Probing quiet Sun magnetism using MURaM simulations and?Hinode/SP results: support for a local dynamo

摘要

Context. Owing to the limited spatial resolution andthe weak polarization signal coming from the quietest regions on theSun, the organization of the magnetic field on the smallest scales islargely unknown. Aims. We obtain information about the magnetic fluxpresent in the quiet Sun by comparing radiative MHD simulations withobservations, with particular emphasis on the role of surface dynamoaction. Methods. We synthesized Stokes profiles on the basisof the MHD simulation results. The profiles are degraded by taking theproperties of the spectropolarimeter (SP) into account onboard theHinode satellite. We used simulation runs with different magneticReynolds numbers ()and observations at different heliocentric angles with different levelsof noise. Results. Simulations with an imposed mixed-polarityfield and below the threshold for dynamo action reproduce the observed verticalflux density, but do not display a high enough horizontal flux density.Surface dynamo simulations at the highest feasible at the moment yield a ratio of the horizontal and verticalflux density consistent with observational results, but the overallamplitudes are too low. Based on the properties of the local dynamosimulations, a tentative scaling of the magnetic field strength by afactor 2-3reproduces the signal observed in the internetworkregions. Conclusions. We find agreement with observations atdifferent heliocentric angles. The mean field strength in internetworkimplied by our analysis is roughly 170G at the optical depthunity. Our study shows that surface dynamo could be responsible formost of the magnetic flux in the quiet Sun outside the network, giventhat the extrapolation to higher is valid. Key words: Sun: granulation - Sun:photosphere