Energetic particle precipitation into the high‐latitude ionosphere and the auroral electrojets: 3. Characteristics of electron precipitation into the morning sector auroral oval

Abstract

Data from the University of Alberta meridian line of magnetometers are utilized to define the poleward and equatorward borders of the westward electrojet in the morning sector. Soft particle spectrometer data from the Isis 2 polar orbiting satellite are organized in the framework of the westward electrojet for cases where the satellite orbital path took it close to the meridian line of magnetometers. It is found that, in the morning sector, the energetic electron data are organized into four distinct regions as a function of latitude. The southernmost region (D) features trapped electrons across a broad energy range. Region C, just poleward of Region D, contains fluxes of hot (several keV) electrons with a Maxwellian spectrum which are precipitating into the southern portion of the westward electrojet. These Region B fluxes are colocated with the poleward portion of the westward electrojet and are less capable of creating ionospheric Hall conductivity than are their more energetic Region C counterparts. Finally, Region A, poleward of the northern border of the westward electrojet, contains irregular latitudinally localized regions of precipitating electrons whose spectrum contains drifting Maxwellians and which are evidently being accelerated along the field lines on which they are being observed. The energies of electrons in Region A are of the order of a few hundred electron volts and rarely exceed ∼1–2 keV. The phenomenology of Region A is remarkably similar to the acceleration region in the poleward portion of the auroral oval in the evening sector although the peak energies of the electrons are smaller in the morning sector compared to the evening sector. Our results suggest that the Harang discontinuity does not signify any significant asymmetry in convection drift paths in the magnetosphere and that asymmetries noted in ionospheric current flow and auroral luminosity are due solely to asymmetries in the energies to which electrons may be accelerated in the morning compared to the evening sector. We present a model of plasma convective flow in the magnetosphere which is consistent with the observations reported in this paper.