Simulating a Solar Flare from Emergence to Eruption

Visualization of coronal temperature after simulated flare
Visualization of coronal temperature after simulated flare. Plasma with a temperature of less than 1 million K is shown in violet, plasma with temperatures from 1-10 million K in red and plasma with more than 10 million K in green. The simulation domain has a horizontal extent of 100,000 km and reaches from 7,000 km beneath the solar photosphere to 42,000 km into the corona.

Solar flares are a key process for understanding the solar origins of space weather events. Solar flares are a multi-scale multi-physics problem that cannot be captured in a single comprehensive model. On the largest scales models need to capture the slow energization of the solar corona over time scales of hours to days in response to new magnetic flux emerging from the solar interior into the solar atmosphere, which leads ultimately to a rapid release of energy on time scale of minutes. As part of larger team effort HAO advanced the capability of the MURaM radiative MHD code to specifically cope with the challenges of solar flares. The resulting extended version of the MURaM radiative MHD code is capable of simulating the coupled solar atmosphere from the upper convection zone into the lower solar corona covering a density contrast of more than 1012. This code was used to simulate the entire life cycle of a solar flare starting with the slow energy built up due to new magnetic flux emerging into the solar corona, fast release of the stored magnetic energy through reconnection leading to substantial heating of the corona, and distribution of the released energy through a combination of heat conduction and plasma flows. The simulation includes the relevant physics needed to synthesize synthetic emission from visible light to extreme UV and X-rays and allows for detailed comparison with available multi-wavelength observations. Specifically this simulation demonstrated the ability to reproduce:

  • GOES X-ray light curves with a fast rise and slow decay
  • Temperature dependence of flows from flare arcade footpoints, showing a transition from down to up flows at a temperature of a few million K
  • Multi-thermal X-ray spectra as consequence of a multi-thermal corona that can have power-law shape even in the absence of a non-thermal particle population
  • Non-Gaussian line-shapes as a result of a superposition of Doppler shifted multi-thermal components
  • Concentrated electron heat fluxes in excess of 1011 erg/cm 2/s in the flare ribbons

 

Cheung, M.C.M, Rempel, M. & 12 co-authors, 2019: A comprehensive three-dimensional radiative magnetohydrodynamic simulation of a solar flare, Nature Astronomy, Volume 3, p. 160-166, doi:10.1038/s41550-018-0629-3.