Impacts of the coupling of the wave and the ocean model to the atmospheric model on the predictability of extreme events

Abstract

<p>Two-way coupling between atmosphere and ocean models has already been widely used to improve the results of atmosphere models during extreme events, as well as long-term simulations. Also the coupling of an ocean surface wave model to an atmosphere model has already been shown to have a positive impact on the atmosphere model enhancing the agreement with observations, especially during extreme wind events. The results of many previous studies by different groups showing an improvement of the simulations with coupled atmosphere – ocean or atmosphere – wave models now leads to the question, whether the inclusion of a wave model into an atmosphere – ocean model system can improve the results of the atmosphere model further. In this study the atmospheric model COSMO-CLM, the wave model WAM and the ocean model NEMO are used. To evaluate the impacts of coupling all three models with respect to two-way coupling on the lower atmosphere during extreme events but also during the year, three experiments are carried out. In one experiment the full exchange between the three models is enabled, whereas in the other two either the wave model is not giving any feedback to the atmosphere and the ocean or the ocean model is disconnected from the atmosphere and wave model. In order to analyse the added value of the inclusion of the wave model, the analysis is split into evaluating the impact on the lower atmosphere throughout the year but also during specific events. These specific events are either where the impact of the wave model is particularly high or extreme events. One focus of this study is on the simulation of storms, since both the wave model and the ocean model have an impact on the atmosphere model during those events. Moreover, it is analysed whether the effect of the wave model opposes or enhances the effect of the ocean model on the lower atmosphere during extreme events as well as throughout the year. Furthermore, to assess the skill of the fully coupled system with respect to the two-way coupled systems the simulation results are compared to observations of wind speed, temperature and pressure in general but especially during extreme events.</p>