Mode conversion and damping of MHD waves in stratified viscous solar atmosphere

Abstract

We study the mode conversion and damping of MHD waves in a gravitationally stratified low-$\beta $ to high-$\beta $ isothermal atmosphere of the Sun permeated by a uniform vertical magnetic field. We solve the MHD equations by MacCormack method to examine the effect of viscosity on amplitudes of physical quantities such as velocity, mass density, gas pressure and magnetic field before and after the $\beta \approx 1$ layer. It is found that mode conversion occurs at the point $z \approx -1.8$ in $\beta \approx 1$ layer and viscosity does not influence the mode conversion phenomenon. In the presence of viscosity, the amplitudes of vertical and horizontal velocity components, horizontal and vertical magnetic field components, gas pressure and mass density decrease and decay of amplitude is stronger for higher values of viscosity. In the low $\beta $ plasma, damping length decreases with the increase in viscosity but remains almost unchanged in the high $\beta $ plasma. When the driving frequency increases, conversion from slow to fast mode decreases.