Waves in the sunspot penumbra

Abstract

Sunspot theory is discussed with reference to the role played by the spot magnetic field in influencing the mode of energy transport. Consideration is given to the stability of a plane parallel polytropic fluid layer with infinite electrical conductivity in the presence of a uniform horizontal magnetic field. The possibility of identifying the running penumbral waves and the penumbral filaments with two different kinds of instabilities is explored. It is found for a reasonable choice of physical parameters that the time scales and wavelengths of fast modes for the disturbances propagating along the field lines roughly correspond to the observed values for the running penumbral waves.