Polar cusp VLF hiss of irregular spectra is observed mainly at geomagnetic invariant latitudes from 74° to 84°, and at geomagnetic local times from 10 to 14 hours. This occurrence region corresponds well to a region of cusp precipitations of lowenergy electrons below 1 keV. Changes of lower cutoff frequency of polar cusp hiss are related with plasma irregularities in the polar cusp ionosphere. The whistler-mode Cerenkov radiation from electrons below I keV is discussed for generating the polar cusp hiss, but this mechanism can not work in the polar cusp ionosphere for VLF frequencies much lower than a local electron gyrofrequency. The whistler-mode VLF Cerenkov radiation is generated from the electrons below 1 keV at high altitude(～6 R_E) cusp magnetosphere, where a local electron gyrofrequency is in VLF band. The whistler-mode cusp hiss generated at high altitudes will propagate along field-aligned cusp plasma down to a strong geomagnetic field region where the cusp structure fades out. Below this region, the whistler-mode hiss spreads over the polar cusp ionosphere where low energy electron precipitations produce ionospheric irregularities.
Generation region of polar cusp hiss observed by ISIS satellites
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KJ00000048043
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概要
