Abstract
Important causes of the precipitation of magnetospheric particles into the ionosphere are reviewed, and critical areas where further study is needed are identified. This review begins with a description of the precipitation that occurs within the region of open, polar-cap magnetic field lines. Precipitation of polar rain, cusp/mantle, and energetic solar particles is described as a result of the direct entry into the magnetosphere of particles that cross the magnetopause along open field lines. An extended region of soft electron precipitation is also often observed poleward of the plasma sheet; however the extent to which this region is within the region of open polar-cap field lines has not yet been definitively ascertained. Next the precipitation of plasma sheet particles by current sheet scattering is considered. It is shown that current sheet scattering can account for the ion precipitation that occurs throughout most of the plasma sheet along field lines that cross the equatorial plane on the nightside. Such scattering also accounts for electron precipitation that occurs in a narrow region adjacent to the poleward boundary of the plasma sheet. However, electron precipitation, as well as ion precipitation, occurs throughout most of the plasma sheet. The electron precipitation away from the poleward boundary of the plasma sheet appears to be predominantly the result of scattering by wave-particle interactions; however the responsible distribution of waves has yet to be identified. Finally, the precipitation of energetic radiation belt electrons and ions by Coulomb collisions, charge exchange, and wave particle interactions is briefly addressed.
Published Version
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