Propagation and Interaction Properties of Successive Coronal Mass Ejections in Relation to a Complex Type II Radio Burst
We examine the propagation and interaction properties of three successive coronal mass ejections (CMEs) from 2001 November 21-22, with a focus on their connection with the behaviors of the associated long-duration complex type II radio burst. In combination with coronagraph and multi-point in situ observations, the long-duration type II burst provides key features for resolving the propagation and interaction complexities of the three CMEs. The two CMEs from November 22 interacted first and then overtook the November 21 CME at a distance of about 0.85 AU from the Sun. The time scale for the shock originally driven by the last CME to propagate through the preceding two CMEs is estimated to be about 14 and 6 hr, respectively. We present a simple analytical model without any free parameters to characterize the whole Sun-to-Earth propagation of the shock, which shows a remarkable consistency with all the available data and MHD simulations even out to the distance of Ulysses (2.34 AU). The coordination of in situ measurements at the Earth and Ulysses, which were separated by about $71.4^{\circ}$ in latitude, gives important clues for the understanding of shock structure and the interpretation of in situ signatures. The results also indicate means to increase geo-effectiveness with multiple CMEs, which can be considered as another manifestation of the "perfect storm" scenario proposed by [liu14a] although the current case is not "super" in the same sense as the 2012 July 23 event.