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Evolution of the sun's polar fields during sunspot cycle 21 - Poleward surges and long-term behavior
Wang, Y.-M.; Nash, A. G.; Sheeley, N. R., Jr.
AA(U.S. Navy, E. O. Hulburt Center for Space Research, Washington, DC), AB(U.S. Navy, E. O. Hulburt Center for Space Research, Washington, DC), AC(U.S. Navy, E. O. Hulburt Center for Space Research, Washington, DC)
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 347, Dec. 1, 1989, p. 529-539. Research supported by the U.S. Navy. (ApJ Homepage)
Publication Date:
Solar Physics
NASA/STI Keywords:
Photosphere, Solar Flux, Solar Magnetic Field, Sunspots, Long Term Effects, Meridional Flow, Polar Regions, Solar Cycles
Bibliographic Code:


Longitudinally averaged observations of the photospheric field during 1976-1986 are analyzed using a flux transport model. The way in which source eruptions, supergranular diffusion, and meridional flow collaborate to produce strong, highly concentrated polar fields near sunspot minimum is clarified as follows: (1) widespread eruptions of individual bipolar magnetic regions, with their leading polarity flux equatorward of their trailing polarity flux, collectively establish a large-scale separation of polarities in latitude; (2) the low-latitude, leading polarity flux diffuses across the equator and merges with its opposite hemisphere counterpart; and (3) meridional flow carries the resulting surplus of trailing polarity flux to the poles, and concentrates it there against the spreading effect of diffusion. Episodic 'surges' of flux to the poles are induced by fluctuations in the source eruption rate. Simulations indicate that relatively weak, trailing polarity surges may occur even in a steady flow field. However, in order to account for the giant surges of alternating polarity and the resulting oscillations in the polar field strength observed during 1980-1982, both accelerated flow and enhanced eruption rates are required.

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