Abstract : 2D.1
The relationship between synoptic scale winds and surface flows in a deep valley

Sharon Zhong, Wenqing Yao, C. David Whiteman
zhongs@msu.edu
Michigan State University

Predictions of local weather and dispersion conditions in a valley require the ability to relate the behavior of valley circulations to synoptic conditions aloft. This study investigates the relationship between circulations within a valley and the synoptic scale flows above the valley using climate data and a numerical model. The valley studied is the Owens Valley, a narrow and deep valley located immediately to the lee of the southern Sierra Nevada of eastern California. The valley circulations were characterized using surface observations at eight stations located along the valley axis, and the synoptic conditions aloft were characterized using output from the North American Regional Re-analysis (NARR). The valley circulations are dominated by thermally driven up- and down-valley flows when the synoptic winds aloft are weak. This happens frequently in the summer season when the region is under the influence of the subtropical Pacific high pressure system. In the spring and fall, strong winds associated with the passage of weather systems are channeled by the valley. The analyses indicate that channeling is predominantly in the form of forced channeling, where the direction and strength of the wind in the valley are determined by the direction and strength of the projected along-valley component of the synoptic winds aloft. Case studies using the Regional Atmospheric Modeling System (RAMS) further confirmed this theory about the relationship between the valley circulations and the synoptic scale flows.