Abstract
Recent attention has been given to mesoscale phenomena across geospace (∼10 s km to 500 km in the ionosphere or ∼0.5 RE to several RE in the magnetosphere), as their contributions to the system global response are important yet remain uncharacterized mostly due to limitations in data resolution and coverage as well as in computational power. As data and models improve, it becomes increasingly valuable to advance understanding of the role of mesoscale phenomena contributions—specifically, in magnetosphere-ionosphere coupling. This paper describes a new method that utilizes the 2D array of Time History of Events and Macroscale Interactions during Substorms (THEMIS) white-light all-sky-imagers (ASI), in conjunction with meridian scanning photometers, to estimate the auroral scale sizes of intense precipitating energy fluxes and the associated Hall conductances. As an example of the technique, we investigated the role of precipitated energy flux and average energy on mesoscales as contrasted to large-scales for two back-to-back substorms, finding that mesoscale aurora contributes up to ∼80% (∼60%) of the total energy flux immediately after onset during the early expansion phase of the first (second) substorm, and continues to contribute ∼30–55% throughout the remainder of the substorm. The average energy estimated from the ASI mosaic field of view also peaked during the initial expansion phase. Using the measured energy flux and tables produced from the Boltzmann Three Constituent (B3C) auroral transport code (Strickland et al., 1976; 1993), we also estimated the 2D Hall conductance and compared it to Poker Flat Incoherent Scatter Radar conductance values, finding good agreement for both discrete and diffuse aurora.
Highlights
A fundamental question at the heart of the dynamics and coupling of Earth’s magnetosphere-ionosphere system is, “How is energy deposited into the ionosphere from the magnetosphere?” That itself has a complex answer comprised of multiple parts such as electromagnetic energy, particle precipitation, and waves
We describe the technique that utilizes the whitelight ASI array that was not detailed in Nishimura et al [20], including important upgrades made through the present work, supplemented by meridian scanning photometers (MSPs) and auroral transport code calculations, to estimate precipitating energy flux, average energy, and Hall conductance, as well as what percent of the energy flux is contributed by mesoscale auroral forms during two back-toback substorms
This paper presented a new methodology to utilize the mosaic of THEMIS all-sky-imagers to study auroral precipitation in 2D over time, estimating parameters such as energy flux, average energy, and Hall conductance
Summary
A fundamental question at the heart of the dynamics and coupling of Earth’s magnetosphere-ionosphere system is, “How is energy deposited into the ionosphere from the magnetosphere?” That itself has a complex answer comprised of multiple parts such as electromagnetic energy, particle precipitation, and waves. PrecipNet better captures the dynamic changes of the auroral flux than OVATION Prime, improving capabilities to reconstruct mesoscale phenomena and making great progress towards nowcasting and forecasting auroral response to solar wind driving Though these and other works make great strides towards resolving the role of mesoscale auroral precipitation, the field still lacks a rigorous understanding and characterization of the contribution of the dynamic and energetic mesoscale auroral forms that are embedded within the large-scale system. Since 2006, NASA’s THEMIS mission has provided an array of white-light ASIs across Canada and Alaska that monitor the majority of the nightside auroral oval at a 3 s cadence and up to 1 km resolution, providing a global view at temporal and spatial resolutions required to study the aurora on mesoscales [19] This allows us to expand upon previous demonstrations of ASI capabilities to estimate precipitated energy flux and average energy in 2D, but on a continental scale. We describe the technique that utilizes the whitelight ASI array that was not detailed in Nishimura et al [20], including important upgrades made through the present work, supplemented by MSPs and auroral transport code calculations, to estimate precipitating energy flux, average energy, and Hall conductance, as well as what percent of the energy flux is contributed by mesoscale auroral forms during two back-toback substorms
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