Theory of Kinetic Alfven Waves on Auroral Field Lines

极光场线上的动力学阿尔芬波理论

• 批准号: 0613473
• 负责人: Robert Lysak
• 金额: $ 30万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-08-01 至 2010-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0613473&HistoricalAwards=false
• 关键词: Theory; Kinetic; Alfven; Waves; Auroral

This project will investigate the theory of kinetic Alfven waves and wave packets along auroral field lines in the Earth's magnetosphere. Such waves play a major role in carrying energy from the outer magnetosphere to lower altitudes where the waves accelerate the precipitating electrons and ions that cause the aurora. Alfven waves also play an important role in generating the out-flowing plasma that populates the outer magnetosphere. While the theory of magnetohydrodynamics (MHD) is adequate to describe a wide variety of space plasma phenomena, the plasma processes that dominate the physics in the lower regions of auroral field lines are inherently kinetic and so are not well described by MHD theory. In addition, the auroral acceleration region is a strongly dynamic and inhomogeneous region, implying that standard local plasma kinetic theory is also limited in its ability to describe these phenomena. In particular, the auroral acceleration region is coupled to the collisional ionosphere, and in fact can change the conductivity of the ionosphere due to the precipitation of charged particles. Thus, a detailed study of the kinetic processes that accelerate auroral particles and the electrodynamic coupling of this region to the ionosphere is necessary to understand the basic plasma processes that power the aurora. In particular, the project will investigate Alfvenic interactions in the ionospheric Alfven resonator. This is the resonant cavity formed in the topside auroral ionosphere by the large increase of the Alfven speed along auroral field lines. The research will focus on three processes that affect the coupling of the magnetosphere and ionosphere: (1) Non-local theory of kinetic Alfven waves that lead to the acceleration of auroral electrons, (2) nonlinear interactions between Alfven waves and wave packets trapped in the ionospheric Alfven resonator that can lead to structuring of the auroral current system and the formation of density cavities by the ejection of plasma into the outer magnetosphere, and (3) Ionospheric feedback interactions due to modifications of the ionospheric conductivity by electron precipitation. These processes will be studied by appropriate theoretical and numerical models based on existing numerical codes. Nonlinear modeling will enable the investigation of density and current structuring on auroral field lines. A three-dimensional model of the propagation of Alfven waves and their interaction with the ionosphere will be used to study the feedback interaction in great detail. This work will also serve the educational purpose of training graduate students in methods of developing and utilizing numerical plasma models. It will contribute to the understanding of the geospace system, which will assist society in its understanding of space weather processes that can impact communication and power systems.

该项目将研究沿地球磁层极光场线的动能阿尔文波和波包理论。这些波在将能量从外磁层携带到较低海拔方面发挥着重要作用，在低海拔地区，波加速了电子和离子的沉淀，从而导致了极光。 阿尔文波在产生外磁层中的流出等离子体方面也发挥着重要作用。虽然磁流体动力学 (MHD) 理论足以描述各种空间等离子体现象，但在极光场线下部区域中主导物理的等离子体过程本质上是动力学的，因此 MHD 理论无法很好地描述。此外，极光加速区域是一个强动态且不均匀的区域，这意味着标准局域等离子体动力学理论在描述这些现象的能力上也受到限制。特别是，极光加速区域与碰撞电离层耦合，并且实际上可以由于带电粒子的沉淀而改变电离层的电导率。因此，有必要详细研究加速极光粒子的动力学过程以及该区域与电离层的电动耦合，以了解为极光提供动力的基本等离子体过程。特别是，该项目将研究电离层阿尔芬谐振器中的阿尔芬相互作用。 这是由于阿尔文速度沿极光场线大幅增加而在极光电离层顶部形成的谐振腔。该研究将重点关注影响磁层和电离层耦合的三个过程：（1）导致极光电子加速的动力阿尔文波非局域理论，（2）阿尔文波与电离层阿尔文谐振器中捕获的波包之间的非线性相互作用，可导致极光电流系统的结构化以及通过喷射形成密度空腔 等离子体进入外磁层，以及（3）由于电子沉淀改变电离层电导率而产生的电离层反馈相互作用。这些过程将通过基于现有数值代码的适当理论和数值模型进行研究。非线性建模将能够研究极光场线上的密度和电流结构。阿尔文波传播及其与电离层相互作用的三维模型将用于详细研究反馈相互作用。这项工作还将服务于培训研究生开发和利用数值等离子体模型的方法的教育目的。它将有助于理解地球空间系统，从而帮助社会理解可能影响通信和电力系统的空间天气过程。