HR: 10:20h
AN: SM12B-01    [Abstracts]
TI: Comparative study of post-midnight ENA flux enhancements during the August 2000 and April 2002 storms
AU: * Ebihara, Y
EM: ebihara@nipr.ac.jp
AF: National Institute of Polar Research, 1-9-10 Kaga, Itabashi, Tokyo, 173-8515 Japan
AU: Fok, M
EM: mei-ching.h.fok@nasa.gov
AF: NASA GSFC, Code 692, Greenbelt, MD 20771 United States
AU: Wolf, R A
EM: rawolf@rice.edu
AF: Rice Univ, Dept Physics and Astronomy , POB 1892 MS 108, Houston, TX 77251 United States
AU: Hairston, M R
EM: hairston@utdallas.edu
AF: Univ Texas Dallas, POB 830688 F022 , Richardso, TX 75083-0688 United States
AU: Brandt C:son, P
EM: pontus.brandt@jhuapl.edu
AF: Johns Hopkins Univ Applied Physics Lab, 11100 Johns Hopkins Rd , Laurel, MD 20723-6099 United States
AU: Mitchell, D G
EM: Donald.G.Mitchell@jhuapl.edu
AF: Johns Hopkins Univ Applied Physics Lab, 11100 Johns Hopkins Rd , Laurel, MD 20723-6099 United States
AU: Immel, T J
EM: immel@ssl.berkeley.edu
AF: Univ California Space Science Lab , Centennial Dr @Grizzly Peak, Berkeley, CA 94720-7450 United States
AU: Moore, T E
EM: tmoore@lepvax.gsfc.nasa.gov
AF: NASA GSFC, Code 692, Greenbelt, MD 20771 United States
AB: The high energy neutral atom (HENA) imager on-board the IMAGE satellite captured remarkable images showing that the peak of the dominant ENA flux sometimes comes from the post-midnight region during magnetic storms(Brandt et al., GRL, 29(20), 1962, doi: 10.1029/2002GL015160, 2002). The peak of the 39-50 keV ENA flux occurred around 0500 MLT during the 12 August 2000 storm, while it peaked near midnight during the April 20, 2002 storm. This means that the post-midnight enhancement of the ENA flux does not always appear during all the magnetic storms. Fok et al. (Space Sci. Rev., 109, 77, 2003) performed the self-consistent ring current simulation that couples with the ionosphere, and found that the post-midnight enhancement appears when the ionospheric convection pattern is highly deformed by charge deposited by the strong Region 2 field-aligned current. Their calculations showed a robust reversal of the convection velocity equatorward of the auroral oval in the post-midnight sector due to the shielding electric field. Indeed, data from DMSP F13 shows that the ionospheric ion flow reversal occurred at -43 MLAT (0442 MLT) and the westward drift velocity reached around 600 m/s when IMAGE captured the post-midnight enhancement on August 12, 2000. The reversal occurred at -50 MLAT (0430 MLT) and the westward drift velocity reached only around 250 m/s when the midnight enhancement was observed on April 20, 2002. This may reflect the fact that the shielding electric field driven on August 12, 2000 is much stronger than on April 20, 2002 and the convection pattern is highly skewed during the August 2000 storm. We performed a self-consistent ring current simulation with realistic polar cap potential distribution from the Weimer 2001 model and a realistic auroral conductivity model derived from the IMAGE/FUV optical data. The result fairly accounts for the tendency of the DMSP observations and the HENA observations, likely meaning that the shielding electric field plays an important role in the formation of the post-midnight enhancement of the ENA flux.
DE: 2463 Plasma convection
DE: 2730 Magnetosphere--inner
DE: 2753 Numerical modeling
DE: 2778 Ring current
DE: 2788 Storms and substorms
SC: SPA-Magnetospheric Physics [SM]
MN: 2004 AGU Fall Meeting