Precipitation pattern of electrons and protons at the onset ofauroral substorms

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Using magnetically conjugate data from DMSP and ground all-sky TV instruments, temporal change in latitudinal structure of electron and proton precipitation is examined for the poleward expansion onsets of aurora during two successive DMSP passes on January 17,1986. Electron precipitation just before an onset consisted of cold BPS precipitation with an inverted-V at its equatorward boundary, but no detectable CPS at lower latitude. Poleward expansion started from an auroral are which corresponded to an inverted-V at the BPS equatorward boundary. During an expansion, when multiple inveretd-V were distributed in BPS, intense CPS electron precipitation was observed at lower latitude. This CPS precipitation was associated with the equatorward expansion of aurora during the recovery of the previous auroral activation. It is suggested that the CPS is not merely a stable precipitation, but rather consists of electrons which are accelerated and injected associated with the substorm. As for the ion precipitation, its dependence on the auroral expansion was significantly different with respect to the latitude. At latitudes higher than the BPS equatorward boundary, energetic ion precipitation intensified drastically associated with the auroral expansion, and the region of strongest ion precipitation was collocated at that of strongest electron precipitation. At lower latitude, energetic ions are rather permanent components which expanded in latitudinal width but did not intensify significantly associated with the expansion. The high latitude ion would consist mainly of ions which are accelerated at the substorm onset region together with electrons, whereas the acceleration of the low latitude ions would be maintained with larger temporal scale than a substorm expansion.
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Precipitation pattern of electrons and protons at the onset ofauroral substorms

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