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Schematic diagrams for (a)-(d) CT ENSO and (e)-(h) WP ENSO recharge oscillator mechanisms in the (a),(e) warm, (b),(f) warm-to-cold, (c),(h) cold, and (d),(g) cold-to-warm phases. The red (blue) shadings on the top planes representing the sea surface denote positive (negative) SST anomalies, and those on the inclined planes representing the climatic thermocline denote positive (negative) subsurface temperature anomalies. The dark gray arrows denote mean upwelling,; the black arrows represent the zonal and meridional upper-ocean geostrophic current anomalies, and the solid yellow arrows stand for wind stress anomalies: W, C, H, and L denote warm, cold, high, and low, respectively.
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The El Nino-Southern Oscillation (ENSO) tends to behave arguably as two different types or flavors in recent decades. One is the canonical cold-tongue-type ENSO with major sea surface temperature anomalies (SSTA) positioned over the eastern Pacific. The other is a warm-pool-type ENSO with SSTA centered in the central Pacific near the edge of the wa...
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... The SSHA and sea current anomaly changes in the eastern Pacific are relatively weaker and slower than those in the central Pacific ( Figures 8B,G), and the poleward Sverdrup transports show less inter-hemispheric asymmetry ( Figure 9B). These oceanic responses to the SWS and the associated negative oceanic feedback are consistent with those revealed by Ren and Jin (2013) that the reversal of the equatorial sea current anomalies provides the initial negative feedback for El Niño phase transition. ...
The dependence of the southward shift of low-level westerly anomalies over the equatorial central Pacific on El Niño intensity during the mature winter was investigated through observational analyses and air–sea coupled model simulations. El Niño events are categorized into two types based on the presence or absence of such a southward westerly shift (SWS). El Niño events with an evident SWS (SWS El Niño) exhibit strong intensity in sea surface temperature anomalies, whereas those without a remarkable SWS (non-SWS El Niño) are weak. The strength of westerly anomalies of SWS El Niño is twice as large as those of non-SWS El Niño in mature winter and can induce larger growth of westerly anomalies south of the equator by two anomalous southward westerly advections. One is the advection of anomalous westerlies by climatological winter-mean northerlies, and the other is the advection of climatological zonal wind by anomalous westerlies. Observations and model simulations both indicate that the two types of El Niño terminate differently. The strong SWS El Niño decays initially in the equatorial central Pacific, induced by a large local discharge of mass and heat content associated with intense SWS and the subsequent westward sea current anomalies starting in the decaying spring. In contrast, the non-SWS El Niño terminates first in the far eastern Pacific by cool advection carried by local westward sea current anomalies in mature winter, which is then enhanced by poleward discharge associated with weak SWS in the equatorial central Pacific.
... The effects of WWV and sea surface zonal currents, corresponding to thermocline feedback and zonal advective feedback, have been regarded as the two major contributors to ENSO evolution [44,45]. Observations indicate that the variation of WWV leads ENSO by 2-3 seasons [40,46], making spring WWV a good indicator for winter ENSO state [44,47]. Furthermore, the variations in WWV and sea surface zonal current are interrelated [48], as they both depend primarily on changes in the thermocline, which is correlated with zonal wind stress over the equatorial central and western Pacific [38,39,48]. ...
... Such eastward sea current anomalies tend to weaken La Niña (Figure 4m,n) by transporting warm water and heat content eastwards from the warm pool (Figure 4u,v). It is observed that the reversal of sea currents leads to the change of WWV, consistent with the analysis of Ren and Jin [47], who suggested a dominant role in the reversal of sea current anomalies in the ENSO phase transition. However, it is noteworthy that a negative NPMM-like SSTA pattern is evident during the decaying spring of La Niña (see Figure 4m). ...
Previous studies suggested that spring precipitation over the tropical western Pacific Ocean can influence the development of El Niño–Southern Oscillation (ENSO). To identify crucial precipitation patterns for post-spring ENSO evolution, a singular value decomposition (SVD) method was applied to spring precipitation and sea surface temperature (SST) anomalies, and three precipitation and ENSO types were obtained with each highlighting precipitation over the Maritime Continent (MC) or western north Pacific (WNP). High MC spring precipitation corresponds to the slow decay of a multi-year La Niña event. Low MC spring precipitation is associated with a rapid El Niño-to-La Niña transition. High WNP spring precipitation is related to positive north Pacific meridional mode and induces the El Niño initiation. Among the three ENSO types, ocean current and heat content behave differently. Based on these spring precipitation and oceanic factors, a statistical model was established aimed at predicting winter ENSO state. Compared to a full dynamical model, this model exhibits higher prediction skills in the winter ENSO phase and amplitude for the period of 1980–2022. The explained total variance of the winter Niño-3.4 index increases from 43% to 75%, while the root-mean-squared error decreases from 0.82 °C to 0.53 °C. The practical utility and limitations of this model are also discussed.
... General circulation models reflect the characteristics of the traditional EP El Niño but do not adequately simulate the CP El Niño that has been dominant since the 2000s (Ham and Kug 2012). The diversity and complexity of El Niño have recently highlighted the significance of these mechanisms for El Niño evolution, yet the argument between EP and CP El Niño continues (McPhaden et al. 2006;Ren and Jin 2013;Guan and McPhaden 2016). ...
El Niño is the largest natural climate variability event on an interannual time scale occurring in the equatorial Pacific Ocean, and is linked to global climate change. The north equatorial countercurrent (NECC) is considered a significant feature of the tropical Pacific current system due to its location and eastward flow direction. The NECC has been suggested as a current that transports the warmer western Pacific waters to the eastern Pacific to trigger the El Niño event in the equatorial Pacific. We investigated how the movements of zonal wind stress (ZWS) and ocean surface currents (OSC) contribute to the sea surface temperature (SST) changes during the El Niño period. During moderate to severe Central Pacific El Niño events, the continuous flow of the NECC extending from the El Niño monitoring region into the eastern Pacific is rarely observed. In addition, a significant increase in ocean heat content compared to the 27-year climatological normal has been identified at temperatures above 28 °C. Therefore, we propose a hypothesis that the additional heat is supplied from the subsurface source and the warm pool is expanded by the subsurface equatorial countercurrent, known as the Equatorial Undercurrent, rather than by the surface currents. The heated water is expected to contribute to the evolution of El Niño by upwelling to the surface along the equator in a north–south symmetric feature.
... The heat budget analysis helps evaluate the respective contributions of atmospheric and ocean processes to the evolution of IODs. Consistent with earlier 7 studies (Kug et al. 2009;Li et al. 2015;Ren and Jin 2013), the partial derivative of ocean temperature anomaly ′ with respect to time can be expressed as: ...
This study identifies two distinct patterns of the summer Indian Ocean Dipole (IOD) — the coastal IOD and the offshore IOD — named based on the proximity of their eastern pole to Sumatra. Their spatial characteristics, evolutionary mechanisms, relationships with ENSO, impacts on precipitation, and the factors controlling the simulation performances of climate models are discussed.
The coastal IOD shares the same eastern pole as the conventional IOD off Sumatra, but its western pole is located in the central southern tropical Indian Ocean (TIO). The offshore IOD shares the conventional western pole off Somalia, but its eastern pole is located in the central southern TIO. Regarding their evolutions, while they initially develop similarly, their later evolutions differ due to their distinct pole locations: the offshore IOD peaks in summer, while the coastal IOD can be sustained into autumn. The coastal IOD correlates to preceding and late ENSO states, but the offshore IOD does not, making it an independent internal mode of TIO. The two IODs affect climate differently, with only the coastal IOD affecting Australian rainfall. Climate models exhibit varied levels of performance in simulating the two IODs. Specifically, a stronger link between spring TIO rainfall and ENSO, as well as stronger southeasterly monsoonal winds in the southern TIO, can enhance the coastal IOD modeling, while a stronger summer Somali jet benefits the simulation of the offshore IOD. Distinguishing these two IODs has implications for accurate diagnosis and prediction of the summer climate surrounding the TIO.
... El differentiations of El Niño phenomena are commonly classified into three categories: (EP (Eastern Pacific type), CP (Central Pacific type), or Mix (mixed type), with undiagnosed cases indicated by a dash [10]. Diverse methodologies are employed to facilitate this categorization, encompassing the Pattern Correlation approach (referred to as the PTN method) and the El Niño Modoki Index (known as EMI). ...
This investigation explores the impact of global warming on the El Nio-Southern Oscillation (ENSO), a pivotal climatic phenomenon with far-reaching consequences for worldwide weather patterns and ecosystems. In the context of ongoing endeavors to mitigate climate change, comprehending ENSO's response assumes a position of utmost significance. Current research suggests that the amplitudes of ENSO events may intensify in response to elevated temperatures, linked to non-linear increments in atmospheric water vapor. Furthermore, careful analysis reveals an augmented variability in sea surface temperature (SST) fluctuations during the 21st century compared to prior periods. The research also sheds light on the concurrent existence and interactions of Eastern Pacific (EP) and Central Pacific (CP) ENSO variations in the context of a warming climate. Ongoing investigations are committed to unraveling the intricacies of these phenomena and their implications for future climatic patterns. Nevertheless, uncertainties persist regarding the drivers of CP-type ENSO and heightened amplitudes, with some attributing these changes to global warming while others associate them with multidecadal rhythms.
... We used the ocean near-surface heat budget equation (Ren and Jin 2013) to diagnose the relative roles of oceanic dynamics (Adv) and sea surface thermal forcing (F t ) in driving SST anomalies and isolate the relative contributions of different physical processes. The near-surface averaged temperature tendency is determined as follows: ...
A meridional dipolar atmospheric teleconnection between the Tasman Sea and the Southern Ocean, which describes a hybrid between the El Niño–Southern Oscillation, Indian Ocean Dipole and Southern Annular Mode, was referred to as the Hybrid Teleconnection (HT) pattern previously. We investigate its connection with East Asian summer rainfall and find the preceding May–June HT can be the precursor of the following July–August East Asian rainfall. The mechanism is examined based on analyses of observational datasets and historical runs of coupled models from phase 6 of the Coupled Model Intercomparison Project (CMIP6). The results suggest that a positive HT with positive 500 hPa geopotential height anomalies over the Tasman Sea but negative over the Southern Ocean in the preceding boreal early summer contributes to generating negative sea surface temperature (SST) anomalies in the western tropical Pacific (WP) by influencing surface heat exchange. The SST anomalies over WP persist into the mid-summer via the thermal memory of seawater, inducing interhemispheric meridional circulation and then exciting a Pacific-Japan-Pattern-like atmospheric circulation anomaly, which manifests as an anticyclone over the subtropical northwestern Pacific along with a cyclone near the Sea of Japan. This pattern induces intensified convergence and vertical ascend motion, and subsequently intensifies rainfall in the Yangtze River Basin.
... This point was investigated in details by Van Kampen [4]. However, it often happens that SDE (1) is the genuine result of a procedure of contraction/elimination of fast or unobservable variables of a complex system (e.g., by using the Mori approach [5][6][7], or by exploiting the temporal multiscale property of the system, see, for example [8][9][10]). In such a case, SDE (1) represents a good qualitative (and often quantitative) description of the complex phenomenon under study (see, for example [11] or [12]). ...
This paper deals with the problem of finding the Fokker Planck Equation (FPE) for the single-time probability density function (PDF) that optimally approximates the single-time PDF of a 1-D Stochastic Differential Equation (SDE) with Gaussian correlated noise. In this context, we tackle two main tasks. First, we consider the case of weak noise and in this framework we give a formal ground to the effective correction, introduced elsewhere (Bianucci and Mannella in J Phys Commun 4(10):105019, 2020, https://doi.org/10.1088/2399-6528/abc54e), to the Best Fokker Planck Equation (a standard “Born-Oppenheimer” result), also covering the more general cases of multiplicative SDE. Second, we consider the FPE obtained by using the Local Linearization Approach (LLA), and we show that a generalized cumulant approach allows an understanding of why the LLA FPE performs so well, even for noises with long (but finite) time scales and large intensities.
... In recent decades, various flavours of El Niño with associated different impacts have received extensive attention, including eastern Pacific (EP) El Niños, central Pacific (CP) El Niños (Hu et al., 2012;Kao & Yu, 2009;Kug et al., 2009;Li et al., 2023;Ren & Jin, 2013;Yu & Kao, 2007;Yuan & Yang, 2012;Zheng et al., 2014), ENSO-Modoki (e.g., Ashok & Yamagata, 2009), coastal El Niños Li et al., 2023) and uncoupled El Niños (Hu et al., 2020c). Due to the differences in the spatial pattern, intensity and temporal evolution in EP and CP ENSO, their distinct impacts on precipitation in the extratropics have been identified (Feng et al., 2010;Hu et al., 2012;Liu et al., 2020aLiu et al., , 2020bLiu et al., , 2021bNg et al., 2019;Wu et al., 2014;Xu et al., 2019;Zheng et al., 2014). ...
... According to CPC's classification, all the El Niño and La Niña years from DJF of 1950/1951 to JJA of 2022 are listed in Table 1. To distinguish the flavour of El Niño, the EP (CP) El Niños (Ren & Jin, 2013) are classified when the Niño3 index (SST anomalies averaged in 5 S-5 N, 150 -90 W) is larger (less) than the Niño4 index (SST anomalies averaged in 5 S-5 N, 160 E−150 W) during its peak phase, representing that the largest atmospheric and ocean anomalies associated with El Niño appear in the eastern (central) equatorial Pacific . ...
... The EP and CP El Niños not only display differences in the spatial patterns of the SST anomalies in the tropical Pacific (Hu et al., 2012;Ren & Jin, 2013), but also have a pronounced asymmetry in their amplitudes with EP stronger than CP El Niños (Hu et al., 2012;Zheng et al., 2014). Meanwhile, it has been noted that the F I G U R E 7 Composites of (a, g) MAM(0), (b, h) JJA(0), (c, i) SON(0), (d, j) DJF(1), (e, k) MAM(1) and (f, l) JJA(1) Z500 anomalies (shading, gpm) in (a-f) El Niño and (g-l) La Niña years, respectively. ...
The El Niño–Southern Oscillation (ENSO) is a major source of seasonal climate predictability and a key predictor for East Asian precipitation. However, the impacts of ENSO on East Asian precipitation are extremely complex and still controversial. Thus, it is necessary and significant to use various (observational and model) data sources to further examine the robustness of the impacts. This study revisits the evolution of the ENSO‐related seasonal precipitation anomalies in East Asia, including symmetric and asymmetric impacts of El Niños and La Niñas, the differences in the influences of eastern Pacific (EP) and central Pacific (CP) El Niños, and the interdecadal change of ENSO influences. The ENSO impact on East Asian precipitation has weakened (strengthened) in the ENSO's developing (decay) phase in the recent two decades. The ENSO impacts are robust in (i) southern China‐lower reaches of the Yangtze River‐southern Japan around the ENSO's mature phase, (ii) western North China in the developing phase and (iii) southwestern China in the decay phase. The distribution of East Asian precipitation anomalies is asymmetric in El Niño and La Niña years. The model simulations forced with observed sea surface temperature generally reproduce the observed evolution of seasonal precipitation anomalies associated with ENSO and confirm the robust impact of ENSO in East Asia. These results indicate the necessity to consider the asymmetric impact of El Niños and La Niñas, to distinguish the El Niño flavours for their impact on the East Asian climate, and to include the interdecadal variation of ENSO influence in addressing East Asian climate anomalies.
... The mentioned feedbacks were shown to contribute differently to the generation of two El Niño types. The thermocline feedback plays a key role in the evolution of El Niño events with the maximum SSTA variability in the eastern Pacific, while the zonal advective feedback is responsible for SSTA growth in the central Pacific [9,[13][14][15]. Zonal advective feedback also plays an important role in the development of strong El Niño events [16], being an important contributor to the SSTA growth both in the central and eastern Pacific [14,17]. ...
The heat budget of the equatorial Pacific mixed layer during El Niño formation was studied based on reanalysis (GLORYS2V4) and model data for the modern climate. The focus of the study is on the so-called El Niño diversity, i.e., the existence of different types of events that are characterized by different locations and intensities, as well as significantly different teleconnection all around the world. The analysis of the processes that participate in the formation of different El Niño types may serve for a better understanding of the El Niño dynamic and contribute to improving its forecast. Two classifications, based on the location and intensity of the events, were considered: strong/moderate and Eastern Pacific (EP)/Central Pacific (CP). The analysis did not reveal a significant difference in the heat budget of the mixed layer between strong and EP El Niño events, as well as between moderate and CP events. The major difference in the generation mechanism of strong (EP) and moderate (CP) El Niño events consists of the magnitude of heating produced by ocean heat budget components with higher heating rates for strong (EP) events. The evolution of sea surface temperature anomalies (SSTA) is governed primarily by oceanic advection. The vertical advection (due to the thermocline feedback) is the main contributor to SSTA growth in the eastern Pacific regardless of El Niño’s type. In the Central Pacific, horizontal advection is more important than vertical one, with a stronger impact of meridional processes for both strong and moderate regimes. Furthermore, the evaluation of the CMIP5 model’s skill in the simulation of the processes responsible for the formation of different El Niño types was carried out. The analysis of the heat budget of the mixed layer in the CMIP5 ensemble demonstrated that the most successful models are CCSM4, CESM1-BGC, CMCC-CMS, CNRM-CM5, GFDL-ESM2M, and IPSL-CM5B-LR. They are capable of reproducing the most important contribution of the advection terms in the SSTA tendency, keeping the major role of the thermocline feedback (and vertical advection) in the eastern Pacific, and do not overestimate the contribution of zonal advective feedback. These models are recommended to be used for the analysis of El Niño mechanism modification in the future climate.
... To diagnose the specific contributions of different dynamical processes to the ocean temperature anomaly during El Niño evolution, a mixed-layer heat budget analysis (An et al., 1999;Kug et al., 2009;Li et al., 2002;Zhang et al., 2007) was conducted. Following the definition by Ren and Jin (2013), the equation for the mixed-layer temperature anomaly tendency (MLTAT), consisting of six feedback terms and a residual term (R), can be expressed as ...
... According to previous studies, ZA is an essential oceanic dynamical process that controls the ENSO growth rate (Jin & Neelin, 1993;Ren & Jin, 2013;Zhang et al., 2007). Hence, this feedback attributed to the biased structure of ZCA might hinder the models' ability to simulate a realistic El Niño evolution. ...
A systematic bias of the extremely westward zonal current (EWZC) was revealed over the equatorial Pacific in Coupled Model Intercomparison Project 6 (CMIP6) models. It tends to weaken the modeled interannual variability of equatorial zonal current anomaly (ZCA) with its maximum variability concentrated in the western Pacific. A mixed‐layer heat budget analysis demonstrates that the simulation of mean circulation effect is slightly affected by the zonal current bias. However, the zonal advective feedback is closely linked to the biased equatorial ZCA variability and is overestimated (underestimated) in the Niño‐4 (Niño‐3) region. The magnitude of zonal advective feedback is even greater than that of thermocline feedback and becomes the most dominant process contributing to the growth of mixed‐layer temperature anomaly tendency in the Niño‐4 region. Such a bias is essential for a more central‐Pacific El Niño‐like performance in CMIP6 models.
