Super-Alfvénic jets, with kinetic energy densities significantly exceeding that of the solar wind, are commonly generated downstream of Earth's bow shock under both high- and low-beta plasma conditions. In this study, we present theoretical evidence that these enhanced kinetic energy flows can be driven by firehose-unstable fluctuations and compressive heating within collisionless plasma environments. Using a fluid formalism that incorporates pressure anisotropy, we estimate that the downstream flow of a collisionless plasma shock can be accelerated by a factor of 2–4 following the compression and saturation of firehose instability. By analyzing quasi-parallel magnetosheath jets observed in situ by the Magnetospheric Multiscale (MMS) mission, we find that approximately 11% of plasma measurements within these jets exhibit firehose-unstable fluctuations. Our findings offer an explanation for the distinctive generation of fast downstream flows in both low (β < 1) and high (β > 1) beta plasmas, and provide new evidence that kinetic processes are crucial for accurately describing the formation and evolution of magnetosheath jets.

中文翻译：

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关于无碰撞激波下游超 Alfvénic 流的形成


在高 β 和低 β 等离子体条件下，动能密度明显超过太阳风的动能密度的超级阿尔夫尼克喷流通常产生于地球弓激波的下游。在这项研究中，我们提出了理论证据，证明这些增强的动能流可以由无碰撞等离子体环境中的不稳定波动和压缩加热驱动。使用结合压力各向异性的流体形式，我们估计在消防水带不稳定性的压缩和饱和之后，无碰撞等离子体激波的下游流动可以加速 2-4 倍。通过分析磁层多尺度 （MMS） 任务在原位观察到的准平行磁层射流，我们发现这些射流中大约 11% 的等离子体测量表现出消防水管不稳定的波动。我们的研究结果为低 （β < 1） 和高 （β > 1） β 等离子体中快速下游流动的独特产生提供了解释，并提供了新的证据，证明动力学过程对于准确描述磁流的形成和演化至关重要。