HR: 1340h
AN: SH53A-1252    [Abstracts]
TI: Mean of Proton Temperature Anisotropy in the Solar Wind is Solely Controlled by the Threshold of its Excited Instabilities and its Implication: Two Years of Geotail Observations
AU: * Lin, T
EM: ltf@bu.edu
AF: Boston University, Astronomy Department 725 Commonwealth Ave, Boston, MA 02135 United States
AU: Spence, H
EM: spence@bu.edu
AF: Boston University, Astronomy Department 725 Commonwealth Ave, Boston, MA 02135 United States
AU: Gary, S P
EM: pgary@lanl.gov
AF: Los Alamos National Laboratory, Mail Stop D466, Group ISR-1 Los Alamos National Laboratory, Los Alamos, NM 87545 United States
AU: Mukai, T
EM: mukai@stp.isas.jaxa.jp
AF: Institute of Space and Astronautical Science, Sagamihara, Kanagewa, Japan, Department of Space Plasma Physics, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1, Yoshinodai,Sagamihara, Kanagewa, Sagamihara, Kan 229-8510 Japan
AU: Kepko, L
EM: lkepko@bu.edu
AF: Boston University, Astronomy Department 725 Commonwealth Ave, Boston, MA 02135 United States
AB: Temperature tensor structure of the space plasma attracts attention because as an important parameter for most of MHD simulations its state as fully Maxwellian is often oversimplified. Linear theory predicts that for a bi-Maxwellian plasma, when the difference between the two components, the anisotropy, is large enough, instabilities will be excited. It has been revealed by simulations that these instabilities, stronger with larger anisotropy, impose upper bounds on the anisotropy. These upper bounds have been confirmed by the recent observations. In contrast, the threshold with marginal instabilities, which may determine the average state of the anisotropy, has not yet been paid attention to. We compare the theoretical threshold with the anisotropy mean measured in the solar wind by the Geotail, and find that they closely match each other. This match may imply that various processes driving the anisotropy away from its marginal stable state doesn't change its average to stay on that state, i.e., mean is determined by the plasma inner force. Further supports come from the results when background field is in the GSM y direction and the study for space regions inside the bow shock, making this match a universal one.
DE: 2164 Solar wind plasma
DE: 7829 Kinetic waves and instabilities
DE: 7839 Nonlinear phenomena (4400, 6944)
DE: 7844 Parametric processes
DE: 7867 Wave/particle interactions (2483, 6984)
SC: SPA-Solar and Heliospheric Physics [SH]
MN: Fall Meeting 2005