El Nino-Southern Oscillation Episodes Research Articles

Observational analysis of surface ozone variability in China from 2015 to 2020: Insights from consecutive ENSO episodes

Utilizing daily surface ozone (O3) concentration data (MDA8-O3) from nearly 1500 monitoring stations across mainland China, complemented by gridded atmospheric reanalysis data, this study conducts a comprehensive analysis of O3 concentration, anomalies, and oscillations. Employing regression and composite analyses, we investigate the potential linkage between O3 variations and the phase and strength of El Niño-Southern Oscillation (ENSO) across diverse regions and seasons in China. Noteworthy findings include the identification of regions exhibiting peak O3 concentrations in autumn or spring, deviating from the typical seasonal cycle, as well as regions exhibiting varying strengths of seasonal and semi-annual O3 oscillations. Moreover, the study unveils the spatiotemporal patterns of synoptic and intra-seasonal O3 oscillations. The analyses reveal a prevailing inverse association between O3 anomalies and ENSO in most Chinese regions except for the southern and southeastern coastal areas. The potential impacts of ENSO on O3 are elucidated by anomalous atmospheric conditions linked to ENSO, the nature of which strongly depends on the region and season. In northern China, anomalous temperature and solar radiation related to ENSO exert a more pronounced influence on O3 anomalies. On the other hand, in southern China, anomalies in wind speed/direction and precipitation associated with anomalous atmospheric circulations play a more predominant role. These findings contribute valuable insights to the nuanced understanding of O3 variability, paving the way for the development of sophisticated O3 forecasting approaches tailored to different regions and seasons across China.

The Context of the 2018–20 “Protracted” El Niño Episode: Australian Drought and Terrestrial, Marine, and Ecophysiological Impacts

Abstract A “protracted” El Niño episode occurred from March–April 2018 to April–May 2020. It was manifested by the interlinked Indo-Pacific influences of two components of El Niño phases. Positive Indian Ocean dipoles (IODs) in 2018 and 2019 suppressed the formation of northwest cloud bands and southern Australia rainfall, and a persistent teleconnection, with enhanced convection generated by positive Niño-4 region sea surface temperature (SST) anomalies and strong subsidence over eastern Australia, exacerbated this Australian drought. As with “classical” El Niño–Southern Oscillation (ENSO) events, which usually last 12–18 months, protracted ENSO episodes, which last for more than 2 yr, show a similar pattern of impacts on society and the environment across the Indo-Pacific domain, and often extend globally. The second half of this study puts the impact of the 2018–20 protracted El Niño episode on both the Australian terrestrial agricultural and marine ecophysiological environments in a broader context. These impacts are often modulated not only by the direct effects of ENSO events and episodes, but by interrelated local to region ocean–atmosphere interactions and synoptic weather patterns. Even though the indices of protracted ENSO episodes are often weaker in magnitude than those of major classical ENSO events, it is the longer duration of the former that poses its own set of problems. Thus, there is an urgent need to investigate the potential to forecast protracted ENSO episodes, particularly when the mid-2020 to current 2022 period has been experiencing a major protracted La Niña episode with near-global impacts. Significance Statement The major 2018–20 Australian drought and its terrestrial and marine impacts were caused by a “protracted” El Niño episode, exacerbated by global warming. Indo-Pacific ocean–atmosphere interactions resulted in a persistent positive western Pacific Niño-4 sea surface temperature anomaly during the period 2018–20 and positive Indian Ocean dipoles (IODs) in 2018 and 2019. These suppressed rainfall across eastern Australia and limited northwest Australian cloud band rainfall across southern Australia. Australian agricultural and ecophysiological impacts caused by protracted El Niño–Southern Oscillation (ENSO) episodes permeate, overstress, and expose society, infrastructure, and livelihoods to longer temporal-scale pressures than those experienced during shorter “classical” ENSO events. Thus, there is an urgent need to investigate the potential to forecast protracted ENSO episodes.

Rainfall erosivity variability over the United States associated with large-scale climate variations by El Niño/southern oscillation

A comprehensive investigation of the contiguous Unites States rainfall erosivity patterns in relation to the warm and cold phases of El Niño/southern Oscillation (ENSO) was described using a set of empirical and statistical analyses, such as harmonic analysis, annual cycle composites, and cross-correlation analysis. Monthly rainfall erosivity index (REI) composites for the first harmonic, covering 24-month ENSO events, are formed for all climate divisions over the United States spanning up to 29 ENSO episodes. From the harmonic vectorial maps plotted on the study area, each vector reveals both intensity and temporal phase of the ENSO-related REI teleconnection, and the corresponding candidate and core regions are determined using a machine learning technique of Gaussian Mixture Model (GMM) based on magnitude and temporal phase of climate signal, and Köppen climate classification. As a result of vectorial mapping, five core regions were designated as the northwest (NW), the north central (NC), the northeast coastal (NEC), the southeast (SE), and the southwest/middle-inland (SWM) regions. During fall (0) to spring (+) seasons, the results of this analysis show negative (positive) rainfall erosivity response to the El Niño events at the NW and NC regions (NEC, SE, and SWM regions), while the opposite patterns are detected for the cold phase of ENSO. The temporal consistency values were 0.62 to 0.86 (0.73 to 0.82), and spatial coherence values ranged from 0.93 to 0.98 (0.94 to 0.97) for the El Niño (La Niña) events. Comparative analyses of rainfall erosivity responses to both warm and cold ENSO events reveal the high significance level of the ENSO-REI correlation with an opposite tendency in monthly rainfall erosivity anomalies. Above normal rainfall erosivity anomalies during the El Niño thermal forcing are more significant than below normal rainfall erosivity departures during the La Niña events. Consequently, middle latitude rainfall erosivity responses to the El Niño and La Niña phenomena are detectable over the contiguous United States.

Teleconnection of ENSO extreme events and precipitation variability over the United States

This study describes a comprehensive investigation of the contiguous United States precipitation patterns in relation to the warm and cold phases of El Niño/southern Oscillation (ENSO) using a set of empirical and statistical analyses, such as harmonic analysis, annual cycle composites, and cross-correlation analysis. Monthly precipitation composites for the first harmonic, covering 24-month ENSO events, are formed for all climate divisions over the United States spanning up to 29 ENSO episodes. From the harmonic vectorial maps plotted on the study area, each vector reveals both intensity and temporal phase of the ENSO-related precipitation teleconnection, and the corresponding candidate and core regions are determined using a machine learning technique of Gaussian Mixture Model (GMM) based on magnitude and temporal phase of climate signal, and Köppen climate classification. As a result of vectorial mapping, five core regions were designated as North-West region (NW), South-West region (SW), Middle-Inland region (MI), South-East region (SE), and North-East region (NE). During fall (0) to spring (+) seasons, the results of this analysis show below (above) normal precipitation response to the El Niño events at the NW region (SW, MI, SE, and NE regions), while the opposite patterns are detected for the cold phase of ENSO. The temporal consistency values were 0.72 to 0.86 (0.77 to 0.82), and spatial coherence values ranged from 0.96 to 0.99 (0.94 to 0.99) for the warm (cold) events. Comparative analyses of precipitation responses to both El Niño and La Niña events reveal the high significance level of the ENSO-related precipitation signals with an opposite tendency in monthly precipitation anomalies. Positive precipitation anomalies during the El Niño thermal forcing are more significant than negative precipitation departures during the La Niña events. Consequently, middle latitude precipitation responses to the El Niño/La Niña phenomena are detectable over the contiguous United States.

Possible Linkage Between Tropical Indian Ocean SST Anomalies and the Date of First and Last Tropical Cyclones Landfalling in the Chinese Mainland

Bases on the NCEP / NCAR reanalysis products, HadISST dataset, and data of tropical cyclone (TC)landfalling in the Chinese mainland during 1960-2019, the possible impacts of Indian Ocean Dipole (IOD) mode andIndian Ocean basin (IOB) mode on the last-TC-landfall date (LLD) and first-TC-landfall date (FLD), respectively, areinvestigated in this study. The LLD is in significantly negative correlation with autumn IOD on the interannual time-scale and their association is independent of El Niño-Southern Oscillation (ENSO). The LLD tends to be earlier when theIOD is positive while becomes later when the IOD is negative. An anomalous lower-level anticyclone is located aroundthe Philippines during October-November, resulting from the change of Walker circulation over the tropical Indo-westPacific Ocean forced by sea surface temperature (SST) anomalies related to a positive IOD event. The Philippinesanticyclone anomaly suppresses TCs formation there and prevents TCs from landfalling in the Chinese mainland due tothe anomalous westerly steering flows over southeast China during October-November, agreeing well with the earlierLLD. However, the robust connection between spring IOB and FLD depends on ENSO episodes in preceding winter.There is an anticyclonic anomaly around the Philippines caused by the tropical SST anomalies through modulating theWalker circulation during May-June when the IOB is warming in the El Niño decaying phase. Correspondingly, the TCsgenesis is less frequent near the Philippines and the mid-level steering flows associated with the expanded westernPacific subtropical high are disadvantageous for TCs moving towards southeast China and making landfall during May-June, in accordance with the later FLD. By contrast, cooling IOB condition in spring of a La Niña decaying year andnegative IOD cases during autumn could produce a completely reversed atmospheric circulation response, leading to anearlier FLD and a later LLD over the Chinese mainland, respectively.

Lagged influence of ENSO regimes on droughts over the Poyang Lake basin, China

The regional drought predictability is strongly influenced by teleconnections factors. Among them, El Niño-Southern Oscillation (ENSO) is important to drought occurrence. However, it is still not fully understood how the probability of regional droughts corresponding to different ENSO regimes varies with time lags. In this study, the event-based coincidence analysis (ECA) is employed to statistically derive the relationships regarding time information and magnitude between conventional ENSO (c-ENSO)/ENSO Modoki (ENSO_M) episodes and drought events. The standardized precipitation evapotranspiration index (SPEI) based on station-records is used to determine meteorological droughts. Our study focuses on the largest freshwater lake of China, Poyang Lake basin (PLB), as severe droughts have occurred there frequently. Results indicate that the summer-autumn continuous drought dominates the severe droughts, with a frequent onset in August/September, and a cessation in October/November. The likelihood of drought occurrence is highest during cool phases of c-ENSO (CEN), followed by warm ENSO_M (WEM), warm c-ENSO (WEN), and cool ENSO_M (CEM). The influence of WEN/WEM on droughts is statistically significant mostly for a time lag of 10 months, whereas CEN/CEM shows no lagged influence. Furthermore, the variability of the 850 hPa wind anomalies during different ENSO episodes at various time lags is corresponding to the lagged influence of ENSO on droughts. The development and persistence of droughts is resulting from strengthened northeasterly wind anomalies over the PLB. Our findings demonstrate that the ENSO anomalies are early warning signals of droughts and hence can be beneficial for increasing the drought predictivity

Investigating links between rainfall variations in the Ogooué River basin and ENSO in the Pacific Ocean over the period 1940–1999

Abstract. This paper investigates links between rainfall variability in the Ogooué River Basin (ORB) and El Niño Southern Oscillation (ENSO) in the Pacific Ocean. Recent hydroclimatology studies of the ORB and surrounding areas resulting in contrasting conclusions about links between rainfall variability and ENSO. Thus, to make the issue clearer, this study investigates the links between ENSO and rainfall in the ORB over the period 1940–1999. The principal component analysis of monthly rainfall in the ORB was done. The temporal mode of the first component corresponds to the interannual variations of rainfall on the ORB. Also, the pattern of the spatial mode of the first component shows that the ORB is a homogeneous hydroclimatic zone. However, no leading mode is significantly correlated to the ENSO index. A cross-wavelet analysis of the time series of basin-scale rainfall and the ENSO index was therefore carried out. The result is a set of periodogram structures corresponding to some ENSO episodes recorded over the study period. And wavelet coherence analysis of both time series confirms that there are significant links between ENSO and rainfall in the ORB.

Contributions of natural climate variability on the trends of seasonal precipitation extremes over China

AbstractThe increased trends of extreme precipitation events over China have been partially attributed to global warming, while it is unclear how the natural climate variability affect these variations in extreme rainfall trends. Here we examine the contributions of large‐scale modes climate variability from the Pacific Ocean, which are represented by El Niño‐Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO), on the trends of seasonal extreme events across China. Results show that the effects of climate variability modes on precipitation extremes exhibit evidently spatiotemporal characteristics at the seasonal scale. A significant positive trend is found over southeastern and northwestern China in four seasons, and substantial increases in two types of extreme events are also seen over northwestern China in spring and winter. Most of the seasonal trends of extreme precipitation events can be explained by the trends of the principal components. El Niño (La Niña) and PDO–like sea surface temperature (SST) anomalies over the Pacific have a close linkage with the variations in precipitation extremes. By modulating the large‐scale atmospheric circulations, these Pacific SST anomalies associated with climatic oscillations, such as ENSO and PDO, provide the conducive conditions responsible for the occurrences of seasonal precipitation extremes across China. The seasonal trends of extreme events can be largely explained by the variability of the ENSO and PDO episodes, with a relatively larger modulation of PDO as compared to ENSO. These researches have important implications for improving seasonal flood disaster predictability and climate model performances.

The precipitation variability of the wet and dry season at the interannual and interdecadal scales over eastern China (1901–2016): the impacts of the Pacific Ocean

Abstract. The spatiotemporal variability of rainfall in the dry (October–March) and wet (April–September) seasons over eastern China is examined from 1901–2016 based on the gridded rainfall dataset from the University of East Anglia Climatic Research Unit. Principal component analysis is employed to identify the dominant variability modes, wavelet coherence is utilized to investigate the spectral features of the leading modes of precipitation and their coherences with the large-scale modes of climate variability, and the Bayesian dynamical linear model is adopted to quantify the time-varying correlations between climate variability modes and rainfall in the dry and wet seasons. Results show that first and second principal components (PCs) account for 34.2 % (16.1 %) and 13.4 % (13.9 %) of the variance in the dry (wet) season, and their variations are roughly coincident with phase shifts of the El Niño–Southern Oscillation (ENSO) in both seasons. The anomalous moisture fluxes responsible for the occurrence of precipitation events in eastern China exhibit an asymmetry between high and light rainfall years in the dry (wet) season. The ENSO has a 4- to 8-year signal of the statistically positive (negative) association with rainfall during the dry (wet) season over eastern China. The statistically significant positive (negative) associations between the Pacific Decadal Oscillation (PDO) and precipitation are found with a 9- to 15-year (4- to 7-year) signal. The impacts of the PDO on rainfall in eastern China exhibit multiple timescales as compared to the ENSO episodes, while the PDO triggers a stronger effect on precipitation in the wet season than the dry half year. The interannual and interdecadal variations in rainfall over eastern China are substantially modulated by drivers originated from the Pacific Ocean. During the wet season, the ENSO exerted a gradually weakening effect on eastern China rainfall from 1901 to 2016, while the effects of the PDO decreased before the 1980s, and then shifted into increases after the 2000s. The finding provides a metric for assessing the capability of climate models and guidance of seasonal prediction.

Severe coral bleaching of Siderastrea stellata at the only atoll in the South Atlantic driven by sequential Marine Heatwaves

Abstract: Threatened by global warming and extreme climatic events, such as El Niño Southern Oscillation (ENSO) and Marine Heatwaves (MHW), coral reefs worldwide faced the worst bleaching and mortality event between 2014 and 2017, induced by the 2015/2016 ENSO. We evaluated the impacts of ENSO and MHW episodes on bleaching and mortality frequencies of Siderastrea stellata at Rocas Atoll, Southwestern Atlantic, using visual censuses conducted in 2016, 2017 and 2019. Bleaching rate varied significantly along the sampling period (11.71% in 2016, 1.52% in 2017, and 88% in 2019), but mortality was always less than 4%. Bleaching events in Atlantic reefs have been constantly associated with ENSO, until these recent events of the last two years. We suggest that MHW were probably the primary driver of the observed bleaching, especially in 2019, when much higher bleaching rates were observed than in ENSO periods. Although Southwestern Atlantic massive corals are considered more resistant to thermal stress than reefs corals worldwide, the strong events registered since 2019 highlight the need for continuous monitoring to better understand coral bleaching dynamics and improve predictions on the effects of global change in the region.

The Impacts of El-Niño-Southern Oscillation (ENSO) on Agriculture and Coping Strategies in Rural Communities of Ethiopia: Systematic Review Article

The principal cause of drought in Ethiopia is asserted to be the fluctuation of the global atmospheric circulation, which is triggered by Sea Surface Temperature Anomaly (SSTA), occurring due to El Niño-Southern Oscillation (ENSO) events. It can make extreme weather events more likely in certain regions in Ethiopia. ENSO episodes and events, and related weather events have an impact on seasonal rainfall distribution and rainfall variability over Ethiopia. Thus, the main aim of this review was to identify and organize the major impacts of El-Niño-Southern Oscillation (ENSO) on agriculture and adaptation strategies of rural communities in Ethiopia. Most of the rural communities in the country depend on rain-fed agriculture, and millions of Ethiopians have lost their source of food, water, and livelihoods due to drought triggered by ENSO. The coping strategies against ENSO induced climate change are creating a collective risk analysis, and Climate-Resilient Green Economy (CRGE) at the national level. In addition, community-based coping strategies for ENSO are integrated with watershed management, livelihood diversification and land rehabilitation to better cope with erratic rainfall and drought risks in the country.

Monitoring and predictive mapping of floristic biodiversity along a climatic gradient in ENSO's terrestrial core region, NW Peru

The tropical dry forests of NW Peru are heavily shaped by the El Niño Southern Oscillation (ENSO), where especially El Niño brings rain to arid to semi‐arid areas. However, the resulting effects on biodiversity patterns remain largely unknown as well as the effect of environmental variables on the floristic composition under varying rainfall patterns. Therefore, we studied the spatio‐temporal effects of different ENSO episodes on floristic biodiversity along a climatic gradient ranging from the coastal desert to the Andean foothills. We sampled 50 vegetation plots in four years representing different ENSO episodes. To highlight the spatio‐temporal changes in floristic composition and beta diversity across ENSO episodes, we predicted ordination scores with a Generalized Additive Model. We applied variation partitioning to test if topographic or edaphic variables gained in importance during more humid ENSO episodes. Additionally, we executed an irrigation–fertilization experiment to quantify the beneficial effects of the water–nutrient interaction under different simulated ENSO rainfall scenarios. Plant species richness increased under humid conditions during the humid La Niña (2012) and the moderate El Niño (2016), and slightly decreased under the very humid conditions during the coastal El Niño (2017). The spatial prediction revealed that specific vegetation formations became more pronounced with increasing water input, but that a large water surplus led to the disruption of the strict order along the climatic gradient. Edaphic and topographic variables gained in importance with increased water availability (2012 and 2016), however, this effect was not further amplified under very wet conditions (2017). The experiment showed that plant cover under Super Niño conditions was three times higher when fertilized. Overall, our spatial predictions concede detailed insights into spatio‐temporal ecosystem dynamics in response to varying rainfall caused by different ENSO episodes while the results of the experiment can support farmers regarding a sustainable agrarian management.

Interannual variability of surface satellite-derived chlorophyll concentration in the bay of La Paz, Mexico, during 2003–2018 period: The ENSO signature

The Bay of La Paz (BLPZ), located in the southwestern Gulf of California, is a region of significant biological productivity and strong environmental variability that remains to be understood. In particular, the spatial signature of different El Niño-Southern Oscillation (ENSO) conditions and their impact on the ecology of the bay remains puzzling because of contrasting field observations. In this context, the available satellite-derived data on surface chlorophyll (ChlSAT), sea surface temperature (SST) derived from the MODIS-Aqua sensor, together with surface wind intensity (WI) derived from reanalysis datasets from the period 2003–2018 were analyzed to identify the influence of local and remote forcing over the interannual variability of chlorophyll pigment concentration in BLPZ using WI, SST, and the Oceanic El Niño Index (ONI) as environmental factors. Significant relationships between environmental factors and ChlSAT were found using exponential models, with the higher slopes and correlations during La Niña events. Empirical orthogonal function (EOF) analysis was used to extract the principal mode of the ChlSAT and SST interannual variability. The first mode (EOF1) accounted for 64% and 89% of the ChlSAT and the SST interannual variance, respectively, showing a strong gradient along the coast of the bay. The corresponding amplitude of the ChlSAT mode was significantly correlated with the independent variables PC1SST, ONI, and WI anomalies (RSST = − 0.60, RONI = − 0.57, and RWI = 0.44, P < 0.001). Monthly time series of ChlSAT anomalies along the coast where examined as a function of each independent variable using a multiple linear regression analysis (LRA), which revealed that during the 2005 to 2013 period, high peaks of positive ChlSAT anomalies in the central and southern coast were related to cold ENSO events and favorable wind forcing, which smoothed the effect of weak and moderate El Niño episodes. This period of high biological productivity was only interrupted by the strong and long 2015–2016 El Niño event. Since late 2013, the ChlSAT and the WI anomalies showed a sharp drop to negative anomaly values, which may be the result of complex interactions of physical and biological processes observed during strong warm ENSO events, showing one peak of persistent warm SST anomalies via a weakening of the wind intensity (i.e., from atmospheric teleconnection) and a second one due to the oceanic connection. It is confirmed that BLPZ maintains high pigment concentration levels, comparable to those reported on the mainland coast of GC, where only strong warm ENSO episodes cause changes in chlorophyll concentration.

Spatio-temporal patterns of Chlorophyll-a in a wide and low-relief shelf sea of the Gulf of Mexico: Insights of interannual climatic patterns on the phytoplankton biomass varying behavior

Chlorophyll-a concentrations were recorded in three oceanographic surveys (GOMEX-4, GOMEX-5, GOMEX-6) during 2015–2018 throughout the Yucatan shelf, southeast Gulf of Mexico (GoM). Such campaigns encompassed the warm-phase, cold-phase, and neutral-phase of El Niño-Southern Oscillation (ENSO), respectively, as well as a progressively increasing upwelling intensification scenario. We undertook the analysis of the Chl-a concentrations in the Yucatan shelf through the multiyear GOMEX series to understand how the interplay between the coastal upwelling, precipitation regime, and wind patterns influence the distribution, magnitude and timing of the phytoplankton biomass. These results suggest that substantial rainfall late summer during ENSO's warm-phase in GOMEX-4 survey improved the coastward Chl-a (1.69 ± 0.07 mg m−3). This pattern could be associated to the increased cold-front activity usually modulated by the wintertime warm-phase of ENSO. The wind-driven mixing during these cold fronts led to water column mix, which contributed to enhance the distinguishing between coastline and marine Chl-a levels. The coastal upwelling pulses depicted a wide-shelf influence over the Chl-a concentration (0.47 ± 0.01 mg m−3 and 0.53 ± 0.03 mg m−3 average concentrations in the marine and coastal areas, respectively). An onshore excursion of cold water masses intermingled with seasonal precipitation traits sustained high nearshore Chl-a in zones already altered by subaqueous freshwater input in the karstified Yucatan seascape (varying within the interval of 1.50–2.76 mg m−3). These results suggest that, similarly to riverine-influenced areas in the northern GoM, warm-phase ENSO episodes have the potential to alter the phytoplankton biomass also in karstified shelves, as the Yucatan platform. This large-scale pattern overlaps processes occurring over a broad spatial and temporal scale, like seasonal rainfall and upwelling, establishing recurrent environmental gradients driving biogeochemical fronts along the seascape. The relationships found allow a better grasp of sound ecologically processes as phytoplankton blooms along the Yucatan shelf, which might be also sensitive to human-driven disturbances.

Analyzing the Hydroelectricity Variability on Power Markets from a System Dynamics and Dynamic Systems Perspective: Seasonality and ENSO Phenomenon

In this paper, the variations in hydropower generation are addressed considering the seasonality and ENSO (El Niño-Southern Oscillation) episodes. The dynamic hypothesis and the stock-flow structure of the Colombian electricity market were analyzed. Moreover, its dynamic behavior was analyzed by using Dynamic Systems tools aimed at providing deep insight into the system. The MATLAB/Simulink model was used to evaluate the Colombian electricity market. Since we combine System Dynamics and Dynamic Systems, this methodology provides a novel insight and a deeper analysis compared with System Dynamics models and can be easily implemented by policymakers to suggest improvements in regulation or market structures. We also provide a detailed description of the Colombian electricity market dynamics under a broad range of demand growth rate scenarios inspired by the bifurcation and control theory of Dynamic Systems.

Meteorological Systems Influences Rainfall in Seropédica.

Rainfall data from 2001-2011 from Seropédica were related to synoptic systems and El Niño Southern Oscillation episodes (ENSO). Evaluation was divided into average, monthly, seasonal and annual. Synoptic data are from Climanálise from 1996 to 2012. Descriptive statistics and non-parametric tests (Mann-Kendall (MK), Pettitt and Sen Method (Se)) were applied to time series from Climanálise. The identified average characteristics showed high interannual and intraseasonal variability of synoptic systems, followed by the interaction between local and mesoscale systems in the rainfall regime. Seasonally, spring (38.06%) and summer (30.35%) were higher than autumn (20.91%) and winter (10.68%). The highest average monthly accumulated were observed in the joint occurrence of SACZ/ MCZ and FS from November to January, followed by the influence of ENSO episodes in Seropédica. FS occurences decreased in 2005, while in 2003 there was an increased SACZ/MCZ. MK test results considering α = 5% showed that there is Significant Increasing Trend (SIT) in SACZ/MCZ (Z &gt; 2.25) and Significant Decreasing Trend (SDT) of FS (Z &lt; 3.68) in Rio de Janeiro. Statistical identified trends and critical periods of synoptic systems. Sistemas Meteorológicos Influenciam a Chuva em Seropédica R E S U M ODados pluviométricos de 2001-2011 de Seropédica foram correlacionados com os sistemas sinóticos e os episódios de El Niño-Oscilação Sul (ENOS). A avaliação foi dividida em: média, mensal, sazonal e anual. Os dados sinóticos são provenientes da Climanálise de 1996 a 2012. Foi aplicada uma estatística descritiva e os testes não paramétricos (Mann-Kendall (MK), Pettitt e Método de Sen (Se)) a série temporal da Climanálise. As características médias identificadas mostraram alta variabilidade interanual e intrasazonal dos sistemas sinóticos, seguido da interação entre os sistemas locais e de mesoescala no regime de chuva. Sazonalmente, a primavera (38,06%) e o verão (30,35%) foram superiores ao outono (20,91%) e o inverno (10,68%). Os maiores acumulados mensais médios foram observados na ocorrência conjunta de ZCAS/ZCOU e SF nos meses de novembro a janeiro, seguido da influência dos episódios de ENOS em Seropédica. Os casos de SF diminuíram em 2005, enquanto 2003 houve um aumento de ZCAS/ZCOU. Os resultados do teste MK, considerando-se α = 5% mostraram que há Tendência Significativa de Aumento (TSA) de ZCAS/ZCOU (Z &gt; 2.25) e Tendência Significativa de Redução (TSR) de SF (Z &lt; 3.68) no Rio de Janeiro. A estatística identificou as tendências e os períodos críticos dos sistemas sinóticos.Palavras chaves: ENOS, Sistemas Sinóticos, testes não paramétricos.

Drought Characterization Using Drought Indices and El Niño Effects

Droughts are extreme meteorological and hydrological events having severe impacts on the natural environment and socioeconomic conditions of the affected region. Drought characterization is vital in planning, design, and management of water resources systems. Drought indices such as standardized precipitation index (SPI) and standardized precipitation evapotranspiration index (SPEI) are generally used as a tool for monitoring changes in drought conditions. The variability of monsoon droughts over India is significantly influenced by the tropical sea surface temperature anomalies. A major portion of the drought variability is influenced by the El Nino–Southern Oscillation (ENSO). Drought characterization for Indo Gangetic alluvial plain demonstrates the efficacy of the present work. The values of SPI and SPEI are found in all the possible ranges representing mild, moderate, and severe drought events in the study area. Most drought events are observed in Raebareli District, as both SPI and SPEI indices showed 27 and 23 severe events. Also, correlation is found between observed drought periods, ENSO episodes, and drought indices.

Resonance Effect in Interaction Between South Asian Summer Monsoon and ENSO During 1958–2018

The study has shown that the shear component of the vertical integrated kinetic energy (Ks) over the box (40oE-100oE, 0-20oN) can be used to measure the intensity of the South Asian summer monsoon (SASM). Based on its value averaged between June and August, the SASM can be divided into strong and weak monsoon episodes. Between 1958 and 2018, there existed 16 (16) strong (weak) monsoon episodes. Based on the calendar year, the relationship between the SASM and ENSO episodes can be grouped into six patterns: weak monsoon - El Nino (WM-EN), normal monsoon - El Nino (NM-EN), weak monsoon - non ENSO (WM-NE), strong monsoon - La Nina (SM-LN), normal monsoon - La Nina (NM-LN) and strong monsoon - non ENSO (SM-NE). Previous studies suggest that the WM-EN and SM-LN patterns reflect the correlated relationship between the SASM and El Nino/Southern Oscillation (ENSO) events. Therefore, we name these two strongly coupled categories WM-EN and SM-LN as the resonance effect. Two important circulations, i.e., Walker circulation (WC) and zonal Asian monsoon circulation (MC), in the vertical plane are found to be not always correlated. The MC is controlled by thermal gradients between the Asian landmass and the tropical Indian Ocean, while the WC associated with ENSO events is primarily the east-west thermal gradient between the tropical South Pacific and the tropical Indian Ocean. Furthermore, the gradient directions caused by different surface thermal conditions are different. The main factor for the resonance effect is the phenomenon that the symbols of SSTA in the tropical Indian Ocean and the equatorial eastern Pacific are the same, but are opposite to that of the SSTA near the maritime continent.

Classifying El Niño-Southern Oscillation Combining Network Science and Machine Learning

Machine learning and complex network theory have emerged as crucial tools to extract meaningful information from big data, especially those related to complex systems. In this work, we aim to combine them to analyze El Nino Southern Oscillation (ENSO) phases. This non-linear phenomenon consists of anomalous (de)increase of temperature at the tropical Pacific Ocean, which has irregular occurrence and causes climatic variability worldwide. We construct temporal Climate Networks from the Surface Air Temperature time-series and calculate network metrics to characterize the warm and cold ENSO episodes. The metrics are used as topological features for classification. We employ ten classifiers and achieved 80% AUC ROC when predicting the intensity of Strong/ Weak El Nino and Strong/Weak La Nina for the next season. The complex network represents the relationship among different regions of the planet and machine learning creates models to classify the different classes of ENSO. This work opens new paths of research by integrating network science and machine learning to analyze complex data like global climate systems.

Placing the AD 2014–2016 ‘protracted’ El Niño episode into a long-term context

Although extended or ‘protracted’ El Niño and La Niña episodes were first suggested nearly 20 years ago, they have not received the attention of other ‘flavours’ of the El Niño–Southern Oscillation (ENSO) or low-frequency ‘ENSO-like’ phenomena. In this study, instrumental variables and palaeoclimatic reconstructions are used to investigate the most recent ‘protracted’ El Niño episode in 2014–2016, and place it into a longer historical context. Although just reaching the threshold for such an episode, the 2014–2016 ‘protracted’ El Niño had very severe societal, agricultural, environmental and ecological impacts, particularly in western Pacific regions like eastern Australia. We show that although ‘protracted’ ENSO episodes of either phase cause similar, near-global modulations of weather and climate as during more ‘classical’ events, impacts associated with ‘protracted’ episodes last longer, with strong influences in eastern Australia. The latter is a response to the dominance of Niño 4 sea surface temperature (SST) and associated atmospheric teleconnection anomalies during ‘protracted’ ENSO episodes. Importantly, while Niño 4 SST anomalies recorded during the austral summer of 2016 were the highest values on record, an analysis of long-term palaeoclimate records indicates that there may have been episodes of greater magnitude and duration than seen in instrumental observations. This suggests that shorter instrumental observations may underestimate the risks of possible future ENSO extremes compared with those observed from multi-century palaeoclimate records. Improved knowledge of ENSO and the potential to forecast ‘protracted’ episodes would be of immense practical benefit to communities affected by the severe impacts of ENSO extremes.