An event of distinct ion polar rain

• Published in: Geophysical research letters Vol. 15; no. 10; pp. 1165 - 1168
• Main Authors: Newell, Patrick T., Meng, Ching -I.
• Format: Journal Article
• Language: English
• Published: Washington, DC Blackwell Publishing Ltd 01.09.1988; American Geophysical Union
• Subjects: Density; Earth, ocean, space; Energy levels; Exact sciences and technology; External geophysics; Flux; Magnetosheath; Magnetospheric configuration; Maxwellian distribution; Physics of the magnetosphere; Precipitation; Rain; Strontium; Polar cap; Particle precipitation; Magnetosheath; Electron precipitation
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/GL015i010p01165

Although the comparatively featureless polarcap precipitation phenomenon of the electron polar rain has been known and studied since the work of Winningham and Heikkila [1974], to date there has been almost no work concerning ion polar rain, apparently because of its low intensity. This report documents a clear instance of ions at magnetosheath energy levels, precipitating in the manner characteristic of polar rain at flux levels of ⪍ 109 eV/cm² ‐s‐ sr—a flux about 10 times larger than that reported in the only previously published discussion of ion polar rain [Hardy et al., 1986]. A Maxwellian distribution with a temperature of 230 eV and a density of 0.02/cm³ fits the ion polar rain reasonably well. The comparatively high intensity permits verification that the strong dayside‐nightside gradient expected and observed in electron polar rain also occurs in the ion polar rain, and that the sign of the dawn‐dusk gradient was appropriate for the IMF By component at the time. A fairly typical (somewhat intense) electron polar rain accompanied the ion polar‐cap precipitation, displaying the same gradients as the ions.