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Structure and Dynamics of Solar Atmosphere

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Solar quiet and active regions at all atmospheric levels are studied to understand the interactions between plasma motions and magnetic field. Emphasis is put on observations that are acquired with medium spatial resolution (2"-4") at the Ondrejov horizontal spectrograph and with very high resolution (better than 0.2") at the Canary Islands Observatories. Global and Large-Scale Dynamic Properties of the Sun are studied analyzing horizontal transport velocities of magnetized plasma in the solar atmosphere.


Observational data come from the Ondřejov 50-cm horizontal telescope and spectrograph HSFA1, the Coimbra spectroheliograph, large solar telescopes located on the Canary Islands observatories, and solar satellites SOHO and TRACE. The operation of the solar magnetograph (SOLMAG) attached to HSFA1 was discontinued. SOLMAG measured the line-of-sight component of the magnetic field and the Doppler velocity in various spectral lines from 1990 to 2001. The properties of the instrument and the data archive can be found on the SOLMAG web site. After an extensive reconstruction, HSFA1 was recently equipped with a new post-focus device SOLSPAN for solar spectra analysis. SOLSPAN will be capable to observe parts of the solar disc in two selectable spectral lines simultaneously. The group took part in the reconstruction of the photographic spectroheliograph of the Astronomical Observatory of the Coimbra University, Portugal, to enable the acquisition of full-disc spectroheliograms using a digital CCD camera. The newly installed device enrich the potential of the telescope, obtaining the information about the full-disc Doppler velocity fields in addition to the spectroheliograms.

Since 2001, the group has been collaborating with the Astrophysikalisches Institut Potsdam, Kiepenheuer-Institut für Sonnenphysik, and Institut für Astrophysik Göttingen on the project GREGOR, a development and construction of a large solar telescope with a diameter of 1.5 m. The telescope is now assembled at Tenerife, Canary Islands, and the first light is planned for 2008. Participation in the project, financed by the Czech Ministry of Education, Youth and Sports, will allow us to share observing time on this unique instrument.

Sunspots show an ample range of fine structures (penumbral filaments and grains, umbral dots, light bridges, and dark nuclei), resulting from the complex behaviour of partially ionized dense gas moving in a strong magnetic field, including various types of magnetoconvection. Sunspot umbrae and penumbrae are associated with complex patterns of magnetic fields and velocities. Using high-resolution images and 2D spectra, obtained and analyzed in collaboration with Instituto de Astrofísica de Canarias, with the Universities of Göttingen and Graz, and with the Midi-Pyrénées Observatory, stratifications of physical parameters, dynamics, evolution, and mutual relations of various types of sunspot fine structures as well as organized flows around sunspots and pores are analyzed. Observations obtained with extremely high spatial resolution (0.12") at the 1-m Swedish Solar Telescope, La Palma, are utilized to refine the current knowledge about the detailed structure of sunspots, small-scale magnetic elements, and solar granulation.

The organization of line-of-sight velocities in evolving magnetic fields of active regions is investigated and the correlation of dynamical changes in magnetic and velocity fields with other activity phenomena is studied. Processes in deeper layers of the convection zone, with dominant influence on the dynamo action, manifest themselves partially in large-scale and global flows in the photosphere. We study velocity fields of these flows using surface magnetic fields and supergranules as tracers. Moving magnetic fields are extrapolated to the corona and compared with observed coronal structures. Global velocities derived from supergranular motions as well as from surface magnetic flux transport are used to study the differential rotation of the Sun, meridional circulation in the photosphere and long-term properties of mean velocity components. Detailed data from the regions occupied by local magnetic fields are used to study the coupling between the surface flows, the underlying magnetic fields, and active phenomena.



(List of grants 1998 - 2008)

Grant Agency AS CR

Grant Agency of the Czech Republic

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