El Nino-Southern Oscillation Variability Research Articles

Western Pacific Warm Pool δ18O Response to the El Niño‐Southern Oscillation

AbstractTropical Pacific seawater and precipitation stable oxygen isotope data aid in understanding modern oceanic and atmospheric interactions, and these data are particularly valuable as they are archived in isotope‐based paleoclimate records. However, the absence of modern seawater isotope time series limits the ability to identify the atmospheric influences on these data, precluding robust paleoclimate interpretations. We present a new 10 year sub‐monthly record of seawater and precipitation stable oxygen isotope values (δ18Osw and δ18Op) from Koror, Palau. Our dataset indicates that temporally, δ18Osw is strongly influenced by local δ18Op. Both monthly δ18Osw and δ18Op are highly correlated with outgoing longwave radiation across the tropical Pacific, reflecting a Walker Circulation imprint on the surface ocean. Changes in the Palau δ18Osw—salinity relationship correspond to NINO3.4 variability, indicating a difference in how these variables record El Niño Southern Oscillation (ENSO) information, but demonstrating the utility of δ18Osw to reconstruct ENSO variability in the western tropical Pacific.

Linking Projected Changes in Seasonal Climate Predictability and ENSO Amplitude

Abstract Recent studies have shown that potential predictability and actual forecast skill have varied throughout the historical record, primarily due to natural decadal variability. In this study, we explore whether and how potential predictability is projected to change in the future as a distinct response to anthropogenic climate change. We estimate the potential predictability of El Niño–Southern Oscillation (ENSO) as well as global surface temperature, precipitation, and upper-atmospheric circulation anomalies from 1921 to 2100, within a perfect model framework, using five coupled model large ensembles. We find that historical and projected ENSO amplitude changes generate global-scale shifts in climate predictability via ENSO-driven changes in the signal-to-noise ratio of seasonal forecasts, with a 10% change in Niño-3.4 standard deviation leading to a 14% change in globally averaged forecast skill at 12-month lead. This relationship suggests that potential predictability changes across much of the globe in the coming decades could be linked to anthropogenic climate change of ENSO. However, since current models substantially disagree on the sign and intensity of projected ENSO change, the trajectory of future global predictability changes cannot yet be determined. This problem is demonstrated by widely varying predictability changes seen across the five large ensembles, with models exhibiting a robust increase, robust decrease, or no significant change in predictability, depending upon their respective projected ENSO amplitude trends. Our results highlight the need for climate model development aimed at better capturing past forced and unforced changes to ENSO variability, which is necessary (if not sufficient) to constrain projected changes to climate predictability worldwide.

Unstable relationship between tropical Indian Ocean SST and spring drought on the Loess Plateau modulated by interdecadal variability of ENSO

Abstract The Loess Plateau (LP) is recognized as a region highly vulnerable to climate change, particularly susceptible to spring droughts. Spring drought intensity is crucial as it significantly impacts crop growth and the occurrence of dust storms. However, the underlying mechanisms of spring drought in LP remain unclear. This study investigates the relationship between spring drought intensity in the LP and interannual sea surface temperature anomalies (SSTAs) in the tropical Indian Ocean (SST_TIO). We found that this relationship is negatively correlated but exhibits instability. It was significant during 1963–2001, a time characterized by homogeneous SST_TIO changes, and became insignificant during 2002–2021, during which SST_TIO changes were inhomogeneous. Homogeneous SST_TIO changes appear to stimulate atmospheric wave trains emanating from North Africa and the Arabian Peninsula, influencing precipitation patterns in the LP via the anomalous height in Northeast Asia. In contrast, inhomogeneous SST_TIO changes do not have this effect. Additionally, the impact of homogeneous SST_TIO changes on LP's spring precipitation during 1963–2001 was slightly enhanced by synergistic SSTAs in the tropical eastern Pacific-Atlantic oceans. sensitivity experiments of numerical model confirm the above physical processes. Moreover, these synergistic changes in the TIO and tropical Pacific-Atlantic are modulated by the interdecadal variability of the preceding winter El Niño-Southern Oscillation (ENSO). SSTAs in Indian Ocean exhibit more homogeneous distributions and a closer linkage with tropical Pacific-Atlantic during the periods with stronger ENSO variability. Conversely, when ENSO variability is weak, inhomogeneous SSTAs of Indian Ocean have a weaker relation with tropical Pacific-Atlantic regions.

The water-energy nexus under ENSO variability in four Colombian hydropower basins

ABSTRACT The El Niño-Southern Oscillation (ENSO) has diverse effects on the interannual variability of river flows in Colombia. Given that 70% of the country's electricity supply is provided by hydroelectric dams located in different regions and operated by different companies linked by a nationally integrated system, the decisions taken by operators in response to ENSO can be just as varied. The present study investigates the spatial and temporal distribution of the ENSO effects in four case studies, its relation to hydropower generation and prices, and assesses the reliability of global ENSO indices for monitoring and anticipating local effects. The results show ENSO-driven variations in streamflow and precipitation in all cases, but their intensity and duration are highly dependent on location. La Niña led to positive precipitation and stream flow anomalies, while El Niño led to negative anomalies. In two dams, Hidrosogamoso and Betania, the ENSO influence is stronger, and has a higher correlation with reservoir operations with lags greater than one month. Urra has more stationary annual operations given the reduced ENSO effects in the reservoir’s basin. On the whole, ENSO indices are insufficient in describing the local variations completely. And operator’s size, market share, and installed capacity contribute to increasing flexibility in operations while facing ENSO challenges.

Comparison of the ENSO‐Related Interannual Variability of the ECS‐Kuroshio Before and After 2005

AbstractThe El Niño‐Southern Oscillation (ENSO)‐related interannual variability of the Kuroshio in the East China Sea (ECS) was revisited based on reanalysis outputs during 1993–2018. Unlike the synchronized variations from 2006 to 2018, the period of 1993–2005 showed regional differences in how the ECS‐Kuroshio responded to ENSO events. Specifically, from the upstream region to the midway of the continental slope, the ECS‐Kuroshio exhibited distinct six‐year interannual modulation during 1993–2005. In contrast, downstream Kuroshio variability primarily followed a four‐year cycle, aligning with ENSO variability during the same period. Further analysis suggested that the sea surface height anomaly (SSHA) east of the Kerama Gap, near the midpoint of the Ryukyu Island chain, extended inside the ECS until the southern side of the Tokara Strait along the ECS‐Kuroshio path and was well correlated with the Kuroshio in the Tokara Strait during 1993–2005. The cause of this SSHA signal was attributed to forcing by ENSO‐related wind stress curl changes in the interior region. There was an obvious difference in the ENSO‐related atmospheric circulation before and after 2005. The wind stress curl pattern in the North Pacific during 1993–2005, characterized by a maximum in the Kerama Gap latitude band, shifted northward compared to that during 2006–2018. The relative northward shift of the ENSO‐related wind stress curl, which stimulates the long baroclinic Rossby wave propagating westward and arriving east of the Kerama Gap, affect the interannual variabilities of both the upstream and downstream Kuroshio.

Impacts of El Niño-Southern oscillation on multi-scale morphodynamics of an embayed beach in southern China

Increased coastal erosion and extreme oceanographic forcing driven by El Niño-Southern Oscillation (ENSO) along the Pacific coast are increasingly receiving concerns. Despite considerable attention, the specific impact of these phenomena on Chinese shorelines, particularly along the South China beaches, remains inadequately understood. To address this gap, this study conducted high-frequency surveys on the Qing'an Bay beach in South China and employ a profile fitting model to refined waterline extraction from monthly satellite images. The goal was to investigate the relationship between high-frequency shoreline changes and interannual climate variability (such as ENSO). The findings indicate that the coastal evolution is intricately linked to a combination of strong wave events, summer storms, winter cold waves, and the amplifying effects of ENSO. During La Niña phase, the sea level in the western Pacific experiences a rise, with associated storms proving particularly destructive to the beach environment, leading to violent oscillations in the coastline. Specifically, in the strong La Niña phases, significant wave heights markedly surpass neutral conditions, precipitating intensified sediment movement. However, it is imperative to recognize that shoreline changes alone do not fully characterize coastal erosion. Assessment must also encompass alterations in beach volume. By calculating beach volume per unit width that accounts for the influence of ENSO variability on the beach, the seasonal characteristics of the beach showed sediment losses in summer and autumn, and gains in winter and spring, which was more obvious during strong La Niña. Additionally, conceptual model analysis reveals that during the La Niña phase, the bay is fully exposed, whereas during the El Niño phase, significant headland sheltering is observed.

Future increase in extreme El Niño supported by past glacial changes

El Niño events, the warm phase of the El Niño–Southern Oscillation (ENSO) phenomenon, amplify climate variability throughout the world1. Uncertain climate model predictions limit our ability to assess whether these climatic events could become more extreme under anthropogenic greenhouse warming2. Palaeoclimate records provide estimates of past changes, but it is unclear if they can constrain mechanisms underlying future predictions3–5. Here we uncover a mechanism using numerical simulations that drives consistent changes in response to past and future forcings, allowing model validation against palaeoclimate data. The simulated mechanism is consistent with the dynamics of observed extreme El Niño events, which develop when western Pacific warm pool waters expand rapidly eastwards because of strongly coupled ocean currents and winds6,7. These coupled interactions weaken under glacial conditions because of a deeper mixed layer driven by a stronger Walker circulation. The resulting decrease in ENSO variability and extreme El Niño occurrence is supported by a series of tropical Pacific palaeoceanographic records showing reduced glacial temperature variability within key ENSO-sensitive oceanic regions, including new data from the central equatorial Pacific. The model–data agreement on past variability, together with the consistent mechanism across climatic states, supports the prediction of a shallower mixed layer and weaker Walker circulation driving more frequent extreme El Niño genesis under greenhouse warming.

Chile Niño/Niña in the coupled model intercomparison project phases 5 and 6

The north and central coast of Chile is influenced by El Niño-Southern Oscillation (ENSO) through oceanic and atmospheric teleconnections. However, it also experiences episodic oceanic warmings off central Chile (30°S) lasting a few months that are not necessarily associated with ENSO. These episodes, called “Chile Niño” events, besides their ecological and socio-economical impacts, have also the potential to influence tropical Pacific variability. Here, we investigate how realistically the models in the Coupled Model Intercomparison Project (CMIP, Phases 5 and 6) simulate Chile Niño/Niña (CN) events, and quantify their changes under anthropogenic forcing. Despite limitations of the global models in simulating realistically coastal upwelling dynamics, we show that they simulate reasonably well the observed spatial pattern, amplitude and seasonal evolution of CN events. They however fail to properly represent the positive skewness from observations. The analysis of a sub-group of models (36) that simulate ENSO realistically reveals that CN events increase in amplitude and variance in the future climate with no changes in their frequency of occurence. This is interpreted as resulting from compensating effects amongst changes in remote drivers and local feedbacks. In particular, ENSO variance increases while that of the South Pacific Oscillation decreases. Conversely, we found that while the Wind-Evaporation-SST feedback tends to increase and the coupling between mixed-layer depth and SST weakens, favoring the development of CN events, the thermocline and wind-SST feedbacks decrease. However, only the change in the thermocline feedback is correlated to changes in CN variance amongst the models, suggesting a dominant role of local oceanic stratification changes in constraining the sensitivity of CN to global warming.

Opposing Changes in Indian Summer Monsoon Rainfall Variability Produced by Orbital and Anthropogenic Forcing

AbstractFuture projections indicate that Indian Summer Monsoon Rainfall (ISMR) faces a “wetter and more variable” climate. However, the reasons remain uncertain. The Last Interglacial (LIG) climate provides a potential analog for future warming. Investigating ISMR responses to these two warming scenarios could help understand the causes of ISMR changes. Using PMIP4 simulations, we find that ISMR became “wetter and more stable” during the LIG, contrasting the future climate. The opposing changes in ISMR variability are related to divergent changes in the El Niño‐Southern Oscillation (ENSO) amplitudes, ENSO‐ISMR relationships, and ENSO‐induced large‐scale atmospheric circulation anomalies. During the LIG, orbital forcing weakened ENSO variability and its impacts on ISMR. A westward positioning of ENSO shifted the atmospheric circulation anomalies westward, suppressing extreme ISMR anomalies. These processes are supported by atmospheric model simulations. Our results suggest that different warming patterns (dynamic effects) are more critical than moisture‐increasing effects in controlling regional climate variability.

Linkage of El Niño-Southern Oscillation to astronomic forcing

Abstract Deciphering the causes of El Niño-Southern Oscillation (ENSO) represents one of the greatest scientific and societal challenges because ENSO impacts people’s safety, food, water, health, and economy. Traditionally, ENSO has been considered a phenomenon that is mostly influenced by the interactions between oceanic and atmospheric processes, i.e. by the internal variability in Earth’s ocean-atmosphere system. However, dendrochronological records of climate indices, ENSO among them, have statistically significant variance at periodicities related to solar activity (sunspots) and lunar precessions. Other studies indicate a modulation by the lunar nodal cycle of ocean’s mixing and its implications on water and air temperatures, steric sea levels, coastal flooding, rain, river discharge and heat transport. Those findings suggest that astronomic forces may influence ENSO. In fact, this study shows that a fit to well-established periodicities from lunar precessions, solar activity and their interactions explains 91% of the variance of an ENSO index smoothed at 5 years, and 67% of a 3 yr filtered ENSO index. Provided that the future Earth’s ocean-atmospheric system remains roughly within historical bounds under a changing climate in the next 2–3 decades, one can venture a projection into the future of 3- and 5 yr smoothed ENSO variability. Such projection is given here and might help in preparations for adaptation and mitigation measures caused by ENSO-related coastal hazards.

Review: The effect of climate change on the distribution pattern of small pelagic fish around the world

Abstract. Yuniar A, Zainuddin M, Hidayat R, Srioktoviana SK, Safruddin, Mustapha MA, Farhum SA. 2024. Review: The effect of climate change on the distribution pattern of small pelagic fish around the world. Biodiversitas 25: 3325-3341. Small pelagic fish populations, which are critical to marine ecosystems and play a crucial part in food availability worldwide, are significantly impacted by climate change. Variations of small pelagic catch could be indicated by indices of climate variability such as AMO (Atlantic Multidecadal Oscillation), ENSO (El-Nino Southern Oscillation), IOD (Indian Ocean Dipole), and Monsoon. The purpose of this study was to provide important insight into the relationship of climate variability with the distribution of dominant species of small pelagic fish such as European sardines, mackerel, Decapterus sp., anchovy, and Sardinella sp. from 1974-2022. On average, the temperature optimum of small pelagic fish is generally 28.31±1.97°C, chlorophyll concentration of 0.68±0.37 mg.m-3, and salinity of 31.44±2.40 psu. In North Atlantic Waters, the dynamic migration and abundance of pelagic fish are influenced by the climate variability of AMO tharough the warm phase and cold phase. The impact of ENSO, IOD, and chlorophyll variability affect the distribution pattern and abundance of small pelagic species (mackerel, lemuru, anchovy, indian scad, and sardine) in tropical and subtropical waters. In the context of climate change impacts, the results show that small pelagic fish with a preference for warm temperatures tend to migrate to higher latitudes. Understanding the effect of climate change on the spatial and temporal dynamics of small pelagic fish could help improve the performance of future small pelagic fishing strategies and management around the world.

Different pacemakers of marine organic carbon burial in the North Yellow Sea from the early to late Holocene

Marginal seas play a crucial role in the global carbon cycle, contributing approximately 20% of the net CO2 uptake by the world's oceans. The North Yellow Sea (NYS), a semi-enclosed marginal sea in the western Pacific Ocean, serves as a significant carbon sink influenced by factors such as sea level changes, monsoon dynamics, ocean currents, and El Niño-Southern Oscillation (ENSO) activity. This study examines a 538 cm-long sediment core W03 from the NYS (10.3 kyr BP to present). We analyzed Organic Carbon (OC) proxies, including total organic carbon (TOC), the stable carbon isotope (δ13C) of TOC, total nitrogen (TN) and marine-produced lipid biomarkers. Our findings demonstrate a strong correlation between OC burial and sea-level fluctuations during the early Holocene, driven by the exposure of the continental shelf. During the mid-Holocene, the intrusion of the Yellow Sea Warm Current increased salinity and temperature conditions and nutrient levels of sea water, thereby enhancing marine OC burial. Over the last 3.3 kyr BP, ENSO variability and intensified East Asian Winter Monsoon (EAWM) strengthened the coastal currents, contributing to better OC preservation. Additionally, human activities on the surrounding mainland increased terrestrial input, altering the OC burial. The heightened activity of the Kuroshio Current also introduced more saline and warm water masses into the NYS, impacting phytoplankton productivity and community structure, as indicated by increased C37 alkenones. This study highlights the complex interplay of geological factors in OC burial processes within the NYS, providing valuable insights into OC dynamics in marginal seas under the impact of global change.

Observed Global Mean State Changes Modulating the Collective Influence of the Tropical Atlantic and Indian Oceans on ENSO

Abstract In the last decades, many efforts have been made to understand how different tropical oceanic basins are able to impact El Niño–Southern Oscillation (ENSO). However, the collective connectivity among the tropical oceans and their associated influence on ENSO are less understood. Using a complex network methodology, the degree of collective connectivity among the tropical oceans is analyzed focusing on the detection of periods when the tropical basins collectively interact and the Atlantic and Indian basins influence the equatorial Pacific sea surface temperatures (SSTs). The background state for the periods of strong collective connectivity is also investigated. Our results show a marked multidecadal variability in the tropical interbasin connection, with periods of stronger and weaker collective connectivity. These changes seem to be modulated by changes in the North Atlantic Ocean mean state a decade in advance. In particular, strong connectivity occurs in periods with colder than average tropical North Atlantic surface ocean. Associated with this cooling, an anomalous convergence of the vertical integral of total energy flux (VIEF) takes place over the tropical north–west Atlantic, associated with anomalous divergence of VIEF over the equatorial eastern Pacific. In turn, an anomalous zonal surface pressure gradient over the tropical Pacific weakens the trades over the western equatorial Pacific. Consequently, a shallower thermocline emerges over the western equatorial Pacific, which can enhance thermocline feedbacks, the triggering of ENSO events, and therefore, ENSO variability. By construction, our results put forward opposite conditions for periods of weak tropical basin connectivity. These results have important implications for seasonal to decadal predictions.

Comparison of machine learning models in forecasting different ENSO types

Accurate forecasting of the El Niño Southern Oscillation (ENSO) plays a critical role in mitigating the impacts of extreme weather conditions linked to ENSO variability on ecosystems. This study evaluates the performance of six machine learning models in forecasting two ENSO types: the Central Pacific El Niño (Niño 4 index) and the East Central Pacific El Niño (Niño 3.4 index). The models analyzed include the Feed Forward Neural Network (FFNN), Long Short-term Memory (LSTM) neural network, eXtreme Gradient Boosting Regressor, K-Nearest Neighbors Regressor, Gradient Boosting Regressor, and Support Vector Regressor, using the ENSO index lagged by six months as the predictor. The models were trained on the monthly ENSO indices from 1870 to 1992 and tested from 1993 to 2023. We also assess the relative predictability of the two ENSO types. Events were defined as when the ENSO index exceeded ±0.4. Our evaluation during the testing period reveals that for the analyzed models, the deep neural network models (LSTM and FFNN) demonstrated superior performance in forecasting ENSO at a 6-month lead time. Furthermore, all models achieved impressive all-season correlations ranging from 0.93 to 0.97 and threat score for the ENSO phases between 0.71 to 0.88 for Niño 3.4 events, and 0.72 to 0.93 for Niño 4 events. The predictability of the two ENSO types depended on the model and strength of the ENSO event. Considering both ENSO phases, La Niña events were forecasted with a higher accuracy relative to El Niño events, and all models, besides the deep learning models, notably fell short in capturing the extreme 2015/2016 Central Pacific El Niño event. These results highlight the potential of machine learning models, particularly the deep learning approaches, for skillful ENSO forecasting, by leveraging its historical data.

Contribution of El Niño Southern Oscillation (ENSO) Diversity to Low‐Frequency Changes in ENSO Variance

AbstractEl Niño Southern Oscillation (ENSO) diversity is characterized based on the longitudinal location of maximum sea surface temperature anomalies (SSTA) and amplitude in the tropical Pacific, as Central Pacific events are typically weaker than Eastern Pacific events. SSTA pattern and intensity undergo low‐frequency modulations, affecting ENSO prediction skill and remote impacts, and resulting in low‐frequency changes in ENSO variance. Yet, how different ENSO types contribute to these decadal variance changes remains unclear. Here, we decompose the low‐frequency changes of ENSO variance into contributions from ENSO diversity categories. We propose a fuzzy clustering of monthly SSTA to allow for non‐binary event category memberships, where each event can belong to different clusters. Our approach identifies two La Niña and three El Niño categories and shows that the major shift of ENSO variance in the mid‐1970s was associated with an increasing likelihood of strong La Niña and extreme El Niño events.

Decreased ENSO post-2100 in response to formation of a permanent El Niño-like state under greenhouse warming

Under transient greenhouse warming, El Niño-Southern Oscillation (ENSO) is projected to increase pre-2100, accompanied by an easier establishment of atmospheric convection in the equatorial eastern Pacific, where sea surface temperature (SST) warms faster than surrounding regions. After 2100, how ENSO variability may change remains unknown. Here we find that under a high emission scenario, ENSO variability post-2100 reverses from the initial increase to an amplitude far smaller than that of the 20th century. The fast eastern warming persists and shrinks the equatorial Pacific non-convective area, such that establishing convection in the non-convective area, as during an El Niño, requires smaller convective anomaly, inducing weaker wind anomalies leading to reduced ENSO SST variability. The nonlinear ENSO response is thus a symptom of the persistent El Niño-like warming pattern. Therefore, the oscillatory ENSO impact could be replaced by that from the permanent El Niño-like mean condition with cumulative influences on affected regions.

Subseasonal Variability of ENSO–East Asia Teleconnections Driven by Tropical Convection Over the Indian Ocean and Maritime Continent

AbstractThe El Niño–Southern Oscillation (ENSO) has a significant impact on the surface climate of East Asia by modulating the atmospheric circulation over the Kuroshio Extension. Here, we show that the ENSO–East Asia teleconnections are strongest in early winter due to the combined effects of the Indian Ocean and Maritime Continent convections, but weakest in mid‐winter as these tropical convections weaken. During the early El Niño winter, convection is enhanced over the Indian Ocean and suppressed over the Maritime Continent. The associated Rossby wave trains constructively interfere over the Kuroshio Extension, resulting in anticyclonic circulation anomalies. The equatorial central Pacific convection has a minimal impact on the East Asia. This result suggests that the Indian Ocean and the Maritime Continent convections, rather than the equatorial central Pacific convection, are the precursors of the early winter ENSO–East Asia teleconnections, and need to be considered for subseasonal‐to‐seasonal prediction in East Asia.

Multi‐Decadal Skill Variability in Predicting the Spatial Patterns of ENSO Events

AbstractSeasonal hindcasts have previously been demonstrated to show multi‐decadal variability in skill across the twentieth century in indices describing El‐Niño Southern Oscillation (ENSO), which drives global seasonal predictability. Here, we analyze the skill of predicting ENSO events' magnitude and spatial pattern, in the CSF‐20C coupled seasonal hindcasts in 1901–2010. We find minima in the skill of predicting the first (in 1930–1950) and second (in 1940–1960) principal components of sea‐surface temperature (SST) in the tropical Pacific. This minimum is also present in the spatial correlation of SSTs, in 1930–1960. The skill reduction is explained by lower ENSO magnitude and variance in 1930–1960, as well as decreased SST persistence. The SST skill minima project onto surface winds, leading to worse predictions in coupled hindcasts compared to hindcasts using prescribed SSTs. Questions remain about the offset between the first and second principal components' skill minima, and how the skill minima impact the extra‐tropics.

The South American precipitation trends under (or not) El Niño‐Southern Oscillation influences and relationship with large‐scale circulation

AbstractThe precipitation trend patterns in South America (SA) are determined using trend empirical orthogonal function analysis for the 1951–2016 period. The associated large‐scale tropical and extratropical anomalous circulation patterns are also examined. The words “total” and “residual” refer to the monthly anomalies and monthly anomalies without the El Niño–Southern Oscillation (ENSO) effects, respectively. The total precipitation features a positive trend in southeastern SA (SESA, southern Brazil, Uruguay, most of eastern Argentina) and northern Chile, and a negative trend over central‐eastern Brazil and central Amazonia. The residual precipitation shows an increased positive trend over most of the coastal extension of northern SA and Colombia; a weak positive trend over southern Brazil, northeastern Argentina, and northern Chile; and a negative trend over central‐eastern SA and western Amazonia. The differences between the total and residual precipitation trend patterns in tropical SA is explained as responses to total and residual zonally asymmetric anomalous sea surface temperature (SST) patterns, respectively. The total SST pattern along the equatorial Pacific configures the Pacific Decadal Oscillation, which impacts ENSO variability and as response intensifies the Walker circulation. Without the ENSO, the Walker cell is mainly driven by the tropical Indian and Atlantic Oceans, which configure residual asymmetric anomalous warming. Furthermore, the warming in the equatorial Indian and eastern Pacific Oceans, in the presence of ENSO, induces a Rossby wave train‐type anomalous pattern that extends across the South Pacific into SA and modulates the atmospheric anomalous circulation over SESA. In this region, an anomalous anticyclonic accompanied by an intensified South American Low‐Level Jet induces a moisture transport to SESA. This anticyclone is also observed in the absence of ENSO but is weaker. The results suggest the importance of ocean warming in the western Pacific‐Indian in the modulation of extratropical teleconnections to SESA in the tropical ocean warming scenario.

Sources of low-frequency variability in observed Antarctic sea ice

Abstract. Antarctic sea ice has exhibited significant variability over the satellite record, including a period of prolonged and gradual expansion, as well as a period of sudden decline. A number of mechanisms have been proposed to explain this variability, but how each mechanism manifests spatially and temporally remains poorly understood. Here, we use a statistical method called low-frequency component analysis to analyze the spatiotemporal structure of observed Antarctic sea ice concentration variability. The identified patterns reveal distinct modes of low-frequency sea ice variability. The leading mode, which accounts for the large-scale, gradual expansion of sea ice, is associated with the Interdecadal Pacific Oscillation and resembles the observed sea surface temperature trend pattern that climate models have trouble reproducing. The second mode is associated with the central Pacific El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode and accounts for most of the sea ice variability in the Ross Sea. The third mode is associated with the eastern Pacific ENSO and Amundsen Sea Low and accounts for most of the pan-Antarctic sea ice variability and almost all of the sea ice variability in the Weddell Sea. The third mode is also related to periods of abrupt Antarctic sea ice decline that are associated with a weakening of the circumpolar westerlies, which favors surface warming through a shoaling of the ocean mixed layer and decreased northward Ekman heat transport. Broadly, these results suggest that climate model biases in long-term Antarctic sea ice and large-scale sea surface temperature trends are related to each other and that eastern Pacific ENSO variability is a key ingredient for abrupt Antarctic sea ice changes.