The Principal Investigator will conduct a study of mesoscale airflow phenomena in the lee of the Sierra Nevada, including terrain-induced waves, rotors, and attendant downslope windstorms, and their interaction with cold air pools and thermally-forced flows in a deep lee-side mountain valley. This study is part of the Terrain-induced Rotor Experiment (T-REX), and builds on results and extends research conducted under a preceding Sierra Rotors study. Atmospheric rotors, intense low-level horizontal vortices that form along an axis parallel to, and downstream of, a mountain ridge crest, most frequently in conjunction with large-amplitude mountain waves, pose a significant hazard to aviation. Despite the significance of rotors, and because of their spatial complexity and intermittency, knowledge of rotor size, internal structure, turbulence intensity, and predictability is still limited. The main observational objective of this study is to document the full three-dimensional structure and temporal evolution of mountain waves and rotors under a wide range of environmental conditions and wave/rotor strengths.
The research will be conducted using both field observations and numerical simulations. Comprehensive observational T-REX data sets from ground-based and airborne, in situ and remotely sensed instruments, including measurements obtained by the mesonetwork of automatic surface stations established during a precursor Sierra Rotors study, will be collected in the central portion of Owens Valley, in the lee of the southern Sierra Nevada. The southern Sierra Nevada is the tallest, steepest, quasi-linear topographic barrier in the contiguous United States. The mesonetwork surface observations will be collected before, during, and after the two-month intensive T-REX observational period, planned for early spring 2006. This study's numerical modeling effort will consist of high-resolution simulations with two state-of-the-art mesoscale numerical models, the Coupled Ocean-Atmosphere Modeling Prediction System (COAMPS) and the Weather Research Forecasting (WRF) modeling system. Dynamical explanations for the evolution, structure and interaction of rotors and waves with cold air pools and thermally forced flows, will be sought through synthesis of high-resolution state-of-the-art numerical model simulations and high-resolution observations. Additionally, longer-term records from the Owens Valley mesonetwork will be used to compile a climatology of the Sierra Nevada windstorms and patterns of thermally forced flow in Owens Valley.
Intellectual merit: Improvement in understanding of airflow dynamics in complex terrain, in particular hazardous phenomena such as rotors, and the limits to their predictability. Understanding the role of upstream moisture in determining the flow response in the lee, and elucidating the role of stagnant flow in cold air pools on the dynamics and evolution of the lee side flows, including waves, rotors, and damaging windstorms.
Broader impacts: Results of this research are expected to lead to improved prediction of aviation hazards associated with rotors and downslope windstorms in complex terrain. The results will be shared with regional operational forecast community including the National Weather Services offices whose regions of coverage include the lee side of the Sierra Nevada, and wider research community in form of guest lectures and seminars. The findings of the proposed research will also be incorporated into graduate courses in mesoscale meteorology at the University of Nevada Reno and the University of Zagreb, Croatia. The project will involve the education and training of at least one graduate student.
