We compare two sets of monthly sea surface wind stress over the tropical Atlantic Ocean. The data sets are based on the ECMWF analyses during 1980-87 (the E-winds) and the monthly pseudo-wind stress from ship observations for the same period (the S-winds). Both data sets give qualitatively similar mean fields and annual cycles. Quantitatively, the zonal component of the E-winds is larger than that of the S-winds, especially in the winter hemisphere. The strongest southeast trades of the E-winds are also shifted to the east of the strongest southeast trades of the S-winds. In the vicinity of the ITCZ, the E-winds are more zonally oriented so that the convergence zone is not as clearly defined. The importance of these differences to ocean modeling is discussed.
Interannually, both data sets show that the northeast trades gradually strengthened from 1980 to 1986. The southeast trade winds, on the other hand, were anomalously strong during 1981-83, but weak during 1984-1986. With the E-winds, the southeast trades decreased gradually during 1981-83 and with the S-winds, the southeast trades are maintained until late 1983, followed by a rapid weakening. In comparison with the E-winds, the S-winds interannual fluctuations over the central and eastern part of the tropical south and equatorial Atlantic are weak.
A comparison between the observed sea surface temperature (SST) anomalies and those produced by ocean general circulation model (OGCM) simulations with both wind stress forcings shows that both simulations are reasonably close to the observations in the tropical north Atlantic Ocean. In the tropical south Atlantic, the E-winds produce a better simulation of the SST anomalies. Especially, the gradual weakening of the E-winds during 1981-83 produces the observed SST tendency, which are not shown in the S-winds simulation. However, the E-winds anomalies are poor during 1980-81 as judged by the comparison between simulated and the observed SST anomalies.
last update: 25 October 1994
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