Photospheric plasma flows around a solar spot

We study photospheric plasma flows in an active region NOAA 8375, by using uninterrupted high-resolution SOHO/MDI observations (137 intensity images, 44 hours of observations). The active region consists of a stable large spot and many small spots and pores. Analyzing horizontal flow maps, obtained with local correlation tracking technique, we found a system of stable persistent plasma flows existing in the active region. The flows start on either side of the sunspot and extend over 100″ to the east. Our measurements show that the speed of small sunspots and pores, averaged over 44 hours, was about 100 m s^-1, which corresponds to root-mean-square longitudinal drifts of sunspots of 0.67°-0.76° day^-1. We conclude that these large-scale flows are due to faster proper motion of the large sunspot relative to the ambient photospheric plasma. We suggest that the flows may be a good carrier to transport magnetic flux from eroding sunspots into the outer part of an active region.