The electrodynamics of fine scale aurora and associated joule heating

Abstract

In this thesis we explore the effects of intense and dynamic electric fields, related to auroral phenomenon, on Joule heating. We present the results of three studies in which we utilised the Auroral Structure and Kinetics (ASK) cameras to obtain high resolution electric field measurements during the auroral events. In the first study we estimated the electric field from both sides of the auroral arc at subsecond resolution. From these electric fields we were able to estimate the extreme Joule heating rates on each side of the arc (up to two orders of magnitude larger than typical values). In the second study we analysed two events using a more precise method for estimating Joule heating. We obtained even more extreme values than in the first study, which we attribute to larger electric fields and more precise estimates of the Pedersen conductivity. Additionally, we have used an independent technique to estimate the increase in neutral temperature, from which we infer the Joule heating. Our results show an order of magnitude larger values than those obtained by the first method. We suggest that a possible reason for the discrepancy is that there is a source of energy in addition to the Joule heating (most likely the heating from field aligned current). In the final study we present the results of a statistical study, in which we analysed 23 auroral events to understand better the electrodynamic drivers behind the large variability of the electric fields at the fine scales. Our results show a significant correlation between the precipitating electron flux magnitude and the variability of the precipitating electron flux, as well as a significant correlation between the variability of the precipitating electron flux and the variability of the tangential component of the electric field. We explain the former by the dynamics of the auroral acceleration region in which more intense acceleration would be associated with more dynamic processes, which would lead to variability in the precipitating flux. For the second significant correlation we propose that both electric field variability and electron flux variability have the same source, which is the variability of the dynamic non-uniform current sheet. In summary, in this thesis we present the potential source of the electric field variability as well as the effects of such a variability in the form of Joule heating. Events presented in this thesis are on fine scales (tens kilometers) and of short duration (4-6 seconds), and individually they would not contribute much to the total Joule heating budget, but the main idea is that the auroral region consists of many small-scale and short-lived auroral features each adding to the overall Joule heating budget.

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Identifiers

ORCID for Robert Fear: orcid.org/0000-0003-0589-7147

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

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