The magnetotail implications of optical observations of the brightening substorm aurora

Details The magnetotail implications of optical observations of the brightening substorm aurora The magnetotail implications of optical observations of the brightening substorm aurora

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm23b1709d&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SM23B-1709

Physics

2704 Auroral Phenomena (2407), 2730 Magnetosphere: Inner, 2740 Magnetospheric Configuration And Dynamics, 2764 Plasma Sheet, 2790 Substorms

Scientific paper

Ground-based optical and topside in situ observations have shown conclusively that many substorm auroral onsets occur immediately poleward of the proton aurora brightness peak. This has long been interpreted as placing a rather stringent constraint on the location of whatever magnetospheric process corresponds to the brightening auroral arc, namely that the relevant field lines thread the region of transition between dipole- and tail-like magnetic field topologies. However, this constraint, by itself, presents us with a number of critical questions. For example, we do not know how abrupt the transition between dipole- and tail-like topologies is, nor do we know the location of that transition in the magnetosphere on either an event by event or even a general basis. Not knowing the radial extent of the transition region limits our ability to explore the nature of the onset instability. Not knowing the actual location of the transition limits our ability to optimally utilize the ionospheric observations in conjunction with contemporaneous satellite observations. In this paper we take a step back from event studies and explore broader implications of the location of the onset arc relative to the peak in proton auroral brightness. More specifically, we use pitch-angle resolved FAST ESA ion observations from more than 20000 transits of the auroral zone to explore the latitudinal separation between the peak precipitating ion energy flux (which corresponds to the peak in proton auroral brightness) and the inner edge of the electron and ion plasma sheets. We use these results, in conjunction with magnetic mapping and published observations of the equatorial location of the inner edge of the ion and electron plasma sheets, to explore the range of locations in the magnetotail to which the onset arc is most likely to map, as well as how the relative distance between the transition region and the inner edge of the plasma sheet varies through the substorm cycle.

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