The Dynamics of a High Mach Number Quasi-Perpendicular Shock: MMS Observations

Abstract

Shock parameters at Earth's bow shock in rare instances can approach the Mach numbers predicted at supernova remnants. We present our analysis of a high Alfvén Mach number ($M_A=27$) shock utilizing multipoint measurements from the Magnetospheric Multiscale (MMS) spacecraft during a crossing of Earth's quasi-perpendicular bow shock. We find that the shock dynamics are mostly driven by reflected ions, perturbations that they generate, and nonlinear amplification of the perturbations. Our analyses show that reflected ions create modest magnetic enhancements upstream of the shock which evolve in a nonlinear manner as they traverse the shock foot. They can transform into proto-shocks that propagate at small angles to the magnetic field and towards the bow shock. The nonstationary bow shock shows signatures of both reformation and surface ripples. Our observations indicate that although shock reformation occurs, the main shock layer never disappears. These observations are at high plasma $\beta$, a parameter regime which has not been well explored by numerical models.

arXiv commentAccepted by the Astrophysical Journal

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• Competitive X-ray and Optical Cooling in the Collisionless Shocks of WR 140
• Direct Multipoint Observations Capturing the Reformation of a Supercritical Fast Magnetosonic Shock
• Direct Evidence for Magnetic Reflection of Heavy Ions from High Mach Number Collisionless Shocks
• Ion Reflection by a Rippled Perpendicular Shock
• Mach Number Dependence of Ion-scale Kinetic Instability at Collisionless Perpendicular Shock: Condition for Weibel-dominated Shock
• Drivers of Magnetic Field Amplification at Oblique Shocks: In-Situ Observations
• Interaction of the Prominence Plasma within the Magnetic Cloud of an ICME with the Earth's Bow Shock