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To what extent the CMIP6 models are capable of simulating the location and amplitude of zonal wind anomalies in tropical Pacific during the mature phase of ENSO is examined. While most of the models capture the southward shift of the maximum zonal wind anomaly, the simulated locations are less southward and more westward and the simulated intensities are weaker compared to the observation. An anti-symmetric momentum budget analysis reveals that the southward shift in the models results from the anomalous meridional advection, consistent with that derived from the observation. An inter-model regression analysis reveals that the longitudinal and latitudinal locations of the model zonal wind response depend on the mean precipitation pattern in the tropical western Pacific (WP). A stronger southward (eastward) mean precipitation gradient leads to a more southward (eastward) location. In addition, the simulated zonal wind intensity is determined by both area-averaged mean precipitation over WP and anomalous SST intensity in the equatorial eastern Pacific. Therefore, an improved mean precipitation simulation in WP may help reproduce realistic atmospheric responses to ENSO. [ABSTRACT FROM AUTHOR]

The study delves into the complexities of prolonged El Niño (PE) and La Niña (PL) events, examining their behaviour, dynamics, and representation in climate models participating in CMIP6. These events deviate from the typical cycles of the El Niño-Southern Oscillation (ENSO) system and significantly impact global weather patterns and socioeconomic systems. The study aims to enhance our understanding of these multi-year ENSO events through a comparative analysis of observational data and model simulations. Observational data reveal the distinct characteristics of PE and PL events, with prolonged warming or cooling anomalies persisting in the equatorial Pacific beyond the usual timeframe associated with canonical El Niño (CE) and La Niña (CL) events. However, while climate models generally capture the general trend of sustained warming or cooling, discrepancies exist in the magnitude and timing of SST anomalies, particularly during peak phases. The analysis highlights limitations in the ability of current climate models to simulate consecutive El Niño events following PE events and strong El Niño events preceding PL events accurately. Furthermore, discrepancies in the representation of subsurface oceanic dynamics and zonal wind stress patterns underscore challenges in capturing the intricate interactions driving ENSO variability. The study emphasizes the importance of refining climate models to capture better the intricacies of prolonged ENSO events, which have significant implications for future climate projections and adaptation strategies. [ABSTRACT FROM AUTHOR]

Observational and modeling studies have elucidated the influential role played by the southern and northern extratropical Pacific (SEP and NEP) forcing in shaping dynamics of tropical Pacific climate variability. However, the relative importance of the NEP and SEP and the timescale on which they impact the tropics remain unclear. Using a linear inverse model (LIM) that selectively incorporates or excludes tropical‐extratropical coupling, we find a reduction in tropical interannual variability (∼40%) and low‐frequency (sub‐decadal to decadal) variability in the southeastern tropical Pacific region (∼70%) in the absence of SEP. Conversely, the absence of NEP yields no significant impact on tropical interannual variability but markedly diminishes low‐frequency variability in the central tropical Pacific region (∼70%). LIM and statistic diagnostics on CMIP6 models show the low‐frequency to total variability ratio in the tropical Pacific depending on their NEP and SEP representation. Models with more (less) low‐frequency power tend to show stronger NEP (SEP) dynamics. Plain Language Summary: The tropical Pacific climate variability exerts a strong impact on global climate, regional weather, and marine ecosystems. The tropical and extratropical Pacific are closely coupled with each other through oceanic and atmospheric processes. Previous studies have shown that the southern and northern extratropical Pacific (SEP and NEP) forcing greatly impact the tropical Pacific climate variability. To understand and predict tropical Pacific variability, it is necessary to study the relative importance and the timescale on which the SEP and NEP exert their influence. In this study, we use an empirical dynamical model to exclude the impacts of SEP or NEP on the tropical Pacific based on the observational data. We find that the absence of SEP leads to a significant reduction of interannual variance (∼40%) and the low‐frequency (sub‐decadal to decadal) variance in the southeastern tropical Pacific region (∼70%), while the absence of the NEP does not change the interannual variance but significantly reduces the low‐frequency variance in the central tropical Pacific region (∼70%). In observations, the ratio of low‐frequency to total tropical variability is 0.36, while CMIP6 models exhibit a wider range, with enhanced low (high) frequency power associated with stronger NEP (SEP) dynamics. Key Points: The SEP dynamics contribute ∼40% of the tropical interannual variance and ∼70% of the southeastern tropical low‐frequency varianceThe NEP dynamics do not impact the tropical interannual variance but lead to ∼70% of the central tropical low‐frequency variabilityCMIP6 models show stronger NEP (SEP) dynamics tend to manifest ENSO with more (less) low‐frequency (>6 years) power [ABSTRACT FROM AUTHOR]

El Niño–Southern Oscillation (ENSO) usually peaks in the boreal winter—November to January of the following year. This particular feature of ENSO is known as the seasonal phase locking of ENSO. In this study, based on 34 climate models from the Coupled Model Intercomparison Project Phase 6 (CMIP6), the seasonal phase-locking characteristics of the model-simulated El Niño and La Niña events are evaluated in terms of the evolution of the SST anomalies associated with ENSO and the probability distribution of the peak month—the time at which ENSO peaks. It is found that CMIP6 models underestimate the phase-locking strength of ENSO for both El Niño and La Niña events. The ensemble mean peak month matches the observations, but the inter-model spread is large. The models simulate the phase locking of El Nino events better than that of La Niña events, and the large simulation bias of CMIP6 for La Niña phase-locking in the models may have an impact on the simulation of seasonal phase-locking in the ENSO. [ABSTRACT FROM AUTHOR]

This study assesses the Hadley circulation (HC) anomalies' structure during the historical El Niño decaying stage, utilizing 29 models from the Coupled Model Intercomparison Project Phase 6 (CMIP6). While all 29 models successfully capture the climatological HC's structure, they exhibit considerable variations in representing HC anomalies during this stage, highlighting noteworthy inter-model differences. The CMIP6 models are categorized into two distinct groups grounded on the correlation coefficient (r) between simulated anomalies of the HC and observed patterns: Type I models (r > 0.5) and Type II models (r < − 0.5). The findings elucidate that the pivotal determinant influencing the successful characterization of HC anomalies lies in the models' capacity to simulate tropical sea surface temperature (SST) variability and the asymmetric decay rates of SST on the equatorial flanks during this stage. Type I models proficiently replicate the asymmetric structure of zonal-mean SST anomalies, which subsequently results in an asymmetric structure of HC anomalies. Conversely, Type II models generate zonal-mean SST anomalies characterized by equatorial symmetry. Therefore, these results underscore the substantial influence of El Niño–Southern Oscillation (ENSO) variability on the connection between tropical atmospheric circulation and SST. Moreover, this research offers valuable insights for improving the models' capacity to simulate tropical air–sea coupling processes effectively. [ABSTRACT FROM AUTHOR]

Diurnal temperature range (DTR), as a core indicator of the Earth system, exhibits obvious temporal and spatial variations, which is not entirely consistent over global. The historical simulation capabilities of 19 Coupled Model Intercomparison Project 6 (CMIP6) models for DTR were firstly evaluated against CRU_TS v4.04 data. Future changes under three shared socioeconomic pathways (SSP1-2.6, SSP2-4.5, SSP5-8.5) in DTR were projected using a multi-model ensemble mean (MME), and its interannual variations were seasonally explored through empirical orthogonal function (EOF) analysis. The results indicated that CMIP6 models could reflect the decreasing trend of DTR during 1901–2014, with the global spatial correlation coefficient between models and observation ranging from 0.4 to 0.7. MME outperformed individual models in both spatial and temporal variations, indicating higher accuracy and reliability. The future changes of DTR exhibited significantly decrease across the northern hemisphere and increase in the South America, and change magnitude enlarged with time extension and emission intensity, especially by more than 0.4 °C under SSP5-8.5. The decreasing trend of global DTR was kept in SSP2-4.5 and SSP5-8.5, while SSP1-2.6 changed increasing trend during 2015–2100. DTR showed seasonal variations and was mainly influenced by colder months. The dominant modes of interannual DTR and their relationship with the 500 hPa geopotential height, the 200 hPa U wind, and the outgoing longwave radiation showed higher features in tropical regions. The highly positive correlation between the first mode of DTR and the Niño3.4 index in December/January/February (DJF) is 0.67, indicating significant influence of the El Niño-Southern Oscillation on DTR. [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 tropical Pacific decadal variability (TPDV) is an important component of the global interdecadal variability. Previous studies have shown that the TPDV in the sea surface temperature (SST) has two clear patterns, the El Niño–Southern Oscillation (ENSO)‐like and ENSO‐induced patterns, but the pattern of TPDV in the ocean subsurface is still a matter of debate in observations and models. The present study analyses the subsurface TPDV in the simulations of 26 CMIP6 models. The ENSO‐like and ENSO‐induced TPDVs in the subsurface are defined by the regression of the interdecadal anomalies of the oceanic subsurface temperature (Tsub) onto the PCs of two leading EOF modes of the interdecadal SST anomalies in the tropical Pacific. The pattern of the ENSO‐like TPDV in the subsurface shows high model consistency, whereas the ENSO‐induced TPDV in the subsurface has two distinct modes among the models, one with a centre in the central Pacific and the other showing a zonal dipole in the equatorial Pacific. The zonal pattern of the ENSO‐induced TPDV in the subsurface is mainly induced by the SST skewness in the equatorial eastern Pacific, which is further related to the surface heat flux feedback during La Niña. [ABSTRACT FROM AUTHOR]

Understanding and elucidating future changes in El Niño teleconnection is crucial because of the influence of El Niño on the globe via teleconnection. Existing climate models have consistently projected an eastward and poleward shift in El Niño teleconnection in the future, but the causes and dynamical processes of this shift have been poorly explained. Particularly, no study has examined the characteristic changes in the barotropic Rossby waves that form the teleconnection. This study investigates dynamic processes by analyzing the wavelength of the Rossby waves through spectral analysis, measuring the distance between circulation anomalies, and exploring the dispersion relationship of the barotropic Rossby waves. The results revealed that the wavelength of waves forming the teleconnection is expected to increase in warmer climate with an increase in the proportion of zonal-wavenumber-2 wave. Because changes in the mean state, including the strengthening of the westerly in the high-emission scenario, alter the frequencies of waves according to their zonal wavenumbers, this process is more notably manifested in the Southern Hemisphere, where the inter-model spread of the mean state is smaller, than in the Northern Hemisphere. Consequently, this will result in a shift in the position of El Niño's influence on the high latitudes of both Hemispheres. Specifically, in the Southern Hemisphere, it is anticipated that ocean warming in the seas in front of West Antartica and moisture transport towards Antarctica, induced by El Niño, will shift eastward in the high-emission scenario compared to its conventional position. • The El Niño teleconnection changes in the future as the wavelength of the wave forming the teleconnection increases. • The mean state changes reduce the frequency of barotropic Rossby waves with smaller zonal wavenumbers, causing the increase. • This can lead to a shift in the location of El Niño's impact on high latitudes. [ABSTRACT FROM AUTHOR]

As a dominant climate mode of the southeast Indian Ocean, Ningaloo Niño/Niña has paramount impacts on regional climate and marine ecosystems. Using outputs from the latest phase of Coupled Model Intercomparison Project (CMIP6), we have systematically evaluated the simulation of Ningaloo Niño/Niña in the state‐of‐the‐art coupled models. Eighteen out of 28 CMIP6 models well reproduce the spatial pattern and seasonality of Ningaloo Niño/Niña, whereas the simulated amplitudes show large spread across the models. Main processes of the oceanic and atmospheric El Niño‐Southern Oscillation teleconnections and the coastal Bjerknes feedback are successfully captured by most of the CMIP6 models, but their uncertainties in the simulation are responsible for the inter‐model difference in amplitude. The CMIP6 models are also skillful in reproducing the regional climate impacts of Ningaloo Niño/Niña. Compared to Coupled Model Intercomparison Project Phase 5, a larger fraction of models in CMIP6 well reproduce the Ningaloo Niño/Niña, which provides a good hope for projecting its future changes. Plain Language Summary: The Ningaloo Niño/Niña is a kind of coastal version of the El Niño‐Southern Oscillation phenomenon in the southeast Indian Ocean, which is characterized by the prominent sea surface temperature variability off the west coast of Australia. As a dominant climate mode of the southeast Indian Ocean, Ningaloo Niño/Niña is known to exert strong impacts on regional climate and ocean biodiversity. For example, the unprecedented marine heatwave event associated with the 2011 extreme Ningaloo Niño severely damaged local fishery and coral reef. More severe impacts are expected under global warming. Hence, the future projection of Ningaloo Niño/Niña is of great importance for mitigating devastating climate impacts. As a prerequisite, we need to study first whether the state‐of‐the‐art coupled general circulation models can successfully reproduce such a coastal climate mode. Using the outputs from the latest Coupled Model Intercomparison Project Phase 6 (CMIP6), we have systematically evaluated the performance in simulating the Ningaloo Niño/Niña, including its basic characteristics, generation mechanisms, and the climate impacts. The results show that most of the CMIP6 models can realistically simulate the Ningaloo Niño/Niña, which provides us with confidence in projecting its future changes under global warming. Key Points: Coupled Model Intercomparison Project Phase 6 (CMIP6) ensemble mean simulation of Ningaloo Niño/Niña captures the observations despite the substantial inter‐model spreadInter‐model magnitude spread is due to different performances in both the El Niño‐Southern Oscillation teleconnections and the coastal Bjerknes feedbackThe CMIP6 models are skillful in reproducing the regional climate impacts of Ningaloo Niño/Niña [ABSTRACT FROM AUTHOR]

This study evaluates the relationship between El Niño‐Southern Oscillation (ENSO) and the East Asian winter monsoon (EAWM) in 26 Coupled Model Intercomparison Project Phase 6 (CMIP6) models. Of particular concern is the plausible factors for the model's capability of simulating the ENSO‐EAWM relationship. Results show that the model's ability of simulating the ENSO‐EAWM relationship is more dependent upon the longitudinal extension of ENSO‐related equatorial Pacific sea surface temperature (SST) anomalies than the amplitude of the equatorial central‐eastern Pacific SST anomalies. The influence of the amplitude of ENSO on the simulation of the ENSO‐EAWM relationship depends on the westward extension of ENSO‐related equatorial Pacific SST anomalies. Another factor for the model's ability of simulating the ENSO‐EAWM relationship is the SST anomalies in the tropical western North Pacific (WNP). A westward extension of the equatorial Pacific SST anomalies shifts the west branch of anomalous Walker circulation too far westward, which causes westward displaced anomalous ascending (descending) motion around the Philippines through modulating regional meridional vertical circulation in El Niño (La Niña) years. The weak SST anomalies in the tropical WNP lead to the failure of inducing anomalous lower‐level anticyclone (cyclone) over the Philippine Sea through a Rossby wave response in El Niño (La Niña) years. The accompanying weak anomalous lower‐level southwesterly (northeasterly) winds along the west flank of the anomalous anticyclone (cyclone) account for the weak ENSO‐EAWM relationship. Key Points: The El Niño‐Southern Oscillation‐East Asian winter monsoon (ENSO‐EAWM) relationship varies largely among the CMIP6 modelsThe longitudinal location of equatorial Pacific sea surface temperature (SST) anomalies is more critical than the amplitude to simulating the ENSO‐EAWM relationshipThe tropical western North Pacific SST anomalies are another important factor in the simulation of the ENSO‐EAWM relationship [ABSTRACT FROM AUTHOR]

The interannual variability of the Northern Hemisphere winter climate is strongly linked to the El Niño-southern oscillation (ENSO). While North Pacific and North America often exhibit a robust response to ENSO, so-called the Pacific–North America pattern, the Arctic and Eurasian climate responses to ENSO remain elusive. This study examines 40 different climate models from the coupled model intercomparison project phase 6 (CMIP6) to find the distinct Arctic and Eurasian temperature response to two types of El Niño events. Specifically, Central Pacific El Niño events are accompanied by significant pan-Arctic warming, whereas Eastern Pacific (EP) El Niño events are accompanied by cooling over the Barents-Kara Seas and Eurasian continent. During the EP El Niño events, pan-Arctic sea-level pressure (SLP) effectively strengthens, leading to weaker westerlies and surface air cooling over the northern Eurasian continent. These distinct Arctic and Eurasian winter temperature responses to two types of El Niño do not appear clearly in reanalysis data, spanning 1979–2021, probably because of the small sample size of El Niño events since the satellite era.

Based on observations and reanalyses, the ability of 24 models from the Coupled Model Inter-comparison Project Phase 6 (CMIP6) in simulating the Hadley circulation's (HC) long-term variability was evaluated, and possible reasons for the simulation uncertainties were analyzed. The results showed that each model utilized in this study can reproduce the HC climatological pattern well, but the simulated HC variability shows large inter-model uncertainties. The first principle mode of the HC's long-term variability (EOF1) exhibited an equatorial asymmetric structure (i.e., asymmetric mode, AM) in observations. The CMIP6 models were divided into two groups according to their abilities to reproduce the AM: models that could simulate the AM well were classified as Type I, and models that could not simulate the AM and exhibited an approximately equatorial symmetric structure of the EOF1 were classified as Type II. The results showed that the EOF1 spatial structure is determined by variations in the meridional gradient of the tropical ocean sea surface temperature (SST). Type I models can significantly reproduce the relationship between the EOF1's variation and the meridional gradient of tropical SST, so as to reproduce the HC's long-term variability characteristics. In Type II models, the EOF1's variation is tightly related to SST distribution, similar to the El Niño-Southern Oscillation (ENSO). Type II models exaggerate the variation of ENSO, which is associated with equatorial symmetric structure of SST anomalies, resulting in enhanced variability in the HC of the equatorial symmetric part. This is the reason why EOF1 of the HC in Type II models exhibits an equatorial symmetric structure. The results point out the possible reasons for the different simulations of CMIP6 models in the HC variability and provide a reference for future climate models to be developed in this area. • CMIP6 models reproduce the HC climatological pattern well, but the HC variability shows large inter-model uncertainties. • A model reproduction of the tropical SST meridional gradient is a key factor in determining the HC variability simulation. • The unsatisfactory performance of the variability of the HC is due to the exaggeration of the ENSO. [ABSTRACT FROM AUTHOR]