On Quantifying the Distinctions Between the Cusp and the CLEFT/LLBL
The distinction between the cusp (the region of fairly direct entry of magnetosheath plasma to low altitudes) and the cleft (the ionospheric signature of the magnetospheric boundary layer) is placed on a firm quantitative foundation. Case examples illustrating the difference are shown; when both regions are seen on a given pass the cusp lies poleward of the cleft, generally with a sharp boundary between the regions. The statistical differences are developed, for example the ion number flux in the cusp is approximately 4 times higher than in the cleft. The different responses of the cusp and the cleft to the interplanetary magnetic field Bz are documented; the cusp (cleft) ion fluxes increase (stay nearly unchanged) and the statistical local time width increases (decreases) when Bz changes from northward to southward. A brief review of the various previous attempts at distinctions between the cusp and the cleft is given, as is a brief summary of all known differences between the two regions as observed at low altitude.
KeywordsBoundary Layer Average Energy Interplanetary Magnetic Field Electron Precipitation Electron Average Energy
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