HR: 0800h
AN: SH31A-1170    [Abstracts]
TI: Polytropic Index at the Bow Shock Inferred From Density and Field Compression
AU: * Saxena, R
EM: rsaxena@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California 7 Gauss Way, Berkeley, CA 94720
AU: Bale, S D
EM: bale@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California 7 Gauss Way, Berkeley, CA 94720
AU: Mozer, F
EM: fmozer@ssl.berkeley.edu
AF: Space Sciences Laboratory, University of California 7 Gauss Way, Berkeley, CA 94720
AU: Horbury, T
EM: t.horbury@ic.ac.uk
AF: Space and Atmospheric Physics Group, The Blackett Laboratory Imperial College, London, SW7 2BW United Kingdom
AU: Decreau, P
EM: pdecreau@cnrs-orleans.fr
AF: CNRS, 3A, Avenue de la recherche scientifique, Orleans, 45071 France
AU: Behlke, R
EM: Rico.Behlke@rymdfysik.uu.se
AF: Swedish Institute of Space Physics, Department of Astronomy and Space Physics, Box 515 SE-751 20, Uppsala, SE-751 20 Sweden
AB: Data from the Cluster spacecraft obtained during crossings of the earth's bow shock is studied to attempt to obtain a value for the polytropic index $\gamma$ of the plasma in that region. Specifically, the compression ratio (average downstream density / average upstream density) and magnetic field ratio (average downstream magnetic field / average upstream magnetic field) are found for numerous instances of the shock and then used to determine the polytropic index, through the use of the MHD Rankine-Hugoniot equations. We find that in both cases, the polytropic index is consistent with a value falling in the range $5/3 < \gamma < 2$ over a wide range of Mach numbers.
DE: 7500 SOLAR PHYSICS, ASTROPHYSICS, AND ASTRONOMY
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2004 AGU Fall Meeting