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A global climatology of wind–wave interaction

By Kirsty E. Hanley, Stephen E. Belcher and Peter P. Sullivan

Abstract

Generally, ocean waves are thought to act as a drag on the surface\ud wind so that momentum is transferred downwards, from the atmosphere\ud into the waves. Recent observations have suggested that when long\ud wavelength waves, characteristic of remotely generated swell,\ud propagate faster than the surface wind momentum can also be\ud transferred upwards. This upward momentum transfer acts to accelerate\ud the near-surface wind, resulting in a low-level wave-driven wind\ud jet. Previous studies have suggested that the sign reversal of the\ud momentum flux is well predicted by the inverse wave age, the ratio of\ud the surface wind speed to the speed of the waves at the peak of the\ud spectrum. ECMWF ERA-40 data has been used here to calculate the global\ud distribution of the inverse wave age to determine whether there are\ud regions of the ocean that are usually in the wind-driven wave regime\ud and others that are generally in the wave-driven wind regime. The\ud wind-driven wave regime is found to occur most often in the\ud mid-latitude storm tracks where wind speeds are generally high. The\ud wave-driven wind regime is found to be prevalent in the tropics where\ud wind speeds are generally light and swell can propagate from storms at\ud higher latitudes. The inverse wave age is also a useful indicator of\ud the degree of coupling between the local wind and wave fields. The\ud climatologies presented emphasise the non-equilibrium that exists\ud between the local wind and wave fields and highlight the importance of\ud swell in the global oceans

Publisher: American Meteorological Society
Year: 2010
OAI identifier: oai:centaur.reading.ac.uk:7479

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