Geoscience Reference
In-Depth Information
Later, we will focus on the interactions in the currents of the
Northern Hemisphere, where three important campaigns have taken
place in the course of the last years (Kuroshio Extension Study
System (KESS), CLImate VARiability programme (CLIVAR) and
Mode Water Dynamic Experiment (CLIMODE)). In the case of the
Gulf Stream, there is also the contribution of the deep returning
circulation from subpolar regions, and of nonlinear variability of these
very intense western boundary currents. The displacement of the
fronts causes major anomalies (at a fixed point) in temperature. In the
first place and when the climate scales are integrated, the air-sea
fluxes of heat associated lead to a negative local retroaction on the
anomalies in temperature, a retroaction that tends elsewhere to damp
the warm vortices and to isolate cold structures from the surface, such
as the famous “rings” of the Gulf Stream. These fluxes, as well as the
deeper thermoclines in some of these structures, contribute to deep
OMLs in warm sectors.
During the seasonal restratification in spring, the waters of the
deep mixed layers, which are called “mode” waters, are isolated from
the surface and flow afterward into the subsurface in the recirculation
of currents West of the subtropical gyres. Thus, the estimations made
during CLIMODE indicate that approximately 50% of the mode water
formed is in the vicinity of the oceanic fronts of the Gulf Stream and
warm seams of currents.
The strong fluxes of sensible and latent heat (and therefore
humidity) have a very important effect on the atmosphere. Locally,
they increase the baroclinicity, can cause particularly deep convection,
and favor, by baroclinic instablility, the development of atmospheric
depressions. This fairly local effect has been well documented in
numerous winter situations since the pioneering work carried out
during the Fronts and Atlantic Storm Track Experiment (FASTEX)
[GIO 01]. For these reasons, and also because of
the retroactions caused by the atmospheric ocean vortexes on the
average circulation, it is thought that the storm tracks tend to be
located close to the eastern coasts of the North-American and Asiatic
