Multiwavelength analysis of a solar quiet region

¹ National Observatory of Athens, Institute for Space Applications and Remote Sensing, 15236 Palea Penteli, Greece e-mail: [georgia;kostas]@space.noa.gr
² Astronomical Institute, Academy of Sciences of the Czech Republic, 25165 Ondřejov, Czech Republic e-mail: [schwartz;pheinzel]@asu.cas.cz

Received: 5 May 2008
Accepted: 10 October 2008

Abstract

Context. We examine oscillatory phenomena in a solar network region from multi-wavelength observations obtained by the ground-based Dutch Open Telescope (DOT) and by the Coronal Diagnostic Spectrometer (CDS) on the spacecraft Solar and Heliospheric Observatory (SoHO). The observations were obtained during a coordinated observing campaign in October 2005.

Aims. We investigate the temporal variations of the intensities and the velocities in two distinct regions of the quiet Sun, one containing several dark mottles and the other several bright points defining the network boundaries (NB). The aim is to find similarities and/or differences in the oscillatory phenomena observed in these two regions and in different spectral lines formed from the chromosphere to the transition region, as well as the propagation characteristics of waves.

Methods. Intensity and velocity variations are studied with wavelet and phase difference analyses.

Results. Both regions (i.e. mottles and NB) show a periodicity of ~5 min in all considered lines. The V-V phase differences in the NB region point to an upward propagation of waves; in the region of mottles, for periods of 250-400 s, the phase difference is mainly negative, which suggests a downward propagation, in turn indicating a refraction of waves from the inclined magnetic field of mottles along the line-of-sight.

Conclusions. The phase differences at the NB arise from a predominance of upward propagating waves. In the mottles' region, the negative phase differences we found suggest that propagating waves encounter a boundary and are refracted and reflected. Of course, several limitations exist in the exact interpretation of the phase differences, e.g. the complex topology of the magnetic field, the formation conditions and heights of the examined spectral lines, and the low spatial resolution.