Evidence of an association between the presence of penumbrae and strong radial outflows in sunspots

Abstract

Time series of high-resolution images of the complex active region NOAA 10786 are studied. The observations were performed in G-band (430.5 nm) and in the nearby continuum (463.3 nm), on July 9, 2005 at the Swedish 1-meter Solar Telecope (SST) in La Palma. Granular proper motions in the surroundings of the sunspots have been quantified. A large-scale radial outflow in the velocity range 0.3 - 1 km s^[-1] has been measured around the sunspots by using local correlation tracking techniques. However, this outflow is not found in those regions around the sunspots with no penumbral structure. This result evidences an association between penumbrae and the existence of strong horizontal outflows (the moat) in sunspots.