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SPACE WEATHER, VOL. 3, S04001, doi:10.1029/2004SW000105, 2005

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

Xinlin Li

Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA


D. N. Baker

Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA


M. Temerin

Space Sciences Laboratory, University of California, Berkeley, California, USA


G. Reeves

Los Alamos National Laboratory, Los Alamos, New Mexico, USA


R. Friedel

Los Alamos National Laboratory, Los Alamos, New Mexico, USA


C. Shen

Laboratory for Space Weather, Chinese Academy of Sciences, Beijing, China


Abstract

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.

Received 15 July 2004; accepted 26 January 2005; published 7 April 2005.

Keywords: radiation belt; MeV electrons; energetic electrons; correlation; geosynchronous orbit; solar wind velocity.

Index Terms: 2720 Magnetospheric Physics: Energetic particles: trapped; 2722 Magnetospheric Physics: Forecasting (7924, 7964); 2730 Magnetospheric Physics: Magnetosphere: inner; 2784 Magnetospheric Physics: Solar wind/magnetosphere interactions; 2788 Magnetospheric Physics: Magnetic storms and substorms (7954).

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Citation: Li, X., D. N. Baker, M. Temerin, G. Reeves, R. Friedel, and C. Shen (2005), Energetic electrons, 50 keV to 6 MeV, at geosynchronous orbit: Their responses to solar wind variations, Space Weather, 3, S04001, doi:10.1029/2004SW000105.