DETERMINING THE MAGNETIZATION OF THE QUIET SUN PHOTOSPHERE FROM THE HANLE EFFECT AND SURFACE DYNAMO SIMULATIONS

Abstract

The bulk of the quiet solar photosphere is thought to be significantly\nmagnetized, due to the ubiquitous presence of a tangled magnetic field at\nsubresolution scales with an average strength <B> ~ 100 G. This conclusion was\nreached through detailed three-dimensional (3D) radiative transfer modeling of\nthe Hanle effect in the Sr I 4607 line, using the microturbulent field\napproximation and assuming that the shape of the probability density function\nof the magnetic field strength is exponential. Here we relax both\napproximations by modeling the observed scattering polarization in terms of the\nHanle effect produced by the magnetic field of a 3D photospheric model\nresulting from a (state-of-the-art) magneto-convection simulation with surface\ndynamo action. We show that the scattering polarization amplitudes observed in\nthe Sr I 4607 line can be explained only after enhancing the magnetic strength\nof the photospheric model by a sizable scaling factor, F=10, which implies <B>\n= 130 G in the upper photosphere. We argue also that in order to explain both\nthe Hanle depolarization of the Sr I 4607 line and the Zeeman signals observed\nin Fe I lines we need to introduce a height-dependent scaling factor, such that\nthe ensuing <B> = 160 G in the low photosphere and <B> = 130 G in the upper\nphotosphere.\n