260
D. H. CUSHINU
or “ roller bearing ” as Hart and Currie (1960) called it, is also an agent
of offshore transport. The secondary upwelling offshore of this boundary
is generated by the vorticity of the wind stress. The divergences in the
equatorial currents and elsewhere are created by the same agency
(Hidaka, 1958). There tend to be divergences along the poleward
boundary of the subtropical anticyclones at the western ends of the
equatorial currents and along the equatorial boundary of the southern
anticyclones ; similarly there are convergences along the eastern
equatorial currents, particularly in summer along the equatorial boundary of the northern anticyclone (Hidaka and Ogawa, 1958). But there
are also upwelling areas where the equatorial currents are formed ; the
Costa Rica Dome is the most well known, at the root of the North
Equatorial Current in the North Pacific, but there are analogous
phenomena in the East Atlantic and East Indian Oceans.
Recently, Smith (1969) has described the development of the theory
of upwelling. Sverdrup (1938) and Sverdrup and Fleming (1941)
examined upwelling in terms of Ekman’s theory of transport ; from the
change in the distribution of properties, during a short time, it was
shown that the surface water was carried away from the coast of
California to be replaced by water from below. Hidaka (1954) and
Yoshida (1955, 1967) developed steady state, transient state and quasi
steady state models. From Yoshida’s theories, it was suggested that
the coastal upwelling zone was about 50 km wide in middle latitudes,
which was observed by Smith et al. (1966) off Oregon, U.S.A. His
theory further suggests that the width of upwelling decreases with
latitude, which explains the extensive areas of upwelling and of the
production of living material in all three eastern tropical oceans;
further, the countercurrent flowing polewards in a major upwelling
system is homologous with the equatorial countercurrent. An interesting consequence of Yoshida’s theory is that coastal processes respond
more quickly t o winds which vary in time than the steady ones. Arthur
(1965) has examined the role of vorticity in upwelling and reaches much
the same point as Yoshida: in addition, he showed that upwelling is
more intense on the equatorial sides of capes. One of Smith’s important
conclusions is that there is quantitative agreement between theory and
observation ; his paper should be consulted for a good introduction to
the physical theory of upwelling.
Figure 2 is a diagram of the upwelling systems in an ideal ocean,
based on observations in the Pacific, showing the coastal upwellings in
the eastern boundary currents, the divergences and convergences in the
equatorial current system and the eastern dome. Also shown are the
divergences on the-poleward boundaries and offshore of the coastal
D. H. CUSHINU
or “ roller bearing ” as Hart and Currie (1960) called it, is also an agent
of offshore transport. The secondary upwelling offshore of this boundary
is generated by the vorticity of the wind stress. The divergences in the
equatorial currents and elsewhere are created by the same agency
(Hidaka, 1958). There tend to be divergences along the poleward
boundary of the subtropical anticyclones at the western ends of the
equatorial currents and along the equatorial boundary of the southern
anticyclones ; similarly there are convergences along the eastern
equatorial currents, particularly in summer along the equatorial boundary of the northern anticyclone (Hidaka and Ogawa, 1958). But there
are also upwelling areas where the equatorial currents are formed ; the
Costa Rica Dome is the most well known, at the root of the North
Equatorial Current in the North Pacific, but there are analogous
phenomena in the East Atlantic and East Indian Oceans.
Recently, Smith (1969) has described the development of the theory
of upwelling. Sverdrup (1938) and Sverdrup and Fleming (1941)
examined upwelling in terms of Ekman’s theory of transport ; from the
change in the distribution of properties, during a short time, it was
shown that the surface water was carried away from the coast of
California to be replaced by water from below. Hidaka (1954) and
Yoshida (1955, 1967) developed steady state, transient state and quasi
steady state models. From Yoshida’s theories, it was suggested that
the coastal upwelling zone was about 50 km wide in middle latitudes,
which was observed by Smith et al. (1966) off Oregon, U.S.A. His
theory further suggests that the width of upwelling decreases with
latitude, which explains the extensive areas of upwelling and of the
production of living material in all three eastern tropical oceans;
further, the countercurrent flowing polewards in a major upwelling
system is homologous with the equatorial countercurrent. An interesting consequence of Yoshida’s theory is that coastal processes respond
more quickly t o winds which vary in time than the steady ones. Arthur
(1965) has examined the role of vorticity in upwelling and reaches much
the same point as Yoshida: in addition, he showed that upwelling is
more intense on the equatorial sides of capes. One of Smith’s important
conclusions is that there is quantitative agreement between theory and
observation ; his paper should be consulted for a good introduction to
the physical theory of upwelling.
Figure 2 is a diagram of the upwelling systems in an ideal ocean,
based on observations in the Pacific, showing the coastal upwellings in
the eastern boundary currents, the divergences and convergences in the
equatorial current system and the eastern dome. Also shown are the
divergences on the-poleward boundaries and offshore of the coastal