  A small flare ribbon above a sunspot umbra in active region 12205 was
observed on November 7, 2014, at 12:00 UT in the blue imaging channel of the
1.5 m GREGOR telescope, using a 1 A Ca II H interference filter. Context
observations from the Atmospheric Imaging Assembly (AIA) onboard the Solar
Dynamics Observatory (SDO), the Solar Optical Telescope (SOT) onboard Hinode,
and the Interface Region Imaging Spectrograph (IRIS) show that this ribbon is
part of a larger one that extends through the neighboring positive polarities
and also participates in several other flares within the active region. We
reconstructed a time series of 140 seconds of Ca II H images by means of the
multiframe blind deconvolution method, which resulted in spatial and temporal
resolutions of 0.1 arcsec and 1 s. Light curves and horizontal velocities of
small-scale bright knots in the observed flare ribbon were measured. Some knots
are stationary, but three move along the ribbon with speeds of 7-11 km/s. Two
of them move in the opposite direction and exhibit highly correlated intensity
changes, which provides evidence of a slipping reconnection at small spatial
scales.
