HR: 0830h
AN: SH21B-0135    [PDF]
TI: Generation of the Foreshock Field-Aligned Beam Observed by Geotail
AU: * Oka, M
EM: oka@space.eps.s.u-tokyo.ac.jp
AF: University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AU: Terasawa, T
EM: terasawa@eps.s.u-tokyo.ac.jp
AF: University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033 Japan
AU: Saito, Y
EM: saito@stp.isas.ac.jp
AF: Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, 229-8510 Japan
AU: Mukai, T
EM: mukai@stp.isas.ac.jp
AF: Institute of Space and Astronautical Science, 3-1-1 Yoshinodai, Sagamihara, 229-8510 Japan
AB: From the intensive measurements achieved during the 1980s, a general consensus has been developed for the generation mechanism of the field-aligned beams (FABs) in the foreshock region of the earth's bow shock. For the shock with a shock angle between 30 and 60 degrees, a fraction ($\sim$2%) of the incoming solar wind ions ($\sim$1keV) are considered to be semi-trapped at or near the shock front and gets accelerated to about 10keV through multiple reflection process. However, there has been no observational evidence of the multiple reflections, although many theoretical attempts by test-particle and hybrid simulation have supported the idea of the multiple reflection. In this paper, we present shock crossing events obtained by Geotail on October 19, 1995. This day is known for an encounter of a large magnetic cloud with the earth, preceded by an interplanetary shock passage on October 18. The shape of the bow shock was such that Geotail could skim along the surface of the shock and experienced about 30 shock crossings during the cloud passage. By focusing on a particular shock event ($M_{A}\sim$3.2, $\theta_{Bn}\sim$57$^\circ$), we will report an observational evidence of the multiple reflection with a help of test-particle simulation. Moreover, a shock angle dependence of the FAB flux will be shown from the statistical analysis utilizing the particle data obtained during the events. Some implications from hybrid simulations will also be presented in order to interpret the observed features.
DE: 2154 Planetary bow shocks
DE: 7851 Shock waves
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting