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sThe fidelity of coupled climate models simulating El Nino-Southern Oscillation (ENSO) patterns has been widely examined. Nevertheless, a systematical narrow bias in the simulated meridional width of the sea surface temperature anomaly (SSTA) of ENSO has been largely overlooked. Utilizing the preindustrial control simulations of 11 coupled climate...
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... significant negative relation in the models indicates that the stronger zonal wind stress favors an occurrence of the wider ENSO SSTA, and vice versa, which is consistent with the theoretical prediction of the simple thermal damped-advective model that we have We also examine how the ENSO period influences the meridional width of ENSO SSTA in the models. Figure 9 displays the scatterplot of the ENSO period and meridional width in models. The ENSO period is estimated from the power spectrum of the SSTA over 58S-58N, 1808-908W, which is the time scale corre- sponding to the maximum power. ...
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... that a minimum of 250 model years is needed to robustly assess ENSO characteristics. Here, the rough evaluation based on a short period is used to qualitatively analyze the relation of ENSO period and meridional width. There is a positive correlation (0.50) between the simulated periods and the meridional widths of ENSO across the models (Fig. 9). The simulated meridional width tends to increase as the ENSO period increases. The simulated ENSO periods in most models are shorter than the observed data. The spectra peak at about 4 years in the observation, whereas the average modeled period is only 3 years. Therefore, the short ENSO period in models could be another factor in the ...
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... tent in a wide equatorial basin, and thus lead to a slow turn around or longer period for ENSO. Our advective conceptual model in section 5 suggests that this longer period in turn will lead to a wider width for ENSO SSTA. A wide SSTA may contribute to a wider zonal wind response, and therefore the relation between ENSO width and period shown in Fig. 9 may be not entirely due to the process captured by the conceptual ...
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We investigate the processes responsible for the intraseasonal displacements of the eastern edge of the western Pacific warm pool (WPEE), which appear to play a role in the onset and development of El Niño events. We use 25 years of output from an ocean general circulation model experiment that is able to accurately capture the observed displacemen...
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Previous observational and modeling studies indicate that the wintertime North Pacific Oscillation (NPO) could significantly impact the following winter El Niño-Southern Oscillation (ENSO) variability via the seasonal footprinting mechanism (SFM). This study explores climate projections of this winter NPO-ENSO relation in a warming climate based on...
Mass exchanges in the upper ocean between the equatorial and
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... The importance of SST anomalies in the midlatitudes should not be underestimated ( Ummenhofer et al., 2009 ). Some previous studies have verified that ENSO events can alter the anomalous MGSST and then trigger the anomalous HC ( Oort and Yienger, 1996 ;Seager et al., 2003 ;Zhang et al., 2009Zhang et al., , 2013Feng et al., 2019 ). As shown in Fig. 3 (b), warm SST anomalies correspond to the anticyclonic circulation center in July. ...
The rainfall over North China (NC) in July 2021 was the most since 1980, and coincided with a meridional gradient of sea surface temperature anomaly (MGSSTA) in the Pacific. The present study shows that the gradient between the positive sea surface temperature anomaly (SSTA) over the northwestern Pacific and the negative SSTA over the tropical central Pacific was the main reason for the enhanced rainfall in NC in July 2021 because of its influence on the anomalous northward movements of the western North Pacific anticyclone (WNPAC) and its
southern cyclone. The associated easterly wind anomalies along the southern flank of the WNPAC converged with the anomalous easterly along the north flank of the anomalous cyclone, transporting more moisture from south to NC. Meanwhile, the MGSSTA likely induced an anomalous reversed Hadley circulation accompanied by distinct southerly wind anomalies in the low troposphere. These anomalies favored a strong monsoon circulation, which is often accompanied by a rain band in a more northern location.
... These interdecadal variations in the ENSO-related connections are partly because the ENSO itself exhibited an interdecadal change (McPhaden et al., 2011;Zhang et al., 2019). Extensive evidence has indicated that the meridional extent (Zhang et al., 2013), temporal evolution (Z. Hu et al., 2013;A. ...
... Schneider & Lindzen, 1977). The SST anomalies related to El Niño and La Niña events during their mature phases are equatorially symmetrical (Feng et al., 2019;Zhang et al., 2013), favoring equatorially symmetrical meridional circulation anomalies and contributing to EOF1 formation. That is, the spatial-temporal variation in the ENSO exerts a significant influence on the HC variability. ...
Plain Language Summary
The Hadley circulation (HC) has significant regulatory impacts on tropical and extratropical interactions. As a thermal‐dynamical circulation, the variability in the HC exhibits a substantial correlation with the underlying thermal conditions. However, strong interdecadal variations have been observed in the tropical sea surface temperature (SST) around 1976/1977, particularly in the SST related to the El Niño–Southern Oscillation (ENSO). The HC variability after 1977 is still unknown. We investigate the spatial‐temporal variation in the boreal winter HC during the period of 1980–2020. The results show that the primary dominant mode (EOF1) of the HC presents an equatorially symmetrical structure with ascension around the equator. This pattern corresponds to the second dominant mode in preceding studies. The different result indicates that a regime shift in HC variability has occurred. We find that the formation of EOF1 is due to the enhanced variation in ENSO, which explains the spatial‐temporal variations in EOF1. This result is further confirmed in model simulations, highlighting a more important role of the ENSO on the HC in recent decades. These results deepen our understanding of HC variability and emphasize the important climatic effects of the ENSO, which is of great interest because more severe ENSO events are projected for the future.
... Note that, since the central and eastern types of ENSO events have been explored, the SSTA as well as climate variations in the MC have been found to be affected by various types of ENSO. The vertical circulations in troposphere and the equatorial Kelvin/Rossby waves play important roles in the connections between two types of ENSO and MC climate anomalies (Tedeschi et al. 2013;Xiang et al. 2013;Zhang et al. 2013Zhang et al. , 2014Zhai et al. 2016;Fang et al. 2016;Wang and Guan 2017;W. Wang et al. 2018). ...
The sea surface temperature anomalies (SSTA) in the Maritime Continent (MC) region are mainly related to local variability, ENSO, and Indian Ocean dipole. Using the reanalysis from NOAA and NCEP/NCAR, by employing the Empirical Orthogonal Function (EOF) analysis, we have explored the principal mode of ENSO-independent summertime SSTA in the MC and its associations with regional climate anomalies. After ENSO signals have been removed, the leading mode of SSTA in the MC exhibits a uniformly signed pattern, which mainly varies on interannual time-scale. The maintenance mechanisms of the ENSO-independent SSTA are different in different sub-regions, especially over south of Java and the tropical northwestern Pacific. When the time-coefficient of the first leading EOF mode (EOF1) is in positive, warmer SSTAs are observed in area south of Java. The oceanic dynamic heating there facilitates the warmer SSTA. Thus, the Gill-type response of the atmosphere is found over region south of Java. The diabatic cooling in atmosphere is dominant over the tropical northwestern Pacific where the warmer SSTA is maintained by the absorption of solar radiation due to less cloud there. A tilted vertical circulation is hence formed, linking the tropical southeastern Indian Ocean with the tropical northwestern Pacific. The anomalous circulations in Asian-Australian monsoon region are affected by this ENSO-independent SSTA mode, resulting in decreased summer rainfall anomaly in region near southeast coast of China and increased winter precipitation anomaly over the extra-tropical region of Australia.
... Correspondingly, La Niña is also divided into the EP and the CP type by Kao and Yu (2009), Yuan and Yan (2013), Zhang et al. (2015) and Wang et al. (2014). The CP El Niño has significant climatic effect on East Asia (Wang et al., 2000;Zhang et al., 2011Zhang et al., , 2013Zhang et al., , 2014Yuan and Yang, 2012), most countries and regions along the Pacific coast (Weng et al., , 2009Feng et al., 2010;Tedeschi et al., 2012;Zhang et al., 2012), and also affect the Indian Ocean SST (Kao and Yu, 2009) and tropical cyclones (Kim et al., 2009;Chen and Tam, 2010). Widespread impact and low prediction skill of the CP El Niño lead us to find more effective prediction signal for it urgently. ...
By use of observational reanalysis data and the CMIP5 data, the relationships of the Central Pacific (CP) El Niño and the Victoria Mode (VM)/North Pacific Oscillation (NPO) are compared. The VM/NPO and the CP El Niño are physically related via negative feedback process of air–sea interaction. The VM/NPO has a delay effect on the CP ENSO in the subsequent winter. Nevertheless, the impact of VM on the CP El Niño is more effective relative to the NPO. When the conventional ENSO (hereafter as ENSO) own cycle is removed, the former's correlation with the EMI (El Niño Modoki index) in the Dec(+1) only decreases from 0.48 to 0.31, which is still significant. But the latter's correlation dose not reach 95% confidence level. Composition analysis also shows that during the D(+1)JF(+2), very few SST anomalies could be found over 95% significant level whether in positive or negative NPO phase. While for the VM cases, a large area of the CP ENSO‐like SST anomalies is observed significantly in the tropical Pacific. Especially, for non‐ENSO year, CP El Niño occurs in 50% positive VM cases' following winter. Although in previous studies, the VM is only considered as a transition stage during the process of NPO affecting the CP El Niño, the regression analysis shows that the VM is a partly natural mode, most of its variation is contributed by its internal evolution. The CP El Niño would still occur during positive VM cases even when NPO phase is negative. Their relationship remains stable in the CMIP5 RCP8.5 simulations, that is, the global warming does not interfere with the impact of positive VM on the CP El Niño. In conclusion, the VM may be a more effective prediction signal for the CP El Niño than the NPO.
... However, systematic errors still exist. For instance, the simulated patterns of ENSO-related sea surface temperature (SST) and precipitation anomalies in the tropical Pacific region are more westward extended and meridionally narrower than observed (Zhang et al. 2013;Ham and Kug 2015;Dai and Arkin 2017). The atmospheric general circulation models (GCMs) are found to play a more important role in setting ENSO characteristics and errors than the oceanic GCMs (Guilyardi et al. 2004). ...
... Bayr et al. (2018) and (2019) found an error compensation between the two feedbacks, which is strongly related to a cold equatorial SST bias that also hinders the development of the correct position of the rising branch of the Walker Circulation, ENSO dynamics, and ENSO-related precipitation (Bayr et al. 2018(Bayr et al. , 2020. In addition, oceanic model biases in thermocline, SST, and sea level pressure (SLP) play a role in aggravating the ENSO-related biases in the Coupled GCMs (CGCMs; Kirtman et al. 2002;Zhang et al. 2013;Ham and Kug 2014) and could also lead to intermodel diversity of projections of ENSO-related changes. ...
... As one of the most robust projected ENSO SST changes will occur in the cold-tongue region (e.g. Zhang et al. 2013), when the mean-state SST warms and the lowlevel easterlies reduce enough in a larger emission scenario, models with severe biases of cold equatorial SST, i.e. too cold, may develop stronger deep convection over the western equatorial Pacific along with amplified atmospheric feedbacks (Bayr et al. 2020), and thus much larger changes in the pattern and amplitude of ENSO-related precipitation anomalies. Intermodel uncertainty of future changes in ENSO-related precipitation may be enlarged if these models are selected. ...
Changes in El Niño-Southern Oscillation (ENSO)-related precipitation anomalies during the twentieth century are poorly known. The ENSO-related precipitation anomalies over the tropical Pacific Ocean are projected to shift eastward during the twenty-first century. However, intermodel diversity in simulating and projecting these changes has not been fully studied. Understanding such diversity is vital for providing robust projections of future changes in the ENSO-related precipitation. Here, we use an approach that can cleanly separate ENSO signals from long-term variations to study multi-decadal and centennial changes of ENSO-related precipitation anomalies during the twentieth and twenty-first centuries in two precipitation reanalyses and two groups of the Coupled Model Intercomparison Project Phase 5 (CMIP5) models. The two precipitation reanalyses disagree in the multi-decadal changes during the twentieth century: precipitation anomalies in the twentieth century global circulation reanalysis indicates zonal shifts of the positive and negative ENSO-related precipitation anomalies, whereas reconstructed precipitation derived from observations suggests an intensification of the anomalies. Most members of the ensemble of 20 CMIP5 models project significant strengthening or zonal shift in ENSO-related precipitation during the twenty-first century, which is almost entirely influenced by changes in the ENSO-related circulation from a moisture budget analysis. The ‘good-ENSO’ group with stronger ENSO atmospheric feedbacks projects an intensification of ENSO-related precipitation anomalies over the eastern-central equatorial Pacific, as a result of strengthened deep convection anomalies in the middle to upper troposphere above. This increased variability of convection is driven by a warmer SST mean state of the central-eastern Pacific Ocean. The underperforming group that simulates colder equatorial SSTs, weaker atmospheric feedbacks, and more westward extended ENSO-related precipitation anomalies, exhibits both strong intensification and eastward shift of the entire ENSO-related air–sea interactive system and the related precipitation over the western-central Pacific during the twenty-first century, in correspondence with a mean-state SST warming in the entire equatorial Pacific. Our clustered results suggest that the changes of ENSO-related precipitation are closely tied with the historical simulation of structure of the ENSO-related air–sea system and the projection of changes in the mean-state SST under global warming.
... However, the intensity and scope of the SST anomalies are distinct. Compared with the anomalies in El Niño Modoki boreal winter (Fig. 6a), stronger cold anomalies occur in the equatorial central and eastern Pacific (Fig. 6c) and the meridional scope of the cold SST anomalies is larger in La Niña Modoki boreal winter (Fig. 6b), which may be attributed to the enhanced trade winds and thus strengthened upwelling and meridional currents, causing SST anomalies to more effectively spread away from the Equator (Zhang et al. 2009(Zhang et al. , 2013. Meanwhile, during La Niña Modoki, warm anomalies, stretching from Southeast Asia northward to about 40 • N in the western North Pacific, are stronger than that in El Niño Modoki events, particularly in the central North Pacific (Fig. 6c). ...
The El Niño–Southern Oscillation (ENSO) Modoki phenomenon has a substantial influence on regional climate. In this study, the results derived from observational and reanalyzed datasets show that the boreal winter climate anomalies over the Pacific and its rim in the different phases of ENSO Modoki are asymmetric during 1979–2017. During El Niño Modoki, an upper-level zonal “convergence–divergence–convergence” anomaly occurred in the Walker circulation over the Pacific sector, associated with anomalous ascending (descending) in the central side (both sides), leading to a wet “boomerang” pattern of rainfall anomalies in the tropical Pacific Ocean. Consequently, a drier winter occurred in Philippines, and warming and drying occurred in western Australia and northern South America. Meanwhile, a dipolar pattern with the wet south and the dry north in the United States occurred, accompanied by a Pacific/North American-like teleconnection. During La Niña Modoki, a roughly reversed Walker circulation anomaly and deeper Hadley circulation anomalies were associated with the strong air–sea feedback, which caused stronger rainfall anomalies in the Pacific Ocean. On land, anomalies of surface temperature and rainfall over the tropical Pacific Rim were more intense compared with El Niño Modoki. However, owing to the lack of a Pacific/North American anomaly, fewer anomalies occurred over the mid-latitude North America. In numerical experiments, the response to the different phases of ENSO Modoki basically reproduces the asymmetric climate anomalies in boreal winter, further confirming that the asymmetry can be partly attributed to tropical sea surface temperature anomalies.
... The meridional width of the ENSO simulated in GloSea5 was limited, compared with the observation (Fig. 8). Studies have shown that the narrow bias in the simulated width of the ENSO is mainly due to a systematic bias in the weak trade winds, which leads to weak ocean meridional currents (Zhang and Jin, 2012;Zhang et al., 2013) associated with a bias toward short ENSO periods. Previous modeling results have also suggested that El Niño events with a short decay phase lead to significant WNPAC anomalies in the following summer (Chen et al., 2012) and that the WNPAC serves as an important atmospheric system in the interaction between ENSO and WNPSH. ...
The western North Pacific subtropical high (WNPSH) dominates the summer climate over East Asia. The intensity, position, and shape of WNPSH influence the spatiotemporal distributions of precipitation, temperature, and tropical cyclone activities in this region. This paper intends to investigate the performance of the UK Met Office Global Seasonal forecast system version 5 (GloSea5) in simulation/prediction of the WNPSH based on a hindcast dataset. Analyses of the hindcast data show a systematic bias in the mean circulation over West Pacific, with negative geopotential height anomalies over the western North Pacific (WNP) and cyclonic anomalies in the 850-hPa winds and water vapor transport, indicating a weakening and eastward shift of the WNPSH. Despite the model’s bias in the climatology, it well captured the interannual variability of the monthly and seasonal-mean intensity of the WNPSH and the position of its ridge line in boreal summer from 1993 to 2015. The seasonal hindcasts indicate that there is significant prediction skill at up to three-month lead time for both the intensity and position of the WNPSH ridge line. The relationship between the WNPSH and different phases of the El Niño-Southern Oscillation (ENSO) in both the observational data and GloSea5 hindcasts was then investigated. The model captured the summer WNPSH anomalies well during most of the ENSO phases, except in the La Niña decaying and neutral summers. The intensity of the anticyclone in the WNP is weak in the decaying phase of El Niño in the GloSea5 hindcasts compared with the reanalysis data. GloSea5 is capable of representing the lagged teleconnection between El Niño events in the previous winter and the intensity of the WNPSH in the following summer. Regression analysis reveals weakened negative sea surface temperature anomalies (SSTAs) over the WNP in GloSea5, which reduced the gradient between the tropical western Pacific and the tropical Indian Ocean, resulting in a weaker easterly anomaly and stronger westerly anomaly, contributing to the weak anomalous anticyclone over the WNP and the weakened WNPSH relative to the reanalysis data.
... Among the various aspects of ENSO, realistically representing the spatial distribution of the ENSO-related sea surface temperature anomaly (SSTA) is still challenging in model simulation (Bellenger et al. 2014). Previous studies have documented the bias in simulating the meridional structure of the ENSO-related SSTA (Zhang et al. 2013). In terms of the bias in representing the SSTA zonal distribution (hereafter, SSTA-ZD) in ENSO simulation, it is noticed that the modeled SSTA-ZD in the tropical Pacific exhibits a significantly westwardshift bias in the models included in phase 3 of the Coupled Model Intercomparison Project (CMIP3) (Leloup, Lengaigne, and Boulanger 2008;Yu and Kim 2010). ...
The simulated sea surface temperature anomaly (SSTA) over the tropical Pacific during El Niño–Southern Oscillation (ENSO) is investigated in three representative coupled models: CESM1-CAM5, FGOALS-s2, and FGOALS-g2. It is found that there is a significant westward shift bias in reproducing the zonal distribution (ZD) of the ENSO-related SSTA in CESM1-CAM5 and FGOALS-s2, whereas the SSTA-ZD simulated by FGOALS-g2 is relatively realistic. Through examining the SSTA-ZD during both warm and cold phases of ENSO separately, the authors reveal that the SSTA-ZD simulation bias during the ENSO cycle mainly lies in the bias during the warm phase. It is noted that both the simulated zonal wind stress anomaly ( τ x ′ ) and shortwave heat flux (SW) anomaly exhibit westward shift biases in CESM1-CAM5 and FGOALS-s2, while the counterparts in FGOALS-g2 are relatively reasonable. The westward shift biases in representing τ x ′ and the SW anomaly (SWA) are attributed to the westward-shifted precipitation anomaly (PrA). It is suggested that the mean SST cold bias over the cold tongue region is the key factor behind the westward-shift bias in simulating the El Niño-related PrA, which leads to the westward-shifted τ x ′ and SWA. Collectively, the aforementioned anomaly fields, including the dynamic part ( τ x ′ ) and thermodynamic part (SWA), contribute to the westward-shift bias in simulating the El Niño-related SSTA. This study provides clues for understanding the ZD simulation biases of ENSO-related fields; however, further in-depth investigation with more model simulations, especially the incoming CMIP6 simulations, is still needed to fully understand the ENSO SSTA-ZD simulation bias in coupled models.
... β us is related to the meridional width of wind stress. Although it is hard to quantify which factor mostly affects the enhanced β w and β us during P2 compared to P1, a relatively shallow mean thermocline depth ( Figure 3h) and a narrow meridional width of wind stress in response to SST anomalies (Zhang et al., 2009;Zhang et al., 2013) probably play an essential role in increasing vertical β 1 during P2 by modifying β w and β us . β 2 is determined by the positive zonal NDH and negative vertical NDH. ...
The linear recharge oscillator model for the El Niño–Southern Oscillation (ENSO) was expanded to a nonlinear model, thus allowing identification of a nonlinear dynamic ENSO index. This index was applied for a dynamic examination of the El Niño‐La Niña asymmetry. Here, the nonlinear physical processes including the nonlinear dynamical heating were implemented into the linear recharge oscillator model in the form of quadratic nonlinearity. This nonlinear recharge oscillator model revealed that nonlinear (linear) physical processes play a critical role in the long‐term ENSO skewness (amplitude) changes quantitatively. Particularly, the large part of the long‐term ENSO skewness change could be explained by the quadratic nonlinearity associated with the nonlinear ocean dynamical heating, which is closely related to change in mean thermocline. This research provides a unified framework to understand better the past‐present‐future ENSO changes by applying the interdecadal change dynamics on a low hierarchical level.
... The meridional width of ENSO is associated with the strength of poleward advection of oceanic temperature anomalies from the equator by mean meridional overturning circulation of the subtropical cell (STC) (43)(44)(45)(46)(47)(48). The simulated STC is weakened by 30% under global warming, as a response to the robust weakening of the mean easterly trade wind over the equatorial CEP ( Fig. 4) (48,49). ...
During El Niño events, increased precipitation occurs over the equatorial central eastern Pacific, corresponding to enhanced convective heating that modulates global climate by exciting atmospheric teleconnections. These precipitation anomalies are projected to shift and extend eastward in response to global warming. We show that this predicted change is caused by narrowing of the meridional span of the underlying El Niño–related sea surface temperature (SST) anomalies that leads to intensification of the meridional gradient of the SST anomalies, strengthening boundary-layer moisture convergence over the equatorial eastern Pacific, and enhancing local positive precipitation anomalies. The eastward shift and extension of these anomalies also intensify and extend eastward negative precipitation anomalies over the tropical western North Pacific, by strengthening equatorward advection of low mean moist enthalpy. Changes in El Niño–induced tropical precipitation anomalies suggest that, under global warming, El Niño events decay faster after their peak phase, thus shortening their duration.
