This research will continue, and expand upon a prior study of low-level turbulent zones - called rotors - associated with the mountain-wave/rotor system. The Front Range of the Colorado Rocky Mountains, which frequently excites lee waves between October and April, will serve as the study area. Results from two-dimensional simulations published under current NSF funding identified two distinct rotor types - the first associated with resonant waves (Type 1), and the second with a mountain-wave system resembling a hydraulic jump (Type 2). In the current project, observations are designed to verify the existence of Type 2 rotors. Progress has been made to explain underlying Type 1 rotor dynamics; those for Type 2 rotors are not yet clear.
The goal of the research is to advance knowledge of the overall structure of rotors, and the mountain-wave/rotor interface. To address this goal, the Principal Investigator will test four hypotheses: 1) Both rotor types exist in nature; their structures are sufficiently distinct to be verifiable by in situ measurements. 2) Negative horizontal vorticity, generated along the lee slope, is the key dynamic quantity to explain a splitting inversion characteristic of Type 2 rotors. 3) The mountain-wave/rotor interface can be measured; its structure depends on an upstream, near-mountaintop inversion, as well as the wind profile. 4) Given similar flow regimes (e.g., similar stability profile and flow component perpendicular to the mountains) the overall mountain-wave/rotor system will exhibit quantifiable structural differences along the Colorado Rocky Mountains compared to the Sierra Nevada Mountains.
The Principal Investigator will utilize observations and three-dimensional (3-D) numerical modeling to achieve the goal. Observations of the mountain-wave/rotor system will be conducted using an instrumented sailplane. This simple, yet sophisticated, measurement and recording platform has many advantages, among them very low maintenance and operating costs. It is anticipated that between 10 and 30 data-collection flights can be conducted annually.
Both real-data and idealized three-dimensional numerical simulations will augment the observations, and will further elucidate the underlying dynamics. The Principal Investigator will further quantify upstream conditions that lead to Type 2 rotors, as well as identify 3-D topography that may modify the mountain-wave/rotor structure. In addition, model studies will aid in understanding how various flow regimes modify the mountain-wave/rotor structure along the Colorado Front Range. The Principal Investigator will use data from the Terrain Induced Rotor Experiment, which will be conducted in the Sierra Nevada range, to quantify similarities and differences in the overall mountain-wave/rotor system between the Sierra Nevada and Rocky Mountains.
The research may ultimately lend guidance to enable more accurate forecasts of rotor location and turbulence intensity, which is important to issues of aviation safety.
