Observations of thermospheric heating signatures associated with sub-kilometer scale auroral electrodynamics

Abstract

This thesis presents analysis of thermospheric neutral temperature-altitude profiles derived from ground-based observations during intervals of auroral emission. Neutral temperature-altitude profiles are obtained in the magnetic zenith at unprecedented spatial (<10 km) and temporal resolution (<5 s). Electrodynamic processes associated with the formation mechanisms of auroral arcs are inferred via enhancements in the neutral temperature. The observations agree with leading arc-formation theories and provide further evidence supporting the existing literature. New evidence for the existence of filamentary field-aligned current (FAC) sheets, embedded in auroral arcs and directly linked to the formation of auroral curls, is presented. This thesis also provides a detailed outline of the development of a novel observational technique for determining neutral temperature-altitude profiles during intervals of auroral emission. This technique combines spectral observations from the High Throughput Imaging Echelle Spectrograph (HiTIES) and images from Auroral Structure and Kinetics (ASK) with radar observations from the EISCAT Svalbard Radar and the Southampton Ionospheric Model. A spectral inversion technique is utilised. Trial temperature profiles are converted into a synthetic emission spectrum via an integration in altitude across modelledN2 volume emission rate profiles. A least squares residual fitting process is used to evaluate the goodness-of-fit of the synthetic spectra that correspond to each random trial altitude-temperature profile, by determining its ability to recreate the HiTIES observed spectrum. Analysis of the outcome of multiple random trial profiles is used to estimate a final true thermospheric temperature profile. Neutral temperature variations are associated with specific auroral dynamics by comparing the temperature profiles with concurrent imaging observations from the ASK instrument.

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ORCID for Daniel Whiter: orcid.org/0000-0001-7130-232X

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