HR: 10:55h
AN: SH32B-03    [Abstracts]
TI: Measured constraints on the suprathermal electron temperature
anisotropy in the solar wind
AU: * Bale, S D
EM: bale@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California, Berkeley, CA 94720, United States
AU: Xu, K
AF: Space Sciences Laboratory, University of California, Berkeley, CA 94720, United States
AU: Salem, C
AF: Space Sciences Laboratory, University of California, Berkeley, CA 94720, United States
AU: Kasper, J C
AF: Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, United States
AU: Quataert, E
AF: Astronomy Department, University of California, Berkeley, CA 94720, United States
AU: Howes, G G
AF: Astronomy Department, University of California, Berkeley, CA 94720, United States
AB: We report on a statistical analysis of the measured electron temperature anisotropy in the solar wind using the 3DP instrument on the Wind spacecraft. Approximately one million independent measurements of the electron velocity distribution were integrated in two energy ranges corresponding to the solar wind 'core' and 'halo' components. The parallel and perpendicular (to the local magnetic field) temperatures were computed from the pressure integral and compared with the parallel electron beta parameter β_{e, \parallel} and the electron 'collisional age' A_e,e. The low-energy core distribution remains relatively isotropic, due to its larger density and correspondingly large Coulomb collision frequency. However, the temperature anisotropy of the halo distribution (E ≥ ~80 eV) shows a striking signature which suggests that it is bounded by a whistler-mode instability from above (T_\perp/T_\parallel > 1) and the electron firehose instability from below (T_\perp/T_\parallel < 1). These results confirm that solar wind electron expansion and compression are limited fundamentally by these instabilities.
DE: 2149 MHD waves and turbulence (2752, 6050, 7836)
DE: 2471 Plasma waves and instabilities (2772)
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2007 Fall Meeting