Proper motion measurements of umbral and penumbral structure

Abstract

Horizontal proper motions of penumbral structure and umbral dots have been measured from a 17-min-long time series of sunspot images by numerical techniques. In the penumbra, inflows are seen to occur predominantly in the inner region, with an average velocity of 290 m s−1. Penumbral outflows take place mostly in the outer part, where they reach velocities as high as 1.5 km s−1, with an average velocity of 500 m s−1. In the umbra, proper motions of 28 bright dots have been measured with an accuracy better than 50 m s−1. The mean velocity of the umbral dots is 210 m s−1. Most of the umbral dots display the well-known inward motion away from the peripheral umbra.