THREE-DIMENSIONAL RADIATIVE TRANSFER MODELING OF THE POLARIZATION OF THE SUN'S CONTINUOUS SPECTRUM

Abstract

Here we formulate and solve the 3D radiative transfer problem of the\npolarization of the solar continuous radiation. Our approach takes into account\nnot only the anisotropy of the continuum radiation, but also the\nsymmetry-breaking effects caused by the horizontal atmospheric inhomogeneities\nproduced by the solar surface convection. Interestingly, our radiative transfer\nmodeling in a well-known 3D hydrodynamical model of the solar photosphere shows\nremarkable agreement with the empirical data, significantly better than that\nobtained via the use of 1D atmospheric models. Although this result confirms\nthat the above-mentioned 3D model was indeed a suitable choice for our\nHanle-effect estimation of the substantial amount of "hidden" magnetic energy\nthat is stored in the quiet solar photosphere, we have found however some small\ndiscrepancies whose origin may be due to uncertainties in the empirical data\nand/or in the thermal and density structure of the 3D model. For this reason,\nwe have paid some attention also to other (more familiar) observables, like the\ncenter-limb variation of the continuum intensity, which we have calculated\ntaking into account the scattering contribution to the continuum source\nfunction. The overall agreement with the observed center-limb variation turns\nout to be impressive, but we find a hint that the model's temperature gradients\nin the continuum forming layers could be slightly too steep, perhaps because\nall current simulations of solar surface convection and magnetoconvection\ncompute the radiative flux divergence ignoring the fact that the effective\npolarizability is not completely negligible, especially in the downward-moving\nintergranular lane plasma.\n