Auroral Energy Deposition and Conductance During the 2013 St. Patrick's Day Storm: Meso-Scale Contributions

Abstract

Geomagnetic storms transfer massive amounts of energy from the sun to geospace. Some of that energy is dissipated in the ionosphere as energetic particles precipitate and transfer their energy to the atmosphere, creating the aurora. We used the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mosaic of all-sky-imagers across Canada and Alaska to measure the amount of energy flux deposited into the ionosphere via auroral precipitation during the 2013 March 17 storm. We determined the time-dependent percent of the total energy flux that is contributed by meso-scale (<500 km wide) auroral features, discovering they contribute up to 80% during the sudden storm commencement (SSC) and >∼40% throughout the main phase, indicating meso-scale dynamics are important aspects of a geomagnetic storm. We found that average conductance was higher north of 65° until SYM-H reached −40 nT. We also found that the median conductance was higher in the post-midnight sector during the SSC, though localized conductance peaks (sometimes >75 mho) were much higher in the pre-midnight sector throughout. We related the post-midnight/pre-dawn conductance to other recent findings regarding meso-scale dynamics in the literature. We found sharp conductance peaks and gradients in both time and space related to meso-scale aurora. Data processing included a new moonlight removal algorithm and cross-instrument calibration with a meridian scanning photometer and a standard photometer. We compared ASI results to Poker Flat Incoherent Scatter Radar (PFISR) observations, finding energy flux, mean energy, and Hall conductance were highly correlated, moderately correlated, and highly correlated, respectively.