WHOI Independent Study Award

Air-sea Interaction on the Oceanic Submesoscales

Hyodae Seo
Physical Oceanography Department
Woods Hole Oceanogrpahic Institution

Award: $49,916
Duration: 2013-2015

Project Summary.

Processes at the air-sea interface are key for the circulation, both in the ocean and atmosphere. Variations in wind stress drive ocean circulation, and the resultant turbulent heat and moisture fluxes influence the atmospheric circulation. On large spatial scales (e.g., greater than 1000 km), the atmosphere is typically thought to drive the ocean: increased wind stress causes a greater heat loss from the ocean, leading to a cooler sea surface temperature (SST). In this “conventional” large-scale scenario, the ocean plays only a passive role in the coupled system; however, the recent satellite observations have indicated that the ocean plays a fundamentally different role on the spatial scales less than 1000 km. Studies show that the warm (cold) mesoscale (say, 10-1000 km) SSTs associated with the semi-permanent ocean currents and the transient mesoscale eddies produce a higher (lower) wind speed and surface stress; this positive correlation between wind and SST indicates the oceanic forcing of the atmosphere. In addition to the mesoscale SST (10-1000 km), the ocean is full of smaller scale (less than 10 km) yet more energetic submesoscale variability (e.g., filaments) and mixed layer fronts that are important for energy dissipation and turbulent transport in the ocean. The ocean submesoscales feature much stronger spatio-temporal variability in SST, raising a question how significant air- sea coupling will be on the submesoscales. However, very little is known about the dynamics of air-sea coupling on the submesoscale range and how it influences the mesoscale and large-scale circulation. We currently do not know whether the observed mesoscale coupling would be amplified on the submesoscale in view of the fact that submesoscales have much broader range of SST variability, or the coupling would break down because of the too short length scale of submesoscales for the atmosphere to respond to. The general lack of dynamical understanding of submesoscale air-sea coupling and its potential importance for air-sea exchange and regional to large-scale climate motivates this study. This project will establish the dynamical framework to interpret the atmospheric response to the oceanic submesoscales using idealized atmospheric modeling, which will eventually aid in the interpretation of oceanic and atmospheric data from the planned observations and models of the submesoscale process. The project may result in a significant shift in our view of air-sea interaction and its role in climate dynamics. The preliminary results will motivate a full proposal with the goal to parameterize the submesoscale coupling effects with physically motivated scalings. Because fine-scale air-sea coupling would strongly influence upwelling and mixing in the upper ocean, we expect that biological productivity will also be modified with the submesoscale air-sea coupling.