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Evolution of magnetic fields and mass flow in a decaying active region

Zhang, Hongqi and Ai, Guoxiang and Wang, Haimin and Zirin, Harold and Patterson, Alan (1992) Evolution of magnetic fields and mass flow in a decaying active region. Solar Physics, 140 (2). pp. 307-316. ISSN 0038-0938. doi:10.1007/bf00146315.

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Five days of coordinated observation were carried out from 24–29 September, 1987 at Big Bear and Huairou Solar Observatories. Longitudinal magnetic fields of an αp sunspot active region were observed almost continuously by the two observatories. In addition, vector magnetic fields, photospheric and chromospheric Doppler velocity fields of the active region were also observed at Huairou Solar Observatory. We studied the evolution of magnetic fields and mass motions of the active region and obtained the following results: (1) There are two kinds of Moving Magnetic Features (MMFs). (a) MMFs with the same magnetic polarity as the center sunspot. These MMFs carry net flux from the spot, move through the moat, and accumulate at the moat's outer boundary. (b) MMFs in pairs of mixed polarity. These MMFs are not responsible for the decay of the spot since they do not carry away the net flux. MMFs in category (b) move faster than those of (a). (2) The speed of the mixed polarity MMFs is larger than the outflow measured by photospheric Dopplergrams. The uni-polar MMFs are moving at about the same speed as the Doppler outflow. (3) The chromospheric velocity is in approximately the opposite direction from the photospheric velocity. The photospheric Doppler flow is outward; chromospheric flow is inward. We also found evidence that downward flow appears in the photospheric umbra; in the chromosphere there is an upflow.

Item Type:Article
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Wang, Haimin0000-0002-5233-565X
Additional Information:© 1992 Kluwer Academic Publishers. Provided by the NASA Astrophysics Data System. Received 31 May, 1990; in revised form 3 March, 1992. We are grateful to the staff at Huairou Solar Observing Station and Big Bear Solar Observatory for their support in the observations. We wish to thank the referee for many helpful comments. This research was supported by the Chinese Academy of Sciences and the National Science Foundation of China and by the National Science Foundation of the United States under grant ATM-8816007.
Funding AgencyGrant Number
Chinese Academy of SciencesUNSPECIFIED
National Science Foundation of ChinaUNSPECIFIED
Subject Keywords:Magnetic Field; Active Region; Mass Flow; Outer Boundary; Mass Motion
Issue or Number:2
Record Number:CaltechAUTHORS:20200520-130618121
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Official Citation:Zhang, H., AI, G., Wang, H. et al. Evolution of magnetic fields and mass flow in a decaying active region. Sol Phys 140, 307–316 (1992).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103358
Deposited By: Tony Diaz
Deposited On:20 May 2020 21:16
Last Modified:16 Nov 2021 18:20

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