University of Minnesota
School of Physics & Astronomy

Space Physics Seminar

Tuesday, October 13th 2009
12:20 pm:
Space Physics Seminar in 143 Physics
Speaker: Dr. Chris Colpitts, Dartmouth University
Subject: “Swishers” and “Stripes”: Examinations of Dispersed Features of Auroral HF Waves Observed with Sounding Rockets

Earth’s high latitude ionosphere, highly disturbed by the particle and energy inputs and associated aurora, is the stage for plasma wave activity across a wide range of frequencies. These waves often exhibit strikingly distinct time-frequency structure which can have relatively direct explanations based on the dispersion relations of the appropriate normal modes of the plasma. Hence, they present an opportunity to confirm basic plasma physics. Moreover, once a physical explanation is proven for these emissions, it is often possible to exploit the structured waves to either measure characteristics of the local plasma or remotely sense characteristics of plasmas through which the waves have propagated. Observations of structured HF emissions from three recent auroral sounding rockets are presented.Identifying the wavemode of observed emissions is the first step in characterizing them, and I will present a novel technique that has been developed to constrain the mode of observed emissions by taking advantage of the orientation of the electric field sensors. In addition, auroral rocket observations of two structured emissions having distinct frequency-time patterns, “swishers” and “stripes,” are investigated. Ray-tracing and growth rate calculations provide effective tests of the mode identification and possible generating mechanisms of these emissions. Lastly, rocket observations of waveform statistics and spectra of short intense bursts of Langmuir waves in the polar cusp ionosphere reveal information about the modulation of these waves and the density fluctuations in which they arise. Taken together, the observations of these dispersed features and the development of new techniques to constrain their modes and identify their generation mechanisms add to our existing knowledge of the auroral ionosphere and show promise in remote sensing plasma characteristics elsewhere in the Earth’s magnetosphere and beyond.

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