Airborne Doppler Lidar Measurements of Valley Flows in Complex Coastal Terrain

Abstract

hree-dimensional winds obtained with an airborne Doppler lidar are used to investigate the spatial structure of topographically driven flows in complex coastal terrain in Southern California. The airborne Doppler lidar collected four hours of data between the surface and 3000 m MSL along a 40-km segment of the Salinas Valley during the afternoon of 12 November 2007. The airborne lidar measurements, obtained at horizontal and vertical resolutions of approximately 1500 and 50 m, respectively, reveal a detailed spatial structure of the atmospheric flows within the valley and their associated aerosol features. Clear skies prevailed on the flight day with northwesterly synoptic flows around 10 m s?1. The data document a shallow sea breeze making a transition into an upvalley flow in the Salinas Valley that accelerates in the upvalley direction. Along with the acceleration of the upvalley wind, the lidar data indicate the presence of enhanced sinking motions. No return flows associated with the sea-breeze or upvalley flows are observed. While synoptic flows are aligned along the valley axis in the upvalley direction, lidar data indicate the presence of a northerly cross-valley flow around the height of the surrounding ridges. This flow intrudes into the valley atmosphere and induces, along with thermally driven slope flows on the sunlit valley sidewall, a cross-valley circulation that causes an asymmetric distribution of the aerosols. This study demonstrates the large potential of airborne Doppler lidar data in describing flows in complex terrain.