Geoscience Reference
In-Depth Information
High pressure
isobar
Low pressure
Coriolis force
Force of pressure
gradient
Geostrophic speed
Northern hemisphere
Figure 2.7.
Diagram representing the equilibrium between the Coriolis force and the
force of horizontal pressure gradient, which creates a geostrophic current, parallel to
the isobars. A case of anticyclonic circulation in the northern hemisphere
2.3.2.
An ocean moved by the wind
One of the most efficient motors for moving the ocean is the wind.
In fact, when comparing a map of oceanic currents and a map of
winds, there are a striking number of similarities between the two
fields. Thus, the winds on the Atlantic Ocean are characterized by
winds from the west at mid-latitudes, in the wake of which we find the
Azores Current oriented east-south-east; further south, we find the
trade winds, in the wake of which we see the North Equatorial
Current, oriented toward the west. Oceanic circulation presents a large
anticyclonic circulation at subtropical latitudes, whereas further north,
in the subpolar region, we find a cyclonic cell. This situation, found in
the North Atlantic, is also found in the North Pacific. In the southern
hemisphere, we also note the large anticyclonic cells at subtropical
latitudes, of which the southern branches combine to rejoin the
Antarctic Circumpolar Current that links the three oceanic basins.
2.3.3.
Ekman, spiral, transport, pumping, upwelling and downwelling
Very early on, oceanographers sought to explain oceanic
circulation by surface winds and to understand the mechanisms by
