Lessons learned from the EUREC4A-OA experiment on the impact of ocean small scales on air-sea interactions in the Northwest Tropical Atlantic

Abstract

EUREC4A-OA is a large international project, connecting experts of ocean and atmosphere observations and modelling to enhance the understanding of key ocean and air-sea processes at the and to improve the skill of forecasts and future projections.The core of EUREC4A-OA has been a one-month (Jan/Feb 2020) field study in the western tropical North Atlantic Ocean where high-resolution, synchronized observational data have been collected using cutting-edge technology on ships, airplanes and autonomous vehicles. EUREC4A-OA investigates heat, momentum, water and CO2 transport within the ocean and exchanges across the air/sea interface using innovative high-resolution ocean observations and a hierarchy of numerical simulations. EUREC4A-OA focuses on ocean dynamics at the small-scale (0.1–100 km) and related atmospheric boundary layer processes. EUREC4A-OA is centered on the tropics where the primary external time scale affecting air-sea exchange is the diurnal cycle. However, the internal ocean and atmosphere dynamics convolute the diurnal, synoptic, seasonal and longer time scales to climate variability.The talk will present some of the results we obtained so far from the observations collected during the field experiment and from numerical simulations. The analyses carried out revealed with unprecedented detail the particular characteristics of the ocean small-scale dynamics, enlightening that such scales are also very active in the tropical regions and not only over the mid and higher latitudes ocean.  Observations and models also unveil that the ocean small scales is important in contributing to the exchanges of heat, freshwater and CO2 between the ocean and the atmosphere. Moreover, the evaluation of the intensity of the coupling between the ocean and the atmosphere assessed from data and high-resolution simulations show that they are very important and intimately linked with the 3D structure of the small-scale ocean dynamics. The project has also provided preliminary results in terms of parametrization of different processes influencing the ocean and atmosphere exchanges that have been uncovered by the EUREC4A-OA field experiment. Notably a better representation of the small-scale freshwater patches due to precipitation has been introduced in the French Earth-System model that improves the overall simulations of air-sea interactions and clouds. A similar parametrization is now been introduced to take into account these physical processes in air-sea fluxes of CO2.