Supersonic downflows in the vicinity of a growing pore

Evidence of unresolved magnetic fine structure at chromospheric heights

Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Straße 2, Katlenburg-Lindau, Germany e-mail: lagg@mps.mpg.de

Received: 16 December 2005
Accepted: 26 October 2006

Abstract

Aims.The velocity and magnetic fine structure of the chromosphere at the leg of an emerging magnetic loop is investigated at a location of supersonic downflows.

Methods.We analyze a time series of spectropolarimetric data in the He i 1083 nm triplet covering a time interval of ≈70 min. The temporal evolution as well as the topology of the magnetic field in the downflow region are investigated. We apply an inversion technique based on a genetic algorithm using the Milne-Eddington approach. The technique is very reliable and robust in retrieving maps of the velocity and the magnetic field vector for both atmospheric components separately.

Results.We observe redshifts corresponding to a downflow speed of up to 40 km s^-1 in the vicinity of a growing pore. These supersonic downflows always coexist with a second atmospheric component almost at rest (slow component) within the same resolution element. The redshifted component is more inclined to the solar normal than the slow component and has a different field strength.

Conclusions.We interpret this downflow as a consequence of the draining of the rising loops. The different magnetic field orientation of the redshifted and the slow component give rise to two possible interpretations: an uncombed structure of the chromosphere, similar to the differently inclined flux-tubes in the penumbra of a sunspot, or a cloud-like structure containing gas at different velocities in two separate height layers of the solar atmosphere.