Flux Buoy, Ship Turbulence Measurements and Wind-Wave Coupling in the Atmospheric Wave Boundary Layer

The field campaign of the Coupled Air-Sea Processes and Electromagnetic ducting Research (CASPER) East project occurred between October 10 and November 6, 2015 with the measurement area extending from near shore out to about 200 km to the Gulf Stream. In the framework of CASPER, 20 Hz turbulence measurements and wave spectra estimates from motion data were obtained with a small spar buoy (Marine-Air-Sea-Flux system, or MASFlux) developed by the Meteorology Department of the Naval Postgraduate School, on a surface Wave Glider, and on the bow mast of R/V Hugh Sharp offshore of Duck, NC. The turbulent fluxes measurements were at 3.5 m above sea level on the MASFlux buoy, 1 m on the wave glider, and 9 m on the R/V Sharp.

Profiles of wind speed, temperature and humidity in the atmospheric wave boundary layer (essentially the first 5-10 m layer near sea surface) were also obtained under different conditions of atmospheric stability, wind sea and swell wave characteristics. Surface waves were also measured by four moored wave buoys in the CASPER-East area operated by the Scripps Institute of Oceanography (SIO). Simultaneous measurements of turbulence and waves with the MASFlux buoy enable estimation of the wave-induced part of wind turbulence. These data are used together with a simple wind-wave coupling model to calculate and validate the profiles of stress and wind speed, and the separate contributions from wind turbulence and waves. The model accounts for the effect of airflow separation due to wave breaking. Drag (or equivalently, roughness length) parameterizations using wave parameters estimated from measurements and the model are also compared.