A Linear Analysis of Equatorial Atlantic Ocean Thermocline Variability

Robert H. Weisberg Department of Marine Science, University of South Florida, St. Petersburg, Florida

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T. Y. Tang Department of Marine Science, University of South Florida, St. Petersburg, Florida

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Abstract

Observed variations in the Atlantic Ocean's equatorial thermocline are compared at four locations with simulations using an analytical reduced-gravity model. The comparison shows the essential features of the seasonal wind-forced thermocline response to be accounted for by a linear superposition of equatorial long waves, evolving basinwide, tending to bring the zonal pressure gradient into balance with the wind stress. A frequency response function is derived whose properties provide a basis for discussing the large scale features of the equatorial Atlantic Ocean's seasonal cycle—for example, its evolution along the equator, the maximum upwelling region observed in the Gulf of Guinea and the secondary upwelling season also observed there. Clarification is also given to the issue of remote versus local forcing for these features.

Abstract

Observed variations in the Atlantic Ocean's equatorial thermocline are compared at four locations with simulations using an analytical reduced-gravity model. The comparison shows the essential features of the seasonal wind-forced thermocline response to be accounted for by a linear superposition of equatorial long waves, evolving basinwide, tending to bring the zonal pressure gradient into balance with the wind stress. A frequency response function is derived whose properties provide a basis for discussing the large scale features of the equatorial Atlantic Ocean's seasonal cycle—for example, its evolution along the equator, the maximum upwelling region observed in the Gulf of Guinea and the secondary upwelling season also observed there. Clarification is also given to the issue of remote versus local forcing for these features.

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