Observations of trapped and precipitating electrons in the auroral zone, and related effects in the ionospheric D‐region

Abstract

This study investigates the relationship between the trapped and precipitated components of the >30 keV and >100 keV auroral electron flux measured by the polar orbiting environmental satellites (POES) which are in sun‐synchronous orbits of 90 minutes period at an altitude of about 850 km. The data are restricted to selected over‐passes of the Kilpisjärvi imaging riometer by the POES NOAA‐12 and NOAA‐14. The analysis of the data addresses the short‐term variation of the fluxes, and the relation between the particle flux and the ionospheric radiowave absorption measured by the imaging riometer. It is found that during each over‐pass the precipitated flux varies more than the trapped, and the amount of variation is greatest in the morning sector and least at noon. The expectation that (absorption)2 flux holds more closely for the trapped than for the precipitated flux, an anomaly which may be explained in part if some of the electrons reaching 90 km are beyond the reception cone of the detector for precipitated particles. Empirical formulae are given for the relations between flux and absorption, and it is shown that the absorption may serve to estimate the diffusion parameter for >30 keV electrons.