Numeric and analytic study of interplanetary coronal mass ejection and shock evolution: Driving, decoupling, and decaying

摘要

We analyze the heliocentric evolution of fast interplanetary counterparts of coronal mass ejections (ICMEs) and their transient shocks to investigate how and where they decelerate in the interplanetary medium. We employ two one-dimensional hydrodynamic models, analytic and numeric, to study three fast CME events. We focus on the transferring of momentum from the ICME to the shock. The two models show that initially the fast ICME propagates at about a constant speed and drives the shock (driving stage) until it reaches a certain distance from which it decelerates and decouples from the shock (decoupling process). Then the ICME and its shock decelerate (decaying stage). This deceleration depends on the speed difference with respect to the ambient wind and tends to a negligible value when the ICME-shock approaches to the ambient wind speed. The location and duration of these propagation stages depend on the initial CME conditions and the ambient wind characteristics. We present a parametric study to compare the results by the analytic and numeric models, showing the variations of their results as a function of the initial conditions. We perform three study cases to compare the model's predictions with a set of speed measurements of ICME-shock events.