Physical properties of the solar magnetic photosphere under the MISMA hypothesis. II. Network and internetwork fields at the disk center

This paper is the second in a series that models photospheric magnetic stru ctures in terms of atmospheres having optically thin fluctuations of magnet ic held and thermodynamic state (the MISMA hypothesis). We apply an inversi on procedure to the polarization of Fe I lambda 6301.5 and Fe I lambda 6302 .5 observed in network and internetwork regions with the Advanced Stokes Po larimeter. Some 5200 independent spectra, comprising mildly asymmetric to v ery abnormal Stokes profiles, were reproduced by a single type of model atm osphere. It has three components, two that are magnetized and one that is n ot. A large fraction among the held strengths we measure are in the kG regi me, but simulations suggest that the polarization of the observed Fe I line s weakens below detectable levels for fields substantially smaller than the observed ones. Synthesis of Stokes profiles of the IR Fe I lambda 15648.5 line in MISMAs reveals the opposite behavior, i.e., an increase of polariza tion for sub-kG fields. The highly transparent MISMAs inferred from observa tions are significantly brighter in the continuum than an unmagnetized atmo sphere. The mass of the magnetic structures tends to be at rest, although a minor fraction undergoes strong downflows. Downflows are also present in t he nonmagnetic environment. A significant number of fitted Stokes profiles require opposite magnetic polarities within the same resolution element. Th e occurrence of mixed polarities increases with weakening degree of polariz ation, such that 25% of the weakest signals require mixed polarity. The wea k polarization signals account for most of the total (unsigned) magnetic fl ux of the observed region. By extrapolation, this indicates that a signific ant fraction of photospheric magnetic flux remains undetected. The MISMA fr amework provides a unified and physically consistent scenario for interpret ation of quiet Sun magnetism. Moreover, it is the only one available at pre sent that is able to fit the abnormal Stokes profiles as revealed by the ne w generation of sensitive Stokes polarimeters.