Journal of Tropical Oceanography >
A preliminary study on the asymmetry of ENSO and its mechanism
Received date: 2009-12-09
Revised date: 2010-05-19
Online published: 2011-09-08
The Simple Ocean Data Assimilation (SODA) product is used to make composite analysis about El Niño and La
Niña events discerned by the sea surface temperature anomaly (SSTA) in the Nino3.4 region. We analyze the asymmetry of the
El Niño-Southern Oscillation (ENSO) events and its mechanism. The difference between the distributions of baroclinic energy
conversion rate and thermocline depth anomaly of composite El Niño and La Niña events is analyzed to find their influence on
the asymmetry of ENSO. Due to the fact that ENSO-related anomalous signals travel mainly in the form of Rossby waves in
the North and South Pacific where the Rossby waves can get energy to grow by unstable mechanism, the larger the baroclinic
energy conversion rate is, the more energy the ENSO-related Rossby waves can obtain to grow. Many researches have shown
that, there is a large domain with significant unstable energy and deeper thermocline in the North Pacific in El Niño events.
Larger baroclinic instable energy helps to enlarge the amplitude of Rossby wave and deeper thermocline helps to speed up
Rossby waves. This explains why the amplitude of SSTA during El Niño events is usually larger than that in La Niña events
and why the process that El Niño transfers into La Niña takes shorter time than the one that La Niño transfers into El Niño.
Baroclinic instable energy forces the Rossby wave to absorb energy to grow, which make it easy for the warm signal propa-
gating to the east and the El Niño transfers into La Niño quickly. So the asymmetry of ENSO can be explained.
Key words： ENSO cycle; asymmetry; the North Pacific; baroclinic instability
YU Yi,MENG Xiang-feng,ZHANG Lei,ZHAO Jie-chen . A preliminary study on the asymmetry of ENSO and its mechanism[J]. Journal of Tropical Oceanography, 2011 , 30(4) : 31 -37 . DOI: 10.11978/j.issn.1009-5470.2011.04.031
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