Search

For modelling the upper solar photosphere and chromosphere, plasma forces are important. Therefore a nonlinear magnetohydrostatic (NLMHS) model is a better approximation of the physical state in these layers than a nonlinear force-free (NLFF) model. The latter one is only valid in the low plasma-beta corona. The magnetohydrostatic model computes self-consistently the magnetic field and plasma distribution. We intensively tested the new code with exact equilibria (Zhu & Wiegelmann, 2018, ApJ, 866, 130) and the NLMHS code has been able to meaningfully recover the plasma density, pressure and magnetic field. Here we present a first application of our new code to an active region (AR 11768), which was observed by IMaX during the second flight of the balloon-borne SUNRISE solar observatory in 2013. The high spatial resolution IMaX vector magnetogram was embedded in SDO/HMI data to cover the entire active region. We were able to model the non-force-free layer in the lower atmosphere. Our model shows strongly localized electric currents and Lorentz forces and self-consistently the corresponding plasma distribution. Such features require the use of a NLMHS model and cannot be reconstructed with linear MHS or NLFFF models. [ABSTRACT FROM AUTHOR]

Modelling the solar coronal magnetic field in 3D is aninteresting research topic on its own right.But field models are also important for combiningthe analysis of data from remote sensing and in-situ instrument on SolarOrbiter by providing the magnetic connectivity. A well tested and frequently applied methodis to use photospheric field measurements, e.g. synoptic vector magnetogramsfrom SDO/HMI, and extrapolate them into the solar corona under the assumptionthat the field is force-free. We do this by a nonlinear force-free code,based on minimizing a functional. The method is very flexible and allowsto incorporate loop shapes from coronal images. Ongoing projects are to gobeyond the force-free approximation, which is necessary in the outer solarcorona beyond the source surface. A first step are magneto-staticextrapolations (including plasma pressure gradient and gravity force).In a second step we compute stationary MHD-equilibria which additionallyconsider the solar wind flow. [ABSTRACT FROM AUTHOR]

Accurately measuring the magnetic field in the solar corona is extremely difficult and hence our knowledge of the coronal magnetic field structure relies on the extrapolation of magnetic field measurements in the lower regions of the solar atmosphere into the corona. Whereas the solar corona generally is a domain of low plasma-beta with largely force-free magnetic fields, this is not the case for the lower parts of the solar atmosphere where the magnetic is measured and the magnetic fields there should be calculated using (non-force-free) magnetohydrostatic equilibria. In this contribution we present a new family of analytical magnetohydrostatic equilibria which could be used as relatively simple and computationally cheap alternative to numerical modelling methods. These equilibria have the capability of combining a non-force-free layer with a domain of linear force-free magnetic field, including a smooth transition between these two domains. The methodology used to calculated these equilibria is based on work by Low (e.g. Low 1991) in the form given by Neukirch and Rastätter (1999).Low, B.C., ApJ 370, 427Neukirch, T. & Rastätter, L., A&A 348, 1000 [ABSTRACT FROM AUTHOR]