230
7 Ocean Currents
usual precursors of an EI Nino event were present. The easterlies in the west had
not been especially strong and there was no tendency for SST to be unusually
low in the east and high in the west, and the thermocline was not unusually
deep there. Anomalously warm sea surface temperature first appeared in the
Central Pacific, instead of off the coast of Peru. Subsequently, this warm sea
surface temperature migrated gradually eastward during most of 1982. These
conditions reached the coast of South America in late 1982, and westerly winds
prevailed over much of the western and central equatorial Pacific. Anomalies
reached their peak amplitude in February 1983, and started to attenuate when
sea level pressure at Darwin began to decline, and the westerly surface winds
in the western tropical Pacific disappeared.
In Fig. 7.12a, the sea surface temperature (SST) anomaly pattern for the
1982-1983 EI Nino is shown. This pattern is different from the canonical
pattern based on previous EI Nino events, observed between 1950 and 1975
(Rasmusson and Wallace, 1984), in terms of the time of EI Nino onset and
the distribution of temperature anomalies. Figure 7.12b shows the corresponding sea-level pressure anomalies at Tahiti and Darwin during the 1982-1983
episode. The difference between two pressures, indicated by shading, represents the Southern Oscillation Index (SOl) - see Eq. (7.30). Because of its
unusual pattern, different from the canonical event, EI Nino 1982-1983 was
unexpected by most scientists.
Most of the weather anomalies occurring in 1982 and 1983 around the world
were linked with the occurrence of EI Nino. Compilation of the damage hypothetically associated with the 1982-1983 EI Nino has been published by the National Oceanic and Atmospheric Administration of the United States (Glantz,
1996). They include severe droughts in Indonesia, Australia, and north central
states of the United States, devastating coastal storms and mud slides along the
southern California coast, sharp decline of salmon harvests along the northwest
coast of the Pacific, severe infrastructure damage in Peru and Ecuador as the
result of heavy flooding, and a major drought in the West African Sahel.
Similar connections have also been observed in the past for other EI Nino
events. A special word, 'teleconnections', is used to describe the linkages between these climate anomalies some distance from each other. It was apparently
first used in 1935 by a Swedish meteorologist, Anders Angstrom, in his article
on the North Atlantic region. Later, Flohn and Fleer (1975) published a chart
illustrating alleged teleconnections, suggesting regional climate connections,
sometimes at very great distances. In particular, they showed the relations between EI Nino and drought in North-East Brazil, water level changes (decline)
of Lake Chad, runoff of the Nile River, and drought in India.
Although in Australia droughts have occurred in the past, and their link
with variations in sea level pressure across the Pacific have been known for
many years, the impact of 1982-1983 EI Nino was devastating: bush fires, dust
storms, agricultural and livestock losses. Droughts turned apocalyptic when
bush fires erupted across southeastern Australia in February 1983. Fireballs
7 Ocean Currents
usual precursors of an EI Nino event were present. The easterlies in the west had
not been especially strong and there was no tendency for SST to be unusually
low in the east and high in the west, and the thermocline was not unusually
deep there. Anomalously warm sea surface temperature first appeared in the
Central Pacific, instead of off the coast of Peru. Subsequently, this warm sea
surface temperature migrated gradually eastward during most of 1982. These
conditions reached the coast of South America in late 1982, and westerly winds
prevailed over much of the western and central equatorial Pacific. Anomalies
reached their peak amplitude in February 1983, and started to attenuate when
sea level pressure at Darwin began to decline, and the westerly surface winds
in the western tropical Pacific disappeared.
In Fig. 7.12a, the sea surface temperature (SST) anomaly pattern for the
1982-1983 EI Nino is shown. This pattern is different from the canonical
pattern based on previous EI Nino events, observed between 1950 and 1975
(Rasmusson and Wallace, 1984), in terms of the time of EI Nino onset and
the distribution of temperature anomalies. Figure 7.12b shows the corresponding sea-level pressure anomalies at Tahiti and Darwin during the 1982-1983
episode. The difference between two pressures, indicated by shading, represents the Southern Oscillation Index (SOl) - see Eq. (7.30). Because of its
unusual pattern, different from the canonical event, EI Nino 1982-1983 was
unexpected by most scientists.
Most of the weather anomalies occurring in 1982 and 1983 around the world
were linked with the occurrence of EI Nino. Compilation of the damage hypothetically associated with the 1982-1983 EI Nino has been published by the National Oceanic and Atmospheric Administration of the United States (Glantz,
1996). They include severe droughts in Indonesia, Australia, and north central
states of the United States, devastating coastal storms and mud slides along the
southern California coast, sharp decline of salmon harvests along the northwest
coast of the Pacific, severe infrastructure damage in Peru and Ecuador as the
result of heavy flooding, and a major drought in the West African Sahel.
Similar connections have also been observed in the past for other EI Nino
events. A special word, 'teleconnections', is used to describe the linkages between these climate anomalies some distance from each other. It was apparently
first used in 1935 by a Swedish meteorologist, Anders Angstrom, in his article
on the North Atlantic region. Later, Flohn and Fleer (1975) published a chart
illustrating alleged teleconnections, suggesting regional climate connections,
sometimes at very great distances. In particular, they showed the relations between EI Nino and drought in North-East Brazil, water level changes (decline)
of Lake Chad, runoff of the Nile River, and drought in India.
Although in Australia droughts have occurred in the past, and their link
with variations in sea level pressure across the Pacific have been known for
many years, the impact of 1982-1983 EI Nino was devastating: bush fires, dust
storms, agricultural and livestock losses. Droughts turned apocalyptic when
bush fires erupted across southeastern Australia in February 1983. Fireballs