Effect of He⁺ temperature and thermal anisotropy on the electromagnetic ion cyclotron instability in the geosynchronous region of GEOS‐2

Abstract

The existence of strong ULF electromagnetic ion cyclotron waves in the magnetosphere have been firmly established through several observations. Some recent studies have shown that an energetic heavy ion component may have a drastic influence on the ion cyclotron instability. By considering several possible sources of He + thermal and anisotropy effects, it is shown that, within the linear theory and uncertainties of the available data, none of these effects have a major influence on the ion cyclotron instablity in the geostationary region of GEOS‐2. The analysis is rigorous for He + parallel temperatures ranging between a few electron volts and a few keV, with a similar tendency for higher temperatures.