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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 36, issue 4
Ann. Geophys., 36, 1047-1055, 2018
https://doi.org/10.5194/angeo-36-1047-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Ann. Geophys., 36, 1047-1055, 2018
https://doi.org/10.5194/angeo-36-1047-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 01 Aug 2018

Regular paper | 01 Aug 2018

Periodic self-reformation of rippled perpendicular collisionless shocks in two dimensions

Takayuki Umeda and Yuki Daicho Takayuki Umeda and Yuki Daicho
  • Institute for Space-Earth Environmental Research, Nagoya University, Nagoya 464-8601, Japan

Abstract. Large-scale two-dimensional (2-D) full particle-in-cell (PIC) simulations are carried out for studying periodic self-reformation of a supercritical collisionless perpendicular shock with an Alfvén–Mach number MA ∼ 6.

Previous self-consistent one-dimensional (1-D) hybrid and full PIC simulations have demonstrated that the periodic reflection of upstream ions at the shock front is responsible for the formation and vanishing of the shock-foot region on a timescale of the local ion cyclotron period, which was defined as the reformation of (quasi-)perpendicular shocks.

The present 2-D full PIC simulations with different ion-to-electron mass ratios show that the dynamics at the shock front is strongly modified by large-amplitude ion-scale fluctuations at the shock overshoot, which are known as ripples.

In the run with a small mass ratio, the simultaneous enhancement of the shock magnetic field and the reflected ions take place quasi-periodically, which is identified as the reformation. In the runs with large mass ratios, the simultaneous enhancement of the shock magnetic field and the reflected ions occur randomly in time, and the shock magnetic field is enhanced on a timescale much shorter than the ion cyclotron period.

These results indicate a coupling between the shock-front ripples and electromagnetic microinstabilities in the foot region in the runs with large mass ratios.

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Short summary
Does the reformation of perpendicular shocks really exist in the real space plasma? The reformation was first reported in numerical simulations in one spatial dimension, and then was indicated by in situ observation by the Cluster spacecraft. The present study aimed to answer this question by performing advanced numerical simulations in two spatial dimensions. The present study suggests that the reformation exists under a limited plasma condition.
Does the reformation of perpendicular shocks really exist in the real space plasma? The...
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