Observations of Running Penumbral Waves

Quiet sunspots with well-developed penumbrae show running intensity waves with period running around 300 seconds. The waves appear connected with umbral flashes of exactly half the period. Waves are concentric, regular, with velocity constant around 10 kIn -1 They are probably sound waves and show intensity fluctuation in Ha centerline or wing of 1() 20 percent. The energy is tiny compared to the heat deflcit of the umbra.