HR: 1330h
AN: SM32A-1137    [PDF]
TI: MHD aspects of fire-hose type instabilities
AU: * Wang, B
EM: bjwang@jupiter.ss.ncu.edu.tw
AF: B.-J. Wang, Institute of Space Science, National Central University, Chung-Li, 320 Taiwan
AU: Hau, L
EM: lnhau@jupiter.ss.ncu.edu.tw
AF: B.-J. Wang, Institute of Space Science, National Central University, Chung-Li, 320 Taiwan
AB: In a homogeneous anisotropic plasma the magnetohydrodynamic (MHD) Alfv\'{e}n wave may become unstable for p$_{\parallel} >$ p$_{\perp}$ + B$^{2}$/$\mu_{0}$. Recently a new type of fire-hose instability is found by Hellinger and Matsumoto [2000] that has maximum growth rate occurring for oblique propagation and may grow faster than the Alfv\'{e}n mode. This new mode is compressional and may be more efficient at destroying pressure anisotropy than the standard fire hose. In this study we examines the fire-hose type (p$_{\parallel} >$ p$_{\perp}$) instabilities based on the linear and nonlinear double-polytropic MHD theory. It is shown that there exist two types of MHD fire-hose instabilities associated with the intermediate and slow modes, respectively, and with suitable choice of polytropic exponents the linear instability criteria become the same as those based on the Vlasov theory in the hydromagnetic limit. Moreover, the properties of the nonlinear MHD fire-hose instabilities are found to have great similarities with those obtained from the kinetic theory and hybrid simulation. In particular, the classical fire-hose instability evolves toward the linear fire-hose stability threshold while the nonlinear marginal stability associated with the new fire hose is well below the condition of $\beta_{\parallel} - \beta_{\perp}$ = 2 but complies with less stringent linear stability threshold for MHD slow-mode wave.
DE: 2752 MHD waves and instabilities
DE: 7839 Nonlinear phenomena
DE: 7843 Numerical simulation studies
SC: SPA - Magnetospheric Physics [SM]
MN: 2003 Fall Meeting