In this letter, we present the results of a conjunction between the SAMPEX satellite and a THEMIS all-sky imager in Gillam, Canada—showing a high correlation between relativistic, >1 MeV, electron microbursts and a type of pulsating aurora called patchy aurora. The correlation was 0.8, and is not serendipitous. While the relationship between pulsating aurora and 10-100s keV microbursts has been previously predicted, here we show a strong association between keV and MeV electron dynamics—possibly spanning two orders of magnitude. Importantly, this result shows that the dynamics of relativistic radiation belt electrons are at times intimately tied to keV electron precipitation, and can not be studied in isolation.

\justify The location of the polar cap boundary is typically determined using low-orbit satellite measurements in which the boundary is identified by its unique signature of a sharp decrease in energy and particle flux poleward of the auroral oval. In principle, this decrease in precipitating particles should appear as a concomitant sharp change in auroral luminosity. Based on a few events, \cite{Blanchard_1995} suggested that a dramatic gradient in redline aurora may also be an indicator of the polar cap boundary. In recent years, advances in capabilities and the deployment of ground-based all-sky imagers have ushered in a new era of auroral measurements. Auroral imaging has moved well beyond the capabilities of the instrumentation in the previous study in terms of both spatial and temporal resolution. We now have access to decades of optical data from arrays spanning a huge spatial range, enabling a fresh examination of the relationship between redline aurora, particle precipitation, and the polar cap open closed boundary. In this study, we use data from the DMSP satellites in conjunction with the University of Calgary’s REGO (630.0nm) data to assess the viability of automated detection of the 2-dimensional polar cap boundary. Our results exhibit good agreement between the optical and particle polar cap boundary and suggest that a luminosity in redline emission could serve as a reasonable proxy for the location of the the electron poleward boundary during, while providing both high temporal and spatial resolution maps of the open-closed boundary.

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 accompany 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.