University of Minnesota
School of Physics & Astronomy
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Cynthia Cattell

Observations of a high latitude stable electron auroral emission near the cusp at 16 LT during a large substorm
C. Cattell, John Dombeck, Adam Preiwisch, Scott Thaller , Pamela Vo , Lynn Wilson III, John Wygant , Stephen Mende , Harald Frey , Raluca Ilie , Gang Lu, Journal of Geophysical Research

Abstract

A stable region of auroral emission was observed on August 17, 2001 in the IMAGE WIC/FUV camera at ~16 MLT, poleward of the main auroral oval, for approximately one hour, from before the onset of a large substorm (AE~1400 nT) through the recovery phase. Strong field-aligned currents and Poynting flux were observed by the Polar satellite (at 1.8 Re in the southern hemisphere) as it transited field-lines mapping to the auroral spot in the northern hemisphere. At the time of the strong Poynting flux, the Polar ion signature shows the energy dispersion expected for the cusp. This event occurred during an interval when the IMF was large, and primarily duskward and southward. Although the observed emission had some characteristics similar to the electron emission ‘HiLDA’ (High-latitude dayside aurora) and to the ‘proton spot’ observed at the foot of reconnecting field lines, there are distinct differences. The data presented herein are consistent with the hypothesis that the long lasting electron auroral spot maps to the magnetopause region where reconnection was occurring. Under the assumption of conjugacy between northern and southern hemisphere on these field lines, the Polar data suggest that the electrons on these field lines were accelerated by Alfven waves and/or a quasi-static electric field, primarily at altitudes below a few Re since the in-situ Poynting flux (mapped to 100 km) is comparable to the energy flux of the emission while the mapped in-situ electron energy flux is much smaller. The observations are consistent with the interpretation that this event provides the first example of an emission due to electrons accelerated at low altitudes at the foot point of a region of quasi-steady dayside reconnection. The Cluster data in the magnetotail indicate that the Poynting flux from the region of magnetotail reconnection during this substorm interval is large enough to account for the observed nightside aurora during this event.