10/28/2016 - Properties of meso-scale flows in the nightside auroral and subauroral ionosphere


3:30 PM - 5:00 PM
Geology 6704

Presented By:
Bea Gallardo-Lacourt - UCLA


Properties of meso-scale flows in the nightside auroral and subauroral ionosphere

In addition to the traditional large-scale convection, nightside plasma sheet transport involves a significant amount of meso-scale fast flows that carry a large amount of magnetic flux. Measuring flows and aurora in the ionosphere allows us to evaluate the instantaneous two-dimensional evolution of these flow bursts. Auroral manifestations of such fast flows include auroral streamers, substorm onset, and enhancements within sub-auroral polarization streams (SAPS and SAID). At the substorm onset, the formation of auroral beads have been studied in detailed using auroral imagers; however, there has been almost no information about their flow pattern, which is fundamental to understand substorm onset instability. In this talk we first determine the flow pattern associated with substorm auroral onset beads, which are considered as the auroral manifestation of the substorm-onset instability occurring in the near-Earth plasma sheet. Our results show that auroral beads are associated with fast and periodic flow structures. We demonstrate the presence of a clockwise flow shear around each auroral bead, consistent with converging electric fields associated with upward field-aligned-currents in the shear center. In the second part of this talk, we analyze SAPS, which are strong westward flows occurring equatorward of the electron auroral oval. It has been reported that SAPS present large variabilities that are not correlated with any of the global indices. We demonstrate that the SAPS have large meso-scale flow enhancements, and that these enhancements are associated with auroral streamers. This implies that these flow enhancements can be understood as a coupling of meso-scale fast flows at auroral and subauroral latitudes. Finally, we present a comparison between SAPS and SAID event. The formation of these two phenomena is usually explained in terms of voltage or current generators, which is called the SAID/SAPS paradigm. A full understanding of the SAPS and SAID development has not yet been achieved, therefore an analysis comparing the conditions under which these phenomena occur is necessary. A preliminary survey interestingly suggests that broad SAPS events show the location of the electron equatorward boundary poleward than the proton boundary; while for narrow (~<1-2┬░mlat) SAID type of events this boundary location is reversed. Our case study suggests that a difference in the location of the injection region could be responsible for the reversal of the boundaries.

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