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Variations in the El Niño/Southern Oscillation (ENSO) are associated with a wide array of regional climate extremes and ecosystem impacts 1 . Robust, long-lead forecasts would therefore be valuable for managing policy responses. But despite decades of effort, forecasting ENSO events at lead times of more than one year remains problematic 2 . Here we show that a statistical forecast model employing a deep-learning approach produces skilful ENSO forecasts for lead times of up to one and a half years. To circumvent the limited amount of observation data, we use transfer learning to train a convolutional neural network (CNN) first on historical simulations 3 and subsequently on reanalysis from 1871 to 1973. During the validation period from 1984 to 2017, the all-season correlation skill of the Nino3.4 index of the CNN model is much higher than those of current state-of-the-art dynamical forecast systems. The CNN model is also better at predicting the detailed zonal distribution of sea surface temperatures, overcoming a weakness of dynamical forecast models. A heat map analysis indicates that the CNN model predicts ENSO events using physically reasonable precursors. The CNN model is thus a powerful tool for both the prediction of ENSO events and for the analysis of their associated complex mechanisms. A statistical forecast model using a deep-learning approach produces useful forecasts of El Niño/Southern Oscillation events with lead times of up to one and a half years.

El Niño events are characterized by surface warming of the tropical Pacific Ocean and weakening of equatorial trade winds that occur every few years. Such conditions are accompanied by changes in atmospheric and oceanic circulation, affecting global climate, marine and terrestrial ecosystems, fisheries and human activities. The alternation of warm El Niño and cold La Niña conditions, referred to as the El Niño–Southern Oscillation (ENSO), represents the strongest year-to-year fluctuation of the global climate system. Here we provide a synopsis of our current understanding of the spatio-temporal complexity of this important climate mode and its influence on the Earth system. Our current understanding of the spatio-temporal complexity of the El Niño–Southern Oscillation phenomenon is reviewed and a unifying framework that identifies the key factors for this complexity is proposed.

Although it is known that the frequency and intensity of heatwaves are affected by the El Niño–Southern Oscillation (ENSO), unknown are the ENSO modulations on the moving properties (e.g., moving distance and speed) of spatiotemporally contiguous heatwaves. Here, we investigate the relationship between ENSO and the moving patterns of contiguous heatwaves. We show that contiguous heatwaves are likely more frequent, more persistent, and longer‐traveling, but slower‐moving during El Niño than La Niña episodes. The differences in the tropical contiguous heatwaves between El Niño and La Niña are influenced by persistent high‐pressure anomalies. During the following summers, El Niño can induce anomalous atmospheric circulation characterized by an intensified subsidence over the western North Pacific and ascending motion over the tropical Indian and Pacific Oceans. These features provide favorable conditions for the occurrence and maintenance of contiguous heatwaves. Plain Language Summary The El Niño–Southern Oscillation (ENSO) is among the strongest climate variation phenomena, which has important effects on the frequency and intensity of heatwaves across the globe. However, how ENSO influences the joint evolution behaviors of heatwaves at both temporal and spatial dimensions (e.g., moving patterns including traveling distance and moving speed) is not fully understood. Here, we first track the spatiotemporally contiguous heatwaves that occur simultaneously in adjacent regions or consecutively in neighboring days, and investigate their moving patterns over global land areas during 1961–2020. Then, we examine the relationship between the ENSO and the moving properties of these contiguous heatwaves. The results show that contiguous heatwaves during El Niño years not only tend to be more frequent and more persistent, but also travel longer distances and at slower moving speed, especially in tropics. This relationship is likely due to persistent high‐pressure anomalies caused by El Niño, which can intensify subsidence over the western North Pacific and ascendance over the tropical Indian and Pacific Oceans. This knowledge is crucial for improving our predictions about heatwaves and adapting their potential impacts. Key Points Contiguous heatwaves tend to be more frequent, more persistent, and longer‐traveling, but slower‐moving during El Niño than La Niña Differences in tropical contiguous heatwaves between El Niño and La Niña episodes are influenced by persistent high‐pressure anomalies El Niño intensifies contiguous heatwaves via inducing sinking over the western North Pacific (WNP) and rising over the tropical Indian Ocean

Hindcasts and real-time predictions of the east-central tropical Pacific sea surface temperature (SST) from the North American Multimodel Ensemble (NMME) system are verified for 1982–2015. Skill is examined using two deterministic verification measures: mean squared error skill score (MSESS) and anomaly correlation. Verification of eight individual models shows somewhat differing skills among them, with some models consistently producing more successful predictions than others. The skill levels of MME predictions are approximately the same as the two best performing individual models, and sometimes exceed both of them. A decomposition of the MSESS indicates the presence of calibration errors in some of the models. In particular, the amplitudes of some model predictions are too high when predictability is limited by the northern spring ENSO predictability barrier and/or when the interannual variability of the SST is near its seasonal minimum. The skill of the NMME system is compared to that of the MME from the IRI/CPC ENSO prediction plume, both for a comparable hindcast period and also for a set of real-time predictions spanning 2002–2011. Comparisons are made both between the MME predictions of each model group, and between the average of the skills of the respective individual models in each group. Acknowledging a hindcast versus real-time inconcsistency in the 2002–2012 skill comparison, the skill of the NMME is slightly higher than that of the prediction plume models in all cases. This result reflects well on the NMME system, with its large total ensemble size and opportunity for possible complementary contributions to skill.

The Madden–Julian Oscillation (MJO) is the leading mode of sub‐seasonal variability in the tropical atmosphere and is a source of predictability for extratropical weather through its teleconnections. MJO teleconnection patterns can be modulated by the El Niño–Southern Oscillation (ENSO) on seasonal to interannual time scales. However, changes over decadal time scales are less well understood. ERA5 reanalysis data are used to show that the boreal winter MJO teleconnection pattern in the Northern Hemisphere has changed in recent decades in line with changes in the Pacific Decadal Oscillation and Atlantic Multidecadal Variability. Changes are seen in the circulation, temperature and precipitation responses. In particular, from 1997, intraseasonal cold anomalies appear over Europe and the eastern United States due to MJO convection over the western Pacific; these were not present 20 years previously. The decadal variability observed is not the product of aliasing of ENSO modulation of the teleconnection. Plain Language Summary Weather in different regions of the globe can be linked by planetary‐scale atmospheric waves, and these links can help forecasters to predict the weather. One such link, or teleconnection pattern, connects changes in rainfall over Indonesia and the tropical Pacific (from a weather system called the Madden–Julian Oscillation or MJO) to changes in the weather in North America and Europe. This study assesses this teleconnection pattern in two separate time periods (roughly the mid‐1970s to mid‐1990s and mid‐1990s to late 2010s) to analyze if and how it has changed. We find that the pattern has changed, and that this is due to large‐scale changes in the background state of the atmosphere. These changes in the link between the tropics and extratropics will have implications for weather forecasts on weekly to monthly time scales. Key Points The extratropical response to the Madden‐Julian Oscillation has changed on decadal time scales This decadal variability coincides with changes in low‐frequency oceanic modes in both the Pacific and Atlantic basins Changes on decadal time scales are different to those modulated by the El Niño‐Southern Oscillation on interannual scales

The Northern Annular Mode (NAM) induces anomalous wintertime weather over the extratropical Northern Hemisphere as the leading mode of atmospheric circulation variability. Yet, modulations of its statistical properties in a changing climate need elucidating. This study investigates the seasonality of NAM variability and its modulations under global warming with a large‐ensemble atmospheric simulation data set. We find that the Aleutian Low anomaly associated with the NAM strengthens in a warmer climate, which is linked to a seasonally earlier emergence of the Aleutian‐Icelandic Low seesaw (AIS). The El Niño‐Southern Oscillation (ENSO) teleconnection extends more eastward under global warming, which increases the ENSO‐NAM correlation through the earlier AIS development. Our findings suggest increased predictability of the NAM under global warming, with uncertainties due to potential ENSO changes.

High‐latitude winter warming was observed following strong tropical volcanism, which has long been believed to be due to the volcanic‐induced positive North Atlantic Oscillation (NAO) phase. However, recent works argue that this warming is caused by El Niño–Southern Oscillation (ENSO) variability instead of volcanoes. Moreover, some studies further argue that El Niño and volcanoes work together to produce this post‐volcanic NAO winter warming. To better understand these arguments on post‐volcanic high‐latitude winter warming, we conducted ENSO‐preconditioned volcanic experiments. Our simulations strongly suggest that the post‐eruption Eurasian winter warming is caused by a post‐eruption positive NAO phase and not by coexisting ENSO‐preconditioned variability. Additionally, we find that the El Niño‐preconditioned volcanic eruption enhances the El Niño phase; however, the neutral and La Niña‐preconditioned eruptions do not lead to an ENSO–like response. These findings are helpful to better understand volcanic‐induced circulation impacts and have important implications for the interpretation of model results and post‐volcanic prediction. Plain Language Summary The El Niño–Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) linkage to volcanism and associated post‐volcanic high‐latitude winter warming is a topic of great interest. However, the origin of this post‐volcanic winter warming is still controversial. Therefore, to resolve the controversies related to post‐volcanic ENSO and NAO variability and high‐latitude winter warming, we conducted a set of ENSO‐preconditioned volcanic experiments using a coupled atmosphere‐ocean model. The model simulations demonstrate that the post‐eruption high‐latitude Eurasian winter warming is mainly related to the post‐eruption positive NAO phase with no linkage to post‐volcanic ENSO variability. Moreover, the strong tropical volcanism initialized with the El Niño state enhances the El Niño phase, while the Neutral and La Niña initialized simulations do not lead to ENSO–like variability. These results strongly suggest that the high‐latitude post‐eruption Eurasian winter warming is caused by NAO pressure changes during volcanism, and not due to strengthened ENSO responses to volcanism. Key Points Volcano‐El Niño–Southern Oscillation (ENSO) sensitivity experiments are conducted to better understand the source of post‐eruption northern hemisphere high‐latitude winter warming We found that the post‐eruption Eurasian winter warming is caused by volcanic‐induced positive North Atlantic Oscillation (NAO)‐phase and not by ENSO teleconnection Coexistence of El Niño with volcanism is not essential to produce volcanic‐induced positive NAO and associated winter warming

Rainfall peaks during austral summer in southern Africa, where most countries are vulnerable to hydroclimate extremes induced by El Niño‐Southern Oscillation (ENSO). Climate models have struggled to simulate the ENSO impact pattern, with excessive southwestward contraction of El Niño‐induced dry anomalies alongside wet anomalies extending too far into central southern Africa. Here we find that the model inability results from an overly‐shallow mean thermocline in the eastern Indian Ocean (IO) that distorts the ENSO teleconnection. During austral summer, instead of an observed basin‐wide IO response to ENSO, the overly‐shallow thermocline leads to a zonal dipole‐like response pattern. Consequently, during El Niño, anomalous equatorial easterly winds promote an onshore moisture transport and a southward shift of summer rainband, leading to a spurious drying in northeast but wetting in southeast and central southern Africa, respectively. Thus, projection of ENSO‐induced rainfall over southern Africa using models with such bias may carry substantial uncertainty.

Australia is one of the regions strongly affected by the El Niño‐Southern Oscillation (ENSO). The recent 2020–2023 La Niña event was marked by record‐breaking rainfall and flooding across eastern Australia. The continuous wet conditions during the triple La Niña motivated us to explore the impacts of single‐year and multi‐year ENSO events on Australian rainfall using observational data sets. We find that, while there is no difference in the rainfall impacts during single or double El Niño events, Australian rainfall tends to increase in the third year of triple La Niña events compared to the first and second years. The enhanced rainfall impact during the third La Niña year occurs despite no strengthening of La Niña in the tropical Pacific, suggesting that other processes such as local rainfall‐soil moisture feedback may play a role in prolonging the effects of multi‐year La Niña events in Australia. Plain Language Summary Australia is strongly affected by the El Niño‐Southern Oscillation (ENSO), with rainfall more likely to increase during La Niña and below‐average rainfall more common during El Niño. The recent 2020–2023 multi‐year La Niña was marked by continuous wet conditions across eastern Australia, leading to record‐breaking rainfall and flooding. Multi‐year La Niña events, where La Niña occurs in two or three consecutive austral summers, happened in about 50% of all La Niña events, including five triple La Niña events since 1900. We explored the impacts of multi‐year ENSO events on Australian rainfall and found that, while there is no difference in the rainfall impacts during single or double El Niño events, rainfall tends to increase in the third year of triple La Niña events compared to the first and second years. This rainfall increase occurs despite no strengthening of La Niña in the tropical Pacific Ocean, suggesting that local processes such as feedback between high/saturated soil moisture and rainfall may play a role in prolonging the effects of multi‐year La Niña events in Australia. Key Points Eastern Australia tends to experience record‐breaking rainfall and flooding during La Niña events Rainfall impact of multi‐year El Niño‐Southern Oscillation (ENSO) persists during double and triple events, despite no strengthening of ENSO Australian rainfall increases in the third year of triple La Niña likely due to soil moisture‐rainfall feedback

The Kuroshio intrusion (KI) is a northwestward‐flowing branch of the Kuroshio Current, which enters the South China Sea (SCS) and regulates its temperature, salinity, and water mass exchanges. However, limited direct observations hinder our understanding of KI's mechanisms and responses to climate change. Here, we present a 60‐year bi‐monthly resolved coral oxygen isotope (δ18Oc) record from Dongsha Atoll, the northern SCS. The dry‐season (December–March) δ18Oc record reveals interannual to decadal variabilities of the KI. The impact of the East Asian winter monsoon (EAWM) on Dongsha δ18Oc was more pronounced during the 1970s and 1980s and after the early 2000s, while the influence of the El Niño‐Southern Oscillation (ENSO) on Dongsha δ18Oc was higher between the 1980s and 1990s. The Pacific Decadal Oscillation (PDO) may have a relatively minor effect on KI strength or may indirectly modulate KI strength through its influence on ENSO activities. Our Dongsha δ18Oc record highlight the importance of the EAWM, ENSO, and PDO in predicting future KI changes. Plain Language Summary The Kuroshio intrusion is a branch of the Kuroshio Current. It flows into the South China Sea and affects its temperature, salinity, and water movement. We however know very little how the Kuroshio intrusion responds to climate changes. Here we present a study on the chemical composition of a coral core from Dongsha Atoll in the northern South China Sea. Our study shows that the intrusion varies markedly over the past 60 years and is connected to changes in sea surface salinity. Stronger intrusions align with stronger East Asian winter monsoon intensity and El Niño events. Understanding how the Kuroshio intrusion reacts to climate change is important for effectively managing the potential impacts of global warming on the marine ecosystem. Key Points A 60‐year‐long coral oxygen isotope record from Dongsha Atoll, South China Sea reveals interannual to decadal variations in the Kuroshio intrusion Strong Kuroshio intrusion, corresponding to high sea surface salinity, is identifiable over the past 60 years The Kuroshio intrusion variations are primarily driven by East Asian winter monsoon changes and also influenced by El Niño‐Southern Oscillation