Abstract

Advances in the understanding and modelling of surface currents have revealed the importance of mesoscale and submesoscale features. These features should have a large influence on wind waves, and in particular wave heights are expected to be modified by refraction. Still, the quantitative impact of currents on waves is not well known due to the complexity of the random wave fields and currents that are found in the ocean, and the lack of observations of both currents and waves at scales shorter than 150 km. Here we combine novel satellite altimetry data with phase-averaged numerical wave models forced by wind and surface currents fields, taken from the oceanic model CROCO, run at 2.5km resolution. The influence of the spatial resolution of the current field is investigated using smoothed versions of the same current field. We find that a numerical wave model forced with surface currents with resolutions of 30 km or less and a directional resolution of 7.5 degrees or less, can provide accurate representations of the significant wave height gradients found in the Agulhas current. Using smoother current fields, such as derived from satellite measurements of dynamic height, generally underestimates wave height gradients. Hence, satellite altimetry provides high resolution wave height with a gradient magnitude that is a constraint on surface current gradients, at resolutions that may not be resolved by today's combination of mean dynamic topography and altimeter-derived anomalies. Beyond a demonstration for relatively steady currents, this may apply to time-varying currents if enough wave measurements are available.