Data-driven Radiative Magnetohydrodynamics Simulations with the MURaM code: the Emerging Active Region Corona

TL;DR

Data-driven radiative MHD simulations with the MURaM code model the emergence and evolution of active region AR11640 over four days by coupling a fast zero-$\beta$ MHD evolution of the coronal magnetic field to slower, physics-rich radiative MHD runs. The bottom boundary is driven by time-dependent observed $B_z$ using a constrained horizontal electric field with a twist parameter $\Omega$, enabling one-to-one comparisons with observations. Synthesized EUV emission from the radiative runs reproduces key coronal loop structures and reveals in 3D the distribution of heating and wave-like plasma dynamics, while highlighting boundary/topology limitations that affect large-scale connectivity. The study demonstrates a practical, extensible framework for data-driven AR corona modeling and provides a platform for investigating coronal heating and wave energetics in evolving active regions.

Abstract

We present the application of the data-driven branch of the MURaM code, which follows the evolution of the actual active region over 4 days and reproduces many key coronal extreme-ultraviolet (EUV) emission features seen in remote sensing observations. Radiative magnetohydrodynamic (MHD) simulations that account for sophisticated energy transport processes, such as those in the real corona, have been extended with the ability to use observations as time-dependent boundaries, such that the models follow the evolution of actual active regions. This opens the possibility of a one-to-one model of a target region over an extensive time period. We use a hybrid strategy that combines fast-evolving idealized zero-$β$ models that capture the evolution of the large-scale active region magnetic field over a long time period and sophisticated radiative MHD models for a shorter time period of interest. Synthesized EUV images illustrate the formation of coronal loops that connect the two sunspots or fan out to the domain boundary. The model reveals in three-dimensional space the finer structures in the coronal heating and plasma properties, which are usually concealed behind the EUV observables. The emission-measure-weighted line-of-sight velocity, which represents the Doppler shift of a spectral line forming in a certain temperature range, reveals vigorous dynamics in plasma at different temperatures and ubiquitous MHD waves, as expected in the real solar corona.

Figures (11)

• Figure 1: The upper panels show the evolution of the observed radial magnetic field of AR11640. Only the central part of the padded array is displayed. The lower panels present the coronal magnetic field in the Bevo_$\Omega$0 run. The angle of view in each panel is set to reflect in the position of the active region on the solar disk at the observed time. The grayscale images show $B_{z}$ at the bottom of the simulation domain. Magnetic field lines are calculated from static seed points that are uniformly distributed in the central part of the domain.
• Figure 2: A comparison of the observed and synthesized AIA 171 images of AR11640. The actual AIA 171 images captured at 2$^{\rm h}$0$^{\rm m}$ UT are displayed in the upper row on a logarithmic scale between 20 and 2000 DN/s/pixel. The synthesized 171 images from the radiative MHD models with $\Omega=0$ (see main text for details) are shown in the lower panels on a logarithmic scale between 10 and 1000 DN/s/pixel. The view angles of the synthesized images are chosen according to the locations of the actual active region on the solar disk on the corresponding days.
• Figure 3: A comparison of synthesized EUV emission from run cases with different $\Omega$ parameter that adds additional twist in the magnetic field while keeping the vertical component unchanged (see main text for details). Each column presents the results from a certain $\Omega$ value. The upper two rows show AIA 171 images from models on Day 1 and Day 2, respectively. The third row displays AIA 131 images, which in this active region highlights cooler plasma, and the bottom row displays AIA 193 images that reveal hotter plasma around 1.5 MK.
• Figure 4: Coronal density and temperature as a function of height. The results from 4 run cases, as indicated by the legend, are compared. The data are averaged over time for a period of more than 1 hour. The 3D cube is averaged in the horizontal dimensions, which provides the height profile shown here. The axis of height is displayed on a logarithmic scale, such that the lower atmosphere of a stronger stratification is stretched, whereas the coronal part with a much larger scale height is compressed. The vertical dashed line is placed at 70 grid point (4.48 Mm) above the bottom boundary and indicates the bottom of the corona or say the top of the transition region.
• Figure 5: A 3D rendering of the coronal density and temperatures in the $\Omega0$ and $\Omega3$ models on Day 2. The opaque features display the plasma density. Only the density values of the loops connecting the sunspots are illustrated, by forcing lower values in the coronal volume to be completely transparent. The density features are colored according to their temperature, as indicated by the color bar. The top and bottom rows show an inclined side view and a top-down view, respectively.