North Atlantic Sea Surface Temperature Research Articles

Relative Contributions of Atmospheric, Oceanic, and Coupled Processes to North Pacific and North Atlantic Variability

AbstractPatterns of sea surface temperature (SST) variability over the northern oceans arise from a combination of atmospheric, oceanic, and coupled processes. Here we use a novel methodology and a suite of observations to quantify the processes contributing to the dominant patterns of interannual SST variability over these regions. We decompose the upper ocean heat content tendency associated with such dominant patterns into contributions from different heat fluxes: (a) atmospherically driven, (b) surface feedbacks, and (c) oceanic. We find that in the subtropics, cloud radiative flux, turbulent heat flux, and residual oceanic processes each contributes substantially to North Pacific SST variability, whereas turbulent heat flux primarily induces North Atlantic SST variability. Cloud radiative fluxes therefore provide a major source of interannual SST variability in the North Pacific but not in the North Atlantic. In midlatitudes, SST fluctuations over the northern oceans are driven by the combination of turbulent and oceanic heat fluxes.

Detection of significant climatic precession variability in early Pleistocene glacial cycles

Despite having a large influence on summer insolation, climatic precession is thought to account for little variance in early Pleistocene proxies of ice volume and deep-water temperature. Various mechanisms have been suggested to account for the dearth of precession variability, including meridional insolation gradients, interhemispheric cancellation of ice-volume changes, and antiphasing between the duration and intensity of summer insolation. We employ a method termed Empirical Nonlinear Orbital Fitting (ENOF) to estimate the amplitudes of obliquity and precession forcing in early Pleistocene proxies and their respective leads or lags relative to the timing of orbital variations. Analysis of a high-resolution North Atlantic benthic δ18O record, comprising data from IODP sites U1308 and U1313, indicates a larger precession contribution than previously recognized, with an average precession-to-obliquity amplitude ratio of 0.51 (0.30-0.76 95% confidence interval) in the rate-of-change of δ18O between 3 and 1 Ma. Averaged when eccentricity exceeds 0.05, this ratio rises to 1.18 (0.84-1.53). Additional support for precession's importance in the early Pleistocene comes from its estimated amplitude covarying with eccentricity, analyses of other benthic δ18O records yielding similar orbital amplitude ratios, and use of an orbitally-independent timescale also showing significant precession. Precession in phase with Northern Hemisphere summer intensity steadily intensifies throughout the Pleistocene, in agreement with its more common identification during the late Pleistocene. A Northern Hemisphere ice sheet and energy balance model run over the early Pleistocene predicts orbital amplitudes consistent with observations when a cooling commensurate with North Atlantic sea surface temperatures is imposed. These results provide strong evidence that glaciation is influenced by climatic precession during the late Pliocene and early Pleistocene, and are consistent with hypotheses that glaciation is controlled by Northern Hemisphere summer insolation.

Interdecadal change in the impact of North Atlantic SST on August rainfall over the monsoon transitional belt in China around the late 1990s

Previous studies indicated that sea surface temperature (SST) anomalies in the Tropical Northern Atlantic (TNAT) have significant impacts on the August rainfall over the monsoon transitional belt (MTB) in China through inducing an atmospheric wave train over Eurasia and an anomalous anticyclone over the subtropical western North Pacific (STWNP). This study reveals that the MTB rainfall-TNAT SST linkage experiences a clear interdecadal shift around the late 1990s. The relationship was strong and significant before the late 1990s, whereas it became fairly weak after the late 1990s. Our result shows that the shift in spatial structure of Eurasian wave train induced by the TNAT SST plays an important role in the changes of the TNAT SST-MTB rainfall relationship. Before late 1990s, positive TNAT SST anomalies induces an atmospheric wave train emanating from the North Atlantic and propagating eastward to East Asia, with negative geopotential height anomalies over the MTB. In addition, a clear anticyclonic anomaly is induced over the STWNP. As such, TNAT SST anomalies have a significant impact on the MTB rainfall. After late 1990s, TNAT SST anomalies can also induce an anticyclonic anomaly over the STWNP and an atmospheric wave train over the Eurasia. However, spatial structure of the Eurasian wave train shows a significant difference. In particular, the negative geopotential height anomaly locates more northward after the late 1990s. Thus, the MTB rainfall-TNAT SST relation is weak. Further analysis also indicates that change in the MTB rainfall-TNAT SST relation is not related to change in the El Nino Southern Oscillation/North Atlantic Oscillation-TNAT SST relation.

West Asian climate during the last millennium according to the EC-Earth model

West Asia is one of the most vulnerable regions to ongoing climate change but has been poorly investigated. Therefore, it is crucial to understand the impact of anthropogenic greenhouse gas, natural forcing, and internal climate variability on temperature and rainfall in this region. In this study, we focus on the climate of West Asia during the last millennium by using a transient simulation of the global earth system model EC-Earth (v3.1). The model performs well in terms of present-day temperature and precipitation patterns and their regional averages. Time series of yearly-mean precipitation and temperature of West Asia show that precipitation increases until the start of the Little Ice Age (1450–1850 CE) and subsequently decreases, whereas temperature shows a cooling trend during the entire last millennium. We first discuss the model output data for climate trends during two periods, 850–1450 CE and 1450–1850 CE. In 850–1450 CE, the largest wetting trend occurred in the eastern regions to the north of the Persian Gulf because of a westward shift of the Indian precipitation core and more moisture transport from the Arabian Sea. The precipitation trend in 1450–1850 CE had a different pattern with a drying trend in the west of the Caspian Sea and overall getting less wet compared with the first period. Temperature showed cooling trends for both periods with the largest values happening in the northern regions. The North Atlantic sea surface temperature cooling and the subsequent change in atmospheric circulation played a role in the wetting and cooling of West Asia. In the second part of the study, we remove the trends and discuss the multi-decadal variability of West Asian climate. It was found that Atlantic multi-decadal and Pacific decadal oscillations strongly contributed to West Asian temperature variability. For West Asian precipitation variability, we found remote connections with the Nordic seas and tropical Pacific Ocean.

Conductors of Heat Content Changes of the North Atlantic Ocean Layers

It is considered that changes of the North Atlantic’s heat content can be a source of surprises in the evolution of the present-day climate, especially the climate of Europe. To investigate this problem, the RAPID monitoring program has been organized. However, results of such monitoring still cover too short a time interval to reach any particular conclusions. In this study, using wavelets, heat content variations in the 0–700 and 0–2000 m oceanic layers were analyzed since the mid-20th century. Their relationships with mean temperature variations of the 0–100 m layer, as well as with earlier analyzed temperature variations of the North Atlantic sea-surface temperature, also are analyzed. It is found that, against a total increase in heat content, variations of all specified characteristics reveal a periodicity similar to the known approximately 22‑year-long Hale heliomagnetic activity cycle. In the 0–700 m layer, this periodicity leading on its phase not only the corresponding periodicity in the 0–2000 m layer, which corresponds well to the generally accepted opinion that heat content anomalies extend from top ocean layers down, but also in the mean temperature of the 0–100 m layer, as well as in the sea-surface temperature. This makes it possible to consider that heliomagnetic activity immediately influences the upper 0–700 m layer of the ocean, thence extending down and up.

Decadal Predictions of the Probability of Occurrence for Warm Summer Temperature Extremes

AbstractWe use a decadal prediction system with the Coupled Model Intercomparison Project Phase 6 version of the coupled Max Planck Institute Earth System Model to predict the probability of occurrence for extremely warm summers in the Northern Hemisphere. An assimilation run with Max Planck Institute Earth System Model shows a robust response of summer temperature extremes in northern Europe and northeast Asia to North Atlantic sea surface temperature via a circumglobal Rossby wavetrain. When the North Atlantic is warm, warm summer temperature extremes occur with a probability of 20% and 24% in northern Europe and northeast Asia, respectively. In a cold North Atlantic phase, these probabilities are 0% and 8%. A similar difference in probability of occurrence is found in the initialized climate predictions. Consequently, the likelihood of a warm summer temperature extreme occurring in the examined regions in the next 10 years can be inferred from predictions of North Atlantic temperature.

Brazilian Dry Forest (Caatinga) Response To Multiple ENSO: the role of Atlantic and Pacific Ocean

The semi-arid region of Northeast Brazil (NEB) experiences severe droughts during El Niño Southern Oscillation (ENSO) years, with major impacts on the dynamics of the native vegetation (Caatinga). However, the effect of these droughts on carbon cycling is not well understood. Here, a numerical model is used to investigate the influence of variations in Pacific and Atlantic sea surface temperatures (SST) on drought and carbon dynamics of the Caatinga during past ENSO events. We demonstrate that precipitation reductions in the Caatinga have a strong influence on vegetation dynamics, with net primary production (NPP) remaining low throughout the droughts. Furthermore, the Caatinga acts as a carbon sink, even in years of severe drought. However, net ecosystem exchange (NEE) is lower in years of low NPP rates, resulting in long periods with limited ecosystem activity. The SST patterns indicate that extreme vegetation changes in the Caatinga are associated with the combination of ENSO events and North Atlantic SST warming.

Comparisons of hot summers in the Mediterranean and North China

In recent years, hot summers (HS) have played an important role in affecting people’s health and causing natural disasters. However, it is not very clear what HS should be attributed to. In order to investigate that, the anomalous of anticyclone associated with HS in the Mediterranean and North China is examined and compared by using data during the time period 1949~2018. Statistical analysis shows that summer temperature in the Mediterranean and North China is revealing a good correlation when removing the global warming trend. The composite results indicate that the anomalous warming during HS over different regions is both dominantly controlled by an anomalous anticyclone, which enhances the subsidence adiabatic heating of the temperature. Furthermore, the subtropical high (STH) variations faithfully represent the fluctuations in summer temperature over the Mediterranean (cor = 0.78) and North China (cor = 0.80). The anticyclonic anomalies over both focus areas are associated with North Atlantic and Northwest Pacific sea surface temperature (sst), respectively. These results indicate that the total influence of the STH position anomaly should be taken into consideration in different places during HS. However, whether such atmosphere-ocean feedback can be improved by numerical experiments is worthy to be further studied.

Coupled Modes of North Atlantic Ocean‐Atmosphere Variability and the Onset of the Little Ice Age

Hydroclimate extremes in North America, Europe, and the Mediterranean are linked to ocean and atmospheric circulation anomalies in the Atlantic, but the limited length of the instrumental record prevents complete identification and characterization of these patterns of covariability especially at decadal to centennial timescales. Here we analyze the coupled patterns of drought variability on either side of the North Atlantic Ocean basin using independent climate field reconstructions spanning the last millennium in order to detect and attribute epochs of coherent basin-wide moisture anomalies to ocean and atmosphere processes. A leading mode of broad-scale moisture variability is characterized by distinct patterns of North Atlantic atmosphere circulation and sea surface temperatures. We infer a negative phase of the North Atlantic Oscillation and colder Atlantic sea surface temperatures in the middle of the 15th century, coincident with weaker solar irradiance and prior to strong volcanic forcing associated with the early Little Ice Age.

Skilful Real‐Time Seasonal Forecasts of the Dry Northern European Summer 2018

AbstractThe Northern European summer of 2018 was the driest for 35 years with resulting impacts on health, agriculture, energy, and water resources. Here we show that this rainfall anomaly was well predicted by a real‐time seasonal forecast. An anticyclonic circulation anomaly was correctly forecast over the North Sea and Scandinavia in 2018 and also in the 1976 record dry summer. In both these exceptionally dry summers, a similar tripole anomaly pattern of North Atlantic sea surface temperatures was present. We perform perturbation experiments that reveal significant circulation, and European rainfall, responses due to changes in the Atlantic meridional temperature gradient. However, consistent with previous work, we find that the model dynamical response is weak relative to that observed and hence large ensembles are required to produce sufficiently skilful predictions. This case study illustrates the potential for the development of summer European climate services.

Ocean and atmosphere influence on the 2015 European heatwave

During the summer of 2015, central Europe experienced a major heatwave that was preceded by anomalously cold sea surface temperatures (SSTs) in the northern North Atlantic. Recent observation-based studies found a correlation between North Atlantic SST in spring and European summer temperatures, suggesting potential for predictability. Here we show, by using a high-resolution climate model, that ocean temperature anomalies, in combination with matching atmospheric and sea-ice initial conditions were key to the development of the 2015 European heatwave. In a series of 30-member ensemble simulations we test different combinations of ocean temperature and salinity initial states versus non-initialised climatology, mediated in both ensembles by different atmospheric/sea-ice initial conditions, using a non-standard initialisation method without data-assimilation. With the best combination of the initial ocean, and matching atmosphere/sea-ice initial conditions, the ensemble mean temperature response over central Europe in this set-up equals 60% of the observed anomaly, with 6 out of 30 ensemble-members showing similar, or even larger surface air temperature anomalies than observed.

Climate signals in carbon and oxygen isotope ratios ofPinus cembratree‐ring cellulose from the Călimani Mountains, Romania

AbstractWe analyse annually resolved tree‐ring stable carbon (δ13C) and oxygen (δ18O) isotopic chronologies from Swiss stone pine (Pinus cembraL.) in Romania. The chronologies cover the period between 1876 and 2012 and integrate data from four individual trees from the Calimani Mts in the eastern Carpathians where climatic records are scarce and starts only from 1961. Calibration trials show that the δ13C values correlate with local April–May relative humidity and with regional to larger scale (European) summer precipitation. δ18O correlates significantly with local relative humidity, cloud cover, maximum temperature, as well as European scale drought conditions. In all cases, the climate effects on δ13C values are weaker than those recorded in the δ18O data, with the latter revealing a tendency toward higher (lower) values of δ18O during extremely dry (wet) years. The most striking signal, however, is the strong link between the interannual δ18O variability recorded in the Calimani Mts and large‐scale circulation patterns associated with North Atlantic and Mediteraneean Sea sea surface temperatures. High (low) values of δ18O occur in association with a high (low) pressure system over the central and eastern part of Europe and with a significantly warmer (colder) Mediterranean Sea surface temperature. These results demonstrate the possibility of using tree ring oxygen isotopes from the eastern Carpathians to reconstruct regional drought conditions in eastern Europe on long‐term time scales and larger scale circulation dynamics over the preinstrumental periods.

Forecast‐Oriented Assessment of Decadal Hindcast Skill for North Atlantic SST

AbstractWe demonstrate in this paper that conventional time‐averaged decadal hindcast skill estimates can overestimate or underestimate the credibility of an individual decadal climate forecast. We show that hindcast skill in a long period can be higher or lower than skill in its subperiods. Instead of using time‐averaged hindcast skill measures, we propose to use the physical state of the climate system at the beginning of the forecast to judge its credibility. We analyze hindcasts of North Atlantic sea surface temperature (SST) in an initialized prediction system based on the MPI‐ESM‐LR for the period 1901–2010. Subpolar North Atlantic Ocean heat transport (OHT) strength at hindcast initialization largely determines the skill of these hindcasts: We find high skill after anomalously strong or weak OHT, but low skill after average OHT. This knowledge can be used to constrain conventional hindcast skill estimates to improve the assessment of credibility for a decadal forecast.

Interdecadal Changes in the Dominant Modes of the Interannual Variation of Spring Precipitation over China in the Mid‐1980s

AbstractIn this study, the leading empirical orthogonal function mode of the interannual variations of boreal spring (April–May) precipitation over China (SPC) is shown to shift from a mono‐sign distribution during 1964–1985 (P1), with the largest loading over southern China, to a north‐south dipole structure during 1986–2004 (P2), with the northern and southern poles centered over the Yangtze River and the Pearl River Delta, respectively. The results show that the El Niño‐Southern Oscillation(ENSO)‐related negative western tropical Pacific sea surface temperature anomalies persist longer from the previous winter into the following spring in P2 than in P1. The ENSO‐related western tropical Pacific anticyclone in spring is stronger and extends farther northeastward after the mid‐1980s. As a result, in P2, the moisture transport by anomalous southerly winds along the western flank of the western tropical Pacific anticyclone penetrates northward to central China, and moisture convergence and divergence are observed over the Yangtze River and southern China, respectively. The SPC‐related North Atlantic sea surface temperature anomalies (NAST) are stronger after the mid‐1980s than before the mid‐1980s, and the NAST‐related atmospheric wave train over the middle‐latitude Eurasian continent is more pronounced in P2 than in P1. Furthermore, to the east of 90°E, the downstream propagation pathway of the NAST‐related wave train turns southeastward, which may be caused by the weakened intensity of the meridional gradient of the potential vorticity over this region. The pronounced wave train‐related positive height anomalies over the western North Pacific favor a north‐south dipole structure in the SPC variation in P2.

Impact of the North Atlantic sea surface temperature on the summer high temperature in northern China

AbstractThis study investigates the relationship between the summer high temperature in northern China and the northern North Atlantic (NNA) sea surface temperature anomalies (SSTAs) in the previous winter and spring during the period 1981–2017. In northern China, mean maximum temperature (Tmax) above 31°C and high frequencies of hot days are concentrated in June–July. SSTAs in the NNA in the previous December–April have a significant positive relationship with the mean Tmax from the Yellow River Basin to the north of the Yangtze River in June–July, and this significant positive correlation still exists after removing the trends. Correlation and composition analysis suggests that the NNA SST and high temperature in northern China are connected by the mid‐latitude wave‐train circulation anomalies across the Atlantic and Europe. Warm SSTAs in the NNA in winter and spring favour anticyclonic circulations in the NNA, Western Europe and the south of Lake Baikal, and cyclonic circulations in the northeastern North Atlantic and the Ural Mountains. The positive height anomaly and anticyclonic circulation in the south of Lake Baikal tend to result in downward motion and high temperature in northern China. The linkage between winter–spring North Atlantic SST and high temperature can be used to facilitate seasonal prediction of extreme high temperature in China.

Impacts of Summer North Atlantic Sea Surface Temperature Anomalies on the East Asian Winter Monsoon Variability

Abstract The present study investigates the impacts of the North Atlantic sea surface temperature (SST) anomalies on the East Asian winter monsoon (EAWM) variability. It is found that the northern component of the EAWM variability is associated with a dipole pattern of preceding summer North Atlantic SST anomalies during 1979–2016. The processes linking preceding summer North Atlantic SST to EAWM include the North Atlantic air–sea interactions and atmospheric wave train triggered by the North Atlantic SST anomalies. Atmospheric wind anomalies in the preceding spring–summer result in the formation of a dipole SST anomaly pattern through surface heat flux changes. In turn, the induced SST anomalies provide a feedback on the atmosphere, modifying the location and intensity of anomalous winds over the North Atlantic. The associated surface heat flux anomalies switch the North Atlantic SST anomaly distribution from a dipole pattern in summer to a tripole pattern in the following winter. The North Atlantic tripole SST anomalies excite an atmospheric wave train extending from the North Atlantic through Eurasia to East Asia in winter, resulting in anomalous EAWM. However, the relationship of the northern component of EAWM to preceding summer North Atlantic SST anomalies is weak before the late 1970s. During 1956–76, due to weak air–sea interaction over the North Atlantic, no obvious tripole SST anomaly pattern is established in winter. The atmospheric wave train in winter is located at higher latitudes, leading to a weak connection between the northern component of EAWM and the preceding summer North Atlantic dipole SST anomaly pattern.

Insights into Decadal North Atlantic Sea Surface Temperature and Ocean Heat Content Variability from an Eddy-Permitting Coupled Climate Model

Abstract An ocean mixed layer heat budget methodology is used to investigate the physical processes determining subpolar North Atlantic (SPNA) sea surface temperature (SST) and ocean heat content (OHC) variability on decadal to multidecadal time scales using the state-of-the-art climate model HadGEM3-GC2. New elements include development of an equation for evolution of anomalous SST for interannual and longer time scales in a form analogous to that for OHC, parameterization of the diffusive heat flux at the base of the mixed layer, and analysis of a composite Atlantic meridional overturning circulation (AMOC) event. Contributions to OHC and SST variability from two sources are evaluated: 1) net ocean–atmosphere heat flux and 2) all other processes, including advection, diffusion, and entrainment for SST. Anomalies in OHC tendency propagate anticlockwise around the SPNA on multidecadal time scales with a clear relationship to the phase of the AMOC. AMOC anomalies lead SST tendencies, which in turn lead OHC tendencies in both the eastern and western SPNA. OHC and SST variations in the SPNA on decadal time scales are dominated by AMOC variability because it controls variability of advection, which is shown to be the dominant term in the OHC budget. Lags between OHC and SST are traced to differences between the advection term for OHC and the advection–entrainment term for SST. The new results have implications for interpretation of variations in Atlantic heat uptake in the CMIP6 climate model assessment.

Why is the North Atlantic Oscillation More Predictable in December?

The prediction skill of the Climate Forecast System, version 2 (CFSv2), for the North Atlantic Oscillation (NAO) is evaluated in three winter months (December, January, and February). The results show that the CFSv2 model can skillfully predict the December NAO one month in advance. There are two main contributors to NAO predictability in December. One is the predictability of the relationship between the North Atlantic sea surface temperature anomaly (SSTA) tripole and the NAO and the other is the second empirical orthogonal function (EOF) mode of the geopotential height at 50 hPa (Z50-EOF2). The relationship between the NAO and SSTA tripole index in December is the most significant in the three winter months. The significant monthly differences of surface heat fluxes in December over the whole North Atlantic are favorable for promoting the interaction between the NAO and North Atlantic SSTAs, in addition to improving the predictability of the December NAO. When the NAO is in a positive phase, easterly anomalies are located at the low and high latitudes and westerly anomalies prevail in the mid-latitudes of the troposphere. The correlation between the December Z50-EOF2 and zonal-mean zonal wind anomalies shows a similar spatial structure to that for the NAO. The possible reason why the CFSv2 model can predict the December NAO one month ahead is that it can reasonably reproduce the relationship between the December NAO and both the North Atlantic SST and stratospheric circulation.

Respective and Combined Impacts of Regional SST Anomalies on Tropical Cyclogenesis in Different Sectors of the Western North Pacific

AbstractIn this study, the interannual variations in the tropical cyclone (TC) over the western North Pacific (WNP) and the influences of regional sea surface temperature (SST) anomalies are documented by separating the WNP into four quadrants considering nonuniform SST‐induced environmental changes. Our analysis shows that the TC variations in the northwest and southeast quadrants are related to both equatorial central‐eastern Pacific Ocean (EPO) and tropical Indian Ocean (TIO) SST anomalies. The TC variation in the northeast quadrant is mainly related to tropical North Atlantic Ocean SST anomalies. The main environmental variables differ for the TC variations in the four quadrants. Lower‐level (850‐hPa) vorticity is important for the TC variations in the northwest, southwest, and southeast quadrants. Midlevel (700‐hPa) humidity contributes to the TC variations in the northwest, northeast, and southeast quadrants. The vertical shear has a supplementary contribution to the TC variation in the southeast quadrant. The potential intensity (PI) negatively affects the TC variations in the southwest and southeast quadrants. The remote SST anomalies modulate different environmental variables over the WNP. The TIO SST influence is manifested in the lower‐level vorticity and vertical motion. The tropical North Atlantic SST impact occurs through the lower‐level vorticity change. The EPO SST effect occurs via changing the lower‐level vorticity and vertical motion as well as the midlevel moisture and vertical shear. The environmental variables experience more prominent changes when SST anomalies coexist in two remote regions. Numerical experiments confirm the EPO and TIO SST anomaly impacts on the environmental conditions affecting the WNP TC variations.

Three-ocean interactions and climate variability: a review and perspective

Interactions among the Pacific, Atlantic and Indian Oceans through ocean–atmosphere coupling can initiate and/or modulate climate variability. The Pacific Ocean is home to ENSO which affects other oceans through atmospheric bridges and the oceanic Indonesian throughflow (ITF). A warm Indian Ocean can produce atmospheric Kelvin waves that propagate eastward and increase equatorial easterly wind anomalies in the western Pacific and thus cool eastern Pacific sea surface temperature (SST). A positive Indian Ocean dipole establishes a southwestward pressure gradient force in the ITF region which increases the ITF transport and decreases ocean heat content in the western Pacific and may cool eastern Pacific SST. The Indian Ocean can also influence the Atlantic by atmospheric bridge and the oceanic Agulhas leakage south of Africa. Midlatitude North Atlantic SSTs may affect Pacific climate variability: (1) The Atlantic multidecadal oscillation (AMO) influences North Pacific variability; (2) The warm AMO phase increases the occurrence of central Pacific (CP)-type El Niño; (3) The warm AMO phase helps induce anomalous cyclonic circulation in the tropical western North Pacific; and (4) A cold midlatitude North Atlantic Ocean in the summer may initiate an El Niño in subsequent year via the East Atlantic/West Russia teleconnection. A warm tropical North Atlantic in the spring can induce a CP-type La Niña in the subsequent winter, via two pathways of the tropical eastern North and South Pacific. Finally, the Atlantic Niño (Niña) in the summer, through the Walker circulation and ocean dynamics, helps induce an eastern Pacific-type La Niña (El Niño) in the subsequent winter. The Atlantic Niño can also warm the tropical western Indian Ocean and weaken Indian monsoon rainfall.