A forecast of the heliospheric termination-shock position by three-dimensional MHD simulations

The effects of heliospheric disturbances on the position of the termination shock (TS) are examined using a three-dimensional MHD model. Variations in the solar wind ram pressure due to the interplanetary shock waves drive the TS away from its steady state equilibrium position and emit shocks and waves downstream. Transmitted/emitted disturbances propagating from the TS to the heliopause (HP) are partially reflected at the HP, and the reflected waves return and collide with the TS. Thus, besides upstream solar wind disturbances, the TS location changes in response to incident downstream disturbances associated with waves reflected from the HP produced R TS by earlier supersonic solar wind disturbances. To determine the time-varying, we incorporate Voyager 2 (V2) R TS plasma data as a boundary condition into our 3D MHD simulations, which allows us to forecast the termination shock movement for nearly a year after the present V2 data. Our simulations indicate that the TS was at similar to 90 AU along the Sun-V1 line on 2007 August 14, the last tentative available date of the V2 data. After this, our simulation forecasts that will decrease to a minimum distance in late 2007 or early 2008. This decrease R-TS will be mainly caused by the heliosheath returned pulse driven by the 2006 March event. Whether V2 will cross the TS or not in this period depends on the future solar wind ram pressure and also on the degree of the north-south asymmetry of the heliospheric structure. Some quantitative discussions are given.