MHD models of the corona
Cool stars like our Sun are surrounded by a million Kelvin hot outer atmosphere, the corona. It is still puzzling what sustains its high temperature, being 100 to 1000 times hotter than the stellar surface. Being related to (changes of) the magnetic field, we can expect the heating mechanism to change the structure of the corona, to drive plasma flows, and to induce wave phenomena. On the Sun we can observe this dynamic evolution of the corona in detail, especially through spectroscopy and imaging at extreme ultraviolet and X-ray wavelengths.
In our group we employ magneto-hydrodynamics (MHD) models including the synthesis of coronal emission. Numerical experiments in 1D, 2D and 3D allow us to directly compare the emission of the synthetic corona to real observations. This aims at understanding the distribution of the heating rate in space and time to understand which coronal heating mechanism(s) produce the hot corona and drive its sometimes violent dynamics.
Visualization of the setup of a coronal simulation. This shows the magnetic field at the bottom of the computational box (greyscale) and the location of the transition region from the chromosphere into the corona (yellow-green). Also shown is a vertical cut through the 3D domain displaying the density in the corona, a coronal loop with enhanced density (yellow) is seen within the ambient corona at lower densities (orange-red).
The problem of coronal heating is considered one of the most interesting problems in stellar astrophysics. Using advanced numerical experiments including the synthesis of coronal emission allows us to study the processes heating the corona and driving its dynamics.
- Dynamic response of the solar corona to driving on the solar surface
- Distribution of the coronal heating rate in space and time
- Matching the emission of a synthetic corona to real observations
- Understanding the variability of the solar coronal emission
- Scaling solar coronal models to other stars
To reach these science goals we employ and further develop different numerical codes to solve the MHD equations, mostly the Pencil Code.The coronal emission that can be expected from the models we synthesize the CHIANTI atomic data base. We compare these model results to solar observations with, e.g., the SUMER EUV spectrograph on SOHO, the Extreme ultraviolet Imaging Spectrometer (EIS) on Hinode, the Atmospheric Imaging Assembly (AIA) on SDO, and most recently the Interface Region Imaging Spectrograph (IRIS).
