Photoelectric observations of chromospheric sunspot oscillations. II - Propagation characteristics

Abstract

Measurements of oscillations in umbrae and penumbrae using the line pairs (Ca II lambda8498--lambda8542) and (Fe I lambda5434--Ca II lambda8498)= are presented for seven sunspots and 11 observing runs. In the umbral chromosphere, the observations reported here, taken with other measurements of umbral oscillations, suggest that the oscillations are upward propagating acoustic (or slow mode) disturbances, and that they become nonlinear and develop into shock waves in the upper layers. They cause a significant increase in the radiative output of the umbral chromosphere, indicating the possibility of nonthermal heating at these levels. On the basis of this picture, umbral chromosphere, indicating the possibility of nonthermal heating at these levels. On the basis of this picture, umbral chromospheres have a greater physical extent in height than predicted by umbral models with coronal pressures greater than those found in the quiet Sun. Oscillations are present in the outer regions of penumbrae with frequencies and phase relationships that suggest the possibility of magneto-gravity waves.