In situ Measurements of Momentum Fluxes in Typhoons

One of the scientific objectives of the U.S. Office of Naval Research-sponsored Impact of Typhoons on the Ocean in the Pacific (ITOP) campaign was improved understanding of air-sea fluxes at high wind speeds. Here the authors present the first-ever direct measurements of momentum fluxes recorded in typhoons near the surface. Data were collected from a moored buoy over 3 months during the 2010 Pacific typhoon season. During this period, three typhoons and a tropical storm were encountered. Maximum 30-min sustained wind speeds above 26 m s super(-1) were recorded. Data are presented for 1245 h of direct flux measurements. The drag coefficient shows evidence of a rolloff at wind speeds greater than 22 m s super(-1), which occurred during the passage of a single typhoon. This result is in agreement with other studies but occurs at a lower wind speed than previously measured. The authors conclude that this rolloff was caused by a reduction in the turbulent momentum flux at the frequency of the peak waves during strongly forced conditions.