Interactions between regional-scale circulations and local wind systems in the Owens Valley

Airflows within mountain valleys are influenced by the interaction of the large-scale flow with the local topography and by thermally-driven circulations. The latter are produced by horizontal temperature contrasts along the valley, across the valley, and in the region surrounding the valley. California's Owens Valley is one of the deepest in the United States and extends for 120 km between the Sierra Nevada to the west and the White/Inyo Mountains to the east. From Mar-Apr 2006, the Terrain-induced Rotors Experiment (TREX) was held in the Owens Valley to examine (1) the development of turbulent rotors associated with high-amplitude mountain waves and (2) valley wind systems and boundary layers.

Motivated by TREX and as part of a senior capstone project at the University of Utah, our team of undergraduate and graduate students investigated how Owens Valley wind systems are influenced by large-scale weather systems and regional-scale surface-heating contrasts. A regional climatology was generated for the Owens Valley region and surrounding southwest United States using the North American Regional Reanalysis. This climatology includes 3-hourly pressure anomaly maps that illustrate the diurnal modulation of regional-scale pressure gradients by surface heating contrasts across the southwest United States. During the late spring and summer, diurnal pressure changes primarily modulate the cross-valley (and cross-Sierra) pressure gradient, with little influence on the along-valley pressure gradient. This suggests that regional scale heating contrasts and associated pressure changes have little direct influence on along-valley flows, but may contribute to diurnal westerly winds that are common along the eastern slopes of the Sierra Nevada and known as the Washoe Zephyr. During the TREX period, however, such regional scale effects were not pronounced because of the high frequency of trough passages and strong dynamically driven wind events.

Although TREX investigated primarily strong downslope wind events and associated rotors, the Owens Valley also observes strong along-valley wind events. The synoptic patterns responsible for these along-valley wind storms are examined, including their relationship to cold-frontal passages.