Stimulated auroral precipitation by wave‐particle interactions: Implications for the CRRES satellite mission

Abstract

The interaction of charged particles with plasma waves is one of the mechanisms which can cause the precipitation of energetic particles from the Earth's radiation belts. In the inner plasma sheet of the magnetotail, electromagnetic cyclotron waves can resonate with the bulk of the ambient energetic electron distribution only if an additional cold dense plasma population is present. In an attempt to artificially stimulate auroral electron precipitation, one experiment to be carried out during the Combined Release and Radiation Effects Satellite (CRRES) mission will be to release lithium close to the Earth's equatorial plane near geosynchronous orbit, along field lines that map to the diffuse auroral region. As the lithium is photoionized, a dense cold plasma cloud will be created within the background energetic population causing increased whistler wave growth. To support the CRRES Stimulated Electron Precipitation (STEP) experiment theoretically, a quantitative study is presented examining wave growth, propagation, and trapping of electromagnetic whistler waves within the released cold plasma cloud. Results show that for a background thermal electron temperature anisotropy of T⊥/T∥ > 1.2, whistler wave growth rates are greatly increased by the presence of the cold electrons, and the waves can be trapped in the cloud. Because of a maserlike effect, intense standing waves with amplitudes the order of a few nanotesla will be generated within a frequency range of about 50–500 Hertz. The waves will reach their largest amplitudes about 20 s after release, causing strong electron pitch angle diffusion into the loss cone, which can be detected as enhanced diffuse aurora at Earth.