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Astronomy & Astrophysics manuscript no. (will be inserted by hand later)

Summary: Astronomy & Astrophysics manuscript no.
(will be inserted by hand later)
Sunspot Plume Observations in the EUV
The gas pressure differential between the umbra and surrounding region
J.G. Doyle 1 and M.S. Madjarska 1,2
1 Armagh Observatory, College Hill, Armagh BT61 9DG, N. Ireland
2 Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT
Abstract. The electron density over a bright sunspot plume region was evaluated using lines within the O # 760 Ć multiplet.
The plume showed an intensity enhancement factor of # 9 in the O # lines compared to regions outside the sunspot umbra.
Internal agreement between the various ratios is excellent which would suggest that the O # lines do not su#er from blending
problems. The derived mean electron densities for the sunspot plume is log N e /cm -3 # 9.9 compared to log N e /cm -3 # 10.20--
10.45 in the surrounding area. The derived gas pressure in the plume compared to that outside leads weight to the suggestion
that it is plasma flowing from outside the spot into the umbra at transition region temperatures that is the main cause of the
down­flows. The plume non­thermal velocities are 5 to 10 km s -1 smaller than those measured in regions external to the spot,
suggesting significantly less turbulence within the umbra.
Key words. Sun: SoHO--SUMER: Transition region: Sunspot plumes: Electron density
1. Introduction
Sunspots, the cool dark features visible on the Sun's surface are
complex magnetic structures, perhaps even more so than pre­


Source: Armagh Observatory


Collections: Physics