Date of Award:
Doctor of Philosophy (PhD)
Vincent B. Wickwar
The Earth's atmosphere is typically characterized by its temperature structure, which naturally divides the atmosphere into several discrete regions. They are in order of increasing altitude the troposphere, stratosphere, mesosphere, and thermosphere. The first layer and a large portion of the second layer of the Earth's atmosphere are routinely measured via weather balloons that are launched twice daily around the globe. Satellites and their development have motivated the study of the thermosphere. It is the middle region of the Earth atmosphere, which is mainly composed of the mesosphere that lacks routine in situ measurements. Routine observations are therefore carried out via remote sensing. Ground-based instruments typically provide high resolution measurements of the atmosphere over a single point on the globe and space-based instrument capture a global picture at lower resolution.
A Rayleigh-scatter lidar has been in operation at Utah State University ( 41 . 7°N III .8°N) starting in September 1993. Observations have continued from that point until the present when funding and observing conditions have permitted. Under normal observational conditions the backscattered photons are proportional to the atmospheric density. These relative density profiles can be used to derive absolute temperature profiles over much of the middle atmosphere. The resulting II years of temperature profiles have been combined into a single composite year which contains - 900 nights and - 5000 hours of observations. This climatology was compared to the mid-latitude climatology from the French lidar group at Haute Provence and relatively good agreement was obtained. It was also compared to the NRL MSIS empirical model to explore the model's validity at mid-latitudes. Some significant differences were found.
The coldest atmospheric temperatures are found at the mesopause near the summer solstice. Small ice crystals formed in this region and can grow to form noctilucent clouds (NLC) which are the highest naturally occurring clouds in the atmosphere. Previously, NLC observations have been limited to the region poleward of so• but NLCs have been observed with the ALO lidar on two occasions. Their formation has been attributed to atmospheric dynamics, a large amplitude wave, rather than a general cooling of the atmosphere.
Herron, Joshua P., "Rayleigh-Scatter Lidar Observations at USU's Atmospheric Lidar Observatory (Logan,UT) - Temperature Climatology, Temperature Comparisons with MSIS, and Noctilucent Clouds" (2007). All Graduate Theses and Dissertations. 4686.
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