Running Umbral Waves Observed with Hinode

Abstract

Abstract Observations of the main sunspot of NOAA 10953 were carried out with the Solar Optical Telescope aboard Hinode with the line Ca II H on 2007 April 30. The high-cadence (up to 10 s) Ca II H intensity images permit us to elaborate on the nature of umbral oscillations. It is found there are 19 wave sources within the sunspot and 82 running umbral waves that periodically appear at the wave sources, and propagate outward while forming ellipses or partial arcs. Due to their own expansion, the running waves become more diffused, and eventually disappear at the edge of the umbra. On the basis of the time-interval distribution between adjacent running waves being centered close to 144 s, we observed an approximate oscillation period of 142 s. By tracing the fronts of the running waves, the propagation speed of the running waves ranges from 30 to 45 km s$^{-1}$. The distribution for all running waves has an average propagation speed of $\sim$ 37.4 km s$^{-1}$. Furthermore, we have found an interesting phenomenon that implies there may be interaction of a microflare with some running umbral waves.