Wind Stress Forcing of the Ocean in the SOC Climatology: Comparisons with the NCEP–NCAR, ECMWF, UWM/COADS, and Hellerman and Rosenstein Datasets

Abstract

Results from an analysis of the Southampton Oceanography Centre (SOC) global wind stress climatology, which is based on in situ reports for the period 1980-93, are presented. The accuracy of the SOC stresses has been assessed at several locations by comparison of individual monthly means with measurements from Woods Hole Oceanographic Institution research buoy deployments. For the subduction buoy array, situated in the subtropical North Atlantic, the random error in the SOC individual monthly mean wind stress ranges from 0.004 to 0.008 N m-2, which corresponds to between 5% and 10% of the mean stress depending on which buoy is considered. The large-scale characteristics of the SOC fields are compared with those of the NCEP-NCAR and ECMWF atmospheric model reanalyses, and the in situ observation based on the University of Wisconsin-Milwaukee/Comprehensive Ocean–Atmosphere Dataset (UWM/COADS) and Hellerman and Rosenstein (HR) climatologies. The NCEP-NCAR fields show noticeably weaker wind stress forcing in the Tropics than SOC, while ECMWF and UWM/COADS are in good agreement. From the Tropics to the midlatitudes, the HR stresses tend to be stronger than SOC and the other recent climatologies. At higher latitudes, differences in the spatial structure of the Northern Hemisphere subpolar gyres in SOC and HR are found that are consistent with variations in the state of the North Atlantic and North Pacific Oscillations within the periods on which the climatologies are based. A detailed comparison of the wind-driven response of the ocean is presented for SOC and HR. The North Atlantic subpolar gyre is more intense in SOC than HR and this leads to a doubling in the strength of the Ekman suction. January mean upwelling velocities in this region deduced from the two datasets are 18.9 and 8.6 m month-1, respectively. In the North Pacific a single large-scale subpolar gyre is evident in SOC compared with two smaller gyres in HR. Seasonal to interannual variability in the wind-driven ocean response is quantified using an extended version of the SOC dataset covering the period 1980–97. Significant variability in the Ekman transport across several latitudes that correspond to WOCE hydrographic sections is observed and related to the major atmospheric pressure oscillations