Global MHD Simulations of the Time-Dependent Corona

TL;DR

This paper presents a new method for incorporating time-dependent surface flux evolution into global MHD models of the solar corona, enabling more realistic simulations of solar phenomena and their impact on the solar wind.

Contribution

The authors introduce a novel correction technique for the electric field boundary condition in MHD models, improving the accuracy of time-dependent solar corona simulations.

Findings

The method accurately reproduces known flows and electric fields in verification tests.

Time-dependent modeling shows evolving open flux boundaries and EUV emission.

Driving surface flux alone does not significantly alter charge state ratios in the solar wind.

Abstract

We describe, test, and apply a technique to incorporate full-sun, surface flux evolution into an MHD model of the global solar corona. Requiring only maps of the evolving surface flux, our method is similar to that of Lionello et al. (2013), but we introduce two ways to correct the electric field at the lower boundary to mitigate spurious currents. We verify the accuracy of our procedures by comparing to a reference simulation, driven with known flows and electric fields. We then present a thermodynamic MHD calculation lasting one solar rotation driven by maps from the magnetic flux evolution model of Schrijver & DeRosa (2003). The dynamic, time-dependent nature of the model corona is illustrated by examining the evolution of the open flux boundaries and forward modeled EUV emission, which evolve in response to surface flows and the emergence and cancellation flux. Although our main goal is to present the method, we briefly investigate the relevance of this evolution to properties of the slow solar wind, examining the mapping of dipped field lines to the topological signatures of the "S-Web" and comparing charge state ratios computed in the time-dependently driven run to a steady state equivalent. Interestingly, we find that driving on its own does not significantly improve the charge states ratios, at least in this modest resolution run that injects minimal helicity. Still, many aspects of the time-dependently driven model cannot be captured with traditional steady-state methods, and such a technique may be particularly relevant for the next generation of solar wind and CME models.