The orientation of auroral arcs in general and in the late growth phase (Invited)

Details The orientation of auroral arcs in general and in the late growth phase (Invited) The orientation of auroral arcs in general and in the late growth phase (Invited)

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm24b..04d&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SM24B-04

Physics

[2704] Magnetospheric Physics / Auroral Phenomena, [2740] Magnetospheric Physics / Magnetospheric Configuration And Dynamics, [2744] Magnetospheric Physics / Magnetotail, [2790] Magnetospheric Physics / Substorms

Scientific paper

While it is a defining feature of auroral arcs that they are more or less east-west aligned in geomagnetic coordinates, there is significant variation in the angle between arcs and constants of geomagnetic latitude. In a statistical survey of arcs observed during a range of geomagnetic activity, I found that the distribution of this orientation angle has a standard deviation of roughly 10 degrees, and that the average orientation as a function of MLT follows the shape of the oval. In a study of late growth phase arcs, I found that the standard deviation of the orientations is significantly smaller (less than 5 degrees), and that the average orientation angle is within 1 degree of being exactly east-west in geomagnetic coordinates. These results are important for several reasons. First, the fact that arcs are aligned with the oval indicates that the arcs most likely correspond to the ionospheric signature of a gradient (of a parameter or parameters that we do not know) in the magnetotail. Second, (I will show that) the significant decrease in the standard deviation of the orientation of arcs in the late growth phase is a consequence of extreme stretching of the magnetic field topology at the inner edge of the magnetotail thin current sheet. Given the proximity of these arcs to the bright proton aurora, the growth-phase evolution of arc orientation provides fresh insight into the late growth phase magnetic field topology as well as the generation mechanism of growth phase arcs.

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