Implementation of A WBLM In COAWST and Its Impact on Coastal Storm simulations

Abstract

<p>In this study, a wave boundary layer model (WBLM) is implemented in the Coupled-Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system for coupling the atmospheric model WRF and the ocean wave model SWAN. The WBLM is implemented as a wind-input source function in SWAN and at the same time provide roughness length over the ocean for WRF. For comparison, the physics-based, Janssen method as well as 3 parametrization methods for roughness length calculation were also implemented. The coupled modeling system is used to investigate modeling of winds and waves with two challenging areas in focus: one is coastal, shallow water zone and the other is the storm center. Both of the two areas are strongly affected by complicated sea surface roughness. This is done through a storm case study and a systematic coupled and uncoupled simulations of storms over the eastern North Sea. Validation using ASAR data, mast and buoy measurements suggests that, the empirical parametrization approach fails to reproduce roughness in coastal areas. The WBLM method outperforms the other methods in terms of the magnitude as well as the spatial distribution of roughness length. It is found that wind-wave coupling is important for wind estimations in coastal zones and at strong wind condition.</p>