The Impact Of Waves On Ocean Surface Currents And Wind Energy Input To The Ekman Layer

Ocean surface currents estimated from the satellite data consist of two terms: Ekman currents from the scatterometer wind stress and geostrophic currents from the altimeter Sea Surface Height(SSH).But the classical Ekman model does not consider the wave effects.By taking the wave-induced Coriolis-Stokes forcing into account,the impact of waves(primarily the Stokes drift)on ocean surface currents is investigated.The products are validated by comparing with OSCAR currents and in situ Lagrangian drifter velocity.The result shows that our products with the Stokes drift are better adapted to the in situ Lagrangian drifter currents.Especially in the Southern Ocean region(40°S–65°S),90%(91%)of the zonal(meridional)currents have been improved compared with currents that do not include Stokes drift.The correlation(Root Mean Square Error)in the Southern Ocean has also increased(decreased)from 0.78(13 cm/s)to 0.81(10.99 cm/s)for the zonal component and 0.76(10.87 cm/s)to 0.79(10.09 cm/s)for the meridional component.This finding provides the evidence that waves indeed play an important role in the ocean circulation,and need to be represented in numerical simulations of the global ocean circulation.Furthermore,based on the daily QuikSCAT and ASCAT wind stress data and the 6-hourly ECMWF Interim surface wave datasets,seasonal variations of wind energy input to the Ekman-Stokes layer(the wave-modified Ekman layer)is investigated.The result shows that for the global ocean,in summer,the maximum of total wind energy input is located in the Antarctic Circumpolar Current,while in winter,that is located in the mid and high latitudes of the North Pacific and North Atlantic regions.Furthermore,the total wind energy input to subinertial motions in the Ekman-Stokes layer is 498.24 GW(winter)and 97.61 GW(summer)in the 40° N~60°N region,the total increased wind energy input is 16.78 GW(4.14 GW)in winter(summer),accounting for 3.5% and 4.4% of the pure energy input to the classical Ekman layer respectively.While in the area 40°S~60°S,the total wind energy input is 585.44 GW(winter)and 1036.26 GW(summer),increased 32.29 GW(winter)and 59.65 GW(summer),the increased ratio of which is 5.8% and 6.1%.