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

Random scattering, refraction and focussing of ocean surface gravity waves (SGWs) by submesoscale currents result in spatial modulation - "patches'' - in the wave field. A signature of patches is that the significant wave height Hs varies by as much as 30% on horizontal scales in the range 10 to 100 km and time scales of a few hours to a day; these scales reflect those of submesoscale currents and are much smaller than those of the wind-stress forcing of SGWs which is traditionally assumed to control the spatio-temporal variability of Hs.

As a result, patches pose a major challenge for the modelling and prediction of SGWs and of their impact on the ocean circulation. This project will tackle this challenge by developing new statistical models of the scattering of SGWs by submesoscale turbulence. We will use these models to explain the main features of patch variability, including a recently discovered relation between the power spectrum of Hs and the submesoscale kinetic energy spectrum, and to develop a parametrization of SGW scattering by submesoscale turbulence that we will incorporate into WAVEWATCH III.

Spatial and temporal fluctuations in Hs are reflected in other properties of the SGW field including the Stokes velocity, and hence the wave-averaged vortex and Stokes-Coriolis forces which control the forcing of currents by SGWs. We will investigate the hypothesis that the interaction between waves and mean flows is strong on patch time and space scales, and develop new modeling tools tailored to these scales.