Solar Wind Energy Transfer to Geospace during Periods with Large Transverse Interplanetary Magnetic Field (IMF)

该奖项由2009年美国复苏和再投资法案(公法111-5)资助。太阳风中控制磁层活动的主要因素是行星际磁场(IMF)的方向和大小。当IMF相对较小，太阳风流的马赫数较大时，磁层对太阳风驱动力的变化做出线性响应。特别是，极帽(调节电离层和磁层等离子体对流)两端的电离层电势与向南的国际货币基金组织的太阳风电场呈线性关系。然而，当IMF很大时，磁层响应是非线性的，极帽电势相对于太阳风电场饱和。该项目将通过使用太阳风与磁层相互作用的全球磁流体力学(MHD)模拟来研究磁层的这种非线性响应。模拟结果将使用来自各种航天器飞行任务和地面观测的数据集进行验证。这项研究的目的是回答这样一个问题：“产生大的行星际磁场(IMF)的非线性磁层响应的基本物理是什么？这一点如何在IMF的不同方向上表现出来？”初步工作表明，基本物理学的一个关键方面是关闭弓激波产生的大电流，以及磁力在决定太阳风绕磁层流动的过程中对等离子体压力梯度的主导作用，以及在低磁声马赫数流动期间太阳风与磁层的相互作用。通过电离层负载的发电机弓激波电流的闭合可提供一种将从弓激波的气流中提取的太阳风机械能直接转移到开放场线上的电离层的手段。这种机制在物理上不同于磁重联和粘性相互作用，是将太阳风能转移到地球空间系统的第三种基本模式。该项目提出了一种新的、可能具有变革性的太阳风能向地球空间系统转移的范例，它不仅将能够解释磁层对国际货币基金组织大值的一系列非线性反应，而且将为重新解释已知但尚未得到很好理解的现象，如叶单元对流和半球间不对称现象提供一个框架。该项目包括对一名研究生通过博士学位的支持和培训。此外，还将涉及几名本科生，包括少数民族学生。所有学生都将在会议上发表演讲，并参与结果的发布。研究结果将在德克萨斯大学阿灵顿天文馆通过可视化向公众展示。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The major factor in the solar wind that controls magnetospheric activity is the direction and magnitude of the interplanetary magnetic field (IMF). When the IMF is relatively small, and the mach number of the solar wind flow is large, the magnetosphere responds linearly to changes in the solar wind driver. In particular, the ionospheric potential across the polar cap (which regulates ionospheric and magnetospheric plasma convection) is linearly related to the solar wind electric field for southward IMF. However, when the IMF is large, the magnetospheric response is non-linear, and the polar cap potential saturates with respect to the solar wind electric field. This project will investigate this non-linear response of the magnetosphere through the use of global magnetohydrodynamic (MHD) simulations of the solar wind interacting with the magnetosphere. Simulations results will be verified using data sets from various spacecraft missions and ground-based observations. The aim of the research is to answer the question "What is the fundamental physics that produces a nonlinear magnetospheric response to large values of the Interplanetary Magnetic Field (IMF) and how does this manifest itself for various orientations of the IMF?" Preliminary work suggests that a crucial aspect of the underlying physics is the closure of the large current produced at the bow shock and the dominance of magnetic forces over plasma pressure gradients in determining the solar wind flow around the magnetosphere and the interaction of the solar wind with the magnetosphere during periods of low magnetosonic Mach number flow. The closure of the dynamo bow shock current through the ionospheric load may provide a means of directly transferring solar wind mechanical energy extracted from the flow at the bow shock to the ionosphere on open field lines. Such a mechanism is physically distinct from both magnetic reconnection and the viscous interaction, and represents a third, fundamental mode of transferring solar wind energy to the geospace system. This projects suggests a new and potentially transformative paradigm for solar wind energy transfer to the geospace system that not only would be able to explain a range of nonlinear magnetospheric responses to large IMF values, but also would provide a framework for the reinterpretation of known, but not well understood phenomena such as lobe cell convection and interhemispheric asymmetries. The project includes support and training for a graduate student through the Ph.D. In addition, several undergraduate students will be involved, including minority students. All students will give presentations at meetings and be involved in publication of the results. Results of the research will be presented to the general public through visualizations at the University of Texas, Arlington Planetarium.