Dual Doppler lidar observations during T-REX

Two coherent Doppler lidars were used during the Terrain-induced Rotor Experiment (T-REX) in spring 2006 to investigate the coupled mountain-wave/rotor system in the Owens Valley. The present talk summarizes the main features of rotors and mountain waves during several IOPs, and discusses the lessons learned from these first dual-Doppler lidar observations of atmospheric rotors. Conceptual models suggested that rotors are a large organized vortex with a horizontal axis beneath a mountain wave, and that the flow structure is fairly two-dimensional. Despite the appearance of rotor clouds over the investigation area, the lidar observations did not show a well-organized vortex associated with a large amplitude mountain wave. Instead, the lidar documented rapidly changing waves, breaking waves, and a number of smaller vortices. The region beneath the rotor cloud was rather characterized by smaller vortices than by a single large vortex, and the stationarity of the main features was limited to time periods between a few minutes and half an hour. In nearly all IOPs, there was a significant along-valley flow and thermally driven turbulence that interacted with the downslope flow. Thus, the flow structure was not nearly two-dimensional and the representation of the along valley flow may also be necessary for the simulation of rotors in the Owens Valley. The lidar measurements outlined the complexity of rotors in the Owens Valley, and the limitations of present numerical models to predict or represent them. However, the unique data set from T-REX provides a profound basis for a better understanding of the mountain wave/rotor system.