Satellite Remote Sensing Study of Dayside Magnetospheric Ultralow-Frequency Waves

Johns Hopkins University, Baltimore MD

Investigators

Abstract

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 orientation Ultralow-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