The Evershed effect in sunspots as a siphon flow along a magnetic flux tube

Benjamín Montesinos and John H. Thomas ()
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Benjamín Montesinos: LAEFF/INTA
John H. Thomas: University of Rochester

Nature, 1997, vol. 390, issue 6659, 485-487

Abstract: Abstract The Evershed effect1—a wavelength shift and profile asymmetry in the spectral lines observed from the outer regions of sunspots (the penumbra)—has been interpreted as a radial outflow of gas from the sunspot, but the dynamics of the flow have not been fully understood2. Although the Evershed effect seems to stop abruptly at the outer edge of the penumbra, the outflow itself must continue, though tracing its path has proved difficult. Theoretical3,4 and observational5,6,7 studies have suggested that much of the continuing flow may follow magnetic field lines that go below the visible surface of the Sun at or just beyond the edge of the penumbra, and recent observations have now confirmed this picture8. Here we show, using theoretical calculations based on a more realistic model, that the flow acts like a siphon3,9,10,11,12 which is driven along a magnetic flux tube by the pressure drop between the endpoints of the tube.

Date: 1997
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DOI: 10.1038/37307

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