288
D. 11. CUSHINO
summer-timc and returns in the late autumn. At the same time,
Fig. 11 shows the shift of upwelling away from thc equator from spring
to summer in both the two major West African upwellings. Between
Cap des Palmcs and Cotonou, i.e. off the Ivory Coast and Ghana, there
is another upwelling, which appears to be linked temporarily to the
Benguela upwelling. But it is likely that it is associated with the WSW
winds in summer in the Guinea Current, which is an extension of the
Equatorial Countercurrent ; during the same season, the Guinea Dome
is established south-west of Dakar as the countercurrent turns into the
North Equatorial Current. The Equatorial Countercurrent is strongest
at this season and the Guinea Dome most intense. Thus the upwelling
off Ghana and the Ivory Coast is directly a result of the westerly winds
and is totally disconnected from that in the same months in the Benguela
Current. In any case, the upwelling in the region of Pointe Noire, in
Congo-Brazzaville, is in an extension of the Benguela Current, for much
of the Benguela swings north-westerly at a higher latitude.
C. The Indian Ocean
From April to September, the Indian Ocean is dominated by the
south-west monsoon and from September to April the north-east monsoon blows. In Indonesia the south-east monsoon, which is really part
of the trade wind system, is the dominant wind during the southern
winter, at the same time as the south-west monsoon north of the
equator. During the southern summer, there are westerly winds. Because there is such a sharp switch from one wind system to the others,
the upwelling areas appear to have only slight seasonal shifts, although
they are noticeable (see Table 111). There are other consequences; for
example the equatorial undercurrent flows most strongly at the end of
the north-east monsoon but is absent during the south-west monsoon
(Knauss, 1963 ; Knauss and Taft, 1964). South of the equator, there is
an eastern boundary current on the coasts of western Australia ;
Wyrtki (1964) and Rochford (1962) have found some evidence of upwelling off north-west Australia from surface temperature observations.
There are a number of upwellings associated with the south-west
monsoon. They are in the Somali Current, off south-west Arabia, and
off the Malabar coast of India. That in the Somali Current is a geostrophic upwelling caused by the tilt in the thermal structure as the
current swings eastwards away from the Horn of Africa (Stommel and
Wooster, 1965 ; Foxton, 1965 ; Warren et al., 1966 ; Swallow and Bruce,
1966). It is associated with the south-west monsoon only in the sense
that the current flows during the period of the monsoon. Being a
western boundary current it is generated by wind stress over the whole
D. 11. CUSHINO
summer-timc and returns in the late autumn. At the same time,
Fig. 11 shows the shift of upwelling away from thc equator from spring
to summer in both the two major West African upwellings. Between
Cap des Palmcs and Cotonou, i.e. off the Ivory Coast and Ghana, there
is another upwelling, which appears to be linked temporarily to the
Benguela upwelling. But it is likely that it is associated with the WSW
winds in summer in the Guinea Current, which is an extension of the
Equatorial Countercurrent ; during the same season, the Guinea Dome
is established south-west of Dakar as the countercurrent turns into the
North Equatorial Current. The Equatorial Countercurrent is strongest
at this season and the Guinea Dome most intense. Thus the upwelling
off Ghana and the Ivory Coast is directly a result of the westerly winds
and is totally disconnected from that in the same months in the Benguela
Current. In any case, the upwelling in the region of Pointe Noire, in
Congo-Brazzaville, is in an extension of the Benguela Current, for much
of the Benguela swings north-westerly at a higher latitude.
C. The Indian Ocean
From April to September, the Indian Ocean is dominated by the
south-west monsoon and from September to April the north-east monsoon blows. In Indonesia the south-east monsoon, which is really part
of the trade wind system, is the dominant wind during the southern
winter, at the same time as the south-west monsoon north of the
equator. During the southern summer, there are westerly winds. Because there is such a sharp switch from one wind system to the others,
the upwelling areas appear to have only slight seasonal shifts, although
they are noticeable (see Table 111). There are other consequences; for
example the equatorial undercurrent flows most strongly at the end of
the north-east monsoon but is absent during the south-west monsoon
(Knauss, 1963 ; Knauss and Taft, 1964). South of the equator, there is
an eastern boundary current on the coasts of western Australia ;
Wyrtki (1964) and Rochford (1962) have found some evidence of upwelling off north-west Australia from surface temperature observations.
There are a number of upwellings associated with the south-west
monsoon. They are in the Somali Current, off south-west Arabia, and
off the Malabar coast of India. That in the Somali Current is a geostrophic upwelling caused by the tilt in the thermal structure as the
current swings eastwards away from the Horn of Africa (Stommel and
Wooster, 1965 ; Foxton, 1965 ; Warren et al., 1966 ; Swallow and Bruce,
1966). It is associated with the south-west monsoon only in the sense
that the current flows during the period of the monsoon. Being a
western boundary current it is generated by wind stress over the whole