Unraveling the Impacts of Ocean Surface Current Gradients and Ocean Surface Waves on Atmospheric Boundary Layer Physical Processes over the Gulf Stream Using COAWST Model

Florida State University, Tallahassee FL

Investigators

Abstract

This research focuses on how ocean surface currents and waves work with the atmosphere to cause winds that move heat and moisture in a manner that influences weather related to the Gulf Stream. Location-to-location differences in currents and waves cause differences in the surface friction felt by the atmosphere, which results in areas of increased vertical motion over these locations. That motion helps transport heat and moisture to heights that influence weather. This study investigates if these processes are important before storms and during storms. If these processes are found to be important, the knowledge obtained will improve weather forecasts. A significant amount of this research will be carried out by a graduate student; thus, contributing to the training of the next generation of modelers with expertise in interaction between the ocean and atmosphere. Modeling tools developed will also help future science investigations of these processes. This research will improve understanding of the atmospheric responses to momentum-related air-sea coupling processes on fine spatial scales (10 to 40 km) and at shorter timescales (from hours to several days). This project will focus on the Gulf Stream region where horizontal gradient of ocean surface current is large and where impacts on weather are more likely to be large. The Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system will be modified to more different types of models of surface drag because prior work has shown surprisingly strong sensitivity to the surface stress parameterization in high-resolution (2-6 km) two-way coupled ocean/wave/atmosphere models. Four twin experiments will determine the atmospheric sensitivity to winds and waves after accounting for how two-way coupling modifies the waves and currents. In each twin experiment, the two-way coupled model is run to obtain the ocean and atmosphere states. Then the ocean state obtained from the coupled run is prescribed to force the atmosphere without the dependency on currents or waves. Differences between couple runs and between members of each pair are diagnosed. Validation of surface characteristics sensitive to stress parameterization will provide insights about the strengths and weakness of each surface stress parameterization. This project is anticipated to (1) determine how coupling of winds, currents, and waves modifies budgets of heat, moisture, and horizontal momentum; (2) determine the extent to which vertical transport within the atmospheric boundary-layer (ABL) and between the ABL and free atmosphere is enhanced by wave and current influences on stress; (3) determine how much the enhanced vertical motion and transport in the coupled model contributes to increased convection and storm intensity; and (4) determine how the answers to the above three questions change depending on weather regimes (e.g., boundary layer stability, wind speed, and interaction with atmospheric fronts). This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.