HR: 17:26h
AN: SH44A-06    [Abstracts]
TI: Evidence for Cyclotron Resonant Damping of Waves by Multiple Ion Species at 1 AU
AU: * Kasper, J C
EM: jck@mit.edu
AF: MIT Center for Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AU: Lazarus, A J
EM: ajl@mit.edu
AF: MIT Center for Space Research, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AB: We explore the role of helium in regulating the absorption of Alfven waves near ion cyclotron frequencies. This is accomplished through a systematic study of the relationships between hydrogen and helium temperatures and temperature anisotropies as a function of plasma parameters such as differential flow speeds, plasma beta, and Coulomb collision rate. It will be demonstrated that this analysis allows us to distinguish between the roles played by adiabatic expansion, Coulmb relaxation, plasma micro-instabilities, and wave-damping in regulating solar wind ion temperatures. Our main observational result is that helium is observed to be preferentially heated relative to hydrogen in directions perpendicular to the magnetic field during intervals with low Coulomb collision rates and small diffrential flow speeds. The ratio of perpendicular temperatures, $T_{\perp \alpha}/T_{\perp p}$ grows with decreasing differential flow speed and can exceed a factor of 5. The fact that $T_{\perp \alpha}/T_{\perp p}$ can become so large and is a strong function of the differential flow speed between the hydogren and helium is interpreted in the light of recent theoretical predictions of the damping rates of cyclotron waves in multi-species plasmas.
DE: 7827 Kinetic and MHD theory
DE: 7839 Nonlinear phenomena
DE: 7867 Wave/particle interactions
DE: 2159 Plasma waves and turbulence
DE: 2164 Solar wind plasma
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2004 AGU Fall Meeting