title: Quasiperpendicular High Mach Number Shocks.
abstract: Shock waves exist throughout the Universe and are fundamental to understanding the nature of collisionless plasmas. Reformation is a process, driven by microphysics, which typically occurs at high Mach number supercritical shocks. While ongoing studies have investigated this process extensively both theoretically and via simulations, their observations remain few and far between. In this Letter we present a study of very high Mach number shocks in a parameter space that has been poorly explored and we identify reformation using in situ magnetic field observations from the Cassini spacecraft at 10 AU. This has given us an insight into quasiperpendicular shocks across 2 orders of magnitude in Alfvén Mach number (M_{A}) which could potentially bridge the gap between modest terrestrial shocks and more exotic astrophysical shocks. For the first time, we show evidence for cyclic reformation controlled by specular ion reflection occurring at the predicted time scale of ~0.3τ_{c}, where τ_{c} is the ion gyroperiod. In addition, we experimentally reveal the relationship between reformation and M_{A} and focus on the magnetic structure of such shocks to further show that for the same M_{A}, a reforming shock exhibits stronger magnetic field amplification than a shock that is not reforming.
authors.affiliation: Space and Atmospheric Physics, Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom.
authors.forename: A H
authors.initials: AH
authors.lastname: Sulaiman
authors.affiliation: Space and Atmospheric Physics, Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom.
authors.forename: A
authors.initials: A
authors.lastname: Masters
authors.affiliation: Space and Atmospheric Physics, Blackett Laboratory, Imperial College London, London SW7 2AZ, United Kingdom.
authors.forename: M K
authors.initials: MK
authors.lastname: Dougherty
authors.affiliation: Astronomy Unit, Queen Mary University of London, London E1 4NS, United Kingdom.
authors.forename: D
authors.initials: D
authors.lastname: Burgess
authors.affiliation: Institute of Space and Astronomical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Fujimoto
authors.affiliation: Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242, USA.
authors.forename: G B
authors.initials: GB
authors.lastname: Hospodarsky