Investigating the response of the electron temperature to field-aligned currents using SWARM observations

Abstract:

A statistic study of the electron temperature (Te) response to field-aligned current (FAC) derived with measurements from the Swarm satellite A are presented in this study. Considering the variability in the widths and latitudes of FACs, simply superposing FACs by each orbit significantly reduces the size and smoothes over the FAC features. Therefore, in order to better represent the FACs patterns, a potential FAC region was extracted from every orbit, and normalized by its meridional width and maximum FAC magnitude. FACs were smoothed within a 20-second window, so as to remove any small variability due to Alfven waves. A potential FAC region was identified as a real FAC region by a logistic regression model. The FAC, as well as the corresponding filtered Te, were superposed at a normalized FAC region for each magnetic local time. The filtered Te was obtained by subtracting an 80-second (~5 degree) average from a 20-second (<1 degree) average in order to extract the variation with a comparable scale as the FACs. It was found that Te tended to increase in the upward-FAC region, while it decreased in the downward-FAC region, which was caused by the combination effects of the thermal advection due to the drift of electrons, and the thermoelectric heating by FACs on electrons. The correlation between Te and FAC was MLT dependent, and was influenced by season and geomagnetic disturbances. A linear relationship between Te and FAC was shown in the dusk sector (from noon to midnight), where 1uA/m² of FAC increased Te by ~100K. The dawn sector (from midnight to noon) showed a weaker correlation between Te and FAC. The correlation between Te and the FAC was higher in winter than it was in summer, and was higher during low geomagnetic conditions (AE<120).