Types Of El Nino-Southern Oscillation Research Articles

The Interdecadal Changes in the Spatial Structure of the South Pacific Oscillation and Its Implication for ENSO Diversity

Abstract The South Pacific Oscillation (SPO), characterized by a north–south dipole-like pattern of sea level pressure anomalies, is one of the key factors in understanding tropical–extratropical interactions in the South Pacific. We show that in boreal summer (June–August), the center of the northern lobe sea level pressure anomalies in the SPO is shifted to the east gradually after the 1960–70s. This study focuses on the relationship between the boreal summer SPO and following winter El Niño–Southern Oscillation (ENSO) diversity before and after the eastward shift of the SPO’s subtropical lobe. The eastward shift of the SPO’s subtropical lobe altered both the seasonal footprint mechanism and the trade wind charging mechanism associated with the SPO and thus profoundly influenced the ENSO diversity. It is revealed that when the northern lobe of the SPO shifts to the west of its average location, it tends to strengthen the eastern Pacific (EP) El Niño mainly via the seasonal footprint mechanism. But after the SPO’s northern lobe shifts to the east of its average location, it tends to promote the development of central Pacific (CP) El Niño mainly via the trade wind charging mechanism. The changes in the spatial structure of convection over the tropical Pacific and Indian Oceans may be one of the possible causes for the eastward shift in the SPO’s northern lobe. The findings in the present study have implications for a better understanding of ENSO diversity. Significance Statement Previous studies have demonstrated that the South Pacific Oscillation (SPO), as an important El Niño–Southern Oscillation (ENSO) precursor in the South Pacific, has the potential to provide an enhancement of the prediction of specific ENSO flavor. However, the historical variation in the SPO’s spatial structure and related changes in the relationship with the diversity of ENSO are still unclear. In this paper, we show that the subtropical lobe of the boreal summer (June–August) SPO is shifted to the east gradually after the 1960–70s. The changes in the spatial structure have also altered both the seasonal footprint mechanism and the trade wind charging mechanism which play important roles in the developmental processes of different types of ENSO. Our work highlights the importance of the interdecadal changes in the spatial structure of the SPO in understanding the relationship between the SPO and ENSO diversity.

Impact of the North Pacific Meridional Mode on the Tropical Pacific Modulated by the Interdecadal Pacific Oscillation

Abstract The North Pacific meridional mode (NPMM) peaking in boreal spring influences El Niño–Southern Oscillation (ENSO) properties in the ensuing winter. Whether the precursory impact of NPMM on the spatial diversity of ENSO has decadal variation remains unknown. Using long-term reanalysis datasets, we find that the interdecadal Pacific oscillation (IPO) significantly modulates the NPMM forcing on two types of ENSO. During the positive IPO (+IPO) phase, a strengthened background Aleutian low and southward-shifted storm track, in comparison to the negative IPO (−IPO) phase, produce stronger basin-scale negative geopotential height tendency anomalies over the North Pacific through synoptic-scale eddy–mean flow interaction. Such strong background negative tendency facilitates an Aleutian low–like pressure monopole rather than a North Pacific Oscillation (NPO)-like pressure dipole in boreal spring, leading to a weak NPMM that cannot effectively promote development of either a central Pacific (CP) or an eastern Pacific (EP) ENSO. By contrast, the NPO-like dipole enhances in boreal spring during −IPO, corresponding to stronger and more frequently occurring NPMM events that induce a robust CP-ENSO-like response in boreal winter. Moreover, the −IPO-related tropical Pacific mean states and the associated positive feedbacks cause a strong decrease in mixed layer temperature variance in the equatorial eastern Pacific, but a slight increase in the central Pacific, thus further contributing to the enhanced correlation between NPMM and CP-ENSO. Therefore, −IPO has played a role in the stronger impact of NPMM on CP-ENSO since the 1990s, and the modulation effects of IPO should be considered in understanding the extratropical–tropical climatic connection and ENSO spatial diversity.

The Impact of the Tropical Sea Surface Temperature Variability on the Dynamical Processes and Ozone Layer in the Arctic Atmosphere

Tropical sea surface temperature (SST) variability, mainly driven by the El Niño–Southern Oscillation (ENSO), influences the atmospheric circulation and hence the transport of heat and chemical species in both the troposphere and stratosphere. This paper uses Met Office, ERA5 and MERRA2 reanalysis data to examine the impact of SST variability on the dynamics of the polar stratosphere and ozone layer over the period from 1980 to 2020. Particular attention is paid to studying the differences in the influence of different types of ENSO (East Pacific (EP) and Central Pacific (CP)) for the El Niño and La Niña phases. It is shown that during the CP El Niño, the zonal wind weakens more strongly and changes direction more often than during the EP El Niño, and the CP El Niño leads to a more rapid decay of the polar vortex (PV), an increase in stratospheric air temperature and an increase in the concentration and total column ozone than during EP El Niño. For the CP La Niña, the PV is more stable, which often leads to a significant decrease in Arctic ozone. During EP La Niña, powerful sudden stratospheric warming events are often observed, which lead to the destruction of PV and an increase in column ozone.

The Potential Influence of Maritime Continent Deforestation on El Niño‐Southern Oscillation: Insights From Idealized Modeling Experiments

AbstractDuring the past two decades, the Maritime Continent (MC) has experienced increased deforestation. Here we show, with ensemble idealized deforestation experiments, that the MC deforestation could potentially alter the complexity (i.e., event‐to‐event differences) of the El Niño‐Southern Oscillation (ENSO) in terms of its spatial pattern and temporal evolution. The deforestation model run increases the occurrences of the Central Pacific and multi‐year types of ENSO compared to the control experiments. This change in ENSO complexity can be attributed to MC's intensification of the subtropical ENSO dynamics, commonly known as the seasonal footprinting mechanism. The deforestation amplifies the mean state of the subtropical high over the northeastern Pacific, leading to an increased dominance of subtropical ENSO dynamics in determining the ENSO pattern and evolution. This idealized coupled climate modeling study suggests that MC deforestation has a potential to alter ENSO's complexity, making El Niño more complex and less predictable.

Insight into Asymmetry in the Impact of Different Types of ENSO on the NAO

Understanding the influence of the El Niño–Southern Oscillation (ENSO) on the North Atlantic Oscillation (NAO) is of critical significance for seasonal prediction. The present study found that both Niño3.4 sea surface temperature anomaly (SSTA) intensity and east-west gradient in the mid-low latitude Pacific determine the linkage between ENSO and the NAO. Based on Niño3.4 SSTA intensity and the east-west gradient, ENSO events are classified into three types: strong intensity, weak intensity-strong gradient (WSG), and equatorial ENSOs. Note that the former two types are usually concurrent with a strong zonal SSTA gradient. In contrast, equatorial ENSO is often associated with weak intensity-weak gradient SSTAs confined in the equatorial Pacific. The anomalous circulation patterns in response to the three types of ENSO exhibit asymmetric features over the North Atlantic. The WSG-El Niño associated circulation anomaly resembles a negative NAO-like pattern, yet the strong and equatorial El Niño associated circulation anomalies show a neutral-NAO pattern. For La Niña events, their impact on the NAO mainly depends on the cold SSTA position rather than their intensity. The strong and WSG-La Niña associated negative SSTAs are centered in the equatorial-central Pacific and favor a steady positive NAO-like anomaly. The cold SSTA center of equatorial La Niña shifts to the equatorial-eastern Pacific and cannot profoundly influence the North Atlantic climate. The physical mechanisms are also investigated with a general circulation model.

The Enhancement of the Summer Precipitation Teleconnection between India and the Northern Part of Eastern China after the Late 1990s

Abstract As subsystems of the Asian summer monsoon, summer precipitation variations in India and the northern part of eastern China (NEC) are physically connected. This study noted that the connection has been significantly enhanced after 1999 compared to 1979–98, which is due to the strengthened water vapor transportation connection between the two regions. That is associated with interdecadal variations of the combined effects of El Niño–Southern Oscillation (ENSO) and sea surface temperature anomalies (SSTAs) over the tropical Indian Ocean (TIO) on the northwest Pacific subtropical high (NWPSH) and the Indo-Pacific Walker cell. Against the background of La Niña, the strengthened NWPSH and Indo-Pacific Walker cell favor water vapor transport to India and the NEC since 1999. Accordingly, summer precipitation in the two regions increases simultaneously, leading to the enhancement of the summer precipitation teleconnection between them. In addition, the influence of TIO SSTAs and the Indian Ocean dipole (IOD) on Indo-Pacific circulations decreases, which further enhances the relative importance of ENSO on the summer precipitation in the two regions. However, during 1979–98, La Niña SSTAs has weak effects on the NWPSH and Indo-Pacific Walker cell, the negative TIO SSTAs significantly weaken NWPSH, and the negative IOD also obstructs the westward extension of the Indo-Pacific Walker cell. Circulations and water vapor transportation related to the Indian Ocean and NEC summer precipitation are inconsistent, resulting in a weak precipitation teleconnection between them. The above conclusions are also validated by extreme case analysis and CMIP6 models. Significance Statement This paper mainly studies the influences of different types of ENSO and Indian Ocean SSTAs on the interdecadal variations of the summer precipitation relationship between India and the northern part of eastern China (NEC). We find that the summer precipitation relationship between them is strengthened again after 1999, which deepens the understanding of summer precipitation in Asia and has great significance for improving dynamic models’ prediction skills. The interdecadal variations of the combined effects of the Indian and Pacific Oceans are the fundamental reasons for the interdecadal variations of precipitation relationships, which promotes the understanding of interactions of different oceans and their impacts on Asian climate.

Recent progress in simulating two types of ENSO – from CMIP5 to CMIP6

The new emerging type of El Niño brings challenges to the state-of-the-art coupled models to simulated features of El Niño - Southern Oscillation (ENSO) diversity. The Coupled Model Intercomparison Project (CMIP), containing the advanced worldwide coupled models, has recently released the model outputs in phase 6. In this paper, the characteristics of two types of ENSO in 19 models from CMIP phase 5 and their counterparts in phase 6 are assessed regarding the spatial and temporal features and the seasonal cycle features. The weaker amplitude of Eastern Pacific (EP) and Central Pacific (CP) ENSO in CMIP5 is increased and the spatial structure of CP ENSO is better depicted in CMIP6. However, no significant improvement in the ENSO periodicity and the ENSO phase-locking behavior compared to CMIP5. A synthetic ENSO score, containing eight metrics, is defined and employed to evaluate the performance of each CMIP model. The average ENSO score for CMIP6 is 2.375, indicating modest improvement compared to the average score of 2.441 for CMIP5. Furthermore, the slight improvement in the ENSO score is partly related to the reduced climatology bias of sea surface temperature in the Niño4 region. The overall evaluation provides necessary information for future investigation about the mechanism exploration of the ENSO diversity based on the models with better performance.

COMPARISON OF VEGETATION ANOMALIES TO EL NIÑO-SOUTHERN OSCILLATION IN CHINA AND AUSTRALIA

Abstract. The El Niño-Southern Oscillation (ENSO), as one of the main factors driving extreme climate events, exerts a major influence on interannual climate variability around the world. However, ENSO effects on vegetation, especially regarding the extent, intensity, direction, are not well understood. Here, we characterize and compare the variability in vegetation response to ENSO across China and Australia and explore their underlying mechanisms. Results show that the spatial extent of ENSO-sensitive vegetation differed between China and Australia and across land cover types. For both China and Australia, the intensity and direction of vegetation anomalies were closely related to the type of ENSO events. In particular, vegetation anomalies to the Central-Pacific (CP) type ENSO events were stronger than that to the Eastern-Pacific (EP) type events of the same intensity and generally responded in an opposite way, resulting from different controls of CP-type and EP-type ENSO on precipitation and temperature. Our findings highlight the diverse response of vegetation triggered by different types of ENSO in China and Australia, which can improve our understanding of ENSO impacts on ecosystems in the northern and southern hemispheres.

Simulation, precursor analysis and targeted observation sensitive area identification for two types of ENSO using ENSO-MC v1.0

Abstract. The global impact of an El Niño–Southern Oscillation (ENSO) event can differ greatly depending on whether it is an eastern Pacific (EP)-type event or a central Pacific (CP)-type event. Reliable predictions of the two types of ENSO are therefore of critical importance. Here we construct a deep neural network with multichannel structure for ENSO (named ENSO-MC) to simulate the spatial evolution of sea surface temperature (SST) anomalies for the two types of events. We select SST, heat content and wind stress (i.e., three key ingredients of Bjerknes feedback) to represent coupled ocean–atmosphere dynamics that underpin ENSO, achieving skilful forecasts for the spatial patterns of SST anomalies out to 1 year ahead. Furthermore, it is of great significance to analyse the precursors of EP-type or CP-type events and identify targeted observation sensitive areas for the understanding and prediction of ENSO. Precursors analysis is to determine what type of initial perturbations will develop into EP-type or CP-type events. Sensitive area identification is to determine the regions where initial states tend to have the greatest impacts on the evolution of ENSO. We use the saliency map method to investigate the subsurface precursors and identify the sensitive areas of ENSO. The results show that there are pronounced signals in the equatorial subsurface before EP events, while the precursory signals of CP events are located in the northern Pacific. It indicates that the subtropical precursors seem to favour the generation of the CP-type El Niño and that the EP-type El Niño is more related to the tropical thermocline dynamics. Furthermore, the saliency maps show that the sensitive areas of the surface and the subsurface are located in the equatorial central Pacific and the equatorial western Pacific respectively. The sensitivity experiments imply that additional observations in the identified sensitive areas can improve forecasting skills. Our results of precursors and sensitive areas are consistent with the previous theories of ENSO, demonstrating the potential usage and advantages of the ENSO-MC model in improving the simulation, understanding and observations of the two ENSO types.

Eastern‐Pacific and Central‐Pacific Types of ENSO Elicit Diverse Responses of Vegetation in the West Pacific Region

AbstractThe El Niño‐Southern Oscillation (ENSO) is one of the main factors causing extreme climate events and, thus, has a significant influence on global climate systems. However, the long‐term effects of ENSO on vegetation are not well understood due to the complexity of the ENSO phenomenon under global warming. Here, we examined the variations in the response of Leaf Area Index (LAI) to different types of ENSO from 1982 to 2017 in the west Pacific region and explored their relationship with climatic factors. Results show that about 34.5% of the vegetated area in the west Pacific region displayed LAI anomalies correlated with ENSO index from 1982 to 2017, which distributed differently across climatic types. Moreover, LAI anomalies elicited by the Central‐Pacific type and by the Eastern‐Pacific type of ENSO events were significantly different, which were contributed to the controls of the different types of ENSO on precipitation and temperature.

Evolution of South China Sea and East Asian monsoon from spring to summer by the progression of daily weather types

AbstractThe monsoon development in the early rainy season in East Asia is analysed by the evolution of daily weather types (WTs). The WTs are classified by a k‐means clustering analysis based on 850 hPa winds from April 1 to July 31 in the 40‐year period of 1979–2018. Five WTs are identified, typifying the progression of weather regimes in the monsoonal evolution. WTs 1 and 2, with easterly winds in the South China Sea (SCS), occurs mostly in April and early May, corresponding to typical WTs before the SCS monsoon onset. In WT3, winds in the SCS turns westerly, and a rain band emerges in South China, extending east‐northeastward to the Pacific Ocean south of Japan, which signifies the May–June Mei‐yu in South China. Then, with the rain band moved to Yangtze River Valley (YRV) in WT4, this WT corresponds to the June–July Mei‐Yu in central and eastern China along the YRV. Finally, WT5 occurs more frequently towards the end of July, and corresponds to the post‐Mei‐Yu WT, indicating the ending of the early summer rainfall season in East Asia. The evolution of the WTs is gradual but intermittent, representing the weather‐within‐climate information. Each WT likely persists to itself. But WT1 and WT2 also progress to each other. The long persistence of WT3 and WT4 up to several weeks indicates the quasi‐stationary Mei‐Yu in South China and the YRV, respectively. The year‐to‐year variability of the WTs is also evident in the WTs. The El Niño–Southern Oscillation (ENSO) impact on the precipitation in the East Asian region is analysed for three types of ENSO: Eastern Pacific, Central Pacific, and mixed El Niño and La Niña. The seasonal mean precipitation anomalies can be interpreted by the frequencies of the daily WTs under different ENSO conditions.

Influence of the Eastern Pacific and Central Pacific Types of ENSO on the South Asian Summer Monsoon

Based on observational and reanalysis data, the relationships between the eastern Pacific (EP) and central Pacific (CP) types of El Nino-Southern Oscillation (ENSO) during the developing summer and the South Asian summer monsoon (SASM) are examined. The roles of these two types of ENSO on the SASM experienced notable multidecadal modulation in the late 1970s. While the inverse relationship between the EP type of ENSO and the SASM has weakened dramatically, the CP type of ENSO plays a far more prominent role in producing anomalous Indian monsoon rainfall after the late 1970s. The drought-producing El Nino warming of both the EP and CP types can excite anomalous rising motion of the Walker circulation concentrated in the equatorial central Pacific around 160°W to the date line. Accordingly, compensatory subsidence anomalies are evident from the Maritime Continent to the Indian subcontinent, leading to suppressed convection and decreased precipitation over these regions. Moreover, anomalously less moisture flux into South Asia associated with developing EP El Nino and significant northwesterly anomalies dominating over southern India accompanied by developing CP El Nino, may also have been responsible for the Indian monsoon droughts during the pre-1979 and post-1979 sub-periods, respectively. El Nino events with the same "flavor" may not necessarily produce consistent Indian monsoon rainfall anomalies, while similar Indian monsoon droughts may be induced by different types of El Nino, implying high sensitivity of monsoonal precipitation to the detailed configuration of ENSO forcing imposed on the tropical Pacific.

A Dipole Mode of Spring Precipitation between Southern China and Southeast Asia Associated with the Eastern and Central Pacific Types of ENSO

AbstractBecause spring precipitation in East Asia is critical for recharging water resources after dry winters, its spatiotemporal variations and related mechanisms need in-depth research. This study analyzed a leading spatiotemporal variability of precipitation over East Asia for boreal spring (March–May) during 1979 to 2017. We found that a dipole mode dominates the anomalous spring precipitation between southern China and Southeast Asia with significant interannual and decadal variations. The interannual dipole mode is attributable to the eastern Pacific (EP)-type El Niño–Southern Oscillation (ENSO) while the decadal dipole mode is related to the decadal variation of the central Pacific (CP)-type ENSO. In the El Niño phases of both time scales, the anticyclonic anomaly over the South China Sea and Philippines causes moisture convergence (divergence) over southern China (Southeast Asia), resulting in positive (negative) precipitation anomalies therein; the opposite occurs in the La Niña phases. The ensemble experiments using the Community Atmosphere Model version 5.1 confirmed that the tropical sea surface temperature (SST) in the EP- and CP-type ENSO can be the major drivers of the interannual and decadal dipole modes, respectively. About half of 15 climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5) showed that the El Niño phase of dipole mode will become dominant in the future. The individual models’ future projections however considerably vary, implying that there is still large uncertainty.

Two Types of ENSO Varying in Tandem Facilitated by Nonlinear Atmospheric Convection

AbstractThe El Niño‐Southern Oscillation (ENSO) has two distinct regimes, one in the eastern Pacific (EP) featuring strong El Niño and the other in the central Pacific (CP) characterized by strong La Niña. Establishment of atmospheric convection in the climatologically cold and dry EP region provides a major source of the nonlinearity, but its role in the relationship between CP‐ and EP‐ENSO variability and their long‐term change remain unclear. By constructing a nonlinear two‐box recharge‐oscillator model, here we show that nonlinear atmospheric convection operates to boost strong EP El Niño, strong CP La Niña, and evolution in tandem of variability and skewness of CP‐ and EP‐ENSO. Further, the observed coherent long‐term increase in frequency of strong EP El Niño, strong CP La Niña, and variability of the two‐type ENSO over the past decades is facilitated by a corresponding increase in the nonlinear atmospheric convection.

A statistical analysis on the contribution of El Niño–Southern Oscillation to the rainfall and temperature over Bangladesh

In this study, the contribution of El Nino–Southern Oscillation (ENSO) to the rainfall and temperature over Bangladesh has been investigated. Rainfall, temperature, and ENSO data have been used for a period of 60 years (1958–2017). This paper examines the spatial distribution of rainfall and temperature across Bangladesh and the results suggest that the distribution of rainfall and temperature varies with seasons. A geographically weighted regression, Student’s t test, correlation coefficient, and cross-wavelet transform were used to reveal whether different types of ENSO contribute strongly or weakly to rainfall and temperature in Bangladesh. Findings indicate that the ENSO has a strong connection with rainfall and temperature over Bangladesh.

Decadal change in ENSO related seasonal precipitation over southern China under influences of ENSO and its combination mode

Existing researches have suggested that the meridionally quasisymmetric El Nino/Southern Oscillation (ENSO) mode and the antisymmetric combination mode (C-mode; reflecting the nonlinear atmospheric interaction between ENSO variability and the annual cycle) can significantly influence the seasonal precipitation over southern China during the boreal winter and spring. By using atmospheric reanalysis data and gridded precipitation observations, this study demonstrates that these influences have an obvious decadal change in their impact intensity and in the region over southern China around 2000, coincident with the climate shift that occurred over the tropical Pacific after the late 1990s. The precipitation anomalies dominantly influenced by ENSO mode shifted from southern China in winter during the 1980s–1990s to the Yangtze River Valley in spring after the 2000s. Additionally, the precipitation anomalies independently affected by C-mode were concentrated over southern China in spring, and their effects were further enhanced in the 2000s–2010s. The direct contribution of ENSO mode to southern China’s precipitation has declined. This decadal change in seasonal precipitation is largely due to different types of ENSO (eastern-Pacific/central-Pacific) accompanied by different atmospheric circulations over the western North Pacific (WNP) associated with C-mode responses. The understanding of this climate shift in the influences of ENSO mode and C-mode on affecting the seasonal precipitation over southern China indicates a potential opportunity for improving the ENSO mode/C-mode-related precipitation predictions over southern China.

El Niño–Southern Oscillations and Pacific Decadal Oscillation as Drivers of the Decadal Dynamics of Benthic Macrofauna in Two Subtropical Estuaries (Southern Brazil)

The El Nino–Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) are large-scale climatic phenomena affecting atmospheric and oceanic teleconnections, and thus triggering weather events at different temporal and spatial scales, both in tropical and extratropical areas. During 11 years (2007–2017), the influence of ENSO events (El Nino, La Nina and neutral), ENSO types (canonical and Modoki) and PDO phases (cold and warm) on meteorological conditions and macrobenthic invertebrates were analyzed in two distinct (tide-dominated and river-dominated) subtropical estuaries of Southern Brazil. The estuarine macrobenthic communities differed markedly, with higher species richness in the tide-dominated estuary (146 taxa) than river-dominated (44). We showed that long-term variability of benthic macrofauna in both estuaries was strongly influenced by the PDO and ENSO events. However, the signs of PDO and ENSO effects differed between the estuaries. While the main modulating force of the decadal variability of the macrofauna of the tide-dominated estuary was the PDO (19%), the river-dominated estuary was primarily influenced by the ENSO (9%). Besides, PDO and ENSO teleconnections have combined effects, with higher macrofauna dissimilarities during constructive periods (PDO Positive/EL Nino vs. PDO Negative/La Nina). Our findings indicate that: (1) The effects of the ENSO on coastal areas are dependent of the spatial scale and the intrinsic characteristics of each estuary; (2) Studies relating ENSO and biodiversity should consider the ENSO type (Modoki and canonical) and interdecadal modes, such as PDO, because the location of the warm pools and the intensity of induced heating affect the atmospheric teleconnections.

Seasonal linkage of the Southern Hemisphere extratropical climate variability to two types of ENSO

This study uses the Climate Forecast System Reanalysis (CFSR) to investigate the responses of the Southern Hemisphere (SH) extratropical climate to two types of El Nino-Southern Oscillation (ENSO)—the eastern Pacific (EP) type and the central Pacific (CP) type in different seasons. The responses are denoted by the anomalies of climate variables associated with one-standard-deviation increase in the Nino3 or Nino4 index. The results show that in austral spring the differences in the ENSO-related anomaly (ERA) patterns of atmospheric circulation between the EP ENSO period (1979–1998) and CP ENSO period (1999–2010) are mainly associated with the change in the ENSO-PSA2 relationship. Such differences affect the ERA fields of surface air temperature and mixed layer temperature, and finally result in significant differences in sea-ice concentration anomalies in the Atlantic sector. In austral summer, significant correlation exists between the variations of SAM and both of the variations of Nino3 and Nino4 in 1979–1998, while the correlation between SAM and Nino4 disappears in 1999–2010. For all seasons, the strength of the climate ERAs depend on if there are close relationship between ENSO and the major climate variation modes of the SH extratropics. For the climate variables, the ERA patterns of surface air temperature are generally controlled by surface wind anomalies and mirrored by the mixed layer temperature anomalies. The mixed layer depth anomalies are primarily modulated by surface heat flux anomalies and occasionally by anomalous wind. There are strikingly strong anomalies of surface heat flux in the autumn of 1979–1998 related to the Nino3 variation, the period when there is only significant correlation between ENSO and PSA2. There are no evidence that the SH extratropical climate variability induced by Nino3 variations are stronger in the EP-ENSO period, and that variability induced by Nino4 variations are stronger in the CP-ENSO period.

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.

Modulation of the southern Indian Ocean dipole on the impact of El Niño–Southern Oscillation on Australian summer rainfall

This study investigates the modulation of the southern Indian Ocean dipole (SIOD) upon the impacts of the El Niño–Southern Oscillation (ENSO) on Australian summer rainfall (ASR) on an inter‐annual timescale. First the SIOD is identified as an important factor influencing rainfall anomalies over northeastern Australia via a zonal vertical circulation spanning from the southern Indian Ocean (SIO) to northern Australia. When ENSO and the SIOD are out of phase, the El Niño‐induced anticyclonic and convection anomalies shift eastwards to Australia and induce pronounced negative rainfall anomalies in northern Australia. When ENSO and the SIOD are in phase, the anticyclonic and convection anomalies extend westwards and generate an anomalous zonal vertical circulation, inducing positive rainfall anomalies in northeastern Australia. These different shifts in the circulation and rainfall anomalies with the two types of ENSO–SIOD occurrences are essentially attributed to the opposite effects of the different phases of SIOD events. The out‐of‐phase and in‐phase combinations of ENSO and the SIOD also largely form the dominant patterns of ASR variation. The significant influence of the SIOD on ASR indicates that the phase of the SIOD should be taken into account in the prediction of austral summer climate over Australia.