Simulation of period doubling of recurrent solar wind structures

In 1974, IMP, Pioneer 11 and Pioneer 10 observed a recurrent solar wind structure over five consecutive solar rotations at three different trajectories between 1 and 6 AU. Using MHD simulations and input functions generated from plasma and magnetic field data observed from Pioneer 11. The authors study the continuing evolution of this solar wind structure between 5 and 20 AU. This simulation uses the shock interactions model which treats MHD shocks as discontinuity surfaces with zero thickness and which uses the exact Rankine-Hugoniot relations to describe the jump conditions. The model can calculate the collision and merging of shocks and the dynamical evolution of the solar wind in the outer heliosphere. The simulation result shows that between 5 and 10 AU there is an evolution from two corotating interaction regions per solar rotation to one merged interaction region (MIR) per solar rotation near 10 AU, i.e., period doubling has occurred. Each MIR was bounded by a forward and a reverse shock and additional weaker shocks may exist inside the MIR. Between 10 and 20 AU the structure of one MIR per solar rotation appears as a very persistent structure