Letter to the Editor

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

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.