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Ocean-atmosphere interactions and multi-scale climate variability in a changing climate
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Asymmetric Tropical Ocean Responses to ENSO: In Observations and CMIP5 Models
Wednesday 9th @ 1530-1550, Concert Hall
Shan He* , Sun Yat-sen University
Jin-Yi Yu, University of California at Irvine
Song Yang, Sun Yat-sen University
Shih-Wei Fang, University of California at Irvine
Presenter Email: heshan9@mail2.sysu.edu.cn |
| Sea surface temperature anomalies (SSTA) associated with El Niño-Southern Oscillation (ENSO) events during 1958-2004 are found to be stronger in the tropical North Atlantic than in the tropical Indian Ocean. It is shown that the atmospheric bridge mechanism (ABM) is a more important contributor to this asymmetric response than the tropospheric temperature mechanism. The ENSO-forced anomalous Walker circulation extends further into the Atlantic than into the Indian Ocean, enabling the ABM to produce an asymmetric response. Therefore, the asymmetric response is a reflection of how the tropical atmospheric circulation responds to ENSO and should be regarded as a key metric of model performance on ENSO simulation. Only five out of thirty-seven CMIP5 models examined realistically simulate the observed asymmetric responses. The multi-model mean overestimates the SSTA response in the Indian Ocean and underestimates it in the Atlantic. This reversed asymmetry is found to be related to the location of ENSO-associated SSTAs in the Pacific, which produce a Walker circulation response that has a stronger impact on the Indian Ocean than on the Atlantic. It is also found that the five models that produce a realistic asymmetric response do so via error cancellation. The error caused by the incorrectly located ENSO SSTAs is compensated for that by an incorrect Walker circulation response stemming from an excessively cold Pacific cold tongue. Therefore, alleviating these model errors in the location of ENSO SSTAs and the strength of the cold tongue SSTs is critical for a realistic simulation of the ENSO impacts on the two neighboring tropical oceans. |
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