania; Miquel Torta, J.; Quintana-Seguí, Pere; Germán Solé, J.; Cid, Òscar; José Curto, Juan; Ibáñez, Miguel; Segarra, Antoni; Lluís Pijoan, Joan; Juan, Juan Miguel

2014-05-01

197

Major Geomagnetic Storms in Solar Cycle 24  

NASA Astrophysics Data System (ADS)

Solar Cycle 24 has produced 11 major geomagnetic storms (where Dstmin < -100 nT) with three in 2011, six in 2012 and two in 2013 (as of 7 August 2013). Detailed analysis of each event will be given in terms of its solar driver(s): CME, coronal hole high speed solar wind stream (HSS), multiple CMEs or interactions between CME and HSS. While some of these storms are associated with a fast and wide CME, the few cases involving slow or common CMEs and interactions with HSS are particularly interesting. These events pose great challenges for accurate space weather forecasting, since operationally the slower or average CMEs tend to receive less attention and are sometimes overlooked altogether. The characteristics of such challenging, not-so-fast yet geoeffective CME events (such as their coronal signatures and interactions with surrounding solar wind structure(s), etc) will be examined in detail, with the goal of extracting common and telltale features, if any, of these CMEs that distinguish them from CMEs in a similar category.

Zheng, Y.

2013-12-01

198

Periodic substorm activity in the geomagnetic tail  

NASA Technical Reports Server (NTRS)

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

199

[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

2013-01-01

200

DIVISION CATEGORY DESCRIPTION ITEM DESCRIPTION AA Advertise Advertising for courses  

E-print Network

Salaries Asst Dir International Recruitment AA Full Time Salaries Asst Dir for Intensive English/ESL AA Salaries Student Aide - New 2 semester staff AA All Other Salaries Faculty Stipends AA All Other Salaries Salaries Student employee salary AA Capital Construction Improvements Scenery Shop Addition AA Capital

Rainforth, Emma C.

201

Outcomes of AA for Special Populations  

Microsoft Academic Search

This chapter reviews research examining outcomes of Alcoholics Anonymous (AA) for special populations. It begins by discussing what is meant by the term “special populations” and why the question of if and how AA is beneficial for special populations needs to be considered. The chapter then examines studies of outcomes of AA participation among women, adolescents, and the elderly, racial

Christine Timko

202

ITEM # 13AA Biomedical Engineering  

E-print Network

ITEM # 13AA Biomedical Engineering http://ecs.utdallas.edu/BME/ Faculty Professors: John H. L Southwestern and UT Dallas) List joint-assignments here Objectives The Biomedical Engineering Program generation of biomedical engineers will address fundamental scientific questions, provide answers to critical

O'Toole, Alice J.

203

Semiannual Variation of Pc-Index for North and South Polar Caps  

NASA Astrophysics Data System (ADS)

Though the semiannual variation of geomagnetic activity with peaks near equinoxes has long been established, its cause is open for discussion. We have suggested earlier a new mechanism for the variation to explain (Adv. Space Res, v. 47, 2011). Phase of the semiannual variation is determined by the annual variation of the geomagnetic moment component My (GSE) caused by sinusoidal oscillations of the moment M at the yz interaction plane during annual motion: extrema at equinoxes (My<0 for the first half of year, My>0 for the second one) and My=0 at the solstices. Amplitude of the annual variation is modulated by the solar wind electric field Ez=VBy. By the other words, annual variation of the My makes extrema at equinoxes that produces maxima of the dawn-dusk component Emv=VByMy at the yz plane at spring equinox for toward polarity of the IMF (By<0, Bx>0) and at fall equinox for away one (By>0, Bx<0). It is logically to search for the semiannual variation of PC-index for north and south polar caps. As is known, the PC index is a measure of the strength of the solar wind electric field derived from magnetic variations measured at a single station near a magnetic pole. We use PC index of south cap Ps, which we could get from the AARS www-page for years 1995, 1998, and Danish north cap Pn for 1975-2012 (Thule. We also use data of the IMF B and wind velocity V measured at 1 a.u. near ecliptic plane for the same years. We show that mean value of E=1 mV/m and mean IMF described by Parker's spiral lies at ecliptic plane. The semiannual variations of both Pn and Ps does not differ from ones of the other indexes (Kp, AA, Dst): smoothed maxima near equinoxes and minima near solstices. As for the other indexes, the spring equinox peak is higher than the fall equinox one. We also obtained annual variations of Ps and Pn for various signs of By. We show that the semiannual variation of both Pn and Ps is determined by the By component. Both Pn and Ps has peak in February-May during the first half of year for By<0, the peak in August-October during the second half one for By>0. The same phase of the statistical semiannual variations of all the indexes is explained by the semiannual variation of the effective dawn-dusk Emv component, which does not depend from ionosphere conductivity and terrestrial induction effects. This Emv variation in turn is caused by the variation of mutual orientation of large-scale electric field E=[VxB] and magnetic moment M in the interaction plane during annual motion of the Earth.

Kuznetsova, Tamara

204

Geomagnetic lunar and solar daily variations during the last 100 years  

NASA Astrophysics Data System (ADS)

This paper describes long-term changes in the geomagnetic lunar (L) and solar (S) daily variations. We analyze the eastward component of the geomagnetic field observed at eight midlatitude stations during 1903-2012. The amplitude and phase for the semidiurnal component of the L and S variations are examined. Both L and S amplitudes correlate with the solar activity index F10.7, revealing a prominent 11 year solar cycle. In both cases, the correlation is slightly better with ?(F10.7) than F10.7. The sensitivity of the L variation to solar activity is comparable with that of the S variation. The solar cycle effect is also found in the phase of the S variation but not apparent in the phase of the L variation. The ratio in the amplitude of the L to S variation shows a long-term decrease (approximately 10% per century), which may be due to a reduction in lunar tidal waves from the lower atmosphere to the upper atmosphere in association with climate change.

Yamazaki, Y.; Kosch, M. J.

2014-08-01

205

[The effect of geomagnetic disturbances in capillary blood flow in ischemic heart disease patients].  

PubMed

A total of 80 patients with ischemic heart diseases (men-47, women-33) were followed up daily during 2-3 weeks. We studied capillary flow in the cuticle above the nail (eponichium) with TV-capillaroscope, allowed to conduct prolonged studies. We evaluated capillary indices for perivascular edema, erythrocytes aggregation, blood velocity. Microcirculations data were compared daily values of geomagnetic activity (A-index), three-hour-range indices (K) and atmospheric pressure. In the first day magnetic storms pathological changes of capillary flow were detected in 71.5% patients with acute myocardial infarction (men-73.7%, women-69.2%). We could see appearance of perivascular edema, red blood cell aggregation, delay and slowing down capillary flow. Similar changes were detected in patient with angina pectoris in 64.8% (men-73.3%, women-56.3%). Number patients with ischemic heart diseases reacted upon geomagnetic disturbances exceed more then 2.5 times quantity patients, who react upon change of atmospheric pressure. PMID:7495904

Gurfinkel', Iu I; Liubimov, V V; Oraevski?, V N; Parfenova, L M; Iur'ev, A S

1995-01-01

206

Intensity of the geomagnetic field in Europe for the last 3 ka: Influence of data quality on geomagnetic field modeling  

NASA Astrophysics Data System (ADS)

of the main challenges of paleomagnetic research is to obtain high-resolution geomagnetic field intensity reconstructions. For the last millennia, these reconstructions are mostly based on archeomagnetic data. However, the quality of the intensity data available in the databases is very variable, and the high scatter observed in the records clearly suggests that some of them might not be reliable. In this work we investigate how the geomagnetic field intensity reconstructions and, hence, our present knowledge of the geomagnetic field in the past, are affected by the quality of the data selected for modeling the Earth's magnetic field. For this purpose we rank the European archeointensity data in four quality categories following widely accepted paleomagnetic criteria based on the methodology used during the laboratory treatment of the samples and on the number of specimens retained to calculate the mean intensities. Four geomagnetic field regional models have been implemented by applying the revised spherical cap harmonic analysis to these four groups of input data. Geomagnetic field models strongly depend on the used data set. The model built using all the available data (without any preselection) appears to be the less accurate, indicating some internal inconsistencies of the data set. In addition, some features of this model are clearly dominated by the less reliable archeointensity data, suggesting that such features might not reflect real variations of the past geomagnetic field. On the contrary, the regional model built on selected high-quality intensity data shows a very consistent intensity pattern at the European scale, confirming that the main intensity changes observed in Europe in the recent history of the geomagnetic field occurred at the continental scale.

Pavón-Carrasco, Francisco Javier; Gómez-Paccard, Miriam; Hervé, Gwenaël.; Osete, María. Luisa; Chauvin, Annick

2014-06-01

207

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.

208

Airport geomagnetic surveys in the United States  

USGS Publications Warehouse

The Federal Aviation Administration (FAA) and the United States military have requirements for design, location, and construction of compass calibration pads (compass roses), these having been developed through collaboration with US Geological Survey (USGS) personnel. These requirements are detailed in the FAA Advisory Circular AC 150/5300-13, Appendix 4, and in various military documents, such as Handbook 1021/1, but the major requirement is that the range of declination measured within 75 meters of the center of a compass rose be less than or equal to 30 minutes of arc. The USGS Geomagnetism Group has developed specific methods for conducting a magnetic survey so that existing compass roses can be judged in terms of the needed standards and also that new sites can be evaluated for their suitability as potentially new compass roses. First, a preliminary survey is performed with a total-field magnetometer, with differences over the site area of less than 75nT being sufficient to warrant additional, more detailed surveying. Next, a number of survey points are established over the compass rose area and nearby, where declination is to be measured with an instrument capable of measuring declination to within 1 minute of arc, such as a Gurley transit magnetometer, DI Flux theodolite magnetometer, or Wild T-0. The data are corrected for diurnal and irregular effects of the magnetic field and declination is determined for each survey point, as well as declination range and average of the entire compass rose site. Altogether, a typical survey takes about four days to complete. ?? 2006 Springer.

Berarducci, A.

2006-01-01

209

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

210

The calculation of corrected geomagnetic coordinates in the high latitude region  

NASA Astrophysics Data System (ADS)

Because the real geomagnetic field in Space, especially during geomagnetic perturbations has very complex spatial distribution, we had to use adjusted geomagnetic coordinates. The calculation of these coordinates is connected with the correct calculation of field lines inclusive the internal IGRF (International Geomagnetic Reference Field) and external geomagnetic field. Tables of such coordinates are somewhat incorrect as they do not account for the coordinates' dependency on geomagnetic activity dynamics. We demonstrate how the coordinates vary with geomagnetic activity in high latitude regions. The calculations revealed that during magnetic storms in a major part of the near pole area the field lines are disclosed and for points of this area on the earth's surface the corrected geomagnetic coordinates cannot be calculated.

Alperovich, Leonid; Levitin, Anatoly; Gromova, Lyudmila; Dremukhina, Lyudmila

211

Solstitial and hemispherical asymmetry in the response of geomagnetic field  

NASA Technical Reports Server (NTRS)

It is shown that the geomagnetic field is more prone to disturbances around the June solstice than around the December solstice, as evidenced from a larger enhancement in geomagnetic activity indices, ap, an, and as, following the onset of transient solar disturbances occurring in the thee-month period around June solstice than in the interval around the December solstice. Further, an asymmetry between the northern and southern hemisphere geomagnetic activity is shown to exist, independent of the level of the activity. This asymmetry, represented by (an - as)/(an + as)/2 shows a regular annual variation with a maximum of 60 percent around the June solstice and is almost absent around the December solstice.

Shah, G. N.; Kaul, R. K.; Kaul, C. L.; Razdan, H.; Merryfield, W. J.; Wilcox, J. M.

1984-01-01

212

Geomagnetic observations on tristan da cunha, south atlantic ocean  

USGS Publications Warehouse

Few geomagnetic ground observations exist of the Earth's strongest core field anomaly, the South Atlantic Anomaly (SAA). The geomagnetic repeat station on the island Tristan da Cunha, located half-way between South Africa and South America at 37?? 05' S, 12?? 18' W, is therefore of crucial importance. We have conducted several sets of repeat station measurements during magnetically quiet conditions (Kp 2o or less) in 2004. The procedures are described and the results are compared to those from earlier campaigns and to the predictions of various global field models. Features of the local crustal bias field and the solar quiet daily variation are discussed. We also evaluate the benefit of continuous magnetic field recordings from Tristan da Cunha, and argue that such a data set is a very valuable addition to geomagnetic satellite data. Recently, funds were set up to establish and operate a magnetometer station on Tristan da Cunha during the Swarm magnetic satellite mission (2011-2014).

Matzka, J.; Olsen, N.; Maule, C.F.; Pedersen, L.W.; Berarducci, A.M.; Macmillan, S.

2009-01-01

213

The Geomagnetic Response to Extreme Solar Wind Conditions  

NASA Astrophysics Data System (ADS)

It is well established that geomagnetic storms are related to interplanetary structures possessing southward interplanetary magnetic field component. Coronal mass ejection counterparts observed in the interplanetary medium, called ICMEs, are found to be one of the most frequent sources of such southward fields. ICME internal fields and sheath fields associated with their interplanetary shocks were found to be the dominant origins of Intense (Dst <100nT) and very intense (Dst<-200nT) geomagnetic storms in the ascending phase and maximum of the solar cycle 23. Extreme events, in which Dst<-400nT, are less frequent, but they are all associated to ICMEs. Recent studies show that these events occur nearly once every 11 year solar cycle. We investigate the geomagnetic response to these extreme solar wind conditions using observations and modeling.

Dal Lago, A.; Echer, E.; Balmaceda, L. A.; Rawat, R.; Vieira, L. A.; Gonzalez, W. D.

2013-12-01

214

The geomagnetic elements in Denmark 1928-1980  

NASA Astrophysics Data System (ADS)

Geomagnetic surveys in Denmark from 1928 till 1980 are reported. The Danish Meteorological Institute initiated a new, geomagnetic survey of Denmark in 1928 by the establishment of 10 repeat statins for observation of the geomagnetic, secular variation. The stations were visited again in 1930 and since then every fifth year. The general survey was started in 1939 and continued during the years 1946 to 1957 with the mapping of Northern Jutland. In 1967 the survey taken with a coarser spacing of the measured points during the following years succeeded in completing the mapping of the country with primary consideration to the declination. The observations on the repeat stations during the time 1928-1980 allowed development of mathematical formulas for the secular change of the magnetic elements D, H and Z at any arbitrary point in the country.

Hansen, H. A.

215

Report of geomagnetic pulsation indices for space weather applications  

USGS Publications Warehouse

The phenomenon of ultra-low frequency geomagnetic pulsations was first observed in the ground-based measurements of the 1859 Carrington Event and has been studied for over 100 years. Pulsation frequency is considered to be “ultra” low when it is lower than the natural frequencies of the plasma, such as the ion gyrofrequency. Ultra-low frequency pulsations are considered a source of noise in some geophysical analysis techniques, such as aeromagnetic surveys and transient electromagnetics, so it is critical to develop near real-time space weather products to monitor these geomagnetic pulsations. The proper spectral analysis of magnetometer data, such as using wavelet analysis techniques, can also be important to Geomagnetically Induced Current risk assessment.

Xu, Z.; Gannon, Jennifer L.; Rigler, Erin J.

2013-01-01

216

An experimental study of the biological effects of geomagnetic disturbances: The impact of a typical geomagnetic storm and its constituents on plants and animals  

NASA Astrophysics Data System (ADS)

Naturally occurring geomagnetic storms have been shown to correlate with changes in organisms' biological processes. Changes in the geomagnetic field during a geomagnetic storm are complex and contain both slow changes of the geomagnetic field with frequencies of up to 0.001 Hz, and various geomagnetic pulsations observed in general to be within the range of 0.001-5 Hz. Little is known about what frequency constituent of geomagnetic storms has the strongest effect on living organisms. This paper uses an experimental approach to demonstrate that organisms from different taxa principally respond to slow changes of the geomagnetic field corresponding with the main phase and the initial period of the recovery phase of a geomagnetic storm. Pc1 type pulsations, which are commonly regarded as biologically effective elements of geomagnetic disturbances, did not affect controlled parameters in our experiments. This paper may serve as a starting point for a thorough inquiry into the influence of slow fluctuations of the geomagnetic field on organisms.

Krylov, Viacheslav V.; Zotov, Oleg D.; Klain, Boris I.; Ushakova, Natalia V.; Kantserova, Nadezhda P.; Znobisheva, Anna V.; Izyumov, Yuri G.; Kuz'mina, Victoria V.; Morozov, Alexey A.; Lysenko, Liudmila A.; Nemova, Nina N.; Osipova, Elena A.

2014-04-01

217

Geomagnetic, cosmogenic and climatic changes across the last geomagnetic reversal from Equatorial Indian Ocean sediments  

NASA Astrophysics Data System (ADS)

High-resolution records of beryllium (10Be) production and relative paleointensity have been obtained across the Matuyama-Brunhes (M-B) reversal from the equatorial Indian Ocean (Maldives area). Both magnetic and geochemical analyses were performed from the same discrete samples to avoid any artificial depth offset. The authigenic 10Be concentrations were normalized with respect to 9Be in order to correct for potential environmental effects, while the relative paleointensity was derived from the remanent magnetization intensity after accounting for changes in magnetic concentration within the sediment. The relative paleointensity and the 10Be/9Be records are both characterized by large deviations, which culminate in the middle of the reversal. In contrast to most previous studies, and despite relative high deposition rate (4.7 cm/ka), we observed a perfect synchronism between the 10Be/9Be peak, the lowest value of relative paleointensity and the switch in direction, which indicates that bioturbation and post-depositional processes did not affect the magnetic record. This leaves no ambiguity for the stratigraphic position of the reversal located within Marine Isotopic Stage 19 as revealed by the planktonic ?18O record from the same core. The magnetic data depict a two-phase process with a precursory event preceding the rapid polarity switch, while only the second phase is present in the 10Be record, similarly to other low latitude records from the Indonesian area. Using an orbitally-tuned age model, we obtain an age of 772 ka±5 ka for the middle of the transition, while the precursory event occurred almost 20 ka before. We believe that the bimodal distribution emerging from the compilations of the ages of the M-B reversal results from the succession of these two events. Microtektites from the Australasian impact were found at 0.6 m below the transition (790 ka±5 ka B.P.) and confirm that this large event occurred 12 ka prior to the polarity transition. The distribution of tektite abundance was used to deconvolve the 10Be/9Be signal. The results confirm that the beryllium changes are concentrated during the transitional period, thus likely in presence of a multipolar geomagnetic field (or in the vicinity of a geomagnetic pole) that favored the penetration of cosmic rays and consequently increased the 10Be production. The absence of 10Be during the precursor indicates that the present site and the Indonesian ones were far away from a geomagnetic pole and that interlatitudinal atmospheric mixing was limited. The geomagnetic pole positions above the Indonesian sites during the precursor would thus be incompatible with the corresponding inclined dipolar field during this period, and suggest the dominance of low-degree harmonics.

Valet, Jean-Pierre; Bassinot, Franck; Bouilloux, Alexandra; Bourlès, Didier; Nomade, Sébastien; Guillou, Valéry; Lopes, Fernand; Thouveny, Nicolas; Dewilde, Fabien

2014-07-01

218

Solar and lunar tides in the geomagnetic field  

Microsoft Academic Search

Amplitudes of spectral geomagnetic field components and signal\\/noise ratios are estimated at frequencies of lunar and solar\\u000a tides based on the data registered at the experimental site of Vladimir State University (VlSU) and Japanese geomagnetic stations\\u000a Kakioka (1913–2006) and Memambetsu (1950–1999). The influence of thermal solar tides S1, S2, S3, and S4 and lunar gravitational\\u000a tides O1, M2, and N2

L. V. Grunskaya; V. N. Morozov; A. A. Zakirov; D. V. Rubai; R. V. Rubai

2011-01-01

219

The Enigma of AA Dor  

E-print Network

AA Dor (LB 3459) is an eclipsing, close binary (P = 0.26d) consisting of a sdOB primary star and an unseen secondary with an extraordinary small mass. The secondary is possibly a former planet which may have survived a common-envelope phase and has even gained mass. In order to investigate on an existing discrepancy between the components' mass derived from NLTE spectral analysis and subsequent comparison to evolutionary tracks and masses derived from radial-velocity and the eclipse curves, we performed phase-resolved high-resolution and high-SN spectroscopy with the UVES attached to the ESO VLT. From the obtained spectra, we have determined AA Dor's orbital parameters (P = 22600.702 +/- 0.005 sec, A = 39.19 +/- 0.05 km/sec, T0 = 2451917.152690) and the rotational velocity (v = 47 +/- 5 km/sec) of the primary.

T. Rauch; K. Werner

2002-12-06

220

Solar energetic particle cutoff variations during the 29–31 October 2003 geomagnetic storm  

Microsoft Academic Search

At low latitudes to midlatitudes the Earth's magnetic field usually shields the upper atmosphere and spacecraft in low Earth orbit from solar energetic particles (SEPs). During severe geomagnetic storms, distortion of the Earth's field suppresses geomagnetic shielding, allowing SEPs access to the midlatitudes. A case study of the 26–31 October 2003 solar-geomagnetic event is used to examine how a severe

B. T. Kress; C. J. Mertens; M. Wiltberger

2010-01-01

221

Research on geomagnetic-matching technology based on improved ICP algorithm  

Microsoft Academic Search

Using geomagnetism aided navigation (GAN) is a new branch of the integrated navigation technique. The principle and the developments of the GAN are introduced and the feature of the geomagnetism field is analyzed in the paper. ICP matching method based on geomagnetic anomaly map is studied. The traditional ICP algorithm is improved in two aspects: firstly, inspired by simulated annealing,

Shitu Luo; Yanling Wang; Yin Liu; Xiaopin Hu

2008-01-01

222

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. ???, XXXX, DOI:10.1029/, Altitude-Adjusted Corrected Geomagnetic Coordinates  

E-print Network

to transform between geo- graphic and Altitude-Adjusted Corrected Geomagnetic (AACGM) coordinates reveals Geomagnetic Coordinates: Definition and Functional Approximations S. G. Shepherd Thayer School of Engineering]. The coordinate system, originally called the PACE geomagnetic (PGM) coordinate system but later referred

Shepherd, Simon

223

Effect of geomagnetic disturbances and solar wind density on relativistic electrons at geostationary orbit  

Microsoft Academic Search

It is well known that fluxes of relativistic electrons in the Earth's magnetosphere well correlate with solar wind speed but surprisingly they show a weaker correlation with geomagnetic activity indices. For a long time, this result seemed puzzling since geomagnetic disturbances, measured by geomagnetic activity indices, are associated with strong electric fields and low-frequency waves, which should significantly affect (directly

Wladislaw Lyatsky; George V. Khazanov

2008-01-01

224

Solar magnetic elds and geomagnetic events. Alexei A. Pevtsov 1 and Richard C. Can eld  

E-print Network

the large-scale solar dipolar magnetic #12;eld pointed southward. We examined geomagnetic storms temporally, eruptions with a southward leading magnetic #12;eld are associated with stronger geomagnetic storms to trigger a major geomagnetic storm [Gonzalez and Tsurutani, 1987]. But how does this relate to magnetic #12

Pevtsov, Alexei A.

225

Solar magnetic fields and geomagnetic events. Alexei A. Pevtsov 1 and Richard C. Canfield  

E-print Network

dipolar magnetic field pointed southward. We examined geomagnetic storms temporally associated with a southward leading magnetic field are associated with stronger geomagnetic storms, but those with a northward southward component of the interplanetary magnetic field is necessary to trigger a major geomagnetic storm

Canfield, Richard

226

Statistical properties of geomagnetic measurements as possible precursors for magnetic storms  

E-print Network

Records of geomagnetic measurements have been analyzed looking for evidences of possible precursors for magnetic storms. With this objective, the main magnetic storms in the period 1998-2002 have been located in Dst index record. Periods immediately before storms and periods well before them were studied by applying a method recently introduced in the literature. Statistical properties of both types of periods have been compared. One of the compared quantities was the slope of the power laws that have been found for some relevant distributions. A systematic deviation between slope distributions was found. This might be the fingerprint of a non self-organized component in records. There has also been found a correlation between slope values and the corresponding storm intensities, which could serve as a probabilistic approach to magnetic storms forecasting. Data is from the low latitude Vassouras Magnetic Observatory.

Andres R. R. Papa; Lilian P. Sosman

2006-05-30

227

Statistical properties of geomagnetic measurements as possible precursors for magnetic storms  

E-print Network

Records of geomagnetic measurements have been analyzed looking for evidences of possible precursors for magnetic storms. With this objective, the main magnetic storms in the period 1998-2002 have been located in Dst index record. Periods immediately before storms and periods well before them were studied by applying a method recently introduced in the literature. Statistical properties of both types of periods have been compared. One of the compared quantities was the slope of the power laws that have been found for some relevant distributions. A systematic deviation between slope distributions was found. This might be the fingerprint of a non self-organized component in records. There has also been found a correlation between slope values and the corresponding storm intensities, which could serve as a probabilistic approach to magnetic storms forecasting. Data is from the low latitude Vassouras Magnetic Observatory.

Papa, A R R; Papa, Andres R. R.; Sosman, Lilian P.

2006-01-01

228

The quiet geomagnetic field at geosynchronous orbit and its dependence on solar wind dynamic pressure  

SciTech Connect

Vector magnetic fields at geosynchronous orbit were measured during 1980-1984 using the operational GOES 2, GOES 5, and GOES 6 spacecraft magnetometers. The authors corrected these spacecraft measurements for offsets due to spacecraft state and then used these field estimates to create a data base with 1-min resolution. Hourly quiet field values were calculated for these years from this data base using the ground-based geomagnetic index criteria AE < 120 nT and {vert bar}Dst{vert bar} < 20 nT. These quiet field components, rotated into dipole HVD coordinates, were approximated by the first two coefficients of a two-dimensional Fourier series in time of day and season. The quiet geosynchronous field components, to first order, are given by mean values of about 90 nT, {minus}60 nT, and 5 nT; and sinusoidal diurnal amplitudes of about 21 nT, 5 nT, and 5 nT, respectively, for H, V, and D where the spacecraft magnetometer was located near the geomagnetic meridian. The second harmonic diurnal amplitudes and the first and second harmonic seasonal amplitudes are typically of the order of a few nanoteslas or less except for the D component, which exhibits a larger seasonal variation. Furthermore, a one-dimensional Fourier series in time of day was used to study the quiet field dependence on solar wind dynamic pressure, P{sub d}, by indexing the measurements into five pressure ranges during 1980. These quiet H measurements, including the pressure dependence, are compared with a first-order field model superimposed with a tail current, resulting in magnetospheric currents (magnetopause and tail) in agreement with previous model values.

Rufenach, C.L.; Schaper, J. (NOAA Space Environmental Lab., Boulder, CO (United States)); McPherron, R.L. (Univ. of California, Los Angeles (United States))

1992-01-01

229

A statistical analysis of low frequency geomagnetic field pulsations at two Antarctic geomagnetic observatories in the polar cap region  

NASA Astrophysics Data System (ADS)

The aim of this study is to investigate the characteristics of low frequency (˜0.5-5 mHz) geomagnetic field fluctuations as recorded at two Antarctic stations within the polar cap: the Italian observatory Mario Zucchelli Station (TNB) and the French-Italian observatory Dome C (DMC) in order to investigate the spatial extension and propagation characteristics of the phenomena observed at very high latitude. The stations have approximately the same geographic latitude, but a very different corrected geomagnetic latitude, being DMC close to the geomagnetic pole and TNB closer to the auroral oval. Our study focused on power spectra, coherence and phase difference between low frequency fluctuations analyzing the horizontal H component measured during the entire year 2006. The fluctuation power behavior during the day can be explained according to the positions of the stations with respect to the polar cap; indeed in the dayside sector it is higher in the cusp region, while in the nightside sector it is higher close to the geomagnetic pole. Furthermore the study of coherent fluctuations, focusing on their phase difference, indicated that the propagation direction within the cap is variable during the day: in the dayside and nightside regions it is from the auroral oval toward the geomagnetic pole, while in the magnetic local morning and afternoon sectors it is from the geomagnetic pole toward the dawn-dusk meridian. Finally the analysis of two individual pulsation events, consisting of short duration wave packets, is shown; it confirms the statistical considerations on the propagation direction and allows to estimate the wave number and apparent phase velocity, whose values are of the order of 3-4 and 30-15 km/s, respectively.

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

2013-09-01

230

A method of predictions geomagnetic activity based on a coronal model of relations between solar and geomagnetic activities  

NASA Technical Reports Server (NTRS)

A method developed to predict both disturbed and quiet geomagnetic periods is described. The method uses solar situations along the CM with the key role of filaments, giving indirect evidence of types of directly unobservable coronal structures above them. The time lag, not to be interpreted in terms of propagation speed, between the CM activity and the commencement of the geomagnetic response is about one to two days. Solar phenomena serve as indicators within approximately 10 deg of the CM and up to the zone of high latitude filaments.

Halenka, J.

1979-01-01

231

Geomagnetic activity study using multifractal and Continuous Wavelet Transform analysis  

NASA Astrophysics Data System (ADS)

This work focuses on short term geomagnetic field activity considered as fractional Brownian motion signal and the development of new technique of investigation which takes into account its non stationary property in order to help detecting main events such as sudden storms (SSC) In this study, we analyze the horizontal component of the magnetic field recorded by 4 InterMagnet observatories located at various latitudes, from high, close to auroral regions to low, close to equator. The analysis is performed using quiet and disturbed days 1 min-value sampling data during more than a decade, starting from 1996. The intrinsic properties of high-frequency signals and the related causative sources are explored thanks to 1-D Continuous Wavelet Transform and especially the Modulus Maxima lines (WTMM). The obtained results clearly show that the major magnetic singularities of the field, such as SSC are characterized by very low values of Holder exponents estimated at the local maxima of the Wavelet Transform. Generalized fractal dimension is then derived and used as a new powerful parameter describing the geomagnetic activity. We show that the main phases of an SSC are uniquely characterized. Holder coefficient could be a good candidate as an efficient key indicator of geomagnetic activity and singularity detection. Keywords: geomagnetic activity, wavelet transform modulus maxima lines, Holder exponent, generalized fractal dimension

Zaourar, N.; Ouadfeul, S. A.; Hamoudi, M.

2009-04-01

232

Possible helio-geomagnetic activity influence on cardiological cases  

NASA Astrophysics Data System (ADS)

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 concerning the possible influence on the human health are published. Increase of the Acute Coronary Syn-dromes and disorders of the Cardiac Rhythm, increase of accidents as well as neurological and psychological disorders (e.g. increase of suicides) during or near to the geomagnetic storms time interval are reported. In this study, we research the problem in Greece, focusing on patients with Acute Myocardial Infraction, hospitalized in the 2nd Cardiological Department of the General Hospital of Nikaea (Piraeus City), for the time interval 1997-2007 (23rd solar cycle) and also to the arrival of emergency cardiological cases to Emergency Department of two greek hospitals, the General Hospital of Lamia City and the General Hospital of Veria City during the selected months, with or without helio-geomagnetic activity, of the 23rd solar cycle. Increase of cases is recorded during the periods with increase helio-geomagnetic activity. The necessity of continuing the research for a longer period and with a bigger sample is high; so as to exact more secure conclusions.

Katsavrias, Christos

233

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

234

Corotating solar wind streams and recurrent geomagnetic activity: A review  

Microsoft Academic Search

Solar wind fast streams emanating from solar coronal holes cause recurrent, moderate intensity geomagnetic activity at Earth. Intense magnetic field regions called Corotating Interaction Regions or CIRs are created by the interaction of fast streams with upstream slow streams. Because of the highly oscillatory nature of the GSM magnetic field z component within CIRs, the resultant magnetic storms are typically

Bruce T. Tsurutani; Walter D. Gonzalez; Alicia L. C. Gonzalez; Fernando L. Guarnieri; Nat Gopalswamy; Manuel Grande; Yohsuke Kamide; Yoshiya Kasahara; Gang Lu; Ian Mann; Robert McPherron; Finn Soraas; Vytenis Vasyliunas

2006-01-01

235

Global response of the plasmasphere to a geomagnetic disturbance  

Microsoft Academic Search

Global images of the plasmasphere obtained by the Extreme Ultraviolet (EUV) imager on the IMAGE satellite are used to study the evolving structure of the plasmasphere during two geomagnetic disturbances. By tracking the location of the plasmapause as a function of L shell and magnetic local time, quantitative measurements of radial and azimuthal motions of the boundary are made for

M. Spasojevic; J. Goldstein; D. L. Carpenter; B. R. Sandel; M. B. Moldwin; B. W. Reinisch

2003-01-01

236

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

237

World-wide Changes in the Geomagnetic Field  

Microsoft Academic Search

It is found that world-wide changes in the geomagnetic field are not limited to sse or si and are frequently observed. Not only an increase but also a decrease in horizontal intensity occurs on a world-wide scale. The form of the change varies, depending both on local time and on latitude. The distribution of the magnitude, and the mode of

A. Nishida; J. A. Jacobs

1962-01-01

238

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

239

Resonant enhancement of relativistic electron uxes during geomagnetically active periods  

E-print Network

. The strong increase in the ¯ux of relativistic electrons during the recovery phase of magnetic storms; storms and substorms). 1 Introduction Magnetic storms cause some of the largest geomagnetic ®eld to be triggered by a persistent southward interplanetary magnetic ®eld. Generally, a magnetic storm is charac

Paris-Sud XI, Université de

240

Compound streams, magnetic clouds, and major geomagnetic storms  

SciTech Connect

Data from ISEE 3, Helios A, and Helios B were used to identify the components of two compound streams and to determine their configurations. (A compound stream is a stream which has formed as a result of the interaction of two or more distinct fast flows.) In one case, ejecta containing a magnetic cloud associated with a disappearing quiescent filament were interacting with a corotating stream. In the second case, ejecta containing a magnetic cloud associated with a 2B flare were overtaking ejecta from a different source. Each of these compound streams produced an unusually large geomagnetic storm, on April 3, 1979, and on April 25, 1979, respectively. The largest geomagnetic storm in the period 1968-1986, which occurred on July 13, 1982, was associated with a compound stream. Thirty geomagnetic storms with Ap > 90 occurred between 1972 and 1983, and there are interplanetary magnetic field and plasma data for 17 of these events. The data suggest that most large geomagnetic storms are associated with compound streams and/or magnetic clouds.

Burlaga, L.F.; Behannon, K.W. (NASA Goddard Space Flight Center, Greenbelt, MD (United States)); Klein, L.W. (Applied Research Corp., Landover, MD (United States))

1987-06-01

241

Coronal mass ejections: The link between solar and geomagnetic activity  

SciTech Connect

Coronal mass ejections are spectacular manifestations of solar activity in which 10[sup +15]--10[sup +16] g of solar material are propelled outward into interplanetary space. Recent work has demonstrated that these events are the prime link between solar activity and large, nonrecurrent geomagnetic storms, closing a loop in a body of research extending back more than 130 years.

Gosling, J.T. (Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States))

1993-07-01

242

Geomagnetic disturbances and their relationship to Interplanetary shock parameters  

E-print Network

magnetic field (IMF) direction might play a useful role in forecasting the severity of geomagnetic storms% of forward IP shocks result in intense magnetic storms when the shock normal is almost perpendicular field and produce only weak or moderate storms [Tsurutani et al., 1995]. [3] Intense magnetic storms

Richardson, John

243

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

244

Some characteristics of intense geomagnetic storms and their energy budget  

Microsoft Academic Search

The present study analyses nine intense geomagnetic storms (?Dst? > 175 nT) with the aid of ACE satellite measurements and ground magnetic field values at Alibag Magnetic Observatory. The study confirms the crucial role of southward IMF in triggering the storm main phase as well as controlling the magnitude of the storm. The main phase interval shows clear dependence on

Geeta Vichare; S. Alex; G. S. Lakhina

2005-01-01

245

(abstract) A Geomagnetic Contribution to Climate Change in this Century  

NASA Technical Reports Server (NTRS)

There is a myth that all solar effects can be parameterized by the sun spot number. This is not true. For example, the level of geomagnetic activity during this century was not proportional to the sunspot number. Instead there is a large systematic increase in geomagnetic activity, not reflected in the sunspot number. This increase occurred gradually over at least 60 years. The 11 year solar cycle variation was superimposed on this systematic increase. Here we show that this systematic increase in activity is well correlated to the simultaneous increase in terrestrial temperature that occurred during the first half of this century. We discuss these findings in terms of mechanisms by which geomagnetics can be coupled to climate. These mechanisms include possible changes in weather patterns and cloud cover due to increased cosmic ray fluxes, or to increased fluxes of high energy electrons. We suggest that this systematic increase in geomagnetic activity contributed (along with anthropogenic effects and possible changes in solar irradiance) to the changes in climate recorded during this period.

Feynman, J.; Ruzmaikin, A.; Lawrence, J.

1996-01-01

246

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

247

Cosmic rays flux and geomagnetic field variations at midlatitudes  

NASA Astrophysics Data System (ADS)

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

Morozova, Anna; Ribeiro, Paulo; Tragaldabas Collaboration Team

2014-05-01

248

1. INTRODUCTION Secular variations of the geomagnetic field during the  

E-print Network

1. INTRODUCTION Secular variations of the geomagnetic field during the Holocene have been sediment cores has revealed long-term (10 to 100 kyr) secular changes of paleointensity during the Pleis]. However, directional secular variation records older than the last ca. 10 kyr are still scarce, although

Yamazaki, Toshitsugu

249

AAS Statistics and the 60% Cohort  

NASA Astrophysics Data System (ADS)

I will present the latest statistics available describing the gender of the AAS membership including an update on the so-called 60% cohort (that group of AAS members from the ages of 18 to 25 who are 60% women and 40% men). The AAS membership has changed significantly in the past 30 years from an overall female membership percentage of about 10% to a level around 30% today. This trend is accelerating and indicates the ongoing inclusion of women in the physical sciences, especially astronomy. By the year 2030, the AAS membership should reach gender parity if the present trend continues.

Marvel, K. B.

2004-05-01

250

Predicting the Size of Sunspot Cycle 24 on the Basis of Single- and Bi-Variate Geomagnetic Precursor Methods  

NASA Technical Reports Server (NTRS)

Examined are single- and bi-variate geomagnetic precursors for predicting the maximum amplitude (RM) of a sunspot cycle several years in advance. The best single-variate fit is one based on the average of the ap index 36 mo prior to cycle minimum occurrence (E(Rm)), having a coefficient of correlation (r) equal to 0.97 and a standard error of estimate (se) equal to 9.3. Presuming cycle 24 not to be a statistical outlier and its minimum in March 2008, the fit suggests cycle 24 s RM to be about 69 +/- 20 (the 90% prediction interval). The weighted mean prediction of 11 statistically important single-variate fits is 116 +/- 34. The best bi-variate fit is one based on the maximum and minimum values of the 12-mma of the ap index; i.e., APM# and APm*, where # means the value post-E(RM) for the preceding cycle and * means the value in the vicinity of cycle minimum, having r = 0.98 and se = 8.2. It predicts cycle 24 s RM to be about 92 +/- 27. The weighted mean prediction of 22 statistically important bi-variate fits is 112 32. Thus, cycle 24's RM is expected to lie somewhere within the range of about 82 to 144. Also examined are the late-cycle 23 behaviors of geomagnetic indices and solar wind velocity in comparison to the mean behaviors of cycles 2023 and the geomagnetic indices of cycle 14 (RM = 64.2), the weakest sunspot cycle of the modern era.

Wilson, Robert M.; Hathaway, David H.

2009-01-01

251

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

252

Manifestation of Strong Geomagnetic Storms in the Ionosphere above Europe  

NASA Astrophysics Data System (ADS)

The solar wind effects on Earth environment are studied for their basic science value as well as for their crucial practical impact on human technological systems. Increased dissipation of solar wind energy in the near-Earth environment is a significant source of consequent perturbations in the upper atmosphere and ionosphere. This chapter addresses the ionospheric manifestation of geomagnetic storms induced by solar wind. Changes in the electron density distribution at the ionospheric F region heights above Europe during strong-to-severe geomagnetic storms, which occurred over present solar cycle, have been analysed. As for the seasonal preference, during storm main phase only negative phases dominate in summer, while during winter occurrence of both negative and positive phases is probable. Enhancements of electron density have been sometimes observed several hours before the onset of geomagnetic storm. Also the existence of few-hours-long periods during storm main phase, when the deviation of the electron density from median was insignificant, has been observed. Independent of the sign of the storm effect on F2 region ionisation, the effect on electron density at the F1 region heights at European higher middle latitudes has been found negative, if any at all. The F1 region response to magnetic disturbances also shows substantial summer/winter asymmetry. The stormy high latitude F region is most variable compared with middle and lower middle latitudes, being strongly influenced by magnetospheric processes, in particular, strong electric fields, which are usually present during geomagnetic storms. Several specific features of the storm-time high latitude ionosphere will briefly be mentioned including behaviour of ionospheric scintillations. The comparative analysis illustrates that the improved IRI-2001 model with the activated STORM option provides better description of the ionisation distribution above Europe under geomagnetic storm conditions. Nevertheless, our results show that model not always estimates correctly the storm phase and the magnitude of the effects on F region electron density

Buresova, D.; Lastovicka, J.; Franceschi, G. De

253

Simulations of the equatorial thermosphere anomaly: Geomagnetic activity modulation  

NASA Astrophysics Data System (ADS)

modulation of geomagnetic activity on the equatorial thermosphere anomaly (ETA) in thermospheric temperature under the high solar activity condition is investigated using the Thermosphere Ionosphere Electrodynamics General Circulation Model simulations. The model simulations during the geomagnetically disturbed interval, when the north-south component of the interplanetary magnetic field (Bz) oscillates between southward and northward directions, are analyzed and also compared with those under the quiet time condition. Our results show that ionospheric electron densities increase greatly in the equatorial ionization anomaly (EIA) crest region and decrease around the magnetic equator during the storm time, resulting from the enhanced eastward electric fields. The impact of both the direct heat deposition at high latitudes and the modulation of the storm time enhanced EIA crests on the ETA are subsequently studied. The increased plasma densities over the EIA crest region enhance the field-aligned ion drag that accelerates the poleward meridional winds and consequently their associated adiabatic cooling effect. This process alone produces a deeper temperature trough over the magnetic equator as a result of the enhanced divergence of meridional winds. Moreover, the enhanced plasma-neutral collisional heating at higher latitudes associated with the ionospheric positive storm effect causes a weak increase of the ETA crests. On the other hand, strong changes of the neutral temperature are mainly confined to higher latitudes. Nevertheless, the changes of the ETA purely due to the increased plasma density are overwhelmed by those associated with the storm time heat deposition, which is the major cause of an overall elevated temperature in both the ETA crests and trough during the geomagnetically active period. Associated with the enhanced neutral temperature at high latitudes due to the heat deposition, the ETA crest-trough differences become larger under the minor geomagnetic activity condition than under the quiet time condition. However, when geomagnetic activity is further elevated, the ETA crests tend to be masked by high temperatures at middle and high latitudes.

Lei, Jiuhou; Wang, Wenbin; Thayer, Jeffrey P.; Luan, Xiaoli; Dou, Xiankang; Burns, Alan G.; Solomon, Stanley C.

2014-08-01

254

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

255

The Microjet of AA Tau  

NASA Astrophysics Data System (ADS)

The microjet of AA Tau A.W. Cox (Atholton High School, Columbia MD), G.M. Hilton (SSAI and GSFC), G.M. Williger (JHU and U. Louisville), C.A. Grady (Eureka Scientific and GSFC) B.Woodgate (NASA's GSFC) AA Tau is a classical T Tauri star with a spatially resolved disk viewed at approximately 70 degrees from pole-on. Photo-polarimetric variability of the star has been interpreted as being caused by the stellar magnetic field being inclined at 30 degrees with respect to the stellar rotation axis, producing a warp in the inner disk. Under these conditions, any jet should be less collimated than typical of T Tauri microjets, and should show signs of the jet axis precessing around the stellar rotation axis. When compared with the microjets imaged in the HST/STIS coronagraphic imaging survey, the AA Tau jet has an opening half-angle of approximately 10-15 degrees rather than the 3-5 degrees typical of the other T Tauri stars which have been coronagraphically imaged by HST/STIS. Using the HST data with ultra-narrowband imagery and long slit spectroscopy obtained with the Goddard Fabry-Perot and the Dual Imaging Spectrograph at the Apache Point Observatory 3.5m telescope, we derive the jet inclination, knot ejection epochs, and ejection frequency. We also compare the jet opening angle with model predictions. Apache Point Observatory observations with the Goddard Fabry-Perot were made through a grant of Director's Discretionary Time. Apache Point Observatory is operated by the Astrophysical Research Consortium. The GFP was supported under NASA RTOP 51-188-01-22 to GSFC. Grady is supported under NASA contract NNH05CD30C to Eureka Scientific.

Cox, A. W.; Hilton, G. M.; Williger, G. M.; Grady, C. A.; Woodgate, B.

2005-12-01

256

Index theorems for quantum graphs  

E-print Network

In geometric analysis, an index theorem relates the difference of the numbers of solutions of two differential equations to the topological structure of the manifold or bundle concerned, sometimes using the heat kernels of two higher-order differential operators as an intermediary. In this paper, the case of quantum graphs is addressed. A quantum graph is a graph considered as a (singular) one-dimensional variety and equipped with a second-order differential Hamiltonian H (a "Laplacian") with suitable conditions at vertices. For the case of scale-invariant vertex conditions (i.e., conditions that do not mix the values of functions and of their derivatives), the constant term of the heat-kernel expansion is shown to be proportional to the trace of the internal scattering matrix of the graph. This observation is placed into the index-theory context by factoring the Laplacian into two first-order operators, H =A*A, and relating the constant term to the index of A. An independent consideration provides an index formula for any differential operator on a finite quantum graph in terms of the vertex conditions. It is found also that the algebraic multiplicity of 0 as a root of the secular determinant of H is the sum of the nullities of A and A*.

S. A. Fulling; P. Kuchment; J. H. Wilson

2007-08-26

257

GPS phase scintillation and proxy index at high latitudes during a moderate geomagnetic storm  

E-print Network

The amplitude and phase scintillation indices are customarily obtained by specialised GPS Ionospheric Scintillation and TEC Monitors (GISTMs) from L1 signal recorded at the rate of 50 Hz. The scintillation indices S[subscript ...

Prikryl, P.

258

Variatons of Geomagnetic Responses and Low-Altitude Radiation Belt Enviroment During Extreme Storm Events  

NASA Astrophysics Data System (ADS)

The October-November 2003 Sun-Earth connection events produced huge geomagnetic storms (Dst as low as -400 nT) and enhancements of the Earth's radiation belt. Using the newly developed Magnetospheric State Quer System (MSQS, http://radbelts.gsfc.nasa.gov), we have identified several additional storm events (July, 1982; September, 1982; March, 1989; October, 1989; March, 1991; November, 1991; July, 2000, March, 2001 and November, 2001) which reached similar magnitude in Dst, i.e. consecutive Dst < -250 nT for more than 5 hours. Using the low-altitude radiation environment data obtained continuously by NOAA POES satellites for more than 20 years, we can study the behaviors of the low-altitude electron and proton belts during these extreme storm events, and contrast them with their quiet-time behaviors. Some events, e.g. March, 1989 and March, 1991, show formation of new proton belts. The formation and enhancement of new proton belts (L less than 2.5) in NOAA POES/MEPED enery channels (0.25 MeV to 80 MeV) will be shown and the decay-time (over years) of the proton belt inferred from these past events will be discussed. Transient evolution of electron belt at energy channels (100 keV and 300 keV) during these extreme condition events will be shown with regard to the variations of the Dst index and other magnetospheric state parameters. Common features and distiguished characteristics in the radiation belt behavior during these extreme storm events will be discussed. In addition, we will apply the recently developed magnetospheric state-based model [Fung and Shao, 2005] to prescribe the geomagnetic responses (AL, Kp, Dst) during the October-November 2003 event using the data from past extreme condition events and assess the model performance. Fung, Shing F., and Xi Shao, Magnetospheric State Specification, submitted to J. Geophys. Res., 2005.

Shao, X.; Fung, S.; Tan, L.

2005-05-01

259

Underlying scaling relationships between solar activity and geomagnetic activity revealed by multifractal analyses  

NASA Astrophysics Data System (ADS)

This paper identifies some scaling relationships between solar activity and geomagnetic activity. We examine the scaling properties of hourly data for two geomagnetic indices (ap and AE), two solar indices (solar X-rays Xl and solar flux F10.7), and two inner heliospheric indices (ion density Ni and flow speed Vs) over the period 1995-2001 by the universal multifractal approach and the traditional multifractal analysis. We found that the universal multifractal model (UMM) provides a good fit to the empirical K(q) and ?(q) curves of these time series. The estimated values of the Lévy index ? in the UMM indicate that multifractality exists in the time series for ap, AE, Xl, and Ni, while those for F10.7 and Vs are monofractal. The estimated values of the nonconservation parameter H of this model confirm that these time series are conservative which indicate that the mean value of the process is constant for varying resolution. Additionally, the multifractal K(q) and ?(q) curves, and the estimated values of the sparseness parameter C1 of the UMM indicate that there are three pairs of indices displaying similar scaling properties, namely ap and Xl, AE and Ni, and F10.7 and Vs. The similarity in the scaling properties of pairs (ap,Xl) and (AE,Ni) suggests that ap and Xl, AE and Ni are better correlated—in terms of scaling—than previous thought, respectively. But our results still cannot be used to advance forecasting of ap and AE by Xl and Ni, respectively, due to some reasons.

Yu, Zu-Guo; Anh, Vo; Eastes, Richard

2014-09-01

260

Seasonal dependence of magnetic field variations from subauroral latitude to the magnetic equator during geomagnetic sudden commencements  

NASA Astrophysics Data System (ADS)

Seasonal dependence of diurnal variation of the main impulse (MI) of geomagnetic sudden commencements (SCs) has been investigated using the long-tern geomagnetic field data with high time resolution of 1 sec within a period from 1996 to 2008 provided from the NSWM [Kikuchi et al., 2008] and CPMN [Yumoto and the CPMN group, 2001] chains and the WDC for Geomagnetism, Kyoto. In the present analysis, we used the geomagnetic field data obtained from the 10 stations. In this study, we defined an SC phenomenon as a rapid increase of the SYM-H value with more than 5 nT and time variation in the SYM-H index. Then, we identified 3163 events of SCs in a period from January 1996 to 2008, which has no Pi 2 signature around 10 minutes at the SC onset. Moreover, the SC amplitude obtained at the above 10 stations has been normalized by that in the SYM-H index with latitude correction in order to minimize the different contribution of the rapid change in solar wind dynamic pressure. As a result, in sub-auroral (ZYK) and middle latitudes (MMB) tends to be larger in summer than in winter in all the magnetic local time. The peak-to-peak amplitude in the daytime sector strongly depends on solar zenith angle. These result imply that ionospheric currents (ICs) and field-aligned currents (FACs) generated during the MI phase of SC are enhanced due to the increase of ionospheric conductivity in summer. This feature suggests that SC current system is the voltage generator. On the other hand, the sesonal variation of SC amplitude in both the low latitude and magnetic equator showed quite a different signature from that in the sub-auroral and middle latitudes. The remarkable feature is that the equatorial enhancement of SC amplitude due to an intensification of the Pedersen currents via the Cowling effect tends to become smaller in summer, compared with that in winter. This tendency suggests that ionospheric conductivity does not depend on only the solar zenith angle. One of the implications of the equatorial seasonal dependence is that the ionospheric conductivity in the low latitude and at the magnetic equator modifies the variation of ionospheric structure around the E-region due to neutral drag of the ionospheric plasma along the magnetic field line via interaction between the meridional neutral wind and ionospheric E-region plasmas. Therefore, in order to verify the existence of the neutral wind and its seasonal dependence, we will need to analyze the thermospheric wind data obtained from the MF and meteor radars provided from the IUGONET database.

Shinbori, A.; Tsuji, Y.; Kikuchi, T.; Araki, T.; Ikeda, A.; Uozumi, T.; Solovyev, S. I.; Shevtsov, B.; Otadoy, R. S.; Utada, H.; Nagatsuma, T.; Hayashi, H.; Tsuda, T.; Yumoto, K.; Iugonet Project Team

2010-12-01

261

Evaluation of Platelet Indexes in Patients with Aortic Aneurysm  

Microsoft Academic Search

The purpose of this study was to investigate whether platelet indexes [platelet count, mean platelet volume (MPV), platelet-large cell ratio (P-LCR), and platelet distribution width (PDW)] could serve as diagnostic tools to evaluate the potential significance of platelet heterogeneity on thrombus formation. Blood samples were obtained from 54 patients with aortic aneurysm (AA; mean age 73 years; 40 males, 14

Akihiro Ihara; Kengo Matsumoto; Toshiharu Kawamoto; Saburou Shouno; Jun Kawamoto; Akira Katayama; Masao Yoshitatsu; Hironori Izutani

2005-01-01

262

An empirical probability density distribution of planetary ionosphere storms with geomagnetic precursors  

NASA Astrophysics Data System (ADS)

The probability of occurrence of the positive and negative planetary ionosphere storms is evaluated using the W index maps produced from Global Ionospheric Maps of Total Electron Content, GIM-TEC, provided by Jet Propulsion Laboratory, and transformed from geographic coordinates to magnetic coordinates frame. The auroral electrojet AE index and the equatorial disturbance storm time Dst index are investigated as precursors of the global ionosphere storm. The superposed epoch analysis is performed for 77 intense storms (Dst?-100 nT) and 227 moderate storms (-100index and Dst index. It is found that AE index better suits to serve as a precursor of the ionosphere storm than Dst index with onset of the average auroral AE storm occurring 6 h before the equatorial Dst storm onset for intense storms and 3 h in advance of moderate Dst storm. The similar space zones advancement of the ionosphere storm is observed with W index (pW+ and pW-) depicting maximum localized in the polar magnetic zone and minimum at magnetic equator. An empirical relation for pW+ and pW- with AE storm precursor is derived which enables the probability of occurrence of the ionosphere storm to be predicted with leading time of 1-2 h for the positive ionosphere storm and 9-10 h for the negative ionosphere storm. The ionosphere storm probability model is validated using data for 2 intense and 20 moderate geomagnetic storms occurred during 2013. Results are discussed in the paper. This study is supported by the joint grant of TUBITAK 112E568 and RFBR 13-02-91370-CT_a.

Gulyaeva, Tamara; Stanislawska, Iwona; Arikan, Feza; Arikan, Orhan

263

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

NASA Technical Reports Server (NTRS)

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.

1993-01-01

264

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

265

The geomagnetic secular variation S parameter: A mathematical artifact  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

266

Mid-latitude airglow variations during geomagnetic storms  

NASA Astrophysics Data System (ADS)

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 630 nm emissions with periods of several hours ( 0.5 -4 hours). The second type of disturbances in the 557.7 and 630 nm emissions is probably caused by particle pre-cipitation. Peculiarities of observed disturbances in emissions, their sources, and connection with magnetospheric-ionospheric structure are discussed. The study has been supported by the RFBR-NSFC Grant No. 08-05-92208 and the RAS Presidium Program No. 16 (part 3).

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

267

Radio interferometer measurements of plasmasphere density structures during geomagnetic storms  

SciTech Connect

The Los Alamos plasmaspheric drift radio interferometer is a ground-based array that regularly measures periodic disturbances in the plasmasphere. These plasmaspheric density structures have been shown to depend on geomagnetic activity, as indicated by Kp. However, a direct storm time analysis of their behavior has not been done. This paper studies the amplitude, drift velocity, and location of these structures before, during, and after the onset of major geomagnetic storms. Distinct large-amplitude, storm time signatures are found during the first night after onset, continuing through the third night; there were significantly more storm time signatures during nighttime than daytime. The L shells on which the disturbances existed were found to decrease after storm onset, indicating a possible shrinking of the plasmasphere.{copyright} 1997 American Geophysical Union

Hoogeveen, G.W.; Jacobson, A.R. [Los Alamos National Laboratory, Los Alamos, New Mexico (United States)] [Los Alamos National Laboratory, Los Alamos, New Mexico (United States)

1997-07-01

268

Geomagnetic field intensity in the middle jurassic - oligocene  

E-print Network

The present paper summarizes results of the studies on the intensity of geomagnetic field in the (167 - 23) Ma interval by sedimentary rocks of the Russian Plate and adjacent territories. The joint analysis of the data paleointensity obtained by sedimentary and thermomagnetized (from PINT12) rocks within this temporal interval is conducted. It is shown that the changes of the paleointensity were occurred chaotically. Alternating bursts and periods of quiet regime of the geomagnetic field are typical for intermittent processes and is a characteristic of the geological interval Jurassic-beginning of Paleogene. The distributions of the paleointensity corresponding to different intervals of geologic time were investigated. It is revealed that the cumulative distribution function (CDF) of the paleointensity values is best approximated by a power function. The indices of the power functions varied depending on geologic time intervals.The analysis of the paleomagnetic data suggests that the medium in which the geoma...

Kurazhkovskii, A Yu; Klain, B I

2014-01-01

269

The geomagnetically trapped radiation environment: A radiological point of view  

NASA Technical Reports Server (NTRS)

The regions of naturally occurring, geomagnetically trapped radiation are briefly reviewed in terms of physical parameters such as; particle types, fluxes, spectrums, and spatial distributions. The major emphasis is placed upon a description of this environment in terms of the radiobiologically relevant parameters of absorbed dose and dose-rate and a discussion of the radiological implications in terms of the possible impact on space vehicle design and mission planning.

Holly, F. E.

1972-01-01

270

Types and Characteristics of Data for Geomagnetic Field Modeling  

NASA Technical Reports Server (NTRS)

Given here is material submitted at a symposium convened on Friday, August 23, 1991, at the General Assembly of the International Union of Geodesy and Geophysics (IUGG) held in Vienna, Austria. Models of the geomagnetic field are only as good as the data upon which they are based, and depend upon correct understanding of data characteristics such as accuracy, correlations, systematic errors, and general statistical properties. This symposium was intended to expose and illuminate these data characteristics.

Langel, R. A. (editor); Baldwin, R. T. (editor)

1992-01-01

271

Concerning System Earth During Geomagnetic Polarity Transitions: Atmospheric Ionisation effects  

NASA Astrophysics Data System (ADS)

Precipitating solar energetic particles ionize the atmosphere. We present a numerical model to determine ionisation rates for protons, electrons and heavier particles in individual solar energetic particle events and on longer time scales. Changes in ionisation rates with varying geomagnetic field and varying levels of solar activity (solar cycle, Gleiss berg cycle, longer time scales) are discussed. From this analysis, conditions for efficient ionisation of the atmosphere will be derived.

Kallenrode, M.-B.; Burrows, J.; von König, M.; Künzi, K.; Stadelmann, A.; Steinhilber, F.

2003-04-01

272

Macroscopic Model of Geomagnetic-Radiation from Air Showers  

E-print Network

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 geo-magnetic 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.

Olaf Scholten; Klaus Werner

2008-08-14

273

Geomagnetic Effects on the Performance of Atmospheric Cerenkov Telescopes  

E-print Network

Atmospheric Cerenkov telescopes are used to detect electromagnetic showers from primary gamma rays of energy > 300 GeV and to discriminate these from cascades due to hadrons using the shape and orientation of the Cerenkov images. The geomagnetic field affects the development of showers and diffuses and distorts the images. When the component of the field normal to the shower axis is sufficiently large (> 0.4 G) the performance of gamma ray telescopes may be affected.

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

1999-06-08

274

Interpreting geomagnetic reversal frequency using numerical dynamos (Invited)  

NASA Astrophysics Data System (ADS)

We derive scaling relationships for the frequency of polarity reversals in numerical geodynamo models powered by thermochemical convection for comparison with the geomagnetic polarity record. We find that the average number of reversals per unit of time scales with the local Rossby number of the convection. For uniform core-mantle boundary conditions, polarity reversals are absent below a critical value of the local Rossby number near 0.05, beyond which reversal frequency increases approximately linearly with that parameter. The relative standard deviation of the dipole intensity fluctuations increases with reversal frequency and the local Rossby number. For tomographic boundary conditions that model the observed large-scale seismic heterogeneity in the Earth's lower mantle, reversal frequency also exhibits linear dependence on the local Rossby number, and in addition, increases approximately as the square root of the amplitude of the boundary heterogeneity. Applied to the history of the geodynamo, our results indicate that outer core convection was relatively weak and homogeneous with small local Rossby number during geomagnetic superchrons and relatively vigorous with larger local Rossby number at times when geomagnetic reversals were frequent. Translated into core energetics, we find that the difference between the present-day geomagnetic reversal frequency and superchron conditions requires a 25% change in the total heat flux across the core-mantle boundary, or alternatively, a 75% change in the amplitude of the boundary heterogeneity. Our results also indicate that polarity reversals were likely throughout Earth history and may also have been commonplace in the early history of other terrestrial planets.

Olson, P.; Amit, H.

2013-12-01

275

Impact of geomagnetic excursions on atmospheric chemistry and dynamics  

NASA Astrophysics Data System (ADS)

Geomagnetic excursions, i.e. short periods in time with much weaker geomagnetic fields and substantial changes in the position of the geomagnetic pole, occurred repeatedly in the Earth's history, e.g. the Laschamp event about 41 kyr ago. Although the next such excursion is certain to come, little is known about the timing and possible consequences for the state of the atmosphere and the ecosystems. Here we use the global chemistry climate model SOCOL-MPIOM to simulate the effects of geomagnetic excursions on atmospheric ionization, chemistry and dynamics. Our simulations show significantly increased concentrations of nitrogen oxides (NOx) in the entire stratosphere, especially over Antarctica (+15%), due to enhanced ionization by galactic cosmic rays. Hydrogen oxides (HOx) are also produced in greater amounts (up to +40%) in the tropical and subtropical lower stratosphere, while their destruction by reactions with enhanced NOx prevails over the poles and in high altitudes (by -5%). Stratospheric ozone concentrations decrease globally above 20 km by 1-2% and at the northern hemispheric tropopause by up to 5% owing to the accelerated NOx-induced destruction. A 5% increase is found in the southern lower stratosphere and troposphere. In response to these changes in ozone and the concomitant changes in atmospheric heating rates, the Arctic vortex intensifies in boreal winter, while the Antarctic vortex weakens in austral winter and spring. Surface wind anomalies show significant intensification of the southern westerlies at their poleward edge during austral winter and a pronounced northward shift in spring. Major impacts on the global climate seem unlikely.

Suter, I.; Zech, R.; Anet, J. G.; Peter, T.

2014-06-01

276

Space Weather Monitoring for ISS Geomagnetic Storm Studies  

NASA Technical Reports Server (NTRS)

The International Space Station (ISS) space environments community utilizes near real time space weather data to support a variety of ISS engineering and science activities. The team has operated the Floating Potential Measurement Unit (FPMU) suite of plasma instruments (two Langmuir probes, a floating potential probe, and a plasma impedance probe) on ISS since 2006 to obtain in-situ measurements of plasma density and temperature along the ISS orbit and variations in ISS frame potential due to electrostatic current collection from the plasma environment (spacecraft charging) and inductive (vxB) effects from the vehicle motion across the Earth s magnetic field. An ongoing effort is to use FPMU for measuring the ionospheric response to geomagnetic storms at ISS altitudes and investigate auroral charging of the vehicle as it passes through regions of precipitating auroral electrons. This work is challenged by restrictions on FPMU operations that limit observation time to less than about a third of a year. As a result, FPMU campaigns ranging in length from a few days to a few weeks are typically scheduled weeks in advance for ISS engineering and payload science activities. In order to capture geomagnetic storm data under these terms, we monitor near real time space weather data from NASA, NOAA, and ESA sources to determine solar wind disturbance arrival times at Earth likely to be geoeffective (including coronal mass ejections and high speed streams associated with coronal holes) and activate the FPMU ahead of the storm onset. Using this technique we have successfully captured FPMU data during a number of geomagnetic storm periods including periods with ISS auroral charging. This presentation will describe the strategies and challenges in capturing FPMU data during geomagnetic storms, the near real time space weather resources utilized for monitoring the space weather environment, and provide examples of auroral charging data obtained during storm operations.

Minow, Joseph I.; Parker, Neergaard

2013-01-01

277

The current systems responsible for SYM and ASY indices variation during geomagnetic storm  

NASA Astrophysics Data System (ADS)

The SYM and ASY indices have been long used to characterize the current systems during geomagnetic storms. We study the contribution of different current systems to the variations of the SYM-H, ASY-H and ASY-D indices. For more than 150 storms, the indices were computed using the empirical magnetospheric models: T01, TS05 (and the newest TS07 for a few events). Comparing the model indices with the real ones we test the models performance in the near-earth region. Of these three models, the T01 was found to be best at predicting the SYM-H and ASY-H indices while TS05 was somewhat better for predicting the ASY-D index. The superposed epoch analysis of the contribution of the different current systems to the SYM and ASY indices revealed the following: (1) During the main phase, the main contribution to SYM-H index comes from the tail module of the models. The symmetric ring current module contribution becomes comparable to or stronger during the recovery phase. (2) The ASY-H and ASY-D indices are controlled entirely by current systems which close via field-aligned currents: the partial ring current and region1/region 2 field-aligned currents. In addition, the analysis was conducted separately for strong and moderate storms as well as for CIR and CME driven storms. No meaningful difference was found between the results obtained for these subsets.

Dubyagin, S.; Ganushkina, N. Y.; Kubyshkina, M.; Liemohn, M. W.

2013-12-01

278

Geomagnetic activity dependence of O+ in transit from the ionosphere  

NASA Astrophysics Data System (ADS)

Energetic O+ ions have important dynamic effects on the ring current. Insights into the effects of O+ on ring current dynamics have come primarily from models, not observations. Here, we discuss observations of O+ populations escaping from the ionosphere and their access to the plasma sheet and ring current. We review data establishing that a significant flux of O+ escapes the ionosphere during geomagnetically quiet intervals. We then estimate the relative magnitude of the O+ population in transit between the ionosphere and ring current during quiet intervals before geomagnetic storms. Our analysis suggests that dynamic reconfigurations of the magnetosphere during geomagnetic storms significantly alter the O+ transport paths from the ionosphere to the ring current. During these reconfigurations some of the pre-existing, quiet time, in-transit O+ populations are captured on magnetic field lines leading to the ring current. The prompt appearance of this O+ population in the ring current could modify the evolution of the ring current in the storm growth phase. Our analysis suggests that the consequences of an activity-dependent O+ transport path to the ring current should be systematically investigated.

Peterson, W. K.; Andersson, L.; Callahan, B.; Elkington, S. R.; Winglee, R. W.; Scudder, J. D.; Collin, H. L.

2009-11-01

279

Evidence that pigeons orient to geomagnetic intensity during homing  

PubMed Central

The influence of the Earth's magnetic field on locomotory orientation has been studied in many taxa but is best understood for homing pigeons (Columba livia). Effects of experimentally induced and naturally occurring perturbations in the geomagnetic field suggest that pigeons are sensitive to changes in geomagnetic parameters. However, whether pigeons use the Earth's magnetic field for position determination remains unknown. Here we report an apparent orientation to the intensity gradient of the geomagnetic field observed in pigeons homing from sites in and around a magnetic anomaly. From flight trajectories recorded by GPS-based tracking devices, we noted that many pigeons released at unfamiliar sites initially flew, in some cases up to several kilometres, in directions parallel and/or perpendicular to the bearing of the local intensity field. This behaviour occurred irrespective of the homeward direction and significantly more often than what was expected by random chance. Our study describes a novel behaviour which provides strong evidence that pigeons when homing detect and respond to spatial variation in the Earth's magnetic field—information of potential use for navigation. PMID:17301015

Dennis, Todd E; Rayner, Matt J; Walker, Michael M

2007-01-01

280

Midlatitude cooling caused by geomagnetic field minimum during polarity reversal  

PubMed Central

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

2013-01-01

281

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

2013-01-22

282

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

283

Geomagnetic Data from the US Magnetic Observatory Network  

NASA Technical Reports Server (NTRS)

The United States operates a network of, at present, 13 ground-based magnetic observatories. Continuous, one-minute digital vector and scalar geomagnetic field values have been recorded for the last decade, and extend about five years further back for several stations. Periodic, 3-component absolute measurements of the magnetic field are made to provide baseline reference data with which to determine calibrated field view values at all intervals. These data are now being made available on CD-ROM. The quality of the data depends upon a number of factors, including the types of instrumentation used to monitor and measure the field, the procedures and equipment used to collect and process the data, and the quality controls employed to check the data for erroneous values. These various factors are described here for the U.S. digital geomagnetic observatory data. The observatories have been undergoing an evolution over the last 15 years that will continue to significantly improve the accuracy, precision, and availability of geomagnetic data.

Herzog, Donald C.

1992-01-01

284

Propagation of low frequency geomagnetic field fluctuations in Antarctica: comparison between two polar cap stations  

Microsoft Academic Search

We conduct a statistical analysis of the coherence and phase difference of low frequency geomagnetic fluctuations between two Antarctic stations, Mario Zucchelli Station (geographic coordinates: 74.7° S, 164.1° E; corrected geomagnetic coordinates: 80.0° S, 307.7° E) and Scott Base (geographic coordinates: 77.8° S 166.8° E; corrected geomagnetic coordinates: 80.0° S 326.5° E), both located in the polar cap. Due to

L. Santarelli; S. Lepidi; L. Cafarella

2007-01-01

285

Geomagnetic observatory GAN Jakub Velimsky K. Chandra Shakar Rao Lars W. Pedersen Ahmed Muslim  

E-print Network

´imsk´y et al. (ETH,UK,DTU,NGRI,GMO) Geomagnetic observatory GAN 27.4.2011/KG MFF UK 1 / 16 #12;Participating, Univ. Stuttgart) John Riddick (BGS, retired) Vel´imsk´y et al. (ETH,UK,DTU,NGRI,GMO) Geomagnetic Measurements and Observatory Practice, 1996) Vel´imsk´y et al. (ETH,UK,DTU,NGRI,GMO) Geomagnetic observatory

Cerveny, Vlastislav

286

Auroral particle instrument onboard the INDEX satellite  

NASA Astrophysics Data System (ADS)

The INDEX satellite is a microsatellite which will be inserted into a low-altitude (650-800km) polar orbit by an H2A rocket as a piggyback payload. A low-energy plasma particle instrument, which consists of two sensor heads (ion/electrons sensors; ISA/ESA), and a multi-spectral auroral camera (MAC) will be installed in the INDEX in order to investigate formation mechanisms of fine-scale structures of optical auroral arc emissions. Because of the low-altitude orbit, the satellite velocity is relatively fast (7.5km/s). A high time-resolution, therefore, is necessary for the plasma measurement. The time resolution of the plasma instruments onboard the INDEX is 20ms, which corresponds to a spatial scale of 150m. The sensor heads are top-hat type analyzers with a planar field-of-view (FOV) which can cover basically 360 degrees in the azimuthal direction in case of no obstacles. Therefore, during the measurements, the attitude of the satellite will be controlled to include a geomagnetic field line within the planar FOV of the plasma instruments. At the same time with the auroral particle observations, the FOV of the optical auroral camera will be pointed to a footprint of the corresponding geomagnetic field line. In this case, pitch-angle distributions of auroral particles can be obtained with the time resolution determined only by a period of internal energy scan, namely, 20ms. Since the instrument is designed to perform the measurement of high-time resolution, the instrument should be able to handle the high count rate. For this purpose, we apply an MCP detector with a position sensitive anode on the basis of a measurement of signal transmission time on the anode pattern. With this detector system, the instrument can handle 106 -107 counts per second.

Asamura, K.; Tsujita, D.; Tanaka, H.; Saito, Y.; Mukai, T.; Hirahara, M.

287

Scintillation Monitoring Using Asymmetry Index  

NASA Astrophysics Data System (ADS)

Variation in electron density can have significant effect on GNSS signals in terms of propagation delay. Ionospheric scintillation can be caused by rapid change of such delay, specifically, when they last for a longer period of time. Ionospheric irregularities that account for scintillation may vary significantly in spatial range and drift with the background plasma at speeds of 45 to 130 m/sec. These patchy irregularities may occur several times during night, e.g. in equatorial region, with the patches move through the ray paths of the GNSS satellite signals. These irregularities are often characterized as either ‘large scale’ (which can be as large as several hundred km in East-West direction and many times that in the North-South direction) or ‘small scale’ (which can be as small as 1m). These small scale irregularities are regarded as the main cause of scintillation [1,2]. In normal solar activity conditions, the mid-latitude ionosphere is not much disturbed. However, during severe magnetic storms, the aurora oval extends towards the equator and the equator anomaly region may stretched towards poles extending the scintillation phenomena more typically associated with those regions into mid-latitudes. In such stormy conditions, the predicted TEC may deviate largely from the true value of the TEC both at low and mid-latitudes due to which GNSS applications may be strongly degraded. This work is an attempt to analyze ionospheric scintillation (S4 index) using ionospheric asymmetry index [3]. The asymmetry index is based on trans-ionospheric propagation between GPS and LEO satellites in a radio occultation (RO) scenario, using background ionospheric data provided by MIDAS [4]. We attempted to simulate one of the recent geomagnetic storms (NOAA scale G4) occurred over low/mid-latitudes. The storm started on 26 September 2011 at UT 18:00 and lasted until early hours of 27 September 2011. The scintillation data for the storm was taken from an ionospheric station in Cairo, Egypt (lat= 29.8641 °, long= 31.3172 °). It was observed that the level of asymmetry was significantly increased during the main phase of the geomagnetic storm. This was due to the changes in ionization, which in turn produced large gradients along occulted ray path in the ionosphere. A very good correlation was found between the evaluated ionospheric asymmetry index and the S4 scintillation index. Additionally, the correlation between evaluated ionospheric asymmetry and errors related to the RO inversion products such as peak electron density (delta NmF2) and Vertical TEC (delta VTEC) estimates also showed promising results. This work is carried out under the framework of the TRANSMIT project (Training Research and Applications Network to Support the Mitigation of Ionospheric Threats - www.transmit-ionosphere.net). [1]Basu Sa. and Basu Su., (1981), ‘Equatorial Scintillation - A Review’, Journal of Atmospheric and Solar-Terrestrial Physics, 43, p. 473. [2]Davies K., (1990), ‘Ionospheric Radio’, IEEE Electromagnetic Waves Series 31, Peter Peregrinus Ltd. [3]Spencer, P., Mitchell, C.N., (2007) ‘Imaging of fast moving electron-density structures in the polar cap’, Annals of Geophysics, vol. 50, no. 3, pp. 427-434. [4]Shaikh, M.M., Notarpietro, R., Nava, B., (2013) ‘The Impact of Spherical Symmetry Assumption on Radio Occultation Data Inversion in the Ionosphere: An Assessment Study’, Advances in Space Research, doi: http://dx.doi.org/10.1016/j.asr.2013.10.025.

Shaikh, Muhammad Mubasshir; Mahrous, Ayman; Abdallah, Amr; Notarpietro, Riccardo

288

The Development of a Dynamic Geomagnetic Cutoff Rigidity Model for the International Space Station  

NASA Technical Reports Server (NTRS)

We have developed a computer model of geomagnetic vertical cutoffs applicable to the orbit of the International Space Station. This model accounts for the change in geomagnetic cutoff rigidity as a function of geomagnetic activity level. This model was delivered to NASA Johnson Space Center in July 1999 and tested on the Space Radiation Analysis Group DEC-Alpha computer system to ensure that it will properly interface with other software currently used at NASA JSC. The software was designed for ease of being upgraded as other improved models of geomagnetic cutoff as a function of magnetic activity are developed.

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

1999-01-01

289

Geomagnetic Field Variation during CME Events at High Latitude in European Zone  

NASA Astrophysics Data System (ADS)

Geomagnetic Field Variation during CME Events at High Latitude in European Zone Babita Chandel, Shailendra Saini ,Sneha Yadav and A.K.Gwal Space Science Laboratory, Department of Physics, Barkatullah University, Bhopal-462026, India Abstract: The concerning results, are the variation of Geomagnetic Field Component in European Zone during CME events. The geomagnetic events selected for this study occurred during 2003-2006, a period of declining phase of solar cycle 23rd at European zone (Tromso, Sodankyla and Rorvik with Geomagnetic Latitude 69.39o N and Long. 18.56o E, Geomagnetic Latitude 67.360o N and Long. 26.363o E and Geomagnetic Latitude 64.56o N and Long.10.59 o E). From this study it is observed that the strength of a geomagnetic storm depends on the interplanetary-magnetospheric coupling parameter VBz. Higher the value of VBz, higher will be the strength of geomagnetic storm. Magnitude of variation at Rorvik is more as compared to Tromso and magnitude of variation is more at Tromso as compared to Sodankyla. Variation in vertical component is less as compared to the north-south and east-west component. Geomagnetic field components shows the variation when either interplanetary magnetic field orientes southward or remains southward for few hours.

Chandel, Babita

290

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

2013-01-01

291

Upper Thermosphere Winds and Temperatures in the Geomagnetic Polar Cap: Solar Cycle, Geomagnetic Activity, and Interplanetary Magnetic Field Dependencies  

NASA Technical Reports Server (NTRS)

Ground-based Fabry-Perot interferometers located at Thule, Greenland (76.5 deg. N, 69.0 deg. W, lambda = 86 deg.) and at Sondre Stromfjord, Greenland (67.0 deg. N, 50.9 deg. W, lambda = 74 deg.) have monitored the upper thermospheric (approx. 240-km altitude) neutral wind and temperature over the northern hemisphere geomagnetic polar cap since 1983 and 1985, respectively. The thermospheric observations are obtained by determining the Doppler characteristics of the (OI) 15,867-K (630.0-nm) emission of atomic oxygen. The instruments operate on a routine, automatic, (mostly) untended basis during the winter observing seasons, with data coverage limited only by cloud cover and (occasional) instrument failures. This unique database of geomagnetic polar cap measurements now extends over the complete range of solar activity. We present an analysis of the measurements made between 1985 (near solar minimum) and 1991 (near solar maximum), as part of a long-term study of geomagnetic polar cap thermospheric climatology. The measurements from a total of 902 nights of observations are compared with the predictions of two semiempirical models: the Vector Spherical Harmonic (VSH) model of Killeen et al. (1987) and the Horizontal Wind Model (HWM) of Hedin et al. (1991). The results are also analyzed using calculations of thermospheric momentum forcing terms from the Thermosphere-ionosphere General Circulation Model TGCM) of the National Center for Atmospheric Research (NCAR). The experimental results show that upper thermospheric winds in the geomagnetic polar cap have a fundamental diurnal character, with typical wind speeds of about 200 m/s at solar minimum, rising to up to about 800 m/s at solar maximum, depending on geomagnetic activity level. These winds generally blow in the antisunward direction, but are interrupted by episodes of modified wind velocity and altered direction often associated with changes in the orientation of the Interplanetary Magnetic Field (IMF). The central polar cap (greater than approx. 80 magnetic latitude) antisunward wind speed is found to be a strong function of both solar and geomagnetic activity. The polar cap temperatures show variations in both solar and geomagnetic activity, with temperatures near 800 K for low K(sub p) and F(sub 10.7) and greater than about 2000 K for high K(sub p) and F(sub 10.7). The observed temperatures are significantly greater than those predicted by the mass spectrometer/incoherent scatter model for high activity conditions. Theoretical analysis based on the NCAR TIGCM indicates that the antisunward upper thermospheric winds, driven by upstream ion drag, basically 'coast' across the polar cap. The relatively small changes in wind velocity and direction within the polar cap are induced by a combination of forcing terms of commensurate magnitude, including the nonlinear advection term, the Coriolis term, and the pressure gradient force term. The polar cap thennospheric thermal balance is dominated by horizontal advection, and adiabatic and thermal conduction terms.

Killeen, T. L.; Won, Y.-I.; Niciejewski, R. J.; Burns, A. G.

1995-01-01

292

Simulating Geomagnetic Depth Sounding using a Time-domain Finite Element Method: Effects of Asymmetric External Source Fields  

NASA Astrophysics Data System (ADS)

The commercial finite element software FlexPDE has been successfully used to simulate electromagnetic induction in Earth's mantle and lithosphere and validated by several previously published results. Estimates of Earth's frequency-dependent electromagnetic response calculated from satellite data are known to be influenced by the local time of the observing frame. We use time-stepping methods scripted within FlexPDE to investigate the hypothesis that this bias results from the rotation of Earth through the asymmetric and highly variable magnetic field associated with the magnetospheric ring current. We evaluate local-time response functions at periods of a few hours to a few months. These are calculated from long 3-dimensional, time-domain simulations of geomagnetic induction and using the magnetic data similar to those gathered by low earth orbiting satellite missions. The spatial structure of the external field is imposed in the form of a time-varying spherical harmonic representation in a geomagnetic coordinate system that rotates with respect to Earth. The symmetric part of the field is controlled by the dipole (degree 1, order 0) term and the asymmetric part controlled by a quadrupole (degree 2, order 1) term. Time variations in the magnitude of the external field are controlled by a high-resolution magnetic index such as the new 1-minute USGS Dst, subsampled at 15 minute intervals.

Ribaudo, J. T.; Constable, C.

2010-12-01

293

MoSST DAS: The First Working Geomagnetic Data Assimilation System  

NASA Technical Reports Server (NTRS)

The Earth possesses an internal magnetic field (geomagnetic field) generated by convection in the outer core (geodynamo). Previous efforts have been focused along two distinct paths: (1) numerical geodynamo modeling to understand the origin of the geomagnetic field, and the mechanisms of geomagnetic secular variations (SV); and (2) geomagnetic field modeling to map the spatial/temporal variations of the field from geomagnetic data, and to derive core properties, e.g. inversion of core flow near the core-mantle boundary (CMB). Geomagnetic data assimilation is a new approach emerged over the past 5 years: surface observations are assimilated with geodynamo models for better understanding of the core dynamical state, and accurately prediction of SV. In collaboration with several geomagnetic research groups, we have developed the first working geomagnetic data assimilation system, Modular, Scalable, Self-consistent, and Three-dimensional (MoSST) DAS, that includes the MoSST numerical dynamo model; 7000 years of geomagnetic field maps from several field models utilizing satellite and ground observatory data, historical magnetic records and archeo/paleo magnetic data; and an ensemble based optimal interpolation (01) assimilation algorithm. With this system, we have demonstrated clearly that the assimilated core dynamical state is substantially different from those of pure geodynamo simulations. Ensemble assimilation runs also show the convergence of the assimilated solutions inside the core, suggesting that the simulation state is pulled closer to the truth via data assimilation. The forecasts from this system are also very accurate: the 5-year forecast of the geomagnetic field agrees very well with the observations; and the 5-year secular variation forecast is more accurate than the IGRF SV forecast models in the past. Using geomagnetic records up to 2009, we have made an SV forecast for the period from 2010-2015, and is a candidate SV model for IGRF-11.

Kuang, Weijia; Wei, Zigang; Tangborn, Andrew

2011-01-01

294

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

NASA Astrophysics Data System (ADS)

It has been well-known that geomagnetic solar quiet (Sq) daily variation is produced by the global ionospheric currents flowing in the E-region, which are generated by dynamo process via interaction between the neutral wind and ionospheric plasma in a region of the lower thermosphere and ionosphere. Then, to investigate the Sq amplitude is essential for understanding the long-term variations in the ionospheric conductivity and neutral wind of the lower thermosphere and ionosphere. Recently, Elias et al. [2010] reported that the Sq amplitude tends to increase by 5.4-9.9 % in the middle latitudes in a period of 1961-2001. They mentioned that the long-term variation of ionospheric conductivity associated with geomagnetic secular variation mainly determines the Sq trend, but that the rest component is due to ionospheric conductivity enhancement associated with cooling effect in the thermosphere due to increasing greenhouse gas. In the present study, we clarify the characteristics of the long-term variation in the Sq amplitude using the long-term observation data of geomagnetic field and neutral wind. In the present analysis, we used the F10.7 solar flux as a good indicator of the variation in the solar irradiance in the EUV and UV range as well as geomagnetic field data with time resolution of 1 hour observed at 184 geomagnetic stations. The definition of the Sq amplitude is the difference of the H-component between the maximum and minimum every day when the Kp index is less than 4. As a result, the long-term variation in the Sq amplitude at all the geomagnetic stations shows a strong correlation with the solar F10.7 flux which depends on 11-year solar activity. The relationship between the Sq amplitude and F10.7 flux was not linear but nonlinear. This nonlinearity could be interpreted as the decrease of production rate of electrons and ions in the ionosphere for the strong EUV and UV fluxes as already reported by Balan et al. [1993]. In order to minimize the solar activity dependence on the Sq amplitude, we calculated second orders of fitting curve between the F10.7 flux and Sq amplitude during 1950-2011, and examined the residual Sq amplitude defined as the deviation from the fitting curve. The residual Sq amplitude clearly shows increase and decrease trends with the periods of 20 years. Then, it seems that the trends in the residual Sq and Sqp fields are related to the long-term variation in the ionospheric conductivities associated with the secular variation of the ambient magnetic field and the upper atmosphere (for example, plasma and neutral densities). In order to verify qualitatively the above signatures, we need to investigate the long-term variation in the ionospheric conductivities using a calculation tool developed by the IUGONET project.

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

2012-12-01

295

Continuous global geomagnetic field models for the past 3000 years  

NASA Astrophysics Data System (ADS)

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 Lake Sediment Geomagnetic Model for the last 3k years (CALS3K.1), can be used to predict both the field and secular variation. Comparisons and tests with synthetic data lead to the conclusion that CALS3K.1 gives a good general, large-scale representation of the geomagnetic field, but lacks small-scale structure due to the limited resolution of the sparse dataset. In future applications the model can be used for comparisons with additional, new data for that time span. For better resolved regions, the agreement of data with CALS3K.1 will provide an idea about the general compatibility of the data with the field and secular variation in that region of the world. For poorly covered regions and time intervals we hope to iteratively improve the model by comparisons with and inclusion of new data. Animations and additional snapshot plots of model predictions as well as the model coefficients and a FORTRAN code to evaluate them for any time can be accessed under http://www.mahi.ucsd.edu/cathy/Holocene/holocene.html. The whole package is also stored in the Earthref digital archive at http://www.earthref.org/...

Korte, Monika; Constable, Catherine

2003-11-01

296

Complexity and Geomagnetic Activity: A Nonlinear Dynamical Analogue Model Approach  

NASA Astrophysics Data System (ADS)

It is clear that if changes in the local magnetic field attributable to the dynamics of a volcano are ever going to be detected, it will require stable, high resolution EarthSs magnetic field readings from a network of sensitive instruments and effective data pro- cessing to reduce the magnetic signal to the level of a few nanotesla which is the ap- parent upper limit of detectability of magnetic anomalies associated with the volcanic activity. With the introduction of the Overhauser proton precession magnetometers, the long-term stability, high sensitivity and fast response to the changing magnetic field for measurements are no longer a problem. On the contrary, the problem of elim- inating from measurements of the total intensity the natural geomagnetic fluctuations of external origin, which may be of the order of several tens of nanotesla, is only partially overcome. Even if data reduction processes are properly employed, however, we often see geomagnetic variations regardless of the state of the volcanic activity. External sources of fluctuations include electric current systems within EarthSs mag- netosphere, which belongs to the class of dissipative chaotic systems. For this reason we propose a method for nonlinear dynamical system identification from measured data. We describe the geomagnetic activity in terms of a relatively simple nonlinear dynamical analogue circuit. The parameters of the circuit are determined in such a way that the electric signal best fits the data acquired by magnetic network installed on Mt. Etna. The synchronization is used to compel the circuit to follow a state trajec- tory that is identical to the one of the magnetic signal. The parameters of system are identified by formulating a global optimization problem.

Currenti, G.; del Negro, C.; Fortuna, L.

297

Validation of Galactic Cosmic Radiation and Geomagnetic Transmissions  

NASA Technical Reports Server (NTRS)

The Alpha Magnet Spectrometer (AMS) was flown on Shuttle flight STS-91 in June 1998 near solar minimum. This unique spectrometer has provided very high resolution, calibrated data on the galactic hydrogen and helium rigidity spectra form approx. 100 MeV/n to approx. 200 GeV/n as a function of magnetic latitude. This paper describes a comparison of the AMS data with the Badhwar-O'Neill GCR model and the geomagnetic transmission calculated using the quiescent DGRF 1990 cutoffs. The results have strong bearing on radiation modeling for the International Space Station.

Badhwar, Gautam D.; Troung, A.; ONeill, P.; Bman, B.

2000-01-01

298

A proposed International Geomagnetic Reference Field for 1965- 1985.  

USGS Publications Warehouse

A set of spherical harmonic models describing the Earth's main magnetic field from 1965 to 1985 has been developed and is proposed as the next revision of the International Geomagnetic Reference Field (IGRF). A tenth degree and order spherical harmonic model of the main field was derived from Magsat data. A series of eighth degree and order spherical harmonic models of the secular variation of the main field was derived from magnetic observatory annual mean values. Models of the main field at 1965, 1970, 1975, and 1980 were obtained by extrapolating the main-field model using the secular variation models.-Authors spherical harmonic models Earth main magnetic field Magsat data

Peddie, N. W.; Fabiano, E. B.

1982-01-01

299

Electro Acceleration in a Geomagnetic Field Line Resonance  

SciTech Connect

A hybrid MHD kinetic electron model in dipolar coordinates is used to sim- ulate the upward current region of a geomagnetic Field Line Resonance (FLR) system for a realistic ambient electron temperatures of a keV. It is found that mirror force e ects result in potential drops su#14;cient to accelerate electrons to energies in excess of a keV in support of eld aligned currents on the or- der of 0.5 #22;µA/m2. The wave energy dissipated in this acceleration would com- pletely damp an undriven FLR with an equatorial width of 0.5 RE within two resonance cycles.

Peter Damiano and J.R. Johnson

2012-08-17

300

Quiet geomagnetic field representation for all days and latitudes  

USGS Publications Warehouse

Describes a technique for obtaining the quiet-time geomagnetic field variation expected for all days of the year and distribution of latitudes from a limited set of selected quiet days within a year at a discrete set of locations. A data set of observatories near 75??E longitude was used as illustration. The method relies upon spatial smoothing of the decomposed spectral components. An evaluation of the fidelity of the resulting model shows correlation coefficients usually above 0.9 at the lower latitudes and near 0.7 at the higher latitudes with variations identified as dependent upon season and field element. -from Authors

Campbell, W.H.; Schiffmacher, E.R.; Arora, B.R.

1992-01-01

301

Sharks can detect changes in the geomagnetic field  

PubMed Central

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 converged on the target when the artificial magnetic field was activated but no food reward was presented thereby demonstrating that they were able to sense the altered magnetic field. This strong response provides a robust behavioural assay that could be used to determine how sharks detect magnetic fields and to measure detection thresholds. PMID:16849172

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

2004-01-01

302

Neutral solar wind properties: Advance warning of major geomagnetic storms  

SciTech Connect

The author discusses the prediction of the arrival of coronal mass ejection events (CMEs) at earth by means of monitoring the arrival of energetic neutral atoms (ENAs) which proceed the CMEs arrival by 3 to 4 hours. Large CME have been identified as triggers for large geomagnetic storms, and advance warning of such events has practical value for health as well as electronic communications. ENAs are formed by recombination in the CME, and slowing of the CME in its traverse to the earth allows the ENAs to arrive in advance. The author discusses the magnitude of such arrivals, the energy characteristics of the atoms, and progress on systems to detect such events.

Gruntman, M.A. [Univ. of Southern California, Los Angeles, CA (United States)

1994-10-01

303

IAGA Geomagnetic Data Analysis format - Analysis_IAGA  

NASA Astrophysics Data System (ADS)

Geomagnetic research involves a continuous Earth's magnetic field monitoring and software for processing large amounts of data. The Analysis_IAGA program reads and analyses files in IAGA2002 format used within the INTERMAGNET observer network. The data is made available by INTERMAGNET (http://www.intermagnet.org/Data_e.php) and NOAA - National Geophysical Data Center (ftp://ftp.ngdc.noaa.gov/wdc/geomagnetism/data/observatories/definitive) cost free for scientific use. The users of this software are those who study geomagnetism or use this data along with other atmospheric or seismic factors. Analysis_IAGA allows the visualization of files for the same station, with the feature of merging data for analyzing longer time intervals. Each file contains data collected within a 24 hour time interval with a sampling rate of 60 seconds or 1 second. Adding a large number of files may be done by dividing the sampling frequency. Also, the program has the feature of combining data files gathered from multiple stations as long as the sampling rate and time intervals are the same. Different channels may be selected, visualized and filtered individually. Channel properties can be saved and edited in a file. Data can be processed (spectral power, P / F, estimated frequency, Bz/Bx, Bz/By, convolutions and correlations on pairs of axis, discrete differentiation) and visualized along with the original signals on the same panel. With the help of cursors/magnifiers time differences can be calculated. Each channel can be analyzed separately. Signals can be filtered using bandpass, lowpass, highpass (Butterworth, Chebyshev, Inver Chebyshev, Eliptic, Bessel, Median, ZeroPath). Separate graphics visualize the spectral power, frequency spectrum histogram, the evolution of the estimated frequency, P/H, the spectral power. Adaptive JTFA spectrograms can be selected: CSD (Cone-Shaped Distribution), CWD (Choi-Williams Distribution), Gabor, STFT (short-time Fourier transform), WVD (Wigner-Ville Distribution). A special filter eliminates spikes over a threshold amplitude / duration without modifying the rest of the signal. File discontinuities (missing data, samples with the same timestamp, and overlapping periods of time) are signaled and corrected by repeating the last value. Data can be saved in the IAG2002 format (corrected file, files concatenated in time for the same station), SAC bin - Unix (a file for every channel) and PC - SUDS (one file with all channels). This feature allows other software to analyze geomagnetic data associated with other atmospheric phenomena. Analysis_IAGA is a LabVIEW application with GNU (General Public License) license.

-Emilian Toader, Victorin; Marmureanu, Alexandru

2013-04-01

304

Comparison of periodic and other characteristics of geomagnetic and meterological rocket data  

Microsoft Academic Search

The temporal variations in stratospheric winds and temperatures with the geomagnetic field elements were compared. From a periodic analysis of the geomagnetic field elements the amplitude and phase of the quasibiennial, annual, and semiannual waves are given for stations from 1 degree S to 89 degree N. These results are then compared with corresponding waves reported in rocketsonde wind and

G. D. Nastrom; A. D. Belmont

1976-01-01

305

Seismo-geomagnetic anomalies and M P 5.0 earthquakes observed in Taiwan during 19882001  

E-print Network

Seismo-geomagnetic anomalies and M P 5.0 earthquakes observed in Taiwan during 1988­2001 J.Y. Liu a, a relationship between M P 5.0 earthquakes and diurnal variations of the total geomagnetic field recorded activity observing earthquake effects. We compute the distribution of diurnal range ratios between

Chen, Yuh-Ing

306

What can we Expect From Present Geomagnetic Field Studies in the Next Years?  

Microsoft Academic Search

The International Decade of Geopotential Field Research, firstly proposed by a resolution of the International Association of Geomagnetism and Aeronomy in 1997, is changing our approaches towards the study of the present geomagnetic field. In a few years, Swarm satellites will complete the cycle of missions started few years ago with Orsted, Champ, and SAC-C with the objective of undertaking

L. R. Gaya-Pique

2007-01-01

307

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

Federal Register 2010, 2011, 2012, 2013

...AD12-13-000] Geomagnetic Disturbances to the Bulk-Power System; Notice of Technical Conference Take notice that the Federal Energy Regulatory...Conference on Geomagnetic Disturbances to the Bulk-Power System on Monday, April 30, 2012, from 11 a.m. to...

2012-04-13

308

The Role of Geomagnetic Cues in Green Turtle Open Sea Navigation  

Microsoft Academic Search

BackgroundLaboratory and field experiments have provided evidence that sea turtles use geomagnetic cues to navigate in the open sea. For instance, green turtles (Chelonia mydas) displaced 100 km away from their nesting site were impaired in returning home when carrying a strong magnet glued on the head. However, the actual role of geomagnetic cues remains unclear, since magnetically treated green

Simon Benhamou; Joël Sudre; Jérome Bourjea; Stéphane Ciccione; Angelo De Santis; Paolo Luschi

2011-01-01

309

Statistical maps of geomagnetic perturbations as a function of the interplanetary magnetic field  

Microsoft Academic Search

Mappings of geomagnetic perturbations are shown for different combinations of the solar wind velocity, interplanetary magnetic field (IMF), and dipole tilt angle (season). Average maps were derived separately for the northward, eastward, and vertical (downward) components of the geomagnetic disturbances, using spherical cap harmonics in least error fits of sorted measurements. The source data are obtained from 104 ground-based magnetometer

D. R. Weimer; C. R. Clauer; M. J. Engebretson; T. L. Hansen; H. Gleisner; I. Mann; K. Yumoto

2010-01-01

310

Evolution of Geomagnetic Cutoff Rigidities on Short-and Long-term Time Scales  

Microsoft Academic Search

The magnetic shielding of the Earth from galactic and solar cosmic radiation is dependent on the magnitude and orientation of the Earth's magnetic field. The amount of shielding at a specific location is defined by the geomagnetic cutoff rigidity (RC), which varies on both short- and long-term time scales. On short time scales, the amount of geomagnetic shielding at any

D. F. Smart; M. A. Shea; N. Lifton

2008-01-01

311

MAGNETIC STRUCTURES OF SOLAR ACTIVE REGIONS, FULL-HALO CORONAL MASS EJECTIONS, AND GEOMAGNETIC STORMS  

E-print Network

) the flares, CMEs, and geomagnetic storms are closely related magnetically, as already suggested by manyMAGNETIC STRUCTURES OF SOLAR ACTIVE REGIONS, FULL-HALO CORONAL MASS EJECTIONS, AND GEOMAGNETIC STORMS Y. Liu,1 D. F. Webb,2, 3 and X. P. Zhao1 Received 2006 February 6; accepted 2006 April 8 ABSTRACT

California at Berkeley, University of

312

Penetration of magnetospheric electric fields to low latitude during geomagnetic storms  

Microsoft Academic Search

Penetration of the magnetospheric electric fields to low latitude ionosphere is examined using magnetometer data from high latitude to the equator for geomagnetic storms characterized by an equatorial enhancement of storm amplitude. To detect the penetrated electric fields, we analyze magnetic disturbances at the geomagnetic equator, Yap (-0.3° GML), subtracted by those at low latitude, Okinawa (14.47° GML). During storm

T. Kikuchi; K. Hashimoto; A. Shinbori; Y. Tsuji; S. Watari

2009-01-01

313

A note on the statistics of the largest geomagnetic storms per solar cycle  

NASA Astrophysics Data System (ADS)

This note points out a problem with the way in which extreme value distributions have been fit to the intensities of the largest geomagnetic storms per solar cycle. An alternative method is described. This method is applied to observations of the three largest geomagnetic storms in solar cycles 11-22.

Solow, A. R.; Beet, A. R.

2004-12-01

314

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

Microsoft Academic Search

Over the last few years various researches have reached the conclusion that cosmic ray variations and geomagnetic disturbances are related to the condition of the human physiological state. In this study medical data regarding 4018 Slovak aviators were analyzed in relation to daily variations of cosmic ray and geomagnetic activity. Specifically daily data concerning mean values of heart rate which

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

2011-01-01

315

Geomagnetic secular variation in the Cretaceous Normal Superchron and in the Jurassic  

Microsoft Academic Search

It is now widely thought that geomagnetic polarity reversals occur spontaneously as a result of normal dynamo action rather than being externally triggered. If this is the case, then it may well be that periods of time in which the geomagnetic reversal frequency was dramatically different were characterised by different styles of secular variation. Two such periods were the Cretaceous

Andrew J. Biggin; Douwe J. J. van Hinsbergen; Cor G. Langereis; Gijs B. Straathof; Martijn H. L. Deenen

2008-01-01

316

Paleointensity of the earth's magnetic field during the Laschamp excursion and its geomagnetic implications  

Microsoft Academic Search

The reversed paleomagnetic direction of the Laschamp and Olby flows represents a specific feature of the geomagnetic field. This is supported by paleomagnetic evidence, showing that the same anomalous direction was recorded at several distinct sites, including scoria of the Laschamp volcano. To examine this anomalous geomagnetic fluctuation, we studied the paleointensity of the Laschamp and Olby flows, using the

P. Roperch; N. Bonhommet; S. Levi

1988-01-01

317

Anomaly geomagnetic field in the center part of the Balcan Peninsula  

NASA Astrophysics Data System (ADS)

An analysis of the structure geomagnetic field from the geomagnetic measurements performed in the last decade in the territory of the Republic of Macedonia. The research area is in the center of the Balkan Peninsula. Geological processes led to complex structure both at the surface of the terrain, and below the surface. The diversity of the rocks produce clear differences in the measurements of the magnetic field in this area. The magnetic field is presented how the sum of two components: Normal and anomalous geomagnetic field. Regional terrain observations implemented from 15 repeat stations, allows us to define both the normal geomagnetic field and the anomalous geomagnetic field from regional aspect. Observation net is not dense, so it is not sufficient to define the local anomalies of the geomagnetic field. The Correlation between maps of regional local anomaly geomagnetic field and the conclusions are also presented. Regarding the former, there is a good correlation between regional anomalous geomagnetic field and neotectonic regionalization in the area differentiating three zones: Western Macedonian zone, Vardar zone and Eastern Macedonian zone.

Delipetrev, Marjan; Doneva, Blagica; Delipetrov, Todor; Dimov, Gorgi

2014-05-01

318

High cycle fatigue of AA6082 and AA6063 aluminum extrusions  

Microsoft Academic Search

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

Nicholas E. Nanninga

2008-01-01

319

Computational Investigation of Hardness Evolution During Friction-Stir Welding of AA5083 and AA2139  

E-print Network

to assess and compare welding behavior of AA5083-H131 and one of the newer high-strength aluminum alloys AA are under way to engineer light-weight, highly mobile, transportable, and lethal battlefield vehicles, higher tensile strength levels offered by these alloys are very desirable for vehicle-hull designs

Grujicic, Mica

320

ON THE ELECTRIC PROPERTIES OF ROCKS UNDER THE NETWORK OF EUROPEAN GEOMAGNETIC OBSERVATORIES AS DERIVED FROM SERIES OF ANNUAL MEANS OF GEOMAGNETIC ELEMENTS  

Microsoft Academic Search

The solar-cycle-related (SC) variation, present in the annual means of geomagnetic elements recorded at European geomagnetic observatories between 1952-1980, is discussed in terms of magnetic a nd electromagnetic induction in the Earth, produced b y v ariations in the e xternal magnetospheric ring current. The vertical component of the SC variation, in which the e ffect of electromagnetic induction is

C. DEMETRESCU; V. DOBRICA

321

Direct-Chill Co-Casting of AA3003/AA4045 Aluminum Ingots via Fusion™ Technology  

NASA Astrophysics Data System (ADS)

Laboratory-scale experiments were conducted to cast AA3003/AA4045 clad ingots via Fusion™ Technology, a novel process developed by Novelis Inc. for the production of aluminum clad materials such as brazing sheet. Experimental results were used to validate a steady-state thermofluids model of the Fusion™ Technology co-casting process. The numerical model was able to accurately predict the temperature field within the AA3003/AA4045 clad ingot as well as the shape of the AA3003 liquid sump. The model was also used to quantify the temperature, fraction solid, and velocity fields in a clad ingot cast with an asymmetrical molten metal-feeding system. Feeding of core and clad molten metals at opposite corners of the mold was found to reduce the risks of hot spots and liquid metal breakthrough from the core sump to the clad side of the Fusion™ Technology mold. The use of a diffuser for the AA3003 core molten metal and of a vertical feeding tube for the AA4045 clad produced different flow patterns and liquid sump shapes on either side of the mold. The quality of the metallurgical bond at the core/clad interface appeared good near the clad inlet and at the ingot centerline, but poor near the edges of the ingot. SEM-EDS analysis of the chemical composition across the interface showed that a 1 to 20- ?m-deep penetration of silicon from the AA4045 clad into the AA3003 core had occurred at visually acceptable interfaces, whereas silicon diffusion across poor interfaces was very limited. A study of the model-predicted fraction solid history at different points along the interface indicated that reheating of the AA3003 core is not required to form a visually acceptable metallurgical bond. However, a sufficient amount of interaction time between the solid AA3003 core shell and the silicon-rich AA4045 clad liquid is required to chemically dissolve the surface of the core and form a good metallurgical bond. An approximate dissolution depth of 750 to 1000 ?m was observed along the visually good interface. Partial dissolution of the Mn-rich AA3003 core led to the formation of Al(Mn,Fe)Si intermetallic particles in the AA4045 clad and an increased manganese concentration near the core/clad interface.

Caron, Etienne J. F. R.; Pelayo, Rosa E. Ortega; Baserinia, Amir R.; Wells, Mary A.; Weckman, David C.; Barker, Simon; Gallerneault, Mark

2014-06-01

322

Effect of local and global geomagnetic activity on human cardiovascular homeostasis.  

PubMed

The authors investigated the effects of local and planetary geomagnetic activity on human physiology. They collected data in Sofia, Bulgaria, from a group of 86 volunteers during the periods of the autumnal and vernal equinoxes. They used the factors local/planetary geomagnetic activity, day of measurement, gender, and medication use to apply a four-factor multiple analysis of variance. They also used a post hoc analysis to establish the statistical significance of the differences between the average values of the measured physiological parameters in the separate factor levels. In addition, the authors performed correlation analysis between the physiological parameters examined and geophysical factors. The results revealed that geomagnetic changes had a statistically significant influence on arterial blood pressure. Participants expressed this reaction with weak local geomagnetic changes and when major and severe global geomagnetic storms took place. PMID:16075902

Dimitrova, Svetla; Stoilova, Irina; Yanev, Toni; Cholakov, Ilia

2004-02-01

323

The contribution of L'Aquila (Italy) Geomagnetic Observatory to MAGDAS project  

NASA Astrophysics Data System (ADS)

The geomagnetic Observatory of L'Aquila (Italy) was founded by Istituto Nazionale di Geofisica e Vulcanologia (INGV) in 1958, on the occasion of the International Geophysical Year. It is the main Italian geomagnetic observatory. Since 1999 L'Aquila Observatory belongs to the Intermagnet system, an International network grouping worldwide geomagnetic observatories able to provide Earth's magnetic field measurements according to precise quality standards. Geomagnetic field measurements in L'Aquila are used to study the variations of the Earth's geomagnetic field, both of internal and external origin. In November 2008 a new magnetometer was installed in L'Aquila within the MAGDAS project, coordinated by SERC. The location of this installation can be useful to complete the MAGDAS monitoring system to study solar-terrestrial events.

Lepidi, S.; Meloni, A.; Palangio, P.; Yumoto, K.

2011-12-01

324

Magnetic polarity fractions in magnetotactic bacterial populations near the geomagnetic equator  

PubMed Central

The relative numbers of North-seeking and South-seeking polarity types in natural populations of magnetotactic bacteria were determined at sites on the coast of Brazil. These sites were South of the geomagnetic equator and had upward geomagnetic inclinations of 1-12°. For upward inclinations >6°, South-seeking cells predominated over North-seeking cells by more than a factor of 10. For upward inclinations <6°, the fraction of North-seeking cells in the population increased with decreasing geomagnetic inclination, approaching 0.5 at the geomagnetic equator. We present a simple statistical model of a stochastic process that qualitatively accounts for the dynamics of the two polarity types in a magnetotactic bacterial population as a function of the geomagnetic field inclination. PMID:19431763

de Araujo, F. F. Torres; Germano, F. A.; Goncalves, L. L.; Pires, M. A.; Frankel, R. B.

1990-01-01

325

Seasonal dependence of magnetic field variations from subauroral latitude to the magnetic equator during geomagnetic sudden commencements  

Microsoft Academic Search

Seasonal dependence of diurnal variation of the main impulse (MI) of geomagnetic sudden commencements (SCs) has been investigated using the long-tern geomagnetic field data with high time resolution of 1 sec within a period from 1996 to 2008 provided from the NSWM [Kikuchi et al., 2008] and CPMN [Yumoto and the CPMN group, 2001] chains and the WDC for Geomagnetism,

A. Shinbori; Y. Tsuji; T. Kikuchi; T. Araki; A. Ikeda; T. Uozumi; S. I. Solovyev; B. Shevtsov; R. S. Otadoy; H. Utada; T. Nagatsuma; H. Hayashi; T. Tsuda; K. Yumoto

2010-01-01

326

On the uniqueness of linear moving-average filters for the solar wind-auroral geomagnetic activity coupling  

NASA Technical Reports Server (NTRS)

The relation between the solar wind input to the magetosphere, VB(sub South), and the auroral geomagnetic index AL is modeled with two linear moving-average filtering methods: linear prediction filters and a driven harmonic oscillator in the form of an electric circuit. Although the response of the three-parameter oscillator is simpler than the filter's, the methods yield similar linear timescales and values of the prediction-observation correlation and the prediction Chi(exp 2). Further the filter responses obtained by the two methods are similar in their long-term features. In these aspects the circuit model is equivalent to linear prediction filtering. This poses the question of uniqueness and proper interpretation of detailed features of the filters such as response peaks. Finally, the variation of timescales and filter responses with the AL activity level is discussed.

Vassiliadis, D.; Klimas, A. J.

1995-01-01

327

Variation of Solar, Interplanetary and Geomagnetic Parameters during Solar Cycles 21-24  

NASA Astrophysics Data System (ADS)

The length of solar cycle 23 has been prolonged up to about 13 years. Many studies have speculated that the solar cycle 23/24 minimum will indicate the onset of a grand minimum of solar activity, such as the Maunder Minimum. We check the trends of solar (sunspot number, solar magnetic fields, total solar irradiance, solar radio flux, and frequency of solar X-ray flare), interplanetary (interplanetary magnetic field, solar wind and galactic cosmic ray intensity), and geomagnetic (Ap index) parameters (SIG parameters) during solar cycles 21-24. Most SIG parameters during the period of the solar cycle 23/24 minimum have remarkably low values. Since the 1970s, the space environment has been monitored by ground observatories and satellites. Such prevalently low values of SIG parameters have never been seen. We suggest that these unprecedented conditions of SIG parameters originate from the weakened solar magnetic fields. Meanwhile, the deep 23/24 solar cycle minimum might be the portent of a grand minimum in which the global mean temperature of the lower atmosphere is as low as in the period of Dalton or Maunder minimum.

Oh, Suyeon; Kim, Bogyeong

2013-06-01

328

Uncovering the nonadiabatic response of geosynchronous electrons to geomagnetic disturbance  

NASA Astrophysics Data System (ADS)

We describe an energy spectrum method for scaling electron integral flux, which is measured at a constant energy, to phase space density at a constant value of the first adiabatic invariant which removes much of the variation due to reversible adiabatic effects. Applying this method to nearly a solar cycle (1995-2006) of geosynchronous electron integral flux (E > 2.0 MeV) from the GOES satellites, we see that much of the diurnal variation in electron phase space density at constant energy can be removed by the transformation to phase space density at constant ? (4000 MeV/G). This allows us a clearer picture of underlying nonadiabatic electron population changes due to geomagnetic activity. Using scaled phase space density, we calculate the percentage of geomagnetic storms resulting in an increase, decrease, or no change in geosynchronous electrons as 38%, 7%, and 55%, respectively. We also show examples of changes in the electron population that may be different from the unscaled fluxes alone suggest. These examples include sudden electron enhancements during storms which appear during the peak of negative Dst for ?-scaled phase space density, contrary to the slow increase seen during the recovery phase for unscaled phase space density for the same event.

Gannon, J. L.; Elkington, S. R.; Onsager, T. G.

2012-10-01

329

An MHD Study of the Geoeffectiveness of Geomagnetic Storms  

NASA Astrophysics Data System (ADS)

In this study, we investigate how the inner magnetosphere responds to geomagnetic storm events. We do so by carrying out high-resolution global magnetohydrodynamic (MHD) simulations using solar wind and interplanetary magnetic field data from upstream spacecraft. We examine the 8 - 9 March 2008 corotating interaction region (CIR)/high-speed stream (HSS) storm event. This storm was characterized by the arrival of a density plug associated with a CIR at ~0730 UT on 8 March, followed by the commencement of the HSS at ~1830 on the same day. This was followed by another density plug at ~0140 UT the following day on 9 March. Minimum Dst occurred at ~0530 UT on 9 March. For this storm, we found that the ring current energy density in the MHD simulation responded linearly to increases in dynamic pressure during the northward IMF intervals of the CIR portion of the event, but that there was no correlation between the ring current energy density and solar wind dynamic pressure during the HSS portion of the event and during the southward IMF intervals of the CIR portion of the event. We extend this analysis to several other CME- and CIR-driven storms in order to determine the geoeffectiveness of various solar wind drivers during geomagnetic storms. We will also compare our MHD simulation results with observations from the THEMIS spacecraft in the magnetotail.

Garg, S.; Peroomian, V.; El-Alaoui, M.

2013-12-01

330

Global ionospheric dynamics and electrodynamics during geomagnetic storms (Invited)  

NASA Astrophysics Data System (ADS)

Globally distributed total electron content (TEC) data has become an important tool for exploring the consequences of storm-time electrodynamics. Magnetosphere-ionosphere coupling during the main phase is responsible for the largest ionospheric effects observed during geomagnetic storms, mediated by global scale electrodynamics. Recent research using case studies reveals a complex picture of M-I coupling and its relationship to interplanetary drivers such as the solar wind electric field. Periods of direct coupling exist where the solar wind electric field is strongly correlated with prompt penetration electric fields, observed as enhanced vertical plasma drifts or an enhanced electrojet in the daytime equatorial ionosphere. Periods of decoupling between low latitude electric fields and the solar wind electric field are also observed, but the factors distinguishing these two types of response have not been clearly identified. Recent studies during superstorms suggest a role for the transverse (y-component) of the interplanetary magnetic field, which affects magnetospheric current systems and therefore may affect M-I coupling, with significant ionospheric consequences. Observations of the global ionospheric response to a range of geomagnetic storm intensities are presented. Scientific understanding of the different factors that affect electrodynamic aspects of M-I coupling are discussed.

Mannucci, A. J.; Tsurutani, B.; Verkhoglyadova, O. P.; Komjathy, A.; Butala, M. D.

2013-12-01

331

Ionospheric modification during moderate geomagnetic storm at low solar activity  

NASA Astrophysics Data System (ADS)

In this report we present an analysis of the ionospheric response to moderate (Dst<70 nT), 11 October 2008, geomagnetic storm. TEC maps over European region were created on the base of GPS observations provided by IGS/EPN. Strong short-term positive effect was detected near noon of 11 October 2008. The TEC enhancement exceeded 100% on latitudes of 65-35N and was decreased to lower latitudes. The positive effect was associated with large scale traveling disturbance. During storm there was observed the increase and modification of horizontal gradients structure and ionospheric trough had moved to equator, until 57-58 geomagnetic latitudes. The electron density profiles, retrieved from the Formosat-3/COSMIC radio occultation measurements and also measurements from European ionospheric sounding stations (DIAS), were analyzed within the case-study to estimate the altitudinal modification of the ionosphere. The considerable enhancement of the peak electron density was observed in European region during 11-15 UT, it reached the factor of 2.8 in comparison with quiet conditions. The height of the ionospheric F2 layer was risen by 60 km. For graphical demonstration of the observed ionospheric effects global electron density maps were calculated on the base of globally distributed COSMIC RO profiles. Electron density maps for different altitude slices were analyzed. This positive effect was revealed distinctly in RO electron density profiles and products based on these data - ionospheric electron content and global maps of electron density.

Krankowski, A.; Shagimuratov, I.; Zakharenkova, I.; Krypiak-Gregorczyk, A.

2010-12-01

332

Experimental Data Demonstrating Augmentation of Ambient Gravitational and Geomagnetic Fields  

NASA Astrophysics Data System (ADS)

Despite significant documentation and rigorously controlled conditions, most research involving extraordinary human-generated phenomena (e.g. remote viewing, teleportation, etc.) has focused either upon the observation of the macro-phenomena itself, or cumulative statistical deviation from chance. This paper, however, examines the influences upon and augmentation of ambient gravitational and geomagnetic fields, a previously unobserved and unrecognized concomitant physics phenomenon during activities requiring singular and total concentration. Utilizing simple field measurement instrumentation, original experimental data is presented, discussed, and compared with controlled baselines. Whereas some previous research has examined the influence of ambient fields upon human subjects, published literature is sparse concerning the influence of human subjects specifically upon ambient fields. As well, research that rigorously pursued the study of the effects of indirect human interference on engineering instrumentation did not consider ambient fields for experimental control, perhaps limiting potential theoretical modeling and integration. The presented empirical data demonstrates that gravitational and geomagnetic field augmentation occurring during such all-consuming activity is neither incidental nor subtle and may well be a worthy consideration for modeling frontier scientific theories and expanding current physics paradigms. Insomuch as natural, human-generated phenomena currently stand as the most accessible and repeatable examples of anomalous environmental interactivity, this data and suggested research protocols presented offer exploratory perspectives for observing the underlying scientific principals and physics concepts of ambient field interface as well as potential applications in developing more effective theoretical models for frontier space science.

Graham, Danielle

2006-01-01

333

Thermosphere-ionosphere coupling in response to recurrent geomagnetic activity  

NASA Astrophysics Data System (ADS)

The paper presents the global thermosphere-ionosphere response to the high-speed solar wind streams and the subsequent recurrent geomagnetic variations with a period of 9 d during the period of time 1 October 2007-31 March 2009. The COSMIC electron density at fixed heights, as well as the ionospheric parameters foF2 and hmF2, and the two coefficients characterizing the top and bottom side vertical gradients of the electron density profile, are used for investigating the ionospheric 9-d (s=0) wave response. The SABER temperature data are utilized for studying the response of the lower thermosphere to the recurrent auroral heating. The COSMIC and SABER measurements are analyzed by one and the same method where the atmospheric tides and planetary waves which are present in the temperature and electron density measurements are simultaneously extracted from the data. The use of such data analysis approach brings to light additional features of the ionospheric response to a recurrent geomagnetic activity which have not been found before.

Mukhtarov, Plamen; Pancheva, Dora

2012-12-01

334

Ionospheric Effects Observed by Radio Tomography during Severe Geomagnetic Storms  

NASA Astrophysics Data System (ADS)

The geomagnetic storms are an important element of space weather. As known, the distributions of all ionospheric parameters are determined by the interplay of many complex diverse processes of solar-terrestrial coupling. The intervals of geomagnetic storms are marked by dramatic changes in the dynamics of the ionosphere, whose parameters experience significant disturbances. The ionospheric signatures of geomagnetic perturbations are highly diverse in both spatiotemporal scales, ranging from a few seconds to few days and from a few meters to dozen thousand kilometers, and intensity. The methods of GNSS-based radio tomography (RT) are suitable for diagnosing the spatiotemporal structure of ionospheric disturbances caused by different space-weather factors. GNSS comprise the first-generation satellite navigation systems such as low-orbiting (LO) Russian Tsikada and American Transit satellites and second-generation satellite systems such as high-orbiting GPS and GLONASS constellations. The LORT methods reconstruct two-dimensional (2D) structure of the ionospheric electron density distribution in the vertical (altitude-latitude) plane within a spatial sector spanning a few thousand km and a time interval of 10-15 min. The horizontal and vertical resolution of LORT is typically 15-25 km and 25-30 km, respectively. The HORT methods use radio transmissions from HO satellites recorded at the receiving ground network of the International Geodetic Service (IGS), which currently comprises about 2000 receivers. The HORT methods are capable of reconstructing the four-dimensional (4D) (three spatial coordinates and time) structure of the ionosphere. Generally, HORT has a spatial resolution of 100 km at best and a time step of 60-20 min. In the regions covered by dense receiving networks (e.g., in Europe, Alaska, USA), the resolution can be improved to 30-50 and the time step reduced to 30-10 min. The resolution of 10-30 km in space and up to 2 min in time is only achievable in Japan and California, where the receiving networks are very dense. We present the results of HORT and LORT imaging of the ionosphere during the periods of geomagnetic storms of 2003-2013 in different regions of the world -- in the European part of Russia and North America. Different factors acting during the storm time make the ionosphere complexly structured. Radio tomography reveals multi-extremal distributions of the ionospheric plasma with the spots of enhanced ionization, wall-like steep gradients of electron concentration; a complex structure of the ionization trough with the polar wall shifted equatorwards is observed. Many reconstructions show various wavelike structures, travelling ionospheric disturbances, wave effects caused by corpuscular emissions, etc. We demonstrate the comparisons of radio tomography with the ionosonde measurements. In contrast to the ionosondes, which use short radio waves, the RT methods are suitable for diagnosing the ionosphere even during the periods of strong geomagnetic storms, since absorption can typically be neglected in the RT problems due to the high frequencies used. The work was supported by the Russian Foundation for Basic Research (grants 14-05-00855 and 13-05-01122). We are grateful to the North-West Research Associates (NWRA) for providing the experimental relative TEC data from the RT system in Alaska.

Andreeva, Elena S.; Kunitsyn, Vyacheslav E.; Tereshchenko, Evgeniy D.; Nazarenko, Marina O.; Nesterov, Ivan A.; Tumanova, Yuila S.

2014-05-01

335

The quiet geomagnetic field at geosynchronous orbit and its dependence on solar wind dynamic pressure  

NASA Astrophysics Data System (ADS)

Vector magnetic fields at geosynchronous orbit were measured during 1980-1984 using the operational GOES 2, GOES 5, and GOES 6 spacecraft magnetometers. These spacecraft measurements are corrected for offsets due to spacecraft state, and these field estimates were used to create a data base with 1-min resolution. Hourly quiet field values were calculated for these years from this data base using the ground-based geomagnetic index criteria AE less than 120 nT and absolute value of Dst less than 20 nT. These quiet field components, rotated into dipole HVD coordinates, were approximated by the first two coefficients of a two-dimensional Fourier series in time of day and season. The quiet geosynchronous field components, to first order, are given by mean values of about 90 nT, -60 nT, and 5 nT; and sinusoidal diurnal amplitudes of about 21 nT, 5 nT, and 5 nT, respectively, for H, V, and D where the spacecraft magnetometer was located near the geomagnetic meridian. The second harmonic diurnal amplitudes and the first and second harmonic seasonal amplitudes are typically of the order of a few nanoteslas or less except for the D component, which exhibits a larger seasonal variation. The H component of the quiet field increased 4.6 nT from 80.2 to 84.8 nT in its mean amplitude, and 20.8 nT from 11.9 to 32.7 nT in its first harmonic amplitude for Pd increasing from 0.71 x 10 exp -8 to 3.31 x 10 exp -8 dyn/sq cm. These quiet H measurements, including the pressure dependence, are compared with a first-order field model (Mead, 1964) superimposed with a tail current, resulting in magnetospheric currents (magnetopause and tail) in agreement with previous model values. The measured field pressure dependence and the Mead model suggest a tail current dependence on pressure.

Rufenach, Clifford L.; Schaper, Justin; McPherron, Robert L.

1992-01-01

336

Short Antimicrobial Lipo-?/?-AA Hybrid Peptides.  

PubMed

The last two decades have seen the rise of antimicrobial peptides (AMPs) to combat emerging antibiotic resistance. Herein we report the solid-phase synthesis of short lipidated ?/?-AA hybrid peptides. This family of lipo-chimeric peptidomimetics displays potent and broad-spectrum antimicrobial activity against a range of multi-drug resistant Gram-positive and Gram-negative bacteria. These lipo-?/?-AA hybrid peptides also demonstrate high biological specificity, with no hemolytic activity towards red blood cells. Fluorescence microscopy suggests that these lipo-?/?-AA chimeric peptides can mimic the mode of action of AMPs and kill bacterial pathogens via membrane disintegration. As the composition of these chimeric peptides is simple, therapeutic development could be economically feasible and amenable for a variety of antimicrobial applications. PMID:25169879

Li, Yaqiong; Smith, Christina; Wu, Haifan; Teng, Peng; Shi, Yan; Padhee, Shruti; Jones, Torey; Nguyen, Anh-My; Cao, Chuanhai; Yin, Hang; Cai, Jianfeng

2014-10-13

337

Compass roses on the Book of Navigation ( Kitab-? Bahriye): Declination data source for geomagnetic field models  

NASA Astrophysics Data System (ADS)

The Earth is surrounded by a geomagnetic field that is generated by dynamo processes in the core like a gigantic magnet. The Earth's geomagnetic field shifts with time and location. There has been a comprehensive effort for modelling the geomagnetic field of the Earth at regional and global scales by several researchers in the recent decades. The magnetic data from historical sources have a great importance in geomagnetic field modelling. The declination was the first measured geomagnetic field element with the early use of compasses for navigation. In this study the declination values estimated from compass roses drawn on the Book of Navigation ( Kitab-? Bahriye) that are georeferenced by an artificial neural network are compared to the declination values based on the geomagnetic field models CALS3K.3 and SCHA.DIF.3K. The results show that the compass roses drawn on the portolan charts of Kitab-? Bahriye can be used as declination data sources for regional or global geomagnetic field models.

Yilmaz, Ibrahim; Gullu, Mevlut; Yilmaz, Mustafa; Dereli, Mehmet A.

2010-10-01

338

Effect of geomagnetic disturbances on physiological parameters: An investigation on aviators  

NASA Astrophysics Data System (ADS)

Over the last years the potential effect that the geomagnetic activity may have on human physiological parameters (such as heart rate, arterial diastolic and systolic pressure) is being widely investigated with irrefutable results. As it is suggested, human health can be affected by solar activity and related geophysical changes. In this study a group of 4018 Slovak aviators was examined from January 1, 1994 to December 31, 2002, covering periods with high solar and geomagnetic activity. Specifically, medical data of mean values of arterial diastolic and systolic blood pressure, which were registered during the medical examinations of the Slovak aviators, were related to daily variations of Dst and Ap geomagnetic indices. All subjects were men (from 18 to 60 years old) in good health. Statistical significance levels (p-values) of the effect of geomagnetic activity on the aforementioned parameters up to three days before and three days after the geomagnetic event were established using the statistical method ANalysis Of VAriance (ANOVA). Statistical analysis of the arterial blood pressure variations for different levels of geomagnetic activity revealed that geomagnetic changes are connected to variations of the human physiological parameters.

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

2011-11-01

339

Observations on the Late Holocene Dynamics of the Boreal Geomagnetic Field From Ellesmere Island Lake Sediments  

NASA Astrophysics Data System (ADS)

The geomagnetic field of the Arctic is complex, poorly understood and a key component of the global system. A prominent feature of the Boreal geomagnetic field is the accelerated motion of the North Magnetic Pole (NMP) away from North America having moved more than 1600 km in the last century. Here we present sediment paleomagnetic observations from Ellesmere Island lakes, calibrated by 400-year historic geomagnetic record, that allow us to constrain polar motion and begin to assess the geomagnetic dynamics that drive these changes over the last several thousand years. Our primary data sets are derived from two Ellesmere Island lakes (Sawtooth Lake, 79.21 N, 83.56 W and Lower Murray Lake, 81.34 N, 69.54 W) that preserve strong, stable, single component remanent magnetizations and possess independently derived varve based chronologies. U-channel paleomagnetic data obtained from multiple cores taken from each lake allow the development of composite directional secular variation and relative paleointensity records. These observations are supported by paleomagnetic data from other Canadian Arctic Archipelago lakes that lack either independent age control or replicate-coring. These data demonstrate that the Arctic geomagnetic field over the late Holocene is dominated by the same complex boundary conditions that influence the historic record including intensity variations of the high latitude flux patches and the westward drift of the polar geomagnetic vortex. The ongoing motion of the NMP appears to reflect the continuation of a millennial scale Late Holocene oscillation that is part of a significant geomagnetic change.

Stoner, J. S.; Davies, M. H.; Bradley, R. S.; Cook, T. L.; Francus, P.; Besonen, M. R.; Channell, J. E.; St-Onge, G.

2009-05-01

340

Relationships of high-latitude geomagnetic variations to interplanetary plasma conditions  

SciTech Connect

As an extension of the United States program at South Pole Station to study in detail the southern magnetospheric cusp region, the authors have initiated geomagnetic studies at Iqaluit (formerly Frobisher Bay), Baffin Island, Northwest Territories, Canada. This location is approximately geomagnetically conjugate to South Pole Station under quiet geomagnetic conditions. Both sites are just inside the equatorward boundary of the dayside magnetospheric cusps in their respective hemispheres. This research includes studies of the conjugacy of geometric activity at these high latitudes, studies of the conditions under which conjugacy breaks down, and the relationship of geomagnetic variations to energy sources in the interplanetary plasma. In both hemispheres, variations in the magnetic field are measured with fluxgate magnetometers over the range from 0.0 to approximately 0.5 hertz. The field variations are measured in three orthogonal components: Geomagnetic north-south (H-component), geomagnetic east-west (D-component), and vertical (V-component). The magnetic field data are analyzed using a number of statistical techniques, including power spectra analysis. Presented here are the results of a study of hourly power spectra computed for the the H-component magnetic field data acquired at both South Pole and Iqaluit for the 30-day interval 17 July to 15 August 1985. After computing the spectra, the geomagnetic power is calculated over several different bandwidths corresponding, roughly, to frequencies related to hydromagnetic waves in the Earth's magnetosphere.

Wolfe, A. (City Univ. of New York, Brooklyn (USA) AT T Bell Laboratories, Murray Hill, NJ (USA)); Lanzerotti, L.J.; Maclennan, C.G.; Medford, L.V. (AT T Bell Laboratories, Murray Hill, NJ (USA))

1987-01-01

341

The response of European Daphnia magna Straus and Australian Daphnia carinata King to changes in geomagnetic field.  

PubMed

This study investigates the effects of lifelong exposure to reversed geomagnetic and zero geomagnetic fields (the latter means absence of geomagnetic field) on the life history of Daphnia carinata King from Australia and Daphnia magna Straus from Europe. Considerable deviation in the geomagnetic field from the usual strength, leads to a decrease in daphnia size and life span. Reduced brood sizes and increased body length of neonates are observed in D. magna exposed to unusual magnetic background. The most apparent effects are induced by zero geomagnetic field in both species of Daphnia. A delay in the first reproduction in zero geomagnetic field is observed only in D. magna. No adaptive maternal effects to reversed geomagnetic field are found in a line of D. magna maintained in these magnetic conditions for eight generations. Integrally, the responses of D. magna to unusual geomagnetic conditions are more extensive than that in D. carinata. We suggest that the mechanism of the effects of geomagnetic field reversal on Daphnia may be related to differences in the pattern of distribution of the particles that have a magnetic moment, or to moving charged organic molecules owing to a change in combined outcome and orientation of the geomagnetic field and Earth's gravitational field. The possibility of modulation of self-oscillating processes with changes in geomagnetic field is also discussed. PMID:23320498

Krylov, Viacheslav V; Bolotovskaya, Irina V; Osipova, Elena A

2013-03-01

342

Healthy Eating Index and Alternate Healthy Eating Index among Haitian Americans and African Americans with and without Type 2 Diabetes  

PubMed Central

Ethnicities within Black populations have not been distinguished in most nutrition studies. We sought to examine dietary differences between African Americans (AA) and Haitian Americans (HA) with and without type 2 diabetes using the Healthy Eating Index, 2005 (HEI-05), and the Alternate Healthy Eating Index (AHEI). The design was cross-sectional N = 471 (225 AA, 246 HA) and recruitment was by community outreach. The eating indices were calculated from data collected with the Harvard food-frequency questionnaire. African Americans had lower HEI-05 scores ? = ?10.9 (?8.67, 13.1); SE = 1.12, P < .001 than HA. Haitian American females and AA males had higher AHEI than AA females and HA males, respectively, (P = .006) adjusting for age and education. Participants with diabetes had higher adherence to the HEI-05 ? = 3.90 (1.78, 6.01), SE = 1.08, P < .001 and lower adherence to the AHEI ? = ?9.73 (16.3, ?3.19), SE = 3.33, P = .004, than participants without diabetes. The findings underscore the importance of disaggregating ethnicities and disease state when assessing diet. PMID:22187639

Huffman, Fatma G.; De La Cera, Maurcio; Vaccaro, Joan A.; Zarini, Gustavo G.; Exebio, Joel; Gundupalli, Deva; Shaban, Lamya

2011-01-01

343

Features of Men with Anabolic-Androgenic Steroid Dependence: A Comparison With Nondependent AAS Users and With AAS Nonusers  

PubMed Central

Background Anabolic-androgenic steroid (AAS) dependence has been a recognized syndrome for some 20 years, but remains poorly understood. Methods We evaluated three groups of experienced male weightlifters: 1) men reporting no history of AAS use (N = 72); 2) nondependent AAS users reporting no history of AAS dependence (N = 42); and 3) men meeting adapted DSM-IV criteria for current or past AAS dependence (N = 20). We assessed demographic indices, lifetime history of psychiatric disorders by the Structured Clinical Interview for DSM-IV, variables related to AAS use, and results from drug tests of urine and hair. Results Nondependent AAS users showed no significant differences from AAS nonusers on any variable assessed. Dependent AAS users, however, differed substantially from both other groups on many measures. Notably, they reported a more frequent history of conduct disorder than nondependent AAS users (odds ratio [95% CI]: 8.0 [1.7, 38.0]) or AAS nonusers (13.1 [2.8, 60.4]) and a much higher lifetime prevalence of opioid abuse and dependence than either comparison group (odds ratios 6.3 [1.2, 34.5] and 18.6 [3.0, 116.8], respectively). Conclusions Men with AAS dependence, unlike nondependent AAS users or AAS nonusers, showed a distinctive pattern of comorbid psychopathology, overlapping with that of individuals with other forms of substance dependence. AAS dependence showed a particularly strong association with opioid dependence – an observation that recalls recent animal data suggesting similarities in AAS and opioid brain reward mechanisms. Individuals with AAS dependence and individuals with “classical” substance dependence may possibly harbor similar underlying biological and neuropsychological vulnerabilities. PMID:19339124

Kanayama, Gen; Hudson, James I.; Pope, Harrison G.

2009-01-01

344

Propagation of low frequency geomagnetic field fluctuations in Antarctica: comparison between two polar cap stations  

NASA Astrophysics Data System (ADS)

We conduct a statistical analysis of the coherence and phase difference of low frequency geomagnetic fluctuations between two Antarctic stations, Mario Zucchelli Station (geographic coordinates: 74.7° S, 164.1° E; corrected geomagnetic coordinates: 80.0° S, 307.7° E) and Scott Base (geographic coordinates: 77.8° S 166.8° E; corrected geomagnetic coordinates: 80.0° S 326.5° E), both located in the polar cap. Due to the relative position of the stations, whose displacement is essentially along a geomagnetic parallel, the phase difference analysis allows to determine the direction of azimuthal propagation of geomagnetic fluctuations. The results show that coherent fluctuations are essentially detectable around local geomagnetic midnight and, in a minor extent, around noon; moreover, the phase difference reverses in the night time hours, indicating a propagation direction away from midnight, and also around local geomagnetic noon, indicating a propagation direction away from the subsolar point. The nigh time phase reversal is more clear for southward interplanetary magnetic field conditions, suggesting a relation with substorm activity. The introduction, in this analysis, of the Interplanetary Magnetic Field conditions, gave interesting results, indicating a relation with substorm activity during nighttime hours. We also conducted a study of three individual pulsation events in order to find a correspondence with the statistical behaviour. In particular, a peculiar event, characterized by quiet magnetospheric and northward interplanetary magnetic field conditions, shows a clear example of waves propagating away from the local geomagnetic noon; two more events, occurring during southward interplanetary magnetic field conditions, in one case even during a moderate storm, show waves propagating away from the local geomagnetic midnight.

Santarelli, L.; Lepidi, S.; Cafarella, L.

2007-11-01

345

The PC index: method of calculation and physical sense  

NASA Astrophysics Data System (ADS)

The PC index has been introduced [Troshichev and Andrezen, 1985; Troshichev et al., 1988] to characterize magnetic activity in the polar caps generated by the solar wind coupling with the magnetosphere. The concept of the antisunward convection within the polar cap, controlled by the interplanetary electric field EKL determined by Kan and Lee (1979), served as a basis for the method of the index calculation. Value of disturbances in the polar cap geomagnetic H and D (or X and Y) components form the basis for derivation of the PC index. The technique of PC index derivation consists of two separate procedures: (1) derivation of the statistically justified regression coefficients determining relationship between the coupling function EKL and vector of polar cap magnetic disturbance ?F, and (2) calculation of PC indices by data on current ?F values with use of the regression coefficients established in course of the first procedure. To exclude from examination the geomagnetic field changes unrelated to the solar wind variations the value of geomagnetic disturbance is calculated in reference to the quiet daily variation. The regression coefficients ? (slope) and ? (intersection) describing a linear link between values ?F and EKL are calculated in combination with the optimal angle ? providing the highest correlation between ?F and EKL. Parameters ?, ? and ? are derived based on the statistically justified sets of data. As a result the PC index corresponding to the value of coupling function EKL, irrespective of UT time, season and point of observation is determined. Validation of the PC proper derivation has been testified by the following requirements imposed on the calculated PCN and PCS indices: PCN and PCS indices should be consistent with the interplanetary electric field EKL; PCN and PCS indices should be in close agreement with each other irrespective of season and UT time; indices should not demonstrate seasonal variation; indices should not demonstrate regular daily variation (i.e. dependence on UT-time). By its derivation, the PC index is regarded as a proxy of the interplanetary electric field EKL affecting the magnetosphere in course of constant solar wind - magnetosphere coupling.

Janzhura, A.; Troshichev, O.

2012-04-01

346

Inversion of geo-magnetic full-tensor gradiometer data  

NASA Astrophysics Data System (ADS)

The fast and sensitive SQUID (Superconducting Quantum Interference Device) system, which was developed at IPHT Jena, allows the geo-magnetic prospection of large land areas. The system's simultaneous high-resolution recording of all components of the Earth's magnetic field gradient tensor represents a high-quality data base for precise inversion calculations. Thus, we developed a software tool for the fast and direct inversion of full-tensor data from especially dipole-like sources. Our motivation is to localize buried magnetic objects and inhomogeneities in the underground only by measuring the gradient components at the surface. The application of the algorithm will be shown by two examples, first on a synthetic data set and second on a real data set measured at the IPHT test site with well-defined buried targets.

Schneider, M.; Stolz, R.; Linzen, S.; Schiffler, M.; Chwala, A.; Schulz, M.; Dunkel, S.; Meyer, H.-G.

2013-05-01

347

Aeromagnetic survey over U.S. to advance geomagnetic research  

NASA Astrophysics Data System (ADS)

A proposed high-altitude survey of the United States offers an exciting and cost effective opportunity to collect magnetic-anomaly data. Lockheed Martin Missile and Space Company is considering funding a reimbursable ER-2 aircraft (Figure 1) mission to collect synthetic aperture radar (SAR) imagery at an altitude of about 21 km over the conterminous United States and Alaska. The collection of total and vector magnetic field data would be a secondary objective of the flight. Through this “piggyback approach,” the geomagnetic community would inherit invaluable magnetic data at a nominal cost. These data would provide insight on fundamental tectonic and thermal processes and give a new view of the structural and lithologic framework of the crust and upper mantle.

Hildenbrand, Thomas G.; Blakely, Richard J.; Hinze, William J.; Keller, G. Randy; Langel, Robert A.; Nabighian, Misac; Roest, Walter

348

A compressed marine data set for geomagnetic field modeling  

NASA Technical Reports Server (NTRS)

Some 13 million scalar magnetic field data points that have been collected from the world's ocean areas reside in the collection of the National Geophysical Data Center. In order to derive a suitable data set for modeling the geomagnetic field of the earth, each ship track is divided into 220 km segments. The distribution of the reduced data in position, time and local time is discussed. The along-track filtering process described has proved to be an effective method of condensing large numbers of shipborne magnetic data into a manageable and meaningful data set for field modeling. This process also provides the benefits of smoothing short-wavelength crystal anomalies, discarding data recorded during magnetically noisy periods, and assigning reasonable error estimates to be utilized in the least squares modeling.

Langel, R. A.; Baldwin, R. T.; Ridgway, J. R.; Davis, W. Minor

1990-01-01

349

Effects of dipole tilt angle on geomagnetic activity  

NASA Astrophysics Data System (ADS)

The relationship between the orientation of the interplanetary magnetic field (IMF), represented by the clock angle which is the angle defined by IMF-By and -Bz components, and the AL and AU indices is examined at various dipole tilt angles for the period of 1978-1988. We use the IMF data obtained from the IMP 8 satellite, AL and AU indices with corrected seasonal variations, and the dipole tilt angle, which is the dipole magnetic latitude of the subsolar point calculated as a function of the day of year and universal time. For both positive (dipole tilted to the Sun) and negative dipole tilt angles, the values of |AL| and AU decrease as the IMF clock angle moves away from 180?, becoming more northward. The indices also tend to become smaller for larger dipole tilt angle, either toward or away from the Sun. This dependence on dipole tilt angle enhances the semiannual variation of geomagnetic activity.

Nowada, M.; Shue, J.-H.; Russell, C. T.

2009-09-01

350

Geomagnetically trapped light isotopes observed with the detector NINA  

NASA Astrophysics Data System (ADS)

The detector New Instrument for Nuclear Analysis (NINA) aboard the satellite Resurs-01-N4 detected hydrogen and helium isotopes geomagnetically trapped, while crossing the South Atlantic Anomaly. Deuterium and tritium at L shell < 1.2 were unambiguously recognized. The 3He and 4He power law spectra, reconstructed at L shell = 1.2 and B < 0.22 G, have indices equal to 2.30 +/- 0.08 in the energy range 12-50 MeV nucleon-1 and 3.4 +/- 0.2 in 10-30 MeV nucleon-1, respectively. The measured 3He/4He ratio and the reconstructed deuterium profile as a function of L shell bring one to the conclusion that the main source of radiation belt light isotopes at Resurs altitudes (~800 km) and for energy greater than 10 MeV nucleon-1 is the interaction of trapped protons with residual atmospheric helium.

Bakaldin, A.; Galper, A.; Koldashov, S.; Korotkov, M.; Leonov, A.; Mikhailov, V.; Murashov, A.; Voronov, S.; Bidoli, V.; Casolino, M.; De Pascale, M.; Furano, G.; Iannucci, A.; Morselli, A.; Picozza, P.; Sparvoli, R.; Boezio, M.; Bonvicini, V.; Cirami, R.; Vacchi, A.; Zampa, N.; Ambriola, M.; Bellotti, R.; Cafagna, F.; Ciacio, F.; Circella, M.; De Marzo, C.; Adriani, O.; Papini, P.; Spillantini, P.; Straulino, S.; Vannuccini, E.; Ricci, M.; Castellini, G.

2002-08-01

351

Observations of geomagnetically trapped light isotopes by NINA  

NASA Astrophysics Data System (ADS)

The detector NINA aboard the satellite Resurs-01N4 detected hydrogen and helium isotopes geomagnetically trapped, while crossing the South Atlantic Anomaly. Deuterium and tritium at L-shell<1.2 were unambiguously recognized. The 3 He and 4 He power-law spectra, reconstructed at L-shell=1.2 and B<0.22 G, have indices equal to 2.30±0.08 in the energy range 12-50 MeV/n, and 3.4±0.2 in 10-40 MeV/n respectively. The measured 3 He/4 He ratio bring to the conclusion that the main source of radiation belt light isotopes is the interaction of trapped protons with residual atmospheric helium.

Bakaldin, A.; Galper, A.; Koldashov, S.; Korotkov, M.; Leonov, A.; Mikhailov, V.; Murashov, A.; Voronov, S.; Bidoli, V.; Casolino, M.; De Pascale, M.; Furano, G.; Iannucci, A.; Morselli, A.; Picozza, P.; Sparvoli, R.; Boezio, M.; Bonvicini, V.; Cirami, R.; Vacci, A.; Zampa, N.; Ambriola, M.; Bellotti, R.; sCafagna, F.; Ciacio, F.; Circella, M.; De Marzo, C.; Adriani, O.; Papini, P.; Spillantini, P.; Straulino, S.; Vannuccini, E.; Bartalucci, S.; Ricci, M.; Castellini, G.; Wizard-NINA Collaboration

2001-08-01

352

Attitude dynamics and control of spacecraft using geomagnetic Lorentz force  

E-print Network

The attitude stabilization of a charged rigid spacecraft in Low Earth Orbit (LEO) using torques due to Lorentz force in pitch and roll directions is considered. A spacecraft that generates an electrostatic charge on its surface in the Earth magnetic field will be subject to perturbations from Lorentz force. The Lorentz force acting on an electrostatically charged spacecraft may provide a useful thrust for controlling a spacecraft's orientation. We assume that the spacecraft is moving in the Earth's magnetic field in an elliptical orbit under the effects of the gravitational, geomagnetic and Lorentz torques. The magnetic field of the Earth is modeled as a non-tilted dipole. A model incorporating all Lorentz torques as a function of orbital elements has been developed on the basis of electric and magnetic fields. The stability of the spacecraft orientation is investigated both analytically and numerically. The existence and stability of equilibrium positions is investigated for different values of the charge to...

Abdel-Aziz, Yehia A

2014-01-01

353

[Biotropic effects of geomagnetic storms and their seasonal variations].  

PubMed

A substantial effect of geomagnetic storms on human health with a confidential probability P = 0.95 was revealed. The quantitative estimates of the biotropic effect are presented. For example, the frequency of occurrence of bursts exceeding the average number of hospitalized patients with mental and cardiovascular diseases during magnetic storms increases approximately 2 times compared with quiet periods (based on the data on 1983-84). The frequency of occurrence of myocardial infarction, angina pectoris, violation of cardial rhythm, acute violation of brain blood circulation during storms increases 2.1; 1.6; 1.6; 1.5 times, respectively compared with magnetically quiet periods (based on the data of 1992-96). A similarity of the seasonal distribution of the magnitude of the biotropic effect is revealed in the case of myocardial infarction and the number of magnetic storms: a maximum in the equinox and a minimum in summer. PMID:11605400

Kuleshova, V P; Pulinets, S A; Sazanova, E A; Kharchenko, A M

2001-01-01

354

Study of Ring Current Dynamics During Geomagnetic Storms  

NASA Technical Reports Server (NTRS)

This research program considered modeling the dynamical evolution of the ring current during several geomagnetic storms. The first year (6/01/1997-5/31/1998) of this successful collaborative research between the University of New Hampshire (UNH) and the University of California Los Angeles (UCLA) was supported by NASA grant NAG5-4680. The second and third years (6/01/1998-5/31/2000) were funded at UNH under NASA grant NAG5-7368. Research work at UNH concentrated on further development of a kinetic model to treat all of the important physical processes that affect the ring current ion population during storm conditions. This model was applied to simulate ring current development during several International Solar-Terrestrial Physics (ISTP) events, and the results were directly compared to satellite observations. A brief description of our major accomplishments and a list of the publications and presentations resulting from this effort are given.

Jordanova, Vania K.

2000-01-01

355

Two successful geomagnetic-field-line tracing experiments.  

NASA Technical Reports Server (NTRS)

Two field-line tracing experiments were conducted on an L = 1.26 magnetic flux tube over Kauai, Hawaii. Barium vapor was created by the detonation of a highly explosive shaped charge aligned with the geomagnetic field at a 467-km altitude. Barium ions traveled along the field line to the conjugate ionosphere in a tube 3 to 5 km in diameter, producing a visible streak along the entire 6900-km path length. Electric fields perpendicular to the magnetic field caused the ions to drift away from the true conjugate during transit, but extrapolation from subsequent ion drift rates allowed the conjugate to be identified and compared with several field models. Differing ion drift rates and directions at the conjugate points indicated that the electric field is not transferred unattenuated along field lines.

Wescott, E. M.; Nielsen, H. C. S.; Murcray, W. B.; Davis, T. N.; Peek, H. M.; Jensen, R. J.

1972-01-01

356

An experimental evaluation of autonomous underwater vehicle localization on geomagnetic map  

NASA Astrophysics Data System (ADS)

This letter reports an experimental evaluation of a three-axis magnetometer into an inertial navigation system (INS) for underwater localization. The magnetometer measurements of geomagnetic field are compared with map values to provide position updates to the INS. The concept of such navigation system is not new but lacks test verification and actual application. We examine the capabilities of the integrated navigation by using a localization algorithm based on the interval knowledge of geomagnetic field values. The underwater experimental result indicates that the use of geomagnetic values significantly reduces the growth of position errors of an INS.

Wu, Zhitian; Hu, Xiaoping; Wu, Meiping; Mu, Hua; Cao, Juliang; Zhang, Kaidong; Tuo, Zhouhui

2013-09-01

357

On the shape of the Geomagnetic Tail at Lunar distances: Preliminary Resuts from Artemis Observations  

NASA Astrophysics Data System (ADS)

Geomagnetic tail is one of the least investigated regions of the magnetosphere behind the Earth owing to the limited number of spacecraft and observations. It is the region where the geomagnetic dipole field lines of the Earth are organized by the solar wind stretching. The characteristics of the geomagnetic tail and its response to IMF were studied by the missions, ISEE-3, IMP-8, Wind, Geotail, visited geomagnetic tail at different distances. The structure of the geomagnetic tail is controlled by the IMF orientation and its own internal dynamics. Geomagnetic tail has different regions where the plasma and magnetic field characteristics are largely depend on the IMF orientation. These characteristics show differences at different tail distances. For example it is determined that the tail twists as result of the reconnection with IMF By and this twist is higher as one move away from the Earth toward the distant tail. Like a windsock, it is expected that the IMF control will increase toward the distant tail. Twisting also displaces the north and south lobes on the dawn and dusk sides. Tail length and the shape are also different for different IMF orientations. Flattening of the geomagnetic tail cross-section occurs during the strong IMF Bys. It becomes an ellipse in the yz plane as the IMF By stress causes the tail to be flattened on the top and bottom. Models estimate that the geomagnetic tail length can be 165 Re while Pioneer spacecraft detected geomagnetic tail as long as 100 Re. These findings are based on the very limited data from brief geomagnetic tail encounters of the spacecraft. Since August 2011, with the repositioning of the two of THEMIS spacecraft pair, ARTEMIS is giving a new opportunity to study the geomagnetic tail at the lunar distances, 60 Re. Using these observations, we will investigate the geomagnetic field shape and its IMF dependence at 60 Re. Based on the magnetopause locations at 60 Re, we will study the shape of the tail on the xy-plane. Available analytical models and the numerical model results will be tested and used to find the best model at lunar distances. In this study, we will present our preliminary results and compare our findings with those from the earlier studies in the literature.

Gencturk Akay, Iklim; Kaymaz, Zerefsan; Sibeck, David G.

2013-04-01

358

Azimuthal propagation of Pc5 geomagnetic field pulsations in the southern polar cap  

Microsoft Academic Search

A statistical analysis of low frequency geomagnetic fluctuations at the two Antarctic stations Mario Zucchelli Station (geographic coordinates: 74.7°S, 164.1°E; corrected geomagnetic coordinates: 80.0°S, 306.8°E) and Dumont D’Urville (geographic coordinates: 66.7°S, 140.0°E; corrected geomagnetic coordinates: 80.4°S, 236.0°E) is shown. The analysis focuses on power spectra, coherence and phase difference between the stations, which are both located in the polar cap,

S. Lepidi; L. Cafarella; M. Pietrolungo; L. Santarelli

2011-01-01

359

Fourier power spectra of the geomagnetic field for circular paths on the Earth's surface.  

USGS Publications Warehouse

The Fourier power spectra of geomagnetic component values, synthesized from spherical harmonic models, have been computed for circular paths on the Earth's surface. They are not found to be more useful than is the spectrum of magnetic energy outside the Earth for the purpose of separating core and crustal sources of the geomagnetic field. The Fourier power spectra of N and E geomagnetic components along nearly polar great circle paths exhibit some unusual characteristics that are explained by the geometric perspective of Fourier series on spheres developed by Yee. -Authors

Alldredge, L.R.; Benton, E.R.

1986-01-01

360

Effect of geomagnetic storms on the erythrocyte sedimentation rate in ischemic patients.  

PubMed

The dynamics of the erythrocyte sedimentation rate (ESR) in patients with ischemic disease shows a significantly different pattern in the days of raised geomagnetic activity as compared to quiet days. This is revealed by a greater intensity of ESR variations during geomagnetic storms as compared to the days of when there was little or no sun activity (quiet sun). Such behavior of red blood cells reflects the patient's individual sensitivity to geomagnetic field fluctuations. This article discusses a possible mechanism of ESR variations. PMID:11321648

Gurfinkel, Y I; Voeikov, V L; Buravlyova, E V; Kondakov, S E

2001-01-01

361

Do geomagnetic storms change the behaviour of the stingless bee guiruçu ( Schwarziana quadripunctata)?  

NASA Astrophysics Data System (ADS)

Six behavioural experiments were carried out to investigate the magnetic field effects on the nest-exiting flight directions of the honeybee Schwarziana quadripunctata ( Meliponini). No significant differences resulted during six experiment days under varying geomagnetic field and the applied static inhomogeneous field (about ten times the geomagnetic field) conditions. A surprising statistically significant response was obtained on a unique magnetic storm day. The magnetic nanoparticles in these bees, revealed by ferromagnetic resonance, could be involved in the observed effect of the geomagnetic storm.

Esquivel, Darci M. S.; Wajnberg, E.; Do Nascimento, F. S.; Pinho, M. B.; de Barros, H. G. P. Lins; Eizemberg, R.

2007-02-01

362

Some properties of trans-equatorial ion whistlers observed by Isis satellites during geomagnetic storms  

NASA Technical Reports Server (NTRS)

Several ion whistlers were observed by the polar orbiting satellites, Isis, during geomagnetic storms associated with large solar flares in 1982. It seems that the proton density ratio to the total ions deduced from the crossover frequency of the transequatorial ion whistlers observed at geomagnetic low latitudes during the main phase of the geomagnetic storm on July 14, 1982 was lower than the usual density ratio. An anomalous pattern seen on the time-compressed dynamic spectra of the ion whistlers on September 6, 1982 may suggest the existence of effects by the component He(3+) in a quite small amount.

Watanabe, S.; Ondoh, T.

1986-01-01

363

Are AA Majors Right for the Community College?  

ERIC Educational Resources Information Center

The associate of arts (AA) major was implemented at Valencia Community College (VCC) in Florida as one of the goals set by an ACE-Kellogg roundtable for 1997. This degree was proposed with the intent of assisting students in making better decisions about choosing careers, majors, and courses. The AA major is equivalent to the current AA degree…

Robinson, Shawn

364

Comparison of methods for modelling geomagnetically induced currents  

NASA Astrophysics Data System (ADS)

Assessing the geomagnetic hazard to power systems requires reliable modelling of the geomagnetically induced currents (GIC) produced in the power network. This paper compares the Nodal Admittance Matrix method with the Lehtinen-Pirjola method and shows them to be mathematically equivalent. GIC calculation using the Nodal Admittance Matrix method involves three steps: (1) using the voltage sources in the lines representing the induced geoelectric field to calculate equivalent current sources and summing these to obtain the nodal current sources, (2) performing the inversion of the admittance matrix and multiplying by the nodal current sources to obtain the nodal voltages, (3) using the nodal voltages to determine the currents in the lines and in the ground connections. In the Lehtinen-Pirjola method, steps 2 and 3 of the Nodal Admittance Matrix calculation are combined into one matrix expression. This involves inversion of a more complicated matrix but yields the currents to ground directly from the nodal current sources. To calculate GIC in multiple voltage levels of a power system, it is necessary to model the connections between voltage levels, not just the transmission lines and ground connections considered in traditional GIC modelling. Where GIC flow to ground through both the high-voltage and low-voltage windings of a transformer, they share a common path through the substation grounding resistance. This has been modelled previously by including non-zero, off-diagonal elements in the earthing impedance matrix of the Lehtinen-Pirjola method. However, this situation is more easily handled in both the Nodal Admittance Matrix method and the Lehtinen-Pirjola method by introducing a node at the neutral point.

Boteler, D. H.; Pirjola, R. J.

2014-09-01

365

Validation of the galactic cosmic ray and geomagnetic transmission models.  

PubMed

A very high-momentum resolution particle spectrometer called the Alpha Magnetic Spectrometer (AMS) was flown in the payload bay of the Space Shuttle in a 51.65 degrees x 380-km orbit during the last solar minimum. This spectrometer has provided the first high statistics data set for galactic cosmic radiation protons, and helium, as well as limited spectral data on carbon and oxygen nuclei in the International Space Station orbit. First measurements of the albedo protons at this inclination were also made. Because of the high-momentum resolution and high statistics, the data can be separated as a function of magnetic latitude. A related investigation, the balloon borne experiment with a superconducting solenoid spectrometer (BESS), has been flown from Lynn Lake, Canada and has also provided excellent high-resolution data on protons and helium. These two data sets have been used here to study the validity of two galactic cosmic ray models and the geomagnetic transmission function developed from the 1990 geomagnetic reference field model. The predictions of both the CREME96 and NASA/JSC models are in good agreement with the AMS data. The shape of the AMS measured albedo proton spectrum, up to 2 GeV, is in excellent agreement with the previous balloon and satellite observations. A new LIS spectrum was developed that is consistent with both previous and new BESS 3He observations. Because the astronaut radiation exposures onboard ISS will be highest around the time of the solar minimum, these AMS measurements and these models provide important benchmarks for future radiation studies. AMS-02 slated for launch in September 2003, will provide even better momentum resolution and higher statistics data. PMID:11855419

Badhwar, G D; Truong, A G; O'Neill, P M; Choutko, V

2001-06-01

366

Intelligent micro-spacecraft constellation for the geomagnetic storm forecasts  

NASA Astrophysics Data System (ADS)

Two micro-spacecraft constellation with solar sails partially compensating the solar gravity allow their placement in the points along the Sun-Earth line behind the standard L1 point i e further out from the Earth and closer to the Sun The distances of the placement from the Earth and the base distances between such satellites depend on the ratios of their mass to the sail area It can be selected in the way needed for the warning of the coronal mass ejection arrival several or many hours before the upcoming geomagnetic storm Measurements of the magnetic field vector are necessary and sufficient for this purpose on each spacecraft No plasma measurements are needed for this purpose which makes the weight of spacecraft minimal The sail can be used also as a solar panel an antenna oriented on the Earth for the radio transmission and device for obtaining a stable mechanical orientation of the spacecraft axis along the Sun-Earth line Time delays and known base distances between satellites allow the solar wind velocity measurements with a sufficient accuracy for the warning of the coronal mass ejection arrival to the Earth Sky maps obtained with micro photo cameras and processed on board can give the accurate spacecraft orientation needed for the determination of the crucial quantity magnetic field vector orientation Together with measured magnetic field strength and the solar wind velocity on can obtain information for the robust forecast of geomagnetic storms The key element of the project is the intelligent on board programming needed for

Veselovsky, I.; Yakovchouk, O.

367

2013 Geomagnetic Storm Observations in the Arctic and Antarctic  

NASA Astrophysics Data System (ADS)

During recent 2013 geomagnetic storms, several tongue of ionization (TOI) events have been observed with polar maps of total electron content (TEC) derived from the global network of GNSS receivers. The TOI plasma originates from plasma that has been transported from the mid-latitudes by a feature known as storm enhanced density (SED). The SED plasma separates from the base of the enhanced mid-latitude ionosphere in the afternoon-dusk sector, and forms a plume that carries the plasma westward to the noon-time cusp. The TOI, as observed by GNSS, extends through the dayside cusp, across the polar cap to the night side, in both hemispheres. The TOI is a source of ionospheric irregularities and its distribution across the high latitude ionosphere is controlled by plasma convection. Here, TOI observations are shown using GNSS TEC polar plots overlaid onto SuperDARN HF radar observations of the high-latitude convection pattern. The locations where HF scatter is observed in the presence of TOI plumes are examined. In addition, we overlay observations of scintillation collected by specially equipped GNSS receivers. We explore the similarities between TOI events observed simultaneously in the two hemispheres and examine the time history of the gradients and irregularities. Finally, we report on cases where the position of the SED base stays fixed in latitude and longitude as the earth rotates. This observation is shown below in Figure 1 and holds true in both hemispheres. We correlate these observations to changes in the IMF geomagnetic field. Illustration of fixed position of SED base in March 17, 2013 storm in Northern and Southern Hemispheres.

Coster, A. J.; Thomas, E. G.; Baker, J. B.; Ruohoniemi, J.; Erickson, P. J.; Foster, J. C.

2013-12-01

368

Geospace environment modeling 2008--2009 challenge: Dst index  

USGS Publications Warehouse

This paper reports the metrics-based results of the Dst index part of the 2008–2009 GEM Metrics Challenge. The 2008–2009 GEM Metrics Challenge asked modelers to submit results for four geomagnetic storm events and five different types of observations that can be modeled by statistical, climatological or physics-based models of the magnetosphere-ionosphere system. We present the results of 30 model settings that were run at the Community Coordinated Modeling Center and at the institutions of various modelers for these events. To measure the performance of each of the models against the observations, we use comparisons of 1?hour averaged model data with the Dst index issued by the World Data Center for Geomagnetism, Kyoto, Japan, and direct comparison of 1?minute model data with the 1?minute Dst index calculated by the United States Geological Survey. The latter index can be used to calculate spectral variability of model outputs in comparison to the index. We find that model rankings vary widely by skill score used. None of the models consistently perform best for all events. We find that empirical models perform well in general. Magnetohydrodynamics-based models of the global magnetosphere with inner magnetosphere physics (ring current model) included and stand-alone ring current models with properly defined boundary conditions perform well and are able to match or surpass results from empirical models. Unlike in similar studies, the statistical models used in this study found their challenge in the weakest events rather than the strongest events.

Rastätter, L.; Kuznetsova, M.M.; Glocer, A.; Welling, D.; Meng, X.; Raeder, J.; Wittberger, M.; Jordanova, V.K.; Yu, Y.; Zaharia, S.; Weigel, R.S.; Sazykin, S.; Boynton, R.; Wei, H.; Eccles, V.; Horton, W.; Mays, M.L.; Gannon, J.

2013-01-01

369

Cormic Index Profile of Children with Sickle Cell Anaemia in Lagos, Nigeria  

PubMed Central

Background. Sickle cell disorders are known to have a negative effect on linear growth. This could potentially affect proportional growth and, hence, Cormic Index. Objective. To determine the Cormic Index in the sickle cell anaemia population in Lagos. Methodology. A consecutive sample of 100 children with haemoglobin genotype SS, aged eight months to 15 years, and 100 age and sex matched controls (haemoglobin genotype AA) was studied. Sitting height (upper segment) and full length or height were measured. Sitting height was then expressed as a percentage of full length/height (Cormic Index). Results. The mean Cormic Index decreased with age among primary subjects (SS) and AA controls. The overall mean Cormic Index among primary subjects was comparable to that of controls (55.0 ± 4.6% versus 54.5 ± 5.2%; 54.8 ± 4.5% versus 53.6 ± 4.9%) in boys and girls, respectively. In comparison with AA controls, female children with sickle cell anaemia who were older than 10 years had a significantly lower mean Cormic Index. Conclusion. There was a significant negative relationship between Cormic Index and height in subjects and controls irrespective of gender. Similarly, a significant negative correlation existed between age, sitting height, subischial leg length, weight, and Cormic Index in both subjects and controls. PMID:24864202

Akodu, Samuel Olufemi; Njokanma, Olisamedua Fidelis; Kehinde, Omolara Adeolu

2014-01-01

370

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

371

Systemic AA amyloidosis: epidemiology, diagnosis, and management  

PubMed Central

The term “amyloidosis” encompasses the heterogeneous group of diseases caused by the extracellular deposition of autologous fibrillar proteins. The global incidence of amyloidosis is estimated at five to nine cases per million patient-years. While amyloid light-chain (AL) amyloidosis is more frequent in developed countries, amyloid A (AA) amyloidosis is more common in some European regions and in developing countries. The spectrum of AA amyloidosis has changed in recent decades owing to: an increase in the median age at diagnosis; a percent increase in the frequency of primary AL amyloidosis with respect to the AA type; and a substantial change in the epidemiology of the underlying diseases. Diagnosis of amyloidosis is based on clinical organ involvement and histological evidence of amyloid deposits. Among the many tinctorial characteristics of amyloid deposits, avidity for Congo red and metachromatic birefringence under unidirectional polarized light remain the gold standard. Once the initial diagnosis has been made, the amyloid subtype must be identified and systemic organ involvement evaluated. In this sense, the 123I-labeled serum amyloid P component scintigraphy is a safe and noninvasive technique that has revolutionized the diagnosis and monitoring of treatment in systemic amyloidosis. It can successfully identify anatomical patterns of amyloid deposition throughout the body and enables not only an initial estimation of prognosis, but also the monitoring of the course of the disease and the response to treatment. Given the etiologic diversity of AA amyloidosis, common therapeutic strategies are scarce. All treatment options should be based upon a greater control of the underlying disease, adequate organ support, and treatment of symptoms. Nevertheless, novel therapeutic strategies targeting the formation of amyloid fibrils and amyloid deposition may generate new expectations for patients with AA amyloidosis. PMID:25378951

Real de Asua, Diego; Costa, Ramon; Galvan, Jose Maria; Filigheddu, Maria Teresa; Trujillo, Davinia; Cadinanos, Julen

2014-01-01

372

Nucleic acid indexing  

DOEpatents

A restriction site indexing method for selectively amplifying any fragment generated by a Class II restriction enzyme includes adaptors specific to fragment ends containing adaptor indexing sequences complementary to fragment indexing sequences near the termini of fragments generated by Class II enzyme cleavage. A method for combinatorial indexing facilitates amplification of restriction fragments whose sequence is not known.

Guilfoyle, Richard A. (Madison, WI); Guo, Zhen (Bellevue, WA)

2001-01-01

373

Nucleic acid indexing  

DOEpatents

A restriction site indexing method for selectively amplifying any fragment generated by a Class II restriction enzyme includes adaptors specific to fragment ends containing adaptor indexing sequences complementary to fragment indexing sequences near the termini of fragments generated by Class II enzyme cleavage. A method for combinatorial indexing facilitates amplification of restriction fragments whose sequence is not known.

Guilfoyle, Richard A. (Madison, WI); Guo, Zhen (Bellevue, WA)

1999-01-01

374

Lobby index in networks  

NASA Astrophysics Data System (ADS)

We propose a new node centrality measure in networks, the lobby index, which is inspired by Hirsch’s h-index. It is shown that in scale-free networks with exponent ? the distribution of the l-index has power tail with exponent ?(?+1). Properties of the l-index and extensions are discussed.

Korn, A.; Schubert, A.; Telcs, A.

2009-06-01

375

KSC Construction Cost Index  

NASA Technical Reports Server (NTRS)

Kennedy Space Center cost Index aids in conceptual design cost estimates. Report discusses development of KSC Cost Index since January 1974. Index since January 1974. Index provides management, design engineers, and estimators an up-to-data reference for local labor and material process. Also provides mount and rate of change in these costs used to predict future construction costs.

Brown, J. A.

1983-01-01

376

Evaluation of solar wind-magnetosphere coupling functions during geomagnetic storms with the WINDMI model  

NASA Astrophysics Data System (ADS)

We evaluate the performance of three solar wind-magnetosphere coupling functions in training the physics-based WINDMI model on the 3-7 October 2000 geomagnetic storm and predicting the geomagnetic Dst and AL indices during the 15-24 April 2002 geomagnetic storm. The rectified solar wind electric field, a coupling function by Siscoe, and a recent formula proposed by Newell are evaluated. The Newell coupling function performed best in both the training and prediction phases for Dst prediction. The Siscoe formula performed best during the training phase in reproducing the AL faithfully and capturing storm time events. The rectified driver was discovered to be the best in overall performance during both training as well as prediction phases, even though the other two coupling functions outperform it in the training phase. The results indicate that multiple drivers need to be concurrently employed in space weather models to yield different possible levels of geomagnetic activity.

Spencer, E.; Rao, A.; Horton, W.; Mays, M. L.

2009-02-01

377

Forecasts of geomagnetic activity by Ottawa Magnetic Observatory: Their reliabilty and application  

NASA Technical Reports Server (NTRS)

A 27 day forecast of geomagnetic activity based on the forecasts from two locations is presented. To evaluate the reliability of the forecasts, the predicted activity was compared with the actual geomagnetic activity at five geomagnetic observatories located in different magnetic zones: Ottawa (57.0N, 351.5E); Meanook (61.8N, 301.0E); Fort Churchill (68.8N, 322.5E); Cambridge Bay (76.7N, 294.0E); and Resolute Bay (83.1N, 287.7E). Results indicate that the percentage of correct predictions varies with the geomagnetic latitude of the observatory used for comparison. The percentage is on the average highest for lower latitude stations and lowest for the northern stations. The number of incorrect predictions ranges from 4.7% for Ottawa to 8.4% for Churchill.

Hruska, J.

1979-01-01

378

INTERNATIONAL JOURNAL OF GEOMAGNETISM AND AERONOMY VOL. 3, NO. 2, PAGES 109116, DECEMBER 2002  

E-print Network

INTERNATIONAL JOURNAL OF GEOMAGNETISM AND AERONOMY VOL. 3, NO. 2, PAGES 109­116, DECEMBER 2002 balance. More specifically, the magnetopause is located at a distance where the planetary magnetic field

Demoulin, Pascal

379

Preliminary analyses of solar flare effects on geomagnetic H component at equatorial and low latitudes  

NASA Astrophysics Data System (ADS)

The study of solar flare effect (SFE) on geomagnetic H component at mid latitudes was carried out using data from INTERMAGNET website. M and X solar flare effects on three stations, Addis Ababa (AAE), Bangui (BNG), and Tamanrasset (TAM) were investigated. It was found that the ratio is greater than zero for all the three stations used, hence SFE enhances geomagnetic field in the equatorial and low latitudes. It was equally noted that the SFE on geomagnetic field is not just a simple augmentation at the pre-flare ionospheric currents over these stations. It is concluded that both pre-flare and solar flare amplitude variations of H are high in low and equatorial stations. Keywords: Solar flare, geomagnetic component, latitudes.

Ugonabo, Obiageli Josephine; Ugwu, Ernest Benjamin Ikechukwu; Nneka Okeke, Francisca

380

A revised corrected geomagnetic coordinate system for Epochs 1985 and 1990  

NASA Astrophysics Data System (ADS)

A new set of corrected geomagnetic coordinates (CGM) has been calculated from the magnetic field model DGRF for Epoch 1985 and the IGRF model for Epoch 1990. A new approach to determine the 'dip' magnetic equator has been developed, which is based on the vertical (along Re) projection on the earth's surface of the B-minimum value point (apex) on each geomagnetic field line. A strip along the 'dip' magnetic equator line has been defined where the corrected geomagnetic coordinates could not be found by the definition of CGM. Linear interpolation between the locations of the two last definable CGM latitudes in both hemispheres has been used to calculate the CGM longitudes in the equatorial region. Interpolation between locations of the last definable CGM latitude and 'dip' equator in both hemispheres has been used to calculate the CGM latitudes in this region. The constant B-min geomagnetic coordinate system (CBM) is proposed and analyzed to replace CGM in the equatorial region.

Gustafsson, G.; Papitashvili, N. E.; Papitashvili, V. O.

1992-12-01

381

Experimental evidence in support of Joule heating associated with geomagnetic activity  

NASA Technical Reports Server (NTRS)

High resolution accelerometer measurements in the altitude region 140 to 300 km from a satellite in a near-polar orbit during a period of extremely high geomagnetic activity indicate that Joule heating is the primary source of energy for atmospheric heating associated with geomagnetic activity. This conclusion is supported by the following observational evidence: (1) There is an atmospheric response in the auroral zone which is nearly simulataneous with the onset of geomagnetic activity, with no significant response in the equatorial region until several hours later; (2) The maximum heating occurs at geographic locations near the maximum current of the auroral electrojet; and (3) There is evidence of atmospheric waves originating near the auroral zone at altitudes where Joule heating would be expected to occur. An analysis of atmospheric response time to this heat shows time delays are apparently independent of altitude but are strongly dependent upon geomagnetic latitude.

Devries, L. L.

1971-01-01

382

Airborne Geomagnetic Investigations at the Haughton Impact Structure, Devon Island, Nunavut, Canada  

NASA Technical Reports Server (NTRS)

This investigation created a broad magnetic map of the 23 Ma Haughton impact structure, in order to characterize its geomagnetic signature. Additional information is contained in the original extended abstract.

Glass, B. J.; Lee, P.

2001-01-01

383

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

USGS Publications Warehouse

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

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

1997-01-01

384

Geomagnetic sudden impulses and storm sudden commencements - A note on terminology  

SciTech Connect

The definitions of and distinctions between storm sudden commencements (SSCs) and geomagnetic sudden impulses (SIs) are examined and present definitions of SIs and SSCs are modernized. Quantitative definitions of the two terms are recommended. 45 refs.

Joselyn, J.A.; Tsurutani, B.T. (NOAA, Space Environment Laboratory, Boulder, CO (United States) JPL, Pasadena, CA (United States))

1990-11-01

385

Solar and geomagnetic activity in cycle 24 and its place in recent history (Invited)  

NASA Astrophysics Data System (ADS)

Multipoint spacecraft observations currently provide unprecedented observations of solar activity and its interplanetary consequences. The solar wind has been continuously measured through the course of cycle 24 ahead of Earth's magnetosphere. Analysis of solar, interplanetary and geomagnetic measurements reveal that, since the last deep and long-lasting solar activity minimum around 2009, the average plasma and magnetic field properties of CMEs, ICMEs and also those of quasi steady-state solar wind flows showed had intensities. As a consequence the level of geomagnetic activity has, after ten previous cycles, been as low as in early 1900. This presentation presents a review of solar and geomagnetic storms in this ongoing cycle 24 and identifies from comparison with previous sunspot and geomagnetic activity records its general place in the history of cycles. Beyond that, implications are drawn for the activity levels to be expected at times of the Solar Probe Plus and Solar Orbiter missions.

Bothmer, V.

2013-12-01

386

Assessing the importance and expression of the 6 year geomagnetic oscillation  

NASA Astrophysics Data System (ADS)

The first time derivative of residual length-of-day observations is known to contain a distinctive 6 year periodic oscillation. Here we theorize that through the flow accelerations at the top of the core the same periodicity should arise in the geomagnetic secular acceleration. We use the secular acceleration of the CHAOS-3 and CM4 geomagnetic field models to recover frequency spectra through both a traditional Fourier analysis and an empirical mode decomposition. We identify the 6 year periodic signal in the geomagnetic secular acceleration and characterize its spatial behavior. This signal seems to be closely related to recent geomagnetic jerks. We also identify a 2.5 year periodic signal in CHAOS-3 with unknown origin. This signal is strictly axially dipolar and is absent from other magnetic or geodetic time series.

Silva, L.; Jackson, L.; Mound, J.

2012-10-01

387

Supplemental summary of cutoff rigidities calculated using the international geomagnetic reference field for various epochs  

Microsoft Academic Search

Tables of cosmic-ray cutoff rigidities using the trajectory-tracing technique are given for three epochs of the geomagnetic field. These values have been determined utilizing the International Geomagnetic Reference Field with time derivatives applied so that the coefficients for the field model are appropriate for the following epochs: 1965.0, 1970.0, and 1975.0. Each table includes the geographic coordinates and L value

M. A. Shea; D. F. Smart

1983-01-01

388

Geomagnetic responses in high latitudes during the storm of july 15—16, 2000  

Microsoft Academic Search

The ionospheric equivalent currents in the high latitudes and the auroral electrojet system during the geomagnetic storm on\\u000a July 15–16, 2000 are analyzed by using geomagnetic data from IMAGE chain. The large-scale vortices of equivalent currents\\u000a are observed in the storm. The vortices on the dusk side of ionosphere correspond to four-celled pattern of plasma convection\\u000a associated with NBZ, region

Gengxiong Chen; Aimin Du; Wenyao Xu; Hongfei Chen; Minghua Hong; Fenglin Peng; Enqi Shi

2002-01-01

389

Space weather effects on Earth's environment associated to the 24-25 October 2011 geomagnetic storm  

NASA Astrophysics Data System (ADS)

Space weather studies have increased due to human society dependence on spaceborne and terrestrial infrastructure vulnerable to its effects. In this paper, we present an interdisciplinary study of the effects of solar activity on the Earth's environment; specifically, we focus on the effects on the ionosphere and the geomagnetic field. A timeline of effects occurring on the Earth produced by one of the first relevant events of the present solar cycle (24-25 October 2011) is given. We have analyzed the solar wind shockwave from satellite data, the storm-time development, the ionospheric effects at global and local scales using the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model fed with geomagnetic field-aligned current data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment, and ground ionosonde data from both hemispheres, at Ebre Observatory and Port Stanley locations. We have compared observed geomagnetic variations at high latitudes with those modeled by the National Center for Atmospheric Research Thermosphere-Ionosphere-Electrodynamics General Circulation Model. We have analyzed rapid geomagnetic variations (e.g., solar flare effect, storm commencement, Pi2) also on both hemispheres, at Ebre Observatory and Livingston Island locations. Finally, we have estimated geoelectric field and geomagnetically induced currents in the northeast of Spain (Catalonia) produced by this geomagnetic disturbance.

Blanch, E.; Marsal, S.; Segarra, A.; Torta, J. M.; Altadill, D.; Curto, J. J.

2013-04-01

390

Azimuthal propagation of Pc5 geomagnetic field pulsations in the southern polar cap  

NASA Astrophysics Data System (ADS)

A statistical analysis of low frequency geomagnetic fluctuations at the two Antarctic stations Mario Zucchelli Station (geographic coordinates: 74.7°S, 164.1°E; corrected geomagnetic coordinates: 80.0°S, 306.8°E) and Dumont D’Urville (geographic coordinates: 66.7°S, 140.0°E; corrected geomagnetic coordinates: 80.4°S, 236.0°E) is shown. The analysis focuses on power spectra, coherence and phase difference between the stations, which are both located in the polar cap, with a 5-h magnetic local time displacement along a geomagnetic parallel; in this situation, the phase difference between geomagnetic fluctuations indicates the direction of their azimuthal propagation. Coherent fluctuations have been found to occur preferably when both stations are on the same side (dawnward or duskward) with respect to the polar cusp; moreover, around local magnetic midnight, they occur essentially during open magnetospheric conditions. The phase difference for coherent fluctuations indicates a propagation direction away from local geomagnetic noon and midnight. Also the analysis of three individual pulsation events, occurring at different times during the day, is shown; they are characterized at the two stations by simultaneous, coherent fluctuations, whose phase difference finds correspondence with the statistical behaviour.

Lepidi, S.; Cafarella, L.; Pietrolungo, M.; Santarelli, L.

2011-03-01

391

Reduction of the field-aligned potential drop in the polar cap during large geomagnetic storms  

NASA Astrophysics Data System (ADS)

We have studied photoelectron flows and the inferred field-aligned potential drop in the polar cap during 5 large geomagnetic storms that occurred in the periods when the photoelectron observations in the polar cap were available near the apogee of the FAST satellite (~4000 km) at solar maximum, and the footprint of the satellite paths in the polar cap was under sunlit conditions most of the time. In contrast to the ~20 V potential drop during geomagnetically quiet periods at solar maximum identified by Kitamura et al. [JGR, 2012], the field-aligned potential drop frequently became smaller than ~5 V during the main and early recovery phases of the large geomagnetic storms. Because the potential acts to inhibit photoelectron escape, this result indicates that the corresponding acceleration of ions by the field-aligned potential drop in the polar cap and the lobe region is smaller during the main and early recovery phases of large geomagnetic storms compared to during geomagnetically quiet periods. Under small field-aligned current conditions, the number flux of outflowing ions should be nearly equal to the net escaping electron number flux. Since ions with large flux originating from the cusp/cleft ionosphere convect into the polar cap during geomagnetic storms [e.g., Kitamura et al., JGR, 2010], the net escaping electron number flux should increase to balance the enhanced ion outflows. The magnitude of the field-aligned potential drop would be reduced to let a larger fraction of photoelectrons escape.

Kitamura, N.; Seki, K.; Nishimura, Y.; Hori, T.; Terada, N.; Ono, T.; Strangeway, R. J.

2013-12-01

392

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

393

Superposed epoch analysis of the dayside ionospheric response to four intense geomagnetic storms  

NASA Astrophysics Data System (ADS)

Prompt daytime ionospheric responses are presented for the following four intense geomagnetic storms: 29 October 2003, 30 October 2003, 20 November 2003, and 7 November 2004. We perform a superposed epoch analysis of the storms by defining the start time of the epoch when the Kan-Lee interplanetary electric field (proportional to the reconnection electric field) first reaches 10 mV/m during a period of continuously southward Bz. Measurements from the GPS receiver onboard the CHAMP satellite at 400 km altitude indicate significant low- to middle-latitude daytime total electron content (TEC) increases above the satellite within 1-2 h of the defined start time for three of the storms (˜1400 local solar time). The 20 November 2003 data follow a different pattern: the largest TEC increases appear several hours (˜5-7) following the interplanetary magnetic field Bz event onset. TEC data obtained from ground-based GPS receivers for the November 2003 storm tend to confirm a "late" TEC increase for this storm at ˜1400 LT. Estimates of vertical plasma uplift near the equator at Jicamarca longitudes (˜281 E) using the dual-magnetometer technique suggest that variability of the timing of the TEC response is associated with variability in the prompt penetration of electric fields to low latitudes. It is also found that for the November 2003 magnetic storm the cross-correlation function between the SYM-H index and the interplanetary electric field reached maximum correlation with a lag time of 4 h. Such a large lag time has never been noted before. The long delays of both the ionosphere and magnetosphere responses need to be better understood.

Mannucci, A. J.; Tsurutani, B. T.; Abdu, M. A.; Gonzalez, W. D.; Komjathy, A.; Echer, E.; Iijima, B. A.; Crowley, G.; Anderson, D.

2008-03-01

394

High-resolution empirical geomagnetic field model TS07D: Present status and outlook  

NASA Astrophysics Data System (ADS)

Increasing sophistication of space weather modeling and forecasting tools requires further increase of spatial and temporal resolution of the empirical geomagnetic field models. A key limitation of the latter models, arising from their pre-defined modular structure, has been overcome in the model TS07D (http://geomag_field.jhuapl.edu/model/). The new model employs for the first time the expansion of the magnetic field of equatorial currents into a series of basis functions without any a priori assumptions on their evolution in time. The latter is reconstructed by fitting the instantaneous set of the model parameters with a subset of the whole database of the available magnetic field data, so-called nearest neighbors (NN), when the global state of the magnetosphere was close to the considered one in the space of the global parameters. These include the average solar wind electric field parameter vBz, Sym-H index, and its time derivative. The model also explicitly takes into account variations of the tilt angle and the solar wind ram pressure. TS07D has been successfully validated for a number of in-sample modeling cases, when the considered event (a magnetic storm) was also a part of the NN subset. Further verification of the model and the development of its forecasting versions require also out-of-sample validation tests. We present some of such tests, including THEMIS observations of the March 2008 storm. Comparison between the model and observations made by five THEMIS probes shows excellent agreement on storm scales. Moreover, every deviation arising during a substorm reveals characteristic signatures of the tail current sheet thinning and dipolarization, suggesting that TS07D can be used as a base-line model for investigations of storm-time substorms. Further development of the model, including the improvement of its field-aligned component, fully-forecasting modes, and the use of the global plasma pressure data derived from ENA imaging, will also be discussed.

Tsyganenko, N. A.; Sitnov, M. I.; Ukhorskiy, A. Y.; Brandt, P. C.; Anderson, B. J.; Lui, A.

2009-12-01

395

The orientation and current density of the magnetotail current sheet: A statistical study of the effect of geomagnetic conditions  

NASA Astrophysics Data System (ADS)

We examine the orientation and current density of the current sheet during current sheet crossings from Cluster's 2001-2007 tail seasons. The curlometer technique is used to estimate the current density and is combined with Minimum Variance Analysis (MVA) to calculate the direction of the current sheet normal. The SYM-H and AE indices at the time of each crossing are employed to assess how the tilt angle (the angle the normal makes with the Z axis in the GSM YZ plane) and current density depend on geomagnetic conditions. Our results indicate a larger current sheet tilt in the YZ plane during intervals of stronger and/or more prolonged substorm activity, as indicated by the AE index. There is also evidence that when the ring current is enhanced during magnetic storms, the current sheet is less tilted even though the AE index is also disturbed. In addition larger current densities are seen during times of both magnetic storms and substorms, compared to crossings during only substorms and a quiet ring current. We conclude that increased substorm activity disrupts the current sheet structure resulting in greater motion of the current sheet (as found by Davey et al. (2012)) and a greater local tilt to the current sheet. We propose that the increased open flux in the tail during magnetic storms stabilizes the current sheet such that the tilt angle of the current sheet is reduced. The increased amount of open flux during magnetic storms also results in larger current densities within the current sheet.

Davey, E. A.; Lester, M.; Milan, S. E.; Fear, R. C.; Forsyth, C.

2012-07-01

396

The role of geomagnetic observatory data during the Swarm mission  

NASA Astrophysics Data System (ADS)

The scientific use of Swarm magnetic data and Swarm-derived products is greatly enhanced through combination with observatory data and indices. The strength of observatory data is their long-term accuracy, with great care being taken to ensure temperature control and correction, platform stability and magnetic cleanliness at each site. Observatory data are being distributed with Swarm data as an auxiliary product. We describe the preparation of the data set of ground observatory hourly mean values, including procedures to check and select observatory data spanning the modern magnetic survey satellite era. Existing collaborations, such as INTERMAGNET and the World Data Centres for Geomagnetism, are proving invaluable for this. We also discuss how observatory measurements are being used to ground-truth Swarm data as part of the Calibration/Validation effort. Recent efforts to improve the coverage and timeliness of observatory data have been encouraged and now over 60 INTERMAGNET observatories and several other high-quality observatories are providing close-to-definitive data within 3 months of measurement. During the Calibration/Validation period these data are gathered and homogenised on a regular basis by BGS. We then identify measurements collected during overhead passes of the Swarm satellites. For each pass, we remove an estimate of the main field from both the data collected at altitude and that collected on the ground. Both sets of data are then normalised relative to the data variance during all passes in the Calibration/Validation period. The absolute differences of the two sets of normalised data can be used as a metric of satellite data quality relative to observatory data quality. This can be examined by universal time, local time, disturbance level and geomagnetic latitude, for example. A preliminary study of CHAMP data, using definitive minute mean observatory data, has shown how this approach can provide a baseline for detecting abnormalities at all local times and at different disturbance levels. Though it is difficult to predict how quasi-definitive data might affect the analysis, we present the results obtained for each Swarm satellite and compare these results with those found for CHAMP.

Ridley, Victoria; Macmillan, Susan; Beggan, Ciaran

2014-05-01

397

Low frequency 1\\/f-like fluctuations of the AE-index as a possible manifestation of self-organized criticality in the magnetosphere  

Microsoft Academic Search

Low frequency stochastic variations of the geomagnetic AE-index characterized by 1\\/f b-like power spectrum (where f is a frequency) are studied. Based on the analysis of experimental data we show that the Bz- component of IMF, velocity of solar wind plasma, and the coupling function of Akasofu are insuÅcient factors to explain these behaviors of the AE-index together with the

V. M. Uritsky; M. I. Pudovkin

1998-01-01

398

Low frequency 1\\/f -like fluctuations of the AE-index as a possible manifestation of self-organized criticality in the magnetosphere  

Microsoft Academic Search

Low frequency stochastic variations of the geomagnetic AE-index characterized by 1\\/fb-like power spectrum (where f is a frequency) are studied. Based on the analysis of experimental data we show that the Bz-component of IMF, velocity of solar wind plasma, and the coupling function of Akasofu are insufficient factors to explain these behaviors of the AE-index together with the 1\\/fb fluctuations

V. M. Uritsky; M. I. Pudovkin

1998-01-01

399

CENDI Indexing Workshop  

NASA Technical Reports Server (NTRS)

The CENDI Indexing Workshop held at NASA Headquarters, Two Independence Square, 300 E Street, Washington, DC, on September 21-22, 1994 focused on the following topics: machine aided indexing, indexing quality, an indexing pilot project, the MedIndEx Prototype, Department of Energy/Office of Scientific and Technical Information indexing activities, high-tech coding structures, category indexing schemes, and the Government Information Locator Service. This publication consists mostly of viewgraphs related to the above noted topics. In an appendix is a description of the Government Information Locator Service.

1994-01-01

400

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

401

Data Behind the Figures in AAS Journals  

NASA Astrophysics Data System (ADS)

Substantial amounts of digital data are produced in the scientific enterprise, and much of it is carefully analyzed and processed. Often resulting from a good deal of intellectual effort, many of these highly-processed products are published in the scholarly literature. Many of these data - or more precisely, representations of these data - are committed to the scholarly record in the forms of figures and tables that appear within articles: the AAS journals publish more than 30,000 figures and nearly 10,000 tables each year. For more than a decade, the AAS journals have accepted machine-readable tables that provide the data behind (some of) the tables, and recently the journals have started to encourage the submission of the data behind figures. (See the related poster by Greg Schwarz.) During this time, the journals have been refining techniques for acquiring and managing the digital data that underlie figures and tables. In 2012 the AAS was awarded a grant by the US NSF so that the journals can extend the methods for providing access to these data objects, through a deeper collaboration with the VO and with organizations like DataCite, and by spearheading discussions about the formats and metadata that will best facilitate long-term data management and access. An important component of these activities is educating scientists about the importance and benefits of making such data sets available.

Biemesderfer, Chris

2013-01-01

402

Ascorbic acid (AA) metabolism in protection against radiation damage  

SciTech Connect

The possibility is considered that AA protects tissues against radiation damage by scavenging free radicals that result from radiolysis of water. A physiologic buffer (pH 6.7) was incubated with /sup 14/C-AA and 1 mM thiourea (to slow spontaneous oxidation of AA). Aliquots were assayed by HPLC and scintillation spectrometry to identify the /sup 14/C-label. Samples exposed to Cobalt-60 radiation had a half time of AA decay of < 3 minutes compared with nonirradiated samples (t/sub 1/2/ > 30 minutes) indicating that AA scavenges radiation-induced free radicals and forms the ascorbate free radical (AFR). Pairs of /sup 14/C-AFR disproportionate, with the net effect of /sup 14/C-dehydroascorbic acid formation from /sup 14/C-AA. Having established that AFR result from ionizing radiation in an aqueous solution, the possibility was evaluated that a tissue factor reduces AFR. Cortical tissue from the kidneys of male rats was minced, homogenized in buffer and centrifuged at 8000 xg. The supernatant was found to slow the rate of radiation-induced AA degradation by > 90% when incubated at 23/sup 0/C in the presence of 15 ..mu..M /sup 14/C-AA. Samples of supernatant maintained at 100/sup 0/C for 10 minutes or precipitated with 5% PCA did not prevent radiation-induced AA degradation. AA may have a specific role in scavenging free radicals generated by ionizing radiation and thereby protect body tissues.

Rose, R.C.; Koch, M.J.

1986-03-05

403

Modeling the effects of secular variation of geomagnetic field orientation on the ionospheric long term trend over the past century  

Microsoft Academic Search

A middle- and low-latitude ionospheric theoretical model is used for the first time to assess the effects of the secular variations of geomagnetic field orientation on ionospheric long-term trends over the past century. It is found that the varied geomagnetic field can produce ionospheric long-term trends in both foF2 and hmF2. Since the amplitudes of geomagnetic field change depend on

Xinan Yue; Libo Liu; Weixing Wan; Yong Wei; Zhipeng Ren

2008-01-01

404

Scripted Finite Element Methods Applied to Global Geomagnetic Induction  

NASA Astrophysics Data System (ADS)

Magnetic field observations from CHAMP, Ø rsted and SAC-C and improved techniques for comprehensive geomagnetic field modeling have generated renewed interest in using satellite and observatory data to study global scale electromagnetic induction in Earth's crust and mantle. The primary external source field derives from variations in the magnetospheric ring current, and recent studies show that over-simplified assumptions about its spatial structure lead to biased estimates of the frequency-dependent electromagnetic response functions generally used in inversions for mantle conductivity. The bias takes the form of local time dependence in the C- response estimates and highlights the need for flexible forward modeling tools for the global induction problem to accommodate 3D time-varying structure in both primary and induced fields. We are developing such tools using FlexPDE, a commercially available script-based finite element method (FEM) package for partial differential equations. Our strategy is to model the vector potential \\mathbf{A}, where \\mathbf{B} = \

Ribaudo, J.; Constable, C.

2007-12-01

405

Morning/Afternoon Asymmetry of Geomagnetic Fluctuations at Discrete Frequencies  

NASA Astrophysics Data System (ADS)

We conducted a worldwide analysis of geomagnetic field measurements during a period of wave activity following the intense magnetospheric perturbation occurred on March 28, 2000. The analysis revealed signals at discrete frequencies (f?1.0, 1.9, 2.3, 2.6, 3.6, 4.7 mHz) that found correspondence in enhancements, approximately at the same frequencies, in the solar wind speed and dynamic pressure, suggesting such fluctuations as an inherent property of the solar wind, possibly driving cavity/waveguide modes in the magnetosphere. The observed frequencies, basically attain the most commonly sets of discrete frequencies identified from auroral to low latitudes in previous investigations. We found a MLT dependence of the frequency power enhancements: those at f?1.9, ?2.6 and ?3.6 mHz were more prominent in the wide afternoon sector (MLT = 13:00-20:30), while those occurring at f?1.0 and ?2.3 mHz were more prominent in the morning sector (MLT = 03:30-11:30). These features possibly reflect an asymmetry of the entire magnetosphere or in the position of its internal boundaries (such as the plasmapause) in the period of interest.

Villante, U.; Del Corpo, A.; Francia, P.

2012-12-01

406

Ezekiel's vision: Visual evidence of Sterno-Etrussia geomagnetic excursion?  

NASA Astrophysics Data System (ADS)

In the Eos article,“Ezekiel and the Northern Lights: Biblical Aurora Seems Plausible” (16 April 2002), Siscoe et al. presented arguments showing that coronal auroras can occur at low latitudes under the condition of increased geomagnetic dipole field strength. From this standpoint, they give an interpretation of the “reported” Ezekiel's vision (the Bible's Book of Ezekiel in the Old Testament). The site of the Ezekiel's vision was about 100 km south of Babylon (latitude ˜32° N, longitude ˜5°E), and the date of the vision was around 593 B.C. Auroral specialists believe that Ezekiel's vision was inspired by a very strong magnetic storm accompanied by coronal auroras at low latitudes. However, as justly noted by Siscoe et al. [2002],to adopt this interpretation, several questions should be answered. Can auroras be seen at the latitude where Ezekiel reportedly was? More important, can they reach a coronal stage of development, which is what the vision requires? Was the tilt of the dipole axis favorable? Was the general level of solar activity favorable? The principal question is, no doubt, the second one.

Raspopov, Oleg M.; Dergachev, Valentin A.; Goos'kova, Elena G.

407

Altitude-adjusted corrected geomagnetic coordinates: Definition and functional approximations  

NASA Astrophysics Data System (ADS)

Analysis of the functional approximations used to transform between geographic and Altitude-Adjusted Corrected Geomagnetic (AACGM) coordinates reveals that errors of >50 km can occur in the auroral and polar regions. These errors are the result of efforts to better approximate AACGM coordinates near the magnetic equator and the South Atlantic Anomaly. In these regions AACGM coordinates are not defined and alternate coordinates have been used. This augmentation and emphasis on the solution in regions near the equator result in spherical harmonic approximating functions that are less accurate than need be in the auroral and polar regions. In response, a new set of spherical harmonic coefficients have been derived that better represent AACGM coordinates in these regions. These new AACGM coefficients are limited to below 2000 km in altitude in order to ensure accuracy. For altitudes above 2000 km, a magnetic field-line tracing solution is recommended. A software package developed to take advantage of the new AACGM coefficients provides the capability of tracing magnetic field lines at any altitude, for improved accuracy. In addition, linear interpolation between 5 year epochs is used to produce coordinates that vary smoothly over the entire period from 1965 to present. The intent of this work is to provide a more accurate procedure for determining AACGM coordinates in the auroral and polar regions for the study of magnetospheric and ionospheric processes.

Shepherd, S. G.

2014-09-01

408

Initial geomagnetic field model from Magsat vector data  

NASA Technical Reports Server (NTRS)

Magsat data from the magnetically quiet days of November 5-6, 1979, were used to derive a thirteenth degree and order spherical harmonic geomagnetic field model, MGST(6/80). The model utilized both scalar and high-accuracy vector data and fit that data with root-mean-square deviations of 8.2, 6.9, 7.6 and 7.4 nT for the scalar magnitude, B(r), B(theta), and B(phi), respectively. The model includes the three first-order coefficients of the external field. Comparison with averaged Dst indicates that zero Dst corresponds with 25 nT of horizontal field from external sources. When compared with earlier models, the earth's dipole moment continues to decrease at a rate of about 26 nT/yr. Evaluation of earlier models with Magsat data shows that the scalar field at the Magsat epoch is best predicted by the POGO(2/72) model but that the WC80, AWC/75 and IGS/75 are better for predicting vector fields.

Langel, R. A.; Mead, G. D.; Lancaster, E. R.; Estes, R. H.; Fabiano, E. B.

1980-01-01

409

The flywheel effect: Ionospheric currents after a geomagnetic storm  

SciTech Connect

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 authors investigate these flywheel' currents by simulating a storm which occurred on the 23rd of November 1982 using the National Center for Atmospheric Research Thermosphere Ionosphere General Circulation Model (NCAR-TIGCM). The resulting high-latitude, height-integrated Hall currents are dominated by the neutral-wind-driven component for several hours after the end of main phase of the storm. The direction of these currents is reversed from normal. Analysis of the neutral and ion components of this current system indicates that the neutral component may drive as much as 80% of the high-latitude current system immediately after the storm has ended, and may continue to dominate this system for 4 to 5 hours.

Deng, W.; Killeen, T.L.; Burns, A.G. (Univ. of Michigan, Ann Arbor (United States)); Roble, R.G. (National Center for Atmospheric Research, Boulder, CO (United States))

1991-10-01

410

Study of mass density enhancements at high geomagnetic latitudes  

NASA Astrophysics Data System (ADS)

We report on mass density deduced from measurements of the accelerometer onboard Gravity Recovery And Climate Experiment (GRACE) satellite. The investigated period starts from the beginning of November 2004 to the end of September 2007. In this time interval maximum mass densities (MMD) have been recorded by GRACE satellite at more than ten occasions. These MMD events are observed when the satellite is located near the auroral regions at high geomagnetic latitudes. We combine the MMD events and radio VLF signals recorded by ICE experiment onboard DEMETER satellite. We principally consider the reception onboard the DEMETER satellite of the VLF signals emitted by ground transmitters in the frequency range between 10 - 40 kHz. The VLF radio signals provide helpful information on the perturbations in the upper-atmosphere/lower-ionosphere layers. We emphasize in this work on the time delay between the observations of the MMS events onboard GRACE satellite in the polar regions and the disturbances of the VLF transmitter signals on DEMETER satellite at sub-polar regions. We discuss the origin of the MMD events by taking into consideration the particle environments in the cusps and auroral regions. Then we attempt to clarify how the maximum mass density events observed close to the polar regions progressed towards the mid-latitude regions and disturbed the detection of the VLF transmitter signals.

Boudjada, Mohammed Y.; Leitzinger, Martin; Pfleger, Martin; Sawas, Sami; Temmer, Manuela; Krauss, Sandro; Veronig, Astrid; Lammer, Helmut; Besser, Bruno

2014-05-01

411

ISEE 3 observations during the CDAW 8 intervals - Case studies of the distant geomagnetic tail covering a wide range of geomagnetic activity  

NASA Technical Reports Server (NTRS)

Observations made by the ISEE 3 spacecraft in the distant geomagnetic tail during the eight CDAW 8 intervals are discussed, along with their relation to concurrent geomagnetic activity. This extensive multiinstrument case study of distant tail data covers a wide range of geomagnetic conditions from extended intervals of magnetic quiet with isolated substorms to prolonged periods of intense disturbance. Plasmoids are observed in the distant tail following disturbance enhancements, the time of their appearance being generally consistent with disconnection from the near-earth region at the time of the enhancement. Their structure is entirely consistent with the neutral line model. However, not all enhancements in geomagnetic activity result in the observation of plasmoids. In particular, the CDAW 8 data suggest that, during extended intervals of strong activity, a continuous neutral line may reside in the near-earth tail and some disturbance enhancements may then relate to an increase in the reconnection rate at a preexisting neutral line, rather than to new neutral line and plasmoid formation.

Richardson, I. G.; Slavin, J. A.; Owen, C. J.; Cowley, S. W. H.; Galvin, A. B.; Sanderson, T. R.; Scholer, M.

1989-01-01

412

Proceedings of the XIIIth IAGA Workshop on Geomagnetic Observatory Instruments, Data Acquisition, and Processing  

USGS Publications Warehouse

The thirteenth biennial International Association of Geomagnetism and Aeronomy (IAGA) Workshop on Geomagnetic Observatory Instruments, Data Acquisition and Processing was held in the United States for the first time on June 9-18, 2008. Hosted by the U.S. Geological Survey's (USGS) Geomagnetism Program, the workshop's measurement session was held at the Boulder Observatory and the scientific session was held on the campus of the Colorado School of Mines in Golden, Colorado. More than 100 participants came from 36 countries and 6 continents. Preparation for the workshop began when the USGS Geomagnetism Program agreed, at the close of the twelfth workshop in Belsk Poland in 2006, to host the next workshop. Working under the leadership of Alan Berarducci, who served as the chairman of the local organizing committee, and Tim White, who served as co-chairman, preparations began in 2007. The Boulder Observatory was extensively renovated and additional observation piers were installed. Meeting space on the Colorado School of Mines campus was arranged, and considerable planning was devoted to managing the many large and small issues that accompany an international meeting. Without the devoted efforts of both Alan and Tim, other Geomagnetism Program staff, and our partners at the Colorado School of Mines, the workshop simply would not have occurred. We express our thanks to Jill McCarthy, the USGS Central Region Geologic Hazards Team Chief Scientist; Carol A. Finn, the Group Leader of the USGS Geomagnetism Program; the USGS International Office; and Melody Francisco of the Office of Special Programs and Continuing Education of the Colorado School of Mines. We also thank the student employees that the Geomagnetism Program has had over the years and leading up to the time of the workshop. For preparation of the proceedings, thanks go to Eddie and Tim. And, finally, we thank our sponsors, the USGS, IAGA, and the Colorado School of Mines.

Love, Jeffrey J.

2009-01-01

413

Addressing Impacts of Geomagnetic Disturbances on the North American Bulk Power System  

NASA Astrophysics Data System (ADS)

In a joint report issued in June 2010, the North American Electric Reliability Corporation (NERC) and the U.S. Department of Energy (DOE) identified geomagnetic disturbances as a high-impact, low-frequency (HILF) event risk to bulk power system reliability. The potential impact of geomagnetic disturbance events has gained renewed attention as recent studies have suggested that solar storms may be more severe and reach lower geographic latitudes than formerly expected and can affect bulk power system reliability. The most well known power system experience with geomagnetic disturbances in North America was the 13-14 March 1989 storm, which led to the collapse of the Hydro-Québec system in the early morning hours of 13 March 1989, lasting approximately 9 hours. NERC is actively addressing a range of HILF event risks to bulk power system reliability through the efforts of four of its task forces: Geomagnetic Disturbance, Spare Equipment Database, Cyber and Physical Attack, and Severe Impact Resilience. These task forces operate under the direction of three NERC committees: Planning, Operating, and Critical Infrastructure Protection. The NERC Geomagnetic Disturbance Task Force (GMDTF), which was established in September 2010, is charged with investigating the implications of geomagnetic disturbances to the reliability of bulk power systems and developing solutions to help mitigate these risks. The objective of these efforts is to develop models to better understand the nature and effects of coronal mass ejections (CMEs), the vulnerabilities of equipment, bulk power system design considerations, our ability to reduce the operational and real-time impacts of geomagnetic disturbances on the bulk power system, and restoration methods, as well as to inventory long-lead-time equipment. For more information on the current activities of the GMDTF, please visit: www.nerc.com/filez/gmdtf.html

Rollison, Eric; Moura, John; Lauby, Mark

2011-08-01

414

The changing geomagnetic field from the ionosphere to the core-mantle boundary  

NASA Astrophysics Data System (ADS)

In this study two aspects of the geomagnetic field have been investigated. The first part focuses on perturbations of the external field, as seen by the CHAMP satellite and predicted by the Thermosphere-Ionosphere Electrodynamic General Circulation Model, for the purpose of helping to separate out ionospheric sources from the ambient geomagnetic field using a physics based approach. Part two looks at variations of the internal field through an examination of the South Atlantic Anomaly. The NCAR Thermosphere-Ionosphere Electrodynamic General Circulation Model (TIE--GCM) is a self-consistent, global, atmospheric model that can be used to estimate magnetic perturbations at satellite altitude. These computed perturbations can then be compared with the magnetic vector data provided by low-earth orbiting satellites. Analogous CHAMP magnetic vector residuals were computed for these intervals using the CHAOS model to remove the core and crustal geomagnetic contributions. Under various input parameters, the TIE--GCM predictions were compared with the CHAMP residuals on an orbit by orbit basis demonstrating a reasonable agreement between the TIE--GCM estimates and the