A comparison of solar proxy-magnetometry diagnostics

Aims. We test various proxy-magnetometry diagnostics, i.e., brightness signatures of small-scale magnetic elements, for studying magnetic field structures in the solar photosphere. Methods. Images are numerically synthesized from a 3D solar magneto-convection simulation for, respectively, the G band at 430.5 nm, the CN band at 388.3 nm, and the blue wings of the H alpha, H beta, Ca II H,and Ca II 854.2 nm lines. Results. Both visual comparison and scatter diagrams of the computed intensity versus the magnetic field strength show that, in particular for somewhat spatially extended magnetic elements, the blue H alpha wing presents the best proxy-magnetometry diagnostic, followed by the blue wing of H beta. The latter yields higher diffraction-limit resolution. Conclusions. We recommend using the blue Ha wing to locate and track small-scale photospheric magnetic elements through their brightness appearance.