Global‐scale ionospheric flow and aurora precursors of auroral substorms: Coordinated SuperDARN and IMAGE/WIC observations

Abstract

We use global-scale polar cap flow vector measurements from the Super Dual Auroral Radar Network (SuperDARN) with the concurrent auroral observations from the Wideband Imaging Camera on board Imager for Magnetopause-to-Aurora Global Exploration (IMAGE/WIC) to study the polar cap flow and auroral precursors during a substorm onset on 26 December 2000. We show, for the first time, close connection between the dayside and nightside polar cap flow enhancements (with the enhanced dayside flow preceding the nightside one by several minutes) and the ensuing poleward boundary intensification (PBI)/streamer, and the later onset, forming a complete preonset sequence for a substorm onset. Our results supplement our previous study by providing further evidence that the dayside polar cap flow disturbance may be the key to initiate the whole process of a certain type of substorm by triggering reconnection somewhere in the tail via applied field (or flow) perturbations on the nightside plasma sheet boundary layer. Our results also indicate that a preexisting double oval structure is likely a favorable precondition for a certain type of substorm to be triggered by polar cap flow disturbance and the associated PBIs/streamers. On the other hand, not all our global-scale preonset auroral sequences support the recent revised onset scenario proposed by Nishimura et al. (2010a) using the all-sky imagers of the Time History of Events and Macroscale Interactions during Substorms mission. This suggests that the preceding PBI/streamer is not a sufficient condition to trigger a substorm. It may not even be a necessary condition considering the existence of various types of substorm onsets.

Physical Processes of Meso-Scale, Dynamic Auroral Forms

“…The modelling work by Ohtani et al (2018), Ohtani and Yoshikawa (2016) seeks to address some of these issues by considering the interaction of plasma vortices with conductivity gradients in the ionosphere, it ignores any reconnection processes occurring in the magnetosphere. Observational studies have also shown the occurrence of dayside and nightside flow enhancements in concert with the onset of PBIs (Shi and Zesta 2014). However, the causal link between these events is yet to be conclusively demonstrated.…”

Severe and localized GNSS scintillation at the poleward edge of the nightside auroral oval during intense substorm aurora

“…In the nightside ionosphere, patches convect into the nightside auroral oval under the influence of tail reconnection. Patches convecting into the auroral oval have been shown to be associated with substorm onset [Lyons et al, 2011;Nishimura et al, 2013Nishimura et al, , 2014Shi and Zesta, 2014]. In the auroral oval, they are termed auroral blobs [Tsunoda, 1988;Crowley et al, 2000;Lorentzen et al, 2004;Pryse et al, 2006].…”

Localized polar cap flow enhancement tracing using airglow patches: Statistical properties, IMF dependence, and contribution to polar cap convection

“…However, recent studies based on radar measurements have revealed mesoscale convection features in the polar cap that are of great importance for triggering nightside auroral intensifications [de la Beaujardière et al, 1994;Nishimura et al, 2010;Lyons et al, 2011;Shi et al, 2012;Pitkänen et al, 2013;Shi and Zesta, 2014]. The observed flow features are of~0.2 h magnetic local time (MLT) wide and have larger velocity than slow, uniform surrounding flows, appearing as channels of velocity enhancements.…”