HR: 1340h
AN: SA13A-1072 [Abstracts]
TI: Azimuthal structure of auroral arcs associated with various disturbed magnetic conditions
AU: * Chang, T
EM: jocelyn@pssc.ncku.edu.tw
AF: Department of Physics, National Cheng-Kung University, No.1 University Road, Tainan City,
70101, Taiwan
AU: * Chang, T
EM: jocelyn@pssc.ncku.edu.tw
AF: Plasma and Space Science Center, No.1 University Road, Tainan City, 70101, Taiwan
AU: Cheng, C
EM: frankcheng@pssc.ncku.edu.tw
AF: Department of Physics, National Cheng-Kung University, No.1 University Road, Tainan City,
70101, Taiwan
AU: Cheng, C
EM: frankcheng@pssc.ncku.edu.tw
AF: Plasma and Space Science Center, No.1 University Road, Tainan City, 70101, Taiwan
AU: Chiang, C
EM: johnson@phys.ncku.edu.tw
AF: Department of Physics, National Cheng-Kung University, No.1 University Road, Tainan City,
70101, Taiwan
AU: Tam, S W
EM: sunwytam@pssc.ncku.edu.tw
AF: Plasma and Space Science Center, No.1 University Road, Tainan City, 70101, Taiwan
AU: Chen, A B
EM: alfred@phys.ncku.edu.tw
AF: Department of Physics, National Cheng-Kung University, No.1 University Road, Tainan City,
70101, Taiwan
AU: Chen, A B
EM: alfred@phys.ncku.edu.tw
AF: Plasma and Space Science Center, No.1 University Road, Tainan City, 70101, Taiwan
AU: Hsu, R
EM: rrhsu@phys.ncku.edu.tw
AF: Department of Physics, National Cheng-Kung University, No.1 University Road, Tainan City,
70101, Taiwan
AU: Su, H
EM: htsu@phys.ncku.edu.tw
AF: Department of Physics, National Cheng-Kung University, No.1 University Road, Tainan City,
70101, Taiwan
AB:
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.
DE: 2407 Auroral ionosphere (2704)
DE: 2704 Auroral phenomena (2407)
DE: 2736 Magnetosphere/ionosphere interactions (2431)
DE: 2790 Substorms
SC: SPA-Aeronomy [SA]
MN: 2007 Fall Meeting