HR: 1300h
AN: SM52A-0565    [PDF]
TI: Contribution of ion flow-out and charge exchange processes to the decay of the storm-time ring current
AU: * Keika, K
EM: keika@kugi.kyoto-u.ac.jp
AF: Department of Geophysics, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwakechou, Sakyou-ku, Kyoto, 6068502 Japan
AU: Nose', M
EM: nose@kugi.kyoto-u.ac.jp
AF: Data Analysis Center for Geomagnetism and Space Magnetism, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwakechou, Sakyou-ku, Kyoto, 6068502 Japan
AU: Takahashi, K
EM: Kazue.Takahashi@jhuapl.edu
AF: The Applied Physics Laboratory Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, MD 20723-6099 United States
AU: Ohtani, S -
EM: ohtani@larmor.jhuapl.edu
AF: The Applied Physics Laboratory Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, MD 20723-6099 United States
AU: C:son Brandt, P
EM: brandpc1@jhuapl.edu
AF: The Applied Physics Laboratory Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, MD 20723-6099 United States
AU: Mitchell, D G
EM: don.mitchell@jhuapl.edu
AF: The Applied Physics Laboratory Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, MD 20723-6099 United States
AU: Christon, S P
EM: SPChriston@aol.com
AF: Focused Analysis and Research, Columbia, Columbia, MD 21044 United States
AU: McEntire, R W
EM: Dick.McEntire@jhuapl.edu
AF: The Applied Physics Laboratory Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, MD 20723-6099 United States
AB: The decay of the ring current during the storm recovery phase can be attributed mainly to loss of energetic ions. Its mechanisms, however, are still open problems. Although ion flow-out and charge exchange processes are the most probable causes of such loss, it is yet to be identified how much these processes contribute to the loss. In this study we evaluate the contribution of each process to the decay of the ring current, using energetic ion data acquired by the EPIC instrument onboard Geotail and energetic neutral atom (ENA) data acquired by the HENA imager onboard IMAGE. The HENA imager observes ENAs ($\ge$~10~keV) that are produced when energetic ring current ions experience charge exchange collisions with cold neutral atoms and molecules. We can calculate the rate of energy loss due to the charge exchange process. The Geotail spacecraft is frequently located in the magnetosheath and upstream of the Earth's bow shock, where the Geotail/EPIC instrument observes energetic ions flowing out from the magnetosphere. Because the instrument provides charge state information of 9~$-$~210~keV/e ions, it can distinguish the leaking ions from solar wind ions accelerated at the Earth's bow shock. From this data we can calculate the energy density of leaking ions. In order to evaluate total energy loss via the ion flow-out process, we investigate if it is possible from HENA images to determine the leakage area. The area can also be estimated from statistical studies on energetic ions outside the magnetosphere. We will present two interesting storms (September 23, 2001 and April 22, 2001). During the recovery phase of these storms, Geotail/EPIC observed energetic protons and singly-charged oxygen ions outside the magnetosphere on the dusk side, and IMAGE was located in a vantage point in the northern hemisphere. We will estimate contributions of the two processes to the decay of the storm-time ring current.
DE: 2114 Energetic particles, heliospheric (7514)
DE: 2731 Magnetosphere--outer
DE: 2778 Ring current
DE: 2788 Storms and substorms
DE: 7837 Neutral particles
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting