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We investigate the possibility for the South Atlantic Convergence Zone (SACZ) to act as a Rossby wave source for global scale teleconnections. A simple heating perturbation is applied to numerical simulations using a baroclinic model with differing basic states. Sixteen days after the perturbation is applied, wave propagation is diagnosed within the subtropical latitudes of the Northern Hemisphere for the basic states corresponding to El Niño and neutral years, which have normal and strong westerly flow in the upper troposphere over the Equatorial Atlantic Ocean. For La Niña basic states, there is very little propagation over the Equatorial Atlantic Ocean because the westerly flow is weak, confining Rossby waves to the Southern Hemisphere. We conclude that the SACZ may act as interhemispheric Rossby wave source, providing the tropical westerly flow is strong enough to permit wave propagation across the Equatorial Atlantic Ocean. [ABSTRACT FROM AUTHOR]

The main goal of the present work is to compare and contrast the characteristics of distinct monsoon systems like the Indian monsoon system (IMS) and South American monsoon system (SAMS) for the period (1979–2022). In addition, we discuss in some detail the theoretical aspects of the two monsoon systems by examining the energetics and the applicability of "convective quasi-equilibrium, (CQE)." We have also analyzed the precipitation interannual variability of SAMS and IMS considering neutral, El Niño, and La Niña years. Then, a discussion of the applicability of CQE along with the recent changes in surface entropy is presented. In our analysis, we found that interannual variability in the case of SAMS is less than that of IMS, and rainfall of SAMS is not drastically affected by ENSO when compared to IMS. We observed that rainfall characteristics over IMS are more complex than SAMS. The annual cycle of the vertically integrated total kinetic energy (KE) over SAMS is maximum in Austral spring, while the precipitation is higher in Austral summer. This is in sharp contrast to the IMS, where the maximum KE and rainfall coincide, both occurring in July and August. Further analysis showed that the conversion from the mean available potential energy PZ to the eddy available potential energy PE and conversion from PE to KE are important over SAMS. This shows that in South America, baroclinic conversions associated with baroclinic instability are important in austral summer, while over IMS, baroclinic conversions are not important in boreal summer. Our results support CQE for the IMS, but in the case of El Niño, we found that CQE is invalid. For SAMS, the applicability of CQE is climatologically doubtful, but during El Niño, the applicability of CQE is robustly visible. [ABSTRACT FROM AUTHOR]

The interannual variability of hydroclimatic conditions in Northwestern South America, especially precipitation, is mainly influenced by the El Niño–Southern Oscillation (ENSO). We explore potential mechanisms that affect precipitation occurrence in Northwestern South America during El Niño and La Niña events over the period 1980–2019, using data from the ERA5 reanalysis. We look at the atmospheric moisture contribution from different sources using the Dynamic Recycling Model to track water vapor trajectories. Interestingly, conditions with reduced precipitation during El Niño events can take place along with increased precipitable water. To understand this, we analyze thermodynamic conditions in the atmosphere that are necessary for precipitation to occur over the region, such as convective available potential energy, convective inhibition, lifting condensation level, and low-level relative humidity. With this approach, we find more favorable thermodynamic conditions for the occurrence of precipitation during La Niña events, even if the content of water vapor is equal or even less than during El Niño events. We also look at the structure of the regional Hadley and Walker circulation in both types of events and find that a weaker ascending motion during El Niño events also inhibits convection. This study provides an integral picture of how precipitation anomalies over Northwestern South America during ENSO events are related to dynamic and thermodynamic conditions and sources of atmospheric moisture. [ABSTRACT FROM AUTHOR]

After consecutive two years with the La Niña phenomenon in 2020–2021, cold sea surface temperature (SST) anomalies in the central-eastern equatorial Pacific persisted in 2022, known as a "triple-dip" La Niña event. These conditions have had a profound impact on global weather and climate. Understanding the underlying processes and mechanisms is crucial for improving ENSO prediction and has significant socioeconomic implications. In this study, we investigate the processes responsible for the evolution of the third-year La Niña event in 2022 based on related observations and an intermediate coupled model (ICM). The results show that two factors are essential for the development of the third-year La Niña event: surface easterly wind anomalies over the central-western equatorial Pacific in early 2022 and the induced cold SST anomalies by the former. In the first half of 2022, mainly due to the off-equatorial downwelling Rossby wave reflection at the western boundary, the equatorial downwelling Kelvin waves continuously induce warming effect in the upper ocean, acting to weaken the cold SST anomalies in the central-eastern Pacific. However, the easterly wind anomalies over the central-western equatorial Pacific during February–March 2022 induce upwelling Kelvin waves, whose cooling effect reverses the warming SST tendency. Afterward, despite the pronounced warming effect induced by the reflected downwelling Kelvin waves, the wind-induced cold SST anomalies persist on the equator during the equatorial cold season, which are further intensified by the Bjerknes feedback. Sensitivity experiments based on the ICM further confirm these outcomes. When the cooling effect induced by the easterly wind anomalies is included in ocean initial conditions, the ICM can accurately capture the reappearance of the La Niña phenomenon. These results highlight the importance of anomalous easterlies in the central-western equatorial Pacific during the decaying phase of the La Niña event. [ABSTRACT FROM AUTHOR]

The El Niño-Southern Oscillation (ENSO) and Quasi-Biennial Oscillation (QBO) have an individual impact on the northern winter stratospheric polar vortex. This study considered the joint impact of ENSO and QBO using the reanalysis and observational data. The combinations of ENSO and QBO winds are split into four groups, El Niño-easterly QBO, El Niño-westerly QBO, La Niña-easterly QBO, and La Niña-westerly QBO, and the impact of each joint group is compared with the linear superposition of the individual impacts of ENSO and QBO with the interference from other factors removed. On average, the stratospheric polar vortex exhibits weakening in the pure El Niño and easterly QBO composites and exhibits strengthening in the pure La Niña and westerly QBO composites as compared with the climatology. The observed joint ENSO and QBO signals in the Arctic stratosphere are mostly a linearly superposed combination between them. This interference of QBO and ENSO's impacts is also observed in the tropospheric circulation and tropical convections, which are related to teleconnection in the upper troposphere controlling the amount of planetary waves entering stratosphere to further impact Artic stratospheric polar vortex. Although El Niño and easterly QBO cooperate to weaken the stratospheric polar vortex, and La Niña and westerly QBO cooperate to strengthen, but their impact on the tropospheric North Pacific circulation and tropical rainfall are opposite with signs reversed. As a consequence, the joint effect of El Niño-easterly QBO/La Niña-westerly QBO on the stratosphere is stronger than that of El Niño-westerly QBO/La Niña-easterly QBO. However, the joint impact of El Niño-easterly QBO on the North Pacific troposphere and tropical rainfall is weaker than that of El Niño-westerly QBO. Further analysis on the wave activities and Brewer-Dobson circulation also confirms the linear interference between effects of ENSO and QBO in the stratosphere, although this linearity is less evident in the troposphere. [ABSTRACT FROM AUTHOR]

Collaborations between archeologists and aquatic scientists are driving forward a whole new subdiscipline of methods to document and understand environmental change. Climate change, food webs, El Niño La Niña oscillations, and alterations to biotic factors such as salinity and stream flow have all been studied via aquatic archeological material. Much of this research is conducted on shell middens, the archeological materials they contain, and substrates they are deposited in. This article provides a primer on the formation of shell middens, procedures of midden archeological excavation, and the recent advances in aquatic environmental change research from analyzing archeological material collected from middens. [ABSTRACT FROM AUTHOR]

The interannual relationships between the southern subtropical cell (SSTC) in the Indian Ocean (IO) and the El Niño‐Southern Oscillation (ENSO) are examined. The results demonstrate that the impacts of ENSO on the boreal winter IO SSTC display a notable negative skewness, with the amplification of the SSTC during La Niña being far stronger than its reduction during El Niño. This difference is mainly attributed to an asymmetry in anomalous meridional geostrophic transport, characterized by more robust southward (weaker northward) geostrophic transport anomalies during La Niña (El Niño) events. Further analyses reveal that the differing longitudinal positions of the ENSO‐related sea surface temperature anomaly (SSTA) are the primary drivers of the asymmetry in anomalous meridional geostrophic transport via the oceanic and atmospheric teleconnections. Compared to the warm SSTA in El Niño events, the La Niña‐related cool SSTA in the central‐eastern equatorial Pacific displays a greater westward extension, which induces stronger surface easterlies over the western equatorial Pacific, and then initiates a more substantial sea surface height anomaly (SSHA) in the southeast Indian Ocean (SEIO) through oceanic waveguides. This leads to a heightened zonal SSHA gradient over the southern IO, resulting in a larger anomalous meridional geostrophic transport. On the other hand, the westward extension of negative SSTA during La Niña winters triggers anomalous cyclonic northerlies along the western coast of Australia by shifting the Walker circulation westward. These coastal northerlies amplify the positive SSHA signals in the SEIO and enhance the anomalous meridional geostrophic transport, ultimately contributing to a more robust IO SSTC response. Plain Language Summary: The southern subtropical cell (SSTC), driven by wind over the Indian Ocean (IO), is characterized by southward surface flow, subduction in the subtropics, and upwelling in the tropics. This study revealed that the boreal winter SSTC weakens during El Niño and enhances during La Niña, with the latter exhibiting a notably stronger response, contrary to the expected El Niño/La Niña amplitudes. These asymmetric ENSO impacts predominantly result from disparities in anomalous meridional geostrophic transport. In‐depth analysis further uncovered that the distinct longitudinal positions of ENSO‐related sea surface temperature anomalies (SSTA) primarily drive the asymmetry in anomalous meridional geostrophic transport. During La Niña events, the cool SSTA in the central‐eastern equatorial Pacific extends significantly westward compared to the El Niño‐related warm SSTA, which is evident during both the preceding season and the contemporaneous winter. During the preceding season, this westwardly extended SSTA leads to a more substantial anomalous meridional geostrophic transport in the subsequent winters through the propagation of oceanic waveguides. In La Niña winters, the westward extension of negative SSTA further amplifies the anomalous meridional geostrophic transport by shifting the Walker circulation westward. These intensified meridional geostrophic transport anomalies ultimately result in a more pronounced SSTC response during La Niña events. Key Points: The boreal winter southern subtropical cell (SSTC) in the Indian Ocean displays a negative skewness in response to El Niño‐Southern Oscillation (ENSO)Such asymmetric SSTC responses are primarily attributed to an asymmetry in anomalous meridional geostrophic transportDiffering longitudes of ENSO‐related sea surface temperature anomaly cause the asymmetric meridional geostrophic transport via oceanic and atmospheric teleconnections [ABSTRACT FROM AUTHOR]

Comprehensive morphometric and hydrometeorological studies on Bacalar Lagoon, Mexico's largest tropical karstic lake and a significant aquatic system of the Yucatán Peninsula, are lacking. This study provides a detailed analysis of its bathymetry, morphometry, and hydrometeorological characteristics. The lake's main basin stretches more than 52.7 km in length, with widths varying from 0.18 km to 2.28 km. It has a volume of 554.4 million cubic meters, with an average depth of 8.85 m, reaching depths of up to 26 m in the north and featuring sub-lacustrine dolines in the south, with depths of 38 m, 48.5 m, and 63.6 m. The study reveals seasonal variations in surface water temperature, closely linked to air temperature (r = 0.89), and immediate responses of water levels to hydrometeorological events. Water level fluctuations also exhibit seasonal patterns that are correlated with regional aquifer conditions, with a lag of 2 months after seasonal rainfall. Interannual variability in rainfall and water levels was observed. From 2010 to 2012, rainfall consistently remained below its mean climatic value, due to a prolonged La Niña event, while the exceptionally wet conditions in 2020 were also associated with La Niña. Extreme and anomalous hydrometeorological events, such as those following tropical storm Cristobal in 2020, revealed the fragility of Bacalar Lagoon, causing a notable transformation in lake color and transparency, shifting it from its typical oligotrophic state to eutrophic conditions that lasted longer than a year. These color changes raise questions about the factors impacting ecological health in tropical karstic regions. Additional factors affecting water quality in the BL in 2020, such as deforestation, coastline changes, and urban growth, warrant further investigation. Our study can serve as a starting landmark. [ABSTRACT FROM AUTHOR]

El Niño Southern Oscillation, a global climate phenomenon, occurs in the tropical Pacific with an anomalous warming phase (El Niño) and a cooling phase (La Niña) spanning for 2–5 years. A substantial decline of Niño3.4 region's spring bloom chlorophyll-a concentration (Chl-a) is an intrinsic characteristic of the central Pacific during the El Niño onset period, which has been considered as a predictor of the El Niño by earlier studies. This study investigated the concept, a marked decline of spring bloom Chl-a as the predictor of the El Niño, using satellite-measured Chl-a from MODIS Aqua for the period 2003–2023 in relation to the Oceanic Niño Index (ONI) and subsurface properties. It revealed that Chl-a exhibits a significant inverse relationship with ONI during past El Niño events. An intense, continuous decreasing phase of Chl-a during the spring season (February–April) of 2023 may indicate the onset of El Niño. The decline of the spring bloom Chl-a concentration has been explained as the response to the weakening of the upwelling strength in the study domain and associated nutrient depletion in the euphotic zone. [ABSTRACT FROM AUTHOR]

In the recent years, extreme temperature i.e. cold in winter and warm in summer has been observed in the coastal Odisha state in the east part of India. Hydro-meteorological disasters such as floods, droughts, heat waves and cold spells being experienced nowadays are unprecedented in living memory. In this work the climate variability over the coastal Odisha region is quantified considering the temperature parameter. A climate departure index (CDI) of three versions (simple, absolute and least-square) are calculated using monthly, annually and seasonally maximum, minimum as well as mean temperature form seven stations in the costal Odisha for the period 1969 to 2018 for assessing the degree of normal/unusual/extreme of a particular year in compared to the long-term average for the specific coast under consideration. Temperature time series data for the period 1969 to 2018 are homogenized by using the relative comparison between station observations and composite reference series by calculating CDI. Results indicates that CDI values of least-square on all cases are comparatively greater than simple and absolute CDIs. Least-square method is the appropriate method for determining the category of a year or a month or a season in terms of the temperature variation. Analysis based on mean temperature infers that only twenty extreme seasons are observed in monsoon season while three normal are observed during the month of October i.e., in post-monsoon season over the coastal Odisha. The relationship of climatic event including El Nino or La Nina feature of a particular year with respect to CDI is also investigated. The climatic variability is very high on some of the years based on analysis of index values of annual average of the temperatures (maximum, minimum and mean) over a region. [ABSTRACT FROM AUTHOR]

El Niño–Southern Oscillation (ENSO) phases and flavors, as well as off-equatorial climate modes, strongly influence sea surface temperature (SST) patterns in the eastern tropical Pacific and downstream climate. Prior studies rely on EOFs (which characterize fractional SST variance) to diagnose climate-scale SST structures, limiting the ability to link individual ENSO flavors with downstream phenomena. Hierarchical and k-means clustering methods are used to construct Eastern Pacific patterns from the ERSST dataset spanning 1950 to 2021. Cluster analysis allows for the direct linkage of individual SST years/seasons to ENSO phase, providing insight into ENSO flavors and associated downstream impacts. In this study, four clusters are revealed, each depicting unique SST patterns influenced by ENSO and Pacific Meridional Mode (PMM) phases. A case study demonstrating the utility of the clusters was also carried out using accumulated cyclone energy (ACE) in the Atlantic and Eastern Pacific basins. Results showed that Eastern Pacific (EP) El Niño suppresses Atlantic tropical cyclone (TC) activity, while Central Pacific (CP) La Niña enhances it. Further, EP El Niño, coupled with positive PMM, amplifies ACE. Ultimately, the methods used herein offer a cleaner analysis tool for identifying dominant SSTA patterns and employing those patterns to diagnose downstream climatic effects. [ABSTRACT FROM AUTHOR]

Much of eastern and southeastern Australia (SEAUS) suffered from historic flooding, heat waves, and drought during the quasi-decadal 2010–2022 period, similar to that experienced globally. During the double La Niña of the 2010–2012 period, SEAUS experienced record rainfall totals. Then, severe drought, heat waves, and associated bushfires from 2013 to 2019 affected most of SEAUS, briefly punctuated by record rainfall over parts of inland SEAUS in the late winter/spring of 2016, which was linked to a strong negative Indian Ocean Dipole. Finally, from 2020 to 2022 a rare triple La Niña generated widespread extreme rainfall and flooding in SEAUS, resulting in massive property and environmental damage. To identify the key drivers of the 2010–2022 period's precipitation and temperature extremes due to accelerated global warming (GW), since the early 1990s, machine learning attribution has been applied to data at eight sites that are representative of SEAUS. Machine learning attribution detection was applied to the 52-year period of 1971–2022 and to the successive 26-year sub-periods of 1971–1996 and 1997–2022. The attributes for the 1997–2022 period, which includes the quasi-decadal period of 2010–2022, revealed key contributors to the extremes of the 2010–2022 period. Finally, some drivers of extreme precipitation and temperature events are linked to significant changes in both global and local tropospheric circulation. [ABSTRACT FROM AUTHOR]

The two phases of El‐Niño‐Southern Oscillation (ENSO) influence both regional and global terrestrial vegetation productivity on inter‐annual scales. However, the major drivers for the regional vegetation productivity and their controlling strengths during different phases of ENSO remain unclear. We herein disentangled the impacts of two phases of ENSO on regional carbon cycle using multiple data sets. We found that soil moisture predominantly accounts for ∼40% of the variability in regional vegetation productivity during ENSO events. Our results showed that the satellite‐derived vegetation productivity proxies, gross primary productivity from data‐driven models (FLUXCOM) and observation‐constrained ecosystem model (Carbon Cycle Data Assimilation System) generally agree in depicting the contribution of soil moisture and air temperature in modulating regional vegetation productivity. However, the ensemble of weakly constrained ecosystem models exhibits non‐negligible discrepancies in the roles of vapor pressure deficit and radiation over extra‐tropics. This study highlights the significance of water in regulating regional vegetation productivity during ENSO. Plain Language Summary: ENSO, a significant climate phenomenon, profoundly influences ecosystem productivity from regional to global scales. Yet, accurately pinpointing the attributions of different climate factors that control Gross Primary Productivity (GPP) during ENSO events remains challenging, partly due to large uncertainties in existing GPP data. Through extensive analysis using various data sets, we found that soil moisture plays a dominant role in controlling GPP across most continents. This implies that current terrestrial biosphere models might underestimate the importance of soil moisture in driving productivity during ENSO events. Addressing this gap in understanding is crucial for refining and properly constraining the related processes in terrestrial biosphere models. Key Points: Soil moisture predominantly governs vegetation productivity changes during El‐Niño‐Southern Oscillation (ENSO) eventsSatellite‐derived vegetation indices consistently support the predominant influence of water on vegetation productivityENSO triggers varying effects on vegetation productivity across different regions, with distinct impacts during El Niño and La Niña [ABSTRACT FROM AUTHOR]

Atlantic hurricane season length is important for emergency management preparation, motivating the need to understand its variability and change. We investigated the influence of ocean variability on Atlantic hurricane season length in observations and a future climate simulated by the Energy Exascale Earth System Model (E3SM). We found that multiple factors influence hurricane season length, through their influence on season start and end. Warm western subtropical Atlantic sea‐surface temperature anomalies (SSTAs) during boreal spring (before the official hurricane season start) drive early starts to the hurricane season, and vice versa for cool SSTAs. Meanwhile, La Niña in autumn (before the official hurricane season end) drives late ends to the hurricane season, and vice versa for El Niño. E3SM projects a 27‐day increase in future Atlantic hurricane season length given La Niña and warm northern tropical Atlantic SSTAs. This research documents sources of predictability for Atlantic hurricane season length. Plain Language Summary: Atlantic hurricane season length is important for emergency management preparation, motivating the need to understand its variability and change. We investigated the influence of ocean variability on Atlantic hurricane season length in historical observations and a future climate simulated by a global climate model. We found that multiple factors influence Atlantic hurricane season length, through their influence on season start and end. Warm sea‐surface temperature anomalies (SSTAs) in the western subtropical Atlantic during boreal spring (before the official hurricane season start) drive early starts to the hurricane season, and vice versa for cool SSTAs. Meanwhile, La Niña events in autumn (before the official hurricane season ends) drive late ends to the hurricane season, and vice versa for El Niño. The global model projects a 27–41‐day increase in future Atlantic hurricane season length. This research documents sources of predictability for Atlantic hurricane season length. Key Points: Multiple oceanic factors influence Atlantic hurricane season length, by influencing the first and last Tropical Storm of the seasonA warm western subtropical Atlantic ocean in boreal spring drives early hurricane season starts; La Niña in autumn drives late season endsFuture Atlantic hurricane season length increases by 27 days in Energy Exascale Earth System Model simulations given La Niña and a positive Atlantic Meridional Mode [ABSTRACT FROM AUTHOR]

The Surface Ocean CO2 Atlas (SOCAT) of CO2 fugacity (fCO2) observations is a key resource supporting annual assessments of CO2 uptake by the ocean and its side effects on the marine ecosystem. SOCAT data are usually released with a lag of up to 1.5 years which hampers timely quantification of recent variations of carbon fluxes between the Earth System components, not only with the ocean. This study uses a statistical ensemble approach to analyze fCO2 with a latency of one month only based on the previous SOCAT release and a series of predictors. Results indicate a modest degradation in a retrospective prediction test for 2021–2022. The generated fCO2 and fluxes for January–August 2023 show a progressive reduction in the Equatorial Pacific source following the La Niña retreat. A breaking‐record decrease in the northeastern Atlantic CO2 sink has been diagnosed on account of the marine heatwave event in June 2023. Plain Language Summary: There is a growing need to monitor carbon emissions and removals over the globe in near real time in order to correctly interpret changes in CO2 concentrations as they unfold. For the oceans, the best information comes from measurements of the surface ocean CO2 fugacity (fCO2) by the international marine carbon research community. So far, this data is mostly available 6 to 18 months behind real time after collection, qualification, harmonization, and processing. Here, we show that a set of biological, chemical, and physical predictors available in near real time, allows the information contained in the "old" fCO2 measurements to be transferred over time. Based on a statistical technique, we combine all these data sources to estimate global monthly maps of fCO2 and of CO2 fluxes at the air‐sea interface within one month behind real time and with good accuracy. Key Points: We demonstrate the capacity of statistical models to generate global maps of fCO2 and air‐sea flux with a latency reduced to one monthA decrease in the CO2 source for January to August 2023 diagnosed in the tropical Pacific coheres with the retreat of the La Niña eventAn unusual northeastern Atlantic sink reduction diagnosed for June 2023 is linked to record heat and exceptionally low winds [ABSTRACT FROM AUTHOR]

Drought events have increased in frequency and severity in recent years, and result in significant economic losses. Although the Brazilian semi-arid northeast has been historically associated with the impacts of drought, drought is of national concern, from 2011–2019, drought events were recorded in all Brazilian territories. Droughts can have major consequences for agricultural production, which is of particular concern given the importance of soybeans for socio-economic development. Due to its regional heterogeneity, it is important to develop accurate drought forecast and assessment tools for Brazil. We explore machine learning as a method to forecast the vegetation health index (VHI), for large scale monthly drought monitoring across agricultural land in Brazil. Furthermore, we also determine spatio-temporal drivers of VHI across the wide variation in climates, as well as evaluate machine learning performance for ENSO variation, forecasting of the onset of drought impact, and how the trade off between spatial variation and sample size affects model performance. We show that machine learning methods such as gradient boosting methods are able to more easily forecast vegetation health in the north and north east Brazil than south Brazil, and perform better during La Niña events than El Niño events. Drought impacts which reduce VHI below the commonly used 40 % threshold can be forecast across Brazil with similar model performance. SPEI is shown to be a useful indicator of drought impact, with 3 month accumulation periods preferred over 1 and 2 months. Results aim to inform future developments in operational drought monitoring at the National Center for Monitoring and Early Warning of Natural Disasters in Brazil (CEMADEN). Future work should build upon methods discussed here to improve drought forecasts for agricultural drought response and adaptation. [ABSTRACT FROM AUTHOR]

The ENSO phase locking to the annual cycle is investigated by applying a spatiotemporal oscillator (STO) model, in which the annual cycle of the climatological thermocline depth and its associated parameter are introduced. It is easy to derive its analytic solution, which demonstrates a harmonic oscillation of a combined variable. The ENSO phase locking can be theoretically proven by discussing the distribution of the calendar months of the peak time of the sea surface temperature anomaly (SSTA) time series. The calendar months of the peak time can be divided into two parts. The first part can evenly distribute in any a month of a year and hence has no phase locking feature whereas the second part, directly associated with the annual cycle, adds an increment onto the first part to make it move toward the phase of the annual cycle to realize the phase locking feature. This is the physical mechanism of the ENSO phase locking. With observed seasonal variation of the climatological thermocline depth, the Niño-3.4 index time series approach to extreme values in November was calculated with higher probability, reproducing the observed phase locking phenomenon quite well. The maximum probability of the calendar month that the ENSO peak time occurs is directly determined by the phase of the annual cycle and the stronger the annual cycle is, the larger the maximum probability is. Significance Statement: El Niño–Southern Oscillation (ENSO) events tend to be strongest in the boreal wintertime. This phenomenon is called ENSO phase locking. This study investigates the dynamics of ENSO phase locking to the annual cycle by introducing the annual cycle to a spatiotemporal oscillator (STO) model that can deal with the complex spatial and temporal variations in SSTAs. The analytic solution can be obtained and then the phase locking feature can be theoretically proven and numerically testified. Therefore, the dynamics and the mechanism of ENSO phase locking can be comprehensively understood. It may be beneficial for the community to have a better understanding of this complex phenomenon. [ABSTRACT FROM AUTHOR]

A rare compound hot and drought (CHD) event occurred in the Yangtze River Basin (YRB) in the summer of 2022, which brought serious social crisis and ecological disaster. The analysis of the causes, spatiotemporal characteristics and impacts of this event is of great significance and value for future drought warning and mitigation. We used the Gravity Recovery and Climate Experiment (GRACE)/GRACE Follow-On (GRACE-FO) data, meteorological data, hydrological data and satellite remote sensing data to discuss the spatiotemporal evolution, formation mechanism and the influence of the CHD event. The results show that the drought severity caused by the CHD event was the most severe during 2003 and 2022. The CHD event lasted a total of five months (from July to November), and there were variations in the damage in different sub-basins. The Wu River Basin (WRB) is the region where the CHD event lasted the longest, at six months (from July to December), while it also lasted four or five months in all the other basins. Among them, the WRB, Dongting Lake Rivers Basin (DLRB) and Mainstream of the YRB (MSY) are the three most affected basins, whose hot and drought severity values are 7.750 and −8.520 (WRB), 7.105 and −9.915 (DLRB) and 6.232 and −9.143 (MSY), respectively. High temperature and low precipitation are the direct causes of the CHD event, and the underlying causes behind this event are the triple La Niña and negative Indian Ocean Dipole event. The two extreme climate events made the Western Pacific Subtropical High (WPSH) unusually strong, and then the WPSH covered a more northerly and westerly region than in previous years and remained entrenched for a long period of time over the YRB and its adjacent regions. Moreover, this CHD event had a devastating impact on local agricultural production and seriously disrupted daily life and production. Our results have implications for the study of extreme disaster events. [ABSTRACT FROM AUTHOR]

Satellite ocean color and sea surface temperature (SST) observations from 2012 to 2021 and sea surface salinity (SSS) measurements from the Soil Moisture Active Passive (SMAP) mission from 2015 to 2021 are used to characterize and quantify the seasonal and interannual variability in the physical, optical, and biological sea surface features in the Costa Rica Thermal Dome (CRTD) region. High-resolution climatology and the seasonal variability in SST, SSS, and ocean color properties are produced. Chlorophyll-a (Chl-a) concentration, SST, and SSS show these three properties are linked with similar spatial patterns and seasonal variations, i.e., elevated Chl-a concentrations, match the depressed SST and increased SSS and vice versa. This reflects that the physical driving force is the same for these three ocean properties and implies that nutrient supply associated with the physical processes is the major driver for the seasonal biological variability. The interannual changes in Chl-a, SST, and SSS also show that these three ocean properties are consistent among themselves. The positive (negative) Chl-a anomaly generally occurs with negative (positive) SST anomaly and enhanced (reduced) SSS. The in situ measurements evidently show that the subsurface ocean dynamics in the upper 100 m controls the sea surface variability for Chl-a, SST, and SSS. We report that no significant enhancement of Chl-a is observed in the CRTD region during the central Pacific (CP)-type 2020–2021 La Niña event, while Chl-a changes are significant in the other three of four ENSO events between 2012 and 2021. Furthermore, the difference in Chl-a variability driven by the CP-type ENSO and eastern Pacific (EP)-type ENSO is further discussed. [ABSTRACT FROM AUTHOR]

This study assesses the variability of coastal extreme sea levels globally by utilizing nearly three decades of along-track, multi-mission satellite altimetry data. An altimetry-based global coastal database of the non-tidal residual sea level component has been produced. The climate variability of extremes is modeled through a parametric, non-stationary statistical model. This model captures intra-annual, inter-annual and long-term variations in non-tidal residual return levels. Comparisons with tide gauge data demonstrate the ability of altimetry data to capture the variability of coastal extreme sea levels. Our findings reveal a greater complexity in the monthly variability patterns of non-tidal residual extremes in tropical latitudes, often exhibiting multiple storm periods, contrasting with coasts in extratropical latitudes, which are mostly controlled by a winter–summer pattern. This study also highlights the significant influence of established climate circulation patterns on sea level extremes. The positive phase of the Arctic Oscillation pattern leads to increases of over 25% in non-tidal residual return levels in Northwestern Europe with respect to a neutral phase. Furthermore, return levels in the western coast of Central America could be 50% higher during El Niño compared to La Niña. Our results show a robust increasing trend in non-tidal residual return levels along most global coastlines. A comparative analysis shows that variations during the 1995–2020 period were primarily driven by intra-annual variations. [ABSTRACT FROM AUTHOR]

The North Pacific sea surface temperature (SST) has a profound climatic influence. The El Niño‐Southern Oscillation (ENSO) significantly impacts the North Pacific SST; however, the influence of the distinct phases of ENSO on SST predictability remains unclear. To overcome the model limitations, this study assessed SST predictability under diverse ENSO phases using reanalysis. The predictability limit of the North Pacific SST under La Niña (8.4 months) is longer than that under Neutral (5.9 months) and El Niño (5.5 months) conditions, which unveils asymmetry. This asymmetry mirrors contemporary multimodal prediction skills. Error growth dynamics reveal La Niña's robust signal strength with a slow error growth rate, in contrast to El Niño's weaker signal and faster error growth. There exhibits intermediate signal strength and elevated error growth in Neutral condition. Physically, predictability signal strength aligns with SST variability, whereas the error growth rate correlates with atmospheric‐ocean heating anomalies. La Niña, which induces positive heating anomalies, minimizes the impact of atmospheric noise, resulting in lower error growth. The result is beneficial for improving North Pacific SST predictions. Plain Language Summary: The North Pacific sea surface temperature (SST) significantly impacts global climate, particularly in East Asia and the United States. Accurate prediction of North Pacific SST, which is crucial for seasonal and interannual forecasting, remains a focal point in atmospheric and oceanic research. This study investigates how the El Niño‐Southern Oscillation (ENSO) influences SST predictability in the North Pacific during different phases (El Niño, La Niña, Neutral). Using reanalysis data, this research introduces the concept of predictability limit (PL), revealing an asymmetry in the PL response: La Niña extends the PL to 8.4 months, El Niño shortens it to 5.5 months, and Neutral falls in 5.9 months. This asymmetry aligns with the existing prediction skills. Examining the error growth dynamics, La Niña exhibits a robust SST signal with slower error growth, whereas El Niño displays a weaker signal with faster error growth. Neutral, meanwhile, shows a high signal strength but large error growth. This study sheds light on these differences in SST predictability and provides valuable insights for refining North Pacific SST predictions through model advancements. Key Points: El Niño‐Southern Oscillation phases asymmetrically impact North Pacific sea surface temperature (SST) predictability: El Niño (5.5 months), La Niña (8.4 months), Neutral (5.9 months)Error growth dynamics vary: La Niña displays strong signals with slow growth, El Niño exhibits weak signals and rapid growthA positive heating anomaly from La Niña reduces atmospheric noise impact, resulting in a smaller error growth rate of the North Pacific SST [ABSTRACT FROM AUTHOR]

In the California Current System (CCS), changes in the phenology (i.e., seasonal timing) of coastal upwelling alter the functioning of this productive marine ecosystem. Recently developed coastal upwelling indices that account for upwelling strength and nutrient flux to the surface provide a more complete understanding of bottom‐up forcing in the region. Using these indices, we describe CCS upwelling phenological variability in vertical transport and nutrient flux. Physical and biogeochemical spring transitions generally co‐occur in winter or spring, followed by increased upwelling and nutrient flux. In the latter half of the year, upwelling continues but nutrient flux wanes as declining source nutrient concentrations limit the biological efficacy of coastal upwelling. Earlier spring transitions and higher season‐integrated upwelling intensity occur during strong La Niña events at all latitudes, driven largely by stronger alongshore wind stress. Understanding phenological changes in coastal upwelling is critical, as they could have significant ecosystem consequences. Plain Language Summary: In the California Current System (CCS), coastal upwelling carries nutrient‐rich waters to the surface, supporting primary production and driving the coastal ecosystem. This upwelling varies on a seasonal and interannual basis, as reflected in recently developed indices that account for the amount of water upwelled to the surface as well as the amount of nutrients carried in that water. Generally upwelling and nutrient transport are high in the first half of the year. Upwelling persists into the second half of the year, but nutrient transport decreases as the deep‐water sources of these nutrients are depleted. Upwelling in the CCS is also affected by the El Niño Southern Oscillation. During La Niña conditions, strong trade winds enhance upwelling and nutrient transport on the California coast. This paper presents regional, seasonal and interannual patterns of upwelling and nutrient delivery in the CCS, which are important drivers of change to this coastal ecosystem. Key Points: We define new upwelling phenology indices for the California Current System that include nutrient transportWe identify spatial, seasonal, and interannual patterns of upwelling and nutrient deliveryWe relate the physical mechanisms of coastal upwelling with its biological efficacy [ABSTRACT FROM AUTHOR]

Recent observations suggest that El Niño–Southern Oscillation (ENSO) impacts basal melting of West Antarctic ice shelves, yet sparse ocean observations limit our understanding of the associated processes. Here we investigate how ENSO events modulate subsurface West Antarctic shelf temperatures using high‐resolution global ocean‐sea ice model simulations. During El Niño, the subsurface shelf warming between 150 m and the shelf bottom can be up to 0.5°C in front of ice shelves. This warming arises from a weaker Amundsen Sea Low (ASL) and weaker coastal easterlies that reduce on‐shelf Ekman transport of cold surface waters, enabling enhanced transport of warm Circumpolar Deep Water (CDW) onto the shelf. A largely opposite response occurs during La Niña, with a stronger ASL and stronger Ekman transport that results in less cross‐shelf CDW transport and cooling in the subsurface. These findings have implications for interpreting basal melting on interannual to decadal time‐scales in West Antarctica. Plain Language Summary: El Niño‐Southern Oscillation (ENSO) is the Earth's dominant year‐to‐year climate variation. The impacts of its two phases, El Niño and La Niña, extend from the tropics to Antarctica through atmospheric waves. Past studies have suggested that West Antarctic ice shelves melt more during El Niño because of warmer ocean waters at the ice shelf bases. However, oceanic changes during El Niño lead to warming on the shelf near the ice which is difficult to isolate. That is because ENSO is only one of many drivers that impact shelf water temperatures. In this work, we simulate isolated ENSO events using an ocean circulation model. We show that during El Niño, the on‐shelf flow of cold surface waters in West Antarctica, driven by coastal easterly winds, is reduced because the winds weaken. To balance out this mass deficit at the surface, more warm CDW flows onto the continental shelf below. During La Niña, we see a largely opposite response. Stronger coastal easterlies increase the on‐shelf flow of cold surface waters and less CDW is flowing onto the shelf. Our results show the link between ENSO and mass loss of the West Antarctic ice shelves and ice sheet. Key Points: Ocean‐sea ice model simulations of El Niño and La Niña events illustrate how they modulate West Antarctic shelf temperaturesEl Niño weakens coastal easterlies, reduces on‐shelf Ekman flow of cold waters, increasing cross‐shelf flow of warm Circumpolar Deep Water (CDW)The La Niña shelf circulation response is largely opposite and reduces cross‐shelf transport of warm CDW [ABSTRACT FROM AUTHOR]

The response of the North Atlantic large‐scale circulation to El Niño–Southern Oscillation (ENSO) exhibits distinct differences between early (November–December) and late (January–February) winter. However, the reasons for this are unclear, particularly regarding the early winter response. Here we examine the role of storm‐track dynamics in influencing the intraseasonal variability of the ENSO teleconnection to the North Atlantic. During late winter there a broad weakening of the eddy heat flux upstream of the North Atlantic storm track during the El Niño phase, which is associated with a broad southward jet shift across North America and the North Atlantic. The late winter response is reinforced by synoptic eddies through enhanced cyclonic wave breaking, consistent with previous studies. However, a stronger teleconnection occurs during early winter. There are modest changes in the North Atlantic eddy heat flux, but strong changes in the upper‐level storm track associated with ENSO, with increased anticyclonic wave breaking during El Niño reinforcing the jet across the central North Atlantic. During early winter there are less frequent northern eddy‐driven jet occurrences in El Niño years and more frequent northern eddy‐driven jet occurrences in La Niña years. These poleward North Atlantic jet excursions typically follow peaks in the eddy heat flux; however, in El Niño years this relationship breaks down and the jet does not transition to the northern position as frequently, despite no clear changes in the upstream eddy heat flux. Composite analysis reveals that precursor storm‐track anomalies upstream over the eastern North Pacific/North America are important in suppressing the poleward jet excursions. These precursors map onto the seasonal mean North Pacific storm‐track anomalies during El Niño. Measured across all years, there is a clear relationship between the mean early winter eastern North Pacific storm‐track activity and eastern North Atlantic eddy‐driven jet, which can explain the early winter ENSO teleconnection to the North Atlantic. [ABSTRACT FROM AUTHOR]

This article explores the impact of consecutive La Niña events on the unusually high temperatures experienced in eastern China during the summer of 2022. It examines the interactions between various systems, including the negative Indian Ocean Dipole phase and the strengthening of the West Pacific Subtropical High and the Iranian High, which contributed to the high terrestrial temperature anomalies. The study also analyzes the role of empirical orthogonal function modes in generating high temperatures in eastern China. The findings emphasize the importance of understanding the effects of La Niña events on temperature and weather patterns in the Asia-Pacific region for climate predictions and preparedness. The article also discusses the relationship between La Niña, the negative phase of the Indian Ocean Dipole (IOD), and heatwaves in East Asia. It investigates the distribution and formation mechanisms of variable fields during La Niña years and the response of the negative phase of IOD to La Niña. The research uses statistical methods and analysis techniques to explore these connections and potentially improve predictions of heatwaves in the future. The study further examines the abnormal heatwave experienced in East Asia and the Middle East during the summer of 2022 and the challenges in predicting such events. It analyzes temperature anomalies, wind fields, and sea surface temperature in the Pacific and Indian Oceans during La Niña events and identifies the contribution of the IOD, height field anomalies, and circulation fields to heatwaves. The article also discusses the relationship between La Niña events, the negative phase of the Indian Ocean Dipole (IOD [Extracted from the article]

Although the summers of 2021 and 2022 are both in the two successive La Niña decaying stages and under the same climate background of negative Pacific Decadal Oscillation (PDO) phase and global warming trend, they exhibit significantly different and even opposite precipitation patterns in the Yangtze River Valley (YRV) as well as in the Indian monsoon region (IMR). In contrast to the abundant precipitation and lower temperature in the YRV in summer 2021, in summer 2022 the YRV experiences severe drought and extremely high temperatures, which is also accompanied by Mega‐floods in the IMR. This study identifies the joint influence of sea surface temperature anomalies (SSTAs) in Niño4 and Barents Sea (BS) regions as the underlying cause for the contrast YRV precipitation anomalies in the summers of 2021 and 2022. Specifically, the cold SSTAs in both Niño4 and BS regions in summer 2021 favor stronger and southward shifted western North Pacific subtropical high (WNPSH), leading to more precipitation in the YRV, which is however generally reversed but more intense in summer 2022 because of the synergistic effect of cold Niño4 and warm BS SSTAs. Moreover, the induced extreme precipitation in the IMR in summer 2022, which is absent in summer 2021 due to the offsetting effect of cold SSTAs in both Niño4 and BS regions, in turn further strengthens the anomalous atmospheric circulations via its released large diabatic heating and serves as a relay pathway for the dramatic drought and heat wave in the YRV. Plain Language Summary: The El Niño‐Southern Oscillation (ENSO) is known to be the most significant interannual signal and one of the major factors for summer precipitation anomaly in East Asia. Nevertheless, the two summers of 2021 and 2022 are characterized by almost opposite precipitation patterns in the Yangtze River Valley (YRV) even though they are both in the two successive La Niña decaying stages. Our study demonstrates that except for the cold sea surface temperature anomalies (SSTAs) with obvious differences in both intensity and position in Niño4 region, the opposite SSTAs in Barents Sea region may play a dominant role in determining the strong contrast precipitation patterns in the YRV as well as in the Indian monsoon region (IMR). As the result of the synergistic effect of cold Niño4 and warm BS, the extreme IMR precipitation also serves as a relay pathway for the dramatic drought and heat wave in the YRV in summer 2022. It suggests that to clearly understand and accurately predict the climate anomalies in East Asia should consider the mid‐high latitude signals besides the tropical ENSO signal, especially in the context of global warming when the signals and influences from the mid‐high latitudes are becoming more and more prominent. Key Points: The two La Niña decaying summers in 2021 and 2022 see nearly opposite precipitation patterns in Yangtze River valleySynergistic effect of cold Niño4 region and warm Barents Sea is the essential cause for the extreme summer drought in Yangtze River valleyIndian monsoon precipitation plays a relaying role in linking the SST forcing and the Yangtze River valley precipitation via teleconnection [ABSTRACT FROM AUTHOR]

A sequence of torrential rainstorms pounded Pakistan in the summer of 2022, shattering records by massive margins (7 sigma). The severe socioeconomic damages underscore the urgency of identifying its dynamic drivers and relationship with human-induced climate change. Here, we find that the downpours were primarily initiated by the synoptic low-pressure systems, whose intensity and longevity far exceeded their counterparts in history as fueled by a historically-high cross-equatorial moisture transport over the Arabian Sea. The moisture transport has been trending upward since the 1960s and, in 2022, along with the anomalous easterly moisture influx caused by the combination of La Niña and negative Indian Ocean Dipole events, created a corridor of heavy rainfall extending from central India toward southern Pakistan. While it is not yet established whether the observed trend of the cross-equatorial moisture transport has exceeded natural variability, model-based analysis confirms that it is consistent with the fingerprint of anthropogenic climate warming and will raise the likelihood of such rare events substantially in the coming decades. [ABSTRACT FROM AUTHOR]

Extreme El Niño events have outsized impacts and strongly contribute to the El Niño Southern Oscillation (ENSO) warm/cold phase asymmetries. There is currently no consensus on the respective importance of oceanic and atmospheric nonlinearities for those asymmetries. Here, we use atmospheric and oceanic general circulation models that reproduce ENSO asymmetries well to quantify the atmospheric nonlinearities contribution. The linear and nonlinear components of the wind stress response to Sea Surface Temperature (SST) anomalies are isolated using ensemble atmospheric experiments, and used to force oceanic experiments. The wind stress-SST nonlinearity is dominated by the deep atmospheric convective response to SST. This wind-stress nonlinearity contributes to ~ 40% of the peak amplitude of extreme El Niño events and ~ 55% of the prolonged eastern Pacific warming they generate until the following summer. This large contribution arises because nonlinearities consistently drive equatorial westerly anomalies, while the larger linear component is made less efficient by easterly anomalies in the western Pacific during fall and winter. Overall, wind-stress nonlinearities fully account for the eastern Pacific positive ENSO skewness. Our findings underscore the pivotal role of atmospheric nonlinearities in shaping extreme El Niño events and, more generally, ENSO asymmetry. [ABSTRACT FROM AUTHOR]

Today's Arctic is characterized by a lengthening of the sea ice melt season, but also by fast and at times unseasonal melt events. Such anomalous melt cases have been identified in Pacific and Atlantic Arctic sector sea ice studies. Through observational analyses, we document an unprecedented, simultaneous marginal ice zone melt event in the Bering Sea and Labrador Sea in March of 2023. Taken independently, variability in the cold season ice edge at synoptic time scales is common. However, such anomalous, short-term ice loss over either region during the climatological sea ice maxima is uncommon, and the tandem ice loss that occurred qualifies this as a rare event. The atmospheric setting that supported the unseasonal melt events was preceded by a sudden stratospheric warming event that, along with ongoing La Niña teleconnections, led to positive tropospheric height anomalies across much of the Arctic and the development of anomalous mid-troposphere ridges over the ice loss regions. These large-scale anticyclonic centers funneled extremely warm and moist airstreams onto the ice causing melt. Further analysis identified the presence of atmospheric rivers within these warm airstreams whose characteristics likely contributed to this bi-regional ice melt event. Whether such a confluence of anomalous wintertime events associated with troposphere-stratosphere coupling may occur more often in a warming Arctic remains a research area ripe for further exploration. [ABSTRACT FROM AUTHOR]

In 2023 Amazonia experienced both historical drought and warm conditions. On October 26th 2023 the water levels at the port of Manaus reached its lowest record since 1902 (12.70 m). In this region, October monthly maximum and minimum temperature anomalies also surpassed previous record values registered in 2015 (+ 3 °C above the normal considering the 1981–2020 average). Here we show that this historical dry and warm situation in Amazonia is associated with two main atmospheric mechanisms: (i) the November 2022–February 2023 southern anomaly of vertical integrated moisture flux (VIMF), related to VIMF divergence and extreme rainfall deficit over southwestern Amazonia, and (ii) the June–August 2023 downward motion over northern Amazonia related to extreme rainfall deficit and warm conditions over this region. Anomalies of both atmospheric mechanisms reached record values during this event. The first mechanism is significantly correlated to negative sea surface temperature (SST) anomalies in the equatorial Pacific (November–February La Niña events). The second mechanism is significantly correlated to positive SST anomalies in the equatorial Pacific, related to the impacts of June–September El Niño on the Walker Circulation. While previous extreme droughts were linked to El Niño (warmer North Tropical Atlantic SST) during the austral summer (winter and spring), the transition from La Niña 2022–23 to El Niño 2023 appears to be a key climatic driver in this record-breaking dry and warm situation, combined to a widespread anomalous warming over the worldwide ocean. [ABSTRACT FROM AUTHOR]

The article analyzes the correlation between winds in the Strait of Gibraltar in summer, monsoons, and ENSO. During the positive phase of ENSO, El Niño, there is a higher frequency of westerly winds in the Strait of Gibraltar, while during the La Niña phase, easterly winds prevail. The Mediterranean climate in summer is influenced by the summer monsoon in India and is limited to certain continental regions. Additionally, the covariability between the summer monsoon in India and ENSO is documented, where during El Niño events, the monsoon is weaker, and during La Niña events, the monsoon is stronger. The relationship between the ENSO climate phenomenon and temperature anomalies in the upper and middle troposphere in northern Africa is also analyzed, observing that these relationships vary on a multi-decadal timescale. It is suggested that these variations may be related to the modulation of upper troposphere temperature in subtropical Africa and Asia. Furthermore, the hypothesis is raised that the intensity of the correlation may have multi-decadal variability in phase with the variability of the West African monsoon. Finally, it is highlighted that there is a weak upward movement on average in the Iberian Peninsula, which can generate significant storms in the eastern interior due to low surface pressures that allow the entry of Mediterranean moist air at low levels. [Extracted from the article]

In recent years, Geoscience Australia has undertaken a successful continental-scale validation program, targeting Landsat and Sentinel analysis-ready data surface reflectance products. The field validation model used for this program was successfully built upon earlier studies, and the measurement uncertainties associated with these protocols have been quantified and published. As a consequence, the Australian earth observation community was well-prepared to respond to the United States Geological Survey (USGS) call for collaborators with the 2021 Landsat 8 (L8) and Landsat 9 (L9) underfly. Despite a number of challenges, seven validation datasets were captured across five sites. As there was only a single 100% overlap transit across Australia, and the country was amidst a strong La Niña climate cycle, it was decided to deploy teams to the two available overpasses with only 15% side lap. The validation sites encompassed rangelands, chenopod shrublands, and a large inland lake. Apart from instrument problems at one site, good weather enabled the capture of high-quality field data allowing for meaningful comparisons between the radiometric performance of L8 and L9, as well as the USGS and Australian Landsat analysis-ready data processing models. Duplicate (cross-calibration) spectral sampling at different sites provides evidence of the field protocol reliability, while the off-nadir view of L9 over the water site has been used to better compare the performance of different water and atmospheric correction processing models. [ABSTRACT FROM AUTHOR]

To explain the recent three-year La Niña event from 2020 to 2022, which has caused catastrophic weather events worldwide, Fasullo et al. (2023) demonstrated that the increase in biomass aerosol resulting from the 2019–20 Australian wildfire season could have triggered this multi-year La Niña. Here, we present compelling evidence from paleo-proxies, utilizing a substantial sample size of 26 volcanic eruptions in the Southern Hemisphere (SH), to support the hypothesis that ocean cooling in the SH can lead to a multi-year La Niña event. This research highlights the importance of focusing on the Southern Ocean, as current climate models struggle to accurately simulate the Pacific response driven by the Southern Ocean. [ABSTRACT FROM AUTHOR]

In this study, a future projection of marine cold spells (MCSs) over the tropical Indian Ocean is made using a fully coupled regional Earth system model, namely ROM, under two representative concentration pathways (RCPs): RCP4.5 and RCP8.5. In both RCPs, the future MCS properties have been estimated across three distinct time intervals: the near future (NF; 2010–2039), the middle future (MF; 2040–2069), and the far future (FF; 2070–2099). The future MCS computations were examined with respect to fixed historical baseline periods and varying baseline periods. MCSs were frequent, intense, and prolonged during the historical period. ROM effectively simulated these historical MCS metrics and their trends and outperformed the forcing general circulation model as well as the multimodel ensemble mean of Coupled Model Intercomparison Project phase 5 models. In the future, MCSs will cease to occur in ∼13% (4%), ∼56% (66%) and ∼69% (93%) of the area of the tropical Indian Ocean in the NF, MF, and FF respectively under the RCP4.5 (RCP8.5) scenario using a fixed historical baseline period. This departure of MCSs led to the disappearance of events, first identified over the Arabian Sea in both RCPs. The decrease in net heat flux and increase in wind speed contribute to the genesis and severity of MCS events. Further, during the El Niño regime, the MCS events dramatically decrease due to the basin‐wide warming, but during the La Niña phase, the MCS intensity and spatial range increase. This study further investigates the sensitivity of MCSs with the choice of baseline period. Adopting varying baseline periods over time does not result in the disappearance of MCSs but does produce declining trends in MCS activity, highlighting the need for careful consideration in choosing a baseline period. [ABSTRACT FROM AUTHOR]

Despite the complexity of the underlying processes, coupled climate models simulate fairly realistic El Niño–Southern Oscillation dynamics and teleconnections. However, there are many long‐standing errors that remain. We use the High Resolution Model Intercomparison Project suite of models to assess how El Niño–Southern Oscillation and its late‐winter teleconnection to the North Pacific changes when ocean resolution is quadrupled from 1° to 0.25°. We find that increased resolution eliminates large errors in the western extent of El Niño and La Niña sea‐surface temperature anomalies, and that there is some improvement in the asymmetry between El Niño and La Niña. In low‐resolution models, the teleconnections from El Niño and La Niña to the North Pacific are both underestimated and are centred too far west. With increased resolution, the position of the teleconnection is highly accurate during El Niño, but there is less improvement during La Niña. We find no significant improvements in teleconnection strength for either phase. Tropical mean‐state sea‐surface temperatures are found to be too cold by around 1°C throughout the central/eastern Pacific in low‐resolution models, but this bias is not present in high‐resolution models. Despite this, a large discrepancy between observed and modelled mean‐state tropical rainfall persists in high‐resolution models, which may limit improvements in the simulation of the La Niña teleconnection. [ABSTRACT FROM AUTHOR]

On 20 July, 2021, an extraordinary rainstorm occurred in Zhengzhou in Central‐North China, which caused hundreds of deaths and serious property damages, and affected 14 million people. The compound anomalous atmospheric circulations were found to be responsible for the occurrence of the extraordinary rainstorm in Zhengzhou, but the influence of large‐scale sea surface temperature anomaly (SSTA) and the contribution of climate change received less attention. This study conducts an attribution analysis based on atmospheric reanalysis and sea surface temperature (SST) observation data combined with Coupled Model Intercomparison Project Phase 6 (CMIP6) model simulation data. The results show that the return period for the extraordinary rainstorm was 250 years, which was caused by the interaction between the abnormally northerly shift of Western North Pacific Subtropical High (WNPSH) that was associated with the negative SSTA over the tropical central‐eastern Pacific (i.e., a moderate La Niña condition) and Typhoon In‐fa and Typhoon Cempaka. A persistent convergence was formed over Zhengzhou by transporting a large amount of water vapour to hinterland. The lagged response of La Niña affected WNPSH and the rainband in China. The attribution analysis shows that climate change due to anthropogenic forcings such as greenhouse gas emissions increased the risk of such a rainstorm event by 12% compared to the conditions under the natural forcings. Under the combined effects of anthropogenic forcings and La Niña, the risk of occurrence increased 47% compared to the effect of natural forcings only on similar precipitation events. This study suggests a synergistic effect of climate change and large‐scale tropical climate variability on compound extremes. [ABSTRACT FROM AUTHOR]

The results of a piControl experiment investigating general circulation models participating in the sixth phase of the Coupled Model Intercomparison Project (CMIP6) were examined. The global interannual variability in the monthly surface temperature (ST) and sea level pressure (SLP) anomalies was considered. The amplitudes of the fluctuations in the anomalies of these meteorological fields between opposite phases of the El Niño–Southern Oscillation (ENSO) were calculated. It was shown that most CMIP6 models reproduced fluctuations in the ST and SLP anomalies between El Niño and La Niña not only in the equatorial Pacific, but also throughout the tropics, as well as in the middle and high latitudes. Some of the CMIP6 models reproduced the global structures of the ST and SLP anomaly oscillations quite accurately between opposite phases of ENSO, as previously determined from observational data and reanalyses. It was found that the models AS-RCEC TaiESM1, CAMS CAMS-CSM1-0, CAS FGOALS-f3-L, CMCC CMCC-ESM2, KIOST KIOST-ESM, NASA GISS-E2-1-G, NCAR CESM2-WACCM-FV2, and NCC NorCPM1 reproduced strong ENSO teleconnections in regions beyond the tropical Pacific. [ABSTRACT FROM AUTHOR]

The number of chilling hours is responsible for maximizing budding and flowering in temperate climate fruit trees, and this number varies widely between years. An important source of variability is the occurrence of the ENSO - El Niño Southern Oscillation. With the intent of further understanding, the objective set was to analyze the influence of ENSO on chilling hours in Rio Grande do Sul State. To perform the analysis it was used data of air temperature - below 7.2 o C - from 24 meteorological stations. The results showed that when La Niña occurs, the percentage of chilling hours was above average for the period analyzed in all locations, and when El Niño occurs, the values were below average in 79% of the locations. The highest number of chilling hours, observed in each location, mainly occurred during the presence of La Niña and the lowest number was mainly observed during the occurrence of El Niño. The largest deviation (%) of chilling hours from the average occurred in May. Despite the month of July having the highest number of chilling hours, the occurrence of El Niño or La Niña does not show any difference between them. The month of September also shows no difference when comparing instances of El Niño and La Niña. [ABSTRACT FROM AUTHOR]

This paper scrutinizes Pakistan's acute water scarcity issues driven by population growth, diminishing supply, and recurrent droughts exacerbated by meteorological phenomena like La Nina. Regions such as Baluchistan and Sindh face severe water stress, jeopardizing livelihoods and potentially precipitating internal displacement, necessitating immediate and decisive governmental action. The absence of a coherent national water policy further complicates challenges in water storage, irrigation, and inter-provincial relations, potentially straining political dynamics. Through a comprehensive evaluation of Pakistan's water resources, this study identifies critical imperatives requiring urgent attention from policymakers. Proposed recommendations advocate for the development and implementation of a robust national water policy, strategic investments in modernized storage and irrigation infrastructure, promotion of water conservation initiatives, fostering inter-provincial collaboration, and the pursuit of cutting-edge sustainable water technologies. The successful execution of these measures would not only optimize water resource management but also underscore the government's commitment to ensuring national stability and prosperity amidst challenging environmental conditions. [ABSTRACT FROM AUTHOR]

The present study aims to investigate the influences of El Niño and Southern Oscillation (ENSO) events on chlorophyll biomass in the tropical Pacific under historical and RCP8.5 scenarios with simulations from the Community Earth System Model Large Ensemble (CESM‐LE) project. Large variance in surface chlorophyll concentrations is identified across the Peruvian Upwelling (PU), Equatorial Upwelling (EU), and Western Pacific (WP) regions within the tropical Pacific. Results suggest that responses of surface chlorophyll to ENSO in these regions are governed by different mechanisms. The increasing chlorophyll during La Niña is a consequence of increasing nutrients, influenced by local upwelling systems in the PU and EU regions, while the supplementary nutrients in the WP region arise from the eastern Pacific through stronger surface westward currents. Under RCP8.5 scenario, stronger water warming in the eastern equatorial Pacific leads to a remarkable reduction in the amplitudes of seasonal cycles and interannual variations of chlorophyll in both PU and EU regions. This results in less responsiveness of the chlorophyll biomass to El Niño and moderate La Niña compared to the historical period. However, though warming induces a decrease in chlorophyll concentrations in the WP region, the interannual variations of chlorophyll have shown an improvement in correlation with ENSO events. Meanwhile, despite the small phytoplankton‐dominated community being observed under future scenario, species dominance is likely to shift back to diatoms once extreme La Niña occurs, which is unseen in all El Niño and moderate La Niña cases. [ABSTRACT FROM AUTHOR]

This paper utilizes a fine scale parameterization scheme based on strain spectra and characterizes the temporal and spatial distributions of diapycnal turbulent mixing in the West Pacific Warm Pool. We use Array for Real‐Time Geostrophic Oceanography (Argo) profiles from 2011 to 2022 to generate the turbulent dissipation rate (ε) as a representative of internal‐wave‐induced mixing. We then discuss the influence of El Niño‐Southern Oscillation (ENSO) on turbulent mixing by considering seafloor topography, thermocline depth, and ENSO phases. Results indicate that ENSO can influence the vertical stratification in the ocean by changing the depth of the thermocline, causing the change of interaction between internal tides and seafloor topography, thereby affecting the intensity and vertical distribution of diapycnal turbulent mixing. During La Niña years, the value of ε is larger compared to that of El Niño years. Compared to rough regions, the thermocline variations induced by ENSO have a more pronounced impact in the smooth regions. The variability in turbulent mixing influenced by ENSO is crucial for heat and substance exchange in the equatorial Pacific. [ABSTRACT FROM AUTHOR]

Using the numerical calculations of exposure time (θ), this study investigated the three‐ dimensional characteristics of water exchanges associated with the coastal‐shelf circulations of the Northern South China Sea (NSCS). The circulation connectivity and its interannual variability under the modulation of El Niño Southern Oscillation (ENSO) were investigated. The θ gradually increased from approximately 50 days over the outer shelf to more than 150 days in the shallower coastal seas with the Beibu Gulf displaying a significantly longer θ (approximately 300 days). The Beibu Gulf played an influential role in the water exchange that had a contribution of over 30% to θ in the most regions. The results from sensitivity experiments indicate that the wind forcing isthe primary controller of θ and the boundary flux plays a secondary role. Specifically, the wind enhances water exchange in western NSCS, particularly in the Beibu Gulf and Yuexi region. Conversely, boundary fluxes facilitate exchanges in the eastern shelf, such as Yuedong region. Analysis revealed a clear modulation from ENSO on water exchange, wherein El Niño and La Niña years displayed symmetrical morphologies in θ distribution anomalies, albeit with varying intensities. During El Niño years, the weakened southwestward shelf current increased θ and the shelf water was less likely to reach the Beibu Gulf, and once arrived, these waters were trapped inside to elongate θ. In contrast, during La Niña years, the strengthened southwestward shelf current shortened θ and more shelf waters were transported away from the NSCS by an intensified southwestward shelf current. [ABSTRACT FROM AUTHOR]

Historical meteorological droughts are analysed over the Coordinated Regional Downscaling Experiment‐Central America, Caribbean and Mexico (CORDEX‐CAM) domain during 1981–2010, with particular emphasis on the North American monsoon (NAM) and the mid‐summer drought (MSD) regions. We analyse droughts based on the standardized precipitation index (SPI‐12) and the standardized precipitation‐evapotranspiration index (SPEI‐12) using observations from CRU, CHIRPS, GPCP and ERA5‐Land reanalysis (ERA5), and assess the skill of the regional climate model RegCM4 (version 7) at 25 km resolution driven by ERA‐Interim (Reg‐ERA) and by three global climate models (Reg‐GCMs: Reg‐Had, Reg‐MPI and Reg‐GFDL). Observational data sets show large spatial variations in drought frequency, and both Reg‐ERA and Reg‐GCMs have difficulties simulating it. RegCM4 shows positive precipitation and water balance biases over mountain regions and negative ones over Central America, possibly due to the complex terrain and poor observational data coverage. Despite differences among observations, the trend in droughts, duration and severity show consistent dry hot spots (regions with long‐duration severe droughts) over the western United States, the United States‐Mexico border region, the NAM, the Yucatan Peninsula and northern Central America, with stronger values of SPEI‐12 than SPI‐12, particularly over the subtropical regions. Reg‐ERA and ERA5 show similar spatial patterns and similar positive and negative spatial biases relative to observations. Reg‐ERA and Reg‐Had adequately simulate the spatial patterns of the trend, duration and severity of droughts, with smaller biases in SPI‐12 than SPEI‐12; in contrast, Reg‐MPI and Reg‐GFDL overestimate the trend biases over northwest CAM. Observations, reanalysis, and RegCM4 capture an inverse drought response between the NAM and the MSD regions linked to climate teleconnections; however, a stronger drought signal is observed in the NAM, which appears to be linked to decadal variations from negative to positive phases of the Atlantic Multidecadal Oscillation combined with La Niña conditions (negative El Niño 1+2 phase). [ABSTRACT FROM AUTHOR]

Clustering extreme weather events are concurrent or consecutive occurrences of disastrous weather in multiple regions, resulting in cumulative impacts. Here we discovered a significant increasing trend in clustering extreme precipitation events over the Indo‐Pacific rim over the past four decades. This trend can be largely attributable to the increasing frequency of the Rossby wave response, including the circum‐Pacific and cross‐Pacific patterns due to Rossby wave activity propagation, and the Pacific anticyclone pattern due to Rossby wave breaking. The three patterns show remarkable disparity in seasonality, persistence, and hydrological impacts. They can increase the occurrences of most severe precipitation by up to 5, 8, and 25 times, respectively. The Indian Summer Monsoon heat sources and La Niña are identified as key drivers, and the mid‐latitude jet streams are modulators contributing to the events. Our findings suggest that specific Rossby wave patterns may influence the potential evolution of future clustering extremes. Plain Language Summary: Extreme precipitation events that occur concurrently or consecutively in multiple regions over a period, can have a cascading effect on human livelihoods. This is a new type of disastrous weather event in the context of climate change, which we call clustering extreme precipitation events. However, there is a lack of understanding about their frequency and underlying mechanisms. To address this, we propose an identification method for clustering extreme precipitation events over the Indo‐Pacific Rim. Here, our findings reveal that three distinct Rossby wave patterns are responsible for these events. Accompanied by more frequent occurrence of the identified Rossby wave patterns, the frequency of clustering extreme precipitation events has increased (0.5 event/decade) in the past 42 years. The Rossby wave patterns set up favorable atmospheric conditions and significantly increase the occurrences of the most severe precipitation in the Northern Hemisphere. The Indian Summer Monsoon heat sources serve as a first‐order driving mechanism for exciting the Rossby waves, while La Niña serves as external forcing. Additionally, the variations of mid‐latitude jet streams modulate the development of the Rossby wave patterns. The results provide a predictability source for the sub‐seasonal to seasonal community. Key Points: Over the past 42 years, there has been an increase in the frequency of clustering extreme precipitation events across the Indo‐Pacific rimThe consecutive occurrences of extreme precipitation in multiple regions are organized by three diverse Rossby wave patternsThe Indian Summer Monsoon heat sources and La Niña are key drivers of the events and the mid‐latitude jet streams are modulators [ABSTRACT FROM AUTHOR]

In around 1990, significant shifts occurred in the spatial pattern and temporal evolution of the El Niño‐Southern Oscillation (ENSO), with these shifts showing asymmetry between El Niño and La Niña phases. El Niño transitioned from the Eastern Pacific (EP) to the Central Pacific (CP) type, while La Niña's multi‐year (MY) events increased. These changes correlated with shifts in ENSO dynamics. Before 1990, El Niño was influenced by the Tropical Pacific (TP) ENSO dynamic, shifting to the Subtropical Pacific (SP) ENSO dynamic afterward, altering its spatial pattern. La Niña was influenced by the SP ENSO dynamic both before and after 1990 and has maintained the CP type. The strengthened SP ENSO dynamic since 1990, accompanied by enhanced precipitation efficiency during La Niña, make it easier for La Niña to transition into MY events. In contrast, there is no observed increase in precipitation efficiency during El Niño. Plain Language Summary: In this study, we explored changes in the El Niño‐Southern Oscillation (ENSO) phenomenon from 1950 to 2022. We discovered significant shifts in ENSO complexity, particularly after 1990, affecting where ENSO events occur and how long they last. Notably, these changes differed between El Niño and La Niña phases. El Niño's location shifted from the Eastern Pacific to the Central Pacific, while La Niña extended its duration, leading to more multi‐year events. These complexities relate to shifts in El Niño and La Niña dynamics. El Niño changed from a Tropical Pacific dynamic to a Subtropical Pacific dynamic, influencing its shift to the central Pacific. La Niña dynamics remained constant, causing La Niña's central location to remain unchanged. After 1990, the tropical precipitation efficiency showed an asymmetric change between El Niño and La Niña phases. The intensified atmospheric response to La Niña cooling enabled more frequent activations of the SP ENSO dynamic, thus increasing the frequency of multi‐year La Niña. These findings advance our understanding of ENSO and can enhance ENSO prediction. Key Points: El Niño‐Southern Oscillation complexity underwent significant asymmetric changes around 1990, especially in spatial pattern and temporal evolutionEl Niño's pattern shifted from Eastern Pacific to Central Pacific, while La Niña's timing transitioned from single‐year to multi‐yearEl Niño's primary dynamic shifted from Tropical Pacific to Subtropical Pacific (SP) whereas La Niña consistently remained in the SP [ABSTRACT FROM AUTHOR]

The timing and geographic extent of a potential "4.2 ky event" remain highly contested. Here we present records of ENSO variability at 3.8 kyBP and 4.1 kyBP derived from a Borneo stalagmite, which suggest a significant change in ENSO properties between these time intervals. The Borneo records show evidence of significantly reduced ENSO activity at 4.1 kyBP, relative to other measured windows within the Holocene. This reduced ENSO activity coincides with a period of drier conditions and enhanced dust events in the Middle East that took place ∼4.0–4.3 kyBP. The Borneo records show evidence of enhanced ENSO activity at 3.8 kyBP. Various hydroclimate changes attributed to the "4.2 ky event" in many regions may thus be reflecting a shift from reduced to enhanced El Niño activity that occurred between 3.8 kyBP to 4.0 kyBP. Plain Language Summary: Research suggests that a significant climate shift may have occurred around 4,000 years ago, though the exact timing and global extent of the event remain uncertain. A change in the frequency or magnitude of the El Niño‐Southern Oscillation (ENSO) is one hypothesized cause, however there are currently few high‐resolution records which resolve ENSO variability 4,000 years ago. We present a new western tropical Pacific stalagmite‐based record of ENSO activity, which shows a significant minimum in ENSO variability around 4,100 years ago. This reduced ENSO activity coincides with a centennial‐scale climate event in the Middle East characterized by drier conditions and enhanced dust events. The Borneo record also shows a significant increase in El Niño/La Niña activity that took place by 3,800 years ago. Hydroclimate changes around 4,000 years ago found in records from multiple regions around the world may therefore reflect a shift from reduced to enhanced El Niño activity. Key Points: Borneo stalagmite record shows anomalously low El Niño‐Southern Oscillation variability in a 135‐year‐long window, centered at 4.1 kyBPBorneo stalagmite record suggests an abrupt shift from low to high El Niño‐Southern Oscillation variability between 3.8 and 4.0 kyBPRecords of tropical hydroclimate change ∼4,000 years ago may reflect a significant increase in El Niño variability [ABSTRACT FROM AUTHOR]

The El Niño‐Southern Oscillation (ENSO) is considered an important driver of rainfall variability in Australia, amongst many other global locations. Despite knowledge of the expected modulation of seasonal rainfall by ENSO, there is no consistently used method to quantify the role that specific ENSO events play in driving the observed anomalous rainfall. In this manuscript we adapt the Fraction of Attributable Risk (FAR) method, commonly used to identify the anthropogenic impact on a particular event, to quantify the impact of ENSO on the occurrence of monthly rainfall anomalies. We also explicitly calculate the ENSO induced change in risk and the FAR for all observed spring rainfall rates for our eastern Australian regions. A prominent role for ENSO in driving the large spring 2022 rainfall anomalies is identified. Though we choose to focus on ENSOs impact on rainfall in various Eastern Australian regions, the results are applicable to other climate modes, regions and climatic variables. Plain Language Summary: The El Niño‐Southern Oscillation (ENSO) is considered an important driver of rainfall variability in Australia, amongst many other global locations. Despite understanding how ENSO is expected to alter rainfall, we do not currently quantify the role ENSO played in driving a observed rainfall anomaly in any given season. In this manuscript we adapt a method that is commonly used to identify the anthropogenic impact on a particular event; and instead, we quantify the impact of ENSO on the occurrence of monthly rainfall anomalies. We then calculate the ENSO‐induced change in risk for all observed spring rainfall rates for our selected eastern Australian regions. A prominent role for ENSO in driving large rainfall anomalies of spring 2022 is also identified. Though we choose to focus on ENSOs impact on rainfall in various eastern Australian regions in this study, the results are applicable to other climate modes, regions and climatic variables. Key Points: We adapt the commonly used Fraction of Attributable Risk method to attribute rainfall variability to the El Niño‐Southern OscillationWe present the ENSO induced change in risk and the FAR for all observed spring rainfall rates for three eastern Australian regionsThe increased spring 2022 East Australian rainfall was >5 times more likely, and largely attributed to the La Niña conditions present [ABSTRACT FROM AUTHOR]

Interannual variations provide insight into the sensitivity of convective processes. Thus, CloudSat and ERA5 are used to explore the relationship among convective cores, outflows and environmental conditions during El Niño‐Southern Oscillation (ENSO) cycles. Results reveal greater upper‐tropospheric stability during El Niño, resulting in a lower level of neutral buoyancy compared to La Niña. However, outflow levels remain relatively consistent across ENSO cycles. This suggests that, despite less favorable conditions for deep convection during El Niño, stronger convective intensity is required to achieve outflow levels comparable to those in La Niña. Indeed, our results suggest that convection observed during El Niño tends to have broader cores and lower entrainment rates, translating to greater intensity compared to La Niña. These findings emphasize the importance of considering both large‐scale and convective‐scale processes, providing an update to the fixed anvil temperature (FAT) and the proportionately higher anvil temperature (PHAT) hypotheses as originally proposed. Plain Language Summary: Examining year‐to‐year variations provides unique insights into understanding how storms may change in a warmer climate. We use CloudSat and ERA5 reanalysis to examine variations in convective outflow (i.e., an airflow pushed out of storms), environmental factors, and cloud properties during ENSO cycles. Comparing El Niño to La Niña, we find that the atmosphere higher up in the troposphere tends to be more stable, which usually slows down the development of storms, during El Niño. However, the heights where convective outflow occurs do not change much during El Niño and La Niña events. This happens because during El Niño, the upward movement of air in storms is more powerful. This stronger upward movement offsets the stabilizing effect of the upper troposphere, so the overall outflow from the storms stays about the same. Our study aligns with the main idea of the FAT hypothesis, which postulates that in a warming climate, the temperature of the anvils (i.e., wide, flat clouds crawling out of the storm top) stays relatively constant primarily due to a thermodynamic constraint. However, our results show that convective‐scale processes with dynamic control play a key role as well, providing an update to the FAT as originally proposed. Key Points: LNB is lower during El Niño due to a greater UT stability, but convective outflow levels remain consistent across ENSO cyclesThe intensity of convective cores during El Niño has to be stronger than that during La NiñaOur finding necessitates a modification to FAT and the proportionately higher anvil temperature (PHAT) [ABSTRACT FROM AUTHOR]

The difference in observed atmospheric anomalies over the Northern Hemisphere winter between 2021–22 and 2020–21 La Niña years indicated a tripole pattern consisting of a Japan cyclone, a Bering Sea anticyclone, and a cyclone over the North American continent. This feature, however, was not replicated in the North American Multi‐Model Ensemble (NMME) forecasts. A set of model sensitivity experiments was performed to better understand the cause of this discrepancy. The results revealed the possible role of the influence of sea surface temperature (SST) anomalies, particularly over the Indian Ocean, on the observed circulation differences that was further modulated by internal atmospheric variability. The failure in predicting circulation changes in NMME was next attributed to the errors in SST predictions over the Indian Ocean and highlights the need for improvements in SST forecasts over this region. Plain Language Summary: The tropical SST anomalies associated with the El Niño‐Southern Oscillation (ENSO) are known to influence the global atmospheric circulation and are the major source of skill in U.S. seasonal predictions. As the cold phase of ENSO, La Niña features below‐normal SST anomalies and suppressed convection over the equatorial central and eastern Pacific. Such a tropical heating distribution favors the formation of the atmospheric circulation pattern that has a roughly opposite effect on U.S. surface climate compared to El Niño, the warm phase of ENSO, although the effect is not strictly symmetric. For the recent two La Niña boreal winters of 2020–21 and 2021–22, the observed circulation patterns differed, but dynamical seasonal prediction failed to replicate this feature. Understanding the cause for the discrepancy of circulation changes between prediction and observations is of fundamental importance for the improvement of seasonal forecasts. Toward this, we designed numerical experiments that are forced with observed and predicted SST anomalies over different ocean basins. The results show that it is the errors in SST prediction over the Indian Ocean that contributed to the failure in the prediction of circulation changes, highlighting the importance of skillful prediction of SST over this region. Key Points: The difference in observed atmospheric anomalies for 2022 versus 2021 La Niña boreal winters featured a Northern Hemisphere tripole patternIndian Ocean SST contributed to the formation of observed tripole pattern, with internal atmospheric variability modulating its magnitudeErrors in SST predictions over the Indian Ocean led to the failure in predictions of the circulation changes in NMME forecasts [ABSTRACT FROM AUTHOR]

We propose a unified statistical method based on deep learning and analysis to quantify the relative contributions of the global oceans to El Niño–Southern Oscillation (ENSO) predictability. By incorporating subsurface signals in the Indian Ocean and Atlantic, the forecast lead can be skillfully extended by about one season. This skill enhancement mainly originates from the tropical Indian Ocean, presumably related to signals of the Indian Ocean Dipole passing to the tropical Pacific through the Indonesian Throughflow. The sea surface temperature anomaly (SSTA) in the Indian Ocean accounts for nearly 50% of surface contributions to both El Niño and La Niña predictions at a 15‐month lead. The north tropical Atlantic SSTA has a moderate impact on La Niña at a 9‐month lead. The Pacific Meridional Mode plays a significant role in both ENSO phases at a 12‐month lead. Thus, our study suggests that trans‐basin effects for ENSO are more vigorous than previously thought. Plain Language Summary: El Niño–Southern Oscillation (ENSO) can excite various modes of climate variability in the Indian Ocean, Atlantic, and extratropical Pacific. However, less understood and quantified than the ENSO‐driven influences is how these regions outside the tropical Pacific in turn affect ENSO. Here, we quantify the impacts of the Indian Ocean, Atlantic, and extratropical Pacific on the predictability of ENSO. The lead time can be skillfully extended by one season by incorporating subsurface signals from the Indian and Atlantic oceans. The extratropical Pacific SST can indeed provide some useful sources of information for ENSO predictability at long lead times. A heatmap analysis further indicates that the triggering precursors freely selected by the deep learning model link to our current understanding of physical pathways for ENSO prediction. The Indian Ocean Dipole, the north tropical Atlantic SSTA, and the Pacific Meridional Mode are the main trans‐basin factors that vigorously influence ENSO at different lead times. Our findings emphasize that the impacts of the global oceans on ENSO are significant, and their influences should be properly considered in the coupled models. Key Points: Heat content in the Indian Ocean can provide extra signals for long‐term El Niño–Southern Oscillation (ENSO) forecasts and extend the lead time by about one seasonThe Indian Ocean Dipole can significantly influence El Niño via both surface and subsurface physical pathways at a 15‐month leadThe north tropical Atlantic warming and the Pacific Meridional Mode also vigorously affect ENSO at lead times of both 12 and 9 months [ABSTRACT FROM AUTHOR]