THE EFFECT OF A TWISTED MAGNETIC FIELD ON THE PERIOD RATIO P sub(1)/P sub(2) OF NONAXISYMMETRIC MAGNETOHYDRODYNAMIC WAVES

We consider nonaxisymmetric magnetohydrodynamic (MHD) modes in a zero-beta cylindrical compressible thin magnetic flux tube modeled as a twisted core surrounded by a magnetically twisted annulus, with both embedded in a straight ambient external field. The dispersion relation is derived and solved analytically and numerically to obtain the frequencies of the nonaxisymmetric MHD waves. The main result is that the twisted magnetic annulus does affect the period ratio P sub(1)/P sub(2) of the kink modes. For the kink modes, the magnetic twist in the annulus region can achieve deviations from P sub(1)/P sub(2) = 2 of the same order of magnitude as in the observations. Furthermore, the effect of the internal twist on the fluting modes is investigated.