Solar wind‐driven variations of electron plasma sheet densities and temperatures beyond geostationary orbit during storm times
Dubyagin, S.; Ganushkina, N. Yu.; Sillanpää, I.; Runov, A.
2016-09
Citation
Dubyagin, S.; Ganushkina, N. Yu.; Sillanpää, I. ; Runov, A. (2016). "Solar wind‐driven variations of electron plasma sheet densities and temperatures beyond geostationary orbit during storm times." Journal of Geophysical Research: Space Physics 121(9): 8343-8360.
Abstract
The empirical models of the plasma sheet electron temperature and density on the nightside at distances between 6 and 11 RE are constructed based on Time History of Events and Macroscale Interactions During Substorms (THEMIS) particle measurements. The data set comprises ∼400 h of observations in the plasma sheet during geomagnetic storm periods. The equatorial distribution of the electron density reveals a strong earthward gradient and a moderate variation with magnetic local time symmetric with respect to the midnight meridian. The electron density dependence on the external driving is parameterized by the solar wind proton density averaged over 4 h and the southward component of interplanetary magnetic field (IMF BS) averaged over 6 h. The interval of the IMF integration is much longer than a typical substorm growth phase, and it rather corresponds to the geomagnetic storm main phase duration. The solar wind proton density is the main controlling parameter, but the IMF BS becomes of almost the same importance in the near‐Earth region. The root‐mean‐square deviation between the observed and predicted plasma sheet density values is 0.23 cm−3, and the correlation coefficient is 0.82. The equatorial distribution of the electron temperature has a maximum in the postmidnight to morning MLT sector, and it is highly asymmetric with respect to the local midnight. The electron temperature model is parameterized by solar wind velocity (averaged over 4 h), IMF BS (averaged over 45 min), and IMF BN (northward component of IMF, averaged over 2 h). The solar wind velocity is a major controlling parameter, and IMF BS and BN are comparable in importance. In contrast to the density model, the electron temperature shows higher correlation with the IMF BS averaged over ∼45 min (substorm growth phase time scale). The effect of BN manifests mostly in the outer part of the modeled region (r > 8RE). The influence of the IMF BS is maximal in the midnight to postmidnight MLT sector. The correlation coefficient between the observed and predicted plasma sheet electron temperature values is 0.76, and the root‐mean‐square deviation is 2.6 keV. Both models reveal better performance in the dawn MLT sector.Key PointsEmpirical models of electron density and temperature at r = 6–11 Re on the nightside are constructedThe model performance has been essentially improved by using lagged and time‐averaged solar wind parameters as a model inputElectron temperature and density correllate best with IMF Bs averaged over substorm growth phase and storm main phase periods, respectivelyPublisher
Wiley Periodicals, Inc.
ISSN
2169-9380 2169-9402
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