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Abstract To understand magnetosphere‐ionosphere conditions that result in thermal emission velocity enhancement (STEVE) and subauroral ion drifts (SAID) during the substorm recovery phase, we present substorm aurora, particle injection, and current systems during two STEVE events. Those events are compared to substorm events with similar strength but without STEVE. We found that the substorm surge and intense upward currents for the events with STEVE reach the dusk, while those for the non‐STEVE substorms are localized around midnight. The Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite observations show that location of particle injection and fast plasma sheet flows for the STEVE events also shifts duskward. Electron injection is stronger and ion injection is weaker for the STEVE events compared to the non‐STEVE events. SAID are measured by Super Dual Auroral Radar Network during the STEVE events, but the non‐STEVE events only showed latitudinally wide subauroral polarization streams without SAID. To interpret the observations, Rice Convection Model (RCM) simulations with injection at premidnight and midnight have been conducted. The simulations successfully explain the stronger electron injection, weaker ion injection, and formation of SAID for injection at premidnight, because injected electrons reach the premidnight inner magnetosphere and form a narrower separation between the ion and electron inner boundaries. We suggest that substorms and particle injections extending far duskward away from midnight offer a condition for creating STEVE and SAID due to stronger electron injection to premidnight. The THEMIS all‐sky imager network identified the east‐west length of the STEVE arc to be ~1900 km (~2.5 h magnetic local time) and the duration to be 1–1.5 h.
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High‐Latitude Ionospheric Electrodynamics During STEVE and Non‐STEVE Substorm Events
Abstract Previous studies have shown that Strong Thermal Emission Velocity Enhancement (STEVE) events occur at the end of a prolonged substorm expansion phase. However, the connection between STEVE occurrence and substorms and the global high‐latitude ionospheric electrodynamics associated with the development of STEVE and non‐STEVE substorms are not yet well understood. The focus of this paper is to identify electrodynamics features that are unique to STEVE events through a comprehensive analysis of ionospheric convection patterns estimated from SuperDARN plasma drift and ground‐based magnetometer data using the Assimilative Mapping of Geospace Observations (AMGeO) procedure. Results from AMGeO are further analyzed using principal component analysis and superposed epoch analysis for 32 STEVE and 32 non‐STEVE substorm events. The analysis shows that the magnitude of cross‐polar cap potential drop is generally greater for STEVE events. In contrast to non‐STEVE substorms, the majority of STEVE events investigated are accompanied by with a pronounced extension of the dawn‐cell into the pre‐midnight subauroral latitudes, reminiscent of the Harang reversal convection feature where the eastward electrojet overlaps with the westward electrojet, which tends to prolong over substorm expansion and recovery phases. This is consistent with the presence of an enhanced subauroral electric field confirmed by previous STEVE studies. The global and localized features of high‐latitude ionospheric convection associated with optical STEVE events characterized in this paper provide important insights into cross‐scale magnetosphere‐ionosphere coupling mechanisms that differentiate STEVE events from non‐STEVE substorm events.
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- PAR ID:
- 10406996
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Space Physics
- Volume:
- 128
- Issue:
- 4
- ISSN:
- 2169-9380
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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