Indirect Oceanic Current Feedback on Atmospheric Dynamics over Western Boundary Currents and Adjacent Continents

Fabien Desbiolles, University of Cape Town, United States, Lionel Renault, University of California Los Angeles, Atmospheric and Oceanic Sciences, Los Angeles, United States, Arsouze Thomas, Barcelona Supercomputing Center, Barcelona, Spain and C.J.C Reason, University of Cape Town, Department of Oceanography, Cape Town, South Africa
Abstract:
Western Boundary Currents (WBCs) are critical to Earth's climate. In the last decade, mesoscale air-sea interactions emerged as an important factor of WBC dynamics. Recently, coupled models including the feedback of surface oceanic currents to the atmosphere confirmed the existence of a physical process called eddy killing, which corrects long-lasting biases in the representation of WBCs by providing an unambiguous energy sink mechanism. In this presentation, we discuss about the long-term effects of later onto ocean currents and the subsequent indirect feedback loop of the ocean current on the atmospheric dynamics over WBCs and adjacent continents at seasonal timescale.

A set of two Global coupled Ocean-Atmosphere experiments has been carried out using the EC-Earth 3.2 model, with both atmospheric and oceanic models at ~10-15km degree of horizontal resolution over a 25 years period. They only differ by taking account or not the ocean current feedback in the calculation of wind stress (CFB – Current FeedBack and NOCFB).

The WBCs paths rectification along with the reduction of EKE cause large difference of Sea Surface Temperature (SST, more than 2 degrees) over the core of WBCs (i.e., Gulf Stream, Kuroshio, Agulhas Brazil and the East Australian currents) between CFB and NOCFB. These SST differences lead to a significant changes in heat fluxes at the air-sea interface. The resulting convection cells and cloud formation processes are then modified between CFB and NOCFB and induce +/- 10% of seasonal rainfall difference over the WBCs, but also, over subtropical gyres and adjacent continents. A significant difference are then found in extratropical storms tracks in both Northern and Southern parts of Atlantic and Pacific oceans, linking the local mesoscale dynamical air-sea interactions with larger atmospheric dynamics and, notably, the strength, the extremes and the variability of extratropical atmospheric jets.