PNNL

Abstract

A Doppler lidar deployed to the center of the Great Salt Lake (GSL) basin during the Vertical Transport and Mixing Experiment (VTMX) in October 2000 found a diurnal cycle of the along-basin winds with northerly, up-basin flow during the day and a southerly, down-basin low-level jet at night. The emphasis of VTMX was on stable atmospheric processes in the cold-air pool that formed in the basin at night. During the night the jet was fully formed as it entered the GSL basin from the south. Thus it was a feature of the complex string of basins draining into the Great Salt Lake, which included at least the Utah Lake basin to the south. The timing of the evening reversal to down-basin flow was sensitive to the larger-scale north-south pressure gradient imposed on the basin complex. On nights when the pressure gradient was not too strong, local drainage flow (slope flows and canyon outflow) was well developed along the Wasatch Range to the east and coexisted with the basin jet. The coexistence of these two types of flow generated localized regions of convergence and divergence, in which regions of vertical motions and transport were focused. Mesoscale numerical simulations captured these features and indicated that updrafts on the order of 5 cm s-1 could persist in these localized convergence zones, contributing to vertical displacement of air masses within the basin cold pool.