Airborne Doppler Lidar Measurements of Valley Flows in Complex Coastal Terrain

Abstract

Three-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 21 . 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 crossvalley 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.

Exchange Processes in the Atmospheric Boundary Layer Over Mountainous Terrain

“…In this respect, methods to estimate accurately the three-dimensional state of the valley atmosphere from observations along aircraft trajectories [20,128,[141][142][143] and from airborne remote sensing [144] have received limited attention so far and should be further improved. Additional considerations on the need of integrating in-situ and remote-sensing measurements for a better understanding of exchange processes in valleys are offered elsewhere in this journal issue [48].…”

“…For instance, at low levels near coastal mountains, sea breezes and up-valley winds often superimpose and enhance the horizontal inland transport of moist air [144,151,161,[163][164][165]. At high elevations over ridges, instead, the above-mentioned mountain venting can locally increase humidity and aerosol content [161], generating horizontal gradients of these quantities.…”

Lidar-Measured Wind Profiles: The Missing Link in the Global Observing System

“…Multiple references provide additional information on coherent detection systems (Kavaya et al 1989(Kavaya et al , 2014Henderson et al 1991;Wagener et al 1995; among others) and their use in atmospheric boundary layer studies (Post and Cupp 1990;Huffaker and Hardesty 1996;Rothermel et al 1998;Grund et al 2001;Banta et al 2002;Koch et al 2010;Tucker et al 2009;Bluestein et al 2011;de Wekker et al 2012), wind turbine studies (Käsler et al 2010), and hazard detection and avoidance at airports (Hannon et al 2005). Coherent airborne DWLs have also been used to explore the potential impact of future spacebased lidars and to develop the necessary advanced signal processing and data interpretation algorithms .…”

Observations of the Boundary Layer near Tornadoes and in Supercells Using a Mobile, Collocated, Pulsed Doppler Lidar and Radar

“…Technical details about the lidar system are found in DeWekker et al (2012). Other details about signal processing techniques and error analyses relevant to Table 1 are found in Frehlich (2001Frehlich ( , 2004.…”

“…McCaul et al (1987) used an airborne pulsed system to map the wind field in gust fronts and nonprecipitating convective clouds. DeWekker et al (2012) also used an airborne system to map the wind field for topographically forced flows in the boundary layer over coastal terrain in California. Ground-based, pulsed Doppler lidars have been used many times to map the finescale structure of clear-air phenomena close to the earth's surface, including surface boundaries and orographically forced flows (Table 1).…”