Day-night coupling by a localized flow channel visualized by polar cap patch propagation
Tuesday, 16 December 2014: 11:53 AM
Although plasma convection in the polar cap is often thought of large-scale two-cell convection, recent radar observations have shown that dynamic meso-scale fast flows of the order of 100 km size are embedded within the large-scale convection. Those flow channels are colocated with polar cap airglow patches in many cases, and thus optical measurements can be used to track the origin of such flows, evolution in the polar cap, and their influence on nightside auroral activity. We present unique coordinated observations of the dayside auroral oval, polar cap, and nightside auroral oval by three All-Sky Imagers (ASIs), two SuperDARN radars, and DMSP. This dataset revealed that a dayside Poleward-Moving Auroral Form (PMAF) evolved into a polar cap airglow patch that propagated across the polar cap, and then nightside poleward boundary intensifications (PBIs). Radar observations detected fast anti-sunward flows associated with the PMAF, and the DMSP satellite, whose conjunction occurred within a few minutes after the PMAF initiation, measured enhanced Low-Latitude Boundary Layer (LLBL) precipitation and enhanced plasma density with a strong anti-sunward flow burst. The polar cap patch was spatially and temporally coincident with a localized anti-sunward flow channel. The propagation across the polar cap and the subsequent PBIs suggest that the flow channel originated from dayside reconnection and then reached the nightside open-closed boundary, triggering localized nightside reconnection and flow bursts within the plasma sheet. In addition, we have also statistically investigated the property of dayside and nightside polar cap flow channels using imagers, radars and low-altitude satellites. The flow channels are typically found to have a ~300 km width, propagate a few hundred km/s faster than background flows, and to occur during a By-dominant IMF with a weak southward component.