Cyclic evolution of structurally unstable shock waves

Abstract

Trans-Alfvénic shocks in a plasma with a finite Larmor radius are considered. It is shown that such shocks are subject to structural instability, i.e., the instability with respect to disintegration into several other structures. Furthermore, the disintegration is a repetitive process, and the shock evolution has a cyclic nature. Implications of the obtained results for interplanetary shocks and planetary bow shocks are discussed. It is suggested that the cyclic behavior is the reason why the trans-Alfvenic shocks are observed in the interplanetary space much more rarely than fast, stable, shocks.