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

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。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较小时，太阳风流马赫数较大时，磁层对太阳风驱动因子的变化有线性响应。特别是，横跨极帽的电离层电势（它调节电离层和磁层等离子体对流）与向南的IMF的太阳风电场呈线性相关。然而，当IMF较大时，磁层响应是非线性的，相对于太阳风电场，极帽电位趋于饱和。该项目将通过使用太阳风与磁层相互作用的全球磁流体动力学（MHD）模拟来研究磁层的非线性响应。模拟结果将使用来自各种航天器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：“对行星际磁场（IMF）的大值产生非线性磁层响应的基本物理原理是什么？这种响应是如何在IMF的不同方向上表现出来的？”初步的工作表明，在确定太阳风在磁层周围的流动和低磁声速马赫数流动期间太阳风与磁层的相互作用时，弓形激波产生的大电流的闭合和磁力在等离子体压力梯度上的优势是潜在物理学的一个关键方面。发电机弓形激波电流通过电离层负荷的闭合，可以提供一种直接将从弓形激波处提取的太阳风机械能在开场线上传递到电离层的方法。这种机制在物理上不同于磁重联和粘性相互作用，它代表了将太阳风能量转移到地球空间系统的第三种基本模式。该项目提出了太阳风向地球空间系统转移的一个新的、潜在的变革范例，它不仅能够解释一系列非线性磁层对大IMF值的响应，而且还将为重新解释已知的、但尚未得到很好理解的现象（如叶细胞对流和半球间不对称）提供一个框架。该项目包括支持和培训一名研究生到博士学位。此外，几名本科生也将参与其中，包括少数民族学生。所有学生都将在会议上做报告，并参与结果的发表。研究结果将在德克萨斯大学阿灵顿天文馆通过可视化呈现给公众。

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.