NSFGEO-NERC: Scattering of ocean surface gravity waves by submesoscale turbulence

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This is a project that is jointly funded by the National Science Foundation’s Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (UKRI/NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own investigators and component of the work. Random scattering, refraction and focusing of ocean surface gravity waves by submesoscale currents results in spatial modulation — or patches — in the wave field. Within these patches the significant wave height may vary by as much as 30% on horizontal scales of 10 to 100 km and time scales of a few hours to a day. As a result, patches pose a major challenge for the modelling and prediction of surface gravity waves and of their impact on the ocean circulation. Patches affect the wave-breaking rate, and climate-relevant air-sea interaction such as gas exchange rates, aerosol production and wind-stress coupling to the ocean. Patches are likely important contributors to sea-state bias errors that complicate altimetric inference of currents. The project will contribute to improving the performance of operational surface gravity wave models by including the statistical effects of unresolved currents, consequently removing errors related to delayed swell arrival. This will improve predictions of wave activity with naval, commercial, and recreational applications. This project will apply kinetic theory, and a new version of generalized Lagrangian mean theory, to demonstrate the effect of submesoscale currents on waves and the reciprocal effect of waves on submesoscale currents. New statistical models of the scattering of surface gravity waves by submesoscale turbulence will be developed. These models will in turn be used to explain the main features of patch variability, including a recently discovered relation between the power spectrum of significant wave height and the submesoscale kinetic energy spectrum, and to develop a parametrization of surface gravity wave scattering by submesoscale turbulence that will be incorporated into WAVEWATCH III. Spatial and temporal fluctuations in significant wave height are reflected in other properties of the surface gravity wave field including the Stokes velocity, and hence the wave-averaged vortex and Stokes-Coriolis forces which control the forcing of currents by surface gravity waves. The hypothesis that the interaction between waves and mean flows is strong on patch time and space scales will be investigated and new modeling tools will be developed and tailored to these scales.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.