Advancing the Performance of Wave Forecast Models Under Low Wind Conditions

Abstract

Abstract Ocean surface is complex and difficult to predict accurately due to its random nature. Ocean surface waves in strong wind conditions have been widely studied for last few decades. Almost half of world’s winds are below 7.5 m/s and the physics of such winds contains a lot of uncertainties. The simulation of ocean waves is largely dependent on the driving winds force accuracy and source term parameterizations. However, low winds are often ignored on the perception of their lesser effect on overall results of existing models. It is important to understand the relative strength/ weaknesses of wave forecast models under low wind conditions from scientific perspective which should lead to improved wave forecast and wave-ocean-weather coupling capabilities. There are many critical thresholds involved in the initial generation and growth of wind waves whereas current parameterizations of wave models are mostly based on moderate – high wind conditions. Wave model’s performance, although not very prominent, contains bias under low winds conditions and these thresholds need to be embedded in current physics of wave forecast models for more accurate simulations. In this study, WAVEWATCH III (v6.07) wave forecast model with observation based source terms parameterizations (ST6 package) is used to simulate waves on a global scale. The model’s output is analyzed with a globally calibrated and cross validated global dataset of 13 altimeters to analyze its performance under low wind conditions. A relative error of −1 to 6 is observed in global significant wave heights simulated by WAVEWATCH III model compared to altimeter’s measured wave heights for wind speeds less than 5ms−1.