%ANishimura, Y. [Department of Electrical and Computer Engineering and Center for Space Physics Boston University Boston MA USA]%AYang, J. [Department of Earth and Space Sciences Southern University of Science and Technology Shenzhen China]%AWeygand, J. [Department of Earth, Planetary and Space Sciences University of California Los Angeles CA USA]%AWang, W. [Department of Earth and Space Sciences Southern University of Science and Technology Shenzhen China, School of Atmospheric Sciences Sun Yat‐sen University Zhuhai China]%AKosar, B. [Department of Physics Catholic University of America Washington DC USA]%ADonovan, E. [Department of Physics and Astronomy University of Calgary Calgary Alberta Canada]%AAngelopoulos, V. [Department of Earth, Planetary and Space Sciences University of California Los Angeles CA USA]%APaxton, L. [The Johns Hopkins University Applied Physics Laboratory Laurel MD USA]%ANishitani, N. [Institute for Space Earth Environmental Research Nagoya University Nagoya Japan]%BJournal Name: Journal of Geophysical Research: Space Physics; Journal Volume: 125; Journal Issue: 8; Related Information: CHORUS Timestamp: 2023-09-05 00:19:18 %D2020%IDOI PREFIX: 10.1029 %JJournal Name: Journal of Geophysical Research: Space Physics; Journal Volume: 125; Journal Issue: 8; Related Information: CHORUS Timestamp: 2023-09-05 00:19:18 %K %MOSTI ID: 10374573 %PMedium: X %TMagnetospheric Conditions for STEVE and SAID: Particle Injection, Substorm Surge, and Field‐Aligned Currents %XAbstract

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.

%0Journal Article