The Observation of Sunspot Light-Bridge Structure and Dynamics

Abstract

We present very high resolution multiwavelength images of a sunspot light bridge in NOAA Active Region 10132 taken at the Swedish 1 m Solar Telescope on La Palma on 2002 September 25. The adaptive optics-corrected images resolve 100 km scale bright grains on either side of an approximately 380 km dark lane in the center of the bridge. Movies of the data show the grains in a steady unidirectional flow with an average speed of 900 m s^-1 along the entire length of the bridge. Overturning motions are seen in the larger grains, suggesting a convective origin for these structures. Simultaneous 160 nm ultraviolet images from the Transition Region and Coronal Explorer (TRACE) satellite show a constant brightness enhancement over the light bridge, implying a steady chromospheric heat source. TRACE 160 nm movies do not resolve the unidirectional flow; instead, they suggest that a horizontal oscillatory motion exists in the chromosphere of the light bridge. A C2.0 flare at 16:00 UT, one ribbon of which occurs directly along the light bridge, indicates a high level of magnetic stress and impulsive dissipation associated with the observed light-bridge dynamics.