Estimation of offshore extreme wind from wind-wave coupled modeling

Abstract

A coupledwind-wave modeling system is used to simulate 23 years of storms and estimate offshore extreme wind statistics. In this system, the atmospheric Weather Research and Forecasting (WRF) model and Spectral Wave model for Near shore (SWAN) are coupled, through a wave boundary layer model (WBLM) that is implemented in SWAN. The WBLM calculates momentum and turbulence kinetic energy budgets, using them to transfer wave-induced stress to the atmospheric modeling. While such coupling has a trivial impact on the wind modeling for 10-m wind speeds less than 20 ms−1, the effect becomes appreciable for stronger winds—both compared with uncoupled WRF modeling and with standard parameterization schemes for roughness length. The coupled modeling output is shown to be satisfactory compared with measurements, in terms of the distribution of surface-drag coefficient with wind speed. The coupling is also shown to be important for estimation of extreme winds offshore, where the WBLM-coupled results match observations better than results from noncoupled modeling, as supported by measurements from a number of stations.