Evolution of small-scale features at the penumbra-photosphere border

Sobotka, M.; Muller, R.; Bonet, J. A.; Márquez, I.
Bibliographical reference

In: SOLMAG 2002. Proceedings of the Magnetic Coupling of the Solar Atmosphere Euroconference and IAU Colloquium 188, 11 - 15 June 2002, Santorini, Greece. Ed. H. Sawaya-Lacoste. ESA SP-505. Noordwijk, Netherlands: ESA Publications Division, ISBN 92-9092-815-8, 2002, p. 579 - 582

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Time series of images of a sunspot, acquired simultaneously in blue light and in G-band at the SVST, La Palma, are used to study horizontal motions of granules in the vicinity of the spot and evolution of penumbral grains (PGs) near the outer penumbral border. Local correlation tracking and feature tracking algorithms have been utilized for this purpose. Around sunspots and pores we can observe numerous centers of diverging local horizontal motions, caused mostly by exploding granules. Around developed spots we find an organized motion directed out from the penumbra. The divergence centers are carried away from the spot by this motion. In the outer penumbra, PGs move mostly outwards, toward the surrounding granulation. About 2/3 of PGs disappear near the penumbra-granulation border. The remaining PGs move across the border, they transform either to granules or to small bright features, and continue moving away from the sunspot.