Implementation of the wave boundary layer model in the OpenIFS model

For more than 30 years, many studies have been carried out to improve the understanding of the air-sea interaction and its impact on the predictions of atmospheric and the oceanic processes. It is well understood that the accuracy in predictions of the wind-driven waves is highly dependent on the source input and dissipation terms. The Wave Boundary Layer (WBL) approach for the estimation of surface stress has previously been used to improve the wind and wave simulations under extreme conditions. However, until recently the WBL was only used to determine the roughness length (z₀) and drag coefficient (C_d), but not to alter the wind input source function in wave models. In this study, the wave boundary layer model (WBLM) was implemented in the OpenIFS coupled model as source functions as suggested by Du et al. (2017, 2019). The new wind input and dissipation terms are then tested using numerical model simulations, with a particular focus on the contribution of the high frequency tail in the source input function.  The comparison of the results of this study with published results hints at better performance of the model on the estimation of the roughness length and drag coefficient. This should improve predictions of the significant wave height and wind speeds, especially under extreme conditions.

Corresponding Author: Nefeli Makrygianni (makrygiannin@cardiff.ac.uk)