Magnetothermal instability in weakly magnetized plasmas with anisotropic resistivity and viscosity

The linear buoyancy instability in magnetized plasmas is investigated in the presence of anisotropic resistivity and viscosity. The magnetic field is assumed to be horizontal and the background heat flux is not taken into account. That is, the magnetic field lines are initially isothermal. The heat is assumed to be primarily transported along the magnetic force lines. The general dispersion relationship of the thermal convective instability in the presence of anisotropic resistive and viscous dissipative effects is derived and discussed in detail in weak magnetic field limit. Our results show that the perturbation is damped when the temperature decreases in the direction of gravity due to the resistive or viscous effect while this situation results in pure oscillation modes in the ideal MHD case. The resistive and viscous effects are shown to reduce the growth rate of the magnetothermal instability when the temperature increases in the direction of gravity.