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Paper: Precursor of Sunspot Penumbral Formation Discovered with Hinode SOT Observation
Volume: 456, The Fifth Hinode Science Meeting
Page: 43
Authors: Shimizu, T.; Ichimoto, K.; Suematsu, Y.
Abstract: We newly found a precursory signature of sunspot penumbral formation in Ca II H images. The precursor is a dark annular zone (width 3"-5") around the umbra (pore), which was formed soon after the pore formation and existed until the penumbral formation. The penumbra was developed as if to fill the annular zone. Pre-existing ambient magnetic field islands were moved to be distributed at the outer edge of the annular zone and did not come into the zone. The observations indicate that the annular zone is different from sunspot moat flow region and that the zone is visible only in chromospheric Ca II H images, not in photospheric G-band images. We conclude that the annular zone reflects the formation of a magnetic canopy overlying the region surrounding the umbra at the chromospheric level, much before the formation of the penumbra at the photospheric level. We can predict the region and size of the penumbra, by looking at the appearance of dark zone around pores.
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