Photospheric Magnetograph Discrepancies and Diversity of Longitudinal Zeeman Splitting

For at least six decades Zeeman effect measurements of average longitudinal magnetic flux density in the solar photosphere using different magnetographs have systemically disagreed, sometimes by large factors. Furthermore, when these measurements are used to estimate the Sun’s open magnetic flux, in situ observations usually show substantially larger true values. Over the decades these discrepancies have been attributed to numerous causes. Wang et al. (2022 ApJ 926, 113) using earlier results from Ulrich et al. (2009 SoPh 255, 53) showed that accounting for variations of the longitudinal Zeeman splitting of different spectrum lines resolves the discrepancies between two magnetographs and also between inferred and actual open magnetic fluxes. Here this work is extended by surveying and analyzing spectropolarimetric observations of longitudinal Zeeman splitting of a wide range of spectrum lines (Stenflo, J.O. 2014, in R. Ramelli (ed.), http://www.irsol.usi.ch/data_archive/#ftsv). Almost all photospheric spectrum lines show weaker inferred longitudinal flux density relative to consistent maximum values found near the cores of spectrum lines having damping wings. To first order, the observed flux density in most photospheric spectrum lines is closely related to the depth within a line profile.