Mountain waves have received considerable research attention over the past several decades, primarily for the important role they play in association with damaging winds and severe turbulence both near the ground and aloft. Yet, little is known about the most turbulent of the phenomena associated with mountain waves, that of atmospheric rotors: intense horizontal vortices occurring under wave crests in the lee of mountain ridges. Rotors pose a serious threat to aviation and are important for the lofting and transport of aerosols and contaminants. The internal structure and dynamics of rotors are extremely difficult to sample with standard atmospheric instrumentation. The temporal and spatial scales as well as the variability of rotors are a considerable hurdle to conventional, ground-based, observational tools. Direct penetrations by aircraft carrying in situ instrumentation, as was done during the recently completed Terrain-induced Rotor Experiment (T-REX), can be challenging. T-REX is part of an initiative focused on atmospheric rotors and turbulence over complex terrain and it represents a response to the need for further, more in depth, investigations on the structure of rotors.
This research focuses on the analysis of remote sensing data collected with the Wyoming Cloud Radar (WCR) installed on board the University of Wyoming King Air (UWKA) research aircraft during two field campaigns. In addition to the T-REX campaign, which took place over the Sierra Nevada range and the lee-side Owens Valley in California, in March and April 2006, the Principal Investigators will use data from the NASA06 field campaign, which was conducted in the winter of 2006, as a series of research flights over the Medicine Bow range in southeastern Wyoming. The researchers will use these observational data in conjunction with a state-of-the-art mesoscale numerical model to investigate the dynamical evolution and internal structure of atmospheric rotors.
The main objective is to describe the radar echo, kinematic structure, and evolution of wave flow and rotor events during T-REX. The Principal Investigators will analyze and merge radar data with in situ and ground-based observations as well as model output from high-resolution numerical simulations in order to provide a multi-dimensional picture of the rotor dynamics and depictions of the boundary-layer structure over complex terrain. A second objective, closely connected to the primary one, specifically deals with the analysis of data from the NASA06 campaign. Although lower and less steep than the Sierra Nevada, the profile of the Medicine Bow and of the adjacent valleys, where the NASA06 campaign took place, induces distinct wave flows aloft. The strong and ubiquitous radar echoes provide a unique opportunity to fill in gaps within the T-REX radar dataset, but also allow for comparisons between different flow regimes as well as extension of T-REX analyses to different environmental conditions.
Intellectual Merit: The scientific merit of the research resides in investigation of mountain waves and rotor events and internal rotor structure through cross-sectional data collected by airborne multi-Doppler radar at high resolution (~30m). The two-dimensional representation of the flow kinematics derived via dual- Doppler retrievals across cap and rotor clouds will add important observational dimension to the understanding of dynamical evolution and structure of atmospheric rotors. For the first time, the Principal Investigators will merge airborne remote sensing data with in situ data at flight level to document the physical properties and structures of waves and internal rotor structure over mountainous terrain. The intellectual merit also lies in the synergistic use of advanced remote sensing techniques and high-resolution atmospheric numerical modeling to achieve further improvements in understanding of airflow dynamics in complex terrain.
Broader Impact: Results of this research have the potential to improve aviation safety in complex terrain. About 60% of general aviation accidents and incidents in the western United States are associated with mountain-wave and clear-air turbulence. FAA and flight schools will benefit from tangible interpretations and realistic portrayals of rotors and large scale turbulence in the lee of the mountains. The results of this research will be shared with a wider research community in the form of lectures, seminars, and conference presentations. They will also be incorporated into upper-level undergraduate and graduate courses in mesoscale meteorology at the University of Nevada Reno, the University of Wyoming, and the University of Zagreb, Croatia.
