HIGH-RESOLUTION OBSERVATIONS OF THE EVERSHED EFFECT IN SUNSPOTS

High spatial resolution movies of sunspots taken at the Swedish Solar Observatory on La Palma reveal that the Evershed effect is time depend ent. Outward proper motions are visible in both the continuum and Dopp lergrams. These can be tracked over most of the width of the penumbra and overlap regions that show inward moving penumbral grains. The radi al spacing between the moving structures is about 2000 km, and they ex hibit an irregular repetitive behavior with a typical interval of 10 m inutes. These are probably the cause of 10 minute oscillations sometim es seen in penumbral power spectra. Higher velocities are spatially co rrelated with the relatively darker regions between bright filaments. Regions with a strong variation in the Doppler signal show peak-to-pea k modulations of 1 km s-1 on an average velocity of about 3-4 km s-1. The proper motion velocity is approximately constant from the inner to outer penumbra and generally larger than the Doppler velocity when bo th are interpreted as projections of horizontal motion. Regions where they are consistent suggest a typical horizontal velocity of 3.5 km s- 1. Some proper motion velocities as high as 7 km s-1 are seen, but the se are less certain. The temporal behavior shows a correlation between increased Doppler signal and increased continuum intensity, the oppos ite of the spatial correlation. When spatially averaged across filamen ts and over time, the averaged Evershed effect has a peak horizontal c omponent near the outer edge of the penumbra of 2.0 km s-1 with eviden ce for a 200-400 m s-1 upward component. The latter depends on an unce rtain absolute velocity calibration. If real it could be an actual upw ard component or a penumbral analogue of the convective blueshift seen in the quiet Sun.