31
Descriptive Oceanography
this current flows north along the western coast of Australia and is augmented by a coastal
current that flows toward the west along the south of Australia. Part of this current flows
west and becomes the South Equatorial Current. The southward current along the south
coast of Africa is called the Agulhas Current and completes the gyre. Part of this current
flows west into the Atlantic to form the Benguela Current.
The equatorial current systems in the Indian Ocean differ from the Atlantic and Pacific
because of seasonal changes in the winds. From November to March, the winds and currents are similar to the other oceans except that they are further south. The South Equatorial
Current (20° S to 8° S) flows west throughout the year. The Equatorial Countercurrent
(8° S to 2° S) flows toward the west. The North Equatorial Current (2° S to 10° N) flows to
the east and is maintained by the northeastern trade winds.
In April, the winds change, and from May to September, the northeastern trade winds
are replaced by winds from the southwest called the southwestern monsoon winds.
These are really a continuation across the equator of the southeastern trade winds. The
North Equatorial Current is replaced by a Southwest Monsoon Current. The Equatorial
Countercurrent also disappears or becomes indistinguishable from the Monsoon Current.
During the monsoon period, the South Equatorial Current turns north, supplying the
Somali Current, which flows north along the eastern coast of Africa.
The temperature and salinity of waters near the equator in the Indian Ocean are similar to
those in the Atlantic and Pacific. Waters in the Bay of Bengal have lower salinities (31 to 34)
because of river runoff, particularly during the monsoon season. Waters in the Arabian Sea
have a high salinity (36.5) because of evaporation. The T- S diagrams of the major water masses
20
0
20
20
0
Africa
Monsoon C.
S o m a l i C .
A
g u l h a s C .
Asia
20
0
20
Aust.
S. Eq. C.
20
40
60
20
Asia
N. Eq. C.
Eq. C. C.
S. Eq. C.
W. Aust. C.
Aust.
Africa
Circumpolar C.
0
20
40
60
Figure 1.38
The surface currents of the Indian Ocean. The top figure is for conditions between November and March, and
the bottom figure is for conditions between May and September.
Descriptive Oceanography
this current flows north along the western coast of Australia and is augmented by a coastal
current that flows toward the west along the south of Australia. Part of this current flows
west and becomes the South Equatorial Current. The southward current along the south
coast of Africa is called the Agulhas Current and completes the gyre. Part of this current
flows west into the Atlantic to form the Benguela Current.
The equatorial current systems in the Indian Ocean differ from the Atlantic and Pacific
because of seasonal changes in the winds. From November to March, the winds and currents are similar to the other oceans except that they are further south. The South Equatorial
Current (20° S to 8° S) flows west throughout the year. The Equatorial Countercurrent
(8° S to 2° S) flows toward the west. The North Equatorial Current (2° S to 10° N) flows to
the east and is maintained by the northeastern trade winds.
In April, the winds change, and from May to September, the northeastern trade winds
are replaced by winds from the southwest called the southwestern monsoon winds.
These are really a continuation across the equator of the southeastern trade winds. The
North Equatorial Current is replaced by a Southwest Monsoon Current. The Equatorial
Countercurrent also disappears or becomes indistinguishable from the Monsoon Current.
During the monsoon period, the South Equatorial Current turns north, supplying the
Somali Current, which flows north along the eastern coast of Africa.
The temperature and salinity of waters near the equator in the Indian Ocean are similar to
those in the Atlantic and Pacific. Waters in the Bay of Bengal have lower salinities (31 to 34)
because of river runoff, particularly during the monsoon season. Waters in the Arabian Sea
have a high salinity (36.5) because of evaporation. The T- S diagrams of the major water masses
20
0
20
20
0
Africa
Monsoon C.
S o m a l i C .
A
g u l h a s C .
Asia
20
0
20
Aust.
S. Eq. C.
20
40
60
20
Asia
N. Eq. C.
Eq. C. C.
S. Eq. C.
W. Aust. C.
Aust.
Africa
Circumpolar C.
0
20
40
60
Figure 1.38
The surface currents of the Indian Ocean. The top figure is for conditions between November and March, and
the bottom figure is for conditions between May and September.