Three-dimensional simulation of solar emerging flux using the earth simulator I. Magnetic Rayleigh-Taylor instability at the top of the emerging flux as the origin of filamentary structure

We present the results of three-dimensional magnetohydrodynamic simulations of solar emerging flux and its interaction with preexisting coronal field. In order to resolve the fine structures and the current sheets. we used high-resolution grids with up to 800 x 400 x 620 points; the calculation was carried out using the Earth Simulator. The model set up is an extension of a previous two-dimensional simulation by Yokoyama and Shibata (1995) to include the variation along the third direction. Based on the same simulation result, we reported in our previous paper (Isobe et al. 2005): (1) Dense filaments similar to Ha arch filament system are spontaneously formed in the emerging flux by the magnetic Rayleigh-Taylor type instability. (2) Filamentary current sheets are created in the emerging flux due to a nonlinear development of the magnetic Rayleigh-Taylor instability, which may cause an intermittent, nonuiform heating of the corona. (3) A magnetic reconnection between the emerging flux and preexisting coronal field occurs in a spatially intermittent way. In this paper we describe the simulation model and discuss the origin and the properties of the magnetic Rayleigh-Taylor instability in detail. It is shown that the top-heavy configuration that causes the instability is formed by the intrinsic dynamics of the emerging flux.