The intensity contrast of solar granulation: comparing Hinode SP results with MHD simulations

TL;DR

This study compares observed solar granulation contrast from Hinode SP data with 3D MHD simulations, demonstrating that considering optical effects and slight defocus aligns simulated contrast with observations, supporting the accuracy of the models.

Contribution

It shows that including optical system effects and defocus in synthetic images reconciles simulation contrast with Hinode observations, validating the MHD models.

Findings

Simulated contrast reduced from 14.4% to 8.5% after optical effects.

Slight defocus further lowers contrast to 7.5%, close to observed 7.0%.

Discrepancies attributed to straylight and instrument imperfections.

Abstract

The contrast of granulation is an important quantity characterizing solar surface convection. We compare the intensity contrast at 630 nm, observed using the Spectro-Polarimeter (SP) aboard the Hinode satellite, with the 3D radiative MHD simulations of V{\"o}gler & Sch{\"u}ssler (2007). A synthetic image from the simulation is degraded using a theoretical point-spread function of the optical system, and by considering other important effects. The telescope aperture and the obscuration by the secondary mirror and its attachment spider, reduce the simulated contrast from 14.4 % to 8.5 %. A slight effective defocus of the instrument brings the simulated contrast down to 7.5 %, close to the observed value of 7.0 %. A proper consideration of the effects of the optical system and a slight defocus, lead to sufficient degradation of the synthetic image from the MHD simulation, such that the contrast reaches almost the observed value. The remaining small discrepancy can be ascribed to straylight and slight imperfections of the instrument, which are difficult to model. Hence, Hinode SP data are consistent with a granulation contrast which is predicted by 3D radiation MHD simulations.