Satellite Remote Sensing Study of Dayside Magnetospheric Ultralow-Frequency Waves

该项目的目标是利用全球远紫外线图像、地球极光区域和极冠来处理有关在Pc5频率范围(2-7兆赫)出现超低频(ULF)波的若干问题。与磁强计和高频雷达等传统的地基Pc5探测技术相比，全球极光图像具有更好的空间覆盖和/或分辨率，并且在磁场扰动方面不受高m超低频波的电离层屏蔽效应的影响。首先要考虑的问题是，太阳风中准周期气压变化激发Pc5波的频率是多少。一个相关的问题是，Pc5超低频波是否在高太阳风速时优先发生。该项目还将解决太阳风压力脉冲与磁通量转移事件在产生Pc5脉动方面的相对重要性的问题。这些问题将通过分析极光紫外线获取的极光图像以及航天器(极地、地尾、星际1号、星系团和THEMIS)的其他现场磁场测量来解决，方法是使用一种称为S变换的频谱分析技术。S变换使得提取全局Pc5超低频波特征成为可能。该项目将确定磁层对准周期太阳风压力变化的响应是作为呼吸模式还是作为腔/波导模式，方法是确定ULF波是否直接驱动并向反太阳传播。它将通过确定开尔文-亥姆霍兹驱动事件和压力脉冲驱动事件是否与太阳风特征有关或往往发生在高速气流中来区分它们；它将通过检查波动是否取决于磁鞘流速和IMF取向来区分与磁通量转移事件有关的Pc5事件和压力脉冲驱动事件。它们构成了对磁层对外部干扰的反应方式的重要诊断。这样的研究产生了大量的文献。然而，目前的理论模型的适用范围仍然不确定。这在很大程度上是由于对Pc5极低频波的全球特征缺乏了解。使用传统技术很难获得这种知识。Pc5频率范围内的波对地球辐射带中电子的能化有重要影响。一种新的、先进的频谱分析工具(S变换)在二维极光图像中的应用可以很容易地推广到研究更高频率的超低频波及其跨尺度耦合

The objective of this project is to use global far-ultraviolet (FUV) images Earth's auroral regions and polar caps to address several questions concerning the occurrence of ultra-low frequency (ULF) waves in the Pc5 frequency range (2 - 7 mHz). Compared to the traditional ground-based Pc5-detecting techniques such as magnetometers and HF radars, the global auroral images have much better spatial coverage and/or resolution, and are not subject to the ionospheric screening effect of the higher-m ULF waves in terms of magnetic disturbances. The first question to be considered is how often quasi-periodic pressure variations in the solar wind excite Pc5 waves. A related question is whether or not Pc5 ULF waves occur preferentially for high solar wind speed. The project will also address the question of the relative significance of solar wind pressure pulses versus magnetic flux transfer events in generating Pc5 pulsations. These questions will be addressed by analyzing auroral images acquired by Polar UVI, along with other in situ magnetic field measurements from spacecraft (Polar, Geotail, Interball-1, Cluster, and THEMIS), using a spectral analysis technique known as the S-Transform. The S-Transform makes it possible to extract the global Pc5 ULF wave features. The project will determine if the magnetosphere responds to quasi-periodic solar wind pressure variations as a breathing mode or as a cavity/waveguide mode by determining whether or not the ULF waves are directly driven and propagate antisunward. It will distinguish between Kelvin-Helmholtz driven and pressure pulse driven events by determining whether they are associated with solar wind features or tend to occur during high speed streams, it will distinguish between Pc5 events associated with magnetic flux transfer events and pressure pulse driven events by checking if the wave motion depends on the magnetosheath flow speed and IMF orientationUltralow-Frequency (ULF) waves in the magnetosphere and ionosphere have been studied in a wide variety of contexts for a very long time. They constitute an important diagnosis of the ways the magnetosphere responds to external disturbances. A great volume of literature has resulted from such studies. Yet, the region of applicability of the current theoretical models are still uncertain. This is in large measure due to the lack of knowledge on the global characteristics of Pc5 ULF waves. This knowledge is hard to obtain using traditional techniques. Waves in the Pc5 frequency range have important effects in the energization of electrons in Earth's radiation belts. Applications of a new, advanced spectral analysis tool (the S-transform) in 2-D auroral images can be readily generalized to the study of ULF waves of higher frequencies and their cross-scale coupling