The Guinea Dome is a permanent, quasi-stationary feature on the eastern side of the thermal ridge extending zonally across the tropical North Atlantic. The dome is a part of the large-scale near-surface flow fields associated with the North Equatorial Current, the North Equatorial Countercurrent and the North Equatorial Undercurrent. In the present study, historical and recently obtained hydrographic data are combined to investigate the thermohaline structure and geostrophic flow field in the vicinity of the dome. It is shown that the Guinea Dome exists throughout the year both in subthermocline and thermocline layers, that it has a corresponding cyclonic geostrophic flow, and that seasonal changes occur with respect to its vertical structure, horizontal extent, and position. The observational results are then compared with simulations from a general circulation model of the tropical Atlantic. A seven-year simulation forced by observed monthly winds is run to compute a monthly climatology. The model adequately simulates the Guinea Dome with respect to its structure, flow field, and seasonal variability.

In February‐April 1991, episodes of 2 to 8 m s−1 westerly winds of 3 to 11 days' duration occurred in the western Pacific warm pool. Resulting modifications of the upper ocean in current and hydrology are quantified using data from an equatorial mooring at 165°E and from three cruises within 30 days of one another along 165°E. During westerly wind bursts (WWB) stronger than 4 m s−1, the upper 50 m becomes isothermal to within 0.1°C and sea surface temperature (SST) drops by 0.3–0.4°C between 5°S and 2.5°N. Conversely, SST starts warming and the upper 50 m restratifies in 4–5 days after the end of WWB. In contrast to previous observations, salinity between 0 and 50 m appears almost unaffected by WWB; it freshens by 0.4 practical salinity unit in March within an area of 1°–2° of latitude around the equator but not necessarily in direct response to WWB. As for zonal circulation, surface equatorial flow accelerates eastward 2–3 days after the beginning of westerlies. Then, after less than 2 weeks, eastward and westward jets both develop from 2°N to 2°S in the upper and lower halves of the temperature mixed layer, respectively. Changes in zonal mass transport in this layer were as much as 30 Sv between 2.5°S and 2.5°N from one cruise to the next.

About three months after the beginning of an El Niño/Southem Oscillation (ENSO) year, a rainfall shortage develops over all of New Caledonia (21"S, 165"E) and lasts for 12 months. There is, on the average, a 22% decrease over the mean monthly rainfalls for one year. This result is based on the study of a rainfall composite and of a composite obtained from the first empirical orthogonal function (EOF) extracting more than half of the variance over 30 years of measurement at 18 stations. I ' 394.

Altimetric data, climatological hydrological data, and numerical model results are compared over the tropical Atlantic Ocean between November 1986 and November 1988. All reproduce the seasonal cycle of the dynamic topography rather well, and the agreement is particularly good between altimetry and the primitive equation model. The study of the 1986–1988 period reveals interannual events evidenced by both the altimetry and the models, especially during spring 1988 in the Gulf of Guinea.

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