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- Title
Warm and Cold Episodes in Western Pacific Warm Pool and Their Linkage With ENSO Asymmetry and Diversity.
- Authors
Chen, Hui; Shi, Jian; Jin, Yishuai; Geng, Tao; Li, Chun; Zhang, Xingzhi
- Abstract
This study investigates the role of temperature anomalies over the western Pacific warm pool (WPWP) in the asymmetry and diversity of El Niño‐Southern Oscillation. Based on observations, we select 12 cold and 13 warm WPWP episodes averaged over July to October. Using composite analyses, we reveal that the occurrence probability of El Niño events is much larger following the cold episodes than that of La Niña events related to warm episodes. The main reason for the different frequencies is that the westerlies associated with cold episodes are stronger and located eastwards than the easterlies for warm episodes, exerting more effective influences on the sea surface temperature in central‐eastern equatorial Pacific through Bjerknes feedback. As for intensity, the El Niño events tend to be stronger when the cold anomalies over WPWP are stronger, evidenced by both observations and Coupled Model Intercomparison Project Phase 6 simulations. The warming rate from July to October for El Niño events following cold episodes is three times greater than that of other historical events, denoting a prominent contribution from WPWP to the quick development of El Niño. Furthermore, we highlight the implication of WPWP on El Niño diversity with a greater probability of EP‐type El Niño under a colder WPWP state and successive westerly wind bursts. As such, the cold state of WPWP can provide an effective modification for the earlier operational prediction on El Niño intensity and flavors. On the contrary, the warm WPWP state may not be useful for future La Niña alerts. Plain Language Summary: The western Pacific warm pool (WPWP) is the warmest area of the open oceans and global heat reservoir with high sea surface temperature (SST) usually warmer than 28°C accompanied by active deep convection. The temperature variation over the WPWP is closely linked with the El Niño‐Southern Oscillation (ENSO), the dominant interannual climate mode in tropical Pacific. This study elucidates the above linkage from the perspective of ENSO asymmetry and diversity. Firstly, we select 12 cold and 13 warm WPWP episodes averaged from July to October. The occurrence probability of El Niño events after cold WPWP episodes is larger than that of La Niña events following warm WPWP episodes. The westerlies associated with cold WPWP episodes are much stronger and located eastwards than the easterlies for warm WPWP episodes, exerting more effective influence on the SST variation in central‐eastern equatorial Pacific. On the other hand, the El Niño events tend to be stronger when the cold anomalies over WPWP are stronger. Furthermore, we highlight the implication of WPWP on El Niño flavors with a greater probability of EP‐type El Niño under a colder WPWP state and successive westerly wind bursts. Key Points: The temperature anomalies over western Pacific warm pool in part explain the El Niño‐Southern Oscillation asymmetry in occurrence frequency and intensityThe anomalous cooling over western Pacific warm pool during summer and autumn greatly amplifies the amplitude of El NiñoA colder western Pacific warm pool with successive westerly wind bursts implies a greater probability of Eastern Pacific El Niño
- Subjects
EL Nino; PACIFIC Ocean currents; SOUTHERN oscillation; OCEANOGRAPHY; OCEAN circulation
- Publication
Journal of Geophysical Research. Oceans, 2021, Vol 126, Issue 12, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2021JC017287