09.02.2026: Ocean Circulation and Climate Dynamics Colloquium
Dr. Aaron Wienkers, ETHZ: "Piecing Apart Air–Sea Interactions: A Mechanistic Analysis of Current and Thermal Feedback Processes from Mesoscales to Global Circulation"
When? Monday 09 February 2026 at 11 am
Where? Conference Room 5-1.214, Building 5, Wischhofstr. 1-3 and online
via Meeting link:https://geomar.webex.com/geomar-en/j.php?MTID=ma73a9dd4db0f5cb6275b471e1c5e6005
Meeting number: 2789 008 5026
Password: nhPGUfGj553
Abstract:
Ocean-atmosphere momentum and heat exchange regulates global circulation patterns and climate variability, yet the scale-dependent physics governing these interactions remains poorly constrained in coupled Earth System Models, particularly at the oceanic mesoscale (10–250 km). Air–sea current feedbacks arise as ocean surface currents modify the wind stress that drives them, while thermal feedbacks emerge through SST-driven atmospheric boundary layer adjustments that modulate surface winds and heat fluxes. Both feedbacks have fundamentally different behaviour at basin versus mesoscales, yet traditional coupling coefficient diagnostics measure only net feedback strength without distinguishing constituent mechanisms. Models may therefore achieve realistic coupling through compensating errors in underlying physics rather than correct process representation. As Earth System Models advance to kilometre-scale resolution and explicitly resolve previously-parameterised physics, this distinction is even more important. Through multi-model analysis of four eddy-resolving coupled ESMs from the European Eddy-Rich Earth System Models (EERIE) project, we characterise the scale-dependent feedbacks and develop decomposition methods that partition net coupling into constituent physical pathways. Current feedbacks inject kinetic energy into large-scale circulation but systematically damp mesoscale eddies through eddy-killing, extracting 20–50% of surface eddy kinetic energy. Thermal feedbacks transition from large-scale Wind-Evaporation-SST instability to mesoscale damping driven by vertical mixing within the marine atmospheric boundary layer. Our framework reformulates coupling coefficients as energy transfer efficiency and partitions thermal feedbacks into Wind-Evaporation-SST versus Vertical Mixing Mechanism pathways through boundary layer turbulence theory. These diagnostics map directly onto model parameterisations, enabling process-level evaluation. A striking emergent pattern in the EERIE model ensemble is the spatial uniformity of mesoscale damping efficiency across dynamically active regions despite order-of-magnitude variations in eddy intensity. This uniformity suggests universal scaling laws governing air-sea interaction physics, providing quantitative targets for scale-aware parameterisations in next-generation climate projections.
