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- Title
Dynamics of Auroral Precipitation Boundaries Associated With STEVE and SAID.
- Authors
Nishimura, Y.; Donovan, E. F.; Angelopoulos, V.; Nishitani, N.
- Abstract
Using Defense Meteorological Satellite Program (DMSP) and National Oceanic and Atmospheric Administration (NOAA) satellite observations and ground‐based observations by the THEMIS all‐sky imagers (ASIs) and SuperDARN radars, we determine how the equatorward boundary locations of ring current ions and plasma sheet electrons at pre‐midnight relate to occurrence of strong thermal emission velocity enhancement (STEVE) and intense subauroral ion drifts (SAID) during substorms. We found that the STEVE events are associated with a sharper gradient of electron precipitating flux, lower precipitating ion flux, and a narrower (<1°) latitudinal gap between the equatorward boundaries of trapped ring current ions and precipitating plasma sheet electrons and narrower region‐2 field‐aligned currents (FACs) than for the non‐STEVE events. The narrow gap of the particle boundaries contains intense SAID, higher upflow velocity, lower trough density, and slightly higher electron temperature than those for the non‐STEVE events. The non‐STEVE substorms have much wider gaps between the trapped ions and precipitating electrons, and subauroral polarization streams (SAPS) do not show intense SAID. These results indicate that subauroral flows and downward FACs for the STEVE events can only flow within the latitudinally narrow subauroral low‐conductance region between the ion and electron boundaries, resulting in intense SAID and heating. During the non‐STEVE events, the SAPS flows can flow in the latitudinally wide region without forming intense SAID. Plain Language Summary: We show that STEVE (strong thermal emission velocity enhancement) is closely related to unusual structures of energetic ion and electron structures. Usually, energetic ions extend a few degrees equatorward of energetic electrons, and a moderate plasma jet stream is located between them. Interestingly, during STEVE, the gap between ions and electrons narrows down below 1°, and the electron flux falls off much more sharply. The plasma jet stream is confined between the ion‐electron boundaries, and the velocity increases an order of magnitude higher. We suggest that the narrow particle boundaries are created by unusual particle injection to the near‐Earth region and form the narrow flow channel that contributes to waves and plasma heating. Key Points: STEVE events are associated with a sharper electron flux gradient, weaker ion precipitation, and a narrower gap of ions and electronsThe narrow gap contains intense SAID, upflow, localized downward R2 FACs, trough, and elevated electron temperatureSubauroral flows and downward FACs can only flow within the narrow gap, resulting in intense SAID and heating
- Subjects
METEOROLOGICAL satellites; UNITED States. National Oceanic &; Atmospheric Administration; ELECTRON precipitation; HEATING; ELECTRON temperature; PLASMA jets
- Publication
Journal of Geophysical Research. Space Physics, 2020, Vol 125, Issue 8, p1
- ISSN
2169-9380
- Publication type
Article
- DOI
10.1029/2020JA028067