224
7 Ocean Currents
effective technique was used to overcome this problem. The simulated ocean
surface temperature pattern is reasonably similar to the observed pattern and
the major ocean current gyre systems are reproduced in the ocean model.
Since the International Geophysical Year of 1957-1958, numerical simulations
of the behaviour of the atmosphere-ocean system have been supplemented by
international projects aimed at understanding the role of the oceans in climate change. The number of various projects is quite numerous; we note
here some of them, such as GATE (Atlantic Tropical Experiment, 1974), NORPAX (North Pacific Experiment, 1972-82), MODE (Mid-Ocean Dynamics Experiment, 1978), POLYMODE, CUEA (Coastal Upwelling Ecosystems Analysis Program, 1972-77), ERFEN (Estudio Regional del Fenomeno de EI Nino,
1974), and TOGA (Tropical Ocean-Global Atmosphere Program, 1985-94).
The reader should consult Perry and Walker (1977), Pond and Pickard (1983),
Glantz (1996), and Anderson et ai. (1998) for in-depth discussions of these
programs. The last three programs have been designed to provide a better
understanding of the EI Nino phenomenon which has attracted an increasing
amount of attention from scientists and the world community as a whole. We
will discuss EI Nino in the next section.
7.6 EI Nino and Southern Oscillation
7.6.1 Introduction
Initially the term El Nino, which in Spanish means child, referring to Jesus as
an infant, described a local current which annually appears off the coast of Peru,
beginning around Christmas time and temporarily replaces the usually cold,
nutrient rich water which wells up to the ocean's euphotic zone. At present,
the term EI Nino describes not only the local current off the coast of Peru, but
the infrequent anomalous warming of sea surface waters off the coast of Peru
and in the central equatorial Pacific Ocean and the associated changes in the
circulations of the Pacific and the global atmosphere when the Trade Winds
diminish. The term EI Nino is also associated with ecological and economic
disasters, correlated with devastating droughts over the western tropical Pacific,
terrential floods over the Eastern Pacific, and unusual weather patterns over
various parts of the world. The term La Nina (child girl) is the opposite of
El Nino and is used to describe a time when sea surface temperatures in the
Central and Eastern Pacific are unusually low and when the Trade Winds are
very intense (Philander, 1990; Glantz, 1996).
Actually the EI Nino event is linked with the Southern Oscillation and the
acronym ENSO is used to describe the much broader basin-wide events in the
equatorial Pacific. The term Southern Oscillation was first used by Walker in
1924 to describe the inter-annual pressure fluctuations over the Indian Ocean
and eastern tropical Pacific. Walker, who was Director General of the Observatories in India, observed that when atmospheric pressure is high in the
Pacific Ocean it tends to be low in the Indian Ocean from Africa to Australia.
7 Ocean Currents
effective technique was used to overcome this problem. The simulated ocean
surface temperature pattern is reasonably similar to the observed pattern and
the major ocean current gyre systems are reproduced in the ocean model.
Since the International Geophysical Year of 1957-1958, numerical simulations
of the behaviour of the atmosphere-ocean system have been supplemented by
international projects aimed at understanding the role of the oceans in climate change. The number of various projects is quite numerous; we note
here some of them, such as GATE (Atlantic Tropical Experiment, 1974), NORPAX (North Pacific Experiment, 1972-82), MODE (Mid-Ocean Dynamics Experiment, 1978), POLYMODE, CUEA (Coastal Upwelling Ecosystems Analysis Program, 1972-77), ERFEN (Estudio Regional del Fenomeno de EI Nino,
1974), and TOGA (Tropical Ocean-Global Atmosphere Program, 1985-94).
The reader should consult Perry and Walker (1977), Pond and Pickard (1983),
Glantz (1996), and Anderson et ai. (1998) for in-depth discussions of these
programs. The last three programs have been designed to provide a better
understanding of the EI Nino phenomenon which has attracted an increasing
amount of attention from scientists and the world community as a whole. We
will discuss EI Nino in the next section.
7.6 EI Nino and Southern Oscillation
7.6.1 Introduction
Initially the term El Nino, which in Spanish means child, referring to Jesus as
an infant, described a local current which annually appears off the coast of Peru,
beginning around Christmas time and temporarily replaces the usually cold,
nutrient rich water which wells up to the ocean's euphotic zone. At present,
the term EI Nino describes not only the local current off the coast of Peru, but
the infrequent anomalous warming of sea surface waters off the coast of Peru
and in the central equatorial Pacific Ocean and the associated changes in the
circulations of the Pacific and the global atmosphere when the Trade Winds
diminish. The term EI Nino is also associated with ecological and economic
disasters, correlated with devastating droughts over the western tropical Pacific,
terrential floods over the Eastern Pacific, and unusual weather patterns over
various parts of the world. The term La Nina (child girl) is the opposite of
El Nino and is used to describe a time when sea surface temperatures in the
Central and Eastern Pacific are unusually low and when the Trade Winds are
very intense (Philander, 1990; Glantz, 1996).
Actually the EI Nino event is linked with the Southern Oscillation and the
acronym ENSO is used to describe the much broader basin-wide events in the
equatorial Pacific. The term Southern Oscillation was first used by Walker in
1924 to describe the inter-annual pressure fluctuations over the Indian Ocean
and eastern tropical Pacific. Walker, who was Director General of the Observatories in India, observed that when atmospheric pressure is high in the
Pacific Ocean it tends to be low in the Indian Ocean from Africa to Australia.