Observations of Offshore Internal Boundary Layers

Abstract

The growth of the marine internal boundary layer (MIBL, height hi) with the shore-normal distance x, is a topic of continuing interest because of its applications in coastal pollution dispersion, offshore wind farm siting, coastal air-sea fluxes and in evaporative ducting. Available data on MIBL are scarce, given the difficulty of measuring the variability of coastal winds. During the Coupled Air-Sea Processes and Electromagnetic Research campaigns, an array of instrumentation was deployed to measure offshore spatial variability and its effect on electromagnetic (EM) wave propagation. Meteorological sensors (flux towers and remote sensing) deployed along the coast of Point Mugu, California, on a research vessel and FLoating Instrument Platform provided surface layer and boundary layer observations. Measurements from multiple remote sensors such as synchronized triple Doppler lidars, small boat operations with tethered lifting system, and radiosondes provided a holistic view of the MIBL growth and its spatial variability in coastal areas. Convective and stable MIBL observed during two intensive operating period days showed distinct growth characteristics off the coast of Point-Mugu. During stable stratified atmospheric conditions, an MIBL was observed to develop least as far as 47 km from the coast. The growth of MIBL within the nearshore adjustment zone was influenced by surrounding atmospheric, oceanographic, and topographic conditions. A parameterization scheme is developed based on advection-diffusion balance equations, accounting for upstream turbulence, and compared with hi observations from a Doppler lidar and profiles taken from a small boat. An evaluation of existing IBL theories is also conducted.