High-latitude outer-zone boundary region for ≥40-keV electrons during geomagnetically quiet period

Abstract

The relationship of locally mirroring and precipitating ≥40-kev electrons was studied on magnetically quiet days in the region of the high-latitude outer-zone boundary with satellite Injun 3. There was usually an enhancement of precipitating ≥40-kev electrons observed in the region of the high-latitude boundary for all local times. On the night side the flux of ≥40-kev electrons was always observed to approach isotropy over the upper hemisphere at the position of the satellite in this boundary region. The condition of isotropy in the boundary region was found to be strongly dependent on local time, being always present on the night side and being less frequently observed with increasing local time around to local dusk (1800 hours) where isotropy was seldom observed in the boundary region. During magnetically quiet periods large intensities of ≥40-kev electrons were observed precipitating into the atmosphere for Λ ≥ 65°, and the position of the high-latitude boundary (intensity cutoff) was observed to vary by ΔΛ ≃ 7° while little magnetic activity was occurring. On the night side, the latitude where the ratio of the trapped to the precipitated ≥40-kev electron fluxes breaks toward one (φ boundary) is introduced as a more meaningful concept of the high-latitude limit to durably trapped ≥40-kev electrons than the usual intensity cutoff. The concept that the high-latitude outer-zone boundary region at all local times is controlled or driven by a mechanism (s) acting primarily on the night side is introduced.