The Evershed effect is named after the British John Evershed and is the radial flow of gas across the photospheric surface of the penumbra of a sunspot from the inner border with the umbra towards the outer edge. Evershed discoverd this back in 1909 when working at the Kokaikanal Solar Observatory in the south of India. See also this video about the Evershed Effect. There is also an inverse Evershed flow (IEF) going in the opposite direction.
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Ref. C. Beck and D. P. Choudhary 2020 ApJ 891 119 |
Above sketch of the magnetic topology of a sunspot and the various wave and flow phenomena. Left panel: side view of a sunspot. The gray and green rectangles indicate photosphere and chromosphere. Gray and red lines indicate magnetic field lines. Orange lines and arrows show the wavefront and assumed propagation of global sunspot oscillations. Black and blue arrows highlight the direction of the EF and IEF. The apparent radial propagation of umbral and penumbral waves is indicated by green and purple arrows. Right panel: magnification of the assumed magnetic field vector and the flows in the penumbra inside the yellow rectangle of the left panel.
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| Ref D. P. Choudhary and C. Beck 2018 ApJ 859 139 |
Above figure of different flow scenarios. A: inverse Evershed flow (IEF) through a siphon flow mechanism. B: IEF caused by mass shedding of rising field lines. C: IEF through coronal rain. D: photospheric Evershed flow. Magnetic field lines in cyan are those that are most relevant for the IEF. The black rectangle indicates the formation height of the Ca ii IR line at 854.2 nm from the continuum-forming layers to a height of about 1 Mm.
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| Postage Stamp India - Evershed Effect |
My picture from April 23, 2022 of Sunspot AR2993/94 showing the penumbra, umbra and fibril structure of the penumbra.
