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.
Plain Language Summary Geomagnetic storms transfer massive amounts of energy from the sun to geospace—some of which is converted into the multi‐colored aurora. Knowing how much energy enters Earth's upper atmosphere helps scientists better understand how Earth reacts to space weather events. The aurora's colors tell us how much energy is being deposited into Earth's atmosphere via energetic particles, which rain down from space and create light as they strike the atmosphere. Less energetic particles create red aurora, more energetic particles create green and blue aurora. We use cameras to measure the aurora's colors and determine the amount of energy entering the system related to smaller, often brighter and more dynamic aurora, in contrast to the more widely studied large‐scale aurora. We discovered <500 km wide aurora contribute >40% of the energy entering the system over time throughout the main phase of the storm—sometimes up to 80%! This shows how important the smaller aurora are. The aurora makes the atmosphere more conductive, allowing it to connect more easily to outer space. Sharp changes in conductance allow electrical currents to flow. Our study found when and where conductance peaked during the storm and found sharp changes related to the <500 km aurora.
Key Points Precipitation trends are investigated: meso‐scales are important throughout the storm SSC and main phase albeit related to SML not SYM‐H Median conductance is largest post‐midnight during SSC but larger localized conductance peaks exist in pre‐midnight sector throughout event We developed an all‐sky‐imager moonlight removal algorithm, allowing for better conductance, energy flux, and mean energy determination