A model of the oscillations in the chromosphere and transition region above sunspot umbrae

In an earlier paper (Solar Phys.82, 369) the present authors proposed a model for the interpretation of velocity and intensity oscillations with periods between 2 and 3 minutes observed above umbrae. The model explains the oscillations by the resonant transmission of slow-mode magnetic-acoustic waves which are semi-trapped in a chromospheric cavity. In this way we get an independent method of checking semi-empirical models of umbral atmospheres.The model has been improved by more detailed calculations and corroborated by recently published observations: The calculations are in good agreement with:(a)the height dependence of the observed phase difference between velocity and intensity oscillations; and(b)the frequency spectrum of oscillations in the transition region above sunspots observed on the SMM spacecraft during the SMY.

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