Kleinskalige Magnetfelder der Sonne und ihr Einfluß auf Chromosphäre, Übergangszone und Korona

Abstract

During coordinated international observation campaign with the ground-based telescopes GCT (Gregory-Coudé-Telescope) and VTT (Vacuum-Tower-Telescope) and the UV/EUV Telescope SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on board the space probe SOHO (Solar and Heliospheric Observatory) a region of small-scale magnetic field structures that belong to the chromospheric network in the center of the solar disk were recorded as a rotation compensated time series for about three hours using the photospheric Fe I line at 630.25 nm, the chromospheric Ca II K line at 393.3 nm, the C I line at 156.10 nm which also belongs to the chromosphere, the C IV line at 154.82 nm which originates in the transition region and the coronal Ne VIII line at 77.04 nm. Information about the photospheric magnetic field was taken from the data set which was generated in the Fe I line using the method of two-dimensional spectro-polarimetry and was presented as a set of images. These images were the basic information source for calculations of magnetic field extrapolation in potential field approximation. Space-time-diagrams from spectra of all lines of intensity and velocity distribution were provided, furthermore wavelength-time-diagrams were assembled from spectra of UV/EUV lines which were observed by the SUMER instrument. In a synoptic view these data sets permit a comprehension of complex and highly dynamic processes of the solar plasma in both a spatial and temporal way. So, for example one could note that despite of the fact that correlated brightenings in different EUV lines at lower intensity can be seen, especially in cases of explosive events and strong brightenings no simultanious reactions in the C IV and the Ne VIII spectra occurred. Basically, the dynamics of the Ne VIII line seem to be almost independent of the C IV line. Moreover during a twelve minute burst of explosive events a highly variable magnetic field of positive polarity could be identified. In addition it has been discovered that the brightenings of the EUV lines which belong to higher layers of the solar atmosphere do not match the magnetic patterns on the photospheric level. That is why it is difficult to deduce the causes of brightenings in the transition region and lower corona directly from the dynamics of the photospheric magnetic fields. In the several thousand kilometers enclosing layer between the photosphere and the lower corona, which is characterized by a dramatic decrease of pressure and density as well as a massive increase of temperature, magneto-hydrodynamic considerations let appear relative complicated magnetic field configurations very plausible. For example, magnetic flux tubes expand substantially with decreasing pressure (canopy-effect). Due to dynamic events flux tubes can also be strongly bent, twisted or deformed in other ways. So those complex and also dynamically magnetic structures of the solar plasma, which in higher layers leed to brightenings, show geometrically no similarity to the pattern of the magnetic areas on the photospheric level.