Correlated electron and X ray measurements of quiet time electron precipitation: A comparative study of Bremsstrahlung production and transport in the atmosphere

Abstract

Five cases of X ray observations from balloons coordinated with measurements of precipitating electrons were obtained during passes of the polar‐orbiting satellite P78‐1 near Siple, Antarctica (L ∼ 4.1), the launch point of the balloons. The observations, made during a geomagnetically quiet period in late December 1980 to early January 1981, showed small enhancements of the X ray fluxes (E > 25 keV) and moderate trapped electron fluxes (E > 68 keV) with pitch angle distributions extending into the edge of the loss cone sufficient to produce the ≲0.5 dB of cosmic noise absorption recorded by the Siple 30‐MHz riometer. Bremsstrahlung production and transport in the atmosphere were calculated using the measured electron fluxes, energy spectra, and pitch angle distributions for the source. The X ray fluxes and spectra calculated for the balloon altitudes were in good agreement with those measured from the balloons when the total energy deposition from electrons, E > 10 keV, exceeded 2×10−3 erg/cm² s. The observed electron fluxes show that a significant continuous electron precipitation occurs at the western edge of the South Atlantic magnetic anomaly even at times of low geomagnetic activity.