COHERENT MICROSCALE SURFACE STRUCTURES OBSERVED BY A SCANNING LIDAR AND THEIR CONTRIBUTION TO MASS EXCHANGE IN THE STABLE BOUNDARY LAYER

The spatial properties of coherent structures in the stable boundary layer have been imaged by a scanning water vapor Raman lidar operated by Los Alamos National Laboratory. Until recently, coherent structures were spatially resolved primarily from the products of high resolution atmospheric models such as direct numerical simulations, since these structures tend to be to small for large eddy simulations. Spatial observations of coherent features within the stable boundary layer are relatively rare; however, the Raman lidar was used in conjunction with other sensors during October of 2000 for the Vertical Mixing and Transport Experiment (VTMX) to observe the multi-dimensional water vapor structure in the first 75 m of the transitional and nocturnal boundary layer. Using traditional micrometeorological analytical techniques, these coherent structures were evaluated and characterized. From the aforementioned analytical approaches, we found that the lidar images showed how 15 to 20 m diameter low frequency, intermittent eddy and plume structures evolve and exchange mass between the surface and the atmosphere. These structures do not grow much beyond capping inversions which limit their height to approximately 20 m to 25 m, and 10 to 20 m in width, they exist for less than 10 minutes but, are apparently affected by wave structures aloft, and carry with them most of the mass transported from the surface into the lowest portion of the stable atmospheric boundary layer.