Examination of wind-wave interaction source term in WAVEWATCH III with tropical cyclone wind forcing
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Examination of wind-wave interaction source term in WAVEWATCH III with tropical cyclone wind forcing ZHAO Wei1∗ , GUAN Shoude1 , HONG Xin1 , LI Peiliang1 , TIAN Jiwei1 1
Physical Oceanography Laboratory, Ocean University of China, Qingdao 266100, China
Received 23 November 2010; accepted 12 January 2011 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2011
Abstract Results of drag coefficient (CD ) from field observations and laboratory wave tank experiments indicate that the operational wave model can overestimate wind energy input under high wind conditions. The wind-wave interaction source term in WAVEWATCH III has been modified to examine its behavior with tropical cyclone wind forcing. Using high resolution wind input, numerical experiments under idealized wind field and tropical cyclone Bonnie (1998) were designed to evaluate performance of the modified models. Both experiments indicate that the modified models with reduced CD significantly decrease wind energy input into the wave model and then simulate lower significant wave height (SWH) than the original model. However, the effects on spatial distribution of SWH, mean wavelength, mean wave direction, and directional wave spectra are insignificant. Due to the reduced wind energy input, the idealized experiment shows that the modified models simulate lower SWH than the original model in all four quadrants. The decrease in the front quadrants is significantly larger than that in the rear quadrants; it is larger under higher winds than lower winds. The realistic experiment on tropical cyclone Bonnie shows that the modified model with the various downward trends of CD in high winds creates a simulation that agrees best with scanning radar altimeter observations. Key words: drag coefficient, wind-wave interaction, tropical cyclone, WAVEWATCH III
fields under tropical cyclones, and these studies have significantly increased knowledge about wave characteristics under high wind conditions. Numerous observations have indicated that the distribution of significant wave height (SWH) is determined mostly by three important factors: maximum wind speed, radius of maximum wind speed (RMW), and storm translation speed (Young and Berchell, 1996). Wright et al. (2001) and Walsh et al. (2002) conducted the first detailed study of spatial variation of directional wave spectra for both open ocean and landfall cases of tropical cyclone Bonnie (1998) using NASA airborne scanning radar altimeter (SRA) carried by a NOAA WP-3D hurricane research aircraft. However, conducting field observations may be difficult under high wind conditions and, generally, these measurements only provide detailed wave characteristics at a specific space and time. Ocean wave modeling is another useful and convenient way of obtaining spatial and temporal distrib-
1 Introduction Modeling and forecasting of ocean surface waves under tropical cyclones (TC) have been of great concern for many years because it can minimize the loss of life and property in maritime and coastal regions. Recent studies (e.
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