Abstract
A mechanism is proposed to explain the cooling of a sunspot in terms of the detailed interactions between the magnetic field and the convective motions. The mechanism provides that an axially symmetric concentration of magnetic field deforms the normal supergranule cell pattern below the sunspot into a radial outflow of plasma over a region of diameter ∼ 60 Mm.
The flow occurs at depths where the magnetic and kinetic energy densities are approximately equal (≈ 5 Mm) and is described in terms of a Carnot refrigeration cycle. Application of the hydromagnetic equations to a very simple model shows that, because the magnetic field concentration causes the outflow, the field will itself decay in a time short compared with the lifetime of a spot. However, a slightly more sophisticated model does suggest conditions under which this decay is considerably reduced.
Observations of the outward drift of magnetic knots around sunspots and of supergranule-type surface motions extending radially outwards from the penumbra of a spot to the nearest faculae are discussed in relation to the mechanism.
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References
Allen, C. W.: 1963, Astrophysical Quantities, Athlone Press, London.
Altschuler, M. D., Nakagawa, Y., and Lilliequist, C. G.: 1968, Solar Phys. 3, 466.
Biermann, L.: 1941, Vierteljahresschr. Astron. Ges. 76, 194.
Bjerknes, V.: 1926, Astrophys. J. 64, 93.
Chandrasekhar, S.: 1961, Hydrodynamic and Hydromagnetic Stability, Oxford, University Press.
Chitre, S. M.: 1963, Monthly Notices Roy. Astron. Soc. 126, 431.
Chitre, S. M. and Shaviv, G.: 1967, Solar Phys. 2, 150.
Cowling, T. G.: 1953, in The Sun (ed. by G. P. Kuiper), Chicago, p. 565.
Danielson, R. E.: 1961, Astrophys. J. 134, 239.
Deinzer, W.: 1965, Astrophys. J. 141, 548.
de Jager, C.: 1966, in Proceedings of Sunspot Symposium (ed. by G. Barbera), Florence, p. 242.
Kiepenheuer, K. O., (ed.): 1968, in ‘Structure and Development of Solar Active Regions’, IAU Symp. 35, 200.
Rosseland, S.: 1926, Astrophys. J. 63, 342.
Russell, H. N.: 1921, Astrophys. J. 54, 293.
Sheeley, N. R.: 1969, Solar Phys. 9, 347.
Sheeley, N. R.: 1971, in R. Howard (ed.), ‘Solar Magnetic Fields’, IAU Symp. 43, 310.
Sheeley, N. R.: 1972, Solar Phys. 25, 98.
Sheeley, N. R. and Bhatnagar, A.: 1971, Solar Phys. 19, 338.
Simon, G. W. and Weiss, N. O.: 1968, Z. Astrophys. 69, 435.
Vrabec, D.: 1971, in R. Howard (ed.), ‘Solar Magnetic Fields’, IAU Symp. 43, 329.
Weiss, N. O.: 1964, Monthly Notices Roy. Astron. Soc. 128, 225.
Weiss, N. O.: 1966, Proc. Roy. Soc. 293, 310.
Wilson, P. R.: 1968, Solar Phys. 3, 243.
Wilson, P. R.: 1971, Solar Phys. 21, 101.
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Wilson, P.R. The cooling of a sunspot. Sol Phys 27, 354–362 (1972). https://doi.org/10.1007/BF00153107
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DOI: https://doi.org/10.1007/BF00153107