The Sierra Rotors Project is an NSF-funded project to study mountain-wave
induced rotors in the lee of the Sierra Nevada in Owens Valley. The rotors,
intense horizontal vorticies with strong turbulence, can pose severe
aeronautical hazards. The eastern slopes of the southern Sierra Nevada make up
the tallest, steepest, quasi-linear topographic barrier in the contiguous United
States, and are well-known for generating large-amplitude mountain waves and
strong rotors over the Owens Valley. The main objective of this project is to
establish quantitative characteristics of the rotor behavior as well as to
evaluate the extent to which current operational mesoscale models can reliably
forecast the occurrence of rotors.
Courtesy of Jay Packer
Additional Images
From Color Landform Atlas of the
United States
Courtesy of Ray Sterner
There are several geographical locations in the U.S. Downwind of mountain ranges that are well known for the frequent occurrence of strong mountain waves. While the most thoroughly documented among them is the Colorado Front Range with its famous severe downslope windstorms (e.g., Lilly and Zipser 1972; Clark et al. 2000), the southern Sierra Nevada in California, is also equally known among scientists, as well as amateur and professional pilots, as a generator of large-amplitude lee waves, rotors, strong updrafts and clear-sir turbulence (Kuettner and Jenkins 1953; Whelan 2000). The Sierra Rotors Project was carried out near the town of Independence in Owens Valley, just east of the southern contiguous United States (Mount Whitney; 4,418 m), is the tallest, steepest, a narrow feature approximately 150 km long and 15-30 km wide. The average elevation change between the Sierra crest and the valley floor is roughly 3,000 m (Powell and Kieforth 2000).
The Owens Valley was the site of the Sierra Wave Project, which was a U.S.-Air-Force-funded study of mountain waves involving a two-phase field experiment: the first phase in the winter of 1951-1952 and the second int he spring of 1955. Some of the knowledge gained in the Sierra Wave Project was helpful for the planning and execution of this effort. A comprehensive overview of the synoptic situations favorable for wave and rotor activity and a description of a dozen case studies documented during this project appear in Holmboe and Kieforth (1957). Here we recap a few of their findings relevant to the proposed research.
Rotors and zones of low-level turbulence were frequently found beneath strong mountain lee waves of wavelengths between 13 and 32 km. The maximum altitude variation of a streamline in these waves ranged from 1.2 to 2.4 km, and the "normal" rotor cloud associated with lee waves paralleling the topographic slope. In the latter case, there is no apparent trailing edge to the rotor, the cloud extends eastward over the White and Inyo Mountains, and the flow is similar in appearance to a hydraulic jump (Kuettner 1959).
In addition to the favorable meteorological conditions in the Owens Valley, the federal and local agencies [Bureau of Land Management (BLM), US Department of Agriculture (USDA), and the Los Angeles Department of Water and Power (LADWP)]. Thus it is relatively easy to locate suitable sites for meteorological instruments without interfering with other land use priorities. Another major advantage of the Owens Valley is that the flow upstream of the Sierra Nevada is relatively unperturbed; the only obstacle is the 1,000 m high Coastal Range roughly 200 km to the west.
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Sierra Rotors Project DRI Network
Sierra Rotors
2004 NCAR ATD
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