Measurement of coronal magnetic fields
Research report (imported) 2004 - Max Planck Institute for Solar System Research
The solar corona harbors gas at temperatures of more than a million degrees. This gas is predominantly trapped on arch-like structures formed by loops of magnetic field. The high temperature and the structure of the coronal gas are attributed to the solar magnetic field. The high degree of order in the corona traces back to the fact that hot gas must follow magnetic field lines. Also magnetic current sheets (“jumps” in the magnetic field) are able to release thermal energy and thus heat the gas. The measurement of coronal magnetic fields is, however, not trivial: the low gas density leads to a weak signature in the spectral lines, i.e. the splitting and polarization caused by the Zeeman-effect. Also, with increasing distance from the solar surface, an effect starts to operate which influences the polarization of the absorbed light. The Max Planck Institute for Solar System Research in Katlenburg-Lindau (MPS) successfully contributed to the solution of this difficult problem of measuring the coronal magnetic field. Two different methods of direct measurement of the magnetic field have been applied: coronal seismology and infrared polarimetry. In addition, based on mathematical models it is possible to infer the coronal magnetic field structure from extrapolations of the reliably determined photospheric magnetic field.