MULTIPLE FLOWS AND THE FINE-STRUCTURE OF THE TRANSITION REGION AROUNDSUNSPOTS

The fine structure in the flow field in the transition region above an d surrounding a sunspot is determined from CIV 1548 angstrom line prof iles, observed with the High Resolution Telescope and Spectrograph (HR TS) during the Spacelab 2 mission. The observed line profiles show one , two, or three distinct velocity components within the resolution ele ment of 1'' x 1''. Supersonic flows occur in small regions where the l ine profile has two or three components. The fine component that shows supersonic speed often is weaker than the subsonic line component, wh ich may explain why some observers have been unable to detect the supe rsonic flow component. The broadening of individual line components sh ows non-thermal velocities close to 20 km s-1. This suggests that turb ulence is less important than usually considered. The presence of mult iple flows, which also occurs in quiet solar regions, suggests that th e transition region above sunspots has a sub-arc-second fine structure , perhaps consisting of thin fibrils. The Evershed flow in the transit ion region appears to have a correspondingly complex character, possib ly consisting of sub- and supersonic siphon flows along the individual fibrils. Time changes in the flow field over 5 min may correspond to characteristic times of individual fine structures. Possible explanati ons of the net downward directed mass flux are presented.