Spatial distribution of energetic plasma sheet electrons

Abstract

The spatial distribution of energetic plasma sheet electrons (E ≥ 50 kev) out to a radial distance of 24 RE using data from the University of California at Los Angeles electron spectrometer and fluxgate magnetometer experiments on Ogo 5 is presented. A comparison of distributions in geocentric solar magnetospheric coordinates (GSM) prepared with and without the use of a neutral sheet model indicates that the use of such a model facilitates organization of plasma sheet data. The distribution in the YGSM- ZN plane, where ZN is the distance above or below the neutral sheet in the ZGSM direction, for limited values of XGSM shows a tendency for the energetic electrons to concentrate near the neutral sheet. However, no characteristic behavior is seen in electron fluxes during individual neutral sheet crossings. The percentage of flux occurrence above a given flux threshold falls off rapidly with distance from the neutral sheet. Contours of constant percentage of occurrence diverge slightly from the neutral sheet at local times away from midnight. This effect decreases with increasing flux threshold. Contours in the XGSM-YGSM plane for a limited range in ZN are extended toward dawn, and thus a limited dawn-dusk asymmetry is indicated. This effect is limited to the extent that percentages of occurrence comparable to those on the dawnside are found in the region about midnight. The degree of asymmetry increases as the flux threshold is increased. The contours in the XGSM-ZN plane converge toward the neutral sheet with increasing distance in the antisolar direction (−XGSM). A comparison of this result with the results from Imp 1 indicates that XGSM is preferable to the radial distance R for organizing tail data.