Geoscience Reference
In-Depth Information
oceanic gyres (similar to atmospheric subtropical
high pressure cells), major jet-like streams such
as sections of the Gulf Stream (see
Figure 7.29
),
large-scale areas of subsidence and uplift, the
stabilizing layer of the permanent thermocline,
boundary layer effects, frontal discontinuities
created by temperature and density contrasts, and
water mass ('mode water') regions.
Mesoscale characteristics that have atmospheric
analogues are oceanic cyclonic and anticyclonic
eddies, current meanders, cast-off ring vortices,
jet filaments, and circulations produced by
irregularities in the North Equatorial Current.
Macroscale
The most obvious feature of the surface oceanic
circulation is the control exercised over it by the
low-level planetary wind circulation, especially by
the subtropical oceanic high pressure cells and the
westerlies. The oceanic circulation also displays
seasonal reversals of flow in the monsoonal
regions of the northern Indian Ocean, off East
Africa and off northern Australia (see
Figure 7.29
).
As water moves meridionally, the conservation of
angular momentum implies changes in relative
vorticity (see pp. 153 and 181), with poleward-
moving currents acquiring anticyclonic vorticity
75°N
29
28
27
70°N
24
26
25
60°N
10
8
22
9
23
45°N
11
21
12
30°N
6
20
1
15°N
1
1
2
2
18
0°
2
3
3
17
15°S
3
19
30°S
13
7
5
16
45°S
14
15
4
4
4
60°S
70°S
45°E
90°E
135°E
180°
135°W
90°W
45°W
0°
> 5°C
< -3°C
1
2
3
4
5
6
North Equatorial Current
Equatorial Counter-current
South Equatorial Current
West Wind Drift
West Australian Current
Kuroshio Current
7
8
9
10
11
12
East Australian Current
Oyashio Current
Aleutian Current
Alaska Current
North Pacific Current
California Current
13
14
15
16
17
18
Peru Current
Falkland Current
South Atlantic Current
Agulhus Current
Benguela Current
Guinea Current
19
20
21
22
23
24
Brazil Current
Canary Current
Gulf Stream
North Atlantic Current
Labrador Current
West Greenland Current
25
26
27
28
29
Irminger Current
East Greenland Current
Norway Current
Spitsbergen Current
North Cape Current
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 US Naval Oceanographic Office.
