Feedback between Air-Sea Turbulent Momentum Flux and Oceanic Submesoscale Processes

Xu Chen1, William K Dewar2, Eric Chassignet3, Mark A Bourassa4 and Steven L Morey2, (1)Florida State University, EOAS, Tallahassee, FL, United States, (2)Florida State Univ, Tallahassee, FL, United States, (3)Center for Ocean-Atmospheric Prediction Studies, Tallahassee, FL, United States, (4)Florida State Univ, Center for Ocean-Atmospheric Prediction Studies, Tallahassee, FL, United States
Abstract:
An accurate representation of air-sea interaction is crucial to the accurate numerical prediction of ocean, weather, and climate. Previous studies found that resolving the mutual feedbacks between mesoscale processes and the atmosphere improved the accuracy of modeling for ocean, weather, and climate. In the submesoscale regime recently revealed by high-resolution numerical models and observations, the SST gradient and surface currents are found to be much stronger than those in the mesoscale. However, the feedbacks between the submesoscale processes and the atmosphere are not well understood. To quantitatively assess the mutual responses between the air-sea fluxes and the submesoscale processes, a non-hydrostatic ocean model coupled with an atmospheric boundary layer module is implemented making it possible to examine the air-sea interactions over the submesoscale regime. The inclusion of surface currents in air-sea bulk flux parameterization and the atmospheric thermodynamic adjustments to the ocean surface are argued to be significant for modeling accurate wind stress and air-sea turbulent heat fluxes in the submesoscale regime. The results show that the linear relationship between wind stress curl/divergence and crosswind/downwind SST gradient, revealed in the mesoscale regime, do not exist in the submesoscale regime. Additionally, the magnitudes of positive and negative wind stress curl introduced by submesoscale processes are much greater than the magnitude of wind stress curl introduced by mesoscale processes. Because different fields of wind stress and turbulent heat fluxes are introduced by the influence of submesoscale surface velocity field and/or temperature field, these wind stress and heat flux fields can interact with submesoscale surface structures and provide different PV injections into the ocean. This study serves as a starting point in the investigation of the two-way feedback between the atmosphere and oceanic submesoscale processes. It shows that numerically resolving the two-way air-sea coupling in the submesoscale regime significantly changes air-sea flux and the oceanic submesoscale dynamics.