Spatial characteristics of the midnight temperature maximum and equatorial spread F from multi-instrument and magnetically conjugate observations
Hickey, Dustin A.
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The upper atmosphere, a region above ~85 km called the ionosphere and thermosphere, has been studied extensively for over one hundred years. Measurements were often considered in isolation, but today, advances in technology and ground-based distributed arrays have allowed concurrent multi-instruments measurements. In this dissertation, I combine measurements from all-sky imagers (ASIs), coherent scatter radars, incoherent scatter radars (ISRs), and Fabry-Perot interferometers (FPIs). I focus on two phenomena, the midnight temperature maximum (MTM) and equatorial spread F (ESF), using observations from equatorial to mid-latitudes. The spatial characteristics of these phenomena are not fully understood. I combine observations at various latitudes and longitudes to extend MTM detection to mid-latitudes. I present the first simultaneous detections of the MTM at multiple altitudes and latitudes over North America and the first observations below the F-region peak using the Millstone Hill Observatory ISR in a south pointing, low-elevation mode. The MTM can also be observed with an ASI and I present concurrent measurements of the MTM with an ASI and ISR. The Whole Atmosphere Model, a global circulation model, was found to be consistent with these observations. This further verifies that the MTM is partially created by lower atmospheric tides, demonstrating coupling between the lower and upper atmosphere. In addition to the MTM, I investigate different aspects of ESF using ASIs concurrently with other instruments. I compare various scale sizes (sub-meter to kilometers) using coherent scatter radar and an ASI and conclude that the lower hybrid drift instability causes radar echoes to occur preferentially on the western wall of large-scale depletions. The source of day-to-day variability in ESF is not fully known but I show that one driver may be large-scale wave structures (~400 km) that modulate the development of ESF. Finally, I compare concurrent observations of ESF plasma depletions with ASIs at magnetically-conjugate foot points and show how the magnitude and structure of the Earth’s magnetic field is responsible for differences in the morphology and velocity of these depletions. In summary, I have used multi-instrument observations of ESF and the MTM to provide a deeper understanding of the dynamics of the upper atmosphere.
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