Abstract
Abstract. The overall structure of quasi-perpendicular, high Mach number collisionless shocks is controlled to a large extent by ion reflection at the shock ramp. Departure from a strictly one-dimensional structure is indicated by simulation results showing that the surface of such shocks is rippled, with variations in the density and all field components. We present a detailed analysis of these shock ripples, using results from a two-dimensional hybrid (particle ions, electron fluid) simulation. The process that generates the ripples is poorly understood, because the large gradients at the shock ramp make it difficult to identify instabilities. Our analysis reveals new features of the shock ripples, which suggest the presence of a surface wave mode dominating the shock normal magnetic field component of the ripples, as well as whistler waves excited by reflected ions.Key words. Space plasma physics (numerical simulation studies; shock waves; waves and instabilities)
Highlights
The structure of high Mach number collisionless shocks, for the case where the angle θBn between the upstream magnetic field and the shock normal is greater than 45◦ (“quasi-perpendicular”), is dominated by the processes of ion thermalization
We demonstrate a number of new features of shock ripples and argue that ripples may be caused by a wave mode which resembles a surface wave
For the first time, some new features of the shock ripples, as seen in the shock normal magnetic field component in two-dimensional hybrid shock simulations
Summary
The structure of high Mach number collisionless shocks, for the case where the angle θBn between the upstream magnetic field and the shock normal is greater than 45◦ (“quasi-perpendicular”), is dominated by the processes of ion thermalization. The first investigations of departures from onedimensional structure were carried out by Winske and Quest (1988), who studied the role of waves and structure transverse to the normal using two-dimensional hybrid simulations of quasi-perpendicular shocks. They found that the anisotropic downstream ion distributions, created at the shock by reflection, produced waves broadly consistent with local linear theory. The role of the reflected ions in the shock foot was investigated by Hellinger et al (1996), who carried out threedimensional hybrid simulations with sufficiently high resolution and low resistivity, to show whistler waves generated near the shock propagating upstream. We find that our ripple properties would be consistent with this
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