SUMER observations of the inverse Evershed effect in the transition region above a sunspot

Free access article

Issue		A&A Volume 491, Number 2, November IV 2008


Page(s)		L5 - L8
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:200810209
Published online		15 October 2008

A&A 491, L5-L8 (2008)
DOI: 10.1051/0004-6361:200810209

Letter

SUMER observations of the inverse Evershed effect in the transition region above a sunspot

L. Teriaca, W. Curdt, and S. K. Solanki

Max-Planck-Institut für Sonnensystemforschung (MPS), 37191 Katlenburg-Lindau, Germany
e-mail: teriaca@mps.mpg.de

Received 16 May 2008 / Accepted 18 September 2008

Abstract
Aims. We analyse SUMER spectral scans of a large sunspot within active region NOAA 10923, obtained on 14–15 November 2006, to determine the morphology and dynamics of the sunspot atmosphere at different heights/temperatures.
Methods. The data analysed here consist of spectroheliograms in the continuum around 142.0 nm and in the Si IV 140.2 nm, O III 70.3 nm, N IV 76.5 nm, and O IV 79.0 nm spectral lines. Gaussian-fitting of the observed profiles provides line-of-sight velocity and Doppler-width maps.
Results. The data show an asymmetric downflow pattern compatible with the presence of the inverse Evershed flow in a region within roughly twice the penumbral radius at transition-region temperatures up to 0.18 MK. The motions, highly inhomogeneous on small scales, seem to occur in a collar of radially directed filamentary structures, with an average width less than the 1 Mm spatial resolution of SUMER and characterised by different plasma speeds. Assuming that the flows are directed along the field lines, we deduce that such field lines are inclined by 10° to 25° with respect to the solar surface.

Key words: Sun: transition region -- Sun: magnetic fields -- Sun: sunspots

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