Interannual El Nino-Southern Oscillation Research Articles

Spatio-temporal rainfall variability of equatorial small island: case study Bintan Island, Indonesia

The water resources of Bintan Island depend much on rainfall since the impervious granitic basement that bears a low water storage capacity dominates the geology of Bintan Island. Water demand in Bintan is increasing due to both population and economic growth. This paper aims to determine the spatial and temporal rainfall variability over Bintan Island using the daily corrected-CHIRPS (Climate Hazards Group InfraRed Precipitation with Station data) version two (v2.0) dataset to a ground-based observation dataset (Kijang station) using quantile-base bias correction for period 1 January 1981–31 August 2018. For the analysis process, we used monthly corrected-CHIRPS, NINO 3.4 anomaly index, the DMI (dipole mode index), zonal and meridional wind, and specific humidity from January 1981 to December 2017. Semi-annual, annual, and interannual variations influence monthly rainfall amounts over the island. Two peaks representing equatorial and monsoonal patterns characterize the temporal variability of rainfall. Spatially, the southern part of the island receives more rainfall than the northern part especially in MAM and SON related to the more convergence of moisture. The effects of interannual variation, ENSO (El Nino-Southern Oscillation) and IOD (Indian Ocean dipole), vary with season. ENSO contributes more to rainfall variability than IOD during the period of study.

A brief review of ENSO theories and prediction

Although the El Nino-Southern Oscillation (ENSO) originates and develops in the equatorial Pacific, it has substantial climatic impacts around the globe. Thus, the ability to effectively simulate and predict ENSO one or more seasons in advance is of great societal importance, but this remains a challenging task. The main obstacles are the diversity, complexity, irregularity, and asymmetry of ENSO. The purpose of this article is to organically integrate the understanding of ENSO based on current progress on the physical mechanisms, prediction, and connections between the interannual ENSO phenomenon and physical processes on other time and space scales, and to provide guidance for future studies by extracting specific important questions.

Extreme ENSO-driven torrential rainfalls at the southern edge of the Atacama Desert during the Late Holocene and their projection into the 21th century

Abstract Extreme precipitation events and multi-annual droughts, especially in arid to semi-arid subtropical regions, are among the most critical El Nino Southern Oscillation (ENSO) and global climate change impacts. Here, we assess the variability of torrential rainfall during the Late Holocene and its projection into the 21st century at the southern edge of the hyperarid Atacama Desert. The analysis of historical data since the beginning of the 20th century reveals that most (76.5%) alluvial disasters in the southern Atacama Desert (26–30°S) have resulted from extreme rainfall events occurring between March and September under El Nino conditions, and more frequently during the warm phase of the Pacific Decadal Oscillation. Particular rainfall events under these ocean-climate conditions are associated with the convective phase of the Madden-Julian Oscillation (MJO) near the central-equatorial Pacific, resulting in warmer sea surface temperature (SST) there and in the triggering of persistent/intense Pacific South America (PSA) tropical-extratropical teleconnection patterns which result in blocking of the westerly flow at high latitudes and the subsequent deviation of storm tracks towards central-northern Chile. On a longer timescale, marine sediments from Tongoy Bay (30°S) reveal an increasing trend of stronger runoff by torrential coastal rain since ca. 3500 cal yr BP and even stronger heavy rainfall since ca. 1700 cal yr BP. Highly variable coastal sea surface temperatures in the same time span deduced from the sedimentary record can be explained by intensified southerly winds in connection with stronger alongshore pressure gradients and reduced coastal low-cloud cover. Both storm intensification and increased intensity of upwelling-favorable winds point to a variable climate conditioned by strengthened interannual ENSO and interdecadal ENSO-like variability during the Late Holocene. Climate projections from the Coupled Model Intercomparison Project Phase 5 (CMIP5) indicate a reduction in annual precipitation of 15–30% during the current century, together with an intensification of the storms, such as the alluvial disaster on March 25, 2015 in Atacama.

Interdecadal variability in pan-Pacific and global SST, revisited

Interest in the “Interdecadal Pacific Oscillation (IPO)” in the global SST has surged recently on suggestions that the Pacific may be the source of prominent interdecadal variations observed in the global-mean surface temperature possibly through the mechanism of low-frequency modulation of the interannual El Nino-Southern Oscillation (ENSO) phenomenon. IPO was defined by performing empirical orthogonal function (EOF) analysis of low-pass filtered SST. The low-pass filtering creates its unique set of mathematical problems—in particular, mode mixing—and has led to some questions, many unanswered. To understand what these EOFs are, we express them first in terms of the recently developed pairwise rotated EOFs of the unfiltered SST, which can largely separate the high and low frequency bands without resorting to filtering. As reported elsewhere, the leading rotated dynamical modes (after the global warming trend) of the unfiltered global SST are: ENSO, Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO). IPO is not among them. The leading principal component (PC) of the low-pass filtered global SST is usually defined as IPO and it is seen to comprise of ENSO, PDO and AMO in various proportions depending on the filter threshold. With decadal filtering, the contribution of the interannual ENSO is understandably negligible. The leading dynamical mode of the filtered global SST is mostly AMO, and therefore should not have been called the Interdecadal “Pacific” Oscillation. The leading dynamical mode of the filtered pan-Pacific SST is mostly PDO. This and other low-frequency variability that have the action center in the Pacific, from either the pan-Pacific or global SST, have near zero global mean.

Spatiotemporal variability in the δ18O-salinity relationship of seawater across the tropical Pacific Ocean.

The relationship between salinity and the stable oxygen isotope ratio of seawater (δ18Osw) is of utmost importance to the quantitative reconstruction of past changes in salinity from δ18O values of marine carbonates. This relationship is often considered to be uniform across water masses, but the constancy of the δ18Osw-salinity relationship across space and time remains uncertain, as δ18Osw responds to varying atmospheric vapor sources and pathways, while salinity does not. Here we present new δ18Osw-salinity data from sites spanning the tropical Pacific Ocean. New data from Palau, Papua New Guinea, Kiritimati, and Galápagos show slopes ranging from 0.09 ‰/psu in the Galápagos to 0.32‰/psu in Palau. The slope of the δ18Osw-salinity relationship is higher in the western tropical Pacific versus the eastern tropical Pacific in observations and in two isotope-enabled climate models. A comparison of δ18Osw-salinity relationships derived from short-term spatial surveys and multi-year time series at Papua New Guinea and Galápagos suggests spatial relationships can be substituted for temporal relationships at these sites, at least within the time period of the investigation. However, the δ18Osw-salinity relationship varied temporally at Palau, likely in response to water mass changes associated with interannual El Niño-Southern Oscillation (ENSO) variability, suggesting nonstationarity in this local δ18Osw-salinity relationship. Applying local δ18Osw-salinity relationships in a coral δ18O forward model shows that using a constant, basin-wide δ18Osw-salinity slope can both overestimate and underestimate the contribution of δ18Osw to carbonate δ18O variance at individual sites in the western tropical Pacific.

PDO modulation of ENSO effect on tropical cyclone rapid intensification in the western North Pacific

This study investigates how the Pacific Decadal Oscillation (PDO) modulates the effect of El Nino/Southern Oscillation (ENSO) on tropical cyclone rapid intensification (RI) in the western North Pacific. The analysis shows that the interannual relationship between ENSO and annual RI number in warm PDO phases is strong and statistically significant. In cold PDO phases, however, there is no significant correlation between ENSO and RI on the interannual timescale. The enhancement of the interannual ENSO–RI relationship in warm PDO phases is mainly attributable to the change of the environmental vertical wind shear. The PDO in warm (cold) phases can strengthen (weaken) an El Nino event to increase (reduce) the effects of the warm pool of water over the equatorial Pacific in typhoon season by local diabatic heating. El Nino events are accompanied by the stronger Walker circulation in the equatorial Pacific in the warm PDO phase than in the cold PDO phase. In contrast, the Walker circulation pattern and amplitude associated with La Nina events is less affected by the alternate PDO phase. This tends to make the atmospheric response to ENSO stronger (weaker) in warm (cold) PDO phase, and so is the atmospheric teleconnection of ENSO. Our results indicate that the stratification of ENSO-based statistical RI forecast by the PDO can greatly improve the accuracy of statistical RI predictions.

EVALUATION OF OXYGEN ISOTOPE AND SR/CA RATIOS FROM A MALDIVIAN SCLERACTINIAN CORAL FOR RECONSTRUCTION OF CLIMATE VARIABILITY IN THE NORTHWESTERN INDIAN OCEAN

Corals are important marine archives for high-resolution reconstructions of low-latitude climate variability in preinstrumental and historical periods. Herein, we present monthly-resolved records of delta O-18 and Sr/Ca for the 20th century (1917-2007) from a Porites lutea colony from the Maldives (northwestern Indian Ocean). Previous studies of annual mean extension rates of this coral revealed a distinct dependency of coral growth on variations of sea surface temperature (SST) and hydraulic energy, driven by El Nino-Southern Oscillation (ENSO) and southwestern Indian monsoon forcing. This enables the investigation of coral delta O-18 and Sr/Ca ratios from the Maldives as archives of historical ENSO and Indian monsoon variability. Unlike other locations in the Indian Ocean, correlation of delta O-18 and SST is weak (r = -0.42; p < 0.001), suggesting interferences of SST and seawater delta O-18 at the location. These interferences probably caused significantly weaker interannual ENSO signatures in delta O-18 as evident in the extension rates of our coral and in geochemical proxies measured at other sites in the northwestern Indian Ocean. Sr/Ca ratios show bias by nontemperature effects, and were not used to estimate seawater delta O-18 and salinity. Strong decadal variability (10-14 years) in delta O-18, indicative of a Pacific ENSO signal, is not found in instrumental SST, and could be explained by variations in salinity. Interannual and decadal monsoon variability (6-7 yrs and 18-19 yrs), found in the extension rates, was not found in delta O-18, suggesting, in agreement with other studies, that geochemical coral proxy records from the northwestern Indian Ocean do not capture temporal variations of the Indian monsoon strength.

Multi-scale meteorological conceptual analysis of observed active fire hotspot activity and smoke optical depth in the Maritime Continent

Abstract. Much research and speculation exists about the meteorological and climatological impacts of biomass burning in the Maritime Continent (MC) of Indonesia and Malaysia, particularly during El Nino events. However, the MC hosts some of the world's most complicated meteorology, and we wish to understand how tropical phenomena at a range of scales influence observed burning activity. Using Moderate Resolution Imaging Spectroradiometer (MODIS) derived active fire hotspot patterns coupled with aerosol data assimilation products, satellite based precipitation, and meteorological indices, the meteorological context of observed fire prevalence and smoke optical depth in the MC are examined. Relationships of burning and smoke transport to such meteorological and climatic factors as the interannual El Nino-Southern Oscillation (ENSO), El Nino Modoki, Indian Ocean Dipole (IOD), the seasonal migration of the Intertropical Convergence Zone, the 30–90 day Madden Julian Oscillation (MJO), tropical waves, tropical cyclone activity, and diurnal convection were investigated. A conceptual model of how all of the differing meteorological scales affect fire activity is presented. Each island and its internal geography have different sensitivities to these factors which are likely relatable to precipitation patterns and land use practices. At the broadest scales as previously reported, we corroborate ENSO is indeed the largest factor. However, burning is also enhanced by periods of El Nino Modoki. Conversely, IOD influences are unclear. While interannual phenomena correlate to total seasonal burning, the MJO largely controls when visible burning occurs. High frequency phenomena which are poorly constrained in models such as diurnal convection and tropical cyclone activity also have an impact which cannot be ignored. Finally, we emphasize that these phenomena not only influence burning, but also the observability of burning, further complicating our ability to assign reasonable emissions.

Relação dos sistemas de monção com as variabilidades tropical interanual e multi-decenal

A variabilidade da circulação tropical, com ênfase nos sistemas monçônicos, é examinada usando diversas variáveis para o período de 1948-1999. A componente monçônica do potencial de velocidade em 200 hPa (χ-transiente), o desvio da média anual do desvio da média zonal, é o parâmetro chave usado para obter os modos monçônicos. A análise de Funções Ortogonais Empíricas (EOF) do χ-transiente fornece dois modos separados. O primeiro modo descreve a variabilidade multi-decenal dos sistemas monçônicos da América do Sul e do Pacífico oeste. Esse modo, chamado monçônico multi-decenal (MMD), ocorre por todo o ano e contém a variabilidade multi-decenal relacionada à dinâmica da Oscilação Decenal do Pacífico (ODP). O segundo modo descreve as variações interanuais opostas entre a Ásia, África e oceano Índico e a região do oeste dos Estados Unidos, México e Pacífico leste. Esse modo, chamado modo interanual (MIA) apresenta algumas similaridades com o modo tropical interanual El Niño - Oscilação Sul. Alguns aspectos desses modos, incluindo sua circulação e características termodinâmicas são discutidas aqui. Finalmente, índices baseados nos padrões das configurações espaciais desses modos são construídos. A eficiência desses índices para fins de monitoramento é analisada. Logo, trata-se de um novo aspecto não proposto em trabalhos anteriores.

Investigating decadal variability of El Nino–Southern Oscillation asymmetry by conditional nonlinear optimal perturbation

The observed El Nino events are generally stronger than the La Nina events. This property of El Nino–Southern Oscillation (ENSO) is termed as ENSO asymmetry. Evidence is presented to show that this asymmetry has changed since the famous 1976 climate shift. Along the thinking of how the tropical background field modulates ENSO cycle, we explore the effect of the climatological basic‐state change on the ENSO asymmetry by applying the approach of conditional nonlinear optimal perturbation (CNOP) in a theoretical coupled model. CNOP is the initial anomaly pattern that evolves into ENSO event most probably. Observation shows that from the preshift (1961–1975) to the postshift (1981–1995) period, significant changes have occurred in climatological background state, i.e., the mean temperature difference between the equatorial eastern and western Pacific basins and between the mixed‐layer and subsurface‐layer water, which control the ENSO oscillation in the theoretical coupled model. By computing the CNOPs of the climatological basic state corresponding to the 1961–1975 (1981–1995) epoch, we reproduce the observed decadal change of ENSO asymmetry qualitatively. On the basis of the physics described by the model, the mechanism of ENSO asymmetry change in interdecadal scale is explored in depth. It is shown that the decadal change of ENSO asymmetry is induced by the change of nonlinear temperature advection, which is closely related to the decadal change of the tropical background state. These indicate that the decadal change of ENSO asymmetry results from the collective effect of the changes of the tropical background state and the nonlinearity. These findings in this study also suggest that the nonlinearity can explain not only the asymmetry of interannual ENSO, but also that of interdecadal ENSO, which may present a powerful evidence to the ENSO chaotic theory.

Summer Drought Patterns in Canada and the Relationship toGlobal Sea Surface Temperatures

Abstract Canadian summer (June–August) Palmer Drought Severity Index (PDSI) variations and winter (December– February) global sea surface temperature (SST) variations are examined for the 63-yr period of 1940–2002. Extreme wet and dry Canadian summers are related to anomalies in the global SST pattern in the preceding winter season. Large-scale relationships between summer PDSI patterns in Canada and previous winter global SST patterns are then analyzed using singular value decomposition (SVD) analysis. The matrix for the covariance eigenproblem is solved in the EOF space in order to obtain the maximum covariance between the singular values of the SST and the PDSI. The robustness of the relationship is established by the Monte Carlo technique, in which the time expansion of the primary EOF analysis is shuffled 1000 times. Results show that the leading three SVD-coupled modes explain greater than 80% of the squared covariance between the two fields. The interannual El Nino–Southern Oscillation (ENSO), the ...

The Decadal ENSO Variability in a Hybrid Coupled Model

In this study, the characteristics of decadal ENSO variability in a long (100-yr) simulation of a hybrid coupled model (HCM) are investigated. To exclude the possibility that the decadal El Nino-Southern Oscillation (ENSO) variability is forced by midlatitude ocean variability, the atmospheric component model is coupled to an ocean model that is restricted to the tropical Pacific. The sea surface temperature anomaly (SSTA) variability from a 100-yr run of HCM compares favorably to the observations and shows fluctuations in the ENSO period and amplitude on decadal time scales. The spatial structure of the interannual ENSO variability in the HCM is similar to the observations, whereas on decadal time scales the spatial structure differs significantly from the observations suggesting the importance of extratropical oceanic processes or deficiencies in the model. The decadal mean of both the SSTA and the wind stress anomaly is too equatorially confined in the HCM compared to the observations. Simple coupled model experiments are performed to determine the source of decadal ENSO variability in the HCM. These experiments indicate that the slow time-scale variations in the mean state have little effect on the character of the ENSO variability. The decadal modulation of ENSO is primarily related to the details of atmospheric noise processes.

The Sensitivity and Response of Terrestrial South American Vegetation to Interannual Climatic Variability Induced by the ENSO

The sensitivity of vegetation to climatic variations operates over a range of spatio-temporal scales. Whilst comprehensive and extensive studies that involve the spatial changes in terrestrial systems using remotely sensed data have been undertaken, only a few investigations have focused on temporal change in these systems. In this study econometric time-series modelling techniques were applied to National Oceanographic and Atmospheric Administration Advanced Very High Resolution Radiometer Normalized Difference Vegetation Index data sets in order to evaluate the resistance and resilience of terrestrial South American vegetation to the interannual El Nino Southern Oscillation perturbations. Lags between vegetation response and the El Nino Southern Oscillation perturbations are identified and quantified. The results indicate that the terrestrial vegetation loses its sensitivity to El Nino Southern Oscillation perturbations in the post 1993 period. This hypothesis is investigated further using stochastic Auto Regressive Integrative Moving Average model simulation techniques.

Pacific decadal oscillation and variability of the Indian summer monsoon rainfall

Recent studies have furnished evidence for interdecadal variability in the tropical Pacific Ocean. The importance of this phenomenon in causing persistent anomalies over different regions of the globe has drawn considerable attention in view of its relevance in climate assessment. Here, we examine multi-source climate records in order to identify possible signatures of this longer time scale variability on the Indian summer monsoon. The findings indicate a coherent inverse relationship between the inter-decadal fluctuations of Pacific Ocean sea surface temperature (SST) and the Indian monsoon rainfall during the last century. A warm (cold) phase of the Pacific interdecadal variability is characterized by a decrease (increase) in the monsoon rainfall and a corresponding increase (decrease) in the surface air temperature over the Indian subcontinent. This interdecadal relationship can also be confirmed from the teleconnection patterns evident from long-period sea level pressure (SLP) dataset. The SLP anomalies over South and Southeast Asia and the equatorial west Pacific are dynamically consistent in showing an out-of-phase pattern with the SLP anomalies over the tropical central-eastern Pacific. The remote influence of the Pacific interdecadal variability on the monsoon is shown to be associated with prominent signals in the tropical and southern Indian Ocean indicative of coherent inter-basin variability on decadal time scales. If indeed, the atmosphere–ocean coupling associated with the Pacific interdecadal variability is independent from that of the interannual El Nino-Southern Oscillation (ENSO), then the climate response should depend on the evolutionary characteristics of both the time scales. It is seen from our analysis that the Indian monsoon is more vulnerable to drought situations, when El Nino events occur during warm phases of the Pacific interdecadal variability. Conversely, wet monsoons are more likely to prevail, when La Nina events coincide during cold phases of the Pacific interdecadal variability.

Wavelet analysis of interannual LOD, AAM, and ENSO: 1997-98 El Niño and 1998-99 La Niña signals

On the basis of the data series of the length of day (LOD), the atmospheric angular momentum (AAM) and the Southern Oscillation Index (SOI) for January 1970–June 1999, the relationship among Interannual LOD, AAM, and the EL Nino/Southern Oscillation (ENSO) is analyzed by the wavelet transform method. The results suggest that they have similar time-varying spectral structures. The signals of 1997–98 El Nino and 1998–99 La Nina events can be detected from the LOD or AAM data.

Climate Variations and Changes in Mass of Three Glaciers in Western North America

Abstract Time series of net and seasonal mass balances for three glaciers in western North America, one in the Pacific Northwest and two in Alaska, show various relationships to Pacific hemisphere climate indexes. During the winter season the two coastal, maritime-regime glaciers, over 2000 km apart, are affected almost identically, albeit inversely, by atmospheric and oceanic conditions in both the tropical and North Pacific. The two Alaska glaciers, only 350 km apart, have almost no coherence. Lag correlations show that in winter the maritime glaciers are influenced by concurrent conditions in the North Pacific, but by conditions in the tropical Pacific in August–September of the prior northern summer. The winter balance variations contain interannual El Nino–Southern Oscillation variability superimposed on North Pacific interdecadal variability; the interdecadal 1976–77 climate regime shift is clearly evident. The summer balances and the continental-regime glacier have a general lack of correlations, w...

On the recent development of simple, coupled ocean-atmosphere models of ENSO

Based on simple model results, I describe the recent progress in our understanding of physical mechanisms directly associated with El Nino-Southern Oscillation (ENSO) phenomena. In particular, I extract two extremes from recent simple coupled models in order to interprete two complementary phases of interannual ENSO events. I also discuss what is most necessary for more complete model studies useful to improve forecasting skills.