3-D MHD model of the Sun-solar wind system : The first results

Abstract

Toward the integrated numerical space weather prediction, we have been developing a three dimensional MHD simulation model of the sun-solar wind combining system. Here we describe the overview of the model and report on the first result of the simulation. Appling the unstructured grid system, we achieved the dense grid spacing at the inner boundary, which enable us to treat the fine structure near the sun, and a size of simulation space of 1AU, simultaneously. The magnetic field at the inner boundary is prescribed with the observational data of photospheric magnetic field during a specific time period. In order to obtain the supersonic solar wind, the parametric source functions are introduced into the energy equation and momentum equation. The source functions are in the exponentially dumping form as has been widely used in previous works. However the intensities of the source functions are newly adjusted so as to reflect the topology of the coronal magnetic field. They are increased inside the magnetic flux tube in sub-radial expansion and reduced inside the magnetic flux tube in over-radial expansion. This adjustment aims to reproduce the variation of the solar wind speed according to the coronal magnetic field. It is confirmed from the data comparison that the MHD model successfully reproduced many features both of the solar coronal region and the solar wind 3-D structure. With the further improvement and refinement, the model will be applied to the integrated space weather simulation system being developed at NiCT (National institute of Information and Communication Technology), Japan.