Coastal Internal Boundary Layer Studies during CASPER-West

The growth of the marine internal boundary layer (MIBL, height ) with the shore-normal distance , has been a topic of interest for several decades because of its role in determining air-sea fluxes and hence evaporative ducting. The electromagnetic wave propagation is expected to strengthen within this layer in the direction of the mean wind. During Coupled Air-Sea Processes and Electromagnetic Research (CASPER)-West campaign, an array of instrumentation was deployed near the Californian coast at Point-Mugu and on the R/V Sally Ride ship. A state-of-art triple Doppler Lidar system was used to map the flow field up to 500 m in height above sea level and to a distance of ~ 4 kilometers from the coast with a spatial resolution of 30 m. Triple Doppler Lidar provides simultaneous vertical profiles of all three velocity components within the marine atmospheric boundary layer. A 20 m flux tower was used to characterize the atmospheric surface layer, especially its stability. On October 14 and 15, 2017, during offshore flow conditions, profiles of temperature and velocity were measured by a small research boat and triple Doppler Lidars covering a swath of atmosphere normal to the coast. The small boat (Rigid hull inflatable boat, RHIB) performed multiple transects from the location of the main ship Sally-Ride (location R₂) to the shoreline and measured vertical profiles of potential temperature and specific humidity within the lowest tens of meters of the marine atmospheric surface layer using a tethered lifting system. The RHIB also simultaneously measured the sea surface temperature (SST) along its track. In this presentation, the results from the RHIB operations and triple Doppler Lidars will be discussed. The growth of the MIBL, during shore-normal as well as shore-oblique wind angles, delineated from the temperature and velocity profiles will be compared with published theoretical formulations and a new simple parameterization scheme of MIBL growth. The effect of skewed wind shear and background atmospheric boundary layer conditions on MIBL growth as well as its impact on electromagnetic ducting will be discussed.