A Subgrid-scale Model for Energy Buildup in the Solar Corona

The solar corona routinely exhibits explosive activity, in particular coronal mass ejections and their accompanying eruptive flares, which have global-scale consequences. These events and their smaller counterparts, coronal jets, originate in narrow filament channels. The key processes that form and evolve the channels operate on still smaller spatial scales and much longer time scales, culminating in a vast separation of the characteristic lengths and times that govern these explosive phenomena. We describe implementation of an efficient subgrid-scale model for generating eruptive structures in magnetohydrodynamics (MHD) coronal simulations. STITCH – Statistical InjecTion of Condensed Helicity – is a physics-based, idealized representation of helicity condensation. In this process, small-scale vortical surface motions inject magnetic helicity, form ubiquitous current sheets, and induce pervasive reconnection across the sheets, which mediate an inverse cascade of magnetic helicity and free energy that forms the filament channels. Our formalism, STITCH, abstracts these complex processes into a single term in the induction equation that directly injects tangential magnetic flux into the low corona. We show that our approach is in very good agreement with a full helicity condensation calculation that treats all of the dynamics explicitly, but simultaneously enables very substantial reductions in temporal duration and the required spatial resolution. We illustrate the flexibility of STITCH at forming localized filament channels and at energizing complex surface flux distributions that have sinuous boundaries. STITCH is simple to implement and computationally efficient, making it a powerful technique for physics-based modeling of solar eruptive events.

This work was funded by NASA ISFM and LWS Programs.