Joint Boost to Super El Niño from the Indian and Atlantic Oceans

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  • 1 State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China.
  • 2 Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, China.
  • 3 Innovation Academy of South China Sea Ecology and Environmental Engineering, Chinese Academy of Sciences, Guangzhou, China.
  • 4 University of Chinese Academy of Sciences, Beijing, China.
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Abstract

Super El Niño has been a research focus since the first event occurred. Based on observations and models, we propose that a super El Niño emerges if El Niño is an early-onset type coincident with the distribution of an Atlantic Niña (AN) in summer and a positive Indian Ocean Dipole (IOD) in autumn which is called Indo-Atlantic Booster (IAB). The underlying physical mechanisms refer to three-ocean interactions with seasonality. Early onset endows super El Niño with adequate strength in summer to excite wind-driven responses over the Indian and Atlantic Oceans, which further facilitate IAB formation by coupling with the seasonal cycle. In return, IAB alternately produces additional zonal winds over the Pacific (U), augmenting super El Niño via the Bjerknes feedback. Adding AN and IOD indices into the regression model of U leads to a better performance than the single Niño3.4 model, with a rise in the total explained variances by 10–20% and a reduction in the misestimations of super El Niños by 50%. Extended analyses using Coupled Model Intercomparison Project models further confirm the sufficiency and necessity of early onset and IAB on super El Niño formation. Approximately, 70% of super El Niños are early-onset types accompanied by IAB and 60% of early-onset El Niños with IAB finally grow into extreme events. These results highlight the super El Niño as an outcome of pantropical interactions, so including both the Indian and Atlantic Oceans and their teleconnections with the Pacific will greatly improve super El Niño prediction.

Corresponding author address: Dr. Chunzai Wang, State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China. Email: cwang@scsio.ac.cn

Abstract

Super El Niño has been a research focus since the first event occurred. Based on observations and models, we propose that a super El Niño emerges if El Niño is an early-onset type coincident with the distribution of an Atlantic Niña (AN) in summer and a positive Indian Ocean Dipole (IOD) in autumn which is called Indo-Atlantic Booster (IAB). The underlying physical mechanisms refer to three-ocean interactions with seasonality. Early onset endows super El Niño with adequate strength in summer to excite wind-driven responses over the Indian and Atlantic Oceans, which further facilitate IAB formation by coupling with the seasonal cycle. In return, IAB alternately produces additional zonal winds over the Pacific (U), augmenting super El Niño via the Bjerknes feedback. Adding AN and IOD indices into the regression model of U leads to a better performance than the single Niño3.4 model, with a rise in the total explained variances by 10–20% and a reduction in the misestimations of super El Niños by 50%. Extended analyses using Coupled Model Intercomparison Project models further confirm the sufficiency and necessity of early onset and IAB on super El Niño formation. Approximately, 70% of super El Niños are early-onset types accompanied by IAB and 60% of early-onset El Niños with IAB finally grow into extreme events. These results highlight the super El Niño as an outcome of pantropical interactions, so including both the Indian and Atlantic Oceans and their teleconnections with the Pacific will greatly improve super El Niño prediction.

Corresponding author address: Dr. Chunzai Wang, State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, China. Email: cwang@scsio.ac.cn
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