Terrain-induced Rotor Experiment: New Insights into the Structure of Atmospheric Rotors, Stratospheric Gravity Waves, and Boundary-Layer Flows within a Deep Valley

The Terrain-induced Rotor Experiment (T-REX) is the second phase of a coordinated effort to explore the structure and evolution of an atmospheric rotor coupled system. Rotors are intense low-level horizontal vortices that form along an axis parallel to, and downstream of, a mountain ridge crest, and are strongly coupled to both the overlying mountain waves as well as the underlying boundary layer. The field campaign of the Terrain-induced Rotor Experiment (T-REX) took place in March and April 2006 in Owens Valley, CA, which was also the location of the Sierra Rotors Project, the initial phase experiment in March and April 2004. Owens Valley lies to the east of the southern Sierra Nevada, which is the tallest, steepest, quasi two-dimensional topographic barrier in the contiguous United States. Mountain waves and attendant rotors are known to reach particularly striking amplitude and strength there.

The main scientific objective of T-REX is a comprehensive study of the coupled mountain-wave--rotor--boundary-layer system. Complimentary scientific issues include stratospheric-tropospheric exchange (STE) and structure and evolution of the complex-terrain boundary layer in a deep valley. Resulting from the need to document atmospheric conditions and processes from the Earth surface up to the upper-tropospheric/lower-stratospheric altitudes, the T-REX field campaign had both a comprehensive ground-based and an airborne observing program. In the first part of the talk we will provide an overview of the integrated observing system deployed in T-REX, key observations, and illustrate how the observations from the integrated observing system are being used to address basic T-REX scientific questions.

New insights into the structure of atmospheric rotors based on T-REX airborne observations will be presented in the second part of the talk. In situ thermodynamic and kinematic data was obtained on rotor circulations and wave structure over Owens Valley in a number of research missions by the University of Wyoming King Air aircraft under strong wave-forcing conditions. Sufficiently strong signal returns from the Wyoming Cloud Radar (WCR) were also granted by the presence of ice particles within different types of clouds associated with the wave/rotor system, including mountain cap clouds over the Sierra crest, "spill over" clouds over the eastern Sierra slopes as well as roll clouds over Owens Valley. In situ measurements by the UW King Air have been used to examine the range of different flow structures over Owens Valley, including trapped lee waves, low-level wave breaking, and internal hydraulic jumps and their relationship to attendant regions of strong turbulence within Owens Valley. Doppler analyses of remote sensing data from WCR reveal a wealth of fine-scale structures within the rotor and cap clouds, over the center of Owens Valley and within the boundary-layer flow over the Sierra crest, respectively.