太阳轨道器观测到的镜像模式风暴
Mirror mode storms observed by Solar Orbiter
摘要：
镜像模是空间等离子体中普遍存在的一种模式，它是由压力各向异性引起的。与其他不稳定性一起，它们在限制等离子体中包含的自由能方面发挥着重要作用。本研究的重点是太阳轨道器观测到的太阳中心距离在0.5和1 AU之间的太阳风的镜像模式。通常，镜像模式具有从几秒到几十秒的时间尺度，并且被认为是准MHD结构。在太阳风中，它们也一般以孤立结构出现。然而，在某些条件下，测量到更高频率镜像模式的延长和突发序列，这在以前被标记为镜像模式风暴。目前，只有少数现有的研究集中在镜像模式风暴，这意味着许多悬而未决的问题仍然存在。在这项研究中，太阳轨道器已被用来调查镜像模式风暴的几个关键方面：他们对日心距离的依赖，与当地等离子体特性，时间/空间尺度，振幅，并与大规模的太阳风瞬变的连接。主要结果是镜模风暴经常接近局域离子尺度，不再被视为准MHD，从而打破了通常使用的长波长假设。它们通常在电流片附近和行星际激波的下游被观察到。这些事件是在太阳风速度缓慢时观测到的，而且有一种倾向，即在离太阳较近的地方发生的事件较多。发生率很低，因此它们在调节环境太阳风方面不起根本作用，但在瞬变过程中可能起更大的作用。
英文摘要：
Mirror modes are ubiquitous in space plasma and grow from pressure anisotropy. Together with other instabilities, they play a fundamental role in constraining the free energy contained in the plasma. This study focuses on mirror modes observed in the solar wind by Solar Orbiter for heliocentric distances between 0.5 and 1 AU. Typically, mirror modes have timescales from several to tens of seconds and are considered quasi-MHD structures. In the solar wind, they also generally appear as isolated structures. However, in certain conditions, prolonged and bursty trains of higher frequency mirror modes are measured, which have been labeled previously as mirror mode storms. At present, only a handful of existing studies have focused on mirror mode storms, meaning that many open questions remain. In this study, Solar Orbiter has been used to investigate several key aspects of mirror mode storms: their dependence on heliocentric distance, association with local plasma properties, temporal/spatial scale, amplitude, and connections with larger-scale solar wind transients. The main results are that mirror mode storms often approach local ion scales and can no longer be treated as quasi-MHD, thus breaking the commonly used long-wavelength assumption. They are typically observed close to current sheets and downstream of interplanetary shocks. The events were observed during slow solar wind speeds and there was a tendency for higher occurrence closer to the Sun. The occurrence is low, so they do not play a fundamental role in regulating ambient solar wind but may play a larger role inside transients.
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