The MUST (Mock Urban Setting Test) trials were conducted on the Horizontal Grid at the Dugway Proving Ground, UT (September 2001) in a multi-organizational effort to gain scientific understanding for improved dispersion modeling in urban areas. During the MUST trials, meteorological and concentration measurements were made around buildings in a 12 x 10 array of shipping containers (each 12.2 m long, 2.6 m wide, 2.6 m high) that were fully immersed in a high Reynolds number, real atmospheric boundary layer. For a normal incident flow angle, the inner buildings were typically in an isolated roughness regime. The data presented here were taken from the evening transition period (~17:30 LST) through the early morning (~8:00 LST) on September 24, 2001.

Previous investigations have suggested that within a building array, mechanically generated turbulence dominates over buoyancy and destroys the upstream stable stratification. In an effort to determine the effects of mechanical turbulence generated by buildings on thermal stratification (in a high Reynolds number flow), mean and fluctuating components of the velocity and temperature were made within the first row of the array with five 3D ultrasonic anemometers and five fine-wire thermocouples mounted on a 5 meter tower at z=0.6 m, 1.0 m, 1.8 m, 2.6 m, 3.7 m. Outside the array, near surface measurements of temperature were made with quartz thermometers at z=0, 0.01, 0.05, 0.10, 0.25, 0.5, 1.0 and 2.0 m. Upstream, mean velocity and turbulence quantities were measured at z=1.6 m with a 3D ultrasonic anemometer. Vertical profiles of temperature and wind speed outside of the array were obtained with a tethered balloon (up to ~300 m). Preliminary results show several interesting features, including: the existence of a persistent warm thermal plume in the wake of the building and, for the most part, a well-mixed wake with strong stable stratification above the building height associated with the upstream flow. Under a range of meteorological conditions, however, the stability within the canyon is non-neutral.