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

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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).