PNNL

Abstract

Six PFT experiments were conducted in Salt Lake City during October 2000 as part of the VTMX field campaign. Four tracers were released at different sites to obtain information on dispersion during stable conditions within down-valley flow, canyon outflow, and interacting circulations in the downtown area. Some of the extensive tracer data that were collected is presented in the context of the meteorological field campaign measurements. Tracer measurements at building top sites in the downtown area and along the lower slopes of the Wasatch Front indicated vertical mixing processes transported material up to at least 180 m above the valley floor. Tracer data provided evidence of downward mixing of canyon outflow, upward mixing within down-valley flow, horizontal transport above the surface stable layer, and transport within horizontal eddies produced by the interaction of canyon and down-valley flows. Although point meteorological measurements are useful in evaluating the forecasts produced by mesoscale models, the tracer data provides information on the time-varying three-dimensional mean and turbulent motions that cannot be obtained in any other way. While the mean tracer transport predicted by the modeling system employed in this study was qualitatively similar to the measurements, improvements are needed in the treatment of turbulent vertical mixing.