Quasiperpendicular High Mach Number Shocks.

Area of Science:

• Space Physics
• Plasma Physics
• Astrophysics

Background:

• Collisionless shock waves are ubiquitous in the Universe and crucial for understanding plasma dynamics.
• Shock reformation, a microphysics-driven process, occurs at high Mach number supercritical shocks.
• Observational evidence for shock reformation remains scarce, particularly in unexplored parameter spaces.

Purpose of the Study:

• To investigate very high Mach number quasi-perpendicular shocks in a poorly explored parameter space.
• To identify and characterize shock reformation using in situ spacecraft observations.
• To bridge the understanding between terrestrial and astrophysical shocks.

Main Methods:

• Utilized in situ magnetic field observations from the Cassini spacecraft at 10 AU.
• Analyzed quasi-perpendicular shocks across two orders of magnitude in Alfvén Mach number (M_{A}).
• Focused on identifying cyclic reformation driven by specular ion reflection.

Main Results:

• Identified shock reformation in a parameter space characterized by very high Mach numbers.
• Provided the first observational evidence for cyclic reformation occurring on a timescale of approximately 0.3 ion gyroperiods (τ_{c}).
• Demonstrated that reforming shocks exhibit stronger magnetic field amplification compared to non-reforming shocks at the same M_{A}.

Conclusions:

• Shock reformation is a cyclic process controlled by specular ion reflection at high Mach numbers.
• The study provides crucial observational data bridging terrestrial and astrophysical shock phenomena.
• Reforming shocks significantly enhance magnetic field strength, impacting plasma dynamics.