Discovery of inward moving magnetic enhancements in sunspot penumbrae

Sunspot penumbrae show a fine structure in continuum intensity that displays considerable dynamics. The magnetic field, in contrast, although also highly structured, has appeared to be relatively static. Here we report the discovery of inward moving magnetic enhancements in the penumbrae of two regular sunspots based on time series of SOHO/MDI magnetograms. Local enhancements of the LOS component of the magnetic field in the inner part of the penumbral region move inward to the umbra-penumbra boundary with a radial speed of about 0.3 km s$^{-1}$. These local inward-moving enhancements of the LOS component of the magnetic fields appear to be relatively common. They are associated with dark structures and tend to display downflows relatively to the penumbral background. Possible explanations are discussed.