A wind comparison study using an ocean general circulation model for the 1999-1998 El Nino

Predictions of the 1997-1998 El Nino exhibited a wide range of forecast ski ll that were dependent, in part, on the wind-driven initial conditions for the ocean. In this study the results of a reduced gravity, primitive equati on, sigma coordinate ocean general circulation model are compared and contr asted when forced by several different wind products for the 1997-1998 El N ino/La Nina. The different wind products include atmospheric model winds, s atellite wind products, and a subjective analysis of ship and in situ winds . The model results are verified against fields of observed sea level anoma lies from TOPEX/Poseidon data, sea surface temperature analyses, and subsur face temperature from the Tropical Atmosphere-Ocean buoy array. Depending o n which validation data type one chooses, different wind products provide t he best forcing fields for simulating the observed signal. In general, the model results forced by satellite winds provide the best simulations of the spatial and temporal signal of the observed sea level. This is due to the accuracy of the meridional gradient of the zonal wind stress component that these products provide. Differences in wind forcing also affect subsurface dynamics and thermodynamics. For example, the wind products with the weake st magnitude best reproduce the sea surface temperature (SST) signal in the eastern Pacific. For these products the mixed layer is shallower, and the thermocline is closer to the surface. For such simulations the subsurface t hermocline variability influences the variation in SST more than in reality . The products with the greatest wind magnitude have a strong cold bias of >1.5 degreesC in the eastern Pacific because of increased mixing. The satel lite winds along with the analysis winds correctly reproduce the depth of t he thermocline and the general subsurface temperature structure.