Currents & waves

Image of the Month - August 2017

Maps for 16 September at 18:00 UTC for (a) modeled surface current magnitude, (b) modeled significant wave height when the current forcing is included, (c) modeled significant wave height without currents (arrows: wind direction from ECMWF) (Credits Ifremer)
Maps for 16 September at 18:00 UTC for (a) surface current magnitude modeled by MITgcm, (b) the modeled significant wave height when the current forcing is included in WAVEWATCH III, (c) wind direction from ECMWF (arrows) and modeled significant wave height without effects of currents. The dashed box is the region used for spectral analysis (Credits Ifremer)

We always showed either wave or sea surface height(current) data, coming from separate studies and applications. However, as both phenomena are occuring on the same interface (the sea surface), it seems logical that some kind of interaction takes place. Currents can indeed influence waves as was shown for the major currents, especially the Agulhas current or the Gulf Stream (mostly using SAR onservations). In fact this interaction is the principal suspect in rogue waves generation.

For smaller currents, the question was not so much studied. And with the coming of SWOT high-resolution data (sea surface heights & derived currents, but also significant wave heights, as any other altimeter ever flown), it is important to better know such scales.  Using a combination of models for currents and waves, and data from the Jason-3 and Saral satellites, it was shown that variations in currents at scales 10 to 100 km are the main source of variations in wave heights at the same scales.

This will help in deciding how SWOT data will have to be processed to arrive at accurate sea level and wave measurements. It will also help in the analysis of wave measurements by the CFOSAT satellite.

See also :

References

  • Ardhuin, F., S. T. Gille, D. Menemenlis, C. B. Rocha, N. Rascle, B. Chapron, J. Gula, and J. Molemaker (2017), Small-scale open ocean currents have large effects on wind wave heights, J. Geophys. Res. Oceans, 122, 4500–4517, doi:10.1002/2016JC012413.