HR: 10:35h
AN: SM31E-02    [PDF]
TI: Statistical properties of cold ion populations in the plasma sheet: GEOTAIL observations
AU: * Seki, K
EM: seki@stelab.nagoya-u.ac.jp
AF: Solar-Terrestrial Environment Laboratory, Nagoya University, 3-13 Honohara, Toyokawa, Aichi, 442-8507 Japan
AU: Hirahara, M
EM: hirahara@rikkyo.ac.jp
AF: Rikkyo University, Toshima, Tokyo, 171-8501 Japan
AU: Mukai, T
EM: mukai@stp.isas.ac.jp
AF: ISAS, Sagamihara, Kanagawa, 229-8510 Japan
AU: Saito, Y
EM: saito@stp.isas.ac.jp
AF: ISAS, Sagamihara, Kanagawa, 229-8510 Japan
AU: Thomsen, M F
EM: mthomsen@lanl.gov
AF: LANL, NIS1, Los Alamos, NM 87545 United States
AB: Recent GEOTAIL observations have revealed that there sometimes exists cold ion component that has density comparable to the "ordinary" hot plasma sheet component even in the central plasma sheet [Seki et al., {\it Nature}, 2003]. It is also reported that during extended intervals of northward IMF, plasma entry from the magnetosheath through LLBL seems to be enhanced and the ion distribution functions show the 2-composition structure in the dawn-side plasma sheet [e.g., Fujimoto et al., {\it ASR}, 2002]. These dense ions can be transported into the inner magnetosphere under certain solar wind conditions [Thomsen et al., {\it JGR}, 2003]. In this study, conditions for cold ion existence in the plasma sheet are investigated based on statistics of 4 years of GEOTAIL data in the central plasma sheet ($-$5 $<$ X$_{GSM}$ $<$ $-$35, $|$Y$_{GSM}|$ $<$ 15 R$_{E}$), aiming at getting clues to supply and transport mechanisms of these cold populations. \\ The results show that the observational probability of the cold ion population having density above 0.1 [1/cc] is about 0.25 and decreases with increasing tailward distances. In the near-Earth regions of X$_{GSM}$ $>$ $-$15 R$_{E}$, the probability goes up to 0.42. The observation also shows that there are two types of cold ion events in the plasma sheet: One is the detection of a dense sheath-like ion component primarily seen in the flank regions, and the other is observations of the colder component with a moderate density. The latter type of the cold population often has the velocity along the local magnetic field, which may suggest the direct supply of the ionospheric ions. The former type has properties similar to cold dense plasma sheet observations reported by previous studies, and primarily seen during/after the northward IMF periods. The cold dense ion observations in the GEOTAIL is often coincide or followed by the dense plasma observations by the Los Alamos Magnetospheric Plasma Analyzer (MPA) at the geosynchronous orbit.
DE: 2736 Magnetosphere/ionosphere interactions
DE: 2740 Magnetospheric configuration and dynamics
DE: 2744 Magnetotail
DE: 2764 Plasma sheet
DE: 2784 Solar wind/magnetosphere interactions
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting