Temporal Evolution of Fine Structures in and around Solar Pores

Abstract

Time series of high-resolution white-light images of six solar pores, observed in 1993 and 1995 at the Swedish Vacuum Solar Telescope (La Palma), are analyzed. The pores constitute an almost ideal laboratory in which to study the interaction of a vertical magnetic field with surrounding convective motions, without the perturbation of the inclined magnetic field in the penumbra. Umbral dots observed in a large (D=89) pore are similar to those in mature umbrae, but they live longer, are brighter, and have a higher filling factor. Granular motions in the vicinity of pores are driven by mesogranular flows. Motions toward the pore dominate in the 2'' zone around the pore boundary, while at larger distances the granules move away from the pore. Pushed by these motions, small granules and granular fragments located close to the pore border sometimes penetrate into the pore, where they move inward as bright short-lived features very similar to umbral dots. The capture of bright features by the pore is probably a microscale manifestation of the "turbulent erosion," which results in the decay of the pore. Formation of a transitory penumbra-like structure at the border of the large pore was observed simultaneously with the appearance of expanding elongated granules, separated by dark filaments, in an adjacent granular field. These effects can be interpreted as a consequence of emerging bipolar magnetic "loops" caused by a temporary protrusion of opposite magnetic polarity.