CORONAL HEATING THROUGH BRAIDING OF MAGNETIC FIELD LINES SYNTHESIZED CORONAL EUV EMISSION AND MAGNETIC STRUCTURE

摘要

The lower corona and transition region of the Sun are highly structured through the magnetic field, and are very dynamic. To account for both the structure and the dynamics an 3D MHD model of a small active region in the corona is employed, with the heating being due to braiding of magnetic field lines. Based hereupon we derive the EUV emission line profiles from the transition region and corona, which can be directly compared to observations. The flux-braiding heating results in the right differential emission measure (DEM) curve, i.e. we can reproduce the increase of DEM for low temperatures, without any spurious assumptions. Furthermore the Doppler shifts of the synthesized lines match the observed Doppler shifts strikingly well, and also the temporal variability described by the rms fluctuations of line intensity and shift compares very well with the observations. Using the synthesized spectra we explore the relation of the transition region and coronal emission to the coronal magnetic field, which is not directly accessible to observations. We discuss these results with respect to the connectivity from the chromosphere to the corona and the plasma-β.To our knowledge this is the first coronal model to reproduce all these features qualitatively and quantitatively. It also provides a unique tool to explore stellar coronae and by this can be used to help defining new proposals for future instrumentation.