Sierra Rotors: A comparative study of two rotor events

The Special Observation Period of the Sierra Rotors experiment took place in March and April 2004 in Owens Valley in the southern Sierra Nevada of California. Terrain-induced rotors are intense horizontal vortices with strong turbulence that form on the lee side of a mountain range in association with mountain waves, and are known to 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 Sierra Waves and attendant strong rotors over Owens Valley.

In this study, we compare and contrast predicted and observed structure and evolution of the Sierra waves and rotors in two SRP SOP cases. The model used for very high-resolution real-data simulations in this study is the Navy's Coupled Ocean/Atmosphere Modeling Prediction System (COAMPS). The two rotor cases are IOP 8 and IOP 14, the two strongest rotors cases of SRP, in which strong cross-mountain winds led to formation of large-amplitude waves and rotors over Owens Valley that were documented with the DRI surface network of automatic weather stations and NCAR Integrated Sounding Systems.