The Impact of Waves and Gustiness on Momentum Fluxes in Typhoons

In the marine boundary layer the ocean and atmosphere are strongly coupled. This coupling is responsible for the exchange of heat, mass, and momentum. During tropical cyclones momentum transfer is important for storm intensity, yet few direct flux measurements have been made under such conditions. Here we present results from the Impact of Typhoons on the Ocean in the Pacific (ITOP) experiment which took place in the Philippine Sea in 2010. Direct fluxes and waves were measured from moored buoys over three months alongside mean oceanic and atmospheric data. These data include measurements collected during three typhoons and a tropical storm. The momentum flux was analyzed in terms of the drag coefficient and found to generally increase with wind speed. This presentation focuses on the drag coefficient variability that cannot be explained by wind speed alone. Secondary factors including wave spectra, gustiness, atmospheric stability, storm quadrant, and storm translation speed and direction are all considered with a focus on improved drag coefficient parameterization.