Spatial Variability of Offshore Internal Boundary Layers

The growth of the marine internal boundary layer (MIBL) with the shore-normal distance, is a topic of continuing interest because of its applications in coastal dispersion, offshore wind farm siting, coastal air-sea fluxes and evaporative ducting. Available data on MIBL are scarce, given the difficulty of measurements and the variability of coastal winds. During the Coupled Air-Sea Processes and Electromagnetic Research (CASPER) 2017 campaign, an array of remote sensing and in-situ sensors were deployed along the coast of point-Mugu, California. Multiple transects of temperature and relative humidity were collected perpendicular to the coast line using a rigid hull inflatable boat during MIBL favorable conditions. Flux towers on the coast and bow mast sensors on the ship were used to characterize the atmospheric surface layer, especially its stability. The triple Doppler Lidar system was used to map the flow field up to 500 m in height above the sea level and approximately 4 kilometers out from the coast, with a spatial resolution of 30 m. Measurements from multiple remote sensing instruments such as synchronized triple Doppler Lidars, small boat operations with tethered lifting system, a motion stabilized Doppler Lidar provided a holistic view of the offshore internal boundary layer growth and its spatial variability from the coast. Comparison of observations with several IBL growth equations in the literature show that the spatial variability of MIBL is a function of the atmospheric stability, wind speed, wind direction with respect to the shoreline, wind veer/shear and other atmospheric forcing entities such as convection. This variability has sizable impacts on the evaporative duct heights in the coastal zone. (Funded by the ONR Grant # N00014-18-1-2472)