Modeled surface dynamic height in 1964–1984: An effort to assess how well the low frequencies in the equatorial Atlantic were sampled in 1982–1984

Abstract

A wind‐forced linear model has been used to produce 21 years (1964–1984) of monthly time series of surface dynamic height in the equatorial Atlantic. The climatological seasonal cycle is subtracted, and the statistical characteristics of the residuals are analyzed. An empirical orthogonal function analysis reveals that the most significant pattern has deviations of one sign in the western equatorial Atlantic associated with near‐simultaneous deviations of the opposite sign in the eastern equatorial Atlantic. The anomalies in the last 2 years, 1983 and 1984, are particularly large. The time component of the first empirical orthogonal function peaks in July 1983, changes sign at the end of 1983, and has an extremum of the opposite sign in April 1984. At that time, the zonal slope of dynamic height had reversed with respect to normal along the equator. In 1983–1984 a large data set was collected to study the seasonal variability in the equatorial Atlantic. We do not analyze the real data here but evaluate the ability of this data set to cover correctly the time and space scales of the modeled anomalies. The model time series are sampled at the positions of the data. An optimal interpolation scheme is used with the adequate statistics extracted from the model time series, and the analysis is compared with the simulation. Our results suggest that the most noticeable features of the model anomalies for 1983–1984 are reproduced in the analysis, although the results would have been better if more data had been collected in the western equatorial Atlantic at the end of 1983. According to this study, subsets which have already been analyzed for the same period (for example, the Programme Français Ocean Climat dans l'Atlantique Equatorial conductivity‐temperature‐depth cruises) would also have retained the reversal of sign of the anomaly between the end of 1983 and early 1984, although the overall accuracy would have been reduced.