Space Weather: Spacecraft Observations of Storm Time Ultra-Low-Frequency Waves

在地磁风暴过程中，外辐射带中相对论电子的通量发生了剧烈的变化。这种流量达到的水平可能会扰乱航天器的运行，并危及人类在太空中的活动。该项目将确定通量变化的机制。一般情况下，需要一个时变的电场来引起粒子数量的时间变化，在风暴时间的情况下，1-10分钟周期内的相对论电子超低频波被认为是该电场的来源。该项目的具体目标是利用卫星的现场测量和地面的相关测量，找出风暴时间的超低频波的模式和幅度。利用Polar和Go航天器的磁场和电场测量以及地面磁强计，确定了Pc3-5频段(周期10-600 S)的超低频波的频率、幅度、极化和空间结构。将波的幅度与航天器测量的电子通量进行比较，以验证波和电子之间的因果关系。以前关于电子通量和超低频波之间的关系的研究是基于在地面上观测到的波。地面观测是有限的，因为它们不提供电场的直接测量，而且它们受到电离层的强烈屏蔽。相比之下，卫星的现场测量提供了关于电场和波的其他特性的直接信息。一旦了解了波的性质，就可以用它们来模拟超低频波对辐射带粒子的影响。这将导致更好地预测粒子通量变化的行为，这是国家空间天气计划(NSWP)的优先目标。

The flux of relativistic electrons in the outer radiation belt changes dramatically during the course of a geomagnetic storm. The flux reaches a level that can cause disruption of spacecraft operations and endanger human activities in space. This project will identify the mechanism of the flux changes. In general, a time varying electric field is required to cause temporal variations of particle populations and in the case of storm time relativistic electrons ULF waves in the 1-10 min period have been suggested as the source of that electric field. The specific objective of project is to find the mode and amplitude of storm time ULF waves using in-situ measurements from satellites and correlative measurements on the ground. Magnetic and electric field measurements from the Polar and GOES spacecraft and ground magnetometers are used to determine the frequency, amplitude, polarization, and spatial structure of ULF waves in the Pc 3-5 bands (period 10-600 s). The amplitude of the wave is compared with the flux of electrons measured by spacecraft in order to verify the causal relationship between waves and electrons. Previous studies of the relationship between electron flux and ULF waves were based on waves observed on the ground. Ground observations are limited in that they do not provide direct measure of the electric field and they are strongly screened by the ionosphere. By contrast, in-situ measurements by satellites provide direct information on the electric field and other properties of the wave. Once the wave properties are understood they can be used to model the effect of ULF waves on the radiation belt particles. This will lead to a better prediction of the behavior of the variations of particle fluxes, which is a high-priority goal of National Space Weather Program (NSWP).