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Free Content What controls the rate of equatorial warm water mass formation?

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Equatorial warm water formation is one important factor in the mass balance of Tropical Surface Water (TSW) in the Atlantic Ocean; another is drainage by the North Brazilian Coastal Current (NBCC). Both are affected by the depth of the TSW layer at the western boundary: deepening of this layer increases the transport of the NBCC and reduces warm water mass formation by shortening the eastern upwelling zone. Strengthening westward wind-stress steepens the thermocline in the western sector of the equatorial band, enhances upwelling in the eastern sector, affecting mass balance on both counts. Recirculation of TSW via a loop containing the North Equatorial Counter Current (NECC), and inflow from the south at the eastern boundary are also important elements of this mass balance: they depend on the wind-stress field over a wider region.

The various elements of this mass balance are parameterized in terms of western boundary layer depth and wind-stress in the western sector. The resulting first order equation describes the response of the system to the annual cycle of wind-stress. With quantitative inputs typical of the equatorial Atlantic, output variables are simulated realistically: upwelling varies from 3 to 18 × 106 m3/s, NBCC transport from 13 to 26 × 106 m3/s, both in accord with observation, as is simulated storage, and TSW depth. An interesting finding is that the east-west length of the upwelling region varies relatively little while everything except storage varies in phase with the wind-stress (the storage lags by 2 months). The lesser variation of upwelling sector length comes about because the steepening of the thermocline in response to increasing wind-stress is accompanied by deepening in the western end, necessary to allow the escape of excess fluid.

The results show the interplay of wind-stress, upwelling and western boundary current transport in the control of the oceanic heat gain in the equatorial band.

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Document Type: Research Article

Publication date: 1987-08-01

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  • The Journal of Marine Research publishes peer-reviewed research articles covering a broad array of topics in physical, biological and chemical oceanography. Articles that deal with processes, as well as those that report significant observations, are welcome. In the area of biology, studies involving coupling between ecological and physical processes are preferred over those that report systematics. Authors benefit from thorough reviews of their manuscripts, where an attempt is made to maximize clarity. The time between submission and publication is kept to a minimum; there is no page charge.
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