Mesoscale Magnetohydrodynamic Processes in the Magnetosphere

磁层中的中尺度磁流体动力学过程

• 批准号: 9314239
• 负责人: Margaret Kivelson
• 金额: $ 51.94万
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1994
• 资助国家: 美国
• 起止时间: 1994-06-01 至 2000-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9314239&HistoricalAwards=false
• 关键词: Mesoscale; Magnetohydrodynamic; Processes; Magnetosphere

9314239 Kivelson The large scale, time-averaged properties of the magnetosphere and its interaction with the solar wind and the ionosphere are now well understood in terms of steady-state theory. The principal challenge that remains is to understand the dynamics of the system on microscales (1RE) and what we shall refer to as mesoscales ( 1RE). Attention need to be focused on those processes that transfer the energy and momentum of the solar wind through the magnetized plasma of the magnetosphere to the ionosphere. In recent years, it has become increasingly apparent that the dynamics of the magnetosphere are patchy or bursty in nature. Intermittency appears to be a fundamental feature of the interactions. Although they are intermittent, the important processes appear to occur on time scales that are long compared with particle gyroperiods; the corresponding spatial scales are large compared with particle gyroradii but small compared with magnetospheric dimensions. Hence, this proposal focuses on processes that can be characterized as "mesoscale" or intermediate in scale. The investigators will use spacecraft data sets and new data analysis approaches to characterize some of the mesoscale structures including: coupling of the solar wind to the magnetosphere through the process of magnetic reconnection, striations in density and field magnitude generally interpreted as the signature of saturated mirror mode waves; the polar cusp which appears to pulsate as successive bursts of reconnected plasma arrive at the ionosphere; large scale field- aligned currents (Region 1 currents) that are frequently highly structured in ways that may arise from bursty reconnection; the magnetotail plasma flows that are intermittent or bursty; and magnetic signatures of thin rope-like structures that carry field- aligned currents along their axes and contain plasma confined by twisted magnetic fields. The investigators will develop new models and theory with a close tie to observations. The analysis will begin by using the tools of MHD, but it is probable that full understanding will require some aspects of plasma kinetic theory. The intent is to develop a framework for the interpretation of existing observations and also to define needs for additional measurements. The proposed work addresses processes that appear to be central to the dynamics of the interacting solar wind/ionosphere/magnetosphere system, and the new results will illuminate the elemental coupling processes. Although the problems addressed are those of the terrestrial magnetosphere, the results are likely to have wider significance as they will apply to the interactions of magnetized plasmas wherever they may be: in other magnetoshperes, in the solar corona, or in the laboratory. ***

[9314239] Kivelson磁层的大尺度、时间平均特性及其与太阳风和电离层的相互作用现在在稳态理论方面得到了很好的理解。仍然存在的主要挑战是了解系统在微观尺度（1RE）和我们称之为中尺度（1RE）上的动力学。需要把注意力集中在那些将太阳风的能量和动量通过磁层的磁化等离子体转移到电离层的过程上。近年来，越来越明显的是，磁层的动力学本质上是不均匀的或突发的。间断性似乎是相互作用的一个基本特征。虽然它们是断断续续的，但与粒子回旋周期相比，重要的过程似乎发生在很长的时间尺度上；相应的空间尺度与粒子陀螺半径相比较大，但与磁层尺度相比较小。因此，本建议侧重于可表征为“中尺度”或中间尺度的过程。研究人员将使用航天器数据集和新的数据分析方法来表征一些中尺度结构，包括：通过磁重联过程太阳风与磁层的耦合，密度和场强的条纹通常被解释为饱和镜像模式波的特征；当重新连接的等离子体连续爆发到达电离层时，极尖似乎在脉动；大规模的场向电流（1区电流），其结构往往高度结构化，可能由突然重接引起；磁尾等离子体流是间歇性或突发性的；以及细绳状结构的磁性特征，这些结构沿着轴线携带着与磁场对齐的电流，并包含被扭曲磁场限制的等离子体。研究人员将发展与观测密切相关的新模型和理论。分析将从使用MHD的工具开始，但很可能完全理解将需要等离子体动力学理论的某些方面。其目的是为解释现有观测结果制定一个框架，并确定对额外测量的需要。提出的工作解决了似乎是相互作用的太阳风/电离层/磁层系统动力学的核心过程，新的结果将阐明元素耦合过程。虽然所讨论的问题是地球磁层的问题，但结果可能具有更广泛的意义，因为它们将适用于磁化等离子体的相互作用，无论它们在哪里：在其他磁层中，在太阳日冕中，或在实验室中。＊＊＊