On the Response of the Equatorial Thermocline in the Atlantic Ocean to the Seasonally Varying Trade Winds

Measurements made during the Seasonal Response of the Equatorial Atlantic experiment in 1983, when the easterly trade winds near the equator ceased and then intensified as part of their annual cycle, show a sequence of events leading to an adjusted thermocline. Both the duration and extent of the downwelling and upwelling associated with the adjustment process were zonally inhomogeneous along the equator. An analytical reduced gravity model was driven by a hierarchy of easterly wind stress forcing functions representative of the Atlantic to compare the integral nature of the forced long-wave responses with the observations. Qualitative agreement was found with upwelling and downwelling sequences within the forced region increasing to the east as observed. Apparent model propagation speeds differed significantly from the prescribed model wave speeds within the forced region owing to the growth parameters of the winds, and boundary reflections distorted the responses to the east of the forced region. The resulting interference patterns tended to separate the region 0°–10°W along the equator from the African coast as one of maximum upwelling.