Central Pacific El Research Articles

The Different Effects of Two Types of El Niño on Eastern China’s Spring Precipitation During the Decaying Stages

El Niño is one of the most significant global climatic phenomena affecting the East Asian atmospheric circulation and climate. This study uses multi-source datasets, including observations and analyses, and statistical methods to investigate the variations and potential causes of boreal spring precipitation anomalies in eastern China under different El Niño sea surface temperature conditions, namely, the Eastern Pacific and Central Pacific (EP and CP) El Niño cases. The findings reveal that, particularly along the Yangtze–Huaihe valley, spring precipitation markedly increases in most regions of eastern China during the EP El Niño decaying stages. Conversely, during the CP El Niño decaying stages, precipitation anomalies are weak, with occurrences of weak negative anomalies in the same regions. Further analyses reveal that during the decaying spring of different El Niño cases, differences in the location and strength of the Northwest Pacific (NWP) abnormal anticyclone, which is associated with the central–eastern Pacific warm sea surface temperature anomaly (SSTA), result in distinct anomalous precipitation responses in eastern China. The SSTA center of the EP El Niño is more easterly and stronger. In the meantime, NWP abnormal anticyclones are more easterly and have a broader range, facilitating water vapor transport over eastern China. By contrast, the CP El Niño SSTA center is westward and relatively weaker, leading to a relatively weak, westward, and narrower anomalous NWP anticyclone that causes less significant water vapor transport anomalies in eastern China. This paper highlights the diverse impacts of El Niño diversity on regional atmospheric circulation and precipitation, providing valuable scientific references for studying regional climate change in East Asia.

Spatiotemporal pattern of ENSO-induced modulation on landscape fires over Pacific Rim from 2001‒2020

While El Niño-Southern Oscillation (ENSO) modulates landscape fire activities across the Pacific Rim, the detailed patterns and mode-specific variations of these effects remain poorly understood. This study aims to address that gap by systematically assessing the spatiotemporal variations in burned areas from 2001‒2020 during different modes of ENSO, namely, Eastern Pacific (EP) El Niño, EP La Niña, Central Pacific (CP) El Niño and CP La Niña. We evaluate the modulation patterns using classical correlation and cross-spectrum analyses, focusing on five hotspot regions: Temperate North America (TENA), Southern Hemisphere South America (SHSA), Northern Hemisphere South America (NHSA), Equatorial Asia (EQAS) and Australia and New Zealand (AUST). El Niño and La Niña exhibit asymmetrical opposite effects on burned areas, as expected. The findings reveal spatial non-uniformity in the impact of ENSO on landscape fires, with La Niña enhancing burned areas in TENA and SHSA, whereas El Niño predominantly affects AUST, EQAS and NHSA. CP and EP ENSO events differ in intensity and their large-scale circulation patterns. These differences cause notable variations in the regional burned area. Water vapour redistribution emerges as the key driver. The study emphasises the heterogeneity in ENSO modes in regulating landscape fires, providing insights for future landscape fire risk assessment and prevention efforts under climate change.

Synchronous decadal climate variability in the tropical Central Pacific and tropical South Atlantic

Pantropical climate interactions across ocean basins operate on a wide range of timescales and can improve the accuracy of climate predictions. Here, we show in observations that Central Pacific (CP) El Niño-like sea surface temperature (SST) anomalies have coevolved with tropical South Atlantic SST anomalies on a quasi-decadal (~10-year) timescale over the past seven decades. During the austral autumn–winter season, decadal warm SSTs in the tropical CP effectively induce tropical SST cooling in the South Atlantic, mainly by strengthening the South Atlantic subtropical anticyclone via an extratropical atmospheric wave teleconnection in the southern hemisphere. Partially coupled pacemaker simulations corroborate the observational findings, indicating that tropical CP decadal SSTs play a primary pacing role, while Atlantic feedback is of secondary importance throughout the study period. Our results suggest that the tropical CP could be an important source of decadal predictability for tropical South Atlantic SST and the surrounding climate.

Responses of the Southern Ocean mixed layer depth to the eastern and central Pacific El Niño events during austral winter

Responses of the Southern Ocean mixed layer depth to the eastern and central Pacific El Niño events during austral winter

Distinct Features of Tropical Cyclone Landfall over East Asia during Various Types of El Niño

Abstract Numerous studies focus on the impacts of ENSO diversity on tropical cyclone (TC) activities in the western North Pacific (WNP). In recent years, there is a growing threat of landfalling and northward-moving TCs in East Asia, accompanying an increase in central Pacific (CP) El Niño. Here, we aim to discover variations in landfalling TCs during various types of CP El Niño (CP-I and CP-II El Niño). It is found that significant changes in landfalling and going northward TCs over East Asia north 20°N are modulated by CP-I El Niño. During CP-I El Niño, TCs tend to landfall more often over the mainland of China with longer duration, moving distance, and stronger power dissipation index (PDI) after landfall and increased TC-induced rainfall, due to favorable conditions (beneficial steering flow, weak vertical wind shear, increased specific humidity, increased soil moisture, and temperature), especially significant over the northeastern part. The situation over the mainland of China is reversed during eastern Pacific (EP) El Niño and CP-II El Niño, with a significant decrease in the characteristics with corresponding unfavorable environments. Over the Korean Peninsula and Japan, the frequency of TC landfalls, as well as the duration and the moving distance after landfall, exhibits greater levels during CP-I and CP-II El Niño than during EP El Niño due to favorable steering flow, and thus, TC-induced rainfall enhances correspondingly. Regarding the PDI over the Korean Peninsula and Japan, it remains relatively consistent across all El Niño types. However, a notable increase in the PDI during EP El Niño could be attributed to the higher intensity of TCs prior to landfall.

Interannual ENSO diversity, transitions, and projected changes in observations and climate models

Abstract Diverse characteristics of El Niño Southern Oscillation (ENSO) events challenge the traditional view of tropical coupled ocean-atmosphere systems. The probability of a transition from one type of event to another is influenced by multiple factors of which many are projected to change. Here we assess the likelihood of ENSO transitions in observations and climate models, including a distinction between events that peak in the Eastern Pacific (EP) and Central Pacific (CP). We find that the initial ENSO state influences the likelihood of certain transitions and that some transitions are not physically possible or stochastically likely. For example, transitions to CP events are more likely than EP events except from a neutral state. We also find that El Niños tend to occur as singular events compared to La Niñas. While consecutive El Niño and La Niña events of EP type are possible, opposing EP events do not occur in succession. We identify several transitions likely driven by internal dynamical processes including neutral conditions to El Niño, CP El Niño to another El Niño, EP El Niño to CP La Niña, CP La Niña to CP El Niño and La Niña, and EP La Niña to neutral and CP El Niño. Projections of future transitions show an increased probability of transitions to CP El Niño events while transitions to EP La Niña events become less frequent under a high-emissions scenario. Accordingly, transitions to these events become more and less likely, respectively. We also find changes in the likelihood of specific transitions in a warming world: consecutive CP El Niño events become more likely while EP El Niño events become less likely to transition into CP La Niña events. These changes are expected to occur as early as 2050 with some changes to be accelerated by the end of the 21st century.

Why does there occur spring predictability barrier for eastern Pacific El Niño but summer predictability barrier for central Pacific El Niño?

Why does there occur spring predictability barrier for eastern Pacific El Niño but summer predictability barrier for central Pacific El Niño?

Enhanced interaction between ENSO and the South Atlantic subtropical dipole over the past four decades

AbstractThis study investigates the relationship between sea surface temperature (SST) anomalies in the subtropical Atlantic Ocean, as represented by the Southern Atlantic subtropical dipole (SASD), and SST anomalies in the tropical Pacific Ocean, identified by the El Niño‐Southern Oscillation (ENSO). Contrary to the previously held notion of a weak relationship between SASD and ENSO as suggested by earlier literature, our analysis reveals a substantial inverse correlation between the two. This correlation exhibits significant multi‐decadal variability, which has notably intensified over the most recent two decades compared with the preceding two decades. This intensification in the SASD–ENSO inverse correlation may be attributed to the shift in ENSO regime from predominance of eastern Pacific El Niño to central Pacific El Niño events around the turn of the century. This transition triggers wavetrains that propagate along different paths, consequently influencing the South Atlantic subtropical high and inducing alterations in anomalous SST patterns in the subtropical Atlantic Ocean. These findings advance our comprehension of the interactions between South Atlantic and Pacific SST variations, which strongly influence rainfall patterns, particularly in South America and southern Africa. Understanding such teleconnection holds promise for improving sub‐seasonal to seasonal precipitation predictions in these regions.

Interdecadal change in the relationship between the South China late rainy season rainfall and equatorial Pacific SSTs

Abstract The South China (SC) late rainy season rainfall (SCLR) is important to people’s livelihoods and properties of this densely populated and economically developed region. Based on observation and reanalysis datasets, this study identifies that the relationship between the SCLR and equatorial Pacific SSTs (EPSSTs) experiences an interdecadal change around the late 1970s. The SCLR is negatively correlated with the eastern EPSSTs during 1948–1977 (the previous epoch) but positively correlated with the central EPSSTs during 1978–2022, especially during the last three decades 1993–2022 (the post epoch). This is due to the interdecadal change in El Niño flavors and EPSSTs-tropical Atlantic SSTs (TASSTs) relationship. With the increasing frequency of central Pacific El Niños in the post epoch, the El Niño-related warm SST anomaly center shifts from the eastern equatorial Pacific (EEP) to the central equatorial Pacific (CEP). Correspondingly, the anomalous cyclone exerted by the CEP warming reaches SC and causes rainfall surplus there (westward propagation pathway). In contrast, the EEP warming in the previous epoch can’t influence the SCLR through the westward propagation pathway, but through shifting the westerly jet southward via heating the tropical troposphere. The southward shifted westerly jet crashes the Qinghai-Tibet Plateau, triggering cyclonic circulations across the northern East Asia and North Pacific, which in turn cause anticyclonic circulations over the western SC and reduce SC rainfall (eastward propagation pathway). On the other hand, the CEP warming in the post epoch barely influence the SCLR through the eastward propagation pathway because of the enhanced negative relationship between EPSSTs and TASSTs.

The Influence of ENSO Diversity on Future Atlantic Tropical Cyclone Activity

Abstract El Niño–Southern Oscillation (ENSO) influences seasonal Atlantic tropical cyclone (TC) activity by impacting environmental conditions important for TC genesis. However, the influence of future climate change on the teleconnection between ENSO and Atlantic TCs is uncertain, as climate change is expected to impact both ENSO and the mean climate state. We used the Weather Research and Forecasting Model on a tropical channel domain to simulate 5-member ensembles of Atlantic TC seasons in historical and future climates under different ENSO conditions. Experiments were forced with idealized sea surface temperature configurations based on the Community Earth System Model (CESM) Large Ensemble representing: a monthly varying climatology, eastern Pacific El Niño, central Pacific El Niño, and La Niña. The historical simulations produced fewer Atlantic TCs during eastern Pacific El Niño compared to central Pacific El Niño, consistent with observations and other modeling studies. For each ENSO state, the future simulations produced a similar teleconnection with Atlantic TCs as in the historical simulations. Specifically, La Niña continues to enhance Atlantic TC activity, and El Niño continues to suppress Atlantic TCs, with greater suppression during eastern Pacific El Niño compared to central Pacific El Niño. In addition, we found a decrease in the Atlantic TC frequency in the future relative to historical regardless of ENSO state, which was associated with a future increase in northern tropical Atlantic vertical wind shear and a future decrease in the zonal tropical Pacific sea surface temperature (SST) gradient, corresponding to a more El Niño–like mean climate state. Our results indicate that ENSO will remain useful for seasonal Atlantic TC prediction in the future.

The Interdecadal Changes in the Spatial Structure of the South Pacific Oscillation and Its Implication for ENSO Diversity

Abstract The South Pacific Oscillation (SPO), characterized by a north–south dipole-like pattern of sea level pressure anomalies, is one of the key factors in understanding tropical–extratropical interactions in the South Pacific. We show that in boreal summer (June–August), the center of the northern lobe sea level pressure anomalies in the SPO is shifted to the east gradually after the 1960–70s. This study focuses on the relationship between the boreal summer SPO and following winter El Niño–Southern Oscillation (ENSO) diversity before and after the eastward shift of the SPO’s subtropical lobe. The eastward shift of the SPO’s subtropical lobe altered both the seasonal footprint mechanism and the trade wind charging mechanism associated with the SPO and thus profoundly influenced the ENSO diversity. It is revealed that when the northern lobe of the SPO shifts to the west of its average location, it tends to strengthen the eastern Pacific (EP) El Niño mainly via the seasonal footprint mechanism. But after the SPO’s northern lobe shifts to the east of its average location, it tends to promote the development of central Pacific (CP) El Niño mainly via the trade wind charging mechanism. The changes in the spatial structure of convection over the tropical Pacific and Indian Oceans may be one of the possible causes for the eastward shift in the SPO’s northern lobe. The findings in the present study have implications for a better understanding of ENSO diversity. Significance Statement Previous studies have demonstrated that the South Pacific Oscillation (SPO), as an important El Niño–Southern Oscillation (ENSO) precursor in the South Pacific, has the potential to provide an enhancement of the prediction of specific ENSO flavor. However, the historical variation in the SPO’s spatial structure and related changes in the relationship with the diversity of ENSO are still unclear. In this paper, we show that the subtropical lobe of the boreal summer (June–August) SPO is shifted to the east gradually after the 1960–70s. The changes in the spatial structure have also altered both the seasonal footprint mechanism and the trade wind charging mechanism which play important roles in the developmental processes of different types of ENSO. Our work highlights the importance of the interdecadal changes in the spatial structure of the SPO in understanding the relationship between the SPO and ENSO diversity.

Coccolithophore Assemblage Response to Indian Monsoon–ENSO Teleconnections During the Last Century

AbstractWe present a new, annually resolved coccolithophore relative abundance record (1889–1993 CE) from a laminated marine sediment core obtained from the northeastern Arabian Sea to document assemblage variations during the last century. Our analysis revealed that ∼80% of the assemblage is composed of the coccolithophore species Gephyrocapsa oceanica, Emiliania huxleyi, and Florisphaera profunda. Hierarchical clustering of the coccolithophore data delineates time intervals (1889–1909 CE, 1910–1959 CE, 1960–1993 CE) comparable to previously reported interdecadal changes of the El Niño–Southern Oscillation (ENSO)–Indian monsoon variance. We find that F. profunda (Fp%) is positively correlated with central Pacific ENSO (Niño 4 and Niño 3.4). Frequency analyses of Fp% match ENSO quasiperiodicity reported from instrumental data and proxy records and support the existence of previously described ENSO–Indian monsoon teleconnections. Furthermore, the increased variance of Fp% and associated decrease in marine primary productivity starting ∼1960 CE appears to be driven by decreased upward nutrient transport linked to increased surface water stratification due to surface ocean warming. With the predicted increases in frequency and strength of central Pacific El Niño as well as surface ocean warming and upper ocean stratification in the Indian Ocean over the coming century, our results imply further impacts on coccolithophores in the northeastern Arabian Sea that may have cascading effects on the marine food web and global biogeochemical cycles.

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.

Distinct Central and Eastern Pacific El Niño Influence on Antarctic Surface Mass Balance

AbstractThe El Niño‐Southern Oscillation causes anomalous atmospheric circulation, temperature and precipitation across southern polar latitudes, but the influence of Central and Eastern Pacific El Niño events on Antarctic surface mass balance and snow accumulation has not yet been assessed. Here, we use reanalysis and reanalysis‐forced regional climate model output and find that Central Pacific El Niño results in significantly increased snow accumulation in the western Ross Sea sector and significantly decreased snow accumulation in the Amundsen Sea sector. Eastern Pacific El Niño is associated with similar but weaker patterns, with some regional exceptions. In some areas, like Dronning Maud Land, or the Wilkes Subglacial Basin, the effect of El Niño on snow accumulation changes from increased to reduced accumulation depending on the type of El Niño. Our results show that projecting El Niño types is important for constraining future changes in Antarctic surface mass balance.

Central-Pacific El Niño-Southern Oscillation less predictable under greenhouse warming

El Niño-Southern Oscillation (ENSO) is the dominant mode of interannual climate variability in the tropical Pacific, whose nature nevertheless may change significantly in a warming climate. Here, we show that the predictability of ENSO may decrease in the future. Across the models in the Coupled Model Intercomparison Project Phase 6 (CMIP6), we find a robust decrease of the persistence and predictability for the Central Pacific (CP) ENSO under global warming, notably in passing through the boreal spring. The strength of spring predictability barrier will be increased by 25% in the future. The reduced predictability of CP ENSO is caused by the faster warming over surface ocean in tropical Pacific and, in turn, the enhanced thermodynamical damping rate on CP ENSO in response to global warming. In contrast, the predictability of Eastern Pacific ENSO will not change. Our results suggest that future greenhouse warming will make the prediction of CP ENSO more challenging, with far-reaching implications on future climate predictions.

Do Sea Surface Winds and Currents in the Equatorial Pacific Ocean Derive the Extreme El Niños?

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.

Impacts of central-Pacific El Niño and physical drivers on eastern Pacific bigeye tuna

Impacts of central-Pacific El Niño and physical drivers on eastern Pacific bigeye tuna

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.

Influence of Eastern, Central and Mix El Niño on the variability of rainfall in southeastern South America

El Niño/Southern Oscillation (ENSO) plays a very important role in modulating rainfall variability in South America. Although the effects of conventional ENSO are well known, there are significant variations in rainfall patterns when sea surface temperature anomalies manifest over the different regions along the equatorial Pacific, namely, Niño 3 (East), Niño 3 and Niño 4 (Mix), and Niño 4 (Central) ENSO. This work aims to analyze the variability of precipitation in southeastern South America associated with different types of El Niño (EN). For this, composite analyzes of precipitation, winds at low and high levels, vertical velocity and geopotential height were carried out. The results indicate that the rainfall pattern associated with Eastern Pacific (EP) El Niño shows the classic features expected from EN described in previous literature, i.e., a stronger and well-defined positive precipitation anomaly over southeast South America, while Central Pacific (CP) El Niño shows weaker and even an opposite sign over the region. Mix (MX) El Niño events present a spatial pattern of precipitation anomalies similar to EP El Niño events, but with lower intensity in the study area. The heterogeneity of EN-related precipitation effects results from a change in large-scale atmospheric circulation patterns: the Walker cell in the tropics, the Rossby waves in the extratropics, and the circulation of low and high-level jet streams. EP El Niño events feature a configuration similar to the South American Low-Level Jet, the strengthening of the subtropical jet, better structured Rossby waves and the Pacific-South America pattern. These characteristics are observed in MX El Niños, but in a weaker way compared to EP El Niños. CP El Niño events, on the other hand, present a weakening and spatial displacement of the aforementioned conditions, which is reflected in negative precipitation anomalies in most seasons. Thus, more significant rainfall variations are noted between the EP El Niños and CP El Niños, with a predominance of positive and negative rainfall anomalies in the study area, respectively.

Impacts of El Niño diversity on East Asian summertime precipitation extremes

This study examines the impacts of Eastern Pacific (EP) and Central Pacific (CP) El Niño on summertime extreme precipitation over East Asia during the El Niño decay phase. The findings reveal distinct patterns of extreme precipitation for the two El Niño types. During EP El Niño, more intense extreme precipitation occurs over south of the Yangtze River (SYR), while suppressed extremes are observed over Mei-Yu rainband in China, Baiu in Japan, and Changma in South Korea (MBC). Conversely, CP El Niño leads to weaker (stronger) extreme precipitation over SYR (MBC). This study also differentiates between tropical cyclone (TC) and non-TC related precipitation, showing that TCs have minimal influence on the overall extreme precipitation compared to non-TC related events. Further investigation reveals that EP and CP El Niño distinctly influence atmospheric circulation patterns, thereby causing different distributions of non-TC extreme precipitation. Specifically, during EP El Niño, sea surface temperature (SST) warming signals in the tropical Indian Ocean induce the southward displacement of the South Asia High (SAH), westerly jet (WJ), and Western Pacific subtropical high (WPSH). This amplifies moisture flux convergence, elevating the likelihood of intense extreme precipitation over SYR. Conversely, MBC experiences moisture flux divergence, resulting in fewer precipitation extremes. During CP El Niño, SST warming signals in the Maritime Continent prompt the northward shift of SAH, WJ, and WPSH by modulating local Hadley circulations. These anomalies lead to strengthened moisture convergence (divergence) over MBC (SYR), consequently resulting in a higher (lower) likelihood of intense extreme precipitation over MBC (SYR).