The Earth's magnetopause as a source and sink for equatorial nightside energetic charged particles

摘要

The Imaging Proton Spectrometer (IPS) and the Imaging Electron Spectrometer(IES) on the Polar satellite have measured temporary deviations in theisotropy of the pitch angle distributions (PADs) of charged particles in theinner magnetosphere. As Polar passes through the nightside equatorial region,the IPS and IES observe dropouts of charged particles with pitch angles near90°, known as butterfly distributions caused by the shadowing of themagnetopause. Additionally, Polar observes a lower energy (<60 keV) intensification of locally mirroring ions while simultaneouslydetecting butterfly PADs in both higher energy ions and electrons. While itis accepted that charged particles can be lost to the magnetopause due toshadowing effects, the modeling here can suggest that the magnetopause canalso be a direct source for particles observed in magnetosphere, with astrong dependence upon both pitch angle and particle energy.