Strong horizontal internetwork magnetic field: numerical simulations in comparison to observations with Hinode

Solar observations with the Hinode space observatory led to the discovery of strong horizontal magnetic fields in the photosphere of quiet internetwork regions. Here we investigate realistic numerical simulations of the surface layers of the Sun with respect to horizontal magnetic fields and compute the corresponding responses in the Fe I 630 nm line pair. We analyze two simulation runs with greatly different initial and boundary conditions. Both show a local maximum in the mean flux density of the horizontal field component at a height of around 500 km in the photosphere, where the horizontal surpasses the vertical component by a factor of 2.0 or 5.6, depending on the initial and boundary conditions. From the synthesized Stokes profiles we derive a mean horizontal field component that is, respectively, 1.5 and 2.8 stronger than the vertical component. This is the consequence of both intrinsically stronger flux densities and the larger area fraction occupied by, the horizontal fields. It is shown that convective overshooting pumps horizontal fields in the vertical direction, leading to a positive vertical Marie Curie Research Fellow ar X iv :0 80 1. 49 15 v1 [ as tr oph ] 3 1 Ja n 20 08