Filling and emptying of the plasma sheet: Remote observations with 1–70 keV energetic neutral atoms

Abstract

This paper shows the first energetic neutral atom (ENA) observations of the extended plasma sheet, taken with the Medium Energy Neutral Atom (MENA) imager on the IMAGE spacecraft. We show that ENA emissions can be routinely observed back to several tens of RE deep in the magnetotail when IMAGE is in an appropriate orbital position. Enhanced emissions (high plasma sheet densities) are associated with high solar wind densities and with super dense plasma sheet observations at geosynchronous orbit. We examine two magnetospheric storm intervals where plasma sheet loading begins prior to the storms and continues under all IMF BZ orientations, reaching its maximum during the peaks of the storms. For several days following these storms ENA emissions are weak, indicating that the plasma sheet is depleted after the storms. This study indicates that routine ENA observations of the plasma sheet content could become an important part of space weather monitoring.