Nonlinear Plasma Waves at the Earth's Bow Shock

它的目的是在地球弓形激波上游的空间区域开展若干与非线性MHD波和朗缪尔波有关的理论和观测研究。计划将大振幅MHD波，特别是其陡直的外观，与非线性波动方程（如导数非线性薛定谔方程（DNLS））的解进行比较。我们将努力将描述共振粒子相互作用、真实粒子分布函数、倾斜传播以及二维和三维等重要物理效应的术语添加到DNLS中。目前正在进行的对上游MHD波中重要的各种线性和非线性波过程的广泛调查将完成。确定了20个上游波活动周期，获得了数据，并计算了功率谱和互相关函数。新的工作将解决笨重的非线性，参数衰减不稳定性和三维波效应可以在数据中识别的程度。在对朗缪尔波的研究中，工作将集中在进一步的数值和分析研究上，其中一部分是利用计算机模拟对波束不稳定性的饱和相位进行研究。这些研究的目标将是更好地理解波的后向散射、低频波的产生以及波束驱动波的长时间演化等现象。

It is intended to carry out several theoretical and observational studies related to nonlinear MHD waves and Langmuir waves in the region of space upstream to the Earth's bowshock. It is planned to compare the large amplitude MHD waves, and in particular their steepened appearance, to the solutions of nonlinear wave equations such as the Derivative Nonlinear Schrondinger Equation (DNLS). Efforts will be made to append terms to the DNLS which describe important physical effects such as resonant particle interactions, realistic particle distribution functions, oblique propagation, and two and three dimensionality. An extensive investigation, currently in progress, of the various linear and nonlinear wave processes which are important in the upstream MHD waves will be completed. Twenty periods of upstream wave activity have been identified, the data acquired, and power spectra and cross correlation functions calculated. New work will address the extent to which pondermotive nonlinearities, the parametric decay instability, and three dimensional wave effects can be discerned in the data. In the study of Langmuir waves, work will concentrate on further numerical and analytic studies of the saturated phase of the beam instability using computer simulations in part. The goal of these studies will be to better understand such phenomena as wave backscattering, generation of low frequency waves, and the long time evolution of the beam-driven waves.