Speaker
Description
The weak-field approximation (WFA) is extensively used to infer solar magnetic fields due to its simplicity and low computational cost, often being applied beyond its formal range of validity. In this work, we reassess its limitations using Generalized Response Functions (GRFs), which quantify the sensitivity of WFA-derived magnetic fields to atmospheric parameters. We derive analytical expressions for these GRFs and evaluate them using synthetic Stokes profiles for representative spectral lines.
Our analysis shows that the WFA depends strongly on the atmospheric magnetic structure (strenght and inclination). We find that the approximation departs from the true magnetic field well below the nominal saturation limit, primarily due to the breakdown of the linear relation between Stokes $V$ and the intensity derivative. Revisiting the original perturbative formulation clarifies that this loss of linearity and the impact of inclination are intrinsic limitations, indicating that the WFA is often applied outside its domain of validity.