AWSoM Magnetohydrodynamic Simulation of a Solar Active Region with Realistic Spectral Synthesis

Abstract

For the first time, we simulate the detailed spectral line emission from a solar active region (AR) with the Alfvén Wave Solar Model (AWSoM). We select an AR appearing near disk center on 2018 July 13 and use the National Solar Observatory’s Helioseismic and Magnetic Imager synoptic magnetogram to specify the magnetic field at the model’s inner boundary. To resolve small-scale magnetic features, we apply adaptive mesh refinement with a horizontal spatial resolution of 0°.35 (4.5 Mm), four times higher than the background corona. We then apply the SPECTRUM code, using CHIANTI spectral emissivities, to calculate spectral lines forming at temperatures ranging from 0.5 to 3 MK. Comparisons are made between the simulated line intensities and those observed by Hinode/Extreme-ultraviolet Imaging Spectrometer where we find close agreement across a wide range of loop sizes and temperatures (about 20% relative error for both the loop top and footpoints at a temperature of about 1.5 MK). We also simulate and compare Doppler velocities and find that simulated flow patterns are of comparable magnitude to what is observed. Our results demonstrate the broad applicability of the low-frequency AWSoM for explaining the heating of coronal loops.

AWSoM Magnetohydrodynamic Simulation of a Solar Active Region. II. Statistical Analysis of Alfvén Wave Dissipation and Reflection, Scaling Laws, and Energy Budget on Coronal Loops

“…For more details about the model in general, refer to van der Holst et al (2014van der Holst et al ( , 2022 and Sachdeva et al (2019Sachdeva et al ( , 2021. For more details about the input parameters, magnetogram, and boundary conditions of this specific simulation, refer to Shi et al (2022).…”

“…The above-mentioned numerical MHD models either focus on a single coronal loop/flux tube, or are confined in a Cartesian box, often with periodic boundary conditions. While such regional models do have huge advantages in high numerical resolution and the possibility to include more physical processes, they do not address the relation between the AR and the global solar corona, connections between the AR and quiet regions/coronal holes, possible open magnetic fields originating near an AR (see an example that is simulated and confirmed by observation in Shi et al 2022), or simulate specific coronal observations (e.g., a total eclipse). Mikić et al (2018) updated the global 3D MHD code MAS (Mikić et al 1999;Lionello et al 2001) to include a physics-motivated transport of low-frequency Alfvén wave turbulence with a phenomenological dissipation rate, by advancing the Alfvén wave amplitude in terms of the Elsässer variables (Matthaeus et al 1999;Lionello et al 2009;Verdini et al 2010;Zank et al 2012).…”

Nonequilibrium Ionization Effects on Synthetic Spectra in the AWSoM Solar Corona

“…In SWMF the spectral calculations used to be performed as a postsimulation step either on a Cartesian box (Szente et al 2019) or the original grid (Shi et al 2022). SPECTRUM has now been fully implemented into the Block Adaptive Tree Solarwind Roe Upwind Scheme (Powell et al 1999), so that the LOS integration of the spectral emission is calculated on the original, block adaptive grid, along with the simulation, in the same way as in Downs et al (2010).…”

Solar Wind Modeling with the Alfvén Wave Solar atmosphere Model Driven by HMI-based Near-real-time Maps by the National Solar Observatory

“…In particular, the modeled CH from the GONG-driven simulation appears to be much darker. Additional refinement of the grid with the AWSoM model can further improve model comparisons by producing brighter active regions (Shi et al 2022).…”