Euv Spectroscopy of the Sunspot Region Noaa 7981 Using Soho – II. Velocities and Line Profiles
ABSTRACT We have studied the dynamics in the sunspot transition region between the chromosphere and the corona and investigated the extension of the flow field into the corona. Based on EUV spectra of a medium size sunspot and its surroundings, NOAA 7981, observed with CDS and SUMER on SOHO, we derive line-of-sight velocities and study the line profiles for a series of emission lines.The flow field in the low corona is found to differ markedly from that in the transition region. In the transition region the relative line-of-sight velocity shows an upflow in the umbra and relatively large areas with downflow that cover part of the penumbra. The spatial extent of these areas with upflow and downflow increases with increasing temperature in the transition region, but the whole flow field changes character as the temperature increases from the upper transition region to the low corona. Based on a calibration of the SUMER wavelength scale we find that the entire sunspot transition zone appears to be moving downwards towards the chromosphere. The relation between this finding and the general tendency for transition-region lines to show a net red shift is discussed.Several of the transition-region spectral line profiles are observed to show two line components with Gaussian shape and line-of-sight velocities that differ markedly. Several of the line profiles that are composed of two spectral line components occur close to the dividing line between up- and downflow. A discussion of this observation is presented. In small regions with spatial extent of a few arc sec we detect enhanced continuum emission underlying explosive events. The similarities between explosive events with continuum emission and the moustaches observed in H close to sunspots are so striking that we are tempted to introduce the notation transition-region moustaches.
- [Show abstract] [Hide abstract]
ABSTRACT: We aim to investigate the overall characteristics of coronal active region loops and their evolution. The Hinode database was searched for observations of active regions as they crossed the Sun centre. NOAA 10926 was selected. The morphology of this young active region did not significantly change over the course of a few days. Persistent redshifts, stronger in cooler lines (about 5-10 km s-1 in Fe XII and 20-30 km s-1 in Fe VIII), were observed in most loop structures with the EUV Imaging Spectrometer. Persistent blueshifts, stronger in the hotter lines (typically 5-20 km s-1 in Fe XII and 10-30 km s-1 in Fe XV), were present in areas of weak emission, in a sharp boundary between the low-lying “hot” 3 MK loops and the higher “cooler” 1 MK loops.Astronomy and Astrophysics 04/2008; 481(1). · 5.08 Impact Factor
Article: Solar Activity on All Scales09/1999; 446:53.
- [Show abstract] [Hide abstract]
ABSTRACT: We study the dynamics of the quiet sun transition region, using observations obtained with the SOHO CDS/NIS and SUMER spectrographs. We examine the morphology of the network as a function of temperature and we compare the intensity features with those of the dopplergrams. The velocity distributions have a different behaviour for the bright features which outline the network and the dark ones, located in the internetwork. A redshift and a smaller standard deviation are observed for the bright feature distributions relative to the dark ones. It should be mentioned that the internetwork is also statistically redshifted, with the exception of the He I line. Velocity distributions from different lines are compared.Astronomy and Astrophysics 10/2001; · 5.08 Impact Factor