Geoscience Reference
In-Depth Information
Figure 7.29
The general ocean current circulation in January. This holds broadly for the year, except that in the northern summer
some of the circulation in the northern Indian Ocean is reversed by the monsoonal airflow. The shaded areas show mean annual
anomalies of ocean surface temperatures (°C) of greater than +5°C and less than -3°C.
Sources
: US Naval Oceanographic Office and Niiler (1992). Courtesy of US Naval Oceanographic Office.
approximately 100 km wide and reach surface velocities
greater than 2 m s
-1
. This contrasts with the slower,
wider and more diffuse eastern boundary currents
such as the Canary and California (approximately 1000
km wide with surface velocities generally less than
0.25 m s
-1
). The northward-flowing Gulf Stream causes
a heat flux of 1.2
intensifies the flow. Within the west wind drift, the
action of the Coriolis force produces a convergence
zone at about 50°S marked by westerly submarine jet
streams reaching velocities of 0.5 to 1 m s
-1
. South of the
west wind drift, the Antarctic divergence with rising
water is formed between it and the east wind drift closer
to Antarctica. In the northern hemisphere, a great deal
of the eastward-moving current in the Atlantic swings
northward, leading to anomalously very high sea
temperatures, and is compensated for by a southward
flow of cold Arctic water at depth. However, more than
half of the water mass comprising the North Atlantic
current, and almost all that of the North Pacific current,
swings south around the east sides of the subtropical
high-pressure cells, forming the Canary and California
currents. Their southern-hemisphere equivalents are the
10
15
W, 75 per cent of which is
lost to the atmosphere and 25 per cent in heating the
Greenland-Norwegian seas area. On the poleward
sides of the subtropical high-pressure cells westerly
currents dominate, and where they are unimpeded by
landmasses in the southern hemisphere they form the
broad and swift west wind drift. This strong current,
driven by unimpeded winds, occurs within the zone 50
to 65°S and is associated with a southward-sloping
ocean surface generating a geostrophic force, which
