Downward pumping of magnetic flux as the cause of filamentary structures in sunspot penumbrae

John H. Thomas (), Nigel O. Weiss, Steven M. Tobias and Nicholas H. Brummell
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John H. Thomas: University of Cambridge
Nigel O. Weiss: University of Cambridge
Steven M. Tobias: The University of Leeds
Nicholas H. Brummell: University of Colorado

Nature, 2002, vol. 420, issue 6914, 390-393

Abstract: Abstract The structure of a sunspot is determined by the local interaction between magnetic fields and convection near the Sun's surface1,2. The dark central umbra is surrounded by a filamentary penumbra, whose complicated fine structure has only recently been revealed by high-resolution observations3,4,5,6,7,8,9,10,11,12,13,14. The penumbral magnetic field has an intricate and unexpected interlocking-comb structure and some field lines, with associated outflows of gas15, dive back down below the solar surface at the outer edge of the spot. These field lines might be expected to float quickly back to the surface because of magnetic buoyancy, but they remain submerged. Here we show that the field lines are kept submerged outside the spot by turbulent, compressible convection, which is dominated by strong, coherent, descending plumes16,17. Moreover, this downward pumping of magnetic flux explains the origin of the interlocking-comb structure of the penumbral magnetic field, and the behaviour of other magnetic features near the sunspot.

Date: 2002
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DOI: 10.1038/nature01174

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