Theory of Kinetic Alfven Waves and Auroral Particle Acceleration

运动阿尔文波和极光粒子加速理论

• 批准号: 1558134
• 负责人: Robert Lysak
• 金额: $ 52.02万
• 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: 2016
• 资助国家: 美国
• 起止时间: 2016-05-15 至 2019-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1558134&HistoricalAwards=false
• 关键词: Theory; Kinetic; Alfven; Waves; Auroral

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.

该提案的重点是为极光形成开发一个全新的范式，如果正确，它将为极光物理学开创性。 出现在极地区域中的动态极光是能量的视觉指标，这些指标因近地空间中的干扰而流入大气中。 电子和离子可以为极光排放动力，从这些干扰中向下沿磁场线行驶，并且必须在途中进一步加速。几十年来，大多数加速度被认为是电子和离子在沿磁场线向下移动时穿越准静态势液的结果。 当在等离子体中形成两个平行电荷的层形成两个平行的电场和相关的电压下降时，就会产生这些势液。 极光通过电压下降加速产生单个能峰。最近，动力学alfven波的时间依赖性加速度的重要性变得清晰。当Alfven波（沿着磁场传播传达该场其他地方变化的影响）在某些情况下形成动力学的Alfven波，形成了一个平行于背景磁场的电场。 与先前的机制相反，平行波电场在广泛的能量范围内加速了电子。 但是，这两个过程都没有很好地理解。 使事物复杂化，这两个过程都受到与电离层的耦合和反馈的影响。 PI开发了一种引人注目的新理论，即两个过程是相关的（即动力学的Alfven波将过渡到准稳态的状态形成平行电位下降）。 这里的重点是测试这一理论。 这项工作的更广泛影响包括对研究生进行培训以及通过公共宣传进行结果的交流。预计该研究将引起其他血浆物理社区的广泛关注。从长远来看，它将有助于更好地理解太空环境，从而改善预测，并制定有效的缓解策略，以保护脆弱的社会价值技术。 该方法结合了理论和建模与包括从时间依赖性到准稳态条件的过渡到涉及的各种时间和空间量表的目的，该条件，较大的参数范围，通过Alfven Wav的电离层反射以及通过对电气界面的电离层电导率的修改以及通过ALFENS型界定效率以及dive fiaun fiaun fiaun fiaur and the形成效应的电离层电导率的反馈。 主要工具是已经开发的线性两流体模型，将修改为：沿磁场线沿线的非线性电子动力学和逼真的偶极磁场几何形状。 该模型与动力学电子模型相结合，将用于研究电子的加速度及其与动力学Alfven波的自洽相互作用。