Transports

convergence

WINDS ■ Westerlie:

Nonti

Equatorial. Current

Equatorial

Coumef-

Current divergence convergence

Soutn

Equatorial

Current

Equatorial a Divergence :.

convergence divergence convergence

Equatorial a Divergence :.

' westerlies i a}

Figure 5.1 (a) The relationships between the wind direction, the surface current and the Ekman transport (the total transport in the wind-driven layer, shown by short blue arrows), In equatorial latitudes. Note the Doldrum belt between about 5° and 10° N.

(b) North-south diagrammatic section showing the vertical and meridional circulation in equatorial latitudes, and the shape of the sea-surface and thermocline. Regions of eastward and westward flow are indicated by the letters E and W. The darker blue region (in which geostrophic current Is assumed to be zero, cf. Figure 3.20(a)) is the deep water below the thermocline. The blue oval at about 100 m depth at the Equator represents the Equatorial Undercurrent (see Section 5.1.1). (Note that the vertical scale is greatly exaggerated.)

Nonn Equaionaf Curent

Ecuatorial Counter-Current outn Equatona' Current /<__

Nonn Equaionaf Curent

Ecuatorial Counter-Current outn Equatona' Current /<__

Figure 5.1(b) is a diagrammatic north-south section across the Equator, showing the vertical and meridional circulation in the mixed surface layer above the thermocline/pycnocline. There is little horizontal variation in density in the upper part of this layer, particularly in the top few tens of metres, and surfaces of constant pressure are more or less parallel to surfaces of constant density, and both are parallel to the sea-surface; in other words, conditions here may be regarded as barotropic. By the depth of the thermocline. however, there are significant lateral variations in density and conditions are baroclinic. The slopes in the thermocline are therefore contrary to those of the sea-surface.

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