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Comparison of polar and equatorial magnetic fields near sunspot minimum

Zhang, L. D. and Zirin, H. and Marquette, W. H. (1997) Comparison of polar and equatorial magnetic fields near sunspot minimum. Solar Physics, 175 (1). pp. 59-80. ISSN 0038-0938. doi:10.1023/a:1004908110483.

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We investigate the polar magnetic fields near sunspot minimum using high-resolution videomagnetograph data from Big Bear Solar Observatory. To avoid the problem of center-to-limb variation of the projected longitudinal field, we compare polar with equatorial field strengths for the same limb distance. Polar fields are stronger than the quiet equatorial field, but no greater than equatorial limb data containing unipolar regions. The difference is entirely in the stronger field elements. The polar background fields are of mixed polarity but show a net weak field opposite in sign to that of the stronger polar elements. We believe this to be the first evidence of widespread background field. No dependence of the measured signal on the B-angle was found, so the high-latitude fields do not change strength near the pole. Further, there was no significant change in the polar fields in the 15-month period studied. We tried to derive a high-latitude rotation rate; our data show motion of high-latitude magnetic elements, but the diurnal trajectory is not much bigger than random motions and field changes, so the result is inconclusive. We suggest that the polar fields represent the accumulation of sunspot remnants, the elements of which last for years in the absence of other fields.

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Additional Information:© 1997 Kluwer Academic Publishers. Received 10 January 1997; accepted 21 February 1997. We would like to thank the staff at the Big Bear Solar Observatory for taking the data, especially Anders Johannesson who has provided the program of videomagnetograph flat fielding. The work is supported by ONR grant N00014–97–1–0080, NSF grant ATM-9525971, and NASA grant NAGW-1972.
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Office of Naval Research (ONR)N00014-97-1-0080
Subject Keywords:Polar Field, Background Field, Magnetic Element, Solar Observatory, Limb Distance
Issue or Number:1
Record Number:CaltechAUTHORS:20200722-163252153
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Official Citation:Zhang, L.D., Zirin, H. & Marquette, W.H. Comparison of Polar and Equatorial Magnetic Fields Near Sunspot Minimum. Solar Physics 175, 59–80 (1997).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:104525
Deposited By: Rebecca Minjarez
Deposited On:23 Jul 2020 18:43
Last Modified:16 Nov 2021 18:32

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