Electron fluxes over the polar cap, 1. Intense keV fluxes during poststorm quieting

Abstract

Intense fluxes of keV electrons were observed over large regions of the north polar cap during two periods of magnetospheric quieting following large storms. These fluxes were distinctly field aligned, had energy spectra peaked at both • 100 eV and •2 keV, and were not observed in the conjugate hemisphere. A search for similar fluxes in the interplanetary medium or the dayside magnetosheath yielded negative results. In one instance the polar cap fluxes were observed for •40 hours during a period of large-scale expansion of the bow shock. The flux intensity and spectrum varied with observed changes in the bow shock configuration. This and other evidence leads us to suggest that these fluxes were accelerated by a potential barrier located either at the downstream bow shock or within the magnetospheric cavity on field lines intersecting the distended bow shock. The flux intensity and energy spectrum above I keV were similar over the polar cap and in the morningside plasma sheet, a finding which suggests that electrons in these regions had a similar source during these events. From the data we infer that the source of the polar cap fluxes was, in general, spatially and temporally uniform and that the structure within the region of their observation was related to processes and field line configurations that are internal to the magnetosphere. Details of the structure of the high-latitude magnetosphere are examined by using the polar cap fluxes as tracer particles. It is found that keV electrons have attenuated access to the postnoon region of closed field lines from high latitudes but are excluded from lower latitudes on the morningside by the prenoon cleft.

Satellite Observations of Polar, Magnetotail Lobe, and Interplanetary Electrons at Low Energies.

“…II) of Foster and Burrows (1976), Meng and Kroehl (1977) and Winningha m and Heikkila (1974) suggest a relationship between the polar electron intensity and magnetically disturbed conditions. However , Yeager and Frank (1976) found no correlation between magnetic activity and polar electron intensities at high altitudes.…”

“…These intensity spikes have been associated with 'sun-aligned' auroral arcs over the polar caps (Winningham and Heikkila, 1974;Foster and Burrows, 1976). Recent observations from the S3-3 satellite of upward flowing ions simultaneous with intense precipitating electron spikes over the polar regions (Fennel et al, 1977;Mizera and Fennel, 1977) indicate that the particle accelerations occur fairly close to the earth.…”

“…They called such distributions polar squalls, which are designated by the upper horizontal grid in Figure 2. Foster and Burrows (1976) have presented 1518-2 data for uniform but intense electron fluxes (shown as the upper vertical grid) following large magnetic storms. Meng and Kroehl (1977) recently published DMSP electron data (shown as upper diagonal lines) for times during magnetic storms, which show enhanced fluxes uniformly distributed over the polar caps.…”

“…-25- (Winningham and Heikkila, 1974;Burrows, 1976 and1977;Meng and Kroehl, 1977). Such accelerations are evidenced by weak field alignment of the angular distributions and/or a hardening of the electron spectra over some regions of the polar cap.…”

Polar cap X‐rays and electrons under low density solar wind conditions: Coordinated PIXIE and DMSP observations on 11 May 1999

“…Fairfield and Scudder [1985] called it the solar wind "strahl" and attributed its relatively high characteristic energy to a relative lack of collisional scattering by interplanetary electrons. Foster and Burrows [1976; reported observations of high-energy electrons in the polar cap with energy spectra peaked at -100 eV and ~2 keV during periods of large-scale bow-shock expansion. Similar fluxes in the interplanetary medium and the dayside magnetosheath were not found while the fluxes above 1 keV were similar to those observed in the morningside plasma were observed during this period.…”