Physics
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm42a..01d&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #SM42A-01
Physics
[2431] Ionosphere / Ionosphere/Magnetosphere Interactions, [2704] Magnetospheric Physics / Auroral Phenomena, [2760] Magnetospheric Physics / Plasma Convection, [2764] Magnetospheric Physics / Plasma Sheet
Scientific paper
Auroral arcs are an important component of the auroral distribution. Given their near-ubiquity, their obvious importance to MI coupling, and their association with dynamic processes such as the substorm and convection, resolving fundamental questions about arcs is of central importance in space physics. I will present recent observations that I believe are important to our ultimate understanding of arcs, focussing on a large statistical survey of arcs observed in the THEMIS-ASI data set and context provided by contemporaneous proton auroral measurements NORSTAR Meridian Scanning Photometers. I focus on two features of auroral arcs, namely their latitudinal location relative to the bright proton auroral distribution, and their orientation relative to local magnetic east-west. I find that arcs do not occur equatorward of the bright proton aurora. At any magnetic local time and latitude the average orientation of auroral arcs follows the average orientation of the auroral oval. The standard deviation of orientations about the mean is in general larger for higher magnetic latitudes and smaller during quiet times and the late growth phase. I will argue that these results shed light on the magnetospheric origin of auroral arcs. They are undeniably a feature associated with stretched magnetic field lines, and their east-west elongation is a consequence of their one-one association with (sharp) gradients of an as-yet-unidentified magnetotail property (or properties). The variation in the orientation appears to be a consequence of the effects of MI coupling on mapping, which become less pronounced during quiet times and the late growth phase and more pronounced in general at higher geomagnetic latitudes. These results need to be accounted for as we develop ultimately successful theories of auroral arcs.
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