HR: 15:10h
AN: SH53B-07    [Abstracts]
TI: GEOTAIL Observations of the Earth's Bow Shock: Whistler Critical Mach Number and the Diffusive Shock Acceleration of Electrons
AU: * Oka, M
EM: moka@kwasan.kyoto-u.ac.jp
AF: Kwasan Observatory, Ohmine-cho, Kita-Kasan, Yamashina-ku, 607-8471, Kyoto, 6078471 Japan
AU: * Oka, M
EM: moka@kwasan.kyoto-u.ac.jp
AF: University of Tokyo, 7-3-1 Bunkyo-ku, Hongo, Tokyo, 1130033 Japan
AU: * Oka, M
EM: moka@kwasan.kyoto-u.ac.jp
AF: Institute of Space and Astronomical Science, JAXA, 3-1-1 Yoshinodai, Sagamihara, 229-8510 Japan
AU: Terasawa, T
SH53B-07 AF: University of Tokyo, 7-3-1 Bunkyo-ku, Hongo, Tokyo, 1130033 Japan
AU: Seki, Y
SH53B-07 AF: Institute of Space and Astronomical Science, JAXA, 3-1-1 Yoshinodai, Sagamihara, 229-8510 Japan
AU: Kasaba, Y
SH53B-07 AF: Institute of Space and Astronomical Science, JAXA, 3-1-1 Yoshinodai, Sagamihara, 229-8510 Japan
AU: Kojima, H
SH53B-07 AF: Research Institute of Sustainable Humanosphere, Gokasho, Uji-shi, Kyoto, 611-0011 Japan
AU: Matsui, H
SH53B-07 AF: University of New Hampshire, 10 West Edge Drive, Durham, NH 03824 United States
AU: Fujimoto, M
SH53B-07 AF: Institute of Tokyo Technology, 2-12-1 Ohokayama, Meguro-ku, Tokyo, 152-8550 Japan
AU: Shinohara, I
SH53B-07 AF: Institute of Space and Astronomical Science, JAXA, 3-1-1 Yoshinodai, Sagamihara, 229-8510 Japan
AU: Matsumoto, H
SH53B-07 AF: Research Institute of Sustainable Humanosphere, Gokasho, Uji-shi, Kyoto, 611-0011 Japan
AU: Saito, Y
SH53B-07 AF: Institute of Space and Astronomical Science, JAXA, 3-1-1 Yoshinodai, Sagamihara, 229-8510 Japan
AU: Mukai, T
SH53B-07 AF: Institute of Space and Astronomical Science, JAXA, 3-1-1 Yoshinodai, Sagamihara, 229-8510 Japan
AB: It has theoretically been expected that whistler waves are emitted upstream of shocks whenever Mach number falls below a critical Mach number. By performing statistical analysis of the upstream waves, we have observationally confirmed the `whistler critical Mach number' at the Earth's bow shock using the GEOTAIL spacecraft. We have further found that the critical Mach number regulates electron acceleration. The spectral index Γ of electron energy spectrum f(E)∝ E^-Γ varied greatly between 3.5 and 5.0 in the sub-critical regime while Γ were concentrated between 3.0 and 3.5 in the super-critical regime. The result suggests different acceleration mechanism for below and above the critical Mach number. In order to understand acceleration mechanisms, we performed detailed studies of two distinct events: One is sub-critical (obtained on 11 February 1995) and the other is super-critical (obtained on 1 July 1996) to the whistler critical Mach number. For the sub-critical shock, we found gradual spatial profile of non-thermal electron flux well associated with the upstream waves, and the event was interpreted by means of the Diffusive Shock Acceleration. For the super-critical shock, we found non-thermal electron flux enhancement at the shock ramp region associated with electrostatic waves. This result will be compared with conventional acceleration models.
DE: 7815 Electrostatic structures
DE: 7845 Particle acceleration
DE: 7851 Shock waves (4455)
DE: 7867 Wave/particle interactions (2483, 6984)
SC: SPA-Solar and Heliospheric Physics [SH]
MN: Fall Meeting 2005