Simultaneous energetic particle observations at geostationary orbit and in the upstream solar wind: Evidence for leakage during the magnetospheric compression event of November 1, 1984

Abstract

Energetic ion (E ≳ 70 keV) and electron (E ≳ 30 keV) observations are presented for three fortuitously positioned geostationary spacecraft during a strong magnetospheric compression event which brought the subsolar magnetopause inward of the synchronous orbit (r = 6.6 RE) on November 1, 1984. Active Magnetospheric Particle Tracer Explorers (AMPTE) Charge Composition Explorer (CCE) field and particle data show that the CCE spacecraft (at r = 8.8 RE) was in the upstream solar wind during the compression event and several upstream particle bursts were observed between 0650 and 0930 UT. Spacecraft 1984‐037 near 2200 LT observed multiple, sharp energetic particle injection events indicative of substorm onsets occurring at ∼0650, 0720, and 0750 UT on November 1. Spacecraft 1981‐025 near local noon observed some brief magnetopause encounters as early as 0635 UT, and after 0650 UT it remained near (and often outside) the magnetopause for most of the ensuing 3 hours. Observations of energetic particle fluxes and anisotropies near the noon magnetopause suggest that magnetospheric particles escaped into the dayside magnetosheath. Spacecraft 1982‐019 (near local dawn) observed strong energetic electron flux enhancements consistent with azimuthal eastward drift following the substorm injections near local midnight. The flux of ions at spacecraft 1982‐019, however, was depleted, particularly at ∼90° pitch angles. This suggests that in their westward drift from local midnight the energetic ions failed to transit the outer dayside magnetosphere in the subsolar region but were instead lost to the magnetosheath, where their drift paths intercepted the postnoon magnetopause surface. Thus the pattern of magnetopause escape established by the synchronous orbit spacecraft together with excellent time association and spectral similarity with the CCE bursts upstream suggests that the process of magnetospheric particle escape is the most likely source for energetic particles in the magnetosheath and the upstream solar wind in this favorably observed case.