Coordinated observations of the quiet Sun transition region using SUMER spectra, TRACE images and MDI magnetograms

Max-Planck-Institut für Aeronomie, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany

Received: 1 June 2001
Accepted: 20 August 2001

Abstract

The relationship between the transition region ultraviolet emission and the underlying magnetic field is explored through a detailed analysis of SUMER Siiv line profiles, TRACE Civ, continuum and 171 Å intensities, and MDI high resolution magnetic field measurements. The observations track a narrow area of quiet Sun near disk center over a period of 3 hours. Highly variable emission is found throughout. The most dramatic line Doppler shift and brightness variations come from a region of complex field evolution. The brightenings sometimes have faint elongated extensions in the TRACE Civ images. In most events with high Doppler shifts, the Siiv line wing reveals plasma flow 1-2 min before the line core brightens which suggests that plasma acceleration precedes plasma compression and/or heating. Simultaneous measurement of transition region densities using Oiv line ratios imply large density fluctuations in the transition region plasma. There is an indication of waves of compression and rarefaction crossing the spectrometer's field-of-view. The waves' speed across the solar surface is between 20-40 km s^-1, and the compression may be as high as 10. In space-time images density fluctuations are much more prevalent and conspicuous than brightenings. In several cases the waves seem to start at the position of Siiv brightenings.