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

Abstract

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, sinuous filament channels. The key processes that form and evolve the channels operate on still smaller spatial scales and much longer timescales, culminating in a vast separation of characteristic lengths and times that govern these explosive phenomena. In this article, we describe implementation and tests 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, reduced representation of helicity condensation: a process wherein small-scale vortical surface convection forms ubiquitous current sheets and pervasive reconnection across the sheets mediates an inverse cascade of magnetic helicity and free energy, thereby forming the filament channels. We have developed a formalism, STITCH, that abstracts these complex processes into a single term in Ohm’s law and 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, while enabling substantial reductions in temporal duration and spatial resolution. In addition, 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.

The Role of Magnetic Shear in Reconnection-driven Flare Energy Release

“…This simulation was performed with the Adaptively Refined Magnetohydrodynamics Solver (ARMS; DeVore & Antiochos 2008) and employed an idealized magnetic configuration consisting of two sets of dipoles located just beneath the solar surface at the equator, forming an elongated polarity inversion line aligned with the equator. Shear flux was injected at this PIL using the STITCH method (Dahlin et al 2022b, and references therein) to form a filament channel that eventually erupted via the breakout mechanism (Antiochos et al 1999).…”

Modeling a Coronal Mass Ejection from an Extended Filament Channel. II. Interplanetary Propagation to 1 au

“…In Paper I, the pre-eruption corona was modeled with a low-order spherical harmonic expansion based on the GONG synoptic map for Carrington Rotation 2165 with an isothermal Parker (1958) solar wind for T = 1.4 MK. The extended filament channel was energized with the STatistical InjecTion of Condensed Helicity (STITCH; Dahlin et al 2022) procedure to introduce sheared horizontal flux along the PIL. The filament eruption begins from the eastern limb and progresses toward the western limb, resulting in a skewed, asymmetric CME flux rope structure, propagating approximately 30°south of the ecliptic plane but expanding significantly in latitude, in agreement with remote-sensing observations of the solar disk and corona.…”