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Deep learning (DL) has achieved notable success in El Niño‐Southern Oscillation (ENSO) forecasts. Most DL‐based models focused on forecasting ENSO indices while the zonal distribution of sea surface temperature anomalies (SSTA) over the equatorial Pacific was overlooked. To provide accurate predictions for the SSTA zonal pattern, this study developed a model through leveraging the merits of the cosine distance in constructing the convolutional neural network. This model can skillfully predict the SSTA zonal pattern over the equatorial Pacific 1 year in advance, remarkably outperforming current dynamical models. Moreover, the physical interpretation of the model prediction reveals that the sources for ENSO predictability at different lead times are distinct. For the 10‐month‐lead predictions, the precursors in the north Pacific, south Pacific and tropical Atlantic play critical roles in determining the model behaviors; while for the 16‐month‐lead predictions, the initial signals in the tropical Pacific associated with the discharge‐recharge cycle are essential. Plain Language Summary The El Niño‐Southern Oscillation (ENSO) is the most prominent climate phenomenon in the Earth system. It significantly affects the worldwide weather and climate via teleconnections. Numerous studies have reported that the ENSO teleconnection and its impacts largely depend on the zonal distribution of SSTA over the equatorial Pacific. Thus, the ENSO forecast with the specific SSTA zonal pattern is important for anticipating the severity of ENSO‐related disasters and mitigating the potential socio‐economic impacts. However, current dynamical models have difficulties in accurately predicting the SSTA zonal pattern, while most of deep learning models only provide predictions of ENSO indices. Hence, we developed a deep learning model based on the convolutional neural network which can effectively predict the SSTA zonal pattern 1 year in advance. Moreover, we investigate the interpretability of this model by analyzing activation maps. The results suggest that crucial factors captured by this model at different lead times are physically reasonable, which verify the credibility of this model. Key Points We develop a deep learning model that can skillfully predict the explicit sea surface temperature anomalies (SSTA) zonal pattern over the equatorial Pacific 1 yr ahead Physical interpretation shows that the source of 10‐month‐lead prediction stems from the Pacific Meridional Mode, South Pacific quadrupole, and tropical Atlantic SSTA The main source of 16‐month‐lead forecast comes from discharge/recharge cycles, implying distinct prediction sources at different lead times

The influence of Atlantic Niño on the following El Niño–Southern Oscillation becomes significant since mid‐1970s. However, exact mechanisms for this inter‐decadal change are still unclear. Here, we perform a set of model pacemaker experiments to probe the relative contributions of the changes in the Atlantic Niño itself and the mean‐state under global warming. The results suggest that the warmer background of the tropical Atlantic plays an essential role in enhancing local mean precipitation, inducing stronger divergence and low‐level easterlies in the Pacific. Under a favorable condition in the Pacific, even a weak Atlantic Niño‐related warming could promote the development of La Niña through cross‐basin Walker circulation and the Indian Ocean‐relayed Kelvin wave response. In contrast, the Atlantic Niño pattern change itself induces feeble convection anomalies in the western Atlantic, which cannot induce significant atmospheric response in the Pacific. These results imply an important modulation of global warming on the inter‐basin connection. Plain Language Summary Climate phenomena in the three tropical oceans are tightly inter‐connected through atmospheric and oceanic pathways. The observations show that the influence of equatorial Atlantic sea surface temperature (SST) on the evolution of the following El Niño–Southern Oscillation displays a noticeable multi‐decadal change. The inter‐basin influence is negligible in early decades but becomes statistically significant since mid‐1970s. To understand this multi‐decadal change, the changes in the remote impacts of the tropical Atlantic Niño are divided into those related to the changes in the Atlantic Niño itself and the background mean SST. By comparing their relative contributions, we find the warmer climatological mean SST excites incremental precipitation around the western tropical Atlantic and Intertropical Convergence Zone (ITCZ), amplifying inter‐basin Walker circulation and the Indian Ocean relayed effect, and thus can more easily promote the evolution of La Niña in the following seasons. In contrast, despite the Atlantic Niño pattern broadens westwards in the recent decades, its induced‐feeble positive convection anomalies in the western Atlantic scarcely induce the atmospheric response over the tropical Pacific. Our results stress the vital role of the multi‐decadal SST warming in the tropical Atlantic and provide a plausible explanation for the multi‐decadal strengthening of this inter‐basin connection in recent decades. Key Points The correlation between summer Atlantic Niño and the following El Niño–Southern Oscillation (ENSO) becomes significantly negative since 1976 The warming‐induced tropical Atlantic mean‐state change, rather than the Atlantic Niño change itself, dominantly modulates the inter‐basin impact on ENSO The climatological sea surface temperature/precipitation strengthened in the tropical Atlantic is important to exert the influence on ENSO

Variabilities in tropical cyclone (TC) activity are commonly interpreted in individual TC basins. We identify an antiphase decadal variation in TC genesis between the western North Pacific (WNP) and North Atlantic (NA). An inactive (active) WNP TC genesis concurs with an enhanced (suppressed) NA TC genesis. We propose that the transbasin TC connection results from a subtropical east–west “relay” teleconnection triggered by Atlantic multidecadal oscillation (AMO), involving a chain atmosphere–ocean interaction in the North Pacific. During a negative AMO phase, the tropical NA cooling suppresses local convective heating that further stimulates a descending low-level anticyclonic circulation in the tropical NA and eastern North Pacific as a Rossby wave response, inhibiting the NA TC genesis. Meanwhile, the anomalous southwesterly to the western flank of the anomalous anticyclonic circulation tends to weaken the surface evaporation and warm the SST over the subtropical eastern North Pacific (southwest–northeast-oriented zone from the tropical central Pacific to the subtropical west coast of North America). The SST warming further sustains a cyclonic circulation anomaly over the WNP by local atmosphere—ocean interaction and the Bjerknes feedback, promoting the WNP TC genesis. This transbasin linkage helps us interpret the moderate amplitude of variations in TC genesis frequency in the Northern Hemisphere.

It has been widely believed that the tropical Pacific trade winds weakened in the last century and would further decrease under a warmer climate in the 21st century. Recent high-quality observations, however, suggest that the tropical Pacific winds have actually strengthened in the past two decades. Precise causes of the recent Pacific climate shift are uncertain. Here we explore how the enhanced tropical Indian Ocean warming in recent decades favors stronger trade winds in the western Pacific via the atmosphere and hence is likely to have contributed to the La Niña-like state (with enhanced east–west Walker circulation) through the Pacific ocean–atmosphere interactions. Further analysis, based on 163 climate model simulations with centennial historical and projected external radiative forcing, suggests that the Indian Ocean warming relative to the Pacific’s could play an important role in modulating the Pacific climate changes in the 20th and 21st centuries.

Multi-year La Niña events often induce persistent cool and wet climate over global lands, altering and in some case mitigating regional climate warming impacts. The latest event lingered from mid-2010 to early 2012 and brought about intensive precipitation over many land regions of the world, particularly Australia. This resulted in a significant drop in global mean sea level despite the background upwards trend. This La Niña event is surprisingly predicted out to two years ahead in a few coupled models, even though the predictability of El Niño-Southern Oscillation during 2002–2014 has declined owing to weakened ocean-atmosphere interactions. However, the underlying mechanism for high predictability of this multi-year La Niña episode is still unclear. Experiments based on a climate model that demonstrates a successful two-year forecast of the La Niña support the hypothesis that warm sea surface temperature (SST) anomalies in the Atlantic and Indian Oceans act to intensify the easterly winds in the central equatorial Pacific and largely contribute to the occurrence and two-year predictability of the 2010–2012 La Niña. The results highlight the importance of increased Atlantic-Indian Ocean SSTs for the multi-year La Niña’s predictability under global warming.

The extreme positive Indian Ocean Dipole (pIOD) in 2019 was followed by tropical Indian Ocean (TIO) basin‐wide warming in summer 2020, which contributed to severe flooding in the Yangtze River basin. Here, the potential relationship between extreme pIOD and subsequent summer TIO basin‐wide warming is explored using observations and model outputs, revealing that this sequential co‐occurrence is significantly influenced by Pacific SST conditions. Extreme pIODs that coincide with El Niño tend to be followed by TIO basin‐wide warming, whereas those cooccurring with neutral or La Niña conditions are comparatively less likely to do so. This is because El Niño can trigger anomalous anticyclone over the southeastern TIO, thereby maintaining and reinforcing the extreme pIOD‐related warm SST anomalies over the southwestern TIO, which subsequently induces SST warming over the northern TIO in summer. Our findings highlight the important modulation role of Pacific SST conditions, with significant implications for regional climate predictions. Plain Language Summary The Indian Ocean basin‐wide warming is the dominant mode of interannual SST variations in the TIO, and has received great attention due to its profound climatic impacts. Particularly, strong TIO basin‐wide warming occurred in early summer 2020 and contributed to extreme floods over Yangtze River and Japan. It can be traced back to the extreme pIOD event in the fall of 2019. Motivated by this, the present study examines the lead‐lag co‐occurrence of extreme pIOD and the following summer TIO basin‐wide warming based on observations and model outputs. The results indicate that the occurrence of TIO basin‐wide warming following an extreme pIOD event is strongly influenced by SST conditions in the tropical Pacific Ocean. Extreme pIOD events that cooccur with El Niño are more likely to be followed by the TIO basin‐wide warming, whereas those that cooccur with neutral conditions or La Niña are less likely to do so. This study contributes to a better understanding of the relationship between extreme pIOD and the following summer TIO basin‐wide warming, as well as the modulation role of ENSO. Key Points Extreme pIOD doesn't necessarily followed by TIO basin‐wide warming in the subsequent summer The co‐occurrence of extreme pIOD and following summer TIO basin‐wide warming is significantly influenced by Pacific SST conditions Extreme pIODs coinciding with El Niño tend to be followed by TIO basin‐wide warming, while those with neutral or La Niña conditions do not

Because of the seasonal northward migration of the East Asian summer monsoon, the mean-state atmospheric circulation in South China (SC) is remarkably different between the early (May–June) and late (July–August) rainy seasons. This study presents distinct teleconnections between the SC precipitation in the two periods and the sea surface temperatures (SSTs) in the tropical oceans. In the early rainy season when the major monsoon rain belt is located in SC, the increased local precipitation is related to the tropical Indian Ocean Basin warming. The basin warming induces an anomalous anticyclone in the South China Sea–western North Pacific (SCS-WNP). The related southwesterly anomalies transport more moisture to SC and lead to more moisture convergence and precipitation there. In the late rainy season when the major monsoon rain belt migrates northward to the Yangtze River valley, the precipitation increase in SC can be caused by the dipole SST anomalies in the tropical Pacific with the cold anomalies near the Maritime Continent and warm ones near the date line. The dipole SST anomalies generate an anomalous cyclone in the WNP with its center more northward than that of the anomalous anticyclone in the early rainy season. The related northeasterly anomalies along its northwestern flank reduce the climatological northward transport of moisture flux out of SC, and increase the moisture convergence and precipitation there. The distinct teleconnections between the SC precipitation and the tropical SSTs in the early and late rainy seasons can be well reproduced in the sensitivity experiments by an atmospheric general circulation model.

Pacific Meridional Mode (PMM) is known to be significantly correlated with tropical cyclone (TC) genesis over the western North Pacific (WNP), while the stability of their relationship remains unknown. Here we found that their relationship is nonstationary, which depends on the phase of Pacific Decadal Oscillation (PDO). During the PDO warm phases, the PMM‐emanated cyclonic circulation and ascending motion can propagate to the entire WNP due to the enhanced background convection. In contrast, during the PDO cold phases, the PMM‐resulted cyclonic circulation and ascending motion are confined to the eastern WNP, while the compensated descending motion prevails in the western WNP. Accordingly, the PMM‐induced consistent (inconsistent) changes in large‐scale conditions across the western and eastern WNP act to strengthen (weaken) the relationship between the PMM and WNP TC genesis during the PDO warm (cold) phases. The result provides further guidance for improving seasonal prediction of TC genesis. Plain Language Summary Billions of people in the Pacific islands and Asian coastal regions are subject to enormous tropical cyclone (TC) induced disasters. The Pacific Meridional Mode (PMM), a seasonally evolving mode of coupled climate variability, has a prominent impact on TC genesis in the western North Pacific (WNP) and is usually used as an important predictor for seasonal forecasting of TC genesis. However, stability in the relationship between PMM and TC genesis remains unclear. Here we found that their relationship is nonstationary and depends on the phase of the Pacific Decadal Oscillation (PDO), a decadal fluctuation of the Pacific Ocean. The result highlights the crucial role of PDO in modulating the relationship between the PMM and WNP TC genesis and thus provides further guidance for seasonal forecasting scheme of TC genesis. Key Points The relationship between the Pacific Meridional Mode (PMM) and tropical cyclone genesis over the western North Pacific is nonstationary The nonstationary relationship stems from the diverse atmospheric responses to PMM that depend on the phase of Pacific Decadal Oscillation

Given the climatic importance of the Madden–Julian oscillation (MJO), this study evaluates the capability of CMIP6 models in simulating MJO eastward propagation in comparison with their CMIP5 counterparts. To understand the representation of MJO simulation in models, a set of diagnostics with respect to MJO-associated dynamic and thermodynamic structures is applied, including large-scale zonal circulation, vertical structures of diabatic heating and equivalent potential temperature, moisture convergence at the planetary boundary layer (PBL), and the east–west asymmetry of moisture tendency relative to the MJO convection. The simulated propagation of the MJO in CMIP6 models shows an overall improvement in realistic speed and longer distance, which displays a robust linear regression relationship against the above-mentioned dynamic and thermodynamic structures. The improved MJO propagation in CMIP6 largely benefits from better representation of premoistening processes that is primarily contributed by improved PBL moisture convergence. In addition, the convergence of moisture and meridional advection of moisture prior to the MJO convection are enhanced in CMIP6, while the zonal advection of moisture is as weak as that in CMIP5. The increased convergence of moisture is a result of enhanced lower-tropospheric moisture and divergence, and the enhanced meridional advection of moisture can be caused by sharpened meridional gradient of mean lower-tropospheric moisture in the western Pacific. Further examination of the lower-tropospheric moisture budget reveals that the enhanced zonal asymmetry of the moisture tendency in CMIP6 is driven by the drying process to the west of the MJO convection, which is attributed to the negative vertical and zonal advections of moisture.

Accurate detection and attribution of past climate change are crucial for projecting future climate change and formulating proper policies. In this study, we show that the warming of the tropical Indian Ocean contributes to the observed wetting trend in the Tibetan plateau. The warming tropical Indian Ocean can lead to more precipitation around the Arabian Sea. The associated diabatic heating triggers the cyclonic atmospheric response in the lower troposphere over the Arabian Sea and eastern Africa. It also causes the enhancement and westward extension of the western North Pacific subtropical high. The in‐between airflow transports more moisture northward to the plateau, leading to the increased precipitation over the plateau. These large‐scale circulation patterns can be detected from the long‐term trends based on the observations and the large‐ensemble historical simulations. They can also be simulated by an atmospheric general circulation model forced by the observed warming merely in the tropical Indian Ocean. Plain Language Summary The Tibetan plateau, often referred to the “Asian water tower,” is the source region of many major rivers in Asia. It has experienced an increasing precipitation trend over the past few decades. In this study, we show that the warming tropical Indian Ocean contributes to this wetting trend. The warming tropical Indian Ocean can cause more precipitation around the Arabian Sea. The associated diabatic heating not only triggers an anomalous cyclone in the lower troposphere around the Arabian Sea and eastern Africa, but also causes the enhancement and westward extension of western North Pacific subtropical high. Consequently, the northward airflow between them transports more moisture to the plateau and causes more precipitation there. Our findings underscore the significant role of the warming tropical Indian Ocean in shaping the changing climate under global warming. Further research efforts are warranted to deepen our understanding of this phenomenon. Key Points The warming tropical Indian Ocean increases the precipitation over the Arabian Sea The associated large‐scale circulation anomalies transport more moisture northward to the plateau Consequently, more moisture converges over the plateau, leading to the increased precipitation