[Eoas-seminar] Oceanography Dissertation defense - Xu Chen - Nov 7, 10:00 - 327OSB

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Fri Oct 26 16:20:36 EDT 2018


Title: TWO-WAY FEEDBACK BETWEEN AIR-SEA TURBULENT FLUXES AND OCEANIC SUBMESOSCALE PROCESSES

Major Professor: Bill Dewar



Abstract:

An accurate representation of air-sea interaction is crucial to the accurate numerical prediction of ocean, weather, and climate. It is known that sea surface temperature (SST) gradients and surface currents in the oceanic mesoscale regime significantly affect air-sea fluxes of momentum and heat, and the mesoscale-modified air-sea fluxes also influence the ocean dynamics on various scales. 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 mutual 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 submesoscale regime. We here argue that the inclusion of surface currents in air-sea bulk flux parameterization and the atmospheric thermodynamic adjustments to the ocean surface are determined 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. This study also finds that the evolution of submesoscale processes is closely associated with the potential vorticity (PV) budget. 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. Therefore, the evolution of submesoscale processes is significantly influenced by the submesoscale-modified air-sea fluxes. 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.

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