Influence of the equatorial irregularities and precipitations in the South Atlantic Magnetic Anomaly on the generation of auroral‐type plasma instabilities

Abstract

Observational evidence of upward field‐aligned beams in the keV range has been obtained in the sub‐equatorial ionosphere above South America. These events can be related to coupled magnetic and ionospheric activity (magnetic storm, ionospheric irregularities). This result is in opposition with the current theory of the low‐latitude ionosphere. Its interpretation must assume that conditions exist for the growth of plasma instabilities. This implies a low plasma density, a close coupling between the ionosphere and the magnetosphere, and field‐aligned currents. Such suitable conditions have independently been observed in ionospheric irregularities (density, currents) or during magnetic storms (energetic particle precipitation) or they are deduced from the structure of the Anomaly (field‐aligned currents). This allows us to suggest that the South Atlantic Anomaly sometimes compares to the auroral oval and may develop some current‐driven plasma instabilities.