MHD waves in magnetically twisted solar atmospheric flux tubes

The propagation of surface and body linear MHD modes in a twisted magnetic flux tube embedded in a magnetically twisted plasma environment is considered. The dispersion relation for surface and body modes is derived assuming constant external twisted field. Analytic approximate solutions to the dispersion equation are found for the long and short wave length cases.It was found, that in case the twisted component of the magnetic field in the environment of the flux tube is constant the index of Bessel functions ν in the corresponding dispersion relation is not integer. In the particular case of a homogen magnetic twist the total pressure is found to be constant across the boundary of the flux tube.