Surface Currents and Significant Wave Height Gradients: Matching Numerical Models and High‐Resolution Altimeter Wave Heights in the Agulhas Current Region

Overview & Synopsis

Advances in the understanding and modeling of surface currents have revealed the importance of internal waves, mesoscale and submesoscale features. Indeed, all these features should have a large influence on wind waves and in particular on wave heights. Still, the quantitative impact of currents on waves is not well known due to the complexity of the random wavefields 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 compare novel satellite altimetry data and state of the art phase-averaged numerical wave models forced both by wind and currents. Currents used are taken from the oceanic model Coastal and Regional Ocean COmmunity, run at high resolution. The influence of current field resolution is investigated by applying Gaussian filters of different width to that same high-resolution current field. We find that a numerical wave model that uses currents with resolutions of ∼30 km or less and a directional resolution of 7.5° can provide accurate representations of the significant wave height gradients found in the Agulhas current. Using smoother current fields such as derived from altimeters measurements alone, coarse directional spectral resolution or larger directional spread of the wave model generally underestimates gradients and extreme wave heights. Hence, satellite altimetry provides high-resolution wave height with a gradient magnitude that is highly sensitive to underlying surface current gradients, at resolutions that may not be resolved by today's altimeters measurements. This is demonstrated here for relatively steady currents averaged over 3 years