Interplanetary shocks generated by expanding magnetic loops

Abstract

We present a self-consistent numerical model of shock wave formation in the heliosphere by an expanding magnetic loop. In the model a coronal mass ejection is initiated by a loss of magnetohydrostatic equilibrium of the loop as a result of an increase of underlying magnetic field strength. The expanding magnetic loops produce propagating shock waves.The plasma motions are described by a system of two-fluid Navier-Stokes equations taking account of modified coefficients for electron and ion heat conduction, ion viscosity and energy exchange between ions and electrons.We obtain shock wave parameters in the outer heliosphere vs initial perturbations of the magnetic loops, and show that the shocks can be divided into two types, depending on their intensity. In the case of relatively weak shocks a typical feature is formation of a dense and cold layer (“piling-up” of material) near the upper boundary of the loop. In the case of strong shocks large-scale turbulence and viscous heating in the relaxation zone behind the front play an important role, and no appreciable piling-up of plasma occurs.We demonstrate that expanding magnetic loops, which are observed as magnetic clouds in the outer heliosphere, can effectively drive transient shocks ahead.