The Substorm Gordian Knot: Onset Patterns and Frequencies

Abstract:

For decades, scientists have struggled to understand what causes the aurora, and have developed two different theories to explain the phenomena. The magnetospheric and ground-based data necessary to test the two competing theories have only recently become available with the launch of NASA's THEMIS mission in 2007 and the Canadian Space Agency's (CSA) deployment of an all-sky imaging network. We present research testing the "Auroral Streamer" hypothesis given by Nishimura, Lyons, et al. in their various papers from 2010 to present. We compiled a list of all their published events (numbering 455, and covering a span from 2007 to 2011) and reviewed ground-based white- and red-light image files, THEMIS satellite bulk plasma velocity and magnetic field strength measurements, ground-based magnetometer observations, and 1-minute Auroral Electrojet (AL) index data. We visually categorized the events by auroral phenomenology, separating events with auroral streamers from those without, and analyzed the characteristics of the events with superposed epoch analyses. Although Nishimura, Lyons et al. argued that every event in their onset list constituted an "Auroral Streamer" onset, our results show that most events in the list are not poleward boundary intensifications (PBIs). In contrast to these previous studies, the results suggest that the "auroral streamer" model is not widely applicable. This is the first time these events have been analyzed with such detail, and call into question fundamental aspects of this model.