Understanding Small Solar Magnetic Structures: Comparing Numerical Simulations to Observations

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Abstract
We present direct comparisons of small magnetic structures observed in the solar photosphere with the results from numerical simulations of those structures. We compare diagnostic signatures derived from emergent Stokes polarization spectra from both the observed and model atmospheres, the former recorded with the National Solar Observatory/High Altitude Observatory Advanced Stokes Polarimeter, the latter from a fully dynamic MHD simulation of a magnetic flux sheet in a convective atmosphere. We focus on the asymmetries in the Stokes V spectra and find, first and foremost, that the asymmetries from the observed Stokes I and V in and around solar pores and azimuth centers (ACs) are quantitatively comparable to those derived from the simulation. We also find enhanced Stokes V asymmetry on the periphery of pores and ACs. We interpret this as a consequence of strong downdrafts in the surroundings of these magnetic structures, accompanied by the expansion of the magnetic field lines with height above these field-free downdrafts (the "canopy effect"). The magnetic canopy can be present whether or not there is a continuum signature (i.e., a dark "pore"). Not surprisingly, the patterns and magnitudes of asymmetries scale with the size of the magnetic element. In the interior of the pores and ACs, we find evidence for mixed up- and downflows, with little spatial correlation between the zero-crossing shift of the V profile and the V amplitude. Finally, we report on asymmetries observed in the linear polarization lin(λ) = [Q(λ)2 + U(λ)2]1/2, finding further support for the presence of the magnetic canopy from those diagnostics. We additionally present expectations for spectropolarimetric observations at significantly higher spatial resolution.