Waves steepen in accelerating currents

Image of the Month - August 2018

Four-year mean (2013-2016) computed using the constellation of 4 satellite altimeters, onto a 0.5°x0.5° grid, of top: significant wave height; middle: normalized gradient of significant wave height; bottom: absolute value of surface current vorticity.(Credits Ifremer)
Four-year mean (2013-2016) computed using the constellation of 4 satellite altimeters, onto a 0.5°x0.5° grid, of top: significant wave height; middle: normalized gradient of significant wave height; bottom: absolute value of surface current vorticity.(Credits Ifremer)


Extreme waves are a known hazard on the shipping routes crossing some of the main currents, since strong ocean currents can modify the height and shape of ocean waves. This can causes extreme sea states in particular conditions (including rogue waves).

As shown last year (Image of the Month, August 2017: Currents & waves), significant wave height variability at scales below 100 km are associated with current variability at similar scales. But, moreover, large significant wave height gradients at a scale of about 10 km are also systematically associated with current gradients - i.e. increased steepness of waves interacting with currents accelerating abruptly over a small distance. The model predictions as of today tend to underestimate wave/current interactions, rendering research and observation necessary to improve them.

Such correlations give perspectives for better understanding and mapping of the surface current signature in the wave field, to improve extreme sea state predictions. It will rely on high quality observations of waves and surface currents from modern altimeters and SAR, CFOSat, Swot and Skim missions.

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