Theory of Kinetic Alfven Waves and Auroral Particle Acceleration

这个提议的重点是开发一个全新的极光弧形成范例，如果正确的话，将是极光物理学的突破性进展。极地地区出现的动态极光是近地空间剧烈扰动导致能量流入大气的视觉指示器。为极光发射提供动力的电子和离子沿着磁场线从这些干扰中移动，并且必须在途中进一步加速。几十年来，大多数加速被认为是电子和离子沿着磁场线移动时穿过准静态电位下降的结果。当等离子体中形成两个平行的带相反电荷的层，形成电场和相关的电压降时，就会产生这些电位下降。极光电子通过电压降被加速，形成一个单一的能量峰值。近年来，动力学阿尔芬波对电子的随时间加速的意义已经变得清晰起来。在某些情况下，当阿尔芬波（沿着磁场传播磁场其他地方变化的影响）发展出与背景磁场平行的电场时，就会形成动态阿尔芬波。与之前的机制相反，平行波电场在很宽的能量范围内加速电子。然而，这两个过程都没有得到很好的理解。更复杂的是，这两个过程都受到与电离层耦合和反馈的影响。PI已经发展了一个令人信服的新理论，这两个过程是相关的（即，动能阿尔芬波过渡到准稳态形成平行电位下降）。这里的重点是检验这个理论。这项工作的更广泛的影响包括培训研究生和通过公共宣传传播结果。这项研究有望引起其他等离子体物理团体的广泛兴趣。从长期来看，它将有助于更好地了解空间环境，从而改进预测，并制定有效的减缓战略，以保护对社会有价值的脆弱技术。该方法将理论和建模相结合，目标是包括从时间依赖到准稳定条件转变的大范围时空尺度，大参数范围，通过电离层反射Alfven波的反馈，以及由于沉淀电子引起的电离层电导率的改变，以及通过沿极光场线的密度空腔的形成和影响。主要工具是已经开发的线性化双流体模型，该模型将被修改为包括：沿磁力线的非线性电子动力学和现实的偶极子磁场几何。该模型将与动力学电子模型相结合，用于研究电子的加速度及其与动力学阿尔芬波的自洽相互作用。

This proposal is focused on developing an entirely new paradigm for auroral arc formation that, if correct, will be groundbreaking for auroral physics. The dynamic auroras that appear in the polar regions are visual indicators of energy flowing into the atmosphere from disturbances raging in near-Earth space. Electrons and ions, that power the auroral emissions, travel down magnetic field lines from these disturbances and must be further accelerated along the way. For several decades, the majority of the acceleration was thought to be the result of electrons and ions traversing quasi-static potential drops while moving down magnetic field lines. These potential drops are created when two parallel oppositely-charged layers form in the plasma setting up an electric field and an associated voltage drop. The auroral electrons are accelerated through the voltage drop creating a single energy peak. Recently the significance of time dependent acceleration of electrons by kinetic Alfven waves has become clear. Kinetic Alfven waves are formed under certain circumstances when Alfven waves (traveling along the magnetic field communicating the effects of changes elsewhere in the field) develop an electric field parallel to the background magnetic field. In contrast to the previous mechanism, the parallel wave electric fields accelerate electrons over a broad energy range. However, neither of these processes is well understood. To complicate things, both processes are influenced by coupling and feedbacks with the ionosphere. The PI has developed a compelling new theory that the two processes are related (i.e., that kinetic Alfven waves transition to a quasi-steady state forming parallel potential drops). The focus here is on testing this theory. Broader impacts of the work include the training of a graduate student and communication of results through public outreach. The research is expected to be of broad interest to other plasma physics communities. In the longer-term, it will contribute to better understanding of the space environment, resulting in improved forecasts, and the development of efficient mitigation strategies to protect vulnerable technologies of value to society. The approach combines theory and modeling with the goal of including a large range of temporal and spatial scales involved in the transition from time-dependent to quasi-steady conditions, a large parameter range, feedbacks through ionospheric reflection of the Alfven waves and by modifications of the ionospheric conductivity due to the precipitating electrons, as well as by the formation and effects of density cavities along the auroral field lines. The primary tool is an already developed linearized two-fluid model, which will be modified to include: nonlinear electron dynamics along the magnetic field line and a realistic dipole magnetic field geometry. This model combined with a kinetic electron model will be used to investigate the acceleration of electrons and their self-consistent interactions with the kinetic Alfven waves.