Solar Physics Key concepts

Atomic concepts to know for the NF2 / solar-coronal-field project.

One-line story

The project story is: magnetic fields organise the corona, but we mainly observe the lower boundary, so extrapolation methods use physics assumptions to infer the 3D coronal field. NF2 is one modern neural/PINN-flavoured way to do that extrapolation.

Magnetic-field modelling hierarchy

• Potential field extrapolation — current-free baseline, $\nabla \times \mathbf{B}=0$.
• Force-free and NLFFF coronal fields — Lorentz-force-free model, $(\nabla \times \mathbf{B})\times \mathbf{B}=0$.
• Full MHD — dynamic plasma model; important context, but outside Andrew’s immediate project scope.

Why extrapolation is needed

• Coronal magnetic-field extrapolation as an inverse problem — infer 3D coronal fields from lower-boundary observations.
• Photosphere versus corona force-free assumption — the data are measured where force-freeness is least clean. Classic solar-physics stitch-up.

Neural / NF2 concepts

• NF2 and physics-informed neural coronal extrapolation
• Residuals in NF2 and PINNs
• NF2 diagnostics for physical credibility

Data concepts

• SHARP data product
• HARP active-region patch ID
• CEA projection
• HMI SHARP CEA vector components
• NOAA AR 11158 as an NF2 benchmark

Parent / nearby maps

• Solar Physics index
• NF2 solar extrapolation MOC