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| Ocean-Atmosphere Interaction in the Lifecycle of ENSO:The Coupled Wave Oscillator |
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Citation： |
Jialin LIN.Ocean-Atmosphere Interaction in the Lifecycle of ENSO:The Coupled Wave Oscillator[J].Chinese Annals of Mathematics B,2009,30(6):715~728 |
| Page view： 1915
Net amount： 1394 |
Authors： |
Jialin LIN; |
Foundation： |
the National Science Foundation (No. ATM-0745872) and NASA Modeling, Analysis
and Prediction Program. |
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| Abstract： |
To explain the oscillatory nature of El Nino/Southern Oscillation (ENSO),
many ENSO theories emphasize the free oceanic equatorial waves propagating/reflecting
within the Pacific Ocean, or the discharge/recharge of Pacific-basin-averaged ocean heat
content. ENSO signals in the Indian and Atlantic oceans are often considered as remote
response to the Pacific SST anomaly through atmospheric teleconnections. This study
investigates the ENSO life cycle near the equator using long-term observational datasets.
Space-time spectral analysis is used to identify and isolate the dominant interannual oceanic
and atmospheric wave modes associated with ENSO. Nino3 SST anomaly is utilized as the
ENSO index, and lag-correlation/regression are used to construct the composite ENSO
life cycle. The propagation, structure and feedback mechanisms of the dominant wave
modes are studied in detail. The results show that the dominant oceanic equatorial wave
modes associated with ENSO are not free waves, but are two ocean-atmosphere coupled
waves including a coupled Kelvin wave and a coupled equatorial Rossby (ER) wave. These
waves are not confined only to the Pacific Ocean, but are of planetary scale with zonal
wavenumbers 1-2, and propagate all the way around the equator in more than three years,
leading to the longer than 3-year period of ENSO. When passing the continents, they
become uncoupled atmospheric waves. The coupled Kelvin wave has larger variance than
the coupled ER wave, making the total signals dominated by eastward propagation. Surface
zonal wind stress (x) acts to slow down the waves. The two coupled waves interact with
each other through boundary reflection and superposition, and they also interact with an
off-equatorial Rossby wave in north Pacific along 15N through boundary reflection and
wind stress forcing. The precipitation anomalies of the two coupled waves meet in the
eastern Pacific shortly after the SST maximum of ENSO and excite a dry atmospheric
Kelvin wave which quickly circles the whole equator and leads to a zonally symmetric
signal of troposphere temperature. ENSO signals in the Indian and Atlantic oceans are
associated with the two coupled waves as well as the fast atmospheric Kelvin wave. The
discharge/recharge of Pacific-basin-averaged ocean heat content is also contributed by the
two coupled waves. The above results suggest the presence of an alternative coupled wave
oscillator mechanism for the oscillatory nature of ENSO. |
Keywords： |
ENSO, Ocean-atmosphere interaction, Equatorial waves |
Classification： |
17B40, 17B50 |
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