These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
1

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

Microsoft Academic Search

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

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

1998-01-01

2

Forecasting geomagnetic activities from the Boyle Index  

NASA Astrophysics Data System (ADS)

The Boyle Index (BI), ? =10-4}( {v{2}/{km/sec) + 11.7({(B)/(nT)})sin 3}{(? /2) kV, has been successful in predicting the geomagnetic activity since its inception in October 2003. It is available in near-real-time from http://space.rice.edu/ISTP/wind.html and provides space weather predictions of geomagnetic indices (Kp, Dst and the AE) in real time through neural network algorithms. In addition, it provides free email alerts to its 700+ subscribers whenever the magnetospheric activity levels exceed certain pre-defined thresholds. We are constantly improving our algorithms, in the interest of either including more data or improving the accuracy and lead-time of forecasts. For example, with the inclusion of two more years of data (2008 and 2009) in the training, we have the advantage of modeling one of the deepest solar minimums, which has been exceptionally low in terms of the activity level. Our algorithms have been successful in capturing the effects of ``preconditioning" and the non-linearity in the solar wind parameters (for example, see figure 1). This paper presents our new attempts to include the effects of solar turbulence by incorporating the standard deviations in the solar wind parameters along with the BI, for greater the turbulence the higher the energy input into the magnetosphere as some of the previous studies have shown. Furthermore, we will also present how 3-hour averaged 1-hour sliding window scheme have improved our predictions with lead times of 3 hours or longer. Our predictions from a recent activity, 03 August 2010.

Bala, R.; Reiff, P. H.

2010-12-01

3

On the local operational geomagnetic index K calculation  

NASA Astrophysics Data System (ADS)

There is an ongoing demand for services that can provide real-time assessment of the (global and local) geomagnetic activity and identified as being of importance to the exploration geophysics, radio communications and precise position/navigation practices, space weather research and modelling, etc. Such services depend largely on the reduction of solar, geomagnetic and ionospheric observations to generate activity indices, one of the most widely used being the K index. The K index is a quasi-logarithmic index characterising the 3-hourly range in transient magnetic activity relative to the regular "quiet-day" activity for a single site location. A derivative "planetary" index (Kp), the mean standardized K index from several globally distributed stations, provides a convenient measure of the global geomagnetic activity. Computer-based derivation of K/Kp indices was a major step towards higher efficiency and lower costs. Nowadays, automated data acquisition, processing and generating the index in real time is mandatory for any reliable service. However, Kp may not be accurate enough when monitoring disturbances of smaller scale, so the local K index (derived from the nearest magnetic station/s) might be considered as the better choice. Moreover, the 3-hour time scale is much larger than the shorter characteristic time of localised ionospheric phenomena that are of particular interest to us. Our experience in developing a novel nowcast system for local operational geomagnetic index K calculation (K-LOGIC) will be presented. The system is based on a fully automated computer procedure for real-time digital magnetogram data acquisition, screening the dataset and removing the outliers, establishing the solar regular (Sr) variation of the geomagnetic field, calculating the K index, and issuing an alert if storm-level activity is indicated. This is a time-controlled (rather than event-driven) system delivering as regular output (time resolution set to 1 hour) the K value, the estimated quality flag, and eventually, an alert. The regular field variation is determined from the hourly medians of the horizontal components' values obtained during the recent magnetically-quiet days. These Sr values are subtracted from the corresponding instantaneous measurement values (in the latest 3 hours) to determine the components' ranges (maximum minus minimum). Finally, the larger of the 2 horizontal components' ranges is used to determine the K value referring to the limits-of-range-classes table for the particular observatory. A very important feature of the K nowcast system is the strict control of data input and processing, allowing for an immediate assessment of the quality of output. The key concept of the implemented quality control (QC) procedure is based on the fact that a complete and sound dataset provides the ideal platform for reliable, closest-to-definite index production. In this sense, any gap or outlier in the dataset can erode the quality of the produced output. The QC matrix takes into account both, the total length of data gaps (shorter or no gaps - the better) and the time elapsed from the latest gaps/outliers (more distant in the past - the better). As a result, a QC flag is assigned to each K nowcast value. The above-described control is of crucial importance for the nowcast system operation since it helps minimising the existing possibility of missing an event or issuing a false alert. The K-LOGIC system's operability, accuracy and precision have been tested with instantaneous measurements from the recent years. A statistical comparison between nowcast and definite index values proves that the average rms error is smaller than 1 K unit. The system is now operational at the RMI Geophysical Centre in Dourbes (50.1N, 4.6E).

Stankov, Stan; Stegen, Koen; Wautelet, Gilles; Warnant, Rene

2010-05-01

4

Method for determining the geomagnetic activity index based on wavelet packets  

NASA Astrophysics Data System (ADS)

A method for determining quiet daily variations ( Sq curve) in automatic mode and calculating the K index of geomagnetic activity based on wavelet packets has been proposed. The method makes it possible to reproduce the Bartels technique and includes the separation of geomagnetic signal informative components, determination of geomagnetic field disturbances, and the formation of quiet daily variations. The method effectiveness was proved experimentally.

Mandrikova, O. V.; Smirnov, S. E.; Solov'ev, I. S.

2012-02-01

5

Interhourly variability index of geomagnetic activity and its use in deriving the long-term variation of solar wind speed  

NASA Astrophysics Data System (ADS)

We describe the detailed derivation of the interhourly variability (IHV) index of geomagnetic activity. The IHV index for a given geomagnetic element is mechanically derived from hourly values or means as the sum of the unsigned differences between adjacent hours over a 7-hour interval centered on local midnight. The index is derived separately for stations in both hemispheres within six longitude sectors spanning the Earth using only local night hours. It is intended as a long-term index and available data allows derivation of the index back well into the 19th century. On a timescale of a 27-day Bartels rotation, IHV averages for stations with corrected geomagnetic latitude less than 55° are strongly correlated with midlatitude range indices (R2 = 0.96 for the am index since 1959; R2 = 0.95 for the aa index since 1980). We find that observed yearly averages of aa before the year 1957 are ˜3 nT too small compared to values calculated from IHV using the regression constants based on 1980-2004. We interpret this discrepancy as an indication that the calibration of the aa index is in error before 1957. There is no systematic discrepancy between observed and similarly calculated ap values back to 1932. Bartels rotation averages of IHV are also strongly correlated with solar wind parameters (R2 = 0.79 with BV2). On a timescale of a year combining the IHV index (giving BV2 with R2 = 0.93) and the recently developed interdiurnal variability (IDV) index (giving interplanetary magnetic field magnitude, B, with R2 = 0.74) allows determination of solar wind speed, V, from 1890 to present. Over the ˜120-year series, the yearly mean solar wind speed varied from a low (inferred) of 303 km/s in 1902 to a high (observed) value of 545 km/s in 2003. The calculated yearly values of the product BV using B and V separately derived from IDV and IHV agree quantitatively with (completely independent) BV values derived from the amplitude of the diurnal variation of the horizontal component in the polar caps since 1926 (and sporadically further back).

Svalgaard, Leif; Cliver, Edward W.

2007-10-01

6

A New Polar Magnetic Index of Geomagnetic Activity and its Application to Monitoring Ionospheric Parameters  

NASA Technical Reports Server (NTRS)

For improving the reliability of Space Weather prediction, we developed a new, Polar Magnetic (PM) index of geomagnetic activity, which shows high correlation with both upstream solar wind data and related events in the magnetosphere and ionosphere. Similarly to the existing polar cap PC index, the new, PM index was computed from data from two near-pole geomagnetic observatories; however, the method for computing the PM index is different. The high correlation of the PM index with both solar wind data and events in Geospace environment makes possible to improve significantly forecasting geomagnetic disturbances and such important parameters as the cross-polar-cap voltage and global Joule heating in high latitude ionosphere, which play an important role in the development of geomagnetic, ionospheric and thermospheric disturbances. We tested the PM index for 10-year period (1995-2004). The correlation between PM index and upstream solar wind data for these years is very high (the average correlation coefficient R approximately equal to 0.86). The PM index also shows the high correlation with the cross-polar-cap voltage and hemispheric Joule heating (the correlation coefficient between the actual and predicted values of these parameters is approximately 0.9), which results in significant increasing the prediction reliability of these parameters. Using the PM index of geomagnetic activity provides a significant increase in the forecasting reliability of geomagnetic disturbances and related events in Geospace environment. The PM index may be also used as an important input parameter in modeling ionospheric, magnetospheric, and thermospheric processes.

Lyatsky, Wladislaw; Khazanov, George V.

2008-01-01

7

Study of the Relationship Between Forbush Decrease and Geomagnetic Storm Events Using Dst Index.  

NASA Astrophysics Data System (ADS)

Abstract A study of the relationship between Forbush decreases (FD) and geomagnetic storms have been carried out using the Dst index. Most important space weather effects including FDs are associated with geomagnetic disturbances (storms). The rigidity cut off of cosmic rays, is related to the latitude of measurement and are affected by geomagnetic disturbances. Four (4) stations hosted by the Bartol research institute, University of Delaware provided continuous CR counts for this study. Clear signatures of Forbush decreases associated with storms happening on days of Kp >7 from 1980-1989 were examined to deduce the level of modulation of CR counts during geomagnetic storms. Enhancement of the count rates are observed during simultaneous Forbush decreases associated with large storms. FD correlated well with Dst for all of the stations with no significant difference observed with regards to rigidity. The anomalous enhancement during the simultaneous FD showed stronger association depending on rigidity and the implications of these results

Dominic, Obiegbuna; Okeke, Fransisca; Okpala, Kingsley

8

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 the 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 Solar Cycle 23 (Chertok et al. in Solar Phys. 282, 175, 2013) revealed that the summarized unsigned magnetic flux in the arcades and dimming regions at the photospheric level, ?, is significantly related to the intensity (Dst index) of geomagnetic storms. This provides the basis for the earliest diagnostics of geoefficiency of solar eruptions. In the present article, using the same data set, we find that a noticeable correlation also exists between the eruptive magnetic flux, ?, and another geomagnetic index, Ap. As the magnetic flux increases from some tens to ? 500 (in units of 1020 Mx), the geomagnetic storm intensity measured by the three-hour Ap index increases on average from Ap ? 50 to a formal upper limit of 400 (in units of 2 nT). The established relationship shows that 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.

2015-02-01

9

Signature of Hale and Gleissberg solar cycles in the geomagnetic activity  

Microsoft Academic Search

The aa index, designed to describe the geomagnetic activity at global scale, has been shown to have increased in the twentieth century by about 65%. The increase in the case of a corrected aa is about 38%, similar to the ones of the recently introduced interhour variability (IHV) and interdiurnal variability (IDV) indices of geomagnetic activity. In terms of 11-year

Crisan Demetrescu; Venera Dobrica

2008-01-01

10

INTERPRETATION OF Kp INDEX AND M-REGION GEOMAGNETIC STORMS  

Microsoft Academic Search

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

A. J. Dessler; Fejer J. A

1963-01-01

11

Periodic variation in the geomagnetic activity - A study based on the Ap index  

NASA Astrophysics Data System (ADS)

The monthly and daily samples of the Ap index for the interval from 1932 through 1982 were studied using the power spectrum technique. Results obtained for Bartel's period (about 27 days), the semiannual period, the dual-peak solar cycle distribution of geomagnetic storms, and certain other medium-scale periodicities are examined in detail. In addition, results on the cumulative occurrence number of storms per decade as a function of the Ap and Dst indices for the storm are presented.

de Gonzalez, Alicia L. C.; Gonzalez, Walter D.; Dutra, Severino L. G.; Tsurutani, Bruce T.

1993-06-01

12

Coincident 1.3-year Periodicities in the ap Geomagnetic Index and the Solar Wind  

NASA Technical Reports Server (NTRS)

Recent observations show an approximately 1.3-year period in the speed of the solar wind detected by the IMP 8 and Voyager 2 spacecraft. A similar period is also seen in the north-south (GSE) component of the magnetic field observed by IMP 8. Since both parameters are commonly used as input to models of geomagnetic activity, the 'ap' index (a measure of geomagnetic disturbance) is examined to look for this periodicity. The Lomb-Scargle periodogram method is used on the ap, plasma, and magnetic field data during the 1973-1994 time range. A dynamic FFT periodogram method is also used to analyze the ap data during this time, as well as to look for periods present between 1932 and 1972. A clear 1.3-year periodicity is present in the post-1986 data when the same period is observed in the plasma and field data. The V(2)B(zsm) and V(2)B(s) proxies for geomagnetic activity also show this periodicity. However, the southward (GSM) component of the magnetic field does not have a 1.3-year period, and neither do solar wind or ap data from 1973-1985. This demonstrates that the ap geomagnetic index can act as a proxy for solar wind periodicities at this time scale. Historic ap data are examined, and show that a similar periodicity in ap exists around 1942. Since auroral data show a 1.4-year periodicity, all these similar periods may result from a common underlying solar mechanism.

Paularena, K. I.; Szabo, A.; Richardson, J. D.

1995-01-01

13

Did Open Solar Magnetic Field Increase During The Last 100 Years? A Reanalysis of Geomagnetic Activity  

Microsoft Academic Search

Long-term geomagnetic activity presented by the aa index has been used to show that the heliospheric magnetic field has more than doubled during the last 100 years. However,\\u000a serious concern has been raised on the long-term consistency of the aa index and on the centennial rise of the solar magnetic field. Here we reanalyze geomagnetic activity during the last 100

K. Mursula; D. Martini; A. Karinen

2004-01-01

14

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

15

Response of the Geomagnetic Activity Index K p to the Interplanetary Magnetic Field  

Microsoft Academic Search

latter half of 1965 have been compared with the 3-hour Kindex. The results are consistent with those obtained by IMP I during three solar rotations in the winter of 1963-1964, indicat- ing a stability in the response of geomagnetic activity during these years near solar activity minimum. On the average an interplanetary magnetic field with a southward component is generally

Kenneth H. Schatten; John M. Wilcox

1967-01-01

16

Superposed epoch analysis and storm statistics from 25 years of the global geomagnetic disturbance index, USGS-Dst  

USGS Publications Warehouse

Statistics on geomagnetic storms with minima below -50 nanoTesla are compiled using a 25-year span of the 1-minute resolution disturbance index, U.S. Geological Survey Dst. A sudden commencement, main phase minimum, and time between the two has a magnitude of 35 nanoTesla, -100 nanoTesla, and 12 hours, respectively, at the 50th percentile level. The cumulative distribution functions for each of these features are presented. Correlation between sudden commencement magnitude and main phase magnitude is shown to be low. Small, medium, and large storm templates at the 33rd, 50th, and 90th percentile are presented and compared to real examples. In addition, the relative occurrence of rates of change in Dst are presented.

Gannon, J.L.

2012-01-01

17

Using the Low-Altitude Ion Boundary MT-Index for Calibrating the Global Geomagnetic Field Models.  

NASA Astrophysics Data System (ADS)

Low-altitude particle data can provide much information on the actual instantaneous configuration of the distant geomagnetic field. Following the ideas put forth by West et al. [1978] and by subsequent studies [Sergeev and Gvozdevsky, 1995, and references therein], we used a magnetotail stretching index (MT-index), derived from observations of energetic ion precipitation boundaries, for parameterizing the strength of the cross-tail current in a new version of the data-based magnetospheric magnetic field model. The magnetospheric vector B-field data, covering the interval from 1984 through 1999, had 5-min resolution and included observations by Polar, Geotail, ISEE-2, AMPTE/CCE/IRM, CRRES, and DE-1, complemented by concurrent interplanetary medium data from IMP-8, WIND, and ACE solar wind monitors. The low-altitude particle data, taken by DMSP satellites, covered the same period 1984-1999 and were used in the least-squares fitting algorithm in the form of concurrent values of the magnetotail stretching parameter (MT-index), calibrating the magnitude of the cross-tail current. Including the MT-associated term in the model expansions was found to significantly improve the correlation between the observed and predicted magnetic field vectors. This and other results of the present modeling effort will be discussed. West, H. I., R. M . Buck, and M. G. Kivelson, On the configuration of the magnetotail near midnight during quiet and weakly disturbed periods: magnetic field modeling, J. Geophys. Res., v.83, 3819, 1978. Sergeev, V. A., and B. B. Gvozdevsky, MT-index - a possible new index to characterize the magnetic configuration of magnetotail, Ann. Geophys., v.13, 1093, 1995.

Tsyganenko, N. A.; Sotirelis, T.

2001-12-01

18

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

19

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

20

Geomagnetic Activity Indicates Large Amplitude for Sunspot Cycle 24  

NASA Technical Reports Server (NTRS)

The level of geomagnetic activity near the time of solar activity minimum has been shown to be a reliable indicator for the amplitude of the following solar activity maximum. The geomagnetic activity index aa can be split into two components: one associated with solar flares, prominence eruptions, and coronal mass ejections which follows the solar activity cycle and a second component associated with recurrent high speed solar wind streams which is out of phase with the solar activity cycle. This second component often peaks before solar activity minimum and has been one of the most reliable indicators for the amplitude of the following maximum. The size of the recent maximum in this second component indicates that solar activity cycle 24 will be much higher than average - similar in size to cycles 21 and 22 with a peak smoothed sunspot number of 160 plus or minus 25.

Hathaway, David H.

2006-01-01

21

Geomagnetic Activity Indicates Large Amplitude for Sunspot Cycle 24  

NASA Technical Reports Server (NTRS)

The level of geomagnetic activity near the time of solar activity minimum has been shown to be a reliable indicator for the amplitude of the following solar activity maximum. The geomagnetic activity index aa can be split into two components: one associated with solar flares, prominence eruptions, and coronal mass ejections which follows the solar activity cycle and a second component associated with recurrent high speed solar wind streams which is out of phase with the solar activity cycle. This second component often peaks before solar activity minimum and has been one of the most reliable indicators for the amplitude of the following maximum. The size of the recent maximum in this second component indicates that solar activity cycle 24 will be much higher than average - similar in size to cycles 21 and 22.

Hathaway, D. H.; Wilson, R. M.

2006-01-01

22

Secular change in geomagnetic indices and the solar open magnetic flux during the first half of the twentieth century  

NASA Astrophysics Data System (ADS)

We examined several long-term geomagnetic indices (u, Ci, and Hm) to substantiate the secular increase in the aa index during the first half of the twentieth century. The long-term increase in aa and other geomagnetic indices was accompanied by a corresponding rise in the envelope of the sunspot number (˜130% increase of cycle averages). We used a correlation between solar cycle averages of sunspot number and solar open magnetic flux for recent cycles to infer a 140 ± 80% increase in the open flux between ˜1900 and ˜1950, comparable to the ˜130% increase in this parameter during the twentieth century deduced by [1999] from solar wind measurements during the space age. While the uncertainty in our result is large, our method, which is not based on aa, provides independent support for a substantial increase in the open magnetic flux during the last century.

Cliver, E. W.; Ling, A. G.

2002-10-01

23

Geomagnetism during solar cycle 23: Characteristics  

PubMed Central

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

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

2012-01-01

24

Persistence in recurrent geomagnetic activity and its connection with Space Climate  

NASA Astrophysics Data System (ADS)

Recurrent geomagnetic activity is mainly linked to the passage of interplanetary corotating solar wind structures in the near-Earth space. We studied geomagnetic recurrences for which an enhanced value of the autocorrelation coefficient exists between the data of two adjacent Bartels rotations in aa, Kp, Dst, AE time series, for the period 1954-2007, covering about 5 solar cycles (from cycle 19 to cycle 23). A new index (P), based on autocorrelation analysis, has been introduced to estimate also the duration up to seven Bartels rotations of each solar structure (or group of structures) producing geomagnetic recurrences with high autocorrelation (correlation coefficient ? 0.3). We could infer whether recurrent geomagnetic activity is due to successive short-lived (at least 2 Bartels rotations) or to long-lasting corotating structures (up to 7 or more Bartels rotations). Generally, time periods characterized by recurrent geomagnetic activity are longer during the descending phase of even-numbered cycles (20, 22). Nevertheless, we found that recurrences determined by long-lived interplanetary structures are detected mainly in the descending phase of cycles 19 and 23. Finally, we point out that the average levels of the computed indices during the descending phase of each solar cycle show a significant anticorrelation with the sunspot area integrated over the subsequent cycle, giving new insights for Space Climate forecast.

Diego, P.; Storini, M.; Laurenza, M.

2010-06-01

25

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

26

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

NASA Technical Reports Server (NTRS)

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

Wilson, Robert M.; Hathaway, David H.

2008-01-01

27

Loss of synchronization in the 27-day spectral component of geomagnetic indices and its relationship with solar activity  

NASA Astrophysics Data System (ADS)

We investigate the “27-day” spectral component of different global (aa and Dst) and local (?) geomagnetic indices in two period ranges relevant to the Sun's synodic rotation, as manifested by magnetic activity: 24-28 days (short) and 28-32 days (long). Cross-correlation analysis of the respective energies of the short and long periods of the 27-day rotation signal in the same geomagnetic index reveals well-defined de-synchronization events during certain solar cycles. The largest de-synchronization in the past century occurred during solar cycle 21. De-synchronization events first occur in indices of the Dst (and ?) family, and then in indices of the aa family. We found no evidence that the strength of the de-synchronization of the solar rotation signal in the ?-index would depend on geomagnetic latitude. Applying the same analysis to proper solar indices (sunspot number, F10.7 radio flux, interplanetary magnetic field (IMF) series, solar wind speed), we find that only the Bz component of the IMF demonstrates a de-synchronization, during solar cycle 21, between the energies of the 27-day solar rotation signal in the short and long period ranges. We discuss possible implications of these results with respect to the evolution of the toroidal and poloidal components of the Sun's magnetic field and to its large-scale structures.

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

2014-09-01

28

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

29

An Examination of Selected Geomagnetic Indices in Relation to the Sunspot Cycle  

NASA Technical Reports Server (NTRS)

Previous studies have shown geomagnetic indices to be useful for providing early estimates for the size of the following sunspot cycle several years in advance. Examined this study are various precursor methods for predicting the minimum and maximum amplitude of the following sunspot cycle, these precursors based on the aa and Ap geomagnetic indices and the number of disturbed days (NDD), days when the daily Ap index equaled or exceeded 25. Also examined is the yearly peak of the daily Ap index (Apmax), the number of days when Ap greater than or equal to 100, cyclic averages of sunspot number R, aa, Ap, NDD, and the number of sudden storm commencements (NSSC), as well the cyclic sums of NDD and NSSC. The analysis yields 90-percent prediction intervals for both the minimum and maximum amplitudes for cycle 24, the next sunspot cycle. In terms of yearly averages, the best regressions give Rmin = 9.8+/-2.9 and Rmax = 153.8+/-24.7, equivalent to Rm = 8.8+/-2.8 and RM = 159+/-5.5, based on the 12-mo moving average (or smoothed monthly mean sunspot number). Hence, cycle 24 is expected to be above average in size, similar to cycles 21 and 22, producing more than 300 sudden storm commencements and more than 560 disturbed days, of which about 25 will be Ap greater than or equal to 100. On the basis of annual averages, the sunspot minimum year for cycle 24 will be either 2006 or 2007.

Wilson, Robert M.; Hathaway, David H.

2006-01-01

30

Geologic Hazards: Geomagnetism  

NSDL National Science Digital Library

Anyone researching or interested in geomagnetism will appreciate the US Geological Survey's Geologic Hazards: Geomagnetism Web site. Visitors will find research publications, various downloadable magnetic charts, models, data plots, an online calculator for magnetic fields, and more.

1997-01-01

31

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

Microsoft Academic Search

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

A. D. Padgaonkar; B. R. Arora

1981-01-01

32

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.

33

Geomagnetic Storms January 2013  

E-print Network

Geomagnetic Storms January 2013 Empower ResultsTM #12;2 Geomagnetic Storms 2 Pear-Shaped Phenomena Contents Pear-Shaped Phenomena Aon Benfield uses "Pear-shaped phenomena" to refer to relatively low swan events which are defined as "unforeseeable" pear-shaped phenomena (PSP) can be anticipated

Schrijver, Karel

34

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

35

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

36

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

37

Solar and geomagnetic precursors of the climate change  

NASA Astrophysics Data System (ADS)

Observed climate change and warming are temporary and spatially non-uniform over the globe whereas the global models tend to predict the gradual increase of temperature due to the antropogenic impact. In particular, rapid climate changes in the Arctic in 1990-2000s can not be accounted solely for the anthropogenic effect since the actually observed changes exceed the predictions of the global climate models. Such discrepancy is usually attributed to the intrinsic variability of the climate system. However, the Sun influences the Earth climate through mechanisms that are not fully understood but which can be linked to solar variations of luminosity, magnetic field, UV radiation, solar flares and modulation of the cosmic ray intensity. In this contribution we (re)examined the long-term behavior of some solar proxies and surface air and see temperatures (SAT and SST). The satellite composite of total solar irradiance (TSI) covered approximately three last solar cycles has been used for determination of the inter-annual solar variability. In the spectrum of anomalies relative to 11-yr cycle a strong 12-month harmonic is clearly seen along with some lower (3-4 yr) periodicities. Examination of the long-term behavior of the solar proxy in the individual months of the year reveals the persisted increase of solar irradiance anomalies in December-February. Although the TSI time series has no overall trend, in Nov-Feb the 0.32 W/m2 upward trend is detected. The largest differential anomaly (between 1983 and 2002) is 1.21 W/m2. The natural seasonal weather cycle may play a role of amplifier of solar annual signal. In order to check further the external (solar) forcing-climate hypothesis, comparisons between the geomagnetic aa index and the update SAT and SST have been made over the time interval of 1868-2009. The long-term variability of the 11-yr running average aa index shows the overall upward trend that rises from 1900 to 1950s, decreases until 1960s, rises again to 1990s and has been decreasing since then, more rapidly after 2003. On a decadal scale the geomagnetic trend correlates well with the evolution of SAT globally averaged over hemispheres and over the particular surface areas. Changes in global temperature are seemed to follow changes in aa with time delay of 6-10 years. If the recent years are included, the correlation between decadal temperature and aa does not obviously fail after 1990s, when solar irradiance and magnetic activity drop, whereas temperature continues an accelerated rise. Thus correlations between solar/magnetic variations and climate may be more significant than previously realized. After the warmest period of 2005-2007 the temperature tends to become cooler and the next years will show whether this trend is stable.

Lukianova, Renata; Alekseev, Genrikh

2010-05-01

38

Geomagnetic Indices Variations And Human Physiology  

NASA Astrophysics Data System (ADS)

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

Dimitrova, S.

2007-12-01

39

Magnetospheric impulse response for many levels of geomagnetic activity  

Microsoft Academic Search

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

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

1985-01-01

40

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

41

Introduction to Geomagnetic Fields  

NASA Astrophysics Data System (ADS)

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

Hinze, William J.

42

Enhancement in Surface Atmospheric Pressure Variability Associated with a Major Geomagnetic Storm  

E-print Network

Observational studies indicate that there is a close association between geomagnetic storm and meteorological parameters. Geomagnetic field lines follow closely the isobars of surface pressure . A Physical mechanism linking upper atmospheric geomagnetic storm disturbances with tropospheric weather has been proposed by the author and her group where it is postulated that vertical mixing by turbulent eddy fluctuations results in the net transport upward of positive charges originating from lower levels accompanied simultaneously by downward flow of negative charges from higher levels. The present study reports enhancement of high frequency (pressure during March 1989 in association with major geomagnetic storm (Ap index = 246) on 13 march 1989.

A. M. Selvam; S. Fadnavis; S. U. Athale; M. I. R. Tinmaker

1998-07-03

43

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

44

On regional geomagnetic charts  

USGS Publications Warehouse

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

Alldredge, L.R.

1987-01-01

45

Forecasting Geomagnetic Conditions in near-Earth space  

NASA Astrophysics Data System (ADS)

Geomagnetic conditions in near-Earth space have been a constantly evolving scientific field, especially during the latest years when the dependence of our everyday life on space environment has significantly increased. The scientific community managed to implement centers for the continuous monitoring of the geomagnetic conditions which resulted into short and long term forecasting of the planetary geomagnetic index Ap. In this work, the centers that have been established and are in operational mode in Russia (IZMIRAN), Greece (Athens), Kazakhstan (Almaty) and Bulgaria (Sofia) are presented. The methods that have been used for the forecasting of Ap index are demonstrated and the forecasted results in comparison to the actual Ap measurements are also discussed.

Abunina, M.; Papaioannou, A.; Gerontidou, M.; Paschalis, P.; Abunin, A.; Gaidash, S.; Tsepakina, I.; Malimbayev, A.; Belov, A.; Mavromichalaki, H.; Kryakunova, O.; Velinov, P.

2013-02-01

46

Prediction of Geomagnetic Activity and Key Parameters in High-Latitude Ionosphere-Basic Elements  

NASA Technical Reports Server (NTRS)

Prediction of geomagnetic activity and related events in the Earth's magnetosphere and ionosphere is an important task of the Space Weather program. Prediction reliability is dependent on the prediction method and elements included in the prediction scheme. Two main elements are a suitable geomagnetic activity index and coupling function -- the combination of solar wind parameters providing the best correlation between upstream solar wind data and geomagnetic activity. The appropriate choice of these two elements is imperative for any reliable prediction model. The purpose of this work was to elaborate on these two elements -- the appropriate geomagnetic activity index and the coupling function -- and investigate the opportunity to improve the reliability of the prediction of geomagnetic activity and other events in the Earth's magnetosphere. The new polar magnetic index of geomagnetic activity and the new version of the coupling function lead to a significant increase in the reliability of predicting the geomagnetic activity and some key parameters, such as cross-polar cap voltage and total Joule heating in high-latitude ionosphere, which play a very important role in the development of geomagnetic and other activity in the Earth s magnetosphere, and are widely used as key input parameters in modeling magnetospheric, ionospheric, and thermospheric processes.

Lyatsky, W.; Khazanov, G. V.

2007-01-01

47

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

48

Geomagnetic Field During a Reversal  

NASA Technical Reports Server (NTRS)

It has frequently been suggested that only the geomagnetic dipole, rather than higher order poles, reverse during a geomagnetic field reversal. Under this assumption the geomagnetic field strength has been calculated for the surface of the Earth for various steps of the reversal process. Even without an eminent a reversal of the field, extrapolation of the present secular change (although problematic) shows that the field strength may become zero in some geographic areas within a few hundred years.

Heirtzler, J. R.

2003-01-01

49

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

50

*(60833005, 60573091); 863 2007AA01Z1552009AA011904; 200800020002  

E-print Network

*(60833005, 60573091); 863 2007AA01Z1552009AA011904; 200800020002 HF-Tree: ( 100872) (cadizhou@gmail.com) HF-Tree: An Update-Efficient Index for Flash Memory Zhou Da, Liang Zhichao, Meng drives. In this paper, we propose a novel index called HF tree to improve the update performance, which

51

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

52

British Geological Survey: Geomagnetism  

NSDL National Science Digital Library

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

53

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

54

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

1999-09-02

55

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

56

Geomagnetic activity and the stability of the solar corpuscular field  

NASA Astrophysics Data System (ADS)

The stability of the structure of solar corpuscular radiation at various phases of the solar activity cycle is studied on the basis of geomagnetic data extending from 1841 to 1979. The data comprise daily mean values of the nine-point C(Pi)9 index derived from observations made at the Petersburg and Pavlovsk magnetic observatories from 1841 to 1910, and daily mean values of the nine-point planetary magnetic index C9 for the period 1890-1979 derived from the work of Chapman and Bartels (1940) and the International Center of the geomagnetic index service. A correlation analysis applied to 27-day series of the geomagnetic indices shows that the structure of the corpuscular radiation may remain stable throughout most solar rotations during the epochs of decay and minimum of the 11-year solar cycle. The existence of two maxima in the geomagnetic activity cycle is also confirmed. Catalogs of the mean daily C(Pi)9 and C9 indices, the monthly and yearly mean indices from 1841 through 1979 and the correlation coefficients derived between successive 27-day series of indices are also presented.

Zosimovich, I. D.

57

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

58

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

59

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

PubMed

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

Conesa, J

1995-06-01

60

Geomagnetic Variability and Predictability  

NASA Technical Reports Server (NTRS)

The Earth's magnetic field varies on time scales from seconds to millions of years. These variations can be measured directly by ground observatories and satellites, and indirectly through laboratories. They are from different electromagnetic processes in magnetosphere and ionosphere (external), ocean and crust (surface), and deep in the Earth's fluid outer core (internal). Of the measured magnetic signals, 95% is from the core, and is called the core field, or internal field. Variation of the core field, often called the geomagnetic secular variation (SV), is the manifestation of the magnetohydrodynamic processes in the core. Therefore, SV provides rich information on the core dynamical state that is then critical for understanding the geophysical mechanisms of the SV, the core-mantle interactions, and contribution of mass transport inside the core on Earth's gravity variation. Traditionally, the core state is probed via two independent methodologies: core flow inversion from the observed SV, and pure numerical dynamo simulation. The former is driven by observations, but does not include necessary interactions among physical variables; the latter is dynamically consistent, but is not constrained by any observation. Therefore, both are very limited in providing appropriate estimates of the core state. To avoid these limitations, a new approach, geomagnetic data assimilation, appears recently. In this approach, simulation results (model forecasts) are constantly corrected with observations, the corrected solutions (analysis), are then used as the initial conditions to make more accurate forecasts of future. Recent studies have demonstrated successfully that assimilation solutions are different from those of free running models. These new solutions are better estimates of the core state, and have been used to provide accurate prediction of SV for the period from 2010 to 2015. This prediction is part of the IGRF field model for international community applications.

Kuang, Weijia

2011-01-01

61

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

62

Geodetic observations at geomagnetic observatories  

NASA Astrophysics Data System (ADS)

Geodetic observations at geomagnetic observatories are used to orient reference directions in relation to a common coordinate grid. This problem is solved with the use of the measuring tools of global navigation satellite systems (GNSS). The results of experimental GNSS determinations at the St. Petersburg Geomagnetic Observatory, Russia, are presented. Combination of magnetic and GNSS observations is proposed in order to reveal the cause-effect relationships between magnetic field variations and global geodynamic processes.

Kaftan, V. I.; Krasnoperov, R. I.

2015-01-01

63

[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

64

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

65

Let A and a be the alleles. Then the genotypes of zygotes are AA, aa, Aa aA.  

E-print Network

Let A and a be the alleles. Then the genotypes of zygotes are AA, aa, Aa aA. Let the corresponding) are independent variables. II) The genotypes AA and Aa have the same phenotype but the phenotype of aa ik, namely, 11 = 12 (1) but 22 is independent of 11. III) The genotypes AA and aa have the same

Kirzhner Valery

66

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

67

Severe geomagnetic storms and their sources on the sun  

NASA Astrophysics Data System (ADS)

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

Krajcovic, S.; Krivsky, L.

1982-05-01

68

Solar wind control of auroral zone geomagnetic activity  

NASA Technical Reports Server (NTRS)

Solar wind magnetosphere energy coupling functions are analyzed using linear prediction filtering with 2.5 minute data. The relationship of auroral zone geomagnetic activity to solar wind power input functions are examined, and a least squares prediction filter, or impulse response function is designed from the data. Computed impulse response functions are observed to have characteristics of a low pass filter with time delay. The AL index is found well related to solar wind energy functions, although the AU index shows a poor relationship. High frequency variations of auroral indices and substorm expansions are not predictable with solar wind information alone, suggesting influence by internal magnetospheric processes. Finally, the epsilon parameter shows a poorer relationship with auroral geomagnetic activity than a power parameter, having a VBs solar wind dependency.

Clauer, C. R.; Mcpherron, R. L.; Searls, C.; Kivelson, M. G.

1981-01-01

69

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

70

Spectrum analysis of short-period K index behaviour at high and mid-latitudes  

NASA Astrophysics Data System (ADS)

Geomagnetic activity levels during the declining phase and solar minimum period of the solar cycle are considerably different from those during the solar maximum phase. Previous studies revealed variations in the pattern of recurrent activity from cycle to cycle as well as variations in the average geomagnetic activity levels during a solar cycle. During the declining phase of a solar cycle (and solar minimum), the solar and interplanetary causes of geomagnetic activity are substantially different from those during the solar maximum phase. Co-rotating fast solar wind streams originating from large polar coronal holes, extending towards the Sun's equator, interact with the Earth's magnetosphere, resulting in recurrent geomagnetic activity particularly during solar cycle minimum periods. This is a well-known phenomenon with respect to 27.0- and 13.5-day recurrence geomagnetic activity, and it is well-known to be related to sectorial (non-axial) poloidal magnetic field structure in the Sun. Published results of the recent solar-cycle-23 minimum showed that the presence of 9.0- and 6.7-day recurrent geomagnetic activities can be attributed to the sectorial spherical harmonic structure present in the solar magnetic field. In this study we performed a wavelet and Lomb-Scargle analysis of the geomagnetic activity K index at Lerwick (LER), Hermanus (HER) and Canberra (CNB) for the period between 1960 and 2010, overlapping with solar cycles 20 to 23. Daily mean K indices are used to identify how several harmonics of the 27.0-day recurrent period change during each solar cycle when comparing high and mid-latitude geomagnetic activity, applying a 95% confidence level. In particular the behaviour of the second (13.5-day), third (9.0-day) and fourth (6.7-day) harmonics are investigated by doing a wavelet analysis of each individual year's K indices at each location. Results obtained show that particularly during solar minima the 27.0-day period is no longer detectable above the 95% confidence level, and that geomagnetic activity is in fact dominated by higher harmonics like 13.5-, 9.0- and 6.7-day periods. These findings in fact are in line with previous investigations and confirm the results obtained by researchers using other geomagnetic activity indices like aa and C9. The wavelet-spectrum analysis also reveals that during the downward phase of cycle 23 and the very long minimum of 23-24 between 2002 and 2008, the 27.0-day activity period drops below the 95% confidence level. This is confirmed by Lomb-Scargle analyses of every year's K index activity. Results obtained in this study support evidence by other investigations that this can be attributed to the lack of coronal-mass ejection (CME)-dominated solar activity during solar minima, periods characterized by strong solar dipolar magnetic fields, less sunspot numbers than at solar maxima, and multiple prominent co-rotating solar wind streams present. This analysis further confirms previous studies by other authors that the pattern of recurrent activity is dictated by the configuration of coronal holes which give rise to related high-speed streams during a solar cycle by analysing K indices at both high- and mid-latitude magnetic observatories.

Kotzé, P. B.

2015-01-01

71

Prediction of Geomagnetic Activity and Key Parameters in High-latitude Ionosphere  

NASA Technical Reports Server (NTRS)

Prediction of geomagnetic activity and related events in the Earth's magnetosphere and ionosphere are important tasks of US Space Weather Program. Prediction reliability is dependent on the prediction method, and elements included in the prediction scheme. Two of the main elements of such prediction scheme are: an appropriate geomagnetic activity index, and an appropriate coupling function (the combination of solar wind parameters providing the best correlation between upstream solar wind data and geomagnetic activity). We have developed a new index of geomagnetic activity, the Polar Magnetic (PM) index and an improved version of solar wind coupling function. PM index is similar to the existing polar cap PC index but it shows much better correlation with upstream solar wind/IMF data and other events in the magnetosphere and ionosphere. We investigate the correlation of PM index with upstream solar wind/IMF data for 10 years (1995-2004) that include both low and high solar activity. We also have introduced a new prediction function for the predicting of cross-polar-cap voltage and Joule heating based on using both PM index and upstream solar wind/IMF data. As we show such prediction function significantly increase the reliability of prediction of these important parameters. The correlation coefficients between the actual and predicted values of these parameters are approx. 0.9 and higher.

Khazanov, George V.; Lyatsky, Wladislaw; Tan, Arjun; Ridley, Aaron

2007-01-01

72

What is a geomagnetic storm?  

Microsoft Academic Search

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

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

1994-01-01

73

Geomagnetic activity associated with Earth passage of interplanetary shock disturbances and coronal mass ejections  

SciTech Connect

Previous work indicates that virtually all transient shock wave disturbances in the solar wind are driven by fast coronal mass ejection events (CMEs). Using a recently appreciated capability for distinguishing CMEs in solar wind data in the form of counterstreaming solar wind electron events, this paper explores the overall effectiveness of shock wave disturbances and CMEs in general in stimulating geomagnetic activity. The study is confined to the interval from mid-August 1978 through mid-October 1982, spanning the last solar activity maximum, when ISEE 3 was in orbit about the L1 Lagrange point 220 R{sub e} upstream from Earth. The authors find that all but one of the 37 largest geomagnetic storms in that era were associated with Earth passage of CMEs and/or shock disturbances, with the large majority of these storms being associated with interplanetary events where Earth encountered both a shock and the CME driving the shock (shock/CME events). Although CMEs and/or shock disturbances were increasingly the cause of geomagnetic activity as the level of geomagnetic activity increased, many smaller geomagnetic disturbances were unrelated to these events. Further, approximately half of all CMEs and half of all shock disturbances encountered by Earth did not produce any substantial geomagnetic activity as measured by the planetary geomagnetic index Kp. The geomagnetic effectiveness of Earth directed CMEs and shock wave disturbances was directly related to the flow speed, the magnetic field magnitude, and the strength of the southward (GSM) field component associated with the events. The initial speed of a CME close to the Sun appears to be the most crucial factor in determining if an earthward directed event will be effective in exciting a large geomagnetic disturbance.

Gosling, J.T.; McComas, D.J.; Phillips, J.L.; Bame, S.J. (Los Alamos National Lab., NM (USA))

1991-05-01

74

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

NASA Astrophysics Data System (ADS)

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

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

75

Acceleration and loss of relativistic electrons during geomagnetic G. D. Reeves, K. L. McAdams, and R. H. W. Friedel  

E-print Network

Acceleration and loss of relativistic electrons during geomagnetic storms G. D. Reeves, K. L. Mc balance between the effects of particle acceleration and loss. INDEX TERMS: 2788 Magnetospheric Physics'Brien, Acceleration and loss of relativistic electrons during geomagnetic storms, Geophys. Res. Lett., 30(10), 1529

Reeves, Geoffrey D.

76

Effects of geomagnetic storm on GPS ionospheric scintillations at Sanya  

NASA Astrophysics Data System (ADS)

The effects of geomagnetic storm on GPS ionospheric scintillations are studied here using GPS scintillation data recorded at Sanya (18.3°N, 109.5°E; geomagnetic: 7.6°N, 180.8°E), the southmost station in the Chinese longitude region. GPS scintillation/TEC and DMSP data are utilized to show the development of irregularities during the period year 2005 (solar minimum). Statistical analysis of K planetary index (Kp) and amplitude scintillation index (S4) indicates that most storms of the year did not trigger the scintillation occurrence at Sanya. However, cases of scintillation occurring during moderate and strong storm (Dst<-100) periods show clearly that the development of irregularities producing scintillations can be triggered by geomagnetic storms during the low scintillation occurrence season. The effects (trigger or not trigger/inhibit) depend on the maximum dDst/dt determined local time sector, and can be explained by the response of the equatorial vertical drift velocities to magnetospheric and ionospheric disturbance electric fields. For station Sanya, the maximum dDst/dt determined local time is near the noon (or post-midnight) sector for most storms of the year 2005, which inhibited (or did not trigger) the post-sunset (or post-midnight) scintillation occurrence and then led to the phenomena that the statistical results presented.

Li, Guozhu; Ning, Baiqi; Zhao, Biqiang; Liu, Libo; Liu, J. Y.; Yumoto, K.

2008-05-01

77

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

78

Prediction of recurrent geomagnetic disturbances by using adaptive filtering  

Microsoft Academic Search

Recurrent geomagnetic disturbances are an important part of geomagnetic activities, which are associated with the neutral sheet structure in the heliosphere and the activities of long lived solar coronal holes. Another significant character is the periodic activities recorded by geomagnetic indices. In this paper an algorithm--Adaptive Filtering (AF), is introduced to forecast recurrent geomagnetic events based on the geomagnetic Kindex.

X.-Y. Zhou; F.-S. Wei

1998-01-01

79

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.

80

Ice ages and geomagnetic reversals  

NASA Technical Reports Server (NTRS)

There have been speculations on the relationship between climatic cooling and polarity reversals of the earth's magnetic field during the Pleistocene. Two of the common criticisms on this relationship have been the reality of these short duration geomagnetic events and the accuracy of their dates. Champion et al. (1988) have reviewed recent progress in this area. They identified a total of 10 short-duration polarity events in the last 1 Ma and 6 of these events have been found in volcanic rocks, which also have K-Ar dates. Supposing that the speculated relationship between climatic cooling and geomagnetic reversals actually exist, two mechanisms that assume climatic cooling causes short period magnetic reversals will be investigated. These two methods are core-mantle boundary topography and transfer of the rotational energy to the core.

Wu, Patrick

1992-01-01

81

Teaching Geomagnetism in High School  

NASA Astrophysics Data System (ADS)

Many high school curricula include a one-year course in Earth Sciences, often in the 9th grade (essentially pre-algebra). That is a good time to teach about geomagnetism. Not only are dipole reversals and sea-floor magnetization central to this subject, but this is a good opportunity to introduce students to magnetism and its connection to electric currents. The story of Oersted and Faraday give a fascinating insight into the uneven path of scientific discovery, the magnetic compass and William Gilbert provide a view of the beginnings of the scientific revolution, and even basic concepts of dynamo theory and its connection to solar physics can be included. A resource including all the suitable material now exists on the world-wide web at http://www-spof.gsfc.nasa.gov/earthmag/demagint.htm (home page). A 1-month unit on geomagnetism will be outlined.

Stern, D. P.

2001-05-01

82

Geomagnetic Field Frequently Asked Questions  

NSDL National Science Digital Library

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

83

The origin of geomagnetic jerks.  

PubMed

Geomagnetic jerks, which in the second half of the twentieth century occurred in 1969 (refs 1, 2), 1978 (refs 3, 4), 1991 (ref. 5) and 1999 (ref. 6), are abrupt changes in the second time-derivative (secular acceleration) of the Earth's magnetic field. Jerks separate periods of almost steady secular acceleration, so that the first time-derivative (secular variation) appears as a series of straight-line segments separated by geomagnetic jerks. The fact that they represent a reorganization of the secular variation implies that they are of internal origin (as has been established through spherical harmonic analysis), and their short timescale implies that they are due to a change in the fluid flow at the surface of the Earth's core (as has also been established through mapping the time-varying flow at the core surface). However, little is understood of their physical origin. Here we show that geomagnetic jerks can be explained by the combination of a steady flow and a simple time-varying, axisymmetric, equatorially symmetric, toroidal zonal flow. Such a flow is consistent with torsional oscillations in the Earth's core, which are simple oscillatory flows in the core that are expected on theoretical grounds, and observed in both core flow models and numerical dynamo models. PMID:12422214

Bloxham, Jeremy; Zatman, Stephen; Dumberry, Mathieu

2002-11-01

84

Forecasts of geomagnetic secular variation  

NASA Astrophysics Data System (ADS)

We attempt to forecast the geomagnetic secular variation based on stochastic models, non-parametric regression and singular spectrum analysis of the observed past field changes. Although this modelling approach is meant to be phenomenological, it may provide some insight into the mechanisms underlying typical time scales of geomagnetic field changes. We follow two strategies to forecast secular variation: Firstly, by applying time series models, and secondly, by using time-dependent kinematic models of the advected secular variation. These forecasts can span decades, to longer periods. This depends on the length of the past observations used as input, with different input models leading to different details in the forecasts. These forecasts become more uncertain over longer forecasting periods. One appealing reason is the disregard of magnetic diffusion in the kinematic modelling. But also the interactions of unobservable small scale core field with core flow at all scale unsettle the kinematic forecasting scheme. A further (obvious) reason is that geomagnetic secular variation can not be mimicked by linear time series models as the dynamo action itself is highly non-linear. Whether the dynamo action can be represented by a simple low-dimensional system requires further analysis.

Wardinski, Ingo

2014-05-01

85

The Geomagnetic Field During a Reversal  

NASA Technical Reports Server (NTRS)

By modifying the IGRF it is possible to learn what may happen to the geomagnetic field during a geomagnetic reversal. If the entire IGRF reverses then the declination and inclination only reverse when the field strength is zero. If only the dipole component of the IGRF reverses a large geomagnetic field remains when the dipole component is zero and he direction of the field at the end of the reversal is not exactly reversed from the directions at the beginning of the reversal.

Heirtzler, James R.

2003-01-01

86

The Causes of Geomagnetic Storms During Solar Maximum  

NASA Technical Reports Server (NTRS)

One of the oldest mysteries in geomagnetism is the linkage between solar and geomagnetic activity. The 11-year cycles of both the numbers of sunspots and Earth geomagnetic storms were first noted by Sabine (1852).

Tsurutani, B. T.; Gonzalez, W. D.

1998-01-01

87

INSTRUCTION MANUAL MODEL AA-2010  

E-print Network

INSTRUCTION MANUAL . MODEL AA-2010 MODEL AA-2015 MODEL AA-2020 MODEL AA-2025 SINGLE CHANNEL NUCLEAR spectroscopy lies in the wide ranging versatility of the technique. From a sub-visual microsecond light flash

Bayindir, Mehmet

88

Removal of the local geomagnetic field affects reproductive growth in Arabidopsis.  

PubMed

The influence of the geomagnetic field-removed environment on Arabidopsis growth was investigated by cultivation of the plants in a near-null magnetic field and local geomagnetic field (45 µT) for the whole growth period under laboratory conditions. The biomass accumulation of plants in the near-null magnetic field was significantly suppressed at the time when plants were switching from vegetative growth to reproductive growth compared with that of plants grown in the local geomagnetic field, which was caused by a delay in the flowering of plants in the near-null magnetic field. At the early or later growth stage, no significant difference was shown in the biomass accumulation between the plants in the near-null magnetic field and local geomagnetic field. The average number of siliques and the production of seeds per plant in the near-null magnetic field was significantly lower by about 22% and 19%, respectively, than those of control plants. These resulted in a significant reduction of about 20% in the harvest index of plants in the near-null magnetic field compared with that of the controls. These results suggest that the removal of the local geomagnetic field negatively affects the reproductive growth of Arabidopsis, which thus affects the yield and harvest index. PMID:23568853

Xu, Chunxiao; Wei, Shufeng; Lu, Yan; Zhang, Yuxia; Chen, Chuanfang; Song, Tao

2013-09-01

89

Sparkling Geomagnetic Field: Involving Schools in Geomagnetic Research  

NASA Astrophysics Data System (ADS)

Solar activity will be reaching a maximum in 2013/2014 as the sun reaches the end of its cycle, bringing with it an opportunity to study in greater detail the effect of solar wind or "space weather" on our planet's magnetic field. Heightened solar activity leads to a larger amount of clouds of energetic particles bombarding the Earth. Although the Earth's magnetic field shields us from most of these particles, the field becomes distorted and compacted by the solar wind, which leads to magnetic storms that we detect from the surface. These storms cause aurorae at higher latitudes and can lead to widespread disruption of communication and navigation equipment all over the Earth when sufficiently strong. This project, "Sparkling Geomagnetic Field," is a part of Austria's Sparkling Science programme, which aims to involve schools in active scientific research to encourage interest in science from a young age. Researchers from the Central Institute for Meteorology and Geodynamics (ZAMG) in Vienna have worked hand-in-hand with three schools across Austria to set up regional geomagnetic stations consisting of state-of-the-art scalar and vector magnetometers to monitor the effects of the solar wind on the geomagnetic field. The students have been an active part of the research team from the beginning, first searching for a suitable location to set up the stations as well as later overseeing the continued running of the equipment and analysing the data output. Through this project the students will gain experience in contemporary scientific methods: data processing and analysis, field work, as well as equipment setup and upkeep. A total of three stations have been established with schools in Innsbruck, Tamsweg and Graz at roughly equal distances across Austria to run alongside the already active station in the Conrad Observatory near Vienna. Data acquisition runs through a data logger and software developed to deliver data in near realtime. This network allows for evaluation of both the spatial and temporal development of magnetic storms across the longitudes. Currently the stations are running in a test phase as the last system wrinkles are ironed out. The geomagnetic network will be running and delivering continuous data by spring 2014.

Bailey, Rachel; Leonhardt, Roman; Leichter, Barbara

2014-05-01

90

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

91

On the limitations of geomagnetic measures of interplanetary magnetic polarity  

NASA Technical Reports Server (NTRS)

The maximum attainable accuracy in inferring the interplanetary magnetic polarity from polar cap magnetograms is about 88%. This is achieved in practice, when high-latitude polar cap stations are used during local summer months, and the signature in the ground records is strong. An attempt by Svalgaard (1972) to use this effect to infer an index of interplanetary magnetic polarity back to 1926 has not been so successful. Furthermore, some of the properties of the index have changed with time. Prior to 1963, the inferred polarities are strongly dependent on geomagnetic activity, while after this time they are not. Thus, this index should not be used to separate solar-magnetic from solar-activity effects prior to 1963.

Russell, C. T.; Rosenberg, R. L.

1974-01-01

92

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

93

Electric utility industry experience with geomagnetic disturbances  

SciTech Connect

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

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

1991-09-01

94

Electric utility industry experience with geomagnetic disturbances  

SciTech Connect

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

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

1991-09-01

95

Snowstorm at the geomagnetic observatory  

NASA Astrophysics Data System (ADS)

The Sinji Vrh Geomagnetic Observatory is situated on Gora above Ajdovš?ina, a highland Karst Plateau, in the southwest part of Slovenia. The observatory operates in exceptional geological and meteorological conditions due to its location. Already first measurements at the time of initial tests showed that weather fronts induce changes in the local magnetic field. The first dedicated measurements for determining the value of this influence were carried out at the end of summer 2011. On January 2013 the first such measurements were carried out during the winter. This article presents the results of these measurements, showing how the snowstorm induced changes in the earth magnetic field.

?op, R.

2015-01-01

96

Daily variation characteristics at polar geomagnetic observatories  

NASA Astrophysics Data System (ADS)

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

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

2011-08-01

97

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

98

Infrared parameters of atmospheric ozone and the great geomagnetic storm of 1953  

NASA Astrophysics Data System (ADS)

Significant effects on the concentration and temperature of ozone in the upper atmosphere were observed during a major solar flare, and subsequent geomagnetic storm, which occurred during the interval August 6 to September 4, 1953. Ozone concentrations, as measured by the absorption of solar radiation by the 9.6 micron ozone band, decreased during the event but retuned to previous levels after the event. Temperature changes were also observed. The changes lag changes in Kp, the geomagnetic activity index, by approximately 5 to 7 days.

Adel, Arthur

1995-02-01

99

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

NASA Astrophysics Data System (ADS)

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

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

2010-10-01

100

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

NASA Astrophysics Data System (ADS)

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

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

2001-08-01

101

Geomagnetic storms, super-storms, and their impacts on GPS-based navigation systems  

NASA Astrophysics Data System (ADS)

data of GPS receivers located worldwide, we analyze the quality of GPS performance during four geomagnetic storms of different intensity: two super-storms and two intense storms. We show that during super-storms the density of GPS Losses-of-Lock (LoL) increases up to 0.25% at L1 frequency and up to 3% at L2 frequency, and up to 0.15% (at L1) and 1% (at L2) during less intense storms. Also, depending on the intensity of the storm time ionospheric disturbances, the total number of total electron content (TEC) slips can exceed from 4 to 40 times the quiet time level. Both GPS LoL and TEC slips occur during abrupt changes of SYM-H index of geomagnetic activity, i.e., during the main phase of geomagnetic storms and during development of ionospheric storms. The main contribution in the total number of GPS LoL was found to be done by GPS sites located at low and high latitudes, whereas the area of numerous TEC slips seemed to mostly correspond to the boundary of the auroral oval, i.e., region with intensive ionospheric irregularities. Our global maps of TEC slips show where the regions with intense irregularities of electron density occur during geomagnetic storms and will let us in future predict appearance of GPS errors for geomagnetically disturbed conditions.

Astafyeva, E.; Yasyukevich, Yu.; Maksikov, A.; Zhivetiev, I.

2014-07-01

102

On the watch for geomagnetic storms  

USGS Publications Warehouse

Geomagnetic storms, induced by solar activity, pose significant hazards to satellites, electrical power distribution systems, radio communications, navigation, and geophysical surveys. Strong storms can expose astronauts and crews of high-flying aircraft to dangerous levels of radiation. Economic losses from recent geomagnetic storms have run into hundreds of millions of dollars. With the U.S. Geological Survey (USGS) as the lead agency, an international network of geomagnetic observatories monitors the onset of solar-induced storms and gives warnings that help diminish losses to military and commercial operations and facilities.

Green, Arthur W.; Brown, William M., III

1997-01-01

103

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

104

Introduction to Geomagnetically Trapped Radiation  

NASA Astrophysics Data System (ADS)

This book is an introductory textbook on the physical processes occurring in the Earth's radiation belts. The presentation is at the advanced undergraduate or first year graduate level, and it is appropriate for students who intend to work in some aspect of magnetospheric physics. The treatment is quantitative and provides the mathematical basis for original work in this subject. The equations describing the motion of energetic ions and electrons in the geomagnetic field are derived from basic principles, and concepts such as magnetic field representations, guiding centre motion, adiabatic invariance, and particle distribution functions are presented in a detailed and accessible manner. Relevant experimental techniques are reviewed and a summary is given of the intensity and energy spectra of the particle populations in the Earth's radiation belts. Problem sets are included as well as appendices of tables, graphs and frequently used formulas.

Walt, Martin

2005-09-01

105

Analysis of Geomagnetic Storms and Substorms with the WINDMI Model  

NASA Astrophysics Data System (ADS)

A computationally optimized low dimensional nonlinear dynamical model of the magnetosphere-ionosphere system called WINDMI is used to analyze large geomagnetic storm events. The results are evaluated focusing on the sawtooth intervals and the overall prediction of the westward auroral electrojet (AL) index and Dst index. The input to the model is the dynamo driving voltage derived from the fluctuating solar wind plasma and the interplanetary magnetic field measured by the ACE satellite. The output of the model is a field aligned current proportional to the AL index and the energy stored in the ring current which is proportional to the Dst index. The model parameters are optimized using a genetic algorithm (GA) to obtain solutions that simultaneously have least mean square fit to the AL and Dst indices and also exhibit substorms of period 2-4 hours. The GA optimization results show that the model is able to predict the Dst index reliably and captures the timing and periodicity of the sawtooth signatures in the AL index reasonably well for the storm events. This work was partially supported by NSF grant ATM-0539099. J. Kozyra would like to acknowledge support for this work under NASA grant NNG05GJ89G and NSF grant ATM-0402163.

Spencer, E.; Horton, W.; Mays, L.; Doxas, I.; Kozyra, J.

2006-05-01

106

Why AA Works  

Microsoft Academic Search

The therapeutic efficacy of AA, though acknowledged, is little understood. An analysis of the addictive experience is conducted to provide explanatory hypotheses for the success of AA. The addictive experience is characterized by intensity of feelings which cannot be rendered symbolically via language. Out of this mode of experiencing emerges three phenomena: (1) an alleration in the sense of the

Ronald E. Hopson; Bethany Beaird-Spiller

1995-01-01

107

A'a' Channel  

USGS Multimedia Gallery

An a'a' channel near the Royal Gardens subdivision on Kilauea Volcano, Hawaii. The flows in the background are from the 1980s. Note that the flow level is below the levees and the pahoehoe overflows emplaced on top of the a'a'.  If lava has the right viscosity, it can travel across a landscape...

108

The Geomagnetic Field: Frequently Asked Questions  

NSDL National Science Digital Library

This is a group of frequently asked questions and answers about Earth's magnetic field and poles, the magnetic compass, magnetic reversals, and geomagnetic models. Links to maps and illustrations are embedded in the text.

109

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

NASA Astrophysics Data System (ADS)

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

Klimenko, Maxim; Klimenko, Vladimir

110

The International Geomagnetic Reference Field, 2005  

USGS Publications Warehouse

This is a set of five world charts showing the declination, inclination, horizontal intensity, vertical component, and total intensity of the Earth's magnetic field at mean sea level at the beginning of 2005. The charts are based on the International Geomagnetic Reference Field (IGRF) main model for 2005 and secular change model for 2005-2010. The IGRF is referenced to the World Geodetic System 1984 ellipsoid. Additional information about the USGS geomagnetism program is available at: http://geomag.usgs.gov/

Rukstales, Kenneth S.; Love, Jeffrey J.

2007-01-01

111

THEMIS observations of plasmaspheric hiss: its dependence on solar wind parameters and geomagnetic activity  

NASA Astrophysics Data System (ADS)

Accurate knowledge of the global distribution of plasmaspheric hiss is essential for radiation belt modeling because it provides a direct link to understanding radiation belt losses in the slot and the inner region of the outer belt. In this study, we show its dependence on solar wind parameters and geomagnetic activity using THEMIS hiss measurements made from 1 July 2008 to 30 June 2012 for all five probes, and develop models of the global distribution of hiss amplitudes based on in-situ measurements of IMF and solar wind parameters as well as geomagnetic indices using an artificial neural network technique. We find that solar wind speed of IMF and solar wind parameters employed as inputs is the most influential parameters that affect the evolution of the magnetospheric hiss while Sym-H of geomagnetic indices is an effective index at capturing the measured hiss variance than AE or Kp index. The solar wind parameter-based hiss model generally results in a higher correlation between measured and modeled hiss amplitudes than any other models including geomagnetic indices AE, Kp, and Dst.

Kim, K.; Shprits, Y.; Cho, J.

2013-12-01

112

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

113

Dependence of Geomagnetic Storms on Their Associated Halo CME Parameters  

NASA Astrophysics Data System (ADS)

We compare the geoeffective parameters of halo coronal mass ejections (CMEs). We consider 50 front-side full-halo CMEs (FFH CMEs), which are from the list of Michalek, Gopalswamy, and Yashiro ( Solar Phys. 246, 399, 2007), whose asymmetric-cone model parameters and earthward-direction parameter were available. For each CME we use its projected velocity [ V p], radial velocity [ V r], angle between cone axis and sky plane [ ?] from the cone model, earthward-direction parameter [ D], source longitude [ L], and magnetic-field orientation [ M] of its CME source region. We make a simple linear-regression analysis to find out the relationship between CME parameters and Dst index. The main results are as follows: i) The combined parameters [( V r D)1/2 and V r ?] have higher correlation coefficients [cc] with the Dst index than the other parameters [ V p and V r]: cc=0.76 for ( V r D)1/2, cc=0.70 for V r ?, cc=0.55 for V r, and cc=0.17 for V p. ii) Correlation coefficients between V r ? and Dst index depend on L and M; cc=0.59 for 21 eastern events [E], cc=0.80 for 29 western events [W], cc=0.49 for 17 northward magnetic-field events [N], and cc=0.69 for 33 southward magnetic-field events [S]. iii) Super geomagnetic storms (Dst?-200 nT) only appear in the western and southward magnetic-field events. The mean absolute Dst values of geomagnetic storms (Dst?-50 nT) increase with an order of E+N, E+S, W+N, and W+S events; the mean absolute Dst value (169 nT) of W+S events is significantly larger than that (75 nT) of E+N events. Our results demonstrate that not only do the cone-model parameters together with the earthward-direction parameter improve the relationship between CME parameters and Dst index, but also the longitude and the magnetic-field orientation of a FFH CME source region play a significant role in predicting geomagnetic storms.

Lee, Jae-Ok; Moon, Y.-J.; Lee, Kyoung-Sun; Kim, R.-S.

2014-06-01

114

Long periods (1 -10 mHz) geomagnetic pulsations variation with solar cycle in South Atlantic Magnetic Anomaly  

NASA Astrophysics Data System (ADS)

The occurrence and intensity of the geomagnetic pulsations Pc-5 (2-7 mHz) and its relationship with the solar cycle in the South Atlantic Magnetic Anomaly -SAMA is presented. The study of geomagnetic pulsations is important to help the understanding of the physical processes that occurs in the magnetosphere region and help to predict geomagnetic storms. The fluxgate mag-netometers H, D and Z, three axis geomagnetic field data from the Southern Space Observatory -SSO/CRS/INPE -MCT, São Martinho da Serra (29.42° S, 53.87° W, 480m a.s.l.), RS, Brasil, a were analyzed and correlated with the solar wind parameters (speed, density and temperature) from the ACE and SOHO satellites. A digital filtering to enhance the 2-7 mHz geomagnetic pulsations was used. Five quiet days and five perturbed days in the solar minimum and in the solar maximum were selected for this analysis. The days were chosen based on the IAGA definition and on the Bartels Musical Diagrams (Kp index) for 2001 (solar maximum) and 2008 (solar minimum). The biggest Pc-5 amplitude averages differences between the H-component is 78,35 nT for the perturbed days and 1,60nT for the quiet days during the solar maximum. For perturbed days the average amplitude during the solar minimum is 8,32 nT, confirming a direct solar cycle influence in the geomagnetic pulsations intensity for long periods.

Rigon Silva, Willian; Schuch, Nelson Jorge; Guimarães Dutra, Severino Luiz; Babulal Trivedi, Nalin; Claudir da Silva, Andirlei; Souza Savian, Fernando; Ronan Coelho Stekel, Tardelli; de Siqueira, Josemar; Espindola Antunes, Cassio

115

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

116

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

NASA Astrophysics Data System (ADS)

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

Kamide, Y.; Joselyn, J. A.

117

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

NASA Astrophysics Data System (ADS)

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

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

2001-08-01

118

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

119

A'a' Channel  

USGS Multimedia Gallery

Detail of levee on an active channelized aa flow. Note the pahoehoe overflows in the levees and the level of the active flow below the tops of the levees. This lower flow level is not allowed in the commonly used

120

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

121

On the geomagnetic storm response and recovery timescales of the thermosphere  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

122

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

123

Gravitational dynamos and the low-frequency geomagnetic secular variation  

E-print Network

Gravitational dynamos and the low-frequency geomagnetic secular variation P. Olson* Department number. Chaotic gravitational dynamos have large-amplitude dipole secular variation with maximum power drift, polarity reversals, and excursions. geodynamo geomagnetic polarity reversals gravitational dynamo

Olson, Peter L.

124

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

125

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

126

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

127

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

128

Toward a possible next geomagnetic critical transition?  

NASA Astrophysics Data System (ADS)

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

Qamili, Enkelejda; De Santis, Angelo; Wu, Lixin

2014-05-01

129

Antarctic geomagnetic reference model updated to 2010 and provisionally to 2012  

NASA Astrophysics Data System (ADS)

The Antarctic Reference Model (ARM) has been here updated using recent geomagnetic data measured over the Antarctic continent from both ground observatories and satellites. This regional geomagnetic model is based on a Spherical Cap Harmonic Analysis (SCHA) of geomagnetic field measurements over a polar cap of 30° half-angle centred at the geographic South Pole, fixing the maximum spatial expansion index kmax = 8 and the maximum temporal order of polynomials qmax = 4. The importance of updating ARM model lies, for instance, in its usefulness for the reduction of magnetic surveys, performed during the period of model validity over the Antarctica, or for geomagnetic anomaly field estimations. Moreover, so far, ARM still remains the only regional reference magnetic model specifically constructed for the Antarctic continent. The present updated version can be considered valid from 1955.5 to 2010.0 with predictive coefficients up to 2012.0. The model includes the most recent available data but, in contrast to previous versions not only does it take advantage of a stricter selection of satellite data in order to consider even quieter periods of external magnetic activity, but it also includes ground observatory data previous to 1960 going back to 1955.8. Like the previous versions, the new updated model has been tested and compared with major global models to show its reliability over the region under investigation.

Tozzi, Roberta; De Santis, Angelo; Gaya-Piqué, Luis-Ricardo

2013-02-01

130

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

NASA Astrophysics Data System (ADS)

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

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

131

Large Geomagnetic Storms: Introduction to Special Section  

NASA Technical Reports Server (NTRS)

Solar cycle 23 witnessed the accumulation of rich data sets that reveal various aspects of geomagnetic storms in unprecedented detail both at the Sun where the storm causing disturbances originate and in geospace where the effects of the storms are directly felt. During two recent coordinated data analysis workshops (CDAWs) the large geomagnetic storms (Dst < or = -100 nT) of solar cycle 23 were studied in order to understand their solar, interplanetary, and geospace connections. This special section grew out of these CDAWs with additional contributions relevant to these storms. Here I provide a brief summary of the results presented in the special section.

Gopalswamy, N.

2010-01-01

132

First geomagnetic measurements in the Antarctic region  

NASA Astrophysics Data System (ADS)

Based on data from literature and archival sources, we have further processed and analyzed the results of geomagnetic measurements made during the 1772-1775 Second World Expedition by James Cook and the 1819-1821 overseas Antarctic Expedition by Russian mariners Bellingshausen and Lazarev. Comparison with the GUFM historical model showed that there are systematic differences in the spatial structure of both the declination and its secular variation. The results obtained can serve as a basis for the construction of regional models of the geomagnetic field for the Antarctic region.

Raspopov, O. M.; Demina, I. M.; Meshcheryakov, V. V.

2014-05-01

133

Geomagnetic storm fields near a synchronous satellite.  

NASA Technical Reports Server (NTRS)

An apparent early recovery of the main phase of geomagnetic storms at the distance of the synchronous satellite is examined in terms of changing electric current distributions in the magnetosphere during magnetic storms. It is suggested that a rapid recession of the edge of the plasma sheet (after the advance toward the earth during an early epoch of the main phase) is partly responsible for the early recovery. Relevant plasma sheet variations during geomagnetic storms are found to be in agreement with the inferred variations.

Kawasaki, K.; Akasofu, S. I.

1971-01-01

134

Local geomagnetic indices and the prediction of auroral power  

NASA Astrophysics Data System (ADS)

aurora has been related to magnetometer observations for centuries and to geomagnetic indices for decades. As the number of stations and data processing power increases, just how auroral power (AP) relates to geomagnetic observations becomes a more tractable question. This paper compares Polar ultraviolet imager AP observations during 1997 with a variety of indices. Local time (LT) versions of the SuperMAG auroral electrojet (SME) are introduced and examined, along with the corresponding upper and lower envelopes (SMU and SML). Also, the east-west component, BE, is investigated. We also consider whether using any of the local indices is actually better at predicting local AP than a single global index. Each index is separated into 24 LT indices with a sliding 3 h magnetic local time (MLT) window. The ability to predict AP varies greatly with LT, peaking at 19:00 MLT, where about 75% of the variance (r2) is predicted at 1 min cadence. The aurora is fairly predictable from 17:00 MLT to 04:00 MLT, roughly the region in which substorms occur. AP is poorly predicted from auroral electrojet indices from 05:00 MLT to 15:00 MLT, with the minimum at 10:00-13:00 MLT. In the region of high predictability, the local index which works best is BE (east-west), in contrast to long-standing expectations. However, using global SME is better than any local index. AP is best predicted by combining global SME with a local index: BE from 15:00 to 03:00 MLT and either SMU or SML from 03:00 to 15:00 MLT. In the region of the diffuse aurora, it is better to use a 30 min average than the cotemporaneous 1 min SME value, while from 15:00 to 02:00 MLT, the cotemporaneous 1 min SME works best, suggesting a more direct physical relationship with the auroral circuit. These results suggest a significant role for discrete auroral currents closing locally with Pedersen currents.

Newell, P. T.; Gjerloev, J. W.

2014-12-01

135

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

136

Magnetospheric impulse response for many levels of geomagnetic activity  

NASA Technical Reports Server (NTRS)

The temporal relationship between the solar wind and magnetospheric activity has been studied using 34 intervals of high time resolution IMP 8 solar wind data and the corresponding AL auroral activity index. The median values of the AL index for each interval were utilized to rank the intervals according to geomagnetic activity level. The linear prediction filtering technique was then applied to model magnetospheric response as measured by the AL index to the solar wind input function VB(s). The linear prediction filtering routine produces a filter of time-lagged response coefficients which estimates the most general linear relationship between the chosen input and output parameters of the magnetospheric system. It is found that the filters are composed of two response pulses speaking at time lags of 20 and 60 min. The amplitude of the 60-min pulse is the larger for moderate activity levels, while the 20-min pulse is the larger for strong activity levels. A possible interpretation is that the 20-min pulse represents magnetospheric activity driven directly by solar wind coupling and that the 60-min pulse represents magnetospheric activity driven by the release of energy previously stored in the magnetotail. If this interpretation is correct, the linear filtering results suggest that both the driven and the unloading models of magnetospheric response are important facets of a more comprehensive response model.

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

1985-01-01

137

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

NASA Astrophysics Data System (ADS)

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

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

2010-01-01

138

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

139

Geomagnetic referencing in the arctic environment  

USGS Publications Warehouse

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

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

2011-01-01

140

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

141

Enhancing model based forecasting of geomagnetic storms  

NASA Astrophysics Data System (ADS)

Modern society is increasingly dependent on the smooth operation of large scale technology supporting Earth based activities such as communication, electricity distribution, and navigation. This technology is potentially threatened by global geomagnetic storms, which are caused by the impact of plasma ejected from the Sun upon the protective magnetic field that surrounds the Earth. Forecasting the timing and magnitude of these geomagnetic storms is part of the emerging discipline of space weather. The most severe geomagnetic storms are caused by magnetic clouds, whose properties and characteristics are important variables in space weather forecasting systems. The methodology presented here is the development of a new statistical approach to characterize the physical properties (variables) of the magnetic clouds and to examine the extent to which theoretical models can be used in describing both of these physical properties, as well as their evolution in space and time. Since space weather forecasting is a complex system, a systems engineering approach is used to perform analysis, validation, and verification of the magnetic cloud models (subsystem of the forecasting system) using a model-based methodology. This research demonstrates that in order to validate magnetic cloud models, it is important to categorize the data by physical parameters such as velocity and distance travelled. This understanding will improve the modeling accuracy of magnetic clouds in space weather forecasting systems and hence increase forecasting accuracy of geomagnetic storms and their impact on earth systems.

Webb, Alla G.

142

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

143

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

144

Geomagnetic effects on atmospheric Cherenkov images  

Microsoft Academic Search

Atmospheric Cherenkov telescopes are used to detect electromagnetic showers from primary gamma rays and to discriminate these from cascades due to hadrons using the Cherenkov images. The geomagnetic field affects the development of showers and is shown to diffuse and distort the images and the effects should be included in interpreting the observations.

P. M. Chadwick; M. K. Daniel; K. Lyons; T. J. L. McComb; J. M. McKenny; S. J. Nolan; K. J. Orford; J. L. Osborne; S. M. Rayner

2001-01-01

145

Geomagnetic effects on atmospheric Cherenkov images  

Microsoft Academic Search

Atmospheric Cherenkov telescopes are used to detect electromagnetic showers from primary gamma rays and to discriminate these from cascades due to hadrons using the Cherenkov images. The geomagnetic field affects the development of showers and is shown to diffuse and distort the images and the effects should be included in interpreting the observations. .

P. M. Chadwick; M. K. Daniel; K. Lyons; T. J. L. McComb; J. M. McKenny; S. J. Nolan; K. J. Orford; J. L. Osborne; S. M. Rayner

2001-01-01

146

Geomagnetic effects on atmospheric Cerenkov images  

Microsoft Academic Search

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

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

1999-01-01

147

Concerning a Lunar Modulation of Geomagnetic Activity  

Microsoft Academic Search

The behavior of the daily Kindex of magnetic activity is investigated as a function of lunar phase by the method of superposed epochs. The analysis indicates a slight but statistically significant enhancement of geomagnetic disturbance during several days fol- lowing full moon and, with marginal significance, a slight diminution of disturbance during several days preceding full moon. A small dip

B. Bell; R. J. Defouw

1964-01-01

148

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

149

Solar magnetic fields and geomagnetic events  

Microsoft Academic Search

Some interplanetary studies lead one to expect that the toroidal fields of individual active regions are directly related to their heliospheric structure. Other studies conclude that the large-scale solar dipolar field is more important. We have carried out two studies that bear on these apparently conflicting views. We first studied geomagnetic events temporally associated with the eruption of 18 individual

Alexei A. Pevtsov; Richard C. Canfield

2001-01-01

150

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

NASA Astrophysics Data System (ADS)

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

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

151

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.

152

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

153

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

154

Geomagnetic storm's precursors observed from 2001 to 2007 with the Global Muon Detector Network (GMDN)  

NASA Astrophysics Data System (ADS)

We use complementary observations from the prototype and expanded Global Muon Detector Network (GMDN) and the Advanced Composition Explorer (ACE) satellite to identify precursors of geomagnetic storm events. The GMDN was completed and started operation in March 2006 with the addition of the Kuwait detector, complementing the detectors at Nagoya, Hobart, and São Martinho da Serra. Analyzed geomagnetic storms sorted by their intensity as measured by the Disturbance storm-time (Dst) index. Between March 2001 and December 2007, 122 Moderate Storms (MS), 51 Intense Storms (IS), and 8 Super Storms (SS) were monitored by the GMDN. The major conclusions are (i) the percentage of the events accompanied by the precursors prior to the Sudden Storm Commencement (SSC) increases with increasing peak Dst, (ii) 15% of MSs, 30% of ISs, and 86% of SSs are accompanied by cosmic ray precursors observed on average 7.2 hours in advance of the SSC.

Rockenbach, M.; Dal Lago, A.; Gonzalez, W. D.; Munakata, K.; Kato, C.; Kuwabara, T.; Bieber, J.; Schuch, N. J.; Duldig, M. L.; Humble, J. E.; Al Jassar, H. K.; Sharma, M. M.; Sabbah, I.

2011-08-01

155

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

NASA Technical Reports Server (NTRS)

Six-month and yearly averages of solar-wind speed from 1962 to 1975 are shown to be highly correlated with geomagnetic activity as measured by averages of the Ap index. On the same time scale the correlation between the southward component of the interplanetary magnetic field and geomagnetic activity is poor. Previous studies with hourly averages gave opposite results. The better correlation with the southward component on an hourly time scale is explained by its large variation compared with the relatively constant solar-wind speed. However, on a yearly time scale the magnitude of the variations in both parameters are about the same. This problem can be solved by invoking an energy transfer mechanism which is proportional to the first power of the southward component and a higher power of the solar-wind speed.

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

1977-01-01

156

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

157

major code major conc codeconcentration program code program degree coll dept AA Associate of Arts NONE No Concentration AA-AA Associate of Arts AA GC WP  

E-print Network

major code major conc codeconcentration program code program degree coll dept AA Associate of Arts NONE No Concentration AA-AA Associate of Arts AA GC WP ABLR Abused Land Rehabilitation NONE Education K-12 Brdfld BA AA ART ARTG Art GRPH Graphic Design ARTG-BFA Graphic Design BFA AA ART ARTH Art

Dyer, Bill

158

Short-term forecasting regional model to predict M(3000)F2 over the European sector: Comparisons with the IRI model during moderate, disturbed, and very disturbed geomagnetic conditions  

NASA Astrophysics Data System (ADS)

The hourly measurements of M(3000)F2 (M(3000)F2meas) and the hourly quiet-time values of M(3000)F2 (M(3000)F2QT) relative to the ionospheric observatories of Poitiers, Lannion, Dourbes, Slough, Rome, Juliusruh, Kaliningrad, Uppsala, Lyckesele, Sodankyla, and Kiruna as well as the hourly time-weighted accumulation series derived from the geomagnetic planetary index ap (ap(?), were considered during the period January 1957-December 2003 and used for the development of 11 short-term forecasting local models (STFLM) of M(3000)F2. Under the assumption that the ionospheric disturbance index ln(M(3000)F2meas/M(3000)F2QT) is correlated to the integrated geomagnetic index ap(?), a set of regression coefficients were established over 12 months and 24 h for each of the 11 observatories under consideration and used as input to calculate the short-term ionospheric forecasting of M(3000)F2 for three different ranges of geomagnetic activity. The 11 short-term forecasting local models all together constitute a single short-term forecasting regional model (STFRM) of M(3000)F2. The monthly median predictions of M(3000)F2 provided by the IRI model at the 11 local stations were used to make some comparisons with the predictions of M(3000)F2 carried out by the STFRM. The results showed that: (1) under moderate geomagnetic activity there are no significantly differences between STFRM and IRI performance because quiet geomagnetic conditions are not so diverse from moderate geomagnetic conditions; (2) under disturbed geomagnetic activity, performances of STFRM significantly better than IRI emerge only in some cases; (3) the STFRM's performances are always significantly better than those provided by IRI under very disturbed geomagnetic activity, consequently the operative use of the STFRM could be valuable in providing short-term forecasting maps of M(3000)F2 over the European area during very disturbed geomagnetic conditions.

Pietrella, M.

2014-07-01

159

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

NASA Astrophysics Data System (ADS)

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

Sharma, A. K.; et al.

2006-11-01

160

AAS Job Register  

NSDL National Science Digital Library

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

161

Steady induction effects in geomagnetism. Part 1A: Steady motional induction of geomagnetic chaos  

NASA Technical Reports Server (NTRS)

Geomagnetic effects of magnetic induction by hypothetically steady fluid motion and steady magnetic flux diffusion near the top of Earth's core are investigated using electromagnetic theory, simple magnetic earth models, and numerical experiments with geomagnetic field models. The problem of estimating a steady fluid velocity field near the top of Earth's core which induces the secular variation indicated by broad-scale models of the observed geomagnetic field is examined and solved. In Part 1, the steady surficial core flow estimation problem is solved in the context of the source-free mantle/frozen-flux core model. In the first paper (IA), the theory underlying such estimates is reviewed and some consequences of various kinematic and dynamic flow hypotheses are derived. For a frozen-flux core, fluid downwelling is required to change the mean square normal magnetic flux density averaged over the core-mantle boundary. For surficially geostrophic flow, downwelling implies poleward flow. The solution of the forward steady motional induction problem at the surface of a frozen-flux core is derived and found to be a fine, easily visualized example of deterministic chaos. Geomagnetic effects of statistically steady core surface flow may well dominate secular variation over several decades. Indeed, effects of persistent, if not steady, surficially geostrophic core flow are described which may help explain certain features of the present broad-scale geomagnetic field and perhaps paleomagnetic secular variation.

Voorhies, Coerte V.

1992-01-01

162

Real-Time WINDMI Predictions of Geomagnetic Storms and Substorms  

NASA Astrophysics Data System (ADS)

The performance of the Real-Time WINDMI model is surveyed for its predictions of storm/substorm events from February 2006 to present time. Three solar wind-magnetosphere dynamo voltage Vsw(t) coupling functions are used: the standard Rectified coupling function, a function due to Siscoe, and a recent function due to Newell. Real-Time WINDMI is a low dimensional, plasma physics-based, nonlinear dynamical model of the coupled solar wind- magnetosphere-ionosphere system. The realtime model at CCMC/GSFC downloads ACE data to predict AL and Dst values approximately one hour before geomagnetic substorm and storm events; subsequently, every ten minutes ground based measurements compiled by WDC Kyoto are compared with model predictions(http://orion.ph.utexas.edu/~windmi/realtime/). Model AL and Dst predictions are validated using the average relative variance (ARV),correlation coefficient (COR), and root mean squared error (RMSE). Model AL predictions correlate at least one standard deviation better with the AL index data than a direct correlation between the input coupling functions and the AL index. The earlier 2006-2008 data analysis showed that the best prediction performance for the Dst came from using the Rectified input. The work is supported by NSF grant AGS 0964692.

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

2010-12-01

163

Geomagnetic modeling by optimal recursive filtering  

NASA Technical Reports Server (NTRS)

The results of a preliminary study to determine the feasibility of using Kalman filter techniques for geomagnetic field modeling are given. Specifically, five separate field models were computed using observatory annual means, satellite, survey and airborne data for the years 1950 to 1976. Each of the individual field models used approximately five years of data. These five models were combined using a recursive information filter (a Kalman filter written in terms of information matrices rather than covariance matrices.) The resulting estimate of the geomagnetic field and its secular variation was propogated four years past the data to the time of the MAGSAT data. The accuracy with which this field model matched the MAGSAT data was evaluated by comparisons with predictions from other pre-MAGSAT field models. The field estimate obtained by recursive estimation was found to be superior to all other models.

Gibbs, B. P.; Estes, R. H.

1981-01-01

164

Prediction of recurrent geomagnetic disturbances by using adaptive filtering  

NASA Astrophysics Data System (ADS)

Recurrent geomagnetic disturbances are an important part of geomagnetic activities, which are associated with the neutral sheet structure in the heliosphere and the activities of long lived solar coronal holes. Another significant character is the periodic activities recorded by geomagnetic indices. In this paper an algorithm--Adaptive Filtering (AF), is introduced to forecast recurrent geomagnetic events based on the geomagnetic Kindex. Adaptive filtering can deal with nonstationary data and can adapt to changes in the data pattern. Therefore it is a very helpful method for forecasting the geomagnetic disturbances and the disturbances in the interplanetary space. By using AF technique a prediction for whole Bartels rotation can be obtained when output length is taken as 27-point. For recurrent periods the prediction efficiency is about 30%, the correlation coefficient is 0.55. For nonrecurrent periods the prediction efficiency and correlation coefficient decrease obviously, but the standard variance does not change very much.

Zhou, X.-Y.; Wei, F.-S.

1998-10-01

165

Isolated sleep paralysis, vivid dreams and geomagnetic influences: II.  

PubMed

This report describes a test of the hypothesis that significant changes in the ambient geomagnetic field are associated with altered normal nighttime dream patterns. Specifically, it was predicted that there would be a greater incidence of isolated sleep, paralysis or vivid dreams with abrupt rises and falls of geomagnetic activity. The author's (JC) and a second subject's (KC) daily reports of dream-recall were analyzed in the context of daily fluctuations of geomagnetic activity (K indices). Two analyses of variance indicated (i) significantly higher geomagnetic activity three days before a recorded isolated sleep paralysis event and (ii) significantly lower geomagnetic activity three days before an unusually vivid dream took place. Conversely, geomagnetic activity did not fluctuate significantly for randomly selected days. Testing a large sample over time is required for confirmation and extension of this work. PMID:9347546

Conesa, J

1997-10-01

166

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

167

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

168

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

169

GEOMAGNETIC INSTRUMENTATION FOR REPEAT STATION SURVEY  

Microsoft Academic Search

Repeat station survey measurements are important geomagnetic data because they are widely used both for fundamental science\\u000a (e. g., study of Earth’s magnetic dynamo) and for applied purposes (e.g., declination charts for aviation safety). To execute\\u000a repeat station surveys, normally three types of instruments are used: absolute scalar magnetometers, threecomponent vector\\u000a variometers, and theodolite-mounted one-component magnetometers. The modern specifications of

VALERY KOREPANOV

170

Domino model for geomagnetic field reversals.  

PubMed

We solve the equations of motion of a one-dimensional planar Heisenberg (or Vaks-Larkin) model consisting of a system of interacting macrospins aligned along a ring. Each spin has unit length and is described by its angle with respect to the rotational axis. The orientation of the spins can vary in time due to spin-spin interaction and random forcing. We statistically describe the behavior of the sum of all spins for different parameters. The term "domino model" in the title refers to the interaction among the spins. We compare the model results with geomagnetic field reversals and dynamo simulations and find strikingly similar behavior. The aggregate of all spins keeps the same direction for a long time and, once in a while, begins flipping to change the orientation by almost 180 degrees (mimicking a geomagnetic reversal) or to move back to the original direction (mimicking an excursion). Most of the time the spins are aligned or antialigned and deviate only slightly with respect to the rotational axis (mimicking the secular variation of the geomagnetic pole with respect to the geographic pole). Reversals are fast compared to the times in between and they occur at random times, both in the model and in the case of the Earth's magnetic field. PMID:23410284

Mori, N; Schmitt, D; Wicht, J; Ferriz-Mas, A; Mouri, H; Nakamichi, A; Morikawa, M

2013-01-01

171

Why utilities respect geomagnetically induced currents  

NASA Astrophysics Data System (ADS)

It has been well known for more than 50 years that electric utilities in northern latitudes can have geomagnetically induced currents (GICs) flowing in their transmission lines and transformer ground points, and that these are caused by geomagnetic storms. Initially, these GICs were considered harmless and very little attention was paid to them. However, in the last 40 years it was realized that large GICs can flow in power systems and become problematic and even severe enough to cause a complete system shutdown. Utilities susceptible to GIC do not expect to rely on luck that the geomagnetic storm will not affect them, or if it does, the loading conditions at the time will allow enough margin to ride through it. This is precisely why many utilities today are studying the cause, effect, and mitigation of GICs and why utilities respect GICs. This paper presents a detailed discussion on how electric utilities are affected by GICs and what can be accomplished to mitigate the harmful effects.

Molinski, Tom S.

2002-11-01

172

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

173

Interplanetary magnetic sector polarity inferred from polar geomagnetic field observations  

NASA Technical Reports Server (NTRS)

In order to infer the interplanetary sector polarity from polar geomagnetic field diurnal variations, measurements were carried out at Godhavn and Thule (Denmark) Geomagnetic Observatories. The inferred interplanetary sector polarity was compared with the polarity observed at the same time by Explorer 33 and 35 magnetometers. It is shown that the polarity (toward or away from the sun) of the interplanetary magnetic field can be reliably inferred from observations of the polar cap geomagnetic fields.

Friis-Christensen, E.; Lassen, K.; Wilcox, J. M.; Gonzalez, W.; Colburn, D. S.

1971-01-01

174

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

175

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.

1992-01-01

176

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

NASA Astrophysics Data System (ADS)

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

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

177

Dependence of neutral temperatures in the lower thermosphere on geomagnetic activity  

NASA Astrophysics Data System (ADS)

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

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

2007-06-01

178

Correlation as a global measure of geomagnetic activity: Phase boundaries and a precedent line of nodes  

NASA Astrophysics Data System (ADS)

This work considers the global correlation of geomagnetic activity as a way to evaluate magnetotail disturbances, such as the substorm. Impulsive magnetotail disturbances are generally associated with geomagnetic pulsations, which can be coherent over wide ranges of latitude and longitude, and which display distinctive phase reversals collocated with power maxima. Analyzing a disturbance period chosen for its breadth in local time, we find that pulsations can be detected from the coherence that they generate within a magnetometer array, and identify an extended line of nodes across which the phase reversals occur. Phase reversals consistent with the same line of nodes persist for five hours, beginning clearly in a 0.7 mHz pulsation one and a half hours before the disturbance, and persisting in a 5.8 mHz pulsation three and one half hours after the initial disturbance. Under the hypothesis that the line of nodes maps to a source in the central plasma sheet (CPS), we note that the persistence of this extended source of disturbances suggests memory in the CPS. We define a quantitative “coherence index” that characterizes geomagnetic activity according to the degree of global coherence that it generates, and observe that a narrowly peaked coherence signal leads a much broader peak in power. We relate these results to models of the magnetosphere based in critical phenomena.

Cosgrove, Russell; Sanchez, Ennio

2012-06-01

179

Correlation as a global measure of geomagnetic activity: Phase boundaries and a precedent line of nodes  

NASA Astrophysics Data System (ADS)

We will describe our recent paper, which considers the global correlation of geomagnetic activity as a way to evaluate magnetotail disturbances, such as the substorm. Impulsive magnetotail disturbances are generally associated with geomagnetic pulsations, which can be coherent over wide ranges of latitude and longitude, and which display distinctive phase reversals collocated with power maxima. Analyzing a disturbance period chosen for its breadth in local time, we find that pulsations can be detected from the coherence that they generate within a magnetometer array, and identify an extended line of nodes across which the phase reversals occur. Phase reversals consistent with the same line of nodes persist for five hours, beginning clearly in a 0.7 mHz pulsation one and a half hours before the disturbance, and persisting in a 5.8 mHz pulsation three and one half hours after the initial disturbance. Under the hypothesis that the line of nodes maps to a source in the central plasma sheet (CPS), we note that the persistence of this extended source of disturbances suggests memory in the CPS. We define a quantitative "coherence index" that characterizes geomagnetic activity according to the degree of global coherence that it generates, and observe that a narrowly peaked coherence signal leads a much broader peak in power. We relate these results to models of the magnetosphere based in critical phenomena.

Cosgrove, R. B.; Sanchez, E. R.

2012-12-01

180

A Superposed Epoch Analysis of Geomagnetic Storms over a Solar Cycle: Geomagnetic and Solar Wind Data, Radar Backscatter & Auroral Imagery  

NASA Astrophysics Data System (ADS)

Geomagnetic storms - episodes of intense solar wind-magnetosphere coupling usually associated with extreme conditions in the solar wind such as coronal mass ejections (CMEs) or co-rotating interaction regions (CIRs) - cause large global disturbances in the Earth’s magnetosphere. During such storms, large amounts of energy are deposited in the magnetotail and inner magnetosphere, producing an enhanced ring current and energising plasma to relativistic levels by as yet unknown excitation mechanisms. By exploiting data from the Advanced Composition Explorer (ACE) spacecraft in conjunction with space- and ground-based measurements of geospace over the last solar cycle, a database of geomagnetic storms has been compiled and analysed. Here we present some statistical findings from a superposed epoch analysis of 143 events identified from the global SYM-H index. We find that the duration of the main phase of storms decreases for increasing storm size, as defined by the maximum negative excursion of SYM-H, contrary to the results of previous studies. We also discuss a comparison of CME and CIR driven storms in terms of storm size, phase duration and evolution, and the associated solar wind-magnetosphere coupling. Initial work has successfully identified characteristic radar backscatter observed by the Super Dual Auoral Radar Network (SuperDARN) and, in particular, the new lower-latitude StormDARN radar network during these storm-time conditions. Here we present early findings of a superposed epoch analysis of auroral imagery from the IMAGE spacecraft and ionospheric convection maps from the SuperDARN radar network. This work further illustrates the storm-time coupling between the solar wind and magnetosphere, and develops the relationship between auroral oval radius and the evolution of the storm-time SYM-H index first reported by Milan et al., (2009). Once completed, this will be the most complete superposed epoch analyses of storms to date, combining multiple datasets and analysis techniques. This will enable us to gain a better understanding of complex storm time processes such as the energisation of ring current plasmas.

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

2010-12-01

181

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

NASA Astrophysics Data System (ADS)

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

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

182

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

183

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.

184

Reconstruction of geomagnetic activity and near-Earth interplanetary conditions over the past 167 yr - Part 1: A new geomagnetic data composite  

NASA Astrophysics Data System (ADS)

We present a new composite of geomagnetic activity which is designed to be as homogeneous in its construction as possible. This is done by only combining data that, by virtue of the locations of the source observatories used, have similar responses to solar wind and IMF (interplanetary magnetic field) variations. This will enable us (in Part 2, Lockwood et al., 2013a) to use the new index to reconstruct the interplanetary magnetic field, B, back to 1846 with a full analysis of errors. Allowance is made for the effects of secular change in the geomagnetic field. The composite uses interdiurnal variation data from Helsinki for 1845-1890 (inclusive) 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 new index is termed IDV(1d) because it employs many of the principles of the IDV index derived by Svalgaard and Cliver (2010), inspired by the u index of Bartels (1932); however, we revert to using one-day (1d) means, as employed by Bartels, because the use of near-midnight values in IDV introduces contamination by the substorm current wedge auroral electrojet, giving noise and a dependence on solar wind speed that varies with latitude. The composite is compared with independent, early data from European-sector stations, Greenwich, St Petersburg, Parc St Maur, and Ekaterinburg, as well as the composite u index, compiled from 2-6 stations by Bartels, and the IDV index of Svalgaard and Cliver. Agreement is found to be extremely good in all cases, except two. Firstly, the Greenwich data are shown to have gradually degraded in quality until new instrumentation was installed in 1915. Secondly, we infer that the Bartels u index is increasingly unreliable before about 1886 and overestimates the solar cycle amplitude between 1872 and 1883 and this is amplified in the proxy data used before 1872. This is therefore also true of the IDV index which makes direct use of the u index values.

Lockwood, M.; Barnard, L.; Nevanlinna, H.; Owens, M. J.; Harrison, R. G.; Rouillard, A. P.; Davis, C. J.

2013-11-01

185

Observed high-latitude GNSS disturbances during a less-than-minor geomagnetic storm  

NASA Astrophysics Data System (ADS)

This paper presents the effects of a weak geomagnetic storm event on 17 January 2013. While the Kp index reached a maximum of only 4, this event still caused severe disturbances for Global Navigation Satellite Systems (GNSS)-based positioning services at high latitudes. We present data from the Norwegian Mapping Authority's Real Time Ionospheric Monitor, based on a dense network of geodetic receivers and scintillation indices from scintillation receivers located in Norway. In northern parts of Norway, the centimeter positioning service was severely disturbed for hours. Service-monitoring measurements showed that the effect was significantly worse for a receiver far away from the nearest network reference station.

Andalsvik, Y. L.; Jacobsen, K. S.

2014-12-01

186

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

187

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

188

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

189

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

190

Using the moon to probe the geomagnetic tail lobe plasma  

Microsoft Academic Search

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

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

1975-01-01

191

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

192

Halo Coronal Mass Ejections and Geomagnetic Storms  

NASA Technical Reports Server (NTRS)

In this letter, I show that the discrepancies in the geoeffectiveness of halo coronal mass ejections (CMEs) reported in the literature arise due to the varied definitions of halo CMEs used by different authors. In particular, I show that the low geoeffectiveness rate is a direct consequence of including partial halo CMEs. The geoeffectiveness of partial halo CMEs is lower because they are of low speed and likely to make a glancing impact on Earth. Key words: Coronal mass ejections, geomagnetic storms, geoeffectiveness, halo CMEs.

Gopalswamy, Nat

2009-01-01

193

Geomagnetically Induced Currents: Progress and Issues  

NASA Astrophysics Data System (ADS)

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

Thomson, Alan

2010-05-01

194

Effects of strong geomagnetic storms on Northern railways in Russia  

NASA Astrophysics Data System (ADS)

Seventeen severe magnetic storms occurred in the period 2000 through 2005. In addition there was a major magnetic storm in March 1989. During each of these storms there was an anomaly in the operation of the system of Signalization, Centralization and Blockage (SCB) in some divisions of the high-latitude (˜58 to 64°N) Russian railways. This anomaly was revealed as false traffic light signals about the occupation of the railways. These signals on the Northern railways appeared exactly during the main phases of the strongest part of the geomagnetic storms characterized by high geomagnetic indices Dst and Kp (Ap). Moreover, the durations of these anomalies coincided with the period of the greatest geomagnetic disturbances in a given event. Geomagnetically induced currents (GICs) during significant strengthening of geomagnetic activity are concluded as the obvious reasons for such kind of anomalies.

Eroshenko, E. A.; Belov, A. V.; Boteler, D.; Gaidash, S. P.; Lobkov, S. L.; Pirjola, R.; Trichtchenko, L.

2010-11-01

195

Recherche d'effets quantitatifs associs aux gnotypes AA et Aa un locus  

E-print Network

Recherche d'effets quantitatifs associés aux génotypes AA et Aa à un locus marqueur avec dominance - Lorsqu'on identifie par épreuve de descendance les individus de génotype AA et Aa à un locus marqueur associated with the AA and Aa genotypes at a marker locus with complete dominance : optimization of progeny

Paris-Sud XI, Université de

196

AA-AAS Misperceptions Page 1 March 10, 2010 National Center on Educational Outcomes (NCEO)  

E-print Network

AA-AAS Misperceptions Page 1 March 10, 2010 National Center on Educational Outcomes (NCEO) National the process of rethinking assumptions about alternate assessments based on alternate achievement standards (AA-AAS performance. Assumptions Underlying Misperception: Some people assume that students who take the AA-AAS have

Minnesota, University of

197

A&AA Faculty & Student Services. Date: ______________  

E-print Network

A&AA Faculty & Student Services. Date: ______________ Date: ______________ Office Use: ____________ Added to authorization list ____________ Printed updated list A&AA Faculty & Student Services. Date list A&AA Faculty & Student Services. Date: ______________ Date: ______________ Office Use

198

An association between geomagnetic activity and dream bizarreness.  

PubMed

Daily disturbances of the earth's magnetic field produce variations in geomagnetic activity (GMA) that are reportedly associated with widespread effects on human health and behaviour. Some of these effects could be mediated by an established influence of GMA on the secretion of melatonin. There is evidence from unrelated research that melatonin influences dream bizarreness, and it is hypothesised here that there is an association between GMA and dream bizarreness. Also reported is a preliminary test of this hypothesis, a case study in which the dreams recorded over 6.5 years by a young adult male were analysed. Reports of dreams from the second of two consecutive days of either low or high GMA (K index sum < or =6 or > or = 28) were self-rated for bizarreness on a 1-5 scale. Dreams from low GMA periods (n=69, median bizarreness=4) were found to be significantly more bizarre than dreams from high GMA periods (n=85, median bizarreness=3; p=0.006), supporting the hypothesised association between GMA and dream bizarreness. Studies with larger samples are needed to verify this association, and to determine the extent to which melatonin may be involved. Establishing that there is an association between GMA and dream bizarreness would have relevance for neurophysiological theories of dreaming, and for models of psychotic symptoms resembling bizarre dream events. PMID:19303220

Lipnicki, Darren M

2009-07-01

199

Geomagnetically induced currents in the New Zealand power network  

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

200

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

201

Solar Wind Charge Exchange During Geomagnetic Storms  

NASA Technical Reports Server (NTRS)

On March 31st. 2001, a coronal mass ejection pushed the subsolar magnetopause to the vicinity of geosynchronous orbit at 6.6 RE. The NASA/GSFC Community Coordinated Modeling Center (CCMe) employed a global magnetohydrodynamic (MHD) model to simulate the solar wind-magnetosphere interaction during the peak of this geomagnetic storm. Robertson et aL then modeled the expected 50ft X-ray emission due to solar wind charge exchange with geocoronal neutrals in the dayside cusp and magnetosheath. The locations of the bow shock, magnetopause and cusps were clearly evident in their simulations. Another geomagnetic storm took place on July 14, 2000 (Bastille Day). We again modeled X-ray emission due to solar wind charge exchange, but this time as observed from a moving spacecraft. This paper discusses the impact of spacecraft location on observed X-ray emission and the degree to which the locations of the bow shock and magnetopause can be detected in images.

Robertson, Ina P.; Cravens, Thomas E.; Sibeck, David G.; Collier, Michael R.; Kuntz, K. D.

2012-01-01

202

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

203

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

204

Characteristics of precipitating energetic electron fluxes relative to the plasmapause during geomagnetic storms  

NASA Astrophysics Data System (ADS)

In this study we investigate the link between precipitating electrons from the Van Allen radiation belts and the dynamical plasmapause. We consider electron precipitation observations from the Polar Orbiting Environmental Satellite (POES) constellation during geomagnetic storms. Superposed epoch analysis is performed on precipitating electron observations for the 13 year period of 1999 to 2012 in two magnetic local time (MLT) sectors, morning and afternoon. We assume that the precipitation is due to wave-particle interactions and our two MLT sectors focus on chorus (outside the plasmapause) and plasmaspheric hiss (inside the plasmapause) waves. We generate simple expressions based on the geomagnetic index, Dst, which reproduce the chorus-driven observations for the >30 keV precipitating electron flux magnitudes. Additionally, we find expressions for the fitted spectral index to describe the flux variation with energy, allowing a full energy reproduction as a function of distance from the plasmapause. The hiss-driven precipitating flux occurs inside the plasmapause but is independent of distance from the plasmapause. In the POES observations the hiss-induced electron precipitation is only detectable above the instrument noise in the >300 keV and P6 (>800 keV) channels of the flux detection instrument. We have derived expressions for the storm time variation in flux inside the plasmapause using Dst as a proxy. The observations show that there is little evidence for >800 keV electron precipitation occurring outside of the plasmapause, in the MLT sectors studied.

Whittaker, Ian C.; Clilverd, Mark A.; Rodger, Craig J.

2014-11-01

205

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

PubMed Central

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

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

2008-01-01

206

CME Link to the Geomagnetic Storms  

NASA Technical Reports Server (NTRS)

The coronal mass ejection (CME) link to geomagnetic storms stems from the southward component of the interplanetary magnetic field contained in the CME flux ropes and in the sheath between the flux rope and the CME-driven shock. A typical storm-causing CME is characterized by (i) high speed, (ii) large angular width (mostly halos and partial halos), and (iii)solar source location close to the central meridian. For CMEs originating at larger central meridian distances, the storms are mainly caused by the sheath field. Both the magnetic and energy contents of the storm-producing CMEs can be traced to the magnetic structure of active regions and the free energy stored in them.

Gopalswamy, Nat

2009-01-01

207

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

208

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

209

Geomagnetic equatorial anomaly in zonal plasma flow  

NASA Technical Reports Server (NTRS)

The observation of a geomagnetic signature in the zonal eastward plasma flow, which is a striking feature of the equatorial ionosphere in the evening quadrant is reported. These observations were derived fronm (E x B)/B-squared measurements made with the cylindrical double-floating-probe experiment carried on the Dynamics Explorer 2 satellite. The signature consists of a crest-trough-crest effect in the latitude dependence of the eastward plasma flow with the crests at + or - 8 dip latitude and the trough nearly centered at the dip equator at all geographic longitudes. This phenomenon can be readily interpreted in terms of the altitude dependence of the F region dynamo electric field, and it is related to dip equator signatures in the plasma density and the magnetic declination which have been reported earlier.

Aggson, T. L.; Herrero, F. A.; Mayr, H. G.; Brace, L. H.; Maynard, N. C.

1987-01-01

210

Studies of geomagnetic field variations in Kamchatka  

NASA Astrophysics Data System (ADS)

Transfer function between the vertical and the horizontal components of geomagnetic field variations was studied Frequency characteristics of function parameters are described The connection with medium geoelectric heterogeneities is analyzed Shore effect is considered On the bases of it the depth curve of apparent electric resistance was obtained according to this curve we gave the evaluation of the occurrence depth of asthenospheric conducting layer The behavior of induction vectors in time-and-frequency region was studied The characteristics of the behavior of induction vector real and imaginary parts were determined in connection with medium geoelectric heterogeneities The monitoring results are correlated with earthquake events with E 13-14 at epicenter distance up to 150 km

Moroz, Yu. F.; Smirnov, S. Ed.; Moroz, T. A.

211

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

212

Klein tunneling and cone transport in AA-stacked bilayer graphene  

NASA Astrophysics Data System (ADS)

We investigate the quantum tunneling of electrons in an AA-stacked bilayer graphene (BLG) n-p junction and n-p-n junction. We show that Klein tunneling of an electron can occur in this system. The quasiparticles are not only chiral but are additionally described by a “cone index.” Due to the orthogonality of states with different cone indexes, electron transport across a potential barrier must strictly conserve the cone index, and this leads to the protected cone transport which is unique in AA-stacked BLG. Together with the negative refraction of electrons, electrons residing in different cones can be spatially separated according to their cone index when transmitted across an n-p junction. This suggests the possibility of “cone-tronic” devices based on AA-stacked BLG. Finally, we calculate the junction conductance of the system.

Sanderson, Matthew; Ang, Yee Sin; Zhang, C.

2013-12-01

213

Historical records of the geomagnetic field  

NASA Astrophysics Data System (ADS)

Records of historical direct measurements of the geomagnetic field are invaluable sources to reconstruct temporal variations of the Earth's magnetic field. They provide information about the field evolution back to the late Middle Age. We have investigated such records with focus on Austria and some neighbouring countries. A variety of new sources and source types are examined. These include 19th century land survey and observatory records of the Imperial and Royal "Centralanstalt f. Meteorologie und Erdmagnetismus", which are not included in the existing compilations. Daily measurements at the Imperial and Royal Observatory in Prague have been digitized. The Imperial and Royal Navy carried out observations in the Adriatic Sea during several surveys. Declination values have been collected from famous mining areas in the former Austro-Hungarian Empire. In this connection, a time series for Banska Stiavnica has been compiled. In the meteorological yearbooks of the monastery Kremsmünster regular declination measurements for the first half of the 19th century were registered. Marsigli's observations during military mapping works in 1696 are also included in our collection. Moreover, compass roses on historical maps or declination values marked on compasses, sundials or globes also provide information about ancient field declination. An evaluation of church orientations in Lower Austria and Northern Germany did not support the hypothesis that church naves had been aligned along the East-West direction by means of magnetic compasses. Therefore, this potential source of information must be excluded from our collection. The gathered records are integrated into a database together with corresponding metadata, such as the used measurement instruments and methods. This information allows an assessment of quality and reliability of the historical observations. The combination of compilations of historical measurements with high quality archeo- and paleomagnetic data in a single database enables a reliable joint evaluation of all types of magnetic field records from different origins. This collection forms the basis for a combined inverse modelling of the geomagnetic field evolution.

Arneitz, Patrick; Heilig, Balázs; Vadasz, Gergely; Valach, Fridrich; Dolinský, Peter; Hejda, Pavel; Fabian, Karl; Hammerl, Christa; Leonhardt, Roman

2014-05-01

214

Some Characteristics of Solar Wind and Plasma Behavior of the Sun with the Geomagnetic Activity 1  

E-print Network

Variations of the 27-day average solar wind proton density and solar wind plasma speed have been examined for a period from 1970 to 2012. The variation of the solar wind plasma temperature and the plasma speed have also been considered for the same period including the flow pressure, the sunspot number and the variation of ap index. In general, the solar wind speed reveals an inverse correlation with the solar wind proton density while the solar wind plasma speed and solar wind plasma temperature exhibit similar nature of variation. The solar wind flow pressure is found to vary in a reverse way with solar activity cycle but the geomagnetic activity index ap falls at solar minimum even at a high flow pressure.

A. B. Bhattacharya; M. Debnath

215

AA&AS minor Vice President of  

E-print Network

AA&AS Jacinda Adams, '98 AA&AS minor Vice President of Marketing and Development with Prevent- edge base that has help shape my interactions professionally and personally. Paul Amla, '03 AA&AS minor am so humbled and at the same time honored by this recognition. Sonal Desai, '91 AA&AS minor

Minnesota, University of

216

Interplanetary magnetic sector polarity inferred from polar geomagnetic field observations  

NASA Technical Reports Server (NTRS)

With the use of a prediction technique it is shown that the polarity (toward or away from the sun) of the interplanetary magnetic field can be reliably inferred from observations of the polar geomagnetic field.

Eriss-Christensen, E.; Lassen, K.; Wilcox, J. M.; Gonzalez, W.; Colburn, D. S.

1971-01-01

217

Geomagnetic field variations in seismic waves traveling across a fault  

NASA Astrophysics Data System (ADS)

The results of regular instrumental observations over geomagnetic field variations in the zones of influence of tectonic faults during movement of seismic waves of varied intensity are presented. It has been shown that seismic waves with an amplitude more than 5-10 ?m/s, traveling across the fault zone, always produced geomagnetic field variations. At weaker seismic disturbances, geomagnetic field variations are of the "glimmer" character, and the relative frequency of appearance of the effect drops as the seismic wave amplitude decreases. The quantitative dependence between the maximal value of the full vector of variations in geomagnetic field induction in a fault zone and the amplitude of the seismic disturbance has been found for the first time.

Lukishov, B. G.; Spivak, A. A.; Ter-Semenov, A. A.

2012-01-01

218

Dependence of low-latitude thermospheric wind on geomagnetic disturbance  

NASA Astrophysics Data System (ADS)

A statistical study has been made on variations in horizontal neutral wind velocity in the thermosphere at altitudes of ~250 km observed as Doppler shifts in 630 nm wavelength night airglow taken by the Fabry-Perot Interferometer (FPI) at Shigaraki (34.8N, 136.1E). The goal of the present study is to examine characteristics of the low-latitude thermospheric wind during geomagnetically active periods and address its role in evolving disturbance dynamo. For this purpose, unlike most of the past studies examining correlations with the Kp index, the present study focuses on correlations with the AE index which directly reflect the Joule heating in the polar region. On the basis of the long-term (2000-2009) FPI data with the filter for 630 nm, we firstly construct the quiet-time model of large-scale thermospheric wind above Shigaraki by sorting the data with very low AE activities by local time, season, and solar activity and then averaging them for each condition. Subtracting the quiet-time averages from the observed wind velocities, we conduct superposed epoch analyses on evolution of the residual wind velocity associated with auroral electrojet activities by referring to the AE index. As a result, the thermospheric wind velocity starts shifting westward and slightly southward 1-2 hours after AE rises from the quiet to high (~several hundreds of nT or greater) level. In particular, the westward shift of low latitude thermospheric wind becomes larger with increasing intensity and duration of AE activity. These changes of wind velocity with AE activities are basically consistent with the scenario of disturbance dynamo that the Joule heating caused by enhanced auroral electrojets in the polar region generates an additional, large-scale equatorward wind and the equatorward wind changes its direction to the west as it comes over to the low-mid. latitude region where the interaction of the westward neutral wind with ionospheric plasma drives a dynamo for an eastward current in the night-time equatorial ionosphere. Our detailed statistics also reveal that the westward shift is more evident in the post-midnight sector than pre-midnight and this local time asymmetry becomes clearer during summer. These spatial structures may be formed by mechanical interactions between the disturbance wind component and the global background wind primarily driven by the thermal tide caused by the Sun.

Hori, T.; Otsuka, Y.; Shiokawa, K.; Shinbori, A.

2013-12-01

219

Statistical analysis of geomagnetic storms, coronal mass ejections and solar energetic particle events in the framework of the COMESEP project  

NASA Astrophysics Data System (ADS)

Geomagnetic storms and Solar Energetic Particle (SEP) radiation storms are hazards in space. It is important to mitigate the effects space weather phenomena may have on technology and human life. The aim of the EU FP7 COMESEP (Coronal Mass Ejections and Solar Energetic Particles) project is to develop forecasting tools both for geomagnetic and SEP storms, and relies on both models and data. This includes a statistical analysis of geomagnetic storms and SEP events during the SOHO era. The goal is to connect the impact of these phenomena with the associated Coronal Mass Ejection (CME) and/or solar flare characteristics. Results of these analyses are being implemented into the COMESEP space weather alert system that is being built based on the produced tools. For the analysis of geomagnetic storms, a representative subset of CMEs from the LASCO/SOHO catalog is selected, and includes associations with Dst index values. The main objective is to determine the probability distributions of Dst and other relationships depending on the CME and flare characteristics. The effect of multiple CME occurrences on the probability of large Dst index values and the treatment of semiannual variations of storms are also evaluated. The analysis of SEP events focuses on the quantification of SEP occurrence probabilities and on the identification of correlations between SEPs and solar events. Both quantities depend on the flare heliographic location, soft X-ray intensity, the CME speed and width. The SEP parameters studied include peak fluxes, fluences, spectral fit parameters and enhancements in heavy ion fluxes. A preliminary estimation of false alarms for our system based on the statistical analysis used is under progress to asses the validity of the alerts. This work has received funding from the European Commission FP7 Project COMESEP (263252).

Malandraki, Olga

2013-04-01

220

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

221

The Geomagnetic Field and Radiation in Near-Earth Orbits  

NASA Technical Reports Server (NTRS)

This report shows, in detail, how the geomagnetic field interacts with the particle flux of the radiation belts to create a hazard to spacecraft and humans in near-Earth orbit. It illustrates the geometry of the geomagnetic field lines, especially around the area where the field strength is anomalously low in the South Atlantic Ocean. It discusses how the field will probably change in the future and the consequences that may have on hazards in near space.

Heirtzler, J. R.

1999-01-01

222

Are migrating raptors guided by a geomagnetic compass?  

USGS Publications Warehouse

We tested whether routes of raptors migrating over areas with homogeneous topography follow constant geomagnetic courses more or less closely than constant geographical courses. We analysed the routes taken over land of 45 individual raptors tracked by satellite-based radiotelemetry: 25 peregrine falcons, Falco peregrinus, on autumn migration between North and South America, and seven honey buzzards, Pernis apivorus, and 13 ospreys, Pandion haliaetus, on autumn migration between Europe and Africa. Overall, migration directions showed a better agreement with constant geographical than constant geomagnetic courses. Tracks deviated significantly from constant geomagnetic courses, but were not significantly different from geographical courses. After we removed movements directed far from the mean direction, which may not be migratory movements, migration directions still showed a better agreement with constant geographical than constant geomagnetic courses, but the directions of honey buzzards and ospreys were not significantly different from constant geomagnetic courses either. That migration routes of raptors followed by satellite telemetry are in closer accordance with constant geographical compass courses than with constant geomagnetic compass courses may indicate that geographical (e.g. based on celestial cues) rather than magnetic compass mechanisms are of dominating importance for the birds' long-distance orientation.

Thorup, Kasper; Fuller, Mark R.; Alerstam, T.; Hake, M.; Kjellen, N.; Standberg, R.

2006-01-01

223

Tsunami effects on the Z component of the geomagnetic field  

E-print Network

The vertical component (Z) of the geomagnetic field observed by ground-based observatories of the INTERMAGNET network has been used to analyze the effects of the movement of electrically conducting sea water through the geomagnetic field due to a propagation of a tsumani. The purpose of this work is to study the geomagnetic variations induced by the tsunamis occurred at 26 December, 2004, 27 February, 2010 and 11 March, 2011. For each case study, we selected four magnetic stations belonging to the INTERMAGNET programme that were influenced or more direct affected by the tsumani. To detect these disturbances in the geomagnetic data, the discrete wavelet technique have been used in four levels of decomposition. We were able to detect the localized behavior of the geomagnetic variations induced by the movement of electrically conducting sea-water through the geomagnetic field, i. e., the identification of transients related to the tsunamis. As well, using the minutely magnetogram data, it was able to localize th...

Klausner, Virginia; Mendes, Odim; Papa, Andres R R

2011-01-01

224

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

225

SS OO UU TT HH AA FF RR II CC AA SS QQ UU AA RR EE KK II LL OO MM EE TT RR EE AA RR RR AA YY SKA South Africa Project Office  

E-print Network

SS OO UU TT HH AA FF RR II CC AA SS QQ UU AA RR EE KK II LL OO MM EE TT RR EE AA RR RR AA YY SKA), CIVIL AND BULK SITE ELECTRICAL WORK FOR THE MEERKAT AND KLEREFONTEIN SITES NEAR CARNARVON, NORTHERN CAPE

Jarrett, Thomas H.

226

Bayesian prediction of geomagnetic storms: Wind data, 1996-2010  

NASA Astrophysics Data System (ADS)

The feature-based Bayesian method previously developed by Chen et al. (1996, 1997) to predict the occurrence, severity, and duration of large geomagnetic storms has been run on a daily basis on the Wind/Magnetic Fields Investigation (MFI) data from January 1996 until March 2010. The algorithm uses as input real-time solar wind magnetic field data obtained at the L1 Lagrange point, and the output is the probability prediction of the magnetic field structure of the upstream solar wind that has yet to arrive, and its geoeffectiveness, where geoeffectiveness is measured by the traditional Dst index. The performance characteristics of the method are evaluated using a four-level contingency table: nonstorm disturbances (-80 nT < Dst ? - 50 nT), weak storms (-120 nT < Dst ? - 80 nT), moderate storms (-160 nT < Dst ? - 120 nT), and strong storms (Dst ? - 160 nT). It is found that the greater the level of disturbances, the more accurate the prediction is. With moderate and strong storms combined, the algorithm correctly predicted 30 out of 37 storms (81%). The false negatives are caused by solar wind structures with short durations (? 1-2 hrs) of strong southward magnetic field (say, Bz ? -30 nT), which are sparsely represented in the probability distribution functions constructed using prior solar wind data (OMNI data set from 1973-1981). The algorithm does not predict the storm onset time, but the results of the present and previous tests show that the average warning time ranges from a few hours to a maximum of 10-15 hours.

Chen, James; Slinker, Steven P.; Triandaf, Ioana

2012-04-01

227

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

228

[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

229

Spatial variation in the plasma sheet composition: Dependence on geomagnetic and solar activity  

NASA Astrophysics Data System (ADS)

study the spatial distribution of plasma sheet O+ and H+ ions using data from the COmposition and DIstribution Function (CODIF) instrument on board the Cluster spacecraft from 2001 to 2005. The densities are mapped along magnetic field lines to produce bidimensional density maps at the magnetospheric equatorial plane for various geomagnetic and solar activity levels (represented by the Kp and F10.7 indexes). We analyze the correlation of the O+ and H+ density with Kp and F10.7 in the midtail region at geocentric distances between 15 and 20 RE and in the near-Earth regions at radial distances between 7 and 8 RE. Near Earth the H+ density slightly increases with Kp and F10.7 while in the midtail region it is not correlated with Kp and F10.7. On the contrary, the amount of O+ ions significantly increases with Kp and F10.7 independently of the region. In the near-Earth region, the effects of solar EUV and geomagnetic activity on the O+ density are comparable. In the midtail region, the O+ density increases at a lower rate with solar EUV flux but strongly increases with geomagnetic activity although the effect is modulated by the solar EUV flux level. We also evidence a strong increase of the proportion of O+ ions with decreasing geocentric distance below ~10 RE. These results confirm the direct entry of O+ ions into the near-Earth plasma sheet and suggest that both energetic outflows from the auroral zone and cold outflow from the high-latitude ionosphere may contribute to feed the near-Earth plasma sheet with ionospheric ions.

Maggiolo, R.; Kistler, L. M.

2014-04-01

230

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

231

Time variations of geomagnetic activity indices Kp and Ap: an update  

NASA Astrophysics Data System (ADS)

Kp and Ap indices covering the period 1932 to 1995 are analysed in a fashion similar to that attempted by Bartels for the 1932-1961 epoch to examine the time variations in their characteristics. Modern analysis techniques on the extended data base are used for further insight. The relative frequencies of occurrence of Kp with different magnitudes and the seasonal and solar cycle dependences are seen to be remarkably consistent despite the addition of 35 years of observations. Many of the earlier features seen in the indices and special intervals are shown to be replicated in the present analysis. Time variations in the occurrence of prolonged periods of geomagnetic calm or of enhanced activity are presented and their relation to solar activity highlighted. It is shown that in the declining phase the occurrence frequencies of Kp = 4-5 (consecutively over 4 intervals) can be used as a precursor for the maximum sunspot number to be expected in the next cycle. The semi-annual variation in geomagnetic activity is re-examined utilising not only the Ap index but also the occurrence frequencies of Kp index with different magnitudes. Lack of dependence of the amplitude of semi-annual variation on sunspot number is emphasised. Singular spectrum analysis of the mean monthly Ap index shows some distinct periodic components. The temporal evolution of ~44 month, ~21 month and ~16 month oscillations are examined and it is postulated that while QBO and the 16 month oscillations could be attributed to solar wind and IMF oscillations with analogous periodicity, the 44 month variation is associated with a similar periodicity in recurrent high speed stream caused by sector boundary passage. It is reconfirmed that there could have been only one epoch around 1940 when solar wind speed could have exhibited a 1.3-year periodicity comparable to that seen during the post-1986 period.

Rangarajan, G. K.; Iyemori, T.

1997-10-01

232

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

233

Geomagnetic main 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, Ørsted, and SAC-C. With the completion of the CHAMP mission in 2010, there has been a multiyear gap in satellite-based vector magnetic field measurements available for main field modeling. In this study, we calibrate the special sensor magnetometer instrument on board DMSP to create a data set suitable for main field modeling. These vector field measurements are calibrated to compute instrument timing shifts, scale factors, offsets, and nonorthogonality angles of 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 15 main field model to the data set and compare with the World Magnetic Model and Ørsted scalar measurements. We call this model DMSP-MAG-1, and its coefficients and software are available for download at http://geomag.org/models/dmsp.html. Our results indicate that the DMSP data set will be a valuable source for main field modeling for the years between CHAMP and the recently launched Swarm mission.

Alken, P.; Maus, S.; Lühr, H.; Redmon, R. J.; Rich, F.; Bowman, B.; O'Malley, S. M.

2014-05-01

234

Dependence of neutral temperatures in the lower thermosphere on geomagnetic activity  

NASA Astrophysics Data System (ADS)

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

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

2006-12-01

235

Geomagnetically induced currents in a power grid of northeastern Spain  

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

236

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

237

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.

238

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

239

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

240

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

241

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

242

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

243

AA/PIRC 2008 Eighth Edition  

E-print Network

AA/PIRC © 2008 Eighth Edition AsiAn AmericAn/ PAcific islAnder RESOURCE GUIDE Asian American/Pacific Islander Resource Center University of California, Santa Cruz #12;Table of Contents 1 AA/PIRC Mission, Resources and Services................................................................................ AA

Belanger, David P.

244

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

245

Using the moon to probe the geomagnetic tail lobe plasma  

NASA Technical Reports Server (NTRS)

We have detected the presence of plasma in the lobes of the geomagnetic tail from observations of magnetic induction in the moon forced by time variations of the earth's magnetotail lobe field. The magnitude of the moon's tangential electromagnetic transfer function when the moon is in the lobes of the geomagnetic tail is less than that when the moon is in the solar wind or geomagnetic tail plasma sheet. The tangential transfer function when the moon is in the magnetotail lobes decreases at frequencies above about 8 mHz due to finite wavelength effects. This shows that the waves in the magnetotail lobes which drive the lunar magnetic induction must have speeds far less than the speed of light and wavelengths comparable to the size of the moon.

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

1975-01-01

246

Pre-seismic geomagnetic anomaly and earthquake location  

NASA Astrophysics Data System (ADS)

Many researchers studied the relationships between appearances of geomagnetic anomalies and their distances to earthquake epicenters or faults. Yet, occasionally some magnetometer stations located nearby earthquake epicenters and/or faults do not observe geomagnetic anomalies. In this paper, a new hybrid system which simultaneously takes the hypocenter and fault plane solution into account is constructed to examine 38 earthquakes interpreted to be associated with geomagnetic anomalies during the period 1988-2001 in Taiwan. The Surface Magnetic Anomaly Reference Tip (SMART) of the new system is used instead of the epicenter or the fault to investigate statistically the distance relationship between the anomalies and the earthquake parameters. Results show that the anomalies gather along the fault and in the belt zone to the SMART. Possible mechanisms causing the anomalies in the two zones are proposed and discussed. Characteristics of the anomaly might shed some light on locations of faults before earthquake occurrences.

Chen, Chieh-Hung; Liu, Jann-Yenq; Lin, Pei-Ying; Yen, Horng-Yuan; Hattori, Katsumi; Liang, Wen-Tzong; Chen, Yuh-Ing; Yeh, Yih-Hsiung; Zeng, Xiaoping

2010-06-01

247

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

Federal Register 2010, 2011, 2012, 2013, 2014

...Commission [Docket No. AD12-13-000] Geomagnetic Disturbances to the Bulk-Power System...hold a Staff Technical Conference on Geomagnetic Disturbances to the Bulk-Power System...the Bulk-Power System as affected by geomagnetic disturbances. The conference will...

2012-04-13

248

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

249

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

250

Investigation of the responses of the general circulation at 700 mb to solar-geomagnetic disturbance  

NASA Technical Reports Server (NTRS)

The Northern Hemisphere 700 mb contour heights from 20 N to 70 N for the period 1947-1970 are studied in conjunction with 272 key days, where the daily increase of the Ci index equals or exceeds 1.0. The superposed epoch method is applied from 33 days before to 66 days after the key day for a variety of zonal and meridional indices. It is shown that the 700 mb height difference between 20 N and 55 N increases significantly in winter 4 days following geomagnetic disturbance (in summer a less prominent but statistically significant increase is found 2 days earlier). The effect is most clear in winter in the quadrant 90-175 W and corresponds to a 7% increase in the mean geostrophic westerly flow. The statistical significance of the results is established by applying Student's t-test to the difference of each daily mean from the continuum.

Stolov, H. L.; Shapiro, R.

1973-01-01

251

Observation of low energy protons in the geomagnetic tail at lunar distances. M.S. Thesis  

NASA Technical Reports Server (NTRS)

Three suprathermal ion detectors stationed on the moon were used to detect a region of plasma flowing antisunward along the ordered field lines of the geomagnetic tail, exterior to the plasma sheet. The particle flow displays an integral flux, a bulk velocity, temperatures, and number densities uniquely different from the other particle regimes traversed by the moon. No consistent deviation in the field was found to correspond with the occurrence of the events, which have an angular distribution extending between 50 and 100 deg and a spatial distribution over a wide region in both the Y sub sm and Z sub sm directions. The duration of observable particles varies widely between tail passages, with an apparent correlation between the number of hours of observation and the Kp index averages over these times. It is proposed that these particles may have entered through the cusp region.

Hardy, D. A.

1974-01-01

252

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

NASA Astrophysics Data System (ADS)

Geomagnetic storms are geomagnetic field disturbances caused by gusts in the solar wind injecting a substantial quantity of energy into the magnetosphere intensifying the ring current becoming strong enough to exceed some key threshold of the quantifying storm time Dst index In this work we analyze three intense geomagnetic storms Dst -100nT occurred in period of July 22nd 24th and 27th 2004 We use images of solar corona made by Large Angle and Spectroscopic Coronagraph LASCO and the solar disk made by the Extreme Ultraviolet Imaging Telescope EIT aboard the Solar and Heliospheric Observatory SOHO Observations of plasma and interplanetary magnetic field obtained by the Advanced Composition Explorer ACE were also used We analyze high energy cosmic ray observations obtained using the Muon Telescope of the Brazilian Southern Space Observatory-SSO of the INPE s Southern Regional Space Research Center at 29o26 24 S 53o48 38 W for identify Forbush decreases in the cosmic ray intensity The main objective of this work is study three intense geomagnetic storms Dst - 100 nT that occurred in a relatively small time interval in order to identify their solar origin interplanetary counterparts and cosmic ray modulation near the Earth This study is important for the study of energetic cosmic rays modulation due to a subsequent chain of interplanetary disturbances and in the near future it will help the understanding of space weather cosmic ray variability

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

253

UU AA00 LL11 AA11 YY AA00 has no direct effect on Y whenhas no direct effect on Y when AA11 is set.is set.  

E-print Network

11 UU AA00 LL11 AA11 YY AA00 has no direct effect on Y whenhas no direct effect on Y when AA11 is set.is set. Arrows fromArrows from LL11 andand AA00 toto AA11 represent randomization probability forrepresent randomization probability for AA11 depends ondepends on AA00 andand LL11 No arrows from U directly

254

Index Numbers  

Microsoft Academic Search

Index numbers are used to aggregate detailed information on prices and quantities into scalar measures of price and quantity levels or their growth. The paper reviews four main approaches to bilateral index number theory where two price and quantity vectors are to be aggregated: fixed basket and average of fixed baskets, stochastic, test or axiomatic and economic approaches. The paper

Erwin Diewert

2007-01-01

255

Poloidal and toroidal fields in geomagnetic field modeling  

NASA Astrophysics Data System (ADS)

The application of surface operator theory to poloidal and toroidal fields in geomagnetic field modeling is described. Surface operators are obtained for the dimensionless surface gradient; the dimensionless surface curl; the dimensionless surface Laplacian, as well as for the Funk-Hecke operators, integral operators, and axisymmetric kernels. Methods are given for interpreting satellite measurements of the geomagnetic field B, assuming B is can vary significantly and rapidly with time, and there are electric fields in the sample. Approximation schemes for ionospheric currents are also described.

Backus, G.

1986-02-01

256

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

257

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

258

AA1 ? : A DYNAMIC INCREMENTAL NETWORK THAT LEARNS BY DISCRIMINATION  

E-print Network

AA1 ? : A DYNAMIC INCREMENTAL NETWORK THAT LEARNS BY DISCRIMINATION Christophe Giraud­Carrier Tony­ gorithm (AA) 1 [10], AA2 [8] and AA3 [9]. AA2 inductively constructs a logic circuit consistent with the training instances. Though its convergence is evident, AA2 does not generalise to previously unseen

Martinez, Tony R.

259

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

260

-Dispersed AA7075 Alloy Composites  

NASA Astrophysics Data System (ADS)

TiO2-dispersed AA7075 alloy composites were produced by mechanical milling followed by hot uniaxial compaction and sintering. The effects of volume fraction and dispersoid size on precipitation kinetics, densification, and hardness of the composites were studied in detail. While the sinterability of the composites decreases with increasing volume fraction of the particulate reinforcement (dispersoid), the same increases with decreasing particle size of the reinforcement. Microstructural analysis using X-ray diffraction and scanning electron microscopy shows an improvement in the distribution of reinforcement with decreasing particle size. The hardness of the composites increases with increasing volume fraction and decreasing TiO2 particle size. Further, the reinforced composites do not show age hardenability unlike unreinforced AA7075 alloy. Microstructural analysis reveals the formation of MgTiO3 and ZnO near the TiO2-AA7075 interface, which suppresses the formation of Guinier-Preston (GP) zone resulting in no age hardenability of the composites.

Karunanithi, R.; Ghosh, K. S.; Bera, Supriya

2014-08-01

261

Electrodynamic control for spacecraft attitude stability in the geomagnetic field  

NASA Astrophysics Data System (ADS)

The electrodynamic method of spacecraft attitude control is studied in an octupole geomagnetic field approximation. An analytical derivation is given for refined laws of control over spacecraft electrodynamic parameters, which ensure the required spacecraft guidance. Spacecraft equilibrium position is proved to be stable under continually acting disturbances. The effectiveness and practical feasibility of the proposed spacecraft attitude control method is confirmed by numerical analysis.

Antipov, K. A.; Tikhonov, A. A.

2014-11-01

262

(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

263

The Physics of Geomagnetic-Field Transduction in Animals  

Microsoft Academic Search

Birds, fish, sea turtles, and various other animals have been reported to sense the geomagnetic field and to use it for orientation, navigation, and homing. In recent years, exciting progress has been made towards elucidating the physical and structural basis of this remarkable phenomenon. This paper focuses on the two hypotheses that drive current research into magnetoreception. One proposal relies

Michael Winklhofer

2009-01-01

264

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

265

Shape of the Geomagnetic Field Solar Wind Boundary  

Microsoft Academic Search

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

Gilbert D. Mead; David B. Beard

1964-01-01

266

Geomagnetic effects on the performance of atmospheric Cerenkov telescopes  

Microsoft Academic Search

ˇ 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 ˇ 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

P. M. Chadwick

1999-01-01

267

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

268

Resonant enhancement of relativistic electron uxes during geomagnetically active periods  

E-print Network

¯ux as the electrons move to higher v shells. The resulting decrease in relativistic electron ¯uxes increase of very energetic electrons b3 MeV at lower v shells often precede the increase of electronsResonant enhancement of relativistic electron ¯uxes during geomagnetically active periods I. Roth1

Paris-Sud XI, Université de

269

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

270

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

271

Archaeomagnetism : An indirect study of geomagnetic secular variation  

Microsoft Academic Search

In recent years techniques have developed which make possible the accurate sampling and measurement of the weak permanent magnetism in Earth materials. Utilizing the magnetism acquired by ancient kilns in the course of their operation, a record of the secular variation of the geomagnetic field in Europe is being obtained. Most of the work reported concerns England during the 1st

J. C. Belshé

1961-01-01

272

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

273

Particle acceleration from reconnection in the geomagnetic tail  

SciTech Connect

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

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

1997-08-01

274

Changes in the distant tail configuration during geomagnetic storms  

Microsoft Academic Search

Changes in the structure of the distant tail associated with geomagnetic storms are studied by using plasma and magnetic field data obtained from Geotail. Thirteen storm intervals between October 1993 and October 1994 are examined when the satellite was located in the distant tail between X=-83RE and X=-210RE. Geotail observed the magnetosheath during all storms including those when the satellite

R. Nakamura; S. Kokubun; T. Mukai; T. Yamamoto

1997-01-01

275

Microstructure and Mechanical Properties of AA5005/AA6061 Laminated Composite Processed by Accumulative Roll Bonding  

NASA Astrophysics Data System (ADS)

The AA5005/AA6061 laminated composite has been fabricated by the accumulative roll bonding (ARB) using commercial AA5005 and AA6061. In the ARB process, one piece of AA5005 sheet and one piece of AA6061 sheet were stacked together and rolled with a 50 pct reduction without any lubrication. The materials were heated at 473 K (200 °C) for 10 minutes before each rolling process and were deformed up to four cycles to accumulate an equivalent strain of 3.2 and form an AA5005/AA6061 laminated composite. Mechanical properties and microstructure of the laminated composites were tested. The hardness and tensile strength increased, and the grain size reduced with the number of ARB cycles. Ultrafine grains elongated along the rolling direction were developed during the ARB process. The thicknesses of the grains of both the AA5005 and AA6061 layers were less than 200 nm after the fourth cycle. The uniform elongation decreased drastically after the first cycle ARB and stayed almost unchanged after further ARB process. The hardness of the AA5005 layer was slightly lower than that of the AA6061 layer. The microstructures from optical microscope and transmission microscope showed that in the AA6061 layer large precipitates in the micron scale and small particles less than 100 nm were present, whereas in the AA5005 layer there were large scale precipitates, but no small-sized particles.

Su, Lihong; Lu, Cheng; Deng, Guanyu; Tieu, Kiet

2014-04-01

276

On the Possibilities of Predicting Geomagnetic Secular Variation with Geodynamo Modeling  

NASA Technical Reports Server (NTRS)

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

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

2004-01-01

277

UK Index  

NSDL National Science Digital Library

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

278

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

NASA Astrophysics Data System (ADS)

The general tendency for magnetic disturbances to be more stormy at equinoxes than at solstices has been recognised for more than 150 years. To explain the seasonal variation three principal hypotheses have been proposed; the axial hypothesis (Cortie, 1912), the equinoctial hypothesis (Bartels, 1932; McIntosh, 1959), and the Russell and McPherron (RM) hypothesis (Russell and McPherron, 1973). The RM hypothesis, which is based on the recognition that the magnetic field in the solar equatorial plane tends to have the largest southward component in geocentric solar magnetospheric (GSM) coordinates in early April and October, has been largely accepted for many years. However, recent studies have confirmed that the RM effect accounts for only a subordinate proportion of the seasonal variation of geomagnetic activity, and that the larger part of the phenomenon is attributable to the equinoctial effect in which the angle between the solar wind flow and the dipole axis of the Earth plays an essential role (Cliver, Kamide and Ling, 2000; Cliver, Kamide, Ling and Yokoyama, 2001; O'Brien and McPherron, 2002). In this paper physical meaning of the equinoctial effect is investigated based on the data of three-hourly am index and solar wind parameters acquired by the ACE satellite. The am indices are well correlated with BsVxVx, where Bs is the southward component of the interplanetary magnetic field (IMF) and Vx is the solar wind velocity in the sun-earth direction. It is found, however, that the am - BsVxVx relation depends on the range of VxVx: The am in higher ranges of VxVx tends to be larger than am in lower ranges of VxVx for both equinoctial and solstitial epochs for the same value of BsVxVx. Using the data sets of the same VxVx range, it is shown that distribution of points in the am - BsVxVx diagram at the solstitial epochs overlaps with that at the equinoctial epochs and the average am values in each BsVxVx bin in solstitial epochs are almost equal to those in equinoctial epochs, if VxVx for each point at solstices are reduced to VxVx sin (c) where c is the geomagnetic colatitude of the sub-solar point. This finding indicates that the emergence of the geomagnetic disturbance is regulated by the component of the solar wind velocity perpendicular to the dipole axis of the geomagnetic field. The magnitude of the perpendicular velocity component varies seasonally even if the solar wind velocity remains constant. This appears to be the long-missed key factor causing the equinoctial effect. It is interesting to note that both the RM and equinoctial effects are related to seasonal changes in the efficiency of solar wind - magnetosphere coupling caused by changes in the geometric configuration between the sun and the geomagnetic dipole field, one in relation to Bs of the IMF, and the other in relation to the component of solar wind velocity perpendicular to the dipole axis.

Yoshida, A.

2008-12-01

279

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

280

Transmission of systemic AA amyloidosis in animals.  

PubMed

Amyloidoses are a group of protein-misfolding disorders that are characterized by the deposition of amyloid fibrils in organs and/or tissues. In reactive amyloid A (AA) amyloidosis, serum AA (SAA) protein forms deposits in mice, domestic and wild animals, and humans that experience chronic inflammation. AA amyloid fibrils are abnormal ?-sheet-rich forms of the serum precursor SAA, with conformational changes that promote fibril formation. Extracellular deposition of amyloid fibrils causes disease in affected animals. Recent findings suggest that AA amyloidosis could be transmissible. Similar to the pathogenesis of transmissible prion diseases, amyloid fibrils induce a seeding-nucleation process that may lead to development of AA amyloidosis. We review studies of possible transmission in bovine, avian, mouse, and cheetah AA amyloidosis. PMID:24280941

Murakami, T; Ishiguro, N; Higuchi, K

2014-03-01

281

The Management of AAS Meetings  

NASA Astrophysics Data System (ADS)

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

Marvel, Kevin B.

2013-01-01

282

Jung Index  

NSDL National Science Digital Library

Compiled by Matthew Clapp of the University of Georgia, the Jung Index is a collection of more than 300 online resources about and related to the life and work of Carl Jung, the Swiss psychologist and psychiatrist who founded analytic psychology. Resources are indexed into ten major topic areas and include sections such as Research Resources, Jungian Psychology, and Psychoanalysis, among others. A What's New? section, a What's Cool? section, and the JungNet Newsletter keep frequent visitors up to date on the latest and greatest resources in analytic psychology. In addition, the site provides a glossary of Jungian terms, a gallery of Jungian images, and a moderated forum for Jungian discussion.

1999-01-01

283

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

284

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

PubMed

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

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

2010-11-01

285

Empirical Forecast of Corotating Interacting Regions and Geomagnetic Storms Based on Coronal Hole Information  

NASA Astrophysics Data System (ADS)

In this study, we suggest an empirical forecast of CIR (Corotating Interaction Regions) and geomagnetic storm based on the information of coronal holes (CH). For this we used CH data obtained from He I 10830 Å maps at National Solar Observatory-Kitt Peak from January 1996 to November 2003 and the CIR and storm data that Choi et al.~(2009) identified. Considering the relationship among coronal holes, CIRs, and geomagnetic storms (Choi et al. 2009), we propose the criteria for geoeffective coronal holes; the center of CH is located between N40° and S40° and between E40° and W20°, and its area in percentage of solar hemispheric area is larger than the following areas: (1) case 1: 0.36 %, (2) case 2: 0.66 %, (3) case 3: 0.36 % for 1996-2000, and 0.66% for 2001-2003. Then we present contingency tables between prediction and observation for three cases and their dependence on solar cycle phase. From the contingency tables, we determined several statistical parameters for forecast evaluation such as PODy (the probability of detection yes), FAR (the false alarm ratio), Bias (the ratio of ``yes" predictions to ``yes" observations) and CSI (critical success index). Considering the importance of PODy and CSI, we found that the best criterion is case 3; CH-CIR: PODy=0.77, FAR=0.66, Bias=2.28, CSI=0.30. CH-storm: PODy=0.81, FAR=0.84, Bias=5.00, CSI=0.16. It is also found that the parameters after the solar maximum are much better than those before the solar maximum. Our results show that the forecasting of CIR based on coronal hole information is meaningful but the forecast of goemagnetic storm is challenging.

Lee, Ji-Hye; Moon, Yong-Jae; Choi, Yunhee; Yoo, Kye-Hwa

2009-09-01

286

Precipitation Behavior of AA2618  

NASA Astrophysics Data System (ADS)

The precipitation behavior of AA2618 was studied by a multitude of characterization techniques: microhardness testing, lattice parameter measurement through X-ray diffraction (XRD), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and atom probe field ion microscopy (APFIM). The matrix lattice parameter increased during the first 20 hours of natural aging, due to the formation of Cu clusters and decreased over the next 24 hours, due to the formation of Mg-rich clusters. Prior natural aging weakened subsequent artificial aging hardening at 180 °C, 200 °C, and 230 °C, due to the cluster reversion that delayed the precipitation of strengthening phases. The matrix lattice parameter exhibited erratic changes during artificial aging that corresponded to the formation and partial dissolution of Guinier Preston Bagaryatsky (GPB) zones, the transformation of GPB zones to GPB2 zones, and the precipitation of S'. The structural changes during the artificial aging of AA2618 occur in this sequence: supersaturated solid solution ? clusters + GPB ? GPB + GPB2 ? GPB2 + S' ? S'+ S ? S.

Lu, H.; Kadolkar, P.; Nakazawa, K.; Ando, T.; Blue, C. A.

2007-10-01

287

Geochemistry Index  

NSDL National Science Digital Library

This site is the index of a book used in a geochemistry course taught by W. M. White at Cornell University. There are 15 chapters and a table of contents available. All of the chapters are large PDF files and take some time to download. Figures and exercises accompany the text.

William M. White

288

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

289

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 Permanent F/T Office Manager AA Memberships and Subscriptions NYU Faculty Resource Network AA - learning communities AA Other Expenses Student/Faculty Res

Rainforth, Emma C.

290

Population Index  

NSDL National Science Digital Library

Two excellent bibliographic resources for population studies are the "Population Index" from the Office of Population Research at Princeton University, and "Population Organizations: Finder's Guide" from the Center for Demography and Ecology at the University of Wisconsin-Madison. "Population Index" is a quarterly publication that has been available since 1935. It "covers all fields of interest to demographers, including fertility, mortality, population size and growth, migration, nuptiality and the family, research methodology, projections and predictions, historical demography, and demographic and economic interrelations. Input is derived from original publications including monographs, journal articles, other serial publications, working papers, doctoral dissertations, machine-readable data files, and relevant acquisitions lists and bibliographies." About 3,500 citations are produced annually. Full text for the Index is available at the "Population Index" Web site for 1986-present (Vol. 52-present). Indexes can be searched by author, subject matter, geographical region, or publication year. There is now an experimental free text search capability for the 1994-present issues. "Population Organizations: Finder's Guide" is a no frills "practical tool for population professionals who need a single source for the quick location of organizations that publish and distribute or post population or family planning documents." It contains hundreds of citations, providing organization addresses, phone and FAX numbers, and Internet addresses when available. The Guide is updated every six months and is maintained by Ruth Sandor, Director of the Library of the Center for Demography and Ecology. Office of Population Research, Princeton University: http://opr.princeton.edu/ "Population Organizations: Finder's Guide": gopher://cde2.ssc.wisc.edu:70/00/addazlis gopher to: cde2.ssc.wisc.edu select: Population Organizations: Finder's Guide Center for Demography and Ecology, University of Wisconsin-Madison: http://www.ssc.wisc.edu/cde/

1986-01-01

291

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

292

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

293

Inferring interplanetary magnetic field polarities from geomagnetic variations  

NASA Astrophysics Data System (ADS)

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

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

2012-06-01

294

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

295

MAGE Project: 4D Visualization of geomagnetic field  

NASA Astrophysics Data System (ADS)

We have developed productions for 3D (spatial) + 1D (temporal) visualization of geomagnetic field (magnetic field lines and observed components on the surface of the Earth) in the Google Earth framework. This project, MAGE (Mapping Applications to Geomagnetic Environments), has three targets, [1] for helping researcher's inspiration, [2] for educational application and [3] for outreach. Now we released KML files showing the fields calculated from several published secular variation models (including a reversal field model) and from a geodynamo simulated model. Moreover we demonstrate a new usage of Google Earth for paleomagnetism and rock magnetism, in which direction data are plotted on the Earth as a unit sphere. Since April 2007, our products, KML files, have been released on the website http://mage-p.org/ for free. Here we introduce the released KML files and show examples of usage of the KML files for researches.

Yamagishi, Y.; Hatakeyama, T.

2010-12-01

296

European Project to Improve Models of Geomagnetically Induced Currents  

NASA Astrophysics Data System (ADS)

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

Viljanen, Ari

2011-07-01

297

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

298

On the Terms of Geomagnetic Daily Variation in Antarctica  

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

299

Neutral wind spectra at the auroral zone mesopause Geomagnetic effect?  

NASA Astrophysics Data System (ADS)

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

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

1985-02-01

300

Recalculation of Contemporary Ae(8) Index Noting Classic Initial Ae(12) Index  

NASA Astrophysics Data System (ADS)

On the basis of classic intensity index of auroral electrojets AE(12), calculated using the data from 12 auroral observatories, correlations were obtained, which are used now for the estimation of energetic budget components of the magnetosphere (joules into heating, particles empting, ring current) and some other problems. However con- temporary AE index is calculated by the data from the less number of observatories. This can not influence the accuracy of estimations of some elements of megneto- spheric activity, which are calculated taken into acount the correlations where insted of real AE(12) or AE(11) indexes AE(9) or AE(8) are used. In this work on the basis of artificial neural nerwork technique (ANN) algorythm was designed permitting to recalculate AE index, obtained using the less number of observatory data, and to re- duce it to initial classic AE(12) index. As an example the ability of designed ANN to restore the amplitude of AE(12) index by the observatiries AE(8) data is shown. This permits to estimate the level of error in the presentation of auroral electrojets activity by contemporary AE indexes when compared to those, which were introduced into the practice of geomagnetic investigations by their creators.

Barkhatov, N.; Korolev, A.; Levitin, A.; Sakharov, S.

301

Effect of Cross-Correlation on Geomagnetic Forecast Accuracies  

NASA Technical Reports Server (NTRS)

Surface geomagnetic observation can determine up to degree L = 14 time-varying spherical harmonic coefficients of the poloidal magnetic field. Assimilation of these coefficients to numerical dynamo simulation could help us understand better the dynamical processes in the Earth's outer core, and to provide more accurate forecast of geomagnetic secular variations (SV). In our previous assimilation studies, only the poloidal magnetic field in the core is corrected by the observations in the analysis. Unobservable core state variables (the toroidal magnetic field and the core velocity field) are corrected via the dynamical equations of the geodynamo. Our assimilation experiments show that the assimilated core state converges near the CMB, implying that the dynamo state is strongly constrained by surface geomagnetic observations, and is pulled closer to the truth by the data. We are now carrying out an ensemble of assimilation runs with 1000 years of geomagnetic and archeo/paleo magnetic record. In these runs the cross correlation between the toroidal and the poloidal magnetic fields is incorporated into the analysis. This correlation is derived from the physical boundary conditions of the toroidal field at the core-mantle boundary (CMB). The assimilation results are then compared with those of the ensemble runs without the cross-correlation, aiming at understanding two fundamental issues: the effect of the crosscorrelation on (1) the convergence of the core state, and (2) the SV prediction accuracies. The constrained dynamo solutions will provide valuable insights on interpreting the observed SV, e.g. the near-equator magnetic flux patches, the core-mantle interactions, and possibly other geodynamic observables.

Kuang, Weijia; Wei, Zigang; Tangborn, Andrew

2011-01-01

302

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

303

Geomagnetic Effects on the Performance of Atmospheric Cerenkov Telescopes  

Microsoft Academic Search

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

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

1999-01-01

304

Wavelet analysis of relative geomagnetic paleointensity at ODP Site 983  

Microsoft Academic Search

We performed spectral analysis of the record of relative geomagnetic paleointensity obtained at ODP Site 983, covering the time interval 0–1.1 Ma. The results confirm the presence of significant power at frequencies corresponding to the earth orbital parameters (eccentricity, obliquity, precession). The construction of the evolutionary spectrum allowed us to establish the non-stationarity of the signal at those frequencies. The

Yohan Guyodo; Philippe Gaillot; James E. T. Channell

2000-01-01

305

Effects of geomagnetic disturbances on electric power transmission systems  

Microsoft Academic Search

A comparative study of the effects of solar storm geomagnetically induced current (SS-GIC) and nuclear detonation induced currents (MHD-EMP-GIC) on the power system is presented. The earth surface electric field of the MHD electromagnetic pulse is given to be on the order of 100 V\\/km, with a duration up to several minutes; and the electric field of the solar storms

A. P. S. Meliopoulos; E. N. Glytsis; G. J. Cokkinides

1991-01-01

306

Variations of total electron content during geomagnetic disturbances  

Microsoft Academic Search

Abstract. This paper studies the ionospheric response to a major geomagnetic,storm of October 18-19, 1995, using the thermosphere-ionosphere electrodynamics general circulation model (TIEGCM) simulations and the global ionospheric maps,(GIM)of total electron content (TEC)observations from the Global Positioning System (GPS) worldwide network. The TIE-GCM results, which,utilize the realistic time-dependent ionospheric convection and auroral precipitation derived from the assimilative mapping,of ionospheric electrodynamics,(AMIE)procedure,as

G. Lu; Lx. Pi; A. D. Richmond; R. G. Roble

307

Further observations of geomagnetically forbidden cosmic ray nuclei  

NASA Technical Reports Server (NTRS)

Cosmic-ray particles with kinetic energies well below cutoff values were detected during a high-altitude balloon flight at 41 deg N geomagnetic latitude. These particles had kinetic energies up to 400 MeV/amu and charges in the range from 6 to 30. They are probably reentrant albedo particles and are of interest primarily because they can be confused with fast ultraheavy primary particles in some experiments.

Friedlander, M. W.; Hoppe, M.

1977-01-01

308

Improving CTIPe neutral density response and recovery during geomagnetic storms  

NASA Astrophysics Data System (ADS)

The temperature of the Earth's thermosphere can be substantially increased during geomagnetic storms mainly due to high-latitude Joule heating induced by magnetospheric convection and auroral particle precipitation. Thermospheric heating increases atmospheric density and the drag on low-Earth orbiting satellites. The main cooling mechanism controlling the recovery of neutral temperature and density following geomagnetic activity is infrared emission from nitric oxide (NO) at 5.3 micrometers. NO is produced by both solar and auroral activity, the first due to solar EUV and X-rays the second due to dissociation of N2 by particle precipitation, and has a typical lifetime of 12 to 24 hours in the mid and lower thermosphere. NO cooling in the thermosphere peaks between 150 and 200 km altitude. In this study, a global, three-dimensional, time-dependent, non-linear coupled model of the thermosphere, ionosphere, plasmasphere, and electrodynamics (CTIPe) is used to simulate the response and recovery timescales of the upper atmosphere following geomagnetic activity. CTIPe uses time-dependent estimates of NO obtained from Marsh et al. [2004] empirical model based on Student Nitric Oxide Explorer (SNOE) satellite data rather than solving for minor species photochemistry self-consistently. This empirical model is based solely on SNOE observations, when Kp rarely exceeded 5. During conditions between Kp 5 and 9, a linear extrapolation has been used. In order to improve the accuracy of the extrapolation algorithm, CTIPe model estimates of global NO cooling have been compared with the NASA TIMED/SABER satellite measurements of radiative power at 5.3 micrometers. The comparisons have enabled improvement in the timescale for neutral density response and recovery during geomagnetic storms. CTIPe neutral density response and recovery rates are verified by comparison CHAMP satellite observations.

Fedrizzi, M.; Fuller-Rowell, T. J.; Codrescu, M.; Mlynczak, M. G.; Marsh, D. R.

2013-12-01

309

Thermoluminescent dating of Lake Mungo geomagnetic polarity excursion  

Microsoft Academic Search

ARCHAEOMAGNETIC studies made by Barbetti and McElhinny1,2 on prehistoric aboriginal fireplaces at Lake Mungo, Australia, indicate the occurrence of a polarity excursion about 30,000 years ago during which the geomagnetic field intensity increased to three times its presentday value; this main excursion was followed by a second one during which the intensity decreased to about one third of the present

J. Huxtable; M. J. Aitken

1977-01-01

310

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

311

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

312

Role of centennial geomagnetic changes in local atmospheric ionization  

Microsoft Academic Search

Many studies of solar-terrestrial relation are based on globally (or hemispherically) averaged quantities, including the average cosmic ray flux. However, regional effects of cosmic ray induced ionization due to geomagnetic changes may be comparable to or even dominate over the solar signal at mid-latitudes on centennial-to-millennial time scales. We show that local changes of the tropospheric ionization due to fast

I. G. Usoskin; M. Korte; G. A. Kovaltsov

2008-01-01

313

Impact of geomagnetic events on atmospheric chemistry and dynamics  

NASA Astrophysics Data System (ADS)

Geomagnetic events, 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 event 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 events 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. 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. This is analogous to today's poleward shift of the westerlies due to the ozone hole. It is challenging to robustly infer precipitation changes from the wind anomalies, and it remains unclear, whether the Laschamp Event could have caused the observed glacial maxima in the southern Central Andes. Moreover, a large impact on the global climate seems unlikely.

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

2013-12-01

314

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

315

Correlation between the Long Radiowave Propagation and the Geomagnetic Field  

NASA Astrophysics Data System (ADS)

The correlation between the intensity of the radioelectric field of 155 kHz (emitted by Bod - Brasov and received by Cluj-Napoca) and the amplitude of the horizontal component of the geomagnetic field during February - March 1970 is estimated (research performed in the framework of the INTERCOSMOS programme). A delay of three days in the ionospheric response is pointed out. The magnetophere-ionosphere-Earth system is modelled by an RL circuit.

Szocs, Geza

316

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

NASA Astrophysics Data System (ADS)

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

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

317

Variations of solar, interplanetary, and geomagnetic parameters with solar magnetic multipole fields during Solar Cycles 21-24  

NASA Astrophysics Data System (ADS)

In this study we compare the temporal variations of the solar, interplanetary, and geomagnetic (SIG) parameters with that of open solar magnetic flux from 1976 to 2012 (from Solar Cycle 21 to the early phase of Cycle 24) for a purpose of identifying their possible relationships. By the open flux, we mean the average magnetic field over the source surface (2.5 solar radii) times the source area as defined by the potential field source surface (PFSS) model of the Wilcox Solar Observatory (WSO). In our result, most SIG parameters except the solar wind dynamic pressure show rather poor correlations with the open solar magnetic field. Good correlations are recovered when the contributions from individual multipole components are counted separately. As expected, solar activity indices such as sunspot number, total solar irradiance, 10.7 cm radio flux, and solar flare occurrence are highly correlated with the flux of magnetic quadrupole component. The dynamic pressure of solar wind is strongly correlated with the dipole flux, which is in anti-phase with Solar Cycle (SC). The geomagnetic activity represented by the Ap index is correlated with higher order multipole components, which show relatively a slow time variation with SC. We also found that the unusually low geomagnetic activity during SC 23 is accompanied by the weak open solar fields compared with those in other SCs. It is argued that such dependences of the SIG parameters on the individual multipole components of the open solar magnetic flux may clarify why some SIG parameters vary in phase with SC and others show seemingly delayed responses to SC variation.

Kim, Bogyeong; Lee, Jeongwoo; Yi, Yu; Oh, Suyeon

2015-01-01

318

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

319

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

320

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.

321

Kelvin-Helmholtz Instability and the Semiannual Variation of Geomagnetic Activity  

Microsoft Academic Search

Kelvin-Helmholtz instability along the flanks of the magnetosphere exhibits a semiannual variation, instability maximums occurring at the equinoxes and instability minimums at the solstices. It is suggested that Kelvin-Helmholtz instabilities, generated at the magnetopause, initiate the modulation of geomagnetic disturbance detected as the semiannual variation of geomagnetic activity. The Kelvin-Helmholtz explanation predicts a universal time variation of geomagnetic disturbance. This

Bruce R. Boller; Harold L. Stolov

1970-01-01

322

The geomagnetic field - An explanation for the microturbulence in coaxial gun plasmas  

NASA Technical Reports Server (NTRS)

The complexity introduced by the geomagnetic field in several regions of a coaxial gun plasma device is described. It is shown that the annihilation of the swept-up geomagnetic flux, trapped within the highly compressed turbulent plasma, provides an explanation for varied performance and experimental results. The results indicate that the device should be aligned along the direction of the local geomagnetic field or enclosed in a mu-metal shield.

Mather, J. W.; Ahluwalia, H. S.

1988-01-01

323

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

324

Probability distribution invariance of 1-minute auroral-zone geomagnetic field fluctuations  

Microsoft Academic Search

A statistical model of short time-scale geomagnetic fluctuations is developed and used to evaluate how geomagnetic dynamics are influenced by different solar wind controlling parameters. The functional form of the probability distribution function (PDF) that describes extreme-value (greater than 4?) minute-to-minute changes in the ground magnetic field (?x) at magnetometer station Sodankylä (geomagnetic latitude and longitude of [63.87,107.61]) is shown

R. S. Weigel; D. N. Baker

2003-01-01

325

Probability distribution invariance of 1-minute auroral-zone geomagnetic field fluctuations  

Microsoft Academic Search

A statistical model of short time-scale geomagnetic fluctuations is developed and used to evaluate how geomagnetic dynamics are influenced by different solar wind controlling parameters. The functional form of the probability distribution function (PDF) that describes extreme-value (greater than 4sigma) minute-to-minute changes in the ground magnetic field (Deltax) at magnetometer station Sodankylä (geomagnetic latitude and longitude of [63.87,107.61]) is shown

R. S. Weigel; D. N. Baker

2003-01-01

326

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

327

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

328

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

329

Variability modes in core flows inverted from geomagnetic field models  

NASA Astrophysics Data System (ADS)

The flow of liquid metal inside the Earth's core produces the geomagnetic field and its time variations. Understanding the variability of those deep currents is crucial to improve the forecast of geomagnetic field variations and may provide relevant information on the core dynamics. The main goal of this study is to extract and characterize the leading variability modes of core flows over centennial periods, and to assess their statistical robustness. To this end, we use flows that we invert from two geomagnetic field models (`gufm1' and `COV-OBS'), and apply principal component analysis and singular value decomposition of coupled fields. The quasi-geostrophic (QG) flows inverted from both geomagnetic field models show similar features. However, `COV-OBS' flows have a less energetic mean and larger time variability. The statistical significance of flow components is tested from analyses performed on subareas of the whole domain. Bootstrapping methods are also used to extract significant flow features required by both `gufm1' and `COV-OBS'. Three main empirical circulation modes emerge, simultaneously constrained by both geomagnetic field models and expected to be robust against the particular a priori used to build them (large-scale QG dynamics). Mode 1 exhibits three large vortices at medium/high latitudes, with opposite circulation under the Atlantic and the Pacific hemispheres. Mode 2 interestingly accounts for most of the variations of the Earth's core angular momentum. In this mode, the regions close to the tangent cylinder and to the equator are correlated, and oscillate with a period between 80 and 90 yr. Each of these two modes is energetic enough to alter the mean flow, sometimes reinforcing the eccentric gyre, and other times breaking it up into smaller circulations. The three main circulation modes added to the mean flow account for about 70 per cent of the flows variability, 90 per cent of the rms total velocities, and 95 per cent of the secular variation induced by the total flows. Direct physical interpretation of the computed modes is not straightforward. Nonetheless, similarities found between the two first modes and time/spatial features identified in different studies of core dynamics, suggest that our approach can help to pinpoint the relevant physical processes inside the core on centennial timescales.

Pais, M. A.; Morozova, A. L.; Schaeffer, N.

2014-01-01

330

Publication Characteristics of Members of the AAS  

NASA Astrophysics Data System (ADS)

For each of the 4995 persons listed in the 1989 American Astronomical Society Membership Directory, we noted their total 1984-88 publications as listed in the Author Index of Astronomy and Astrophysics Abstracts. The members are subdivided as retired (mean of 0.61 paper/yr), foreign (3.89), Full (3.34), Division Affiliates (1.76), Associate (1.48), and Junior (0.79) members. For Full members the frequencies of various publication rates are listed; the median is 2.28 papers/yr. The Full members are subdivided by affiliations, namely private institutions (mean of 4.71 papers/yr), university (3.89), government-funded (3.46), commercial company (1.81), and unknown affiliations (0.84). We looked up the listed publications for four high producers who each average 25.7 papers/yr. We found that 55% of those are preprints, abstracts, conference papers, and other secondary material. Furthermore, they average 4.2 authors per original research paper. If we divide each original research paper by the number of authors, these four average only the equivalent of 4.0 single-author research papers/yr. A sample of moderate producers also have 53% of their publications as abstracts, conference papers, etc., and they average 4.2 authors per original research paper. We conclude that the average Full AAS member produces the equivalent of 1/2 single-author original-research paper/yr and 23% of them produce more than 1 such paper/yr.

Abt, Helmut A.

1990-10-01

331

High-Speed Plasma Flows Observed in the Magnetotail during Geomagnetically Quiet Times: Relationship between Magnetic Reconnection, Substorm and High-Speed Plasma Flows  

NASA Astrophysics Data System (ADS)

It has been widely accepted that a major mechanism for generating the high-speed plasma flows (HSPFs) observed in the magnetotail is the magnetic reconnection. Furthermore, these magnetotail HSPFs are observed during both geomagnetically quiet and active times. However, it has been open question and controversial whether the magnetic reconnection is main mechanism to produce the magnetotail HSPFs as observed even during geomagnetically quiet times, and how the relationship between the HSPFs and substorm is. In this study, we focused on the 4 events of the magnetotail HSPFs observed by THEMIS (the details are listed in Table), where the value of the GSM-X component for the plasma velocity (|Vx|) was higher than 300 km/s and that of the velocity perpendicular to the local magnetic field (|V?x| and |V?|) ranged between about 200 km/s and 500 km/s during which simultaneous AL and AU indices were lower than 40 nT and the range of the Kp index was between -1 and 1. Simultaneous all magnetic field components were varying and magnetic field intensity showed the enhancement in almost all events, suggesting that the HSPFs induced some magnetic perturbations, and the magnetic flux was transported and piled up by the HSPFs in the magnetotail even during geomagnetically quiet times. Interestingly, some HSPF events were associated with the Pi 2 waves, but the others were not. Based on this result, the magnetic reconnection might not always play a crucial role for producing the HSPFs during geomagnetically quiet times. Furthermore, the striking auroral activation was not observed in all events. This result suggests that the HSPFs during geomagnetically quiet times can occur in association with not only "substorm" but also "substorm-like phenomena", such as pseudo-substorm.
4 Events of "Magnetotail High-Speed Plasma Flows during Geomagnetically Quiet Times"

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

2011-12-01

332

Cumulative Index  

E-print Network

CUMULATIVE INDEX I. Articles (i) By Author Abate, Charles J. "Has Dretske Really Refuted Skepticism?", v.4, n.3 (June, 1977), pp. 169- 175. Abugattas, Juan A. "On the Relation Between Morality and the Notion of God". v.7, n.l (November, 1979...), pp. 47-81. Algeo, Donald. "Why Art?", v.7, n.2 (Spring, 1980), pp. 105-129. Austin, James W. "Rorty's Materialism", v.3, n.l (November, 1975), pp. 20-28. Bell, Gary. "A Characterization of Mathematics". v.8, n.2 (Summer, 1981), pp. 96-104. Bell...

1981-12-01

333

An analysis of the solar wind parameters responsible for the main phase of the super geomagnetic storm on March 31, 2001  

NASA Astrophysics Data System (ADS)

In this paper, the solar wind parameters responsible for the main phase of the super geomagnetic storm occurred on March 31, 2001 is analyzed taking into account the delayed geomagnetic effect of solar wind at the L1 point and using the SYM-H index. The solar wind responsible for the main phase is split into two periods. The solar wind parameters in the two periods contributed differently to the main phase. A comparative study of solar wind parameters in the two periods shows the evidence that the solar wind density defines energy transfer to the magnetosphere. Analysis is also made to understand a range of key factors that may define the development of the storm's main phase, including the time integral of the southward component of interplanetary magnetic field (IMF) or the solar wind electric field, and a solar wind energy coupling function established by Akasofu (1981). Additionally, the paper discusses the assumption that a strong southward IMF and high inclination to the ecliptic plane would contribute to the occurrence of a super geomagnetic storm, and assesses the rationality behind an empirical formula relating the Dst peak value to solar wind parameters established by Wang Y M et al.(2003). The paper is concluded with a summary of the key solar wind parameters that may define the development of a storm's main phase.

Le, G.; Zheng, L.

2012-12-01

334

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

335

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

336

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

337

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

338

springeronline.com ADIS 20 AA DD VV AA NN CC EE SS II NN II NN FF OO RR MM AA TT II OO NN SS EE CC UU RR II TT YY AA DD VV AA NN CC EE SS II NN II NN FF OO RR MM AA TT II OO NN SS EE CC UU RR II TT YY  

E-print Network

springeronline.com ADIS 20 AA DD VV AA NN CC EE SS II NN II NN FF OO RR MM AA TT II OO NN SS EE CC UU RR II TT YY AA DD VV AA NN CC EE SS II NN II NN FF OO RR MM AA TT II OO NN SS EE CC UU RR II TT YY attractive for applications requiring a large quantity of parallel processing. This work extends

Yang, Junfeng

339

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

Federal Register 2010, 2011, 2012, 2013, 2014

...Docket No. AD12-13-000] Staff Technical Conference on Geomagnetic Disturbances to the Bulk-Power System; Technical Conference...the reliability of the Bulk-Power System as affected by geomagnetic disturbances. The conference will explore the risks...

2012-04-26

340

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. ???, XXXX, DOI:10.1029/, Geomagnetic activity signatures in wintertime1  

E-print Network

of geomagnetic activity in zonal mean zonal wind, temperature,5 and Eliassen-Palm flux in the Northern Hemisphere extended winter (November­6 March). We found that for high geomagnetic activity levels the stratospheric7 polar vortex becomes stronger in late winter, with more planetary waves be-8 ing refracted equatorward

Otago, University of

341

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

342

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

343

Temporal Variation in the Geomagnetic Response to IMF Sector Boundary Passage  

Microsoft Academic Search

The geomagnetic response, as characterized by the change in daily Ap, in relation to the passage of solar magnetic sector boundaries is studied for different epochs using data for the years 1947-1978. The results derived from the whole year data indicate that the response of geomagnetic activity to a +\\/boundary has remained unaltered, whereas that for a -\\/+ boundary has

B. R. Arora; G. K. Rangarajan

1981-01-01

344

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

345

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

E-print Network

Are secular correlations between sunspots, geomagnetic activity, and global temperature significant an important role in global temperature change over the past century or so. We treat this possibility, geomagnetic activity, and global surface temperature for the years 1868­2008, solar cycles 11­23. The data

Tsai, Victor C.

346

PARTICLE TRAJECTORIES IN MODEL CURRENT SHEETS. 2. APPLICATIONS TO AURORAS USING A GEOMAGNETIC TAIL MODEL  

Microsoft Academic Search

Individual particle trajectories are determined analytically and numerically in two possible configurations of electric and magnetic fields in the geomagnetic tail. The models are based on reconnection models incorporating a neutral point with associated neutral or current sheet and on the observed neutral sheet in the geomagnetic tail. Both models contain magnetic field lines oppositely directed on either side of

T. W. Speiser

1967-01-01

347

Observations of the plasma density enhancement in the high-altitude polar region during geomagnetic storms  

Microsoft Academic Search

Recent satellite observations have clarified that plasma outflows play an important role in abrupt changes in the ion composition in the plasmasheet and ring current during geomagnetic storms. In the present study, we perform case studies of enhancement of the plasma density and ion upflow in the high-altitude polar region during geomagnetic storms using the data observed by the Akebono

Naritoshi Kitamura; Atsuki Shinbori; Yukitoshi Nishimura; Takayuki Ono; Masahide Iizima; Atsushi Kumamoto; Manabu Yamada; Shigeto Watanabe; Takumi Abe; Andrew W. Yau

2008-01-01

348

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

349

Concerning the system earth during geomagnetic polarity transitions: Impact on the neutral atmosphere  

Microsoft Academic Search

During a geomagnetic polarity transition, the strength and structure of the earth geomagnetic field can vary very much from the current state. This means that regions which are at the moment shielded from extraterrestrical energetic particles can become subject to particle precipition. We use a 2 dimensional chemistry, photolysis and transport model of the atmosphere to investigate how different configurations

M. von Koenig; J. Burrows; K. Kuenzi; E. Wolff; M. Kallenrode

2003-01-01

350

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

E-print Network

1 Solar magnetic #12;elds and geomagnetic events. Alexei A. Pevtsov 1 and Richard C. Can#12;eld-scale solar dipolar #12;eld dominates the solar cycle modulation of the magnetic structure of interplanetary clouds. We have carried out two studies of solar magnetic #12;elds and geomagnetic events that bear

Pevtsov, Alexei A.

351

Role of centennial geomagnetic changes in local atmospheric ionization I. G. Usoskin,1  

E-print Network

irradiance. Since the flux of CR is modulated by the solar magnetic activity, this can provide a link between are modulated also by the slowly changing geomagnetic field. While terrestrial effects of the solar irradiation., 2007] of a relation between the geomagnetic field strength and cold episodes in the Earth's history

Usoskin, Ilya G.

352

Geomagnetic pulsations as the result of a solar flare (March 23, 1976).  

NASA Astrophysics Data System (ADS)

Analysis of the data of observations of geomagnetic pulsations at the mid-latitude Soroa (Cuba) and Borok (USSR) observatories has shown that chromospheric flares accompanied by appreciable X-ray emission exceeding the background values by 2 - 3 orders can lead to the appearance of a burst of geomagnetic pulsations with periods of 60 - 80 sec both in the dayside and nightside ionospheres.

Perez, J.; Lazo, B.; Klejmenova, N. G.; Kozyreva, O. V.

1989-08-01

353

Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and Cenozoic  

Microsoft Academic Search

Recently reported radioisotopic dates and magnetic anomaly spacings have made it evident that modification is required for the age calibrations for the geomagnetic polarity timescale of Cande and Kent (1992) at the Cretaceous\\/Paleogene boundary and in the Pliocene. An adjusted geomagnetic reversal chronology for the Late Cretaceous and Cenozoic is presented that is consistent with astrochronology in the Pleistocene and

S. C. Cande; D. V. Kent

1995-01-01

354

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

355

Geomagnetic Cutoff Rigidity Computer Program: Theory, Software Description and Example  

NASA Technical Reports Server (NTRS)

The access of charged particles to the earth from space through the geomagnetic field has been of interest since the discovery of the cosmic radiation. The early cosmic ray measurements found that cosmic ray intensity was ordered by the magnetic latitude and the concept of cutoff rigidity was developed. The pioneering work of Stoermer resulted in the theory of particle motion in the geomagnetic field, but the fundamental mathematical equations developed have 'no solution in closed form'. This difficulty has forced researchers to use the 'brute force' technique of numerical integration of individual trajectories to ascertain the behavior of trajectory families or groups. This requires that many of the trajectories must be traced in order to determine what energy (or rigidity) a charged particle must have to penetrate the magnetic field and arrive at a specified position. It turned out the cutoff rigidity was not a simple quantity but had many unanticipated complexities that required many hundreds if not thousands of individual trajectory calculations to solve. The accurate calculation of particle trajectories in the earth's magnetic field is a fundamental problem that limited the efficient utilization of cosmic ray measurements during the early years of cosmic ray research. As the power of computers has improved over the decades, the numerical integration procedure has grown more tractable, and magnetic field models of increasing accuracy and complexity have been utilized. This report is documentation of a general FORTRAN computer program to trace the trajectory of a charged particle of a specified rigidity from a specified position and direction through a model of the geomagnetic field.

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

2001-01-01

356

Geodynamo model and error parameter estimation using geomagnetic data assimilation  

NASA Astrophysics Data System (ADS)

We have developed a new geomagnetic data assimilation approach which uses the minimum variance' estimate for the analysis state, and which models both the forecast (or model output) and observation errors using an empirical approach and parameter tuning. This system is used in a series of assimilation experiments using Gauss coefficients (hereafter referred to as observational data) from the GUFM1 and CM4 field models for the years 1590-1990. We show that this assimilation system could be used to improve our knowledge of model parameters, model errors and the dynamical consistency of observation errors, by comparing forecasts of the magnetic field with the observations every 20 yr. Statistics of differences between observation and forecast (O - F) are used to determine how forecast accuracy depends on the Rayleigh number, forecast error correlation length scale and an observation error scale factor. Experiments have been carried out which demonstrate that a Rayleigh number of 30 times the critical Rayleigh number produces better geomagnetic forecasts than lower values, with an Ekman number of E = 1.25 × 10-6, which produces a modified magnetic Reynolds number within the parameter domain with an `Earth like' geodynamo. The optimal forecast error correlation length scale is found to be around 90 per cent of the thickness of the outer core, indicating a significant bias in the forecasts. Geomagnetic forecasts are also found to be highly sensitive to estimates of modelled observation errors: Errors that are too small do not lead to the gradual reduction in forecast error with time that is generally expected in a data assimilation system while observation errors that are too large lead to model divergence. Finally, we show that assimilation of L ? 3 (or large scale) gauss coefficients can help to improve forecasts of the L > 5 (smaller scale) coefficients, and that these improvements are the result of corrections to the velocity field in the geodynamo model.

Tangborn, Andrew; Kuang, Weijia

2015-01-01

357

Reconstructing Holocene geomagnetic field variation: new methods, models and implications  

NASA Astrophysics Data System (ADS)

Reconstructions of the Holocene geomagnetic field and how it varies on millennial timescales are important for understanding processes in the core but may also be used to study long-term solar-terrestrial relationships and as relative dating tools for geological and archaeological archives. Here, we present a new family of spherical harmonic geomagnetic field models spanning the past 9000 yr based on magnetic field directions and intensity stored in archaeological artefacts, igneous rocks and sediment records. A new modelling strategy introduces alternative data treatments with a focus on extracting more information from sedimentary data. To reduce the influence of a few individual records all sedimentary data are resampled in 50-yr bins, which also means that more weight is given to archaeomagnetic data during the inversion. The sedimentary declination data are treated as relative values and adjusted iteratively based on prior information. Finally, an alternative way of treating the sediment data chronologies has enabled us to both assess the likely range of age uncertainties, often up to and possibly exceeding 500 yr and adjust the timescale of each record based on comparisons with predictions from a preliminary model. As a result of the data adjustments, power has been shifted from quadrupole and octupole to higher degrees compared with previous Holocene geomagnetic field models. We find evidence for dominantly westward drift of northern high latitude high intensity flux patches at the core mantle boundary for the last 4000 yr. The new models also show intermittent occurrence of reversed flux at the edge of or inside the inner core tangent cylinder, possibly originating from the equator.

Nilsson, Andreas; Holme, Richard; Korte, Monika; Suttie, Neil; Hill, Mimi

2014-07-01

358

An overset grid method for global geomagnetic induction  

NASA Astrophysics Data System (ADS)

A new finite difference solution to the global geomagnetic induction problem is developed and tested, based on a modified Lorenz gauge of the magnetic vector and electric scalar potentials and implementing a novel, overset `Yin-Yang' grid that avoids unnecessary mesh refinement at the geographic poles. Previously used in whole-earth mantle convection models, the overset grid is built from a pair of partially overlapping mid-latitude latitude-longitude (lat/lon) grids, one of which is rotated with respect to the other for complete coverage of the sphere. Because of this symmetry, only one set of finite difference templates is required for global discretization of the governing Maxwell equations, a redundancy that is exploited for computational efficiency and multithreaded parallelization. Comparisons between solutions obtained by the proposed method show excellent agreement with those obtained by independent integral equation methods for 1-D, 2-D and 3-D problem geometries. The computational footprint of the method is minimized through a (non-symmetric) matrix-free BiCG-STAB iterative solver which computes finite difference matrix coefficients `on the fly' as needed, rather than pulling stored values from memory. Scaling of the matrix-free BiCG-STAB algorithm with problem size shows behaviour similar to that seen with the (symmetric) QMR algorithm used in the Cartesian case from which the present algorithm is based. The proposed method may therefore provide a competitive addition to the existing body of global-scale geomagnetic induction modelling algorithms, allowing for resource-efficient forward modelling as the kernel for large-scale computing such as inversion of geomagnetic response functions, computational hypothesis testing and parametric studies of mantle geodynamics and physiochemical state.

Weiss, Chester J.

2014-07-01

359

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

360

Latest pleistocene and holocene geomagnetic paleointensity on Hawaii  

USGS Publications Warehouse

Geomagnetic paleointensity determinations from radiocarbon-dated lava flows on the island of Hawaii provide an estimate of broad trends in paleointensity for Holocene time and offer a glimpse of intensity variations near the end of the last glacial period. When the data from Hawaii are compared with others worldwide, the intensity of the gemagnetic field seems to have been reduced from the Holocene average by about Jt, percent between 45,000 and 10,000 years ago. A long-term reduction of this magnitude is compatible with reported increases in the production rate of cosmogonic nuclides during the same interval.

Mankinen, E.A.; Champion, D.E.

1993-01-01

361

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

362

Localized sudden changes in the geomagnetic secular variation.  

USGS Publications Warehouse

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

Alldredge, L.R.

1987-01-01

363

On derivation and significance of geomagnetic equivalent amplitude indices  

NASA Astrophysics Data System (ADS)

Linear geomagnetic activity indices designated as equivalent amplitudes are compared. Bartel's daily Ap and Mayand's corresponding Am and An are considered. It is demonstrated that a good correlation exists between Ap and Am. However, for the Ap data, a noticeable divergence appears in the years after 1965. A statistical variance analysis of the semiannual wave shows that the scattering for Ap is considerably smaller than for An and thus is the probable error of the average wave. It is concluded that Ap should be preferred.

Siebert, M.; Meyer, J.; Damaske, D.

364

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

365

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

366

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

367

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

368

Geomagnetic polarity epochs: new data from Olduvai Gorge, Tanganyika  

USGS Publications Warehouse

The lower lava flow of Bed I in Olduvai Gorge, Tanganyika, carries natural remanent magnetization (NRM) having normal polarity. Thermal demagnetization experiments demonstrate the stability of this NRM. Thus the Olduvai geomagnetic polarity event, which was originally named from the upper lava flow in Bed I, is represented in its type locality by two normally magnetized lavas. These lavas have been shown to be 1.9 m.y. old, and although they are distinct from each other in composition and surface structure, their eruptions appear to have been closely spaced in time. ?? 1967.

Gromme, C.S.; Hay, R.L.

1967-01-01

369

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

370

The clustering of polarity reversals of the geomagnetic field  

E-print Network

Often in nature the temporal distribution of inhomogeneous stochastic point processes can be modeled as a realization of renewal Poisson processes with a variable rate. Here we investigate one of the classical examples, namely the temporal distribution of polarity reversals of the geomagnetic field. In spite of the commonly used underlying hypothesis, we show that this process strongly departs from a Poisson statistics, the origin of this failure stemming from the presence of temporal clustering. We find that a Levy statistics is able to reproduce paleomagnetic data, thus suggesting the presence of long-range correlations in the underlying dynamo process.

V. Carbone; L. Sorriso-Valvo; A. Vecchio; F. Lepreti; P. Veltri; P. Harabaglia; I. Guerra

2006-03-10

371

Geomagnetically induced currents in an electric power transmission system at low latitudes in Brazil: A case study  

Microsoft Academic Search

Geomagnetically induced currents (GICs) are a ground end manifestation of space weather processes. During large geomagnetic storms, GICs flow between the grounding points of power transformers and along electric power transmission lines connecting the transformers. In high-latitude regions, damages to power transformers are reported where storm time geomagnetic variations are very rapid and large (>1000 nT), and hence the GICs

Nalin B. Trivedi; Ícaro Vitorello; Wanderli Kabata; Severino L. G. Dutra; Antonio L. Padilha; Mauricio S. Bologna; Marcelo B. de Pádua; Alexandre Pinhel Soares; Guilherme Sarcinelli Luz; Fabio de A. Pinto; Risto Pirjola; Ari Viljanen

2007-01-01

372

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

373

High-resolution empirical geomagnetic field model TS07D: Investigating run-on-request and forecasting modes of operation  

NASA Astrophysics Data System (ADS)

The dramatic increase of the geomagnetic field data volume available due to many recent missions, including GOES, Polar, Geotail, Cluster, and THEMIS, required at some point the appropriate qualitative transition in the empirical modeling tools. Classical empirical models, such as T96 and T02, used few custom-tailored modules to represent major magnetospheric current systems and simple data binning or loading-unloading inputs for their fitting with data and the subsequent applications. They have been replaced by more systematic expansions of the equatorial and field-aligned current contributions as well as by the advanced data-mining algorithms searching for events with the global activity parameters, such as the Sym-H index, similar to those at the time of interest, as is done in the model TS07D (Tsyganenko and Sitnov, 2007; Sitnov et al., 2008). The necessity to mine and fit data dynamically, with the individual subset of the database being used to reproduce the geomagnetic field pattern at every new moment in time, requires the corresponding transition in the use of the new empirical geomagnetic field models. It becomes more similar to runs-on-request offered by the Community Coordinated Modeling Center for many first principles MHD and kinetic codes. To provide this mode of operation for the TS07D model a new web-based modeling tool has been created and tested at the JHU/APL (http://geomag_field.jhuapl.edu/model/), and we discuss the first results of its performance testing and validation, including in-sample and out-of-sample modeling of a number of CME- and CIR-driven magnetic storms. We also report on the first tests of the forecasting version of the TS07D model, where the magnetospheric part of the macro-parameters involved in the data-binning process (Sym-H index and its trend parameter) are replaced by their solar wind-based analogs obtained using the Burton-McPherron-Russell approach.

Stephens, G. K.; Sitnov, M. I.; Ukhorskiy, A. Y.; Vandegriff, J. D.; Tsyganenko, N. A.

2010-12-01

374

1 stepped pressure equilibrium code : pq00aa 1 stepped pressure equilibrium code : pq00aa 1  

E-print Network

1 stepped pressure equilibrium code : pq00aa Contents 1 stepped pressure equilibrium code : pq00aa are provided by bf00aa. 5. The residue is related to the tangent map, and provides information regarding is employed for this. pq00aa.h last modified on 2013-04-23 ; [1] J. M. Greene. A method for determining

Hudson, Stuart

375

45 CFR 170.503 - Requests for ONC-AA status and ONC-AA ongoing responsibilities.  

Code of Federal Regulations, 2012 CFR

...2012-10-01 2012-10-01 false Requests for ONC-AA status and ONC-AA ongoing responsibilities. 170.503 Section 170...Certification Program for HIT § 170.503 Requests for ONC-AA status and ONC-AA ongoing responsibilities....

2012-10-01

376

45 CFR 170.503 - Requests for ONC-AA status and ONC-AA ongoing responsibilities.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 2013-10-01 false Requests for ONC-AA status and ONC-AA ongoing responsibilities. 170.503 Section 170...Certification Program § 170.503 Requests for ONC-AA status and ONC-AA ongoing responsibilities....

2013-10-01

377

1 stepped pressure equilibrium code : pp00aa 1 stepped pressure equilibrium code : pp00aa 1  

E-print Network

1 stepped pressure equilibrium code : pp00aa Contents 1 stepped pressure equilibrium code : pp00aa; The magnetic field (and tangent field) is given by bf00aa. 2. Additional trajectories are followed inside rotational transform is determined (in pq00aa) by field line integration. 1.3 format of output: Poincar´e 1

Hudson, Stuart

378

Comparison of Dst Forecast Models for Intense Geomagnetic Storms  

NASA Technical Reports Server (NTRS)

We have compared six disturbance storm time (Dst) forecast models using 63 intense geomagnetic storms (Dst <=100 nT) that occurred from 1998 to 2006. For comparison, we estimated linear correlation coefficients and RMS errors between the observed Dst data and the predicted Dst during the geomagnetic storm period as well as the difference of the value of minimum Dst (Delta Dst(sub min)) and the difference in the absolute value of Dst minimum time (Delta t(sub Dst)) between the observed and the predicted. As a result, we found that the model by Temerin and Li gives the best prediction for all parameters when all 63 events are considered. The model gives the average values: the linear correlation coefficient of 0.94, the RMS error of 14.8 nT, the Delta Dst(sub min) of 7.7 nT, and the absolute value of Delta t(sub Dst) of 1.5 hour. For further comparison, we classified the storm events into two groups according to the magnitude of Dst. We found that the model of Temerin and Lee is better than the other models for the events having 100 <= Dst < 200 nT, and three recent models (the model of Wang et al., the model of Temerin and Li, and the model of Boynton et al.) are better than the other three models for the events having Dst <= 200 nT.

Ji, Eun-Young; Moon, Y.-J.; Gopalswamy, N.; Lee, D.-H.

2012-01-01

379

Predicting geomagnetic storms as a space weather project  

NASA Astrophysics Data System (ADS)

To be successful, space weather researchers need to establish a new discipline by synthesizing and integrating the traditional four major disciplines: solar physics, interplanetary physics, magnetospheric physics and ionospheric physics (aeronomy). Although much progress within the four major disciplines and their sub-disciplines has been made in the past and more progress is still needed, such efforts alone cannot accomplish the task of forecasting space weather and predicting geomagnetic storms. This paper describes an example of the integration efforts—entirely physically-based. It is not intended to be a review. Elements that need to be integrated include modeling of the background solar wind flow; parameterizing of solar events on the source surface; modeling of the propagation of the shock waves; detecting of the shock waves by IPS, comets and other methods; characterizing geomagnetic storms by the ? parameter (or any others); estimating the Dst and AE indices from the ? parameter (or any others); simulating ionospheric effects; examining effects on power line systems and oil pipeline systems, etc. It is emphasized that in this whole series of research, one of the major missing links is related to our present inability to predict the IMF polar angle ? as a function of time. A concerted effort among the four disciplines is needed in making this prediction possible.

Akasofu, Syun-Ichi

380

Gravitational dynamos and the low-frequency geomagnetic secular variation  

PubMed Central

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

Olson, P.

2007-01-01

381

A geomagnetically induced current warning system: model development and validation  

NASA Astrophysics Data System (ADS)

Geomagnetically Induced Currents (GIC), which can flow in technological systems at the Earth's surface, are a consequence of magnetic storms and Space Weather. A well-documented practical problem for the power transmission industry is that GIC can affect the lifetime and performance of transformers within the power grid. Operational mitigation is widely considered to be one of the best strategies to manage the Space Weather and GIC risk. Therefore in the UK a magnetic storm warning and GIC monitoring and analysis programme has been under development by the British Geological Survey and Scottish Power plc (the power grid operator for Central Scotland) since 1999. Under the auspices of the European Space Agency's service development activities BGS is developing the capability to meet two key user needs that have been identified. These needs are, firstly, the development of a near real-time solar wind shock/ geomagnetic storm warning, based on L1 solar wind data and, secondly, the development of an integrated surface geo-electric field and power grid network model that should allow prediction of GIC throughout the power grid in near real time. While the final goal is a `seamless package', the components of the package utilise diverse scientific techniques. We review progress to date with particular regard to the validation of the individual components of the package. The Scottish power grid response to the October 2003 magnetic storms is also discussed and model and validation data are presented.

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

382

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

383

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

384

Geomagnetic effects on mid-latitude railways: A statistical study of anomalies in the operation of signaling and train control equipment on the East-Siberian Railway  

Microsoft Academic Search

Intense geomagnetically induced currents (GIC) can hamper rail traffic by disturbing signaling and train control systems. GIC threats have been a concern for technological systems at high-latitude locations due to geomagnetic disturbances driven by substorm expansion electrojet or convection electrojet intensifications. However, other geomagnetic storm processes such as storm sudden commencement (SSC) and geomagnetic pulsations can also cause GIC concerns

N. G. Ptitsyna; V. V. Kasinskii; G. Villoresi; N. N. Lyahov; L. I. Dorman; N. Iucci

2008-01-01

385

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

E-print Network

Computational Investigation of Hardness Evolution During Friction-Stir Welding of AA5083 and AA2139 coupled thermo-mechanical finite-element analysis of the friction-stir welding (FSW) process developed, finite-element analysis, friction- stir welding, hardness prediction 1. Introduction Having a more mobile

Grujicic, Mica

386

Transform (60833005, 60573091), 863 2007AA01Z1552009AA011904  

E-print Network

Transform (60833005, 60573091), 863 2007AA01Z1552009AA011904 200800020002 xfmeng@ruc.edu.cn Transform ( 100872) (wwcd2005@163.com) Algebra-based Transform query optimization strategy Wang Wei 100872) Abstract XQuery/Update defines a special Transform query, which is similar to be hypothetical

387

Intermolecular interaction between Cry2Aa and Cyt1Aa and its effect on larvicidal activity against Culex quinquefasciatus.  

PubMed

The Cyt1Aa protein of Bacillus thuringiensis susbp. israelensis elaborates demonstrable toxicity to mosquito larvae, but more importantly, it enhances the larvicidal activity of this species Cry proteins (Cry11Aa, Cry4Aa, and Cry4Ba) and delays the phenotypic expression of resistance to these that has evolved in Culex quinquefasciatus. It is also known that Cyt1Aa, which is highly lipophilic, synergizes Cry11Aa by functioning as a surrogate membrane-bound receptor for the latter protein. Little is known, however, about whether Cyt1Aa can interact similarly with other Cry proteins not primarily mosquitocidal; for example, Cry2Aa, which is active against lepidopteran larvae, but essentially inactive or has very low toxicity to mosquito larvae. Here we demonstrate by ligand binding and enzyme-linked immunosorbent assays that Cyt1Aa and Cry2Aa form intermolecular complexes in vitro, and in addition show that Cyt1Aa facilitates binding of Cry2Aa throughout the midgut of C. quinquefasciatus larvae. As Cry2Aa and Cry11Aa share structural similarity in domain II, the interaction between Cyt1Aa and Cry2Aa could be a result of a similar mechanism previously proposed for Cry11Aa and Cyt1Aa. Finally, despite the observed interaction between Cry2Aa and Cyt1Aa, only a 2-fold enhancement in toxicity resulted against C. quinquefasciatus. Regardless, our results suggest that Cry2Aa could be a useful component of mosquitocidal endotoxin complements being developed for recombinant strains of B. thuringiensis subsp. israelensis and B. sphaericus aimed at improving the efficacy of commercial products and avoiding resistance. PMID:23727800

Bideshi, Dennis K; Waldrop, Greer; Fernandez-Luna, Maria Teresa; Diaz-Mendoza, Mercedes; Wirth, Margaret C; Johnson, Jeffrey J; Park, Hyun-Woo; Federici, Brian A

2013-08-01

388

Impressions of Alcoholics Anonymous (AA) Group Cohesion: A Case for a Nonspecific Factor Predicting Later AA Attendance  

Microsoft Academic Search

Social support for abstinence in Alcoholics Anonymous (AA) has been reported to be a consistent factor accounting for AA benefit. However, the nonspecific or unintended effects of such support remain poorly understood and rarely investigated. This prospective study investigated how one nonspecific factor—perceived AA group cohesiveness—predicted increased practice of AA-related behaviors. Findings indicated that impressions of AA group cohesion predicted

Samara Lloyd Rice; J. Scott Tonigan

2011-01-01

389

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

390

Geomagnetic Field Reversals and Life on the Earth in Phanerozoic Time  

NASA Astrophysics Data System (ADS)

Global paleomagnetic and biostratigraphic data are generalized. As a result it is found out that the direct connection between geomagnetic reversals, biozones and maxima of mass extinction of a biota is absent. At the same time it is noted close to a synchronous total picture of consistent changes of biozones and geomagnetic polarity. It is explained by the general source - the Earth's diurnal rotation. The reversal polarity of a geomagnetic field prevailed during the Phanerozoic that is agreed with the Earth's counterclockwise rotation. Change of polarity of a field, most likely, is connected with acceleration or deceleration of rotation speed of the internal core relative to the Earth's mantle. Lack of direct interrelation between changes in the biosphere and geomagnetic field indicate a lack of influence of a field on life evolution on Earth. It follows also from the fact that life on Earth developed from primitive unicellular forms to mammals and the man and diversity of biota was grew against a close condition of a geomagnetic field during ~2,5 billion years and irrespective of numerous geomagnetic reversals. Main conclusion: evolutionary development of life on Earth doesn't depend both on large changes of a geomagnetic field, and on the extreme catastrophic events conducting to mass extinction of a biota.

Pechersky, D. M.

2014-10-01

391

Methods of analysis of geomagnetic field variations and cosmic ray data  

NASA Astrophysics Data System (ADS)

In the present paper, we propose a wavelet-based method of describing variations in the Earth's magnetic field, such as the horizontal component of the geomagnetic field, in addition to methods for evaluating changes in the energy characteristics of the field and for isolating the periods of increased geomagnetic activity. Based on a combination of multiresolution wavelet decompositions with neural networks, we propose a method of approximation of the cosmic ray time course and the allocation of anomalous variations (Forbush effects) that occur during periods of high solar activity. During the realization of the method, an algorithm was created for selecting the level of the wavelet decomposition and adaptive construction of the neural network. By using the proposed methods, we performed a joint analysis of the geomagnetic field and cosmic rays during periods of strong magnetic storms. The strongest geomagnetic field perturbations were observed in periods of abnormal changes in cosmic ray level. Assessment of the intensity of geomagnetic disturbances on the eve of and during magnetic storm development allowed us to highlight local increases in intensity of the geomagnetic field occurring at different frequency ranges prior to the development of the storm's main phase. Implementation of the proposed method with theoretical tools in combination with other methods will improve the estimation accuracy of the geomagnetic field state during space weather forecasting.

Mandrikova, Oksana V.; Solovev, Igor S.; Zalyaev, Timur L.

2014-12-01

392

Fast Solar Wind and Geomagnetic Variability during the 24th Solar Cycle (2009 - 2013)  

NASA Astrophysics Data System (ADS)

Solar activity and its extensions in the heliosphere govern and perturb the geo-space. The response of the terrestrial magnetosphere displayed as geomagnetic disturbances is measured by several geomagnetic indices. This paper analyses the geomagnetic variability during 2009 - 2013 under the influence of the fast solar wind. A preliminary catalogue of the high speed streams in the solar wind was set up using OMNI Data Base for the first five years of the 24th solar cycle. Our catalogue lists the basic parameters of the fast streams: the time of start (calendar date by year, month, and day as well as the corresponding day of Bartels Rotation), the initial and maximum speeds (in km/sec), the maximum gradient of the plasma speed, the duration (in days) and the solar source (coronal holes or solar eruptive phenomena). The correlation between the geomagnetic indices and the high speed stream parameters during the analysed interval is examined in detail. Some individual pairs of events 'high speed stream - geomagnetic disturbance' (cause - effect) are analysed to reveal the peculiarities of the geomagnetic disturbance as a function of the stream parameters and the nature of its solar source. The most powerful geomagnetic disturbances were registered as a consequence of some complex external perturbation.

Maris Muntean, Georgeta; Besliu-Ionescu, Diana; Dobrica, Venera; Lacatus, Dana Adriana; Razvan Paraschiv, Alin

2014-05-01

393

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

394

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

395

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

396

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

397

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

398

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

PubMed

The contribution of geomagnetic variation to the occurrence of UFORs (reports of UFOs) within the New Madrid States during the 6-mo. increments before increases in the numbers of IV-V or less intensity earthquakes within the central USA was determined. Although statistically significant zero-order correlations existed between measures of earthquakes, UFORs and geomagnetic variability, the association between the latter two deteriorated markedly when their shared variance with earthquakes was held constant. These outcomes are compatible with the hypothesis that geomagnetic variability (or phenomena associated with it) may enhance UFORs but only if tectonic stress and strain are increasing within the region. PMID:3982943

Persinger, M A

1985-02-01

399

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

400

The CRRES AA 2 release: HF wave-plasma interactions in a dense Ba+ cloud  

NASA Astrophysics Data System (ADS)

An ionospheric chemical release, designated AA 2, was performed on July 12, 1992, as part of the NASA Combined Release and Radiation Effects Satellite (CRRES) El Coqui rocket campaign. The purpose of the AA 2 experiment was to study the interaction between a powerful radio wave and a high ion mass (Ba+), ``collisionless'' plasma. Approximately 35 kg of Ba were explosively released near the center of the Arecibo high-frequency (HF) beam at 253 km altitude. This was the largest Ba release of the CRRES experiments; it yielded a distinctive ionospheric layer having a maximum plasma frequency of 11 MHz. At early times (<1 min after the release) the HF beam produced the strongest Langmuir waves ever detected with the Arecibo 430-MHz radar. Resonantly enhanced Langmuir waves were observed to be excited principally at the upshifted plasma line (i.e., near 430 MHz+fHF, where fHF is the frequency of the modifying HF wave), and only weakly excited waves were apparent at the downshifted plasma line (430 MHz-fHF). The upshifted plasma-line spectrum contained a dominant peak at the ``decay line,'' that is, at the frequency 430 MHz+fHF-?, where ? is close to the Ba+ ion-acoustic frequency (~2 kHz). Downshifted plasma-line echoes occurred at frequencies near 430 MHz-fHF and 430 MHz-fHF-1 kHz and exhibited little or no signal strength at the decay line (430 MHz-fHF+?). During an initial period of intense upshifted plasma-line excitation, the power asymmetry between the upshifted and downshifted plasma lines was of the order of 105 at the decay line. The upshifted plasma line was accompanied by strong HF-enhanced ion waves that were present only at the downshifted acoustic sideband. After geomagnetic field-aligned irregularities formed in the plasma the amplitudes of the upshifted and downshifted plasma lines equalized, and each exhibited spectra characteristic of the parametric decay instability. At early times in the Ba+ plasma the symmetry of wave excitation anticipated for a parametric instability in a stationary, homogeneous plasma was absent. The experimental results indicate that the development of the parametric decay instability needs to be reexamined for a smooth plasma having a small (~5 km) vertical scale length. Moreover, ion flow down geomagnetic field lines appears to suppress instabilities responsible for the formation of field-aligned irregularities and may also have an impact on the way parametric instabilities are excited. New theoretical approaches are needed to resolve many of the issues raised by this experiment.

Djuth, F. T.; Sulzer, M. P.; Elder, J. H.; Groves, K. M.

1995-09-01

401

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

402

Geomagnetic pulsation generation as a result of whistler wave scattering  

SciTech Connect

Nonlinear scattering of whistler mode waves by kinetic Alfv{acute e}n waves (KAWs) is considered. The evolution of whistler mode wave decay instability in time and two spatial dimensions is studied under the approximation of two-fluid magnetohydrodynamics. It is shown that efficient coupling between whistler waves and KAWs is possible due to the finite Larmor radius effect for Alfv{acute e}n waves. The considered process can lead to significant enhancement of KAWs. The nonlinear scattering of whistler waves by KAWs is proposed as a possible mechanism of enhancement and generation of geomagnetic pulsations in the magnetosphere and ionosphere of the Earth. {copyright} {ital 1999 American Institute of Physics.}

Yukhimuk, V.; Roussel-Dupre, R.; Symbalisty, E. [EES-8, MS D401, Los Alamos National Laboratory, Los Alamos, New Mexico, 87545 (United States)] [EES-8, MS D401, Los Alamos National Laboratory, Los Alamos, New Mexico, 87545 (United States)

1999-01-01

403

Separation of the geomagnetic variation of cosmic rays  

NASA Astrophysics Data System (ADS)

The contributions of geomagnetic variations and complex variations in cosmic ray intensities to measured variations in the neutron component of cosmic ray flux are separated by a study of normalized neutron intensities recorded at three stations with different cut-off rigidities. The correlation between Dst variations and temporal variations in normalized intensity differences is calculated for stations with rigidities of 0.0, 4.0 and 13 GV during the large magnetic storm (300 nT) of March 5-13, 1970. Results show the increase in cosmic ray intensities observed during the storm to be due to a decrease in cosmic ray cut-off rigidities. The maximum Dst decrease of 280 nT is found to lead to a 3.2 percent variation in the intensity difference between Dallas and Churchill stations, and a 4.2 percent variation in the difference between Chacataya and Churchill, in agreement with theoretical calculations.

Zhumabaev, B. T.; Kozin, I. D.

404

A new trajectory concept for exploring the earth's geomagnetic tail  

NASA Technical Reports Server (NTRS)

An innovative trajectory technique for a magnetotail mapping mission is described which can control the apsidal rotation of an elliptical earth orbit and keep its apogee segment inside the tail region. The required apsidal rotation rate of approximately 1 deg/day is achieved by using the moon to carry out a prescribed sequence of gravity-assist maneuvers. Apogee distances are alternately raised and lowered by the lunar-swingby maneuvers; several categories of the 'sun-synchronous' swingby trajectories are identified. The strength and flexibility of the new trajectory concept is demonstrated by using real-world simulations showing that a large variety of trajectory shapes can be used to explore the earth's geomagnetic tail between 60 and 250 R sub E.

Farquhar, R. W.; Dunham, D. W.

1981-01-01

405

Ionospheric Features Diagnosed by Radio Tomography during Strong Geomagnetic Disturbances  

NASA Astrophysics Data System (ADS)

During the periods of geomagnetic storms, the ionosphere has a particularly complicated and rapidly changing structure. Each storm is marked by its own set of specific manifestations, which reflect rearrangement of the dynamical pattern of the ionosphere and strong perturbations in its parameters. The complexity and global scale of the ionospheric processes that occur during the storms call for the nonlocal methods for diagnosing the spatiotemporal structure of the ionospheric disturbances. Here, we present the results of studying the ionospheric structure by the methods of low orbital radio tomography (RT). The ionospheric radio tomography is rapidly developing during the last two decades. Due to the sufficiently high satellite velocity (~7.9 km/s) and, correspondingly, quite fast (compared to the characteristic times of the ionospheric processes) passage of the satellite through the ionospheric region under study, the radio tomographic approach is suitable for making nearly instantaneous (covering an interval of 5-10 min) 2D snapshots of the ionosphere in the altitude-latitude plane. The vertical and horizontal resolution of RT is 30-40 km and 20-30 km, respectively. We consider the ionospheric manifestations of strong geomagnetic storms (1991-2012) in different regions worldwide including the European part of Russia and North America. We note that during the geomagnetic disturbances, the ionosondes frequently show unstable operation. In contrast to the ionosondes that use HF radio waves, the RT methods are suitable for imaging the ionosphere even during severe solar and geophysical disturbances. During the periods of strong perturbations, RT detected various wavelike structures, travelling ionospheric disturbances, and different manifestations of acoustic gravity waves in the ionosphere. Using the RT methods, the wave effects of particle precipitation were analyzed, and plasma flows were estimated. Radio tomographic imaging of the ionosphere during severe disturbances reveals multiextremal spotty patterns with steep wall-like gradients in electron density in the north. Thin enhancements of electron concentration that are elongated by hundreds of kilometers along the magnetic field lines and attain dozens of kilometers in the transversal direction are identified. The complexly structured ionospheric trough with a tilted polar wall shifted towards the equator is revealed. Many RT reconstructions show the ionospheric trough to split. For example, the RT imaging of the storm of March 24-28, 1991 indicates that the ionospheric structures that are normally typical of the subauroral and auroral ionosphere (the troughs and anomalous ionization in the F-region) reached middle latitudes at that time. During the strongest geomagnetic storm on October 30-31, 2003, the ionosphere over the European part of Russia was marked by anomalously high electron concentration; the distribution of electron density in the region of increased ionization was extremely complicated in space and highly variable in time. We are grateful to the North-West Research Associates (NWRA) for providing the experimental data on relative TEC measured at the RT system in Alaska. The work was supported by the Russian Foundation for Basic Research (grants 11-05-01157 and 13-05-01122).

Andreeva, Elena S.; Kunitsyn, Vyacheslav E.; Tereshchenko, Evgeniy D.; Kozharin, Maksim A.; Nazarenko, Marina O.

2013-04-01

406

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

407

Index des mots-cls Keywords index  

E-print Network

Index des mots-clés Keywords index A Abies, 823 Abies alba, 265 acacia, 93 Acacia cyanophylla Lindl., 335 Acacia mearnsii De Wild., 833 acclimation, 19 AFLP, 627 AFLP, SSR, EST markers, 637 Agrobacterium

Boyer, Edmond

408

Validation of the galactic cosmic ray and geomagnetic transmission models  

NASA Technical Reports Server (NTRS)

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. Published by Elsevier Science Ltd.

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

2001-01-01

409

Relation of reverse geomagnetic polarity to biological evolution  

NASA Astrophysics Data System (ADS)

We have studied the connection between a number of insect and terrestrial tetrapods families and the duration of periods with normal and reverse polarities from Cenozoic period 84 Mya towards the Neogene 23-0 Mya It was found that the duration of periods of normal and reverse polarities decreased from Paleogene to Neogene In concordance with the rate of changes of the magnetic polarity the number of living families are increasing Following each revitalization the dipole field strength is fluctuating This means that the geomagnetic cut-off should be also fluctuating during changes of polarity from a minimum theoretically zero to maximum as for actual dipole field strength in the equatorial regions where vertical cosmic ray cut-off is about 13-17 GeV In the present time the influence of the Earth s dipole magnetic field configuration results in a better protection against high energetic particles near the equator than in the polar areas which leads to lower dose of irradiation in equatorial than in polar regions Hence when the geomagnetic cut-off is low the exposure to cosmic rays of living systems is high The more often the polarity changes the more often living systems should be exposed to high intensity of cosmic rays and consequently the rate of biological evolution should be higher This is that we can see in Neogene Our experiments carried out during a great solar events when the solar particle fluxes increase in 10 5 in near-earth space and when secondary cosmic rays near Earth s surface also increase revealed the

Belisheva, N. K.; Biernat, H. K.; Lammer, H.; Getselev, I. V.

410

Modelling geomagnetic reversals as a Gaussian Cox Process  

NASA Astrophysics Data System (ADS)

The mean rate of reversal of the geomagnetic field, as recorded in the Geomagnetic Polarity Time Scale (GPTS), has long been an object of study. The significance of the apparent long-term variations in the mean rate of reversals - including the occurrence of superchrons - has been debated, as has the possible origins of these variations in external control of the geodynamo (e.g. by the time-varying boundary conditions imposed by mantle convection). Here we model the long-term variations in the reversal rate nonparametrically, in terms of an inhomogeneous Poisson process. Specifically, we consider a Gaussian Cox process, a type of doubly-stochastic Poisson process where the mean rate (or intensity) is modelled in terms of a Gaussian process. Such processes are amenable to likelihood-based inference using Bayesian Markov Chain Monte-Carlo (MCMC) methods, which we employ to provide posterior distributions of the model parameters. The specification of a Gaussian process requires a covariance function, relating the intensity at nearby times; crucially, however, the timescale of the covariance function is not prescribed, but appears as a model hyperparameter, whose posterior distribution is an important output of the analysis. For the geodynamo, this hyperparameter should robustly characterise the timescale of long-term variations. Two different types of Gaussian Cox process are considered: a Log Gaussian Cox Process, applied to binned reversal data; and a Sigmoidal Gaussian Cox Process, applied to the discrete reversal data using a technique involving latent variables. Different MCMC algorithms for sampling the posterior distribution of the model parameters are investigated for both types of process, to check (and to optimise) the convergence of the MCMC chains. This analysis is applied to different records of the GPTS, including those of Cande & Kent (1995) and Gradstein & Ogg (1996). The implications of this analysis for the geodynamo, and the possibility of comparable analysis of the output of numerical geodynamo simulations, are discussed.

Sarson, Graeme; Boys, Richard; Golightly, Andrew; Henderson, Daniel

2013-04-01

411

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

412

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

413

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

414

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 analysed to replace CGM in the equatorial region.

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

415

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

416

Inferring the interplanetary magnetic field by observing the polar geomagnetic field.  

NASA Technical Reports Server (NTRS)

Svalgaard (1968, 1972) and Mansurov (1969) have shown that it is possible to infer the polarity of the interplanetary magnetic field quite reliably from observations of the diurnal variation of polar geomagnetic fields. The effect is most prominent in the vertical component of geomagnetic observatories near the geomagnetic poles during several hours near noon. The interplanetary magnetic field observed with spacecraft near the earth is very similar to the mean solar magnetic field (i.e., the sun observed as though it were a star); thus the fact that observations of the polar geomagnetic field have existed without interruption since 1926 at the Danish Meteorological Institute station at Godhavn, Greenland, means that in effect the inferred solar magnetic field during five sunspot cycles is available for analysis.-

Wilcox, J. M.

1972-01-01

417

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

418

Solar, interplanetary and geomagnetic phenomena in March 1991 and their association with spacecraft and terrestrial problems  

SciTech Connect

The solar activity that occurred on 22 and 23 March 1991 resulted in major interplanetary and geomagnetic disturbances. In spite of measurements in the earth`s magnetosphere, near Venus, and by the Ulysses spacecraft (at 2.48 AU), it is not possible to identify unambiguously the source of each perturbation. A very powerful shock resulted in large geomagnetic disturbances and contributed to the generation of a third radiation belt, as measured by the CRRES spacecraft.

Smart, D.F.; Shea, M.A.; Fluekiger, E.O.; Sanahuja, B.

1995-12-31

419

Revised calibration of the geomagnetic polarity timescale for the Late Cretaceous and Cenozoic  

NASA Astrophysics Data System (ADS)

Recently reported radioisotopic dates and magnetic anomaly spacings have made it evident that modification is required for the age calibrations for the geomagnetic polarity timescale of Cande and Kent (1992) at the Cretaceous/Paleogene boundary and in the Pliocene. An adjusted geomagnetic reversal chronology for the Late Cretaceous and Cenozoic is presented that is consistent with astrochronology in the Pleistocene and Pliocene and with a new timescale for the Mesozoic.

Cande, S. C.; Kent, D. V.

1995-04-01

420

Coronal holes, solar wind streams, and recurrent geomagnetic disturbances: 1973–1976  

Microsoft Academic Search

Observations of coronal holes, solar wind streams, and geomagnetic disturbances during 1973–1976 are compared in a 27-day pictorial format which shows their long-term evolution. The results leave little doubt that coronal holes are related to the high-speed streams and their associated recurrent geomagnetic disturbances. In particular, these observations strongly support the hypothesis that coronal holes are the solar origin of

N. R. Sheeley; J. W. Harvey; W. C. Feldman

1976-01-01

421

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

422

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

423

Extended study of extreme geoelectric field event scenarios for geomagnetically induced current applications  

NASA Astrophysics Data System (ADS)

Geomagnetically induced currents (GIC) flowing in man-made ground technological systems are a direct manifestation of adverse space weather. Today, there is great concern over possible geomagnetically induced current effects on power transmission networks that can result from extreme space weather events. The threat of severe societal consequences has accelerated recent interest in extreme geomagnetic storm impacts on high-voltage power transmission systems. As a result, extreme geomagnetic event characterization is of fundamental importance for quantifying the technological impacts and societal consequences of extreme space weather. This article reports on the global behavior of the horizontal geomagnetic field and the induced geoelectric field fluctuations during severe/extreme geomagnetic events. This includes (1) an investigation of the latitude threshold boundary, (2) the local time dependency of the maximum induced geoelectric field, and (3) the influence of the equatorial electrojet (EEJ) current on the occurrence of enhanced induced geoelectric fields over ground stations located near the dip equator. Using ground-based and satellite-borne Defense Meteorological Satellite Program measurements, this article confirms that the latitude threshold boundary is associated with the movements of the auroral oval and the corresponding auroral electrojet current system, which is the main driver of the largest perturbations of the ground geomagnetic field at high latitudes. In addition, we show that the enhancement of the EEJ is driven by the penetration of high-latitude electric fields and that the induced geoelectric fields at stations within the EEJ belt can be an order of magnitude larger than that at stations outside the belt. This has important implications for power networks located around the electrojet belt and confirms that earlier observations by Pulkkinen et al. (2012) were not isolated incidences but rather cases that can occur during certain severe geomagnetic storm events.

Ngwira, Chigomezyo M.; Pulkkinen, Antti; Wilder, Frederick D.; Crowley, Geoffrey

2013-03-01

424

The geomagnetic seasons in the auroral zone: dayside magnetopause reconnection versus solar illumination  

Microsoft Academic Search

There are three mechanisms that are proposed to explain the geomagnetic seasons. The most widely accepted mechanism is the Russell-McPherron (R-M) effect, which attributes the dependence to seasonal changes in an external driver of geomagnetic activity, the dayside magnetopause reconnection rate. The second mechanism results from a dipole tilt modulation of dayside magnetopause reconnection that depends on season. The third

R. S. Weigel

2004-01-01

425

Geomagnetic pulsations as a result of the solar flare of March 23, 1976  

NASA Astrophysics Data System (ADS)

Geomagnetic pulsations connected with the flare of March 23, 1976 are examined on the basis of data obtained at midlatitude stations on Cuba and in the USSR. The data indicate that chromospheric flares accompanied by considerable X-ray fluxes (exceeding background values by 2-3 orders of magnitude) can lead to the appearance of a burst of geomagnetic pulsations with periods of 60-80 sec both in the dayside and the nightside ionosphere.

Perez, J.; Lazo, B.; Kleimenova, N. G.; Kozyreva, O. V.

1989-01-01

426

Index Funds Online  

NSDL National Science Digital Library

Matthew Roberts recently released Index Funds Online in response to the lack of index investment fund information on the Internet. Site features include the market performance newsletter Indexing Quarterly, background and definitional information on major US Indexes such as the S&P 500, and a library of new and interesting financial Websites, articles, and book reviews. Links to