Reformation of an oblique shock observed by Cluster

摘要

On 16 March 2005, the Cluster spacecraft crossed a shock almost at the transitionbetween the quasi-perpendicular and quasi-parallel regimes (BB, = 46°) preceded by anupstream low-frequency (0.02 Hz in the spacecraft frame) wave train observed formore than 10 mn. The wave semicycle nearest to the shock was found to grow in time,steepen and reflect an increasing fraction of the incoming ions. This gives strongindication that this pulsation is becoming a new shock front, standing --,5Ap upstream ofthe main front and growing to shock-like amplitude on a timescale of 35R.Downstream Of the main shock transition, remnants of an older front are found indicatingthat the reformation is cyclic. This provides a unique example where the dynamics ofshock reformation can be sequentially followed. The process shares many characteristicswith simulations of reforming quasi-parallel shocks.