MMS Magnetotail Observations of the Complete Cycle of Substorm Growth, Dipolarization, Expansion, and Recovery Phases
Abstract
The Magnetospheric Multiscale (MMS) four-spacecraft constellation has provided numerous opportunities to examine plasma, energetic particle, and magnetic field dipolarization behavior in the near-Earth tail region (r~20 RE) during magnetospheric substorms. In this presentation, we study an isolated substorm sequence on 17 July 2017. WIND upstream data showed strong southward IMF Bz turning at ~1330 UT. Clear substorm growth phase signatures were detected in the AE index and at geostationary orbit spacecraft (GOES, LANL) beginning at ~1340 UT. All four MMS spacecraft at X = -21.8 RE detected strong tailward plasma flow at 1438:20 UT, consistent with near-Earth X-line (NEXL) formation just Earthward of MMS. We thus infer that substorm onset was initiated by reconnection at X ~ -21 RE at about 1438 UT. Energetic electron and proton injections along with field dipolarization were detected slightly later at GOES-15 and Los Alamos spacecraft (LANL 01-A and 02-A) at ~1441 UT. We suggest that the primary large-scale plasmoid was rapidly ejected downtail at 1438 UT from the plasma sheet at substorm onset and this left the thin, residual plasma sheet tailward of r ~20 RE. This allowed the four closely spaced MMS spacecraft to all pass readily back and forth across the thin current sheet (N→S at 1441:10 UT and S→N at 1444:30 UT). After ~1445 UT, MMS sensors concurrently saw Earthward plasma flow implying that the NEXL had then moved somewhat tailward of MMS. From 1447:30 until 1454:00 UT, clear small-scale magnetic islands (X-O pairs) were seen flowing rapidly Earthward in the residual plasma sheet away from the X-line that was downtail of MMS. At ~1458 UT, MMS detected very strong (V > 500 km/s) Earthward plasma jetting just as the westward electrojet (AE) reached its greatest strength. We interpret this as the signal of rapid tailward retreat of the X-line and we also ascribe the "poleward leap" of the auroral oval to this recovery time. MMS data indicate fast expansion of the plasma sheet thickness at this same time with strong energetic electron (E>50 keV) flux increase including fascinating unidirectional particle streaming [see companion paper by Leonard et al.]. Taken together, all these data show a remarkably complete sequence of all expected substorm dynamical features of substorm growth, expansion and recovery phases.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMSM0410015B
- Keywords:
-
- 2427 Ionosphere/atmosphere interactions;
- IONOSPHERE;
- 2736 Magnetosphere/ionosphere interactions;
- MAGNETOSPHERIC PHYSICS;
- 2740 Magnetospheric configuration and dynamics;
- MAGNETOSPHERIC PHYSICS;
- 2788 Magnetic storms and substorms;
- MAGNETOSPHERIC PHYSICS