Joint responses of geosynchronous magnetic field and relativistic electrons to external changes in solar wind dynamic pressure and interplanetary magnetic field

摘要

This paper studied statistically the joint responses of magnetic field and relativistic (>0.5 MeV) electrons at geosynchronous orbit to 201 interplanetary perturbations during 6 years from 2003 (solar maximum) to 2008 (solar minimum). The statistical results indicate that during geomagnetically quiet times (H_(SYM) > -30 nT, and AE < 200 nT), ~47.3% changes in the geosynchronous magnetic field and relativistic electron fluxes are caused by the combined actions of the enhancement of solar wind dynamic pressure (P_d) and the southward turning of interplanetary magnetic field (IMF) (ΔP_d > 0.4 nPa and IMF B_z < 0 nT), and only ~18.4% changes are due to single dynamic pressure increase (ΔP_d > 0.4 nPa, but IMF B_z > 0 nT), and ~34.3% changes are due to single southward turning of IMF (IMF B_z < 0 nT, but |ΔP _d| < 0.4 nPa). Although the responses of magnetic field and relativistic electrons to the southward turning of IMF are weaker than their responses to the dynamic pressure increase, the southward turning of IMF can cause significant dawn-dusk asymmetric perturbations that the magnetic field and relativistic electron fluxes increase on the dawnside (LT ~ 00:00-12:00) but decrease on the duskside (LT ~ 13:00-23:00) during the quiet times. Furthermore, the variation of relativistic electron fluxes is adiabatically controlled by the magnitude and elevation angle changes of magnetic field during the single IMF southward turnings. However, the variation of relativistic electron fluxes is independent of the change in magnetic field in some magnetospheric compression regions during the solar wind dynamic pressure enhancements (including the single pressure increases and the combined external perturbations), indicating that nonadiabatic dynamic processes of relativistic electrons occur there. Key Points Relativistic electron response to the southward turning of IMF is adiabaticElectron response to dynamic pressure increase is nonadiabatic in some regionsThe southward IMF causes the dawn-dusk asymmetric variations of electron fluxes