Geoscience Reference
In-Depth Information
good correspondence between global air temperature, the PDO, the Atmospheric Circula-
tion Index and the Regime Indicator series over a century (Chavez
et al.
,
2003
).
The tropical ocean plays a major role in the natural climate variability at interannual
scales. In the tropical Pacific Ocean the El Niño-Southern Oscillation, ENSO phenomen-
on, represents the most pronounced climate variability process on Earth, with strong effects
on the weather in many parts during El Niño occurrences. The reversed, cold period, La
Niña, also has strong effects, with opposite characteristics. Initial model results had sug-
gested that with rising SST the frequency of the El Niño would increase, with associated
extreme weather events. It has been observed that high growth rates of atmospheric car-
bon dioxide generally correspond with El Niño, meaning relatively low ocean uptake or
high degassing. But some episodes do not reflect this, as during the 1992-1993 El Niño,
resulting from the volcanic eruption of Mt Pinatubo in mid 1991. A similar but not as pro-
nounced phenomenon has recently been clarified in the form of the Indian Ocean Dipole.
This is observed as SST anomalies. These are coupled with zonal winds, changing in dir-
ection from westerlies to easterlies when the SST is cool in the east and warm in the west.
This can have a very strong influence on the south-west monsoon, and on related drought
or precipitation conditions in parts of Africa and south-east Asia and Australia (Yamagata
