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1. Diverse NPMM conditions deviate the 2023/24 El Niño from the 1997/1998 and 2015/2016 extreme El Niño events

   https://doi.org/10.1038/s41612-025-01013-z  

   Lin, Yong-Fu; Chen, Mengyan; Liu, Lingling; Zheng, Fei; Ding, Ruiqiang; Wang, Xin; Wu, Chau-Ron; Lo, Min-Hui; Hsu, Huang-Hsiung; Chen, Jiepeng; et al (December 2025, npj Climate and Atmospheric Science)

   Abstract The 2023/24 El Niño commenced with an exceptionally large warm water volume in the equatorial western Pacific, comparable to the extreme 1997/98 and 2015/16 events, but did not develop into a super El Niño. This study highlights the critical role of contrasting Northern Pacific Meridional Mode (NPMM) conditions in this divergence. Warm NPMM conditions during the 1997/98 and 2015/16 events created a positive zonal sea surface temperature (SST) gradient in the equatorial western-central Pacific and enhanced Madden-Julian Oscillation (MJO) propagation, driving sustained westerly wind bursts (WWBs) and downwelling Kelvin waves that intensified both events. In contrast, the cold NPMM during 2023/24 induced a negative SST gradient and suppressed MJO activity, resulting in weaker WWBs and limited eastward wave activity, preventing the event from reaching super El Niño intensity. A 2,200-year CESM1 pre-industrial simulation corroborates these observational findings, underscoring the importance of NPMM interference in improving El Niño intensity predictions. 

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2. Why Does the CP El Niño less Frequently Evolve Into La Niña than the EP El Niño?

   https://doi.org/10.1029/2020GL087876  

   He, Shan; Yu, Jin‐Yi; Yang, Song; Fang, Shih‐Wei (August 2020, Geophysical Research Letters)
3. El Niño and the shifting geography of cholera in Africa

   https://doi.org/10.1073/pnas.1617218114  

   Moore, Sean M.; Azman, Andrew S.; Zaitchik, Benjamin F.; Mintz, Eric D.; Brunkard, Joan; Legros, Dominique; Hill, Alexandra; McKay, Heather; Luquero, Francisco J.; Olson, David; et al (April 2017, Proceedings of the National Academy of Sciences)
4. The El Niño–Southern Oscillation Pattern Effect

   https://doi.org/10.1029/2021GL095261  

   Ceppi, Paulo; Fueglistaler, Stephan (October 2021, Geophysical Research Letters)

   Abstract El Niño–Southern Oscillation (ENSO) variability is accompanied by out‐of‐phase anomalies in the top‐of‐atmosphere tropical radiation budget, with anomalous downward flux (i.e., net radiative heating) before El Niño and anomalous upward flux thereafter (and vice versa for La Niña). Here, we show that these radiative anomalies result mainly from a sea surface temperature (SST) “pattern effect,” mediated by changes in tropical‐mean tropospheric stability. These stability changes are caused by SST anomalies migrating from climatologically cool to warm regions over the ENSO cycle. Our results are suggestive of a two‐way coupling between SST variability and radiation, where ENSO‐induced radiative changes may in turn feed back onto SST during ENSO. 

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5. The climate variability trio: stochastic fluctuations, El Niño, and the seasonal cycle

   https://doi.org/10.1186/s40562-023-00305-7  

   Stuecker, Malte F. (November 2023, Geoscience Letters)

   Abstract Climate variability has distinct spatial patterns with the strongest signal of sea surface temperature (SST) variance residing in the tropical Pacific. This interannual climate phenomenon, the El Niño-Southern Oscillation (ENSO), impacts weather patterns across the globe via atmospheric teleconnections. Pronounced SST variability, albeit of smaller amplitude, also exists in the other tropical basins as well as in the extratropical regions. To improve our physical understanding of internal climate variability across the global oceans, we here make the case for a conceptual model hierarchy that captures the essence of observed SST variability from subseasonal to decadal timescales. The building blocks consist of the classic stochastic climate model formulated by Klaus Hasselmann, a deterministic low-order model for ENSO variability, and the effect of the seasonal cycle on both of these models. This model hierarchy allows us to trace the impacts of seasonal processes on the statistics of observed and simulated climate variability. One of the important outcomes of ENSO’s interaction with the seasonal cycle is the generation of a frequency cascade leading to deterministic climate variability on a wide range of timescales, including the near-annual ENSO Combination Mode. Using the aforementioned building blocks, we arrive at a succinct conceptual model that delineates ENSO’s ubiquitous climate impacts and allows us to revisit ENSO’s observed statistical relationships with other coherent spatio-temporal patterns of climate variability—so called empirical modes of variability. We demonstrate the importance of correctly accounting for different seasonal phasing in the linear growth/damping rates of different climate phenomena, as well as the seasonal phasing of ENSO teleconnections and of atmospheric noise forcings. We discuss how previously some of ENSO’s relationships with other modes of variability have been misinterpreted due to non-intuitive seasonal cycle effects on both power spectra and lead/lag correlations. Furthermore, it is evident that ENSO’s impacts on climate variability outside the tropical Pacific are oftentimes larger than previously recognized and that accurately accounting for them has important implications. For instance, it has been shown that improved seasonal prediction skill can be achieved in the Indian Ocean by fully accounting for ENSO’s seasonally modulated and temporally integrated remote impacts. These results move us to refocus our attention to the tropical Pacific for understanding global patterns of climate variability and their predictability. 

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