Effects Of Temperature Gradients On Transverse Oscillations Of Solar Magnetic Flux Tubes
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Solar magnetic flux tubes support three fundamental modes: longitudinal, transverse and torsional tube waves. Previous studies showed that the propagation of longitudinal and transverse waves along thin and isothermal magnetic flux tubes is affected by the cutoff frequency, which are global quantities that restricts the wave propagation to only those frequencies that are higher than the cutoff. It was also demonstrated that the tubes respond to freely propagating longitudinal and transverse tube waves by oscillating at the corresponding cutoff frequency. No cutoff frequency was found for torsional waves propagating along thin and isothermal magnetic flux tubes. Since the solar atmosphere is not isothermal, the effects of different temperature gradients on the cutoff for transverse tube waves are investigated. It is shown that this cutoff frequency becomes a local quantity and its physical meaning is different than the global cutoff. The obtained results are used to explain the observed frequencies of oscillations of solar magnetic flux tubes.