GEM: What Determines the Magnetosphere Plasma Entropy Distribution

这个项目将解决关于控制地球磁层的能量学和动力学过程的令人信服的问题，磁层是地球磁场向太空延伸而形成的一个区域。磁层中的物质以等离子体的形式存在，等离子体是一种完全电离的气体，含有大约等量的离子和电子，其运动受到磁场的强烈影响。描述这个系统的能量状态的一个基本量叫做熵。当一个物理过程在这个系统中是绝热的，这意味着没有能量或质量从系统传递到周围环境，那么比熵是守恒的。例如，当一个等离子体包裹绝热地穿过磁层时，它的体积会增加或减少，但它包含的粒子数量是相同的。它的密度和温度会发生变化以保持它开始运动时的熵不变。如果包裹的熵改变了，那么包裹就被加热了或者粒子丢失了。这项研究的方法是利用全球磁流体动力学（MHD）模拟和观测来绘制整个地球磁层的特定熵图。然后，这些地图将被用来确定等离子体加热发生的位置，并调查相关过程的特征。这些区域的位置和熵变的时间历史为所涉及的过程提供了重要的线索，并为磁层的能量学和动力学提供了基本的见解。该项目具有重大的广泛影响。所解决的问题是理解空间天气干扰如何在地球附近起源和演变的关键。这些干扰能够破坏或摧毁作为关键社会基础设施基础的卫星，对人类探险者产生危险的辐射，并在固体地球上产生对电网运行造成问题的强流。从长远来看，了解太空天气的进展将直接促进对社会有价值的太空天气预报模型的改进。此外，该项目还为新罕布什尔大学的研究生和早期职业科学家提供培训，为未来的科学劳动力做出贡献。在这个项目中解决的问题集中在提高磁层中等离子体片的熵的过程，而不是提供它的等离子体源的熵。在磁层中，熵可以用来确定给定区域内等离子体的起源。提供磁层的等离子体只有两种来源——太阳风和电离层。在源区，这些种群的熵值差别很大。如果将这些等离子体包裹移动到磁层的过程是绝热的，那么熵就保留了源区域的值，就像染料一样标记了等离子体包裹的起源和进入途径。然而，如果沿着这些路径存在熵变化的区域，那么这些区域就标记了包裹中的等离子体丢失、混合、加热或冷却的位置。据信，提高等离子体片熵的过程包括：磁重联、暴体流（BFFs）、双极化锋（DFs）、双叶重联、开尔文-赫姆霍兹波和湍流加热。我们将对每一种情况进行研究，以了解它们在不同条件下对等离子体片中熵增加的贡献。

This project will address compelling questions about the processes that control the energetics and dynamics of Earth's magnetosphere, a region carved out by the extension of Earth's magnetic field into space. The matter in the magnetosphere is in the form of plasma, a fully ionized gas containing approximately equal numbers of ions and electrons, the motion of which is strongly affected by magnetic fields. A fundamental quantity that describes the energy state(s) of this system is called entropy. When a physical process in this system is adiabatic, meaning no energy or mass is transferred to the surroundings from the system, then the specific entropy is conserved. For example, when a parcel of plasma travels through the magnetosphere adiabatically, it's volume will increase or decrease but it will contain the same number of particles. It's density and temperature will change in order to keep constant the entropy it had when it started it's journey. If the entropy of the parcel changes, then the parcel is being heated or particles are being lost. The methodology for this investigation is to produce maps of specific entropy throughout the Earth's magnetosphere using both global magnetohydrodynamic (MHD) simulations and observations. These maps will then be used to identify the locations where plasma heating is taking place and to investigate the characteristics of the processes responsible. The location of these regions and the time history of the entropy changes provide important clues to the processes involved, and fundamental insights into the energetics and dynamics of the magnetosphere. The project has significant broader impacts. The questions addressed are key to understanding how space weather disturbances originate and evolve in the Earth's vicinity. These disturbances are capable of damaging or destroying satellites that underlie critical societal infrastructures, of creating hazardous radiation for human explorers, and of inducing strong currents in the solid Earth problematic for power grid operation. In the longer term, advances in understanding space weather will feed directly into improved space weather forecast models of value to society. In addition, the project provides training for a graduate student and early career scientist at the University of New Hampshire contributing to the future scientific workforce.Questions addressed in this project focus on the processes that raise the entropy of the plasma sheet in the magnetosphere compared to the entropy of the plasma sources that feed it. In the magnetosphere, entropy can be used to identify the origins of the plasma in a given region. There are only two sources of plasma supplying the magnetosphere - the solar wind and the ionosphere. In the source regions, the entropy values of these populations are very different. If the processes that move these parcels of plasma into the magnetosphere are adiabatic, then the entropy retains the value of the sourch region and is like a dye that marks the origin and entry pathway of the plasma parcel. However, if along these pathways there are regions where the entropy is changing, then these mark the locations where the plasma in the parcel is being lost, mixed, heated or cooled. The processes that are believed to raise the entropy of the plasma sheet include: magnetic reconnection, Bursty Bulk Flows (BFFs), Dipolarization Fronts (DFs), dual lobe reconnection, Kelvin-Hemholtz waves, and turbulent heating. Each of these will be examined to understand their contributions to the increases in entropy in the plasma sheet under different conditions.