High-Latitude Ionospheric Electrodynamics Characterizing Energy and Momentum Deposition during STEVE Events Reported by Citizen Scientists

The mysterious subauroral phenomenon STEVE (Strong Thermal Emission Velocity Enhancement) was recently discovered in 2016 by citizen observers, yet its physical mechanism is not completely understood. STEVE events are characterized by the presence of a thin, dynamic aurora-like structure with purple and green emission features that propagate to the west, typically located in the pre-midnight mid-latitude sector [MacDonald et al., 2018].

The focus of this paper is to investigate the magnetosphere-ionosphere coupling processes during STEVE events by characterizing global and local high-latitude electrodynamics features using an AMGeO (Assimilative Mapping of Geospace Observation) procedure [e.g., Richmond and Kamide, 1989; Matsuo et al., 2005; Cousins et al., 2013; Matsuo, 2019]. AMGeO is designed to derive maps of high-latitude electrodynamic variables by optimally combining geospace observations with climatological models of ionospheric convection and aurora. Among 33 STEVE events identified using THEMIS and REGO all sky imagers [Gallardo-Lacourt, 2018], six STEVE events are selected when coincident citizen scientists' aurora sighting exists in the Aurorasaurus database [ Kosar et al., 2018 ] over 2015-2016. For this purpose, SuperDARN plasma drifts and ground-level magnetic field observations are ingested into AMGeO to estimate the electrostatic potential distribution and Joule heating rate over thirty minute time intervals for the entirety of STEVE events. Precipitating auroral particle flux and magnetic perturbation as measured by Defense Meteorological Satellite Program (DMSP) F16, F17, and F18 satellites are also used. Preliminary analysis of the convection patterns shows the development of enhanced westward plasma drifts (>1 km/s) in the pre-midnight mid-latitude sector, which is characteristic of subauroral ion drift, accompanied by the westward extension of a region of sharp convection reversal, likely associated with a substorm.