A first glimpse from the EUREC4A-OA/ATOMIC air-sea experiment

Ocean mesoscale eddies create specific air-sea interaction patterns that can have an integral effect on the large scale atmosphere and ocean dynamics. Recent advances in the state of the art of these processes has been predominately obtained from modeling efforts, but only very few observational studies exist, and there are all located in the extra-tropics. Adding a dedicated ocean mesoscale eddy air-sea interaction experiment to the EUREC4A campaign will enhance the objectives and success of the whole program as it sets a local, oceanic constrain to the atmospheric evolution (as been outlined in the overall EUREC4A design: www.eurec4a.eu; Bony et al. 2017). Temporal variability over a fixed mesoscale (500 km x 500 km) study area allows for sampling varying atmospheric states, on the time-scales of the EUREC4A field study. The oceanographic component that add on EUREC4A consists of four ships and many autonomous platforms (gliders, Saildrones, specific surface drifters, Argo floats) sampling the mesoscale ocean and air-sea exchanges at different edges of the Northwest Atlantic tropical region. This will enable the extended spatial sampling required to characterize ocean variability and gather enough air-sea observations at different locations to assess with accuracy the involved processes and impacts.

The western tropical Atlantic is an ideal laboratory for the proposed study. It hosts rich ocean mesoscale variability under an atmosphere characterized by a rather steady trade wind regime. In this region, eddies have a diameter of 200 to 300 km and lifetimes of several months up to years. In particular south of Barbados, very energetic and long-lived anticyclonic North Brazil Current rings are commonly found. These eddies are key for the northward transport of properties from the South to the North Atlantic within the Atlantic Meridional Ocean Circulation. Moreover, preliminary studies based on satellite observations have suggested that they play a crucial role in air-sea interactions and on the atmosphere. This region and eddies are the focus of EUREC4A-OA, the French oceanographic component of the larger EUREC4A field experiments.

In this talk we will present the preliminary lessons learned and results obtained by this unprecedented observing effort.