Tropical Pacific Precipitation Research Articles

Large-Amplitude Quasi-Stationary Rossby Wave Events in ERA5 and the CESM2: Features, Precursors, and Model Biases in Northern Hemisphere Winter

Abstract High-amplitude quasi-stationary Rossby waves (QSWs) have been connected to extreme weather events. By identifying particularly high-amplitude QSW events (QWEs) over Europe and North America, we study their characteristics in ERA5 data and in ensemble simulations from the CESM2 general circulation model. The CESM2 reproduces the overall statistics of QWEs, with ERA5 results within the ensemble spread. The ensemble spread is large, indicating a strong influence of internal variability. Composites of meridional wind anomalies for QWEs show a phase preference in both ERA5 and CESM2, resembling the climatological wave pattern. This is partly due to the definition of QSWs; with the day-of-year climatological meridional wind removed when identifying QSWs, the phase preference remains, albeit with a weaker signal. Significant tropical Pacific precipitation anomalies are seen 5–15 days before observed QWEs; the location of these anomalies is broadly reproduced in CESM2, but the magnitude is substantially underestimated and the time scale is biased. We find a narrowed and strengthened jet stream over the Pacific at the early stage of European QWEs, which may create enhanced waveguidability; this signal is generally reproduced in the models. Overall, the CESM2 can simulate QWEs; differences between the model ensemble mean and the reanalysis could result from model bias or internal variability, although biases are not reduced in CESM2 simulations forced with observed SSTs.

Large-amplitude quasi-stationary Rossby wave events in ERA5 and the CESM2: features, precursors, and model biases in Northern Hemisphere winter

Abstract High amplitude quasi-stationary Rossby waves (QSWs) have been connected to extreme weather events. By identifying particularly high amplitude QSW events (QWEs) over Europe and North America we study their characteristics in ERA5 re-analysis data and in ensemble simulations from the CESM2 general circulation model. The CESM2 reproduces the overall statistics of QWEs, with ERA5 results within the ensemble spread. The ensemble spread is large, indicating a strong influence of internal variability. Composites of meridional wind anomalies for QWEs show a phase preference in both ERA5 and CESM2, resembling the climatological wave pattern. This is partly due to the definition of QSWs; with the day-of-year climatological meridional wind removed when identifying QSWs, the phase preference remains, albeit with a weaker signal. Significant tropical Pacific precipitation anomalies are seen 5-15 days before observed QWEs; the location of these anomalies is broadly reproduced in CESM2, but the magnitude is substantially underestimated and the time scale is biased. We find a narrowed and strengthened jet stream over the Pacific at the early stage of European QWEs, which may create enhanced waveguidability; this signal is generally reproduced in the models. Overall, the CESM2 can simulate QWEs; differences between the model ensemble mean and re-analysis could result from model bias or internal variability, although biases are not reduced in CESM2 simulations forced with observed SSTs.

Interannual Variability of the Wintertime Asian–Bering–North American Teleconnection Linked to Eurasian Snow Cover and Maritime Continent Sea Surface Temperature

Abstract Recent studies propose that the Asian–Bering–North American (ABNA) teleconnection is a distinct atmospheric pattern that is related to Eurasian and North American winter climate besides the Pacific–North America (PNA) pattern, while its origin remains elusive. This study investigates the interannual variability of the ABNA during the past 42 winters (1979–2020) and the associated prior surface boundary forcings. The ABNA explains coherent surface air temperature changes in northern Asia, eastern Siberia–Alaska, and eastern North America, even after removing the impacts of the PNA, the Arctic Oscillation, the North Atlantic Oscillation, and the North Pacific Oscillation. Surface boundary conditions linked to the ABNA could be traced back to a Eurasian snow cover dipole pattern (ESCDP) and a Maritime Continent sea surface temperature anomaly (MCSST) in November. The ESCDP leads to a displacement of the Arctic stratospheric polar vortex via troposphere–stratosphere coupling. The anomalous polar vortex propagates downward in the following winter and generates the tropospheric ABNA pattern. The MCSST induces a diabatic heating anomaly, which is associated with a tropical western Pacific precipitation anomaly (TWPP) in winter. The TWPP excites a poleward Rossby wave train that propagates across the North Pacific and directly strengthens the ABNA. The above physical processes can be well reproduced by a linear baroclinic model (LBM). Based on the ESCDP and MCSST predictors, an empirical model is established and shows a promising prediction skill of the ABNA during the hindcast period. This can provide a useful strategy for seasonal prediction of winter climate in the Northern Hemisphere extratropics. Significance Statement Extreme cold events have influenced both Asian and North American continents during the past decades, causing huge socioeconomic impacts. The Asian–Bering–North American teleconnection is found to be responsible for coherent changes of winter climate in these two continents besides the Pacific–North America pattern. Our results indicate that Eurasian snow cover and the Maritime Continent sea surface temperature are important sources of predictability for the Asian–Bering–North American teleconnection, and can be used to predict coherent and cross-continent variations of winter surface air temperature. We propose that the Asian–Bering–North American teleconnection and these two predictors should be included in operational monitoring and prediction systems, helping to improve the prediction skill of winter climate in the Northern Hemisphere continents.

El Nio-Southern Oscillation variations based on a background of global warming

ENSO stimulates large-scale teleportation by modulating convection heating anomalies in the tropics of the Pacific, which in turn affects agriculture, ecosystems and the global climate worldwide. The tropical Pacific precipitation anomaly excited by ENSO moves eastward as the central Pacific region sea surface temperature continues to rise. In order to observe and study this anomaly, the sea surface temperature and rainfall changes in the Pacific region is investigated. The impact of global warming on human society is introduced, and then the data sources and reasons for selection are introduced. Then use the data to draw and analyze, the most results and explain the reasons, indicating the importance of the study.

On the Varying Responses of East Asian Winter Monsoon to Three Types of El Niño: Observations and Model Hindcasts

AbstractUsing observational data and model hindcasts produced by a coupled climate model, we examine the response of the East Asian winter monsoon (EAWM) to three types of El Niño: eastern Pacific (EP) and central Pacific I (CP-I) and II (CP-II) El Niños. The observational analysis shows that all three El Niño types weaken the EAWM with varying degrees of impact. The EP El Niño has the largest weakening effect, while the CP-II El Niño has the second largest, and the CP-I El Niño has the smallest. We find that diverse El Niño types impact the EAWM by altering the responses of two anomalous anticyclones during El Niño mature winter: the western North Pacific anticyclone (WNPAC) and Kuroshio anticyclone (KAC). The WNPAC responses are controlled by the Gill response and Indian Ocean warming processes that both respond to the eastern-to-central tropical Pacific precipitation anomalies. The KAC responses are controlled by a poleward wave propagation responding to the northwestern tropical Pacific precipitation anomalies. We find that the model hindcasts significantly underestimate the weakening effect during the EP and CP-II El Niños. These underestimations are related to a model deficiency in which it produces a too-weak WNPAC response during the EP El Niño and completely misses the KAC response during both types of El Niño. The too-weak WNPAC response is caused by the model deficiency of simulating too-weak eastern-to-central tropical Pacific precipitation anomalies. The lack of KAC response arises from the unrealistic response of the model’s extratropical atmosphere to the northwestern tropical Pacific precipitation anomalies.

Millennial-scale interaction between the East Asian winter monsoon and El Niño-related tropical Pacific precipitation in the Holocene

Both the East Asian winter monsoon (EAWM) and El Niño (EN) activities are vital climate modes that regulate the Pacific hydrologic cycle. However, the Holocene interactions among the EAWM, EN activities, and tropical Pacific precipitation remain unclear due to the lack of appropriate EAWM proxies. Here, we present high-resolution grain size records from the East China Sea shelf along with a transient climate model simulation to study the Holocene EAWM evolution and compare the findings with paleo-EN precipitation-related proxies records. The millennial-scale oscillations of grain size records, which are indicative of the intensity of the EAWM-driven coastal current, reveal an anti-phase coupling between the EAWM and EN-related tropical Pacific precipitation on a millennial timescale since 5.8 ka. These results, which are consistent with simulation results, indicate that the intensified EAWM could not only reduce equatorial western Pacific precipitation by reducing the sea surface temperature but also likely change boundary conditions in the tropical Pacific (i.e., the east-west Pacific temperature gradient and westerly anomaly) to favor the formation of subsequent intensive EN activities. The enhanced EN activities, inferred by the positive tropical eastern Pacific precipitation anomalies, could subsequently suppress the EAWM through anomalous low-level anticyclones and associated southerly anomalies, thereby generating intensified tropical western Pacific (mainly tropical monsoon areas) precipitation. Our study highlights these intrinsic interactions during the mid- to late Holocene and has useful implications for understanding this millennial-scale climate oscillation, which may represent periodic atmospheric exchange between high- and low-latitude climate systems by mediating the EAWM.

The changes in ENSO-induced tropical Pacific precipitation variability in the past warm and cold climates from the EC-Earth simulations

The El Niño-Southern Oscillation (ENSO) is one of the most significant climate variability signals. Studying the changes in ENSO-induced precipitation variability (ENSO precipitation) in the past climate offers a possibility to a better understanding of how they may change under future climate conditions. This study uses simulations performed with the European community Earth-System Model (EC-Earth) to investigate the relative contributions of dynamic effect (the circulation anomalies together with the climatological specific humidity) and thermodynamic effect (the specific humidity anomalies together with the climatological circulation) on the changes in ENSO precipitation in the past warm and cold climates, represented by the Pliocene and the Last Glacial Maximum (LGM), respectively. The results show that the changes in ENSO precipitation are intensified (weakened) over the tropical western Pacific but weakened (intensified) over the tropical central Pacific in Pliocene (LGM) compared with the pre-industrial (PI) simulation. Based on the decomposed moisture budget equation, these changes in ENSO precipitation patterns are highly related to the dynamic effect. The mechanism can be understood as follows: the zonal gradient of the mean sea surface temperature (SST) over the tropical Indo-Pacific is increased (reduced) during the Pliocene (LGM), leading to the strengthening (weakening) of Pacific Walker Circulation as well as a westward (eastward) shift. In the Pliocene, the westward shift of Walker Circulation results in an increased (decreased) ENSO-induced low-level vertical velocity variability in the tropical western Pacific (central Pacific), and, in turn, favoring convergent (divergent) moisture transport through a dynamic process, and then causing intensified (weakened) ENSO precipitation there. The opposite mechanism exists in LGM. These results suggest that changes in the zonal SST gradient over tropical Indo-Pacific under different climate conditions determine the changes in ENSO precipitation through a dynamic process.

The seesaw response of the intertropical and South Pacific convergence zones to hemispherically asymmetric thermal forcing

Arguments based on atmospheric energetics and aqua-planet model simulations link the latitudinal position of the intertropical convergence zone (ITCZ) to atmospheric cross-equatorial energy transport—a greater southward transport corresponds to a more northerly position of the ITCZ. This idea is often invoked to explain an interhemispheric dipole pattern of precipitation anomalies in paleoclimates. In contrast, here we demonstrate that in the tropical Pacific the response of the fully coupled ocean-atmosphere system to a hemispherically asymmetric thermal forcing, modulating this energy transport, involves an interplay between the ITCZ and its counterpart in the South Pacific—the Southern Pacific convergence zone (SPCZ). This interplay leads to interhemispheric seesaw changes in tropical precipitation, such that the latitudinal position of each rain band remains largely fixed, but their intensities follow a robust inverse relationship. The seesaw behavior is also evident in the past and future coupled climate simulations of the Climate Model Intercomparison Project Phase 5 (CMIP5). We also show that the tropical Pacific precipitation response to thermal forcing is qualitatively different between the aqua-planet (without ocean heat transport), slab-ocean (with climatological ocean heat transport represented by a “Q-flux”) and fully-coupled model configurations. Specifically, the induced changes in the ITCZ latitudinal position successively decrease, while the seesaw precipitation intensity response becomes more prominent, from the aqua-planet to the slab-ocean to the fully-coupled configuration. Thus, the ITCZ/SPCZ seesaw can explain the paleoclimate precipitation dipole pattern without invoking a too strong climate forcing and is relevant to future projections of tropical precipitation.

How does ENSO diversity limit the skill of tropical Pacific precipitation forecasts in dynamical seasonal predictions?

The prediction skill of tropical Pacific sea surface temperature (SST) and precipitation has been investigated, based on retrospective forecasts from 1983 to 2005 of the APEC Climate Center multimodel ensemble (MME) 6-month climate prediction, with a focus on El Nino-Southern Oscillation (ENSO) and its diversity. It was found that the MME prediction skill is related to both strength and flavor of ENSO. To better analyze the relationship between ENSO diversity and tropical climate predictions on a year-to-year basis, anomalous SST data were stratified into those due to typical ENSO and their residue. The former is defined as the reconstruction of data based on the leading empirical orthogonal function of the Pacific SST itself. It was found that typical ENSO and its impacts on tropical rainfall are well captured by dynamical seasonal prediction systems. Singular vector decomposition (SVD) analyses were further carried out, in order to identify climate modes related to the co-variability between residual SST signals and precipitation. Observational results show that the first SVD mode gives a SST singular vector that greatly resembles the east–west shift from typical El Nino features to El Nino diverse patterns. Dynamical models, on the other hand, have difficulties in reproducing the strength of this mode on the interannual scale. Their skill in predicting the temporal variation of this mode is also much lower than that for typical ENSO. Finally, the role of ENSO diversity on SST and precipitation potential predictability was also examined. Typical ENSO is the major predictability source of tropical Pacific SST. On the other hand, it was demonstrated that residual ENSO variability actually acts as a limit to tropical rainfall predictability. In other words, residual ENSO plays a rather crucial role in seasonal forecasting of tropical Pacific rainfall.

Contribution of El Niño amplitude change to tropical Pacific precipitation decline in the late 1990s

Equatorial central Pacific precipitation experienced a prominent decline in the late 1990s. This change was previously attributed to a La Nina-like mean sea surface temperature (SST) change in the ...

Regulation of atmospheric circulation controlling the tropical Pacific precipitation change in response to CO2 increases

The spatial pattern of precipitation responses to CO2 concentration increases significantly influences global weather and climate variability by altering the location of tropical heating in a warmer climate. In this study, we analyze the Coupled Model Intercomparison Project Phase 5 (CMIP5) climate model projections of tropical Pacific rainfall response to quadrupled increase of CO2. We found that the precipitation changes to the CO2 concentration increase cannot be interpreted by a weakening or strengthening of large-scale east–west coupling across the tropical Pacific basin, i.e., Walker circulation. By calculating the water vapor transport, we suggest instead that different responses of the Walker and Hadley circulations to the increasing CO2 concentration shape the details of the spatial pattern of precipitation in the tropical Pacific. Therefore, more regionally perturbed circulations over the tropical Pacific, which is influenced by the mean state change in the tropical Pacific and the enhanced precipitation outside the tropical Pacific, lead to greater increases in precipitation in the western equatorial Pacific as compared to the eastern tropical Pacific in a warmer climate.

Using High-Resolution Reanalysis Data to Explore Localized Western North America Hydroclimate Relationships with ENSO

Many studies have used observational data to explore associations between El Niño–Southern Oscillation (ENSO) and western North America (NA) hydroclimate at regional spatial scales. However, relationships between tropical Pacific sea surface temperature (SST) variability and western NA hydroclimate at local scales using reanalysis data are less understood. Here, the current understanding of relationships between large-scale tropical Pacific SST variability and western NA hydroclimate is extended to localized headwaters. To accomplish this, high-resolution reanalysis data (i.e., monthly mean surface precipitation rate, 2-m temperature, 850-mb specific humidity, and 500-mb omega) were used for gridpoint correlation analyses with Niño-3.4 SST and El Niño Modoki indices. Reanalysis time series data were provided by the National Centers for Environmental Prediction North American Regional Reanalysis (NARR) product. To validate the accuracy of NARR surface data, observational Livneh precipitation and temperature data were used. Resulting correlations between tropical Pacific indices and NARR surface precipitation and 2-m temperature are consistent with previous research both spatially and temporally, indicating that the strongest correlations occur primarily over southwestern NA during the winter (DJF). The results herein demonstrate the potential of high-resolution reanalysis data to reveal distinct correlations over topographically complex watersheds in the U.S. Intermountain West (IMW) over the recent record, 1979–2015. The use of the high-resolution NARR product as a viable option to explore western NA hydroclimate is demonstrated here.

Present-day constraint for tropical Pacific precipitation changes due to global warming in CMIP5 models

The sensitivity of the precipitation responses to greenhouse warming can depend on the present-day climate. In this study, a robust linkage between the present-day precipitation climatology and precipitation change owing to global warming is examined in inter-model space. A model with drier climatology in the present-day simulation tends to simulate an increase in climatological precipitation owing to global warming. Moreover, the horizontal gradient of the present-day precipitation climatology plays an important role in determining the precipitation changes. On the basis of these robust relationships, future precipitation changes are calibrated by removing the impact of the present-day precipitation bias in the climate models. To validate this result, the perfect model approach is adapted, which treats a particular model’s precipitation change as an observed change. The results suggest that the precipitation change pattern can be generally improved by applying the present statistical approach.

Inter-model diversity of Arctic amplification caused by global warming and its relationship with the Inter-tropical Convergence Zone in CMIP5 climate models

Surface-based Arctic amplification (AA) has experienced a remarkable increase in recent decades. Therefore, it is important to understand how Arctic warming might change in response to global warming. By analyzing the Coupled Model Intercomparison Project Phase 5 (CMIP5) multi-model dataset, we examine how AA correlates with changes in tropical Pacific precipitation in response to global warming. It is found that that the changes in the latitudinal position of the Inter-tropical Convergence Zone (ITCZ) are associated to the simulated AA strength in the CMIP5 climate models. Specifically, AA tends to be stronger (weaker) in models where the ITCZ shifts relatively more northward (southward). Further analysis indicates that the inter-model diversity of AA strength in the CMIP5 climate models is related to the changes in large-scale atmospheric circulation associated with the meridional shift of the ITCZ. These results emphasize a close relationship between AA and changes in tropical Pacific precipitation in response to global warming.

Interdecadal Change in the Tropical Pacific Precipitation Anomaly Pattern around the Late 1990s during Boreal Spring

Abstract The leading mode of boreal spring precipitation variability over the tropical Pacific experienced a pronounced interdecadal change around the late 1990s. The pattern before 1998 features positive precipitation anomalies over the equatorial eastern Pacific (EP) with positive principle component years. The counterpart after 1998 exhibits a westward shift of the positive center to the equatorial central Pacific (CP). Observational evidence shows that this interdecadal change in the leading mode of precipitation variability is closely associated with a distinctive sea surface temperature (SST) anomaly pattern. The westward shift of the anomalous precipitation center after 1998 is in tandem with a similar shift of maximum warming from the EP to CP. Diagnostic analyses based on a linear equation of the mixed layer temperature anomaly exhibit that an interdecadal enhancement of zonal advection (ZA) feedback process plays a vital role in the shift in the leading mode of both the tropical Pacific SST and the precipitation anomaly during spring. Moreover, the variability of the anomalous zonal current at the upper ocean dominates the ZA feedback change, while the mean zonal SST gradient associated with a La Niña–like pattern of the mean state only accounts for a relatively trivial proportion of the ZA feedback change. It was found that both the relatively rapid decaying of the SST anomalies in the EP and the La Niña–like mean state make it conceivable that the shift of the leading mode of the tropical precipitation anomaly only occurs in spring. In addition, the largest variance of the anomalous zonal current in spring might contribute to the unique interdecadal change in the tropical spring precipitation anomaly pattern.

Phase‐locked tropical Pacific precipitation

AbstractPrior studies of the El Niño/La Niña index SST3.4 showed periodicity of exactly 2 or 3 years which were ‘phase‐locked’ to the annual solar cycle. Ten such phase‐locked intervals since 1870 were found. This article extends this work by studying precipitation data (P34) for the same region. We find phase‐locked segments corresponding to those found in SST3.4. Each segment agrees both in the period of oscillation and the date interval. However, the temperature‐precipitation relationship changes from segment to segment, demonstrating the non‐stationarity of the system. The beginnings and ends of these time segments agree with previously reported abrupt climate shifts.

Impact of Tropical Pacific Precipitation Anomaly on the East Asian Upper-Tropospheric Westerly Jet during the Boreal Winter

Abstract The leading mode of boreal winter precipitation variability over the tropical Pacific for the period 1980–2010 shows a west–east dipole pattern with one center over the western North Pacific (WNP) and Maritime Continent and the other center over the equatorial central Pacific (CP). Observational evidence shows that the variability of the East Asian upper-tropospheric subtropical westerly jet (EAJ) has a significant correlation with precipitation anomalies over the WNP and CP and that tropical precipitation anomalies over WNP and CP have a distinct influence on the variation of the EAJ. A series of numerical experiments based on a linear baroclinic model are performed to confirm the influence of the heating anomalies associated with precipitation perturbations over the WNP and CP on the EAJ. The results of numerical experiments indicate that a heat source over the WNP can excite a northward-propagating Rossby wave train in the upper troposphere over East Asia and facilitate a poleward eddy momentum flux. It results in the acceleration of the westerlies between 30° and 45°N, which favors a northward displacement of the EAJ. The response induced by a heat sink over the CP features a zonal easterly band between 25° and 40°N, suggesting that the response to heat sink associated with negative precipitation anomalies over the CP may weaken the EAJ. A strengthened relationship was found between tropical Pacific precipitation and the EAJ since 1979. The modeling results suggest that the shift of mean states might be responsible for the strengthened EAJ–rainfall relationship after 1979.

Modelled Rainfall Response to Strong El Niño Sea Surface Temperature Anomalies in the Tropical Pacific

AbstractEl Niño–Southern Oscillation strongly influences the interannual variability of rainfall over the Pacific, shifting the position and orientation of the South Pacific convergence zone (SPCZ) and intertropical convergence zone (ITCZ). In 1982/83 and 1997/98, very strong El Niño events occurred, during which time the SPCZ and ITCZ merged into a single zonal convergence zone (szCZ) extending across the Pacific at approximately 5°S. The sea surface temperature anomalies (SSTAs) reached very large values and peaked farther east compared to other El Niño events. Previous work shows that tropical Pacific precipitation responds nonlinearly to changing the amplitude of the El Niño SSTA even if the structure of the SSTA remains unchanged, but large canonical El Niño SSTAs cannot reproduce the szCZ precipitation pattern. This study conducts idealized, SST-forced experiments, starting with a large-amplitude canonical El Niño SSTA and gradually adding a residual pattern until the full (1982/83) and (1997/98) mean SST is reproduced. Differences between the canonical and strong El Niño SSTA patterns are crucial in generating an szCZ event. Three elements influence the precipitation pattern: (i) the local meridional SST maxima influences the ITCZ position and western Pacific precipitation, (ii) the total zonal SST maximum influences the SPCZ position, and (iii) the equatorial Pacific SST influences the total amount of precipitation. In these experiments, the meridional SST gradient increases as the SSTAs approach szCZ conditions. Additionally, the precipitation changes evident in szCZ years are primarily driven by changes in the atmospheric circulation, rather than thermodynamic changes. The addition of a global warming SST pattern increases the precipitation along the equator and shifts the ITCZ farther equatorward.

Tropical Biases in CMIP5 Multimodel Ensemble: The Excessive Equatorial Pacific Cold Tongue and Double ITCZ Problems*

Abstract Errors of coupled general circulation models (CGCMs) limit their utility for climate prediction and projection. Origins of and feedback for tropical biases are investigated in the historical climate simulations of 18 CGCMs from phase 5 of the Coupled Model Intercomparison Project (CMIP5), together with the available Atmospheric Model Intercomparison Project (AMIP) simulations. Based on an intermodel empirical orthogonal function (EOF) analysis of tropical Pacific precipitation, the excessive equatorial Pacific cold tongue and double intertropical convergence zone (ITCZ) stand out as the most prominent errors of the current generation of CGCMs. The comparison of CMIP–AMIP pairs enables us to identify whether a given type of errors originates from atmospheric models. The equatorial Pacific cold tongue bias is associated with deficient precipitation and surface easterly wind biases in the western half of the basin in CGCMs, but these errors are absent in atmosphere-only models, indicating that the errors arise from the interaction with the ocean via Bjerknes feedback. For the double ITCZ problem, excessive precipitation south of the equator correlates well with excessive downward solar radiation in the Southern Hemisphere (SH) midlatitudes, an error traced back to atmospheric model simulations of cloud during austral spring and summer. This extratropical forcing of the ITCZ displacements is mediated by tropical ocean–atmosphere interaction and is consistent with recent studies of ocean–atmospheric energy transport balance.

Nonlinear precipitation response to El Niño and global warming in the Indo-Pacific

Precipitation changes over the Indo-Pacific during El Nino events are studied using an Atmospheric General Circulation Model forced with sea-surface temperature (SST) anomalies and changes in atmospheric CO2 concentrations. Linear increases in the amplitude of the El Nino SST anomaly pattern trigger nonlinear changes in precipitation amounts, resulting in shifts in the location and orientation of the Intertropical Convergence Zone (ITCZ) and the South Pacific Convergence Zone (SPCZ). In particular, the maximum precipitation anomaly along the ITCZ and SPCZ shifts eastwards, the ITCZ shifts south towards the equator, and the SPCZ becomes more zonal. Precipitation in the equatorial Pacific also increases nonlinearly. The effect of increasing CO2 levels and warming SSTs is also investigated. Global warming generally enhances the tropical Pacific precipitation response to El Nino. The precipitation response to El Nino is found to be dominated by changes in the atmospheric mean circulation dynamics, whereas the response to global warming is a balance between dynamic and thermodynamic changes. While the dependence of projected climate change impacts on seasonal variability is well-established, this study reveals that the impact of global warming on Pacific precipitation also depends strongly on the magnitude of the El Nino event. The magnitude and structure of the precipitation changes are also sensitive to the spatial structure of the global warming SST pattern.