A numerical study of the interaction between two ejecta in the interplanetary medium: one- and two-dimensional hydrodynamic simulations

摘要

We studied the heliospheric evolution in one and two dimensionsof the interaction between twoejecta-like disturbances beyond the critical point:a faster ejecta 2 overtaking a previouslylaunched slower ejecta 1.The study is based on ahydrodynamic model using the ZEUS-3-D code.This model can be applied to those cases where the interaction occursfar away from the Sun and there is no merging(magnetic reconnection) between the two ejecta.The simulation shows that when the fasterejecta 2 overtakes ejecta 1 there isan interchange of momentum between the two ejecta, where the leadingejecta 1 accelerates and the tracking ejecta 2 decelerates. Both ejecta tendto arrive at 1AU having similar speeds, but with the front of ejecta 1propagating faster than the front of ejecta 2.The momentum is transferred from ejecta 2 to ejecta 1 when the shockinitially driven by ejecta 2 passes through ejecta 1.Eventually the two shock waves driven by the two ejecta merge together into asingle stronger shock. The 2-D simulation shows that the evolution ofthe interaction can be very complex and there are very differentsignatures of the same event at different viewing angles; however, thetransferring ofmomentum between the two ejecta follows the same physical mechanismdescribed above. These results are in qualitative agreement within-situ plasma observations of "multiple magnetic clouds" detected at 1AU.