Azimuthal structure of auroral arcs associated with various disturbed magnetic conditions

Details Azimuthal structure of auroral arcs associated with various disturbed magnetic conditions Azimuthal structure of auroral arcs associated with various disturbed magnetic conditions

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsa13a1072c&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SA13A-1072

Physics

2407 Auroral Ionosphere (2704), 2704 Auroral Phenomena (2407), 2736 Magnetosphere/Ionosphere Interactions (2431), 2790 Substorms

Scientific paper

We investigated the mode numbers of azimuthally spaced auroral forms in various disturbed magnetic conditions using limb-view images of ISUAL (The Imager of Sprites and Upper Atmospheric Lightnings ) on board FORMOSAT-2 satellite. We choose 557.7nm and 630.0nm as our filter wavelengths. The 557.7nm green transition line of OI(1S→1D) is mainly produced by energetic electrons with energy ≥ 1keV and the 630.0nm red-line emission of OI(1D→3P) (triplet) is mainly produced by electrons with energy ~O(100eV). The auroral arcs have bright spots with approximately equal-spaced separation, in the azimuthal direction, which allows estimate of the azimuthal mode number. The azimuthal mode number of quiet time arcs is higher (m~720) and becomes lower at moderately disturbed times (m~360). For the breakup arcs at onset, the azimuthal mode number is lower with m~220. After onset, the observed breakup arcs move explosively in poleward direction from 64° to 70° latitude in about 2 minutes. The observed azimuthal structure of the substorm breakup arc at onset is similar to the events observed by THEMIS All Sky Imagers at Fort Yukon (m~250) and is consistent with the kinetic theory of ballooning modes [Cheng, Zaharia and Gorelenkov, 2004], which showed the most unstable mode at about -8RE with azimuthal mode number m~300.

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