Theoretical Study of Auroral Radio Waves

地球的电离层是一个等离子体，由大约相等数量的离子和电子组成。 除了影响所有物质的重力外，电力和磁力在决定电离层等离子体的行为方面也很重要。等离子体的行为就像流体一样，即使粒子之间很少发生碰撞，因为电力和磁力在一定距离上作用。类似于海洋中的波浪，等离子体波通过电离层传输能量。 电磁场、压力场和速度场的组合产生了各种各样的等离子体波。这种波浪环境非常复杂，具有一系列生成机制，波浪频率和源位置。然而，由于这种复杂性，许多这些波及其生成机制知之甚少。 极光区对地球的自然无线电波环境有着重要的贡献。本计画主要探讨极光咆哮现象及其产生机制，这是一个复杂且非线性的现象，涉及到波与波、波与粒子的相互作用。由于产生的波的类型取决于等离子体条件，并且可以在远离源区的地方观察到，因此它们提供了一种远程推断等离子体特性的方法。 因此，关于极光区波的知识可以用来解释产生这些波的天体物理和行星环境中的条件。 为了研究极光咆哮的起源，这个项目使用并进一步发展了弱湍流理论。 这本身就是该项目的一个重要成果。 其主要目的是促进发展一个关于在地球电离层和磁层观测到的等离子体和无线电发射的统一理论。极光咆哮的非线性研究可能会导致对波粒相互作用的基本物理学的更深入的理解。详细探讨了四个问题：（1）极光咆哮发射精细频率结构的形成;（2）强烈的上混合波衰减成多个谐波和低频波;（3）4fce极光咆哮的非线性合并产生;（4）上混合波、下混合波和伯恩斯坦波的衰减不稳定性。

The Earth's ionosphere is a plasma composed of approximately equal numbers of ions and electrons. In addition to gravity that affects all matter, electric and magnetic forces are important in determining the behavior of the ionospheric plasma. The plasma behaves as a fluid even if there are few collisions between particles because electric and magnetic forces act at a distance. Analogous to waves in the ocean, plasma waves transmit energy through the ionosphere. Electromagnetic, pressure and velocity fields in combination produce a wide variety of plasma waves. This wave environment is extremely complex with a range of generation mechanisms, wave frequencies, and source locations. However, because of this complexity, many of these waves and their generation mechanisms are poorly understood. The auroral region contributes significantly to the natural radio wave environment of the Earth. This project investigates auroral roar and its generation mechanisms, which are complex and nonlinear involving wave-wave and wave-particle interactions. Because the types of waves generated depend on plasma conditions and can be observed far from the source region, they provide a means to infer the characteristics of plasmas remotely. As a result, what is learned about waves in the auroral region can be used to interpret conditions in astrophysical and planetary environments where these same waves are generated. To study the origins of auroral roar, this project uses, and develops further, weak turbulence theory. This, in itself, is an important outcome of the project. A main aim is to contribute to the development of a unifying theory of plasmas and radio emission observed in the Earth's ionosphere and magnetosphere. Non-linear studies of auroral roar are likely to lead to a deeper understanding of the fundamental physics of wave-particle interactions. Four problems are explored in some detail: (1) the formation of the fine frequency structure of auroral roar emissions; (2) the decay of intense upper hybrid waves into multiple harmonics and lower frequency waves; (3) nonlinear coalescence generation of 4fce auroral roar; and (4) decay instability of upper-hybrid, lower-hybrid, and Bernstein waves.