Abstract
AbstractWe present results that indicate the existence of two distinct neutral heating processes associated with a discrete auroral arc over Svalbard. Within the order of seconds, the thermospheric temperature profile displays a significant response to the arc on spatial scales smaller than 10 km. It is suggested that both heating signatures are associated with the electrodynamic system responsible for the formation of the arc. Pedersen currents produce a temperature increase of approximately 100 K, observed at altitudes between 80 and 160 kilometres, directly adjacent to the arc structure and on its poleward edge only. In contrast, field‐aligned currents produce a variable temperature increase, of approximately 50 K, which is observed within the arc itself and constrained to a narrow altitude range between 90 and 110 km. By utilizing a range of observations and new analysis methods we are able to measure the atmospheric neutral temperature profile, over auroral altitudes, at unprecedented temporal and spatial scales. The High Throughput Imaging Echelle Spectrograph records high‐resolution emission spectra of the aurora, which are then fitted with synthetic N2 spectra, generated with modeled N2 volume emission rate profiles and a library of trial temperature profiles. The N2 volume emission rate profiles are retrieved from the Southampton ionospheric model using precipitating particle energies and fluxes obtained from Auroral Structure and Kinetics and the EISCAT Svalbard Radar. The application of this technique allows us to produce a time series of neutral temperature profiles and measure the localized heating of the neutral atmosphere resulting from the electrodynamics of the arc.
Highlights
It has long been understood that the auroral displays present at high latitudes are a consequence of complex magnetosphere-ionosphere interactions that are governed by a system of extensive magnetic field-aligned currents (FAC; Iijima & Potemra, 1976, 1978)
We present a novel technique for the measurement of E region neutral temperature altitude profiles at unprecedented temporal and spatial resolutions, allowing for further investigation of the thermospheric response to the arc-associated electrodynamic system, neutral temperature changes
We have provided direct observational evidence of the large-scale electrodynamical system responsible for the formation of an auroral arc and of small-scale FAC sheets embedded within the arc, associated with its dynamical structure
Summary
It has long been understood that the auroral displays present at high latitudes are a consequence of complex magnetosphere-ionosphere interactions that are governed by a system of extensive magnetic field-aligned currents (FAC; Iijima & Potemra, 1976, 1978). The general picture is of two large (oval scale) rings of FAC sheets, separated into “Region 1” currents at high latitudes (∼66–76◦) and “Region 2” currents at lower latitudes (∼62–72◦), with some crossover depending on the magnetic local time They display opposite polarities in the dusk and dawn sectors of the polar cap and are closed through the ionosphere via meridional Pedersen currents. A second ionospheric current system is found in the form of significant Hall currents flowing both sunward, across the center of the polar cap, and antisunward, along the oval in both the morning and evening sectors The latter of these Hall currents are known as the westward and eastward auroral electrojets, respectively (Boström, 1964). Simulations have shown that the formation of these small-scale currents is driven by Alfvén waves propagating and reflecting in the ionosphere (Zhu et al, 2001)
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