High-latitude low-energy electron fluxes and variation of the magnetospheric Structure with the direction of the interplanetary magnetic field and with the geomagnetic activity

Abstract

The variation of the high-latitude boundary of the low-energy (E > 35 kev) outer-zone electrons with the direction of the interplanetary magnetic field (IMF) is discussed. The particle data from the polar-orbiting satellite Alouette 2 and magnetic-field data from Explorer 33 and 35 are used. Structure of the high-latitude fluxes of electrons (E > 35 kev) on the nightside of the earth is analyzed on the basis of Alouette 2 and Isis 1 particle data. Predictions about the magnetotail structure, based on these data are tested by using data from the Imp 3 magnetic-field experiment. If the IMF has a southward component, the electron boundary is displaced poleward with respect to the average position in the interval from approximately 2000 to 1000 MLT and is displaced equatorward from 1000 to about 2000 MLT. The intensity versus latitude profiles, which are displaced poleward with respect to the average boundary latitude, are characterized by structured fluxes near the high-latitude boundary seen most clearly around and/or after midnight. The probability of the occurrence of such structured profiles depends strongly on the direction of the IMF and increases with the geomagnetic activity. Dawn-dusk asymmetry in the occurrence and structure of the high-latitude electron fluxes is associated with a dawn-dusk asymmetry in the structure of the geomagnetic tail such that the magnetic field in the plasma sheet is weaker on the dawnside than on the duskside.