  Local correlation tracking techniques are used to measure proper motions in a
series of high angular resolution (~0.1 arcsec) penumbra images. If these
motions trace true plasma motions, then we have detected converging flows that
arrange the plasma in long narrow filaments co-spatial with dark penumbral
filaments. Assuming that these flows are stationary, the vertical
stratification of the atmosphere and the conservation of mass suggest downflows
in the filaments of the order of 200 m/s. The association between downflows and
dark features may be a sign of convection, as it happens with the non-magnetic
granulation. Insufficient spatial resolution may explain why the estimated
vertical velocities are not fast enough to supply the radiative losses of
penumbrae.
