Coupling across the Spheres: the Chemical Hydrological Atmospheric Ocean wave System (CHAOS)

The thought that the Earth’s spheres should be considered as a single system at short and longer spatiotemporal scales is nowadays dominant among scientific community. However, the complex interaction processes in Earth’s system are insufficiently modeled by the standalone atmospheric models. To narrow this gap, it is important to implement modeling systems that bidirectionally connect Earth’s spheres. In this context, this study presents a fully coupled multi-model system named CHAOS (Chemical Hydrological Atmospheric Ocean wave System) that bridges atmosphere, ocean and land, by representing many interaction processes. The study presents the design, the implementation and the operation of the CHAOS system, highlighting also its advantages in the simulation of severe weather events in the Mediterranean Sea and the Atlantic Ocean. The CHAOS system consists of three main components: the Advanced Weather Research Forecasting (WRF-ARW) model, the Wave model (WAM) and the Nucleus for European Modeling of the Ocean (NEMO). The three components are coupled using the OASIS Model Coupling Toolkit (OASIS3-MCT) that enables them to “online” communicate and exchange the information required. Moreover, two sub-components of the WRF-ARW model are suitably introduced in the CHAOS system to additionally simulate chemical (WRF-Chem) and hydrological (WRF-Hydro) processes, depending on the application. Regarding the hydrological processes, CHAOS is also “offline” coupled with the HEC-RAS hydraulic-hydrodynamic model to provide high-resolution flash-flood simulation and mapping. CHAOS has been applied in several high-impact cases focusing on the processes arising from the air-sea interaction. Thus, it has been implemented to study the hurricane Sandy (2012) in the Atlantic Ocean and various Mediterranean tropical-like cyclones (medicanes). It is also able to represent the sea-atmosphere-hydro-land chain processes in a severe flash flood event occurred at western Attica in Greece (2017) and to simulate the sea-salt aerosol emissions through an advanced parameterization scheme based on the sea-state conditions instead of the trivial approach that it depends exclusively on the atmospheric flow. An one-year assessment of CHAOS operation is also presented, based on the results of continuous, operational-like forecasting simulations that showcased the effects of the two-way atmosphere-wave interactions. Summarizing, in the light of the increasing high-impact weather events and the climate change, the CHAOS system and its multidisciplinary applications could be exploited not only by the scientific community as an all-in-one modeling platform able to resolve fluxes and processes across Earth’s spheres but also by decision makers for operational forecasting and civil protection applications, facilitating the safekeeping of human lives and socio-economic activities in the future.