Research example:
High-resolution 1:1 model on an active region

The goal is to employ a 3D magnetohydrodynamics (MHD) model including spectral synthesis to model the corona in an observed solar active region. This will allow us to judge on the merits of the coronal heating mechanism built into the 3D model.

Photospheric observations of the magnetic field and horizontal velocities in an active region are used to drive our coronal simulation from the bottom. The currents induced by this heat the corona through Ohmic dissipation. Heat conduction redistributes the energy that is in the end lost through optically thin radiation. Based on the MHD model we synthesize profiles of coronal emission lines which can be directly compared to actual coronal observations of the very same active region.

In the synthesized model data we find hot coronal loops which host siphon flows or which expand and lose mass through draining. These synthesized loops are at the same location and show similar dynamics in terms of Doppler shifts as the actually observed structures, as shown in the figure below. This match is shown through a comparison with Hinode data as well as with three-dimensional stereoscopic reconstructions of data from STEREO.

The considerable match to the actual observations shows that the field-line braiding mechanism leading to the energy input in our corona provides the proper distribution of heat input in space and time. From this we conclude that in an active region the field-line braiding is the dominant heating process - at least on the spatial scales available to current observations.

click on image for a larger version
Direct comparison between observations and 3D MHD forward model. The left column shows the active region as observed by EIS on 14.Nov.2007. Panel (a) displays the intensity map in Fe XV (284 Å) on a linear inverse scale normalized to the peak intensity. In panel (c) we plot the Doppler map in Fe XII (195 Å). The scale of the doppler map covers ±10km/s. The right column shows the corresponding quantities synthesized from the 3D MHD model with the same color coding.
A short loop system can be seen spanning from one of the two main polarities to the network of the quiet Sun (SL 1-3), as well as a loop (system) in the core of the AR between the two main polarities (CL 1). In the model we traced two magnetic fieldlines, rooted in the centers of CL 1 and 2, that are overplotted in green. The circles are located at the same positions in all panels.

More inforation can be found in the following publications:

Observationally driven 3D MHD model of the solar corona above an active region
Bourdin Ph.A, Bingert S., Peter H. (2013) A&A 555, A123
Link to ADS

Coronal loops above an active region: Observation versus model
Bourdin Ph.A, Bingert S., Peter H. (2013) PASJ 66, S7
Link to ADS

Coronal energy input and dissipation in a solar active region 3D MHD model
Bourdin Ph.A, Bingert S., Peter H. (2013) A&A, in press (arXiv:1507.03573)
Link to ADS