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Video image selection studies of granules, pores, and penumbral flows near a large sunspot

Zirin, Harold and Wang, Haimin (1989) Video image selection studies of granules, pores, and penumbral flows near a large sunspot. Solar Physics, 119 (2). pp. 245-255. ISSN 0038-0938. doi:10.1007/bf00146178.

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An excellent high-resolution movie in the green continuum was produced by shift-and-add treatment of two 60-min videotapes obtained at the Big Bear Solar Observatory. We have studied the digitized images by direct measurement, cross-correlation techniques, and correlation tracking. The seeing-limited resolution was about 0.3 arc sec. While the cross-correlation lifetime for granules is about five minutes, we find that actually tracking the growth and decay of a granule gives lifetimes from 10 to 22 minutes, the longest lifetimes pertaining to the largest granules. The longer lifetime comes from tracking the granule while it undergoes large changes in size and shape, while the cross-correlation lifetime is just the time in which it grows by a factor two. All the granules followed began as small elements, grew to some size, and either faded (88%), exploded (2%) or were hit by an exploding granule (10%). The major variation in granule structure appears to be due to substantial variations in the dark lanes, which often double in width. The granulation shows the typical exploding granule behavior; we find the probability that any granule will be affected by an exploding granule during its lifetime to be 10%. We also observed a larger scale explosion covering about 10 granules. This ‘explosion’ was marked by rapid (1 km s⁻¹) outward flux of the granules. We tracked the development of six small pores, one of which could be followed for two hours. The latter showed four maxima of absorption separated by about 30 min each, virtually disappearing in between. Another was observed to form in about 20 min, but no changes occur in less than granule lifetime. We confirm the inflow in penumbral fibrils observed by Muller. The inflow velocity is about 0.5 km s⁻¹, and all bright spots disappear into the umbra. The inflow which affects bright and dark features in the penumbral fibrils, is also observed in the smaller spots. We surmise that the Evershed flow is limited to the areas between the bright fibrils. We confirm granular outflow outside the penumbra.

Item Type:Article
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Wang, Haimin0000-0002-5233-565X
Additional Information:© 1989 Kluwer Academic Publishers. Provided by the NASA Astrophysics Data System. Received 15 August, 1988; in revised form 19 September, 1988. We are indebted to Bill Marquette and Randy Fear for their assistance in obtaining the data. We are indebted to the referee for a number of valuable comments. This work is supported by NSF under grant ATM-8513577 and NASA under grant NGL 05 002 034.
Funding AgencyGrant Number
NASANGL 05 002 034
Subject Keywords:Fibril; Longe Lifetime; Inflow Velocity; Solar Observatory; Large Granule
Issue or Number:2
Record Number:CaltechAUTHORS:20200529-084253264
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Official Citation:Zirin, H., Wang, H. Video image selection studies of granules, pores, and penumbral flows near a large sunspot. Sol Phys 119, 245–255 (1989).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103541
Deposited By: Tony Diaz
Deposited On:29 May 2020 15:53
Last Modified:16 Nov 2021 18:22

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