Periodicity of Twisting Motions in Sunspot Penumbral Filaments

Solar Physics (Impact Factor: 4.04). 07/2009; 257(2):251-260. DOI: 10.1007/s11207-009-9373-2


We study the periodicity of twisting motions in sunspot penumbral filaments, which were recently discovered from space (Hinode) and ground-based (SST) observations. A sunspot was well observed for 97 minutes by Hinode/SOT in the G-band (4305 Å) on 12November 2006. By the use of the time – space gradient applied to intensity space – time
plots, twisting structures can be identified in the penumbral filaments. Consistent with previous findings, we find that the
twisting is oriented from the solar limb to disk center. Some of them show a periodicity. The typical period is about ≈ four
minutes, and the twisting velocity is roughly 6 km s−1. However, the penumbral filaments do not always show periodic twisting motions during the time interval of the observations.
Such behavior seems to start and stop randomly with various penumbral filaments displaying periodic twisting during different
intervals. The maximum number of periodic twists is 20 in our observations. Studying this periodicity can help us to understand
the physical nature of the twisting motions. The present results enable us to determine observational constraints on the twisting

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