Swiss Virtual Institute for Solar Science
Magnetic fields
Solar Magnetic Fields
One of the areas in which ETH Zurich has played the internationally leading role over the past decades is in the exploration of solar magnetic fields at the smallest spatial scales. The magnetic field is the key physical parameter that governs the structuring, variability, and thermodynamics of the solar atmosphere, processes that are prototypical for the atmospheres of other stars. It is now realized that the magnetoturbulence of the photospheric plasma generates a fractal-like pattern that continues on scales well beyond the resolution limits of current telescopes (cf. figure below). At ETH Zurich diagnostic techniques to explore the properties of this field at scales beyond the resolution limit have been developed.
Illustration of the fractal-like pattern of magnetic fields on the quiet Sun. The rectangular area covered by the left map is about 15% of the area of the solar disk, while the map to the right covers an area that is 100 times smaller. The two maps represent patterns of circular polarization caused by the Zeeman effect. The blue and red areas correspond to magnetic flux of positive and negative polarities, separated by green voids of seemingly no flux. Analysis of Hanle-effect observations of atomic and molecular lines made at IRSOL have now shown that these green regions are actually no voids at all, but are teeming with turbulent magnetic fields that carry a significant magnetic energy density. Since these turbulent fields are tangled with mixed polarities on very small scales, they are invisible to the Zeeman effect, while they get revealed by the Hanle effect, based on the Second Solar Spectrum. From Nature 430 (2004), 304-305.
Solar magnetic fields
are successfully studied with novel diagnostics based on molecular
spectro-polarimetry. Here ETH Zurich has the world leading position. In
the presence of a magnetic field many molecular spectral lines exhibit
the Zeeman effect and, thus, are useful to diagnose cool magnetized
stellar atmospheres. For instance, molecular lines are formed at
different heights of the sunspot atmosphere and are also strongly
temperature and pressure sensitive. Therefore, an analysis of their
Stokes profiles provides valuable information on the thermal and
magnetic structure of sunspots. The exploration of the molecular Zeeman,
Paschen-Back and Hanle effects is carried out in close collaboration of
ETH Zurich and IRSOL where polarimetric records of many molecular
transitions in the presence of magnetic fields have been recorded for
the first time.