  Torsional Alfven waves are likely excited with bursts in rotating magnetars.
These waves are probably propagated through corotating atmospheres toward a
vacuum exterior. We have studied the physical effects of the azimuthal wave
number and the characteristic height of the plasma medium on wave transmission.
In this work, explicit calculations were carried out based on the three-layered
cylindrical model. We found that the coupling strength between the internal
shear and the external Alfven modes is drastically enhanced, when resonance
occurs in the corotating plasma cavity. The spatial structure of the
electromagnetic fields in the resonance cavity is also investigated when Alfven
waves exhibit resonance.
