Ultraviolet Observations of Periodic Annular Intensity Fluctuations Propagating around Sunspots

Abstract

We analyze UV observations of an isolated sunspot taken with the Transition Region and Coronal Explorer. We produced ``space/time slice images,'' which reveal periodic, inward-propagating, intensity fluctuations in the inner photospheric penumbra and periodic, outward-propagating, annular intensity fluctuations in the outer penumbra and the area around the sunspot. The average propagation velocity of the inward- and outward-propagating intensity flows is about 0.5 and 1 km s^-1, respectively, and the distance between subsequent crests is about 2500 km. Using observations obtained with the Michelson Doppler Imager, we found propagating magnetic field enhancements that present a spatial and temporal coherence with the UV intensity fluctuations. We have not observed any waves similar or related to the chromospheric 5 minute waves. Based on observations taken with the Transition Region and Coronal Explorer and the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory.