Magnetohydrodynamic simulation of the interaction between two interplanetary magnetic clouds and its consequent geoeffectiveness: 2. Oblique collision

The numerical studies of the interplanetary coupling between multiple magnetic clouds (MCs) are continued by a 2.5-dimensional ideal magnetohydrodynamic (MHD) model in the heliospheric meridional plane. The interplanetary direct collision (DC) / oblique collision (OC) between both MCs results from their same/different initial propagation orientations. Here the OC is explored in contrast to the results of the DC (Xiong et al., 2007). Both the slow MC1 and fast MC2 are consequently injected from the different heliospheric latitudes to form a compound stream during the interplanetary propagation. The MC1 and MC2 undergo contrary deflections during the process of oblique collision. Their deflection angles of |δθ1| and |δθ2| continuously increase until both MC-driven shock fronts are merged into a stronger compound one. The |δθ1|, |δθ2|, and total deflection angle ∆θ (∆θ = |δθ1| + |δθ2|) reach their corresponding maxima when the initial eruptions of both MCs are at an appropriate angular difference. Moreover, with the increase of MC2’s initial speed, the OC becomes more intense, and the enhancement of δθ1 is much more sensitive to δθ2. The |δθ1| is generally far less than the |δθ2|, and the unusual case of |δθ1| ≃ |δθ2| only occurs for an extremely violent OC. But because of the elasticity of the MC body to buffer the collision, this deflection would gradually approach an asymptotic degree. As a result, the opposite deflection between the two MCs, together with the inherent magnetic elasticity of each MC, could efficiently relieve the external compression for the OC in the interplanetary space. Such deflection effect for the OC case is essentially absent for the DC case. Therefore, besides D R A F T May 23, 2009, 6:29pm D R A F T XIONG ET AL.: MC-MC INTERACTION AND ITS GEOEFFECTIVENESS: 2. X 3 the magnetic elasticity, magnetic helicity, and reciprocal compression, the deflection due to the OC should be considered for the evolution and ensuing geoeffectiveness of interplanetary interaction among successive coronal mass ejections (CMEs). D R A F T May 23, 2009, 6:29pm D R A F T X 4 XIONG ET AL.: MC-MC INTERACTION AND ITS GEOEFFECTIVENESS: 2.