Magnetic Reconnection in High Definition

地球周围的空间区域是高度动态的，由一种称为磁重联的基本物理过程驱动。重连发生在被称为等离子体的高温气体中。当两个等离子体接触时，两个区域中的磁场可以相互连接，从而释放出大量的能量。重连发生在整个宇宙中;它是太阳活动的原因，它发生在各种天体和实验室等离子体中（如实验聚变反应堆中的燃料）。然而，可用于观测地球环境中重连的仪器的范围和质量使其成为研究这一过程的最佳场所;这也是重连对我们日常生活影响最大的环境，因为重连驱动的动态对现代技术（空间天气）有负面影响。例如，地磁暴是由重连驱动的，对地面基础设施造成损害;它们还造成辐射带强度的变化，可能损害卫星。地球上的极光最终也是由重连过程驱动的。地球上的重连发生在两个等离子体之间的界面上：太阳风，它从太阳流向太阳系的外部;磁层，它是太阳风中的一个空腔，是由地球磁场雕刻出来的。这两个等离子体都有相关的磁场：行星际磁场（IMF）和地球磁场。在磁层和太阳风之间的界面，即磁层顶，IMF和地球磁场之间可以发生重连--正是在这个界面处的重连将能量和动量从太阳风转移到磁层，并为所有磁层动力学提供了最终的驱动力。在这里，重联发生在稳态和称为通量转移事件（FTE）的突发。太阳系中大多数磁化行星的动力学或多或少都受到重连的控制，因此重连对大多数磁化系外行星来说也可能是一个重要的过程。2014年10月，美国宇航局将发射一个由四个航天器组成的星座，称为磁层多尺度（MMS）使命，这将提供对地球磁层等离子体环境的观测，其时间分辨率远远高于以前的任务。MMS社区的大部分研究工作可能会致力于理解重连的微观物理学，而与此提案相关的研究金计划中概述的工作将使用以前任务的数据解决与突发重连（FTE）的全球规模贡献有关的未决问题。在这里，我们建议使用MMS提供的仪器，以获得更大的了解FTE的中尺度，分离这两个极端（微观和全球尺度）。因此，它将补充研究金方案中概述的全球规模效应研究和MMS小组目前计划的研究，这项提议的目的是测试在地球磁层顶发生突发重联的方式的竞争机制。这对于验证磁层动力学的全球模拟是必要的，但它也将使我们了解重连的基本性质，这种性质往往是随时间变化的（原因尚不清楚）。这将通过应用一系列已经单独测试但没有组合的技术来完成;它们的单独应用导致了一个不完整的画面，有时似乎相互冲突。通过将这些方法一起应用于来自新型高分辨率仪器的共同数据集，我们将更深入地了解这一基本物理过程发生的方式。

The region of space around the Earth is highly dynamic, driven by a fundamental physical process called magnetic reconnection. Reconnection occurs in hot gases called plasmas. When two plasmas come into contact, the magnetic fields in the two regions can become interconnected, causing the release of large amounts of energy. Reconnection occurs throughout the Universe; it is responsible for solar activity, it occurs in various astrophysical bodies and in laboratory plasmas (such as the fuel in experimental fusion reactors). However, the range and quality of instrumentation available to observe reconnection in Earth's environment makes this the best place to study this process; this is also the environment in which reconnection has the most impact on our day-to-day life, as the dynamics that are driven by reconnection have negative effects on modern day technology (space weather). For example, geomagnetic storms are driven by reconnection and cause damage to infrastructure on the ground; they also cause variations in intensity of the radiation belts which can harm satellites. Earth's auroras are also ultimately driven by the reconnection process.Reconnection at Earth occurs at the interface between two plasmas: the solar wind, which flows from the Sun to the outer reaches of the Solar System, and the magnetosphere, which is a cavity in the solar wind that is carved out by the Earth's magnetic field. These two plasmas have associated magnetic fields: the interplanetary magnetic field (IMF) and terrestrial magnetic field respectively. Reconnection can occur between the IMF and the terrestrial field at the interface between the magnetosphere and solar wind, which is called the magnetopause - it is reconnection at this interface that transfers energy and momentum from the solar wind into the magnetosphere and provides the ultimate driver for all magnetospheric dynamics. Here, reconnection occurs both in steady state and in bursts called flux transfer events (FTEs). Reconnection similarly controls the dynamics, to greater or lesser degrees, of most magnetised planets in the Solar System, and hence it is likely to be a significant process at most magnetised exoplanets too.In October 2014, NASA will launch a constellation of four spacecraft called the Magnetospheric Multiscale (MMS) mission, which will provide observations of the plasma environment in the Earth's magnetosphere at temporal resolutions that are far greater than previous missions. Most of the research effort in the MMS community is likely to be directed towards understanding the microphysics of reconnection, whilst the work outlined in the fellowship programme associated with this proposal will be resolving outstanding issues relating to the global scale contribution of bursty reconnection (FTEs) using data from previous missions. Here, we propose the use of the instrumentation provided by MMS to obtain a much greater understanding of FTEs on the mesoscale, which separates these two extremes (micro- and global scales). Hence it will complement both the study of the global-scale effects that is outlined in the fellowship programme and the research currently planned by the MMS team.The objective of this proposal is to test competing mechanisms for the manner in which bursty reconnection occurs at the Earth's magnetopause. This is necessary for the verification of global simulations of magnetospheric dynamics, but it will also inform our understanding of the underlying nature of reconnection, which is often time-varying (for reasons that are unclear). This will be done by applying a range of techniques that have individually been tested, but not combined; their separate application has led to a patchy picture with results that at times appear to conflict. By applying these methods together to a common data set derived from novel high resolution instrumentation, we will gain a deeper understanding of the manner in which this fundamental physical process occurs.