Wednesday

Magnetic field in the solar photosphere is inhomogeneous at scales as small as few kilometres. Observations with limited resolution yield the magnetic flux per pixel, rather than the actual (intrinsic) magnetic field. Usually, the intrinsic photospheric magnetic field is evaluated using the magnetic line ratio (MLR) method (see e.g. Smitha & Solanki 2017), which is reliable for moderate magnetic field values, but saturates above 1-2 kG. Gordovskyy et al. (2018) suggested an alternative method, based on measuring the widths of Stokes V peaks, which does not show saturation for stronger fields.

In this study, 3D MHD models of magneto-convection in the photosphere developed using the MURAM code and the NICOLE radiative transfer code are used to calibrate and test the SVW method for several classical magnetographic lines. We show that the SVW does not saturate for fields up to 2-3 kG and, unlike MLR, requires observations in minimum one spectral line, making it a very promising method for fast photospheric field measurements using the existing spectrapolarimetric data, as well as observation from the forthcoming optical solar instruments, such as DKIST.