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.
- Indicates paper has been withdrawn from meeting
- Indicates an Award Winner