Theory of Kinetic Alfven Waves on Auroral Field Lines

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。该项目将研究地球磁层中极光场线上的阿尔芬波动力学理论。这种波在将能量从外层磁层输送到较低的高度方面发挥了重要作用，在那里它加速了导致极光的沉淀电子和离子。控制极光场线下部物理的等离子体过程本质上是动力学的，因此磁流体动力学(MHD)理论不能很好地描述这一过程。极光加速区与碰撞电离层耦合，可以改变电离层的电导率。对加速极光粒子的动力学过程以及该区域与电离层的电动力学耦合进行详细研究，对于了解为极光提供动力的基本等离子体过程是必要的。本研究将集中于影响磁层和电离层耦合的三个主要过程：(1)阿尔芬波和波包的非线性相互作用的跨尺度耦合，(2)极光区等离子体密度的演化，(3)三维电离层中的电子动力学效应和电离层反馈。这些过程将在现有数值程序的基础上，用解析理论方法和数值模型进行研究。基于施特劳斯方程的简化MHD描述将用于研究极光区垂直空间尺度上的非线性相互作用。这个非线性模型将扩展到包括双流体并行动力学，这将使研究极光场线上的密度演化和极光密度空穴的形成成为可能。这项工作将服务于培养研究生开发和利用数值等离子体模型的方法的教育目的。它将有助于了解地球空间系统，这将有助于社会了解可能影响通信和电力系统的空间天气过程。对地球极光带等离子体物理的了解可以作为日冕和其他宇宙等离子体中粒子加速过程的模型。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).This project will investigate the theory of kinetic Alfven waves 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 it accelerates the precipitating electrons and ions that cause the aurora. 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 magnetohydrodynamic (MHD) theory. The auroral acceleration region is coupled to the collisional ionosphere and can change the conductivity of the ionosphere. 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. This research will focus on three main processes that affect the coupling of the magnetosphere and ionosphere: (1) cross-scale coupling by nonlinear interactions of Alfven waves and wave packets, (2) evolution of the plasma density in the auroral zone, and (3) electron kinetic effects and ionospheric feedback in the three-dimensional ionosphere. These processes will be studied by analytical theoretical methods and numerical models based on existing numerical codes. A reduced MHD description based on the Strauss equations will be used to investigate nonlinear interactions across perpendicular spatial scales in the auroral zone. This nonlinear model will be extended to include two-fluid parallel dynamics which will enable the investigation of density evolution on auroral field lines and the formation of auroral density cavities. This work will 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. An understanding of the plasma physics of the Earth's auroral zone may serve as a model for particle acceleration processes in the solar corona as well as other cosmic plasmas.