Alfvénic Turbulence Simulation in a Realistic Solar Wind

Abstract

We present initial results from a new numerical model to simulate magnetohydrodynamic (MHD) turbulence in the solar wind above the Alfvénic critical point. Previously, we had defined a “virtual” heliosphere that contained a tilted rotating current sheet, microstreams, as well as Alfvén waves (Goldstein et al. 1999a). In this new restructured approach, we use the global, time-stationary, WKB Alfvén wave-driven solar wind model (Usmanov & Goldstein 2003a) to define the initial state of the system. Consequently, current sheets, and fast and slow streams are computed self-consistently from an inner photospheric boundary. To this steady-state configuration, we add fluctuations close to, but above, the surface where the flow becomes super-Alfvénic. The time-dependent MHD equations are then solved using a semi-discrete third-order Central Weighted Essentially Non-Oscillatory (CWENO) numerical scheme in the frame of reference corotating with the Sun. The computational domain now includes the entire sphere; the geometrical singularity at the poles is removed using the multiple grid approach described in Usmanov (1996). Wave packets are introduced at the inner boundary such as to satisfy Faraday’s Law (Yeh & Dryer 1985) and their nonlinear evolution is followed in time.