Magnetic Energization of the Corona
Structures in the corona often exhibit features of magnetic non-potentiality - magnetic energy above the potential state (the lowest energy state possible). Magnetic shear/twist is especially evident along magnetic polarity inversion lines (PILs), in the form of prominences (referred to as filaments when seen on the disk), and is also present in active regions. This energization of the magnetic field can structurally change the shape of the overlying streamers and the connectivity of the underlying fields.
Sources of this energization include currents present in active region fields when they emerge from below the photosphere, large-scale photospheric motions (e.g. meridional flow and differential rotation), and smaller scale flows (e.g. supergranular motions). We assimilate the radial magnetic field (Br), which provides no information about the magnetic shear.
In earlier coronal eclipse simulations based on static magnetic maps, we noticed that introducing shear along selected PILs resulted in more realistic coronal structures that matched better with observations (Mikic et al. 2018). For the 2024 eclipse, we developed a procedure to continuously introduce shear into the magnetic field by automatically identifying PILs and applying time-dependent electric fields at the boundary. We again apply this procedure (described by Downs et al. 2025) for the 2026 eclipse. The bottom left figure shows the continuously updated PIL identification (colored by length). The time-dependent electric fields are controlled by a potential function Φ shown below on the right. This potential is added to the potential described here.
The introduction of this magnetic shear/twist, combined with flux emergence and cancellation in the flux transport model, leads to occasional eruptions and small CMEs in the MHD model. On the real Sun, active regions can emerge with highly energized fields that can lead to major eruptions (X-class flares and wide, fast CMEs). Our procedure will not produce such strongly energized fields, so our model will not predict such events.
