Speaker
Description
We investigate the height dependence of the line-of-sight (LOS) magnetic field in an active-region (AR) plage from the upper photosphere to the upper chromosphere using co-spatial ultraviolet (UV) and infrared (IR) spectropolarimetric observations. We analyze the Stokes I and V profiles acquired during the Sunrise III stratospheric balloon flight with the SUSI and SCIP instruments. The Ca II K line observed by SUSI and the Ca II 8542A line observed by SCIP provide complementary chromospheric diagnostics, while nearby Fe I lines sample photospheric layers. The LOS magnetic field is inferred by applying the weak field approximation (WFA) within a Markov chain Monte Carlo (MCMC) framework, allowing us to obtain best-fit values and confidence intervals. The photospheric Fe I lines reveal strong, finely structured magnetic fields reaching up to ∼1.2 kG. In contrast, the chromospheric Ca II diagnostics yield systematically weaker magnetic fields, typically in the range ∼100–400 G, and with a more spatially diffuse distribution. Furthermore, magnetic-field maps inferred from the Ca II K line, formed in the upper chromosphere, appear smoother and more extended than those derived from the Ca II 8542A line, which forms lower in the chromosphere. These results provide quantitative observational evidence that AR magnetic fields weaken and expand with height, transitioning from kilogauss, highly structured photospheric concentrations to weaker, more diffuse fields in the upper chromosphere.