GEM: Resolving the Unique Characteristics of Substorms that Precede Strong Thermal Emission Velocity Enhancement (STEVE) Events

A Strong Thermal Emission Velocity Enhancement (STEVE) is a latitudinally narrow and longitudinally elongated optical emission that appears in the night sky before midnight, equatorward of the auroral oval. Importantly, STEVE is not an aurora in the classic sense - as far as we can tell STEVE's emissions are not generated by charged particles streaming down magnetic field lines and colliding with the neutral atmosphere to produce optical emissions. In fact, the exact mechanism for STEVE's optical emissions have yet to be identified. However, STEVEs are correlated with events called substorms which involve energy releases in the Earth's nightside magnetic field, which often manifest as dynamic auroral displays. This research focuses on the observation that most substorms do not result in a STEVE event (approximately only 3% do), indicating that substorms that occur with STEVE events are unique. To better understand STEVE associated substorms and the conditions under which STEVEs occur, we will use data from all-sky imagers, spacecraft, radars, magnetometers, and citizen scientists – who were the ones who initially discovered STEVE. Using these datasets, the evolution from substorm to STEVE (or no STEVE) will be monitored. Additionally, we will investigate and specify the geomagnetic conditions unique to STEVE events. This work will strengthen our understanding of the upper atmosphere and the near-Earth geospace environment, allowing us to better mitigate space weather effects. Furthermore, given the team and collaborations this project will support, this research will promote education and diversity, and strengthen collaborations within the solar-terrestrial science community.Strong Thermal Emission Velocity Enhancement (STEVE) events are bright mauve optical emissions that periodically occur between dusk and midnight in subauroral regions after a substorm onset. It has been established that STEVE is correlated with substorms, and more specifically the recovery phase of a substorm. Importantly, not all substorms are associated with a STEVE event, but all STEVE events are associated with a substorm. The motivation of this work is to determine how the substorms associated with STEVE events are unique compared to other substorms. This will be done by addressing three science questions: 1) What is the temporal response of the magnetosphere-ionosphere system to substorm onset in associated STEVE events? 2) What are the conditions of the magnetosphere-ionosphere system prior to a STEVE event; can preconditioning be identified? and 3) How are the auroral and sub-auroral mesoscale flow patterns associated with STEVE events different from those associated with substorm events in general? We will use all-sky imagers, spacecraft, radars, magnetometers, and citizen science data to address the aforementioned questions. A novel and compelling component of this research effort will be the incorporation of radar data, in particular Incoherent Scatter Radar (ISR) data. This will allow us to complement existing measurements provided by imagers and spacecraft and also enhance our ability to identify undiscovered STEVE events. The ionospheric signature of a STEVE event in ISR data has recently been identified and will be used to find and characterize additional STEVE events in the work.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.