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Ionospheric Signatures of Ultra Low Frequency Waves

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posted on 2011-03-15, 13:26 authored by James David Borderick
Ultra Low Frequency (ULF) waves have been studied for many years and the observation and modelling of such phenomena reveals important information about the solar-terrestrial interaction. Being ubiquitous in the collisionless terrestrial space plasma environment, ULF waves represent important physical processes in the transfer of energy and momentum. This thesis comprises three distinct studies to observe, model and analyse ULF phenomena. The first two studies focus on ULF wave observations at high-latitudes in the terrestrial ionosphere using a collection of both space- and ground-based instruments. The first study provides a detailed analysis of the time evolution of a ULF wave using the characteristics of the observed ULF wave as input-parameters to a 1-D numerical model. As the wave signature evolves towards a Field Line Resonance (FLR) a change in the incident wave mode from a partially Alfvénic wave to a purely shear Alfvénic wave is observed. The second study presents statistics of 25 large spatial-scale ULF waves with observations from a high-latitude Doppler sounder and ground-based magnetometers, complemented by model results. The third and final study describes the implementation of a well established radar technique ("double-pulse"), which is new for the Super Dual Auroral Radar Network (SuperDARN), which aims to provide an unprecedented temporal resolution for ULF wave studies. The new pulse sequence increases the temporal resolution of SuperDARN by a factor of three. Preliminary findings suggest this technique yields impressive results for ionospheric scatter with steady phase values but that the method cannot be used for data when the phase is rapidly changing or if the data originates from slowly decorrelating plasma irregularities. The running of two independent pulse sequences on the stereo channels of the Hankasalmi radar has also enabled, for the first time, the observation of cross-contamination between the radar channels.



Yeoman, Tim K.; Milan, Stephen

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University of Leicester

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