Energetic electrons, 50 keV to 6 MeV, at geosynchronous orbit: Their responses to solar wind variations

[1] Using simultaneous measurements of the upstream solar wind and of energetic electrons at geosynchronous orbit, we analyze the response of electrons over a wide energy range, 50 keV to 6 MeV, to solar wind variations. Enhancements of energetic electron fluxes over this whole energy range are modulated by the solar wind speed and the polarity of the interplanetary magnetic field ( IMF). The solar wind speed seems to be a dominant controlling parameter for electrons of all energy. Electron enhancements occur after solar wind speed enhancements with a time delay that increases with energy and that also depends on the average polarity of the IMF. The electron enhancements have a shorter delay if the IMF B-z < 0 and a longer delay if the IMF B-z > 0 during the solar wind speed enhancement. The dependence on solar wind condition varies for different energy electrons, with lower-energy electrons (< 200 keV) responding more to the polarity of the IMF and higher energy electrons (> 1 MeV) responding more to the solar wind speed. The variations of different energy electrons are well correlated among themselves. For five years, 1995-1999, the correlation coefficients of 1.1-1.5 MeV electrons with lower-energy electrons, 50-75, 105-150, 225-315, and 500-750 keV, are 0.55, 0.64, 0.74, and 0.90. This correlation is enhanced if a time shift proportional to their energy difference is included. The optimal time shifts and the corresponding correlation coefficients for the four lower energy electrons are 36, 32, 13, and 7 hours and 0.75, 0.77, 0.81, and 0.92, respectively.