6.4
Investigation of anti-winds in Owens Valley, California through observations and high-resolution simulations
Fotini Katopodes Chow, Univ. of California, Berkeley, CA; and M. H. Daniels and C. D. Whiteman
This study examines valley flow circulations observed during calm conditions in March and April 2006 during the Terrain-induced Rotor Experiment (T-REX) in Owens Valley, California. In particular, the dynamics of anti-winds and secondary flow circulations are investigated through combined analysis of observation data and high-resolution large-eddy simulations. Simulations are performed using the Advanced Regional Prediction System (ARPS) using several grid nesting levels down to 350 m horizontal resolution.
With a strong inversion at ridge crest height, valley flows can become trapped, generating a closed circulation with the thermally-driven valley flow near the surface and a return flow aloft. Anti-winds or return flows are rarely observed because they are usually weaker and spread over a larger area than the valley flows which they oppose. Night-time observations in Owens Valley during a quiescent period with an elevated inversion at ridge crest height, however, indicate the presence of down-valley surface winds coupled with strong anti-winds just below ridge tops. The down-valley flow at the surface has a magnitude of 5-10 m/s and is initially coupled with a return flow of weaker magnitude which occurs between 2600 and 3400 m asl. The anti-wind grows and the down-valley wind weakens during the night, with anti-winds of magnitude 5-10 m/s occurring between 2000 and 3300 m asl just before sunrise. These winds are entirely decoupled from winds above the surrounding mountain tops, being separated by a strong inversion. The capping inversion subsides during the night, with the valley boundary layer depth decreasing from ridge crest height (~4200 m) to 3300 m asl by sunrise. Within an hour or two after sunrise, the down-valley flow disappears entirely, and up-valley flow is observed over the whole boundary layer depth. These flow patterns are observed in rawinsonde and lidar data, as well as in the simulated flow fields.
Session 6, Boundary Layers in Complex Terrain: Part II
Tuesday, 29 August 2006, 10:30 AM-12:00 PM, Ballroom South
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