Studies of shocks have long suggested that a shock can undergo cyclical self-reformation on a timescale of ion cyclotron period. This process has been proposed as a primary mechanism for energy dissipation and energetic particle acceleration at shocks. Unambiguous observational evidence, however, has remained elusive. Here, we report direct observations for the self-reformation process of a collisionless, high Mach number, quasi-perpendicular shock using Magnetospheric Multiscale (MMS) measurements. We find that reflected ions by the old shock ramp form a clear phase-space vortex, which gives rise to a new ramp. The new ramp observed by MMS2 has not yet developed to a mature stage during the self-reformation, and is not strong enough to reflect incident ions. Consequently, these ions are only slightly slowed down and show a flat velocity profile from the new ramp all the way to the old one. The present results provide direct evidence of shock self-reformation, and also shed ligh...

中文翻译：

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MMS动力学尺度冲击自重的直接观察

长期以来，对电击的研究表明，电击可以在离子回旋加速器周期的时间尺度上发生周期性的自重整。已经提出该过程作为冲击时能量耗散和高能粒子加速的主要机制。但是，明确的观察证据仍然难以捉摸。在这里，我们报告使用磁层多尺度（MMS）测量对无碰撞，高马赫数，准垂直冲击的自重过程的直接观察。我们发现，旧的冲击坡道反射的离子形成了清晰的相空间涡流，从而产生了新的坡道。MMS2观察到的新斜波在自重组期间尚未发展到成熟阶段，并且强度不足以反射入射离子。所以，这些离子仅略微减慢了速度，并显示了从新斜面一直到旧斜面的平坦速度曲线。目前的结果提供了震荡自我改造的直接证据，也减轻了冲击力。