GEM: What Determines the Magnetosphere Plasma Entropy Distribution

这个项目将解决有关控制地球磁层的能量学和动力学的过程的引人注目的问题，地球磁层是通过将地球磁场延伸到太空而划分出来的。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，含有大约相同数量的离子和电子，其运动受到磁场的强烈影响。描述这个系统能量状态(S)的一个基本量称为熵。当这个系统中的一个物理过程是绝热的，意味着没有能量或质量从系统转移到环境中，那么比熵是守恒的。例如，当一块等离子体绝热地穿过磁层时，它的体积会增加或减少，但它包含的粒子数量相同。它的密度和温度会发生变化，以保持它开始旅程时的熵不变。如果包裹的熵发生变化，则包裹正在被加热或粒子正在丢失。这项调查的方法是利用全球磁流体力学(MHD)模拟和观测，绘制整个地球磁层的特定熵地图。然后，这些地图将被用来确定发生等离子体加热的地点，并调查相关过程的特征。这些区域的位置和熵变化的时间历史为所涉及的过程提供了重要线索，并为磁层的能量学和动力学提供了基本的见解。该项目具有重大的更广泛的影响。所讨论的问题是理解空间天气扰动如何在地球附近产生和演变的关键。这些干扰能够损坏或摧毁作为关键社会基础设施基础的卫星，为人类探险者制造危险的辐射，并在固体地球上引发强流，对电网运行造成问题。从长远来看，在理解空间天气方面的进步将直接促进改进的空间天气预报模型，对社会有价值。此外，该项目为新汉普郡大学的一名研究生和早期职业科学家提供培训，为未来的科学工作做出贡献。该项目中涉及的问题侧重于与馈送它的等离子体源的熵相比，提高磁层中等离子体片的熵的过程。在磁层中，可以使用熵来确定给定区域内等离子体的起源。只有两种等离子体来源供应磁层--太阳风和电离层。在源区，这些种群的熵值非常不同。如果将这些等离子体块移动到磁层的过程是绝热的，那么熵保留了源区的值，就像一种染料，标记了等离子体块的起源和进入路径。然而，如果沿着这些路径存在熵正在变化的区域，那么这些区域就会标记出包裹中的等离子体正在丢失、混合、加热或冷却的位置。据认为，提高等离子体片的熵的过程包括：磁重联、爆发性体流(BFF)、偶极锋面(DFS)、双瓣重联、开尔文-亨霍尔兹波和湍流加热。其中的每一个都将被检查，以了解它们在不同条件下对等离子体片中的熵增加的贡献。

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.