Ocean general circulation model sensitivity to forcing from scatterometer winds

Enhanced global surface wind fields are constructed from a blend of NASA sc atterometer (NSCAT) and ERS 2 scatterometer data and National Centers for E nvironmental Prediction (NCEP) analyses, at 6-hour intervals, for a repeata ble annual cycle from August 1996 through July 1997. Wind field properties (wind speed, zonal and meridional wind stresses, wind stress curl, and kine tic energy input) for the enhanced winds are compared with the NCEP analyse s for the same time period. Large-scale, zonal patterns dominate annual ave rage difference maps for wind speed and both components of wind stress. Win d stress curl differences are largest in the subpolar North Atlantic and in the midlatitudes of the southern hemisphere. The importance of wind field differences are measured by their impacts on the response of an ocean gener al circulation model (OGCM). Twin experiments are performed using the Natio nal Center for Atmospheric Research Climate System Model ocean component in stand-alone mode. The annual mean OGCM responses to the enhanced winds and to surface winds from the NCEP analyses are compared for barotropic stream function, surface velocities, upper ocean upwelling, sea surface temperatu re (SST), surface heat flux, meridional overturning stream function, and to tal northward heat transport. Differences in the annual mean responses are attributable to differences in the mean forcing and not to the mesoscale si gnal that is present in the enhanced winds but not resolved by the OGCM. Di fferences in SST and surface heat flux are partitioned between local thermo dynamic balances and balances involving ocean dynamics as well. Northward h eat transport differences of order -0.2 PW in the southern hemisphere midla titudes are consistent with weaker eastward and southward stresses in the w esterlies and a 27% reduction in kinetic energy input from enhanced winds. This difference in northward heat transport is compensated in the southern hemisphere tropical Pacific where surface stresses and the OGCM surface res ponse to enhanced winds are more westward and more divergent, resulting in 27% greater kinetic energy input. An extensive appendix details the realist ic high-wavenumber character of the enhanced winds.