Substorm Onset by New Plasma Intrusion 4: SuperDARN-THEMIS ASI-POES Observations

Details Substorm Onset by New Plasma Intrusion 4: SuperDARN-THEMIS ASI-POES Observations Substorm Onset by New Plasma Intrusion 4: SuperDARN-THEMIS ASI-POES Observations

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm41b1711z&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SM41B-1711

Physics

[2431] Ionosphere / Ionosphere/Magnetosphere Interactions, [2455] Ionosphere / Particle Precipitation, [2463] Ionosphere / Plasma Convection, [2790] Magnetospheric Physics / Substorms

Scientific paper

In a companion study, we found that substorm onsets are frequently preceded by equatorward extension of a north-south auroral structure from the polar cap boundary to the east-west pre-existing growth phase arc. It was suggested that this north-south auroral structure is associated with new and low entropy plasma, which enters the plasma sheet from the separatrix, moves earthward, and then turns around near the Harang reversal region where it leads to plasma instability responsible for onset. In this study, we superpose 2D convection flows obtained by the northern hemisphere SuperDARN radars with auroral images taken by the THEMIS ASI and study their mutual evolution. We find that equatorward flows near the eastern edge of the auroral Harang reversal enhance several minutes before onset and its front moves equatorward. These equatorward flows are then diverted azimuthally and a substorm onset occurs near the Harang reversal region. This enhanced equatorward flow is likely to be the ionospheric counterpart of the low entropy plasma channel in the equatorial plane. Further studies are needed to confirm the generality of this phenomenon. In addition, energetic particle precipitation measured by the NOAA POES spacecraft is studied in two cases when the spacecraft passed near the onset region at the onset time. In both cases, onsets were located just poleward of and quite close to the peak of the energetic proton precipitation and near the equatorward boundary of the energetic electron precipitations. This observation is consistent with previous results obtained from optical observations. Combined with the convection flow and auroral image observations, this gives a morphological mapping of the onset location and related low entropy channel between the magnetosphere and ionosphere.

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