Effect of heat flux on Alfven ballooning modes in isotropic Hall-MHD plasmas

摘要

abstract_textpThe magnetosphere undergoes a transition from a dipole-like to taillike structure in the antisunward direction. In this region, Alfven ballooning instability has been considered as a leading candidate to be responsible for the onset and expansion phase of observed impulsive substorms. We apply the generalized Ohm's law in isotropic Hall-MHD equations and study the effect of heat flux on the ballooning modes under substorm circumstances. The set of partial differential equations is obtained for a general ballooning dispersion relation from which all classical Alfven waves and fundamental ballooning modes are recovered, e.g., the decoupled shear Alfven and magnetosonic modes, the classical ballooning instability in incompressible plasmas. In the absence of the heat flux, the ballooning mode is featured by the coupling of the two modes by the superposition of the independent Hall effect and the independent plasma inhomogeneity effect. By contrast, heat flux exerts its influence on the ballooning mode by updating the coefficients of the terms in the dispersion relation. The results expose that the growth rate (gamma(BM)) has two branches. If k(p) is beta free, one branch shifts versus beta, while the other branch is damped substantially by the heat flux, leading to a more stable ballooning mode; if k(c) is beta free, one branch shifts little versus beta, but the other one has higher gamma(BM) driven by the heat flux, leading to a more unstable ballooning mode./p/abstract_text