La Niña Research Articles

Dynamics of dissolved inorganic carbon (DIC) and stable C isotope ratios (δ13CDIC) in a tropical watershed with diversified land use in São Paulo State, Brazil

The fluvial transport of dissolved inorganic carbon (DIC) is an important component of the global carbon cycle. Herein, we assessed the dynamics of DIC and the C stable isotopic composition (δ13CDIC) in a watershed with diversified land use in São Paulo State (Brazil), more specifically in the Sorocaba River basin (SRB) and considered the temporal and spatial scales. For this purpose, twelve fluvial samples at each sampling point (e.g., S1, S2, S3, S4 and S5) were collected in the SRB, from June 2009 to May 2010, which represented one complete hydrological cycle that included the extremes of the rainfall and discharge regimes. In addition, the δ13CDIC values were also characterized in the wet and dry season at all sampling points to verify their seasonal variability. The results reflected the seasonal variation in discharges, water temperatures, and electrical conductivities. Most of the DIC was transported in the wet season at all sampling points, where the less negative δ13CDIC values were characterized. The natural sources of DIC are associated with atmospheric/soil CO2 consumption. The anthropogenic impacts on both [DIC] and δ13CDIC are linked to untreated urban sewage that is discharged directly into the Sorocaba River, as well as to aquatic photosynthesis in the Itupararanga Reservoir. From 1970 to 2020, the modeling proposed in this study indicated that the annual flux of DIC (Friver) varied from 9.0 to 78.7 t km−2 a−1, confirming that the El Niño Southern Oscillation (ENSO) controlled Friver in the SRB, with higher and lower Friver values occurring during strong El Niño (EN) and La Niña (LN) years. The average Friver value was 20 t km−2 a−1, which is higher than those obtained in natural several temperate and tropical watersheds due to the influences of urban areas on [DIC] in the SRB.

PENGARUH LA NINA DAN EL NINO TERHADAP PENYAKIT DEMAM BERDARAH DENGUE DAN MALARIA DI INDONESIA

The phenomena of El nino and La nina are closely related to rainfall and its impact on various fields. Rainfall is an element of weather and climate that greatly influences all aspects of life including health, especially mosquito vector-borne diseases in Indonesia such as Dengue hemorrhagic fever (DHF), malaria, chikungunya, zika, and others. In this regard, an analytical study was carried out on the effect of El nino and La nina on DHF and malaria cases in Indonesia. This paper is the result of data analysis from the study "The Influence of El nino and La nina on Seasonal Variability in South Kalimantan" and the data of DHF and malaria cases obtained from the Data and Information Center of the Ministry of Health of Indonesia. Descriptive analysis was carried out on the trend of DHF and malaria cases fluctuation associated with El nino and La nina phenomena that occurred throughout the time period 2007-2017. El nino and La nina phenomena affect fluctuations in DHF and malaria cases related to increased and decreased of rainfall which affect the growth and development and also the activity patterns of mosquito as vectors of transmitting DHF and malaria. The increase of DHF cases in Indonesia was influenced by "strong" El nino and "moderate" La nina while the increase of malaria cases in Indonesia was more influenced by "strong" and "moderate" La nina events.

Does ENSO Impact Equity Returns? Evidence via Country and Panel Regression

This study employs a panel local projections (LP) model to analyze the influence of El Niño (EN), La Niña (LN) Southern Oscillation (ENSO) on real equity returns based on twenty economies, collectively accounting for 80.2% of global output. We demonstrate that an ENSO shock has a delayed and oscillatory effect on equity returns, where the most significant impact is positive (negative) during an EN (LN) phase. We further analyze the climate state by each of the twenty economies. The literature shows that the effect of an ENSO shock on economic growth can vary across different economies. A main finding is that we show a near uniform result similar to the panel LP model, which we posit is driven in part by strong interconnections of financial markets on a global scale. These findings offer valuable insights for policymakers and investors. Highlights We estimate a panel and economy-specific climate ENSO switching via LP model. Twenty economies representing 80.2% of global output are analyzed. ENSO shock has a delayed and oscillatory effect on equity returns. Most significant impact of an ENSO shock on equity returns is positive (negative) during an EN (LN) phase.

ENSO Modulation of Global MJO and Its Impacts on South America

Abstract Changes in the Madden–Julian oscillation (MJO) and its impacts on the South American monsoon season during different El Niño–Southern Oscillation (ENSO) states [El Niño (EN), La Niña (LN), neutral (NT)] are analyzed in the global context of the MJO-propagating anomalies of convection and circulation. The background ENSO-related changes influence several aspects of MJO (relative occurrence of phases, propagation, convection, and teleconnections), and therefore modify the MJO impacts on South America (SA), such as precipitation anomalies and frequency of extreme events, as well as their distribution throughout the MJO cycle. Among the changes are the following: 1) a delay in the teleconnection between the central-east Pacific and SA, from MJO phase 8 in LN (MJOLNphase8) to MJO phase1 in EN (MJOENphase1); 2) enhanced MJO convection in the central-east subtropical South Pacific in MJOLNphases7 + 8 and a little farther east in MJOENphases8 + 1, in a region efficient in generating teleconnections that produce rainfall anomalies over central-east SA (CESA), especially the South Atlantic convergence zone (SACZ), strongest one phase earlier in LN (MJOLNphase8) than in EN (MJOENphase1), and a little shifted east in the latter than in the former; 3) enhancement of the extratropical teleconnection and its impacts over the SACZ in both EN and LN (with regard to NT), indicating nonlinear effects on MJO impacts over SA; 4) predominant increase (or reduction) in the frequency of extreme events over SA regions where both ENSO and MJO contribute in the same direction, with the greatest increase over CESA during EN in MJOENphase1 and over Southeast SA (SESA) in MJOENphase3. Significance Statement The changes produced by different El Niño–Southern Oscillation background states (neutral, El Niño, La Niña) in the Madden–Julian oscillation (MJO) and its impacts on precipitation over South America (SA) are disclosed for the austral summer monsoon season, when MJO is strongest. The reliability of the results is enhanced by using observed rainfall data. The background states affect MJO propagation, circulation, and convection, producing significant differences in precipitation and extremes over densely populated regions, besides phase shifts of the strongest impacts. The results are relevant to subseasonal prediction, since MJO is a key predictability source, to validate models and describe realistically the impacts over SA in each MJO phase. Models’ skill in simulating these results is assessed in a follow-up work.

Overemphasized role of preceding strong El Niño in generating multi-year La Niña events

Previous studies have emphasized the significance of a strong El Niño preceding La Niña (LN) in the formation of multi-year LN events due to the slow recharge-discharge ocean heat content process. However, observational analyses from 1900 to 2022 reveal that the majority (64%) of multi-year LN events did not necessitate a preceding strong El Niño to generate their second LN, suggesting an overemphasis on traditional views. Instead, here we show that a negative phase of the North Pacific Meridional Mode (PMM) during spring, when the first LN begins to decay, activates the mechanism responsible for triggering another LN and producing a multi-year event. The westward extension of the first LN’s cold anomalies, which interact directly with the eastern edge of the western Pacific warm pool, is highlighted as a crucial factor in the occurrence of a negative PMM. Additionally, the PMM mechanism can create a third LN, leading to triple-dip events.

Diverse Impacts of ENSO on the Intensity of Tropical Western North Pacific Synoptic‐Scale Disturbances During Boreal Summer

AbstractPresent study analyzes diverse impacts of El Niño–Southern Oscillation (ENSO) on the intensity of synoptic‐scale disturbances (SSDs) over the tropical western North Pacific (TWNP) during boreal summer. Asymmetric changes in the SSD intensity are detected in El Niño (EN) and La Niña (LN) developing summers. The increase in the SSD intensity is larger and located more eastward in EN developing summers compared to the decrease in LN developing summers. The asymmetric SSD intensity changes are associated with an eastward shift of anomalous low‐level cyclone and mid‐level ascent during EN developing summers relative to opposite anomalies during LN developing summers. The above difference is attributed to zonally asymmetric anomalous equatorial central‐eastern Pacific heating and cooling in EN and LN years. Sensitivity experiments with an atmospheric general circulation model illustrate that the major reason for asymmetric TWNP SSD intensity changes is the asymmetric atmospheric response to opposite sea surface temperature (SST) anomalies in EN and LN years. Comparisons between strong and moderate ENSO events show an obvious dependence of the SSD intensity change on the amplitude of EN, but not on the amplitude of LN. This indicates a stronger sensitivity to warmer SST than to colder SST. The enhancement of the TWNP SSD intensity is confined to a more westward longitude in Central than Eastern Pacific EN years with a comparable magnitude.

Influence of extreme cold and warm oceanographic events on larval fish assemblages in the southern region of the California Current

The larval fish community in the southern region of the California Current (CC) was analyzed to test the hypothesis of a northward expansion of tropical species for the summer-fall seasons of La Niña (LN) 2010-2011, The Blob 2014, and El Niño (EN) 2015-2016. Interannual temperature anomalies (-5 to +2°C), as well as decreases in chlorophyll a (68%) and zooplankton density (71%), resulted in dramatic changes in the larval fish community, such as an 82% decline in larval fish density, unprecedented for the CC. Tropical species richness increased in the north by 46%, while temperate species decreased by 65% in the south. Mesopelagic species richness and relative abundance increased in the north by 53 and 92%, respectively. In the south, the species richness of the demersal component increased up to 39%, although demersal species were co-dominant with mesopelagic species, accounting for 47% of the relative abundance compared to 49% for the mesopelagic species. The magnitude of the changes in the community was unparalleled when compared with other warming events, such as EN 1983-1984 or EN 1997-1998. The differences were probably related to the presence of The Blob, which favored the transport of oceanic species into the neritic region of the CC. In both cold and warm years, fronts and mesoscale eddies in the middle part of the Baja California Peninsula represented barriers to the latitudinal distribution of species, even during intense tropicalization processes, since no latitudinal extensions in species distribution occurred.

On the interpretation of changes in the subtropical oxygen minimum zone volume off Chile during two La Niña events (2001 and 2007)

Oxygen minimum zones (OMZs) are extended oceanic regions for which dissolved oxygen concentration is extremely low. They are suspected to be expanding in response to global warming. However, currently, the mechanisms by which OMZ varies in response to climate variability are still uncertain. Here, the variability of the subtropical OMZ off central Chile of a regional coupled physical–biogeochemical regional model simulation was analyzed for the period 2000–2008, noting that its fluctuations were significant despite the relatively weak amplitude of the El Niño/Southern Oscillation (ENSO). In particular, the interannual variability in the OMZ volume (OMZVOL, defined as the volume with dissolved oxygen concentration (DO) ≤ 45μM) was approximately 38% larger than that of the seasonal cycle, with maximum and minimum anomalies of OMZVOL taking place during two cold La Niña (LN) years (2001 and 2007). The model analyses further reveal that these anomalies resulted from a combined effect of changes in (1) the oxygen-poor waters poleward transport by the Peru–Chile undercurrent (PCUC), (2) the intensity of quasi-zonal jets influencing the transport of water to and from the OMZ, and (3) the zonal DO transport related to mesoscale eddy activity. Specifically, the interannual variability of the PCUC modulated primarily the DO contents of the OMZ core [(DO) ≤ 20μM] and secondarily the OMZVOL, while cross-shore DO transport by the zonal jets and the eddy fluxes played a major role in ventilating and shaping the offshore extent of the OMZ. When the OMZVOL was maximum (minimum), the PCUC transport was slightly increased (reduced), which was associated with a reduction (increase) in the ventilation of the OMZ through negative (positive) anomalies of zonal advection and DO eddy fluxes. Our results demonstrate that significant natural interannual variability in the subtropical OMZ off Chile originates from the interplay between oceanic equatorial teleconnection (PCUC transport) and local non-linear dynamics (the zonal jets and mesoscale eddies).

Linking the solar cycle and Earth’s climate

In this paper, the authors have made an effort to investigate the impact of the solar cycle on Earth’s climate in the context of rainfall and temperature over a location, on El Nino/ La Nina, and world famines. The study shows that the peak sunspot number (SSN) often occurs in pairs. Multiple peaks are also seen frequently. The La Ninas follow multiple peaks, or sometimes associated with it. The El Ninos usually follow the solar minima, though not always. This study shows that the SSN trough will occur in 2020, thereby causing El Nino during 2019-2021. The multiple SSN peak is likely to occur during 2023-2028, predicting a La-Nina during this period. Multiple SSN peaks and very high SSN values bring about famines. The study shows that the total solar irradiance (TSI) bears a strong correlation with the SSN. Besides, the cosmic ray flux decreases as the SSN and the TSI increases. The monthly and yearly variations of SSN, TSI, and temperature show increasing trends over the years, indicating increased warming as the years advance. However, none of these parameters bears significant correlations with the temperature, either independently or together, implying that some other factors are also responsible for determining the temperature. The study shows no direct relationship between rainfall and the SSN. However, several years show a similar trend between the two. The investigation indicates a strong influence of the solar cycle on world climate.

On the Influence of ENSO on Sudden Stratospheric Warmings

AbstractUsing the extended ERA5 reanalysis and three state‐of‐the‐art models, this study explores how El Niño‐Southern Oscillation (ENSO) can influence the total frequency, seasonal cycle and preconditioning of sudden stratospheric warmings (SSWs). Reanalysis data shows that in the last seven decades, winters with SSWs were more common than winters without, regardless El Niño (EN) or La Niña (LN) occurrence or the ENSO/SSW definitions. In agreement with previous studies, our models tend to simulate a linear ENSO‐SSW relationship, with more SSWs for EN, around mid‐winter (January–February) as in reanalysis, and less for LN when compared to neutral conditions. Independently of ENSO, the main tropospheric precursor of SSWs appears to be an anomalous wave‐like pattern over Eurasia, but it is dominated by wavenumber 1 (WN1) for EN and shows an enhanced wavenumber 2 (WN2) for LN. The differences in this Eurasian wave pattern, which is largely internally generated, emerge from the distinct configuration of the background, stationary wave pattern induced by ENSO in the North Pacific, favoring a stronger WN1 (WN2) component during EN (LN). Our results suggest that the ENSO‐forced signal relies on modulating the seasonal‐mean polar vortex strength, becoming weaker and more displaced (stronger and more stable) for EN (LN), while ENSO‐unforced wave activity represents the ultimate trigger of SSWs. This supports the view that ENSO and SSWs are distinct sources of variability of the winter atmospheric circulation operating at different time‐scales and may reconcile previous findings in this context.

ENSO and PDO Effect on Stratospheric Dynamics in Isca Numerical Experiments

The deterministic forecast of the stratospheric polar vortex intensity (iSPV) is limited by 2 weeks, but it can be probabilistically predicted for a longer period due to low-frequency components of the climate system, such as large-scale sea surface temperature anomalies (SSTAs) (e.g., El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO)). For a qualitative and quantitative assessment of the effect of the large-scale Pacific SSTAs on the iSPV anomalies formation, idealized model experiments were carried out using the Isca platform. There is no statistically significant response of the SPV dynamics to the SSTAs corresponding to PDO phases, but they noticeably correct the effect of ENSO modes when added to it. The effect of the El Niño (EN) and La Niña (LN) events with neutral PDO phases on the iSPV is asymmetric; in the “single” EN experiment the vortex is 40% weaker relative to the control values, and, in the “single” LN, the SPV is weakened by no more than 20%. When EN accompanied with the positive PDO phase, iSPV is reduced by 58%. When the negative PDO phase is added, the EN effect is significantly weakened. The LN effect is weakened by both positive and negative PDO phases.

Interdecadal Pacific Oscillation modulation of ENSO teleconnections in its decaying stages: Relations with Indian Ocean basin‐wide mode and South American precipitation

AbstractThis study examines the Interdecadal Pacific Oscillation (IPO) modulation of the El Niño–Southern Oscillation (ENSO) teleconnections in its decaying stages with the tropical ocean by focusing on the Indian Ocean Basin‐Wide (IOBW) mode and the precipitation over South America (SA) in the 1901–2012 period. Composite analyses revealed that the ENSO teleconnections are IPO‐modulated due to the differential ENSO decaying speed, which is slower during the positive than negative IPO phase, for both El Niño (EN) and La Niña (LN) cases. Negative precipitation anomalies related to EN persist over northeastern SA until austral winter for the positive IPO phase (POS IPO), while significant opposite sign anomalies occur in this region for the negative IPO phase (NEG IPO). These results are associated with the Walker circulation's reversal during NEG IPO which is, in turn, accompanied by negative IOBW. During the POS IPO, the positive IOBW causes upward movements over there and, by continuity, downward movements over SA. In the NEG IPO, for LN events the wave train originating in the north of Australia propagates toward subtropical SA, which, coupled with the surface circulation, causes dryness in this region. In addition, the rapid decay of LN in the NEG IPO, followed by the emergence of EN, caused changes in the Walker circulation, such that enhanced upward movements occurred over the Pacific and SA region, and downward movements over the Indian Ocean until austral winter. In turn, the slower decay of the LN in the POS IPO maintains strong subsidence over the central Pacific and weak upward motions over western SA. So, the EN (LN) and positive (negative) IOBW during the POS (NEG) IPO prolong the scarcity of precipitation over equatorial (subtropical) SA. Persistent dry periods over these regions during the ENSO decaying stage might have important implications for the seasonal forecasts.

The definitive cause of La Nina and El Nino events

Rather than being strictly random events, it has been proven that all La Ninas and El Ninos are caused by the increase or decrease of reflective SO2 aerosols in Earth’s atmosphere, from both volcanic eruptions and industrial activity. Although volcanic eruptions are random events, an eruption usually signifies a forthcoming La Nina/El Nino cycle, and thus can have some predictive value.

Agrometeorological conditions in western Pará compared to agricultural production variables using principal component analysis

Description of the subject. Since the beginning of the twenty-first century, soybean cultivation areas have been expanding in the Legal Amazon. Among the factors that contribute to the process of expansion of cultivation of grains in the Amazon, favorable climate conditions are one of the most important, and these include high rainfall indices and good thermal regimes during the cultivation period. Objectives. In this context, the objective of this study was to describe responses of soybean production as a function of climate variables, considering data from an important grain production center in the Amazon. Method. Principal Component Analysis (PCA) was used including the following response variables: rainfall (R), air temperature (T), real evapotranspiration, water stress (WST) and surplus, soybean area harvested (HVA), quantity produced (PD), occurrence of El Niño and La Niña (LAN). Results. Production variables were negatively correlated with precipitation and water surplus. There was also a negative correlation between El Niño, temperature and water stress. The variables that had greater weight in component 1 were R, T and WST. Considering component 2, the variables that most contributed to the variation were HVA, PD and LAN. Conclusions. The strong or severe occurrence of La Niña influences the soybean production in the region of Belterra-PA, due to the high rainfall index causing excess water in the soil, leading the plants to stress. The moderate occurrence of La Niña positively influences soybean production in the region to maintain the water supply at adequate levels for the plants. These results show the importance of monitoring climate variables for agriculture in the region.

Spatiotemporal variability of precipitation and surface temperature in the southern mesoregion of amazonas, Brazil, during the occurrence of ENSO

Impacts of El Niño – Southern Oscillation (ENSO) climatic phenomena in the southern mesoregion of the Amazon is still poorly understood. Thus, the objective of this study was to analyze the impacts of ENSO of moderate and strong categories on precipitation (ppt) and surface temperature (ts) in the southern mesoregion of Amazonas. The research was carried out with ppt data obtained by the product TRMM_3B43 and ts of the product MOD11C3 in the municipalities of Apuí, Boca do Acre, Canutama, Humaitá, Lábrea, Manicoré and Novo Aripuanã. The Niño Indices were obtained from the National Oceanic Atmospheric Administration. Ts was organized into averages and ppt in seasonal totals from 1998 to 2019, to obtain its provisional climatological normal in the dry and wet seasons. The results showed that ENSO significantly influenced the pattern of ppt and ts in the southern mesoregion of Amazonas. El Niño (EN) had more impact on changing the pattern of ppt and ts than La Niña (LN). The largest reductions in ppt and increases in Ts occurred in the EN periods of 1998/01 and 2015/16, while the occurrence of LN decreased the ppt more expressively in the periods of 2007/08 and 2011/12.

The Western Pacific North Equatorial Countercurrent Responses to Two Forms of El Niño during the Period 1978 to 2017

This research aims to examine how the Western Pacific North equatorial countercurrent (NECC) flow reacts to two different forms of El Niño (EN) over a 40-year period. To establish the prevailing modes for each season, we implemented Empirical Orthogonal Function (EOF) analysis on the eastward current component of the Ocean Reanalysis System 5 (ORAS5) dataset. In comparison to the Central Pacific (CP) episode, the time series principal component of the first mode (PC1) demonstrated that the strongest NECC’s magnitude often emerged during the development period (spring to fall) of the Eastern Pacific (EP) EN event. However, in episode CP 2002/2003, we witnessed an abnormal behavior in which the stronger NECC manifested. This was due to the emergence of a strong anomalous westerly wind, which differed from other CP events and forced the NECC’s magnitude to be greater. When approaching the peak stage, on the other hand, the magnitude of the NECC during the CP episode was typically greater than that of the EP episode. The NECC’s magnitude fell greatly in the second year of the EP episode, particularly during the spring season, since most EP episodes would transition into an La Niña (LN) event in the succeeding event. During the EP EN, it was found that the strength of the westerly wind had a bigger effect on the NECC than during the CP EN.

Multiyear La Niña effects on the precipitation in South America

AbstractThe effect of multiyear La Niña (LN) events on precipitation in South America (SA) was assessed considering 10 persistent LN events over two successive years, referred to as Y1 and Y2 for the 1901–2012 period. Y1 spans from the austral winter of the first year to autumn of the second year, and Y2 spans from the austral winter of the second year to autumn of the third year. Comparisons were performed season by season of the Y1 and Y2. Composites revealed that the teleconnections related to a multiyear LN event during its Y1 and Y2 years, responsible for distinct seasonal precipitation anomaly patterns in SA, were associated with different tropical ocean conditions. In spring, the negative sea surface temperature (SST) dipole in the Indian Ocean during the Y2 was not observed during Y1. Different LN‐related SST anomaly patterns in the tropical Atlantic between Y1 and Y2 occurred in the other seasons. Over northern/northeastern SA, the positive precipitation anomalies became weaker (stronger) during austral summer and autumn (winter and spring) of the Y2 than Y1 and were associated with changes in the Walker cells. During austral spring and summer, southeastern presented drier conditions during the Y2 than Y1. In the spring of Y2, two Rossby wave trains, one associated with the LN‐related anomalous cooling in the equatorial Pacific and another triggered by the upper‐level anticyclone in the tropical Indian Ocean, characterized the circulation pattern over SA which explains the difference in precipitation anomalies between the Y2 and Y1. These drier (wetter) conditions during austral spring and summer (winter and spring), particularly over southern and southeastern Brazil (Colombia) in the Y2, might have more severe effects on the regional hydrological cycle than those in the Y1. The results here indicate that accurate prediction of LN duration is crucial in a climate‐monitoring context.

The Impact of El Nino and La Nina Towards The Prices of Cabbage and Shallot in Indonesia

This study examines the impact of El Nino and La Nina on cabbage and shallot prices by applying the spatial correlation analysis method with 34 provinces from 2010 to 2020 to classify affected areas. The next method is a spatial panel with the main variables: rainfall as an indicator of El Nino and La Nina, commodity prices, spatial effects, and other supporting variables such as income, productivity, wages, and COVID-19 dummy. To get the output model, it is necessary to analyze the selection of the best model between the Structural Equation Model and the Spatial Autoregressive. The results of the study provide findings: (1) there are 16 provinces affected by El Nino and La Nina in Indonesia; (2) the best spatial panel model used is Spatial Autoregressive with the resulting La Nina has a large effect on increasing of cabbage and shallots prices because excess soil water content will cause crops and bulbs to rot easily. The spatial aspect has a significant influence, meaning that the price of cabbage and shallots in one area will affect the prices of the two commodities in other areas through distribution patterns. Policy implications of the impact of El Nino and La Nina in this study are classified into managerial, mitigation, and adaptation strategies including the policy of the Regional Inflation Control Team in the form of inter-regional cooperation. Keywords: cabbage, el nino, la nina, shallot, spatial

Influences of different intensities of El Niño–Southern Oscillation on South American precipitation

AbstractEl Niño–Southern Oscillation (ENSO) phenomena occur in the equatorial Pacific and differentially affect the global climate. Recently, studies have begun to analyse the influence of ENSO intensity on the global climate, but how this intensity affects South American precipitation remains unclear. This work defined the ENSO intensities each season (versus annually, as is more commonly done) because understanding this seasonal intensity is essential for seasonal forecasting. The atmospheric patterns identified in this study showed that the stronger the sea surface temperature (SST) anomalies (SSTA) in the equatorial eastern Pacific were, the stronger the atmospheric responses. The known South American precipitation pattern occurred at all ENSO intensity categories but had different intensities. However, the most important patterns in this study differed from the main pattern. Central‐eastern South America did not have a notable precipitation pattern during all El Niño (EN) years, but there was a negative pattern of strong ENs. In addition, the intensity of the precipitation anomaly during weak EN and La Niña (LN), mainly in northeastern South America, was stronger in austral autumn than in austral summer because the intensity in a previous season can influence the current season's precipitation pattern and the total SST in autumn is stronger than that in summer. Asymmetries between EN and LN events are important to consider; EN tends to be more intense than LN, and deep convection anomalies during EN are displaced eastward relative to those during LN. In this study, categories were defined based on ENSO intensities, but asymmetries appeared in atmospheric patterns, mainly in omega patterns during strong events. The intensities of SSTAs over the equatorial eastern Pacific affected the intensities of the Walker circulation and Rossby waves and, consequently, the intensity of precipitation patterns in different South American regions.

Tropical and Subtropical Pacific Sources of the Asymmetric El Niño‐La Niña Decay and Their Future Changes

AbstractEl Niños (EN) are known to decay more rapidly, while La Niñas (LN) tend to decay more slowly. Observational analyses and coupled model experiments are conducted to show that sea surface temperature (SST) anomalies over the subtropical northeastern Pacific (SNEP) and equatorial western Pacific (EWP) are key factors to determine the decay pace of the EN and LN and their asymmetry. In the present climate the LN produces larger cold SST anomalies over the regions than the warm SST anomalies produced by the EN. The magnitude difference over the SNEP and EWP helps to slow down the LN decay via subtropical footprinting and tropical thermocline variation mechanisms, respectively. Coupled Model Intercomparison Project Phase 6 models project the magnitude differences of SNEP SST anomalies between EN and LN to reduce in the future warming world, causing the asymmetric EN‐LN decay to weaken.