7.6 EI Nino and Southern Oscillation
229
atmosphere interactions, some of which are not well understood. However, it
is recognized that the sea surface temperature gradients - the cold water off
Peru and the warm water in the western tropical Pacific - are necessary for the
atmospheric pressure gradients that drive the Walker Circulation.
As the processes in the Pacific Ocean and atmosphere and resulting interactions are quite complicated, there are suggestions to monitor the changes in
sea surface temperatures in a specific areas, or the surface winds, or directly
focus on the Southern Oscillation as the leading indicators of an EI Nino event.
In particular, four such regions in the equatorial Pacific have been identified
(Glantz, 1996):
• Region 1 - coastal upwelling area off the coast of Peru and Ecuador.
This area is particularly sensitive to variations in air-sea interactions in
the central and eastern equatorial Pacific.
• Region 2 - the Galapagos Islands area is sensitive to seasonal, as well as
to EI Nino induced changes in the marine environment. These islands
are normally dry for half of the year (from June to December) and wet
from January to May. However, during EI Nino heavy rains fall over the
Galapagos. For example, during the 1982-83 event, the rainfall reached
3224 mm for the year, while the yearly average is about 200 mm. This
causes flora and fauna changes on the islands.
• Region 3 - central equatorial Pacific where there is a large EI Nino signal
in terms of changes in surface winds and warming of sea surface water.
• Region 4 - western equatorial Pacific with its warm pool. During an
EI Nino event there is a change in sea surface temperature, with warm
waters tending to move toward the Central Pacific.
A particularly comprehensive observing system has been developed as a result
of the Tropical Ocean-Global Atmosphere (TOGA) experiment in 1985-1994
(McPhaden et al., 1998). TOGA initiated and supported efforts to provide realtime measurements of the key oceanographic variables such as surface winds,
sea surface temperature, subsurface temperature, sea level and ocean current
velocity. More details on the TOGA program are given in Sect. 7.6.4 and in a
set of review articles edited by Anderson et al. (1998).
7.6.3 El Nino of 1982-1983
Having defined an EI Nino event, and identified its major oceanic and atmospheric characteristics, the historical records show that similar events were
observed in the past, in 1957-1958, 1965, 1969, 1972, 1976, and 1982-1983. In
the last decade, two or more EI Nino events took place: in 1986-1987, 19911995 and 1996-1997. However, no major objective accounting of the physical,
social and economic impacts and consequences of these events has yet been
undertaken.
The EI Nino of 1982-1983 was exceptional because of the very large amplitude
it attained and because of the unusual way in which it evolved. None of the
229
atmosphere interactions, some of which are not well understood. However, it
is recognized that the sea surface temperature gradients - the cold water off
Peru and the warm water in the western tropical Pacific - are necessary for the
atmospheric pressure gradients that drive the Walker Circulation.
As the processes in the Pacific Ocean and atmosphere and resulting interactions are quite complicated, there are suggestions to monitor the changes in
sea surface temperatures in a specific areas, or the surface winds, or directly
focus on the Southern Oscillation as the leading indicators of an EI Nino event.
In particular, four such regions in the equatorial Pacific have been identified
(Glantz, 1996):
• Region 1 - coastal upwelling area off the coast of Peru and Ecuador.
This area is particularly sensitive to variations in air-sea interactions in
the central and eastern equatorial Pacific.
• Region 2 - the Galapagos Islands area is sensitive to seasonal, as well as
to EI Nino induced changes in the marine environment. These islands
are normally dry for half of the year (from June to December) and wet
from January to May. However, during EI Nino heavy rains fall over the
Galapagos. For example, during the 1982-83 event, the rainfall reached
3224 mm for the year, while the yearly average is about 200 mm. This
causes flora and fauna changes on the islands.
• Region 3 - central equatorial Pacific where there is a large EI Nino signal
in terms of changes in surface winds and warming of sea surface water.
• Region 4 - western equatorial Pacific with its warm pool. During an
EI Nino event there is a change in sea surface temperature, with warm
waters tending to move toward the Central Pacific.
A particularly comprehensive observing system has been developed as a result
of the Tropical Ocean-Global Atmosphere (TOGA) experiment in 1985-1994
(McPhaden et al., 1998). TOGA initiated and supported efforts to provide realtime measurements of the key oceanographic variables such as surface winds,
sea surface temperature, subsurface temperature, sea level and ocean current
velocity. More details on the TOGA program are given in Sect. 7.6.4 and in a
set of review articles edited by Anderson et al. (1998).
7.6.3 El Nino of 1982-1983
Having defined an EI Nino event, and identified its major oceanic and atmospheric characteristics, the historical records show that similar events were
observed in the past, in 1957-1958, 1965, 1969, 1972, 1976, and 1982-1983. In
the last decade, two or more EI Nino events took place: in 1986-1987, 19911995 and 1996-1997. However, no major objective accounting of the physical,
social and economic impacts and consequences of these events has yet been
undertaken.
The EI Nino of 1982-1983 was exceptional because of the very large amplitude
it attained and because of the unusual way in which it evolved. None of the