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strip, along the Equator, a discontinuity appears, with the sinking of
surface water and the formation of an SST front. This front can
produce changes of 2-3°C during spring.
Changes in the boundary layer and fluxes due to the wind blowing
from the cool water to the warm water in the north of the gulf are
associated with the development of this frontal structure. Thus, the
ABL becomes thicker on the Northern than on the Southern side, and
the flux and pressure changes lead to the development of a low-
pressure area, favoring deep convection over the warm water in the
North of the Gulf and in the vicinity of the coast. The preservation and
stability of this phenomenon over several weeks is supported by an
overturning atmospheric circulation in the troposphere, from North to
South. Thus, convective precipitation is concentrated on the Guinean
coast of Africa in spring, before shifting over the continent as far as
Sahel [LED 12].
3.3.3. The interactions close to strong oceanic fronts
At 25°N, ocean and atmosphere contribute around the same
proportion of heat transported toward the Poles. Seventy-percent of
the oceanic contribution to this transport is lost between 25°N and
45°N, mainly in the regions of western boundary currents and during
the season from December to March.
These regions are the location of great contrasts in ocean
temperature, often with more than 10°C variation over 100 km across
the ocean fronts that, on their side nearer the coasts, border the large
seams of currents rising from the tropics that are the Gulf Stream and
its branches and the Kuroshio/Oyashio, as well as the numerous ocean
vortexs that detach from it. Strong fronts and strong ocean-
atmosphere interactions are also found in the Southern Hemisphere, in
certain sectors of the circumpolar current when it meets the Western
boundary currents (such as the retroflection of the current of the
Agulhas).
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