Observations and modeling of thermally driven wind jets at the exit of a Utah canyon

This thesis investigates summertime thermally driven wind circulations in a Utah canyon. The study is focused around Weber Canyon, Utah, which is a main tributary canyon that feeds into the Great Salt Lake basin. A measurement campaign was conducted during July-September 2010 to observe and characterize the wind flow patterns in Weber Canyon and specifically the nature of the summertime fair-weather wind jet that has been observed to form at the exit region of Weber and other Utah canyons. This thesis research uniquely combines many meteorological data sources including existing automatic weather stations, measurement equipment borrowed from several generous parties, and equipment owned by the University of Utah's Atmospheric Sciences department. Winds within the canyon and at the exit exhibited a strong seasonal and diurnal variation that is linked to the yearly course of solar insolation. Strong nocturnal low-level wind jets formed on 75 of 90 nights (83%) at the Weber Canyon exit during the measurement campaign. Winds inside the canyon consisted of a weak but deep down valley flow layer that occupied most of the depth of the canyon. The flow was observed to descend, thin and compress at the exit where winds were typically twice as strong as inside the canyon and much more shallow. Flow within the canyon and at the exit was influenced by the larger scale synoptic conditions. Clear skies and weak regional pressure gradients along with light winds aloft were conducive to the development of strong canyon exit flows. Four canyon flow regimes were observed depending upon the strength and orientation of the synoptic flow. Observations of flow properties within and at the exit of the canyon were compared to Large Eddy numerical simulations using the Advanced Research Weather Research and Forecast (ARW) numerical weather prediction (NWP) model developed by NCAR. Good agreement between the observations and model simulations has been achieved. The wind power potential at the exit region is shown to be excellent.