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High-resolution observations of the polar magnetic fields of the sun

Lin, H. and Varsik, J. and Zirin, H. (1994) High-resolution observations of the polar magnetic fields of the sun. Solar Physics, 155 (2). pp. 243-256. ISSN 0038-0938.

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High-resolution magnetograms of the solar polar region were used for the study of the polar magnetic field. In contrast to low-resolution magnetograph observations which measure the polar magnetic field averaged over a large area, we focused our efforts on the properties of the small magnetic elements in the polar region. Evolution of the filling factor - the ratio of the area occupied by the magnetic elements to the total area - of these magnetic elements, as well as the average magnetic field strength, were studied during the maximum and declining phase of solar cycle 22, from early 1991 to mid-1993. We found that during the sunspot maximum period, the polar regions were occupied by about equal numbers of positive and negative magnetic elements, with equal average field strength. As the solar cycle progresses toward sunspot minimum, the magnetic field elements in the polar region become predominantly of one polarity. The average magnetic field of the dominant polarity elements also increases with the filling factor. In the meanwhile, both the filling factor and the average field strength of the non-dominant polarity elements decrease. The combined effects of the changing filling factors and average field strength produce the observed evolution of the integrated polar flux over the solar cycle. We compared the evolutionary histories of both filling factor and average field strength, for regions of high (70°–80°) and low (60°–70°) latitudes. For the south pole, we found no significant evidence of difference in the time of reversal. However, the low-latitude region of the north pole did reverse polarity much earlier than the high-latitude region. It later showed an oscillatory behavior. We suggest this may be caused by the poleward migration of flux from a large active region in 1989 with highly imbalanced flux.

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Additional Information:© 1994 Kluwer Academic Publishers. Provided by the NASA Astrophysics Data System. Received 8 December, 1993; in revised form 10 August, 1994. We would like to thank the observers at Big Bear Solar Observatory for their efforts in collecting the data. HL is grateful to Dr H. Wang for many discussions. This research is supported by ONR grant number N00014-89-J-1069. The Big Bear Solar Observatory is supported by NASA grant number NAGW-1972, and NSF grant number ATM-9122023.
Funding AgencyGrant Number
Office of Naval Research (ONR)N00014-89-J-1069
Subject Keywords:Solar Cycle; Polar Region; Filling Factor; Magnetic Element; Polar Magnetic Field
Issue or Number:2
Record Number:CaltechAUTHORS:20200519-143509351
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Official Citation:Lin, H., Varsik, J. & Zirin, H. High-resolution observations of the polar magnetic fields of the sun. Sol Phys 155, 243–256 (1994).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:103326
Deposited By: Tony Diaz
Deposited On:19 May 2020 21:42
Last Modified:19 May 2020 21:42

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