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The ocean plays an essential role in regulating global and regional climate, which is mainly achieved through sea surface temperature anomaly (SSTA) changes. Studies on global sea surface temperature (GSST) are primarily carried out under linear assumption, which is not capable of fully revealing the evolution characteristics of sea surface temperature (SST) due to the non-linear and non-stationary nature of the SST. Here, the evolution of the GSST trend in the past century is investigated by using an adaptive and local spatial-temporally multidimensional ensemble empirical mode decomposition method. The results show that the global ocean has been warming except for the subpolar North Atlantic, the equatorial central Pacific, and the Southern Ocean in the Pacific sector. The equatorial central Pacific turned from cooling to warming around the middle of the last century made it one of the fastest-warming regions in recent decades with other regions located in the Arctic Ocean and the western-boundary current regions and their mid-latitude extensions in both hemispheres. The strongest warming during recent decades is found in the Arctic Ocean, east of the continents in the northern hemisphere, the entire Indian Ocean, and especially in the tropical Pacific Ocean. From a zonal average perspective, warming (>0.1 K since 1900) first took place in the subtropical regions of the Northern Hemisphere and 50 degrees S of the Southern Hemisphere almost simultaneously around 1910, then followed by the subpolar warming in the Northern Hemisphere. The first two bands of warming both expanded equatorward leading to the fast warming of tropical oceans, especially for the Pacific Ocean.

Precipitation falling in the Snowy Mountains region of south-east Australia is a critical resource-providing water for hydroelectricity, as well as irrigated agriculture and environmental flows throughout the economically important Murray River system. Improved understanding of the drivers of precipitation variability is therefore a key research aim. Focussing on synoptic types responsible for delivering precipitation ≥10 mm per day, an analysis is presented of the large-scale atmospheric circulation drivers ("teleconnections") of seasonal synoptic type frequency using cross-wavelet and boosted regression tree methods. Results demonstrate that relationships are not stationary over the period 1900-2012, and complex interactions between teleconnections and synoptic atmospheric circulation drive precipitation variability. Importantly, we demonstrate that teleconnections do not act in isolation. Relationships with the tropical Pacific Ocean are shown to be key drivers of synoptic types associated not only with the dominant tropical moisture pathways to the Snowy Mountains, but also with extra-tropical sources. Tropical sea surface temperatures are therefore shown to drive synoptic type frequency and facilitate the dominance of synoptic types with tropical moisture sources, most notability since the 1950s.

The influences of natural forcings (i.e. solar radiation and volcanic aerosol) and anthropogenic forcings (i.e. greenhouse gases) on the tropical Pacific zonal sea-surface temperature (SST) gradient are investigated through numerical sensitivity experiments, forced by natural forcing, anthropogenic forcing, or full forcing (both natural and anthropogenic forcing) using the Community Earth System Model (CESM) over the past two millennia. Under full forcing, during the present warming period (PWP; 1901–1999), the Pacific SST shows a larger warming over the tropical Pacific region than the subtropical Pacific region. This pattern is composed of an El Nino-like SST gradient (due to the greenhouse gas forcing) and a La Nina-like SST gradient (due to natural forcing). Two sensitivity experiments, the PWP under greenhouse gas forcing and the medieval warming period (MWP; 751–1250) under natural forcing, were used to examine the mechanisms. The results showed that under the greenhouse gas forcing, the larger warming over the eastern tropical Pacific is induced by an increased surface net heat flux, which is mainly caused by short-wave radiation and long-wave radiation. Under natural forcing, a larger warming is induced over the western tropical Pacific by changes in the ocean vertical heat transportation, caused by surface wind anomalies.

The modulation of the Pacific Decadal Oscillation (PDO) to the relationship between the El Nino-Southern Oscillation (ENSO) events and the winter climate over North America (NA) was investigated using both observational data and a simple general circulation model. ENSO events are divided into strong and moderate events according to their amplitudes. These ENSO events are further categorized into two groups according to the phases of the PDO. The present study focuses on the impact of moderate ENSO events on the wintertime climate over NA. The results show that a moderate El Nino signal is strong and stable and can significantly influence the wintertime climate variability over NA during a cold PDO phase, whereas climate anomalies are weak and are not significantly associated with moderate El Nino events during a positive PDO phase. Possible mechanisms accounting for the modulation of the impacts of moderate El Nino events on the wintertime climate over NA are analysed. Two factors may contribute to the different impacts of moderate El Nino events during warm and cold PDO phases. First, the different characteristics of the tropical Pacific sea surface temperature anomalies (SSTAs) associated with moderate El Nino events. Second, the difference in the climatological mean state between the warm and cold phases of PDO years. Our numerical experiments suggest that the cold PDO mean state is more favourable to a wavetrain-like atmospheric response to an El Nino-like tropical Pacific forcing over the North American sector than the warm PDO mean state is.

The inter-decadal change of the inter-annual relationship between the frequency of intense tropical cyclone (TC) over the western North Pacific (WNP) and the El Nino-Southern Oscillation (ENSO) is studied based on the TC best track and global reanalysis data. The results show that during 1983–2014 (the recent period), the frequency of intense TC and the November–January (NDJ) Nino3.4 are closely correlated, whereas during 1950–1971 (the prior period), their correlation is not statistically significant. The westward shift of positive sea-surface temperature anomaly SSTA over the tropical Pacific in the recent El Nino developing years is a key factor that enhanced the relationship between the Nino3.4 index and annual frequency of intense TC. The enhancement of positive (negative) MPI, positive (negative) relative humidity and negative (positive) vertical wind shear anomalies in the southeastern quadrant of the tropical WNP in the El Nino (La Nina) developing years during the recent period are favourable (unfavourable) to TC genesis in the southeastern quadrant of the tropical WNP and enhanced the inter-annual relationship between the frequency of intense TC and ENSO in the recent period. This is because the TCs forming in the southeastern quadrant are more likely to move over the warm tropical ocean and intensify into intense TCs. In the recent period, more intense TCs formed in the southeastern quadrant in the El Nino developing years, moreover, the difference of the genesis location and lifespan of intense TCs between the El Nino developing years and La Nina developing years has been significantly enlarged in the recent period, compared to that in the prior period.

This study focuses on improving the El Nino–Southern Oscillation (ENSO) prediction in Climate Forecast System version 2 (CFSv2) of the National Centers for Environmental Prediction through the development and application of an analogue-based correction method. We show that errors in sea surface temperature (SST) forecasts in CFSv2 in the tropical Pacific are strongly correlated with the observed SST anomaly index in the Nino3.4 region at the forecast initiation time, indicating that SST forecast errors in CFSv2 is similar in cases in which the corresponding initial SST states are also similar. Therefore, the analogue-based correction method is developed, in which SST forecast errors in CFSv2 can be corrected empirically using historical forecast errors, which are calculated by the same model, initiated from states that are analogues of the present initial state. Results show that the corrected SST anomaly forecasts have improved skills, as measured by the temporal correlation coefficient and root-mean-square error, compared with uncorrected forecasts. This is true for several different Nino SST indices, at most of lead months, and for most of initiation calendar months. Particular improvement is found for forecasts of the SST anomaly indices that are specially used to depict the two different ENSO flavours/types. With regard to the Nino3.4 index, the analogue-based correction method also predicted the 2014/2016 El Nino event relatively successfully. The results indicate that the analogue-based correction method provides an effective means of empirically improving ENSO prediction in CFSv2.

This study investigates impacts of two types of La Nina events, eastern Pacific (EP) La Nina and central Pacific (CP) La Nina, on Australian summer rainfall during 1951–2009. Results show that Australian summer rainfall is sensitive to the change in the location of sea surface temperature (SST) anomalies in equatorial Pacific. During CP La Nina, maximum cold SST anomaly is located in the equatorial CP west of 150°W, and significant northeasterly wind anomalies tend to prevail over northeastern Australia during austral summer. This brings more moist and warm flow from the tropics to Australia and leads to significant positive rainfall anomalies over northern and eastern Australia. In contrast, during EP La Nina, maximum cold SST anomaly is confined to equatorial EP east of 150°W and atmospheric circulation anomalies tend to be weak. As a result, rainfall anomalies are generally weak over Australia in EP La Nina. The differences in the Australian summer rainfall anomalies between CP La Nina and EP La Nina are attributed to the differences in atmospheric circulation anomalies. Specifically, the atmospheric circulation anomalies over tropical Pacific tend to be stronger and located more westward in CP La Nina. Higher climatological SST in the equatorial CP than equatorial EP, larger magnitude and westward shift of cold SST anomaly centre in CP La Nina than EP Nina may explain stronger and westward shift of the atmospheric anomalies in CP La Nina. Atmospheric model numerical experiments confirm the contribution of stronger circulation response in CP La Nina to the positive rainfall anomalies in Australia. Results in this study suggest that it is important to classify the La Nina events into different types when predicting Australian summer rainfall.

This study has investigated the influence of the decadal component of the Pacific Decadal Oscillation (PDO) on the Indian monsoon in observations and coupled climate model. A major part of the conventionally defined PDO is shown to be dominated by interannual variability. By extracting the pure decadal part of the North Pacific variability, this study has shown that the Indian monsoon rainfall exhibits different relations with the conventionally defined PDO and the pure decadal component of the PDO. This result may have implications for decadal prediction of the monsoon. The analysis suggests that the warm (cold) phase of pure decadal variability of PDO is associated with deficit (excess) rainfall over the west central part of India. In contrast, the conventional warm (cold) PDO index is associated with deficit (excess) rainfall over most of India. The warm phase of the pure decadal PDO opposes the moisture flow beyond 20°N over the Indian monsoon region via the meridional winds extending from the North Pacific and leads to reduced rainfall over west central India. The Community Climate System Model version 4 of the National Center for Atmospheric Research shows reasonable simulation of the decadal PDO mode in both the North Pacific sea surface temperature and the Indian monsoon rainfall and the relation between them. Further, the observed and simulated PDO–monsoon relation is substantiated through a regionally de-coupled experiment. The coupled model experiment also provides supporting evidence for the mechanism involving the intermediary role played by the tropical Pacific Ocean in the PDO–monsoon relation.

In order to clearly classify El Nino–Southern Oscillation (ENSO) events into eastern Pacific (EP) and central Pacific (CP) types, we develop two new indices defined as pattern correlation coefficients (PCCs) between monthly sea surface temperature (SST) anomalies (SSTAs) and first two leading empirical orthogonal function modes of tropical Pacific (20°S–20°N, 110°E–70°W) SSTAs. These new indices not only show close relationships with ENSO indices derived from several previous methods, but also demonstrate reasonable abilities to distinguish between two types of ENSO event. The major characteristic features of the EP-type and CP-type ENSO forcings are well captured from SST responses regressed onto each new index. Furthermore, the monthly frequencies of occurrences derived from two indices are quite similar to variation patterns of phase-locking behaviours of two types of ENSO event.

The spatial structure and temporal evolution of the intraseasonal variability (ISV) of the subsurface ocean temperature (STA) in the equatorial Pacific associated with the two flavours of El Nino [i.e. the canonical or eastern Pacific (EP) El Nino and the central Pacific (CP) El Nino] are investigated using observations and 1.5-layer linear reduced gravity model. Results suggest that the ISV characteristics show some differences in the two types of El Nino, although both oscillate along the thermocline in the form of the intraseasonal equatorial Kelvin wave (IEKW), which is excited in the western tropical Pacific by the zonal wind stress associated with the Madden-Julian oscillation (MJO). First, the period of dominant mode of the STA ISV during CP El Nino broadly distributes in 50-80 days with the spectra peaking in 60-65 days. By contrast, the spectrum of STA ISV during EP El Nino shows a peak in 75-80-day period. This indicates that the wave speed is faster in the CP El Nino than in EP El Nino. Second, the ISV activity peaks in previous spring during the developing phase of EP El Nino, whereas during CP El Nino it becomes the most active during the mature phase. Third, the strongest IEKW occurs in the CP around the dateline during CP El Nino and attenuates quickly east of 130 degrees W due to strong eddy viscosity dissipation, while the IEKW during the EP El Nino propagates efficiently from the western to the eastern Pacific with a relative weak diffusion.

Previous studies suggested that the variability of boreal spring Arctic Oscillation (AO) can exert a significant influence on the sea surface temperature (SST) anomalies in the Nino-3.4 region during the following winter. This study further reveals that AO in November can have a pronounced influence on the tropical central-eastern Pacific SST anomalies during the following spring and summer. When the November AO is in its positive (negative) phase, SST anomalies tend to be positive (negative) during the following spring and summer in the tropical central-eastern Pacific. The influence of the AO is accomplished by atmospheric circulation anomalies over the subtropical North Pacific through an interaction between the synoptic-scale eddy and the low-frequency mean flow. In the positive November AO years, pronounced cyclonic circulation and atmospheric heating anomalies are observed over the subtropical North Pacific. The atmospheric heating anomalies sustain westerly wind anomalies over the tropical western North Pacific through a Gill-like atmospheric response. The westerly wind anomalies extend eastward subsequently through positive air–sea feedback mechanism, and result in SST warming during the following spring and summer in the tropical central-eastern Pacific. Results of this study imply that the November AO index can be used as an effective predictor of SST anomalies in the Nino-3.4 region during the following spring and summer.

Summer precipitation over most of the tropical Americas exhibits maxima in June and September, and a relative minimum in July. The minimum in summer precipitation over the northeastern (NE) tropical Pacific is known as the midsummer drought (MSD). Several theories have been put forward to explain the origin of the MSD, but most of them fail at addressing simultaneously the various elements that characterize it. The temporal evolution of summer precipitation over the NE tropical Pacific warm pool and over the Intra-Americas Seas (IAS) is related, but not the result of the same process. Over the NE Pacific warm pool, the temporal evolution of convective activity is closely related to sea surface temperature (SST) variations, whereas over the IAS, the Caribbean low-level jet (CLLJ) with maximum intensity in July appears to be the key factor. The CLLJ produces ‘gap flow’ over Central America that reaches the NE tropical Pacific and stronger easterly winds. This low-level flow leads to a decrease in SSTs and a westward shift of low-level moisture convergence that combined with subsidence result in the MSD. At the CLLJ exit region, intense tropical convection enhances during July reducing the chances that large-scale circulations, such as the North Atlantic Subtropical High (NASH) inhibit precipitation over the entire tropical Americas. The strong ascending motion off the Caribbean coast of Nicaragua and Costa Rica contributes to enhanced subsidence in the surrounding regions and to the MSD. As the CLLJ and tropical convection in the western Caribbean weaken during August and September, tropical convection increases once more over most of the tropical Americas and produces the second maximum in precipitation that completes the two peaks distribution of summer precipitation. Therefore, the fluctuations in the intensity of the CLLJ appear to be a key dynamical element to explain the MSD.

Analysis of observational and reanalysis data shows that the autumn precipitation in South China is closely related to the east-west sea surface temperature (SST) contrast in the tropical Pacific. An east-west contrast (EWC) index, defined as the difference of the normalized area-averaged SST between the tropical eastern Pacific (150 ∘ W-90 ∘ W, 5 ∘ S-5 ∘ N) and the tropical western Pacific (WP; 110 ∘ E-180 ∘ E, 5 ∘ S-5 ∘ N), is proposed to delineate this feature. When the EWC index is positive, the tropical eastern (western) Pacific is warmer (colder) than normal. It would cause significant southerly wind anomalies from the Indochina Peninsula to eastern China, leading to enhanced water vapour convergence and anomalous ascending motion over South China. Therefore, enhanced autumn precipitation is observed in South China. Further analysis suggests that the SST of the tropical WP dominates the lower-tropospheric meridional wind and the resultant water vapour transport and convergence over subtropical East Asia, and that the SST of both the tropical eastern and the tropical WP contributes to the anomalous ascending motions over South China. These results highlight the combined effects of tropical eastern and WP on the autumn precipitation in South China and specifically emphasize the role of tropical WP SST. Given the performance of the EWC index in describing the autumn precipitation as well as the leading time and the persistence of the EWC index, it could be used as a good indicator in the monitoring and prediction of the autumn precipitation in South China, which is demonstrated by a simple statistical prediction model.

Proxy-based reconstructions of the Pacific Decadal Oscillation (PDO) are essential for understanding pre-instrumental variability in this low-frequency oscillation. Multiple reconstructions of the PDO exist but demonstrate weak coherence prior to the 20th century. Analyses of atmospheric moisture and pressure patterns in teleconnected tree-ring sites used for the reconstructions indicate that terrestrial climate impact patterns associated with northern Pacific conditions have been spatially variable over the instrumental period. Tropical Pacific and Northern Hemisphere climate modes influence these surface patterns and are reflected in the PDO reconstructions. Divergence prior to the 20th century calibration period may be due to time-dependent nonlinearities in the PDO and changes in the influence of the El Nino-Southern Oscillation system over time.

Rainfall records for 23 countries and territories in the western Pacific have been collated for the purpose of examining trends in total and extreme rainfall since 1951. For some countries this is the first time that their data have been included in this type of analysis and for others the number of stations examined is more than twice that available in the current literature. Station trends in annual total and extreme rainfall for 1961–2011 are spatially heterogeneous and largely not statistically significant. This differs with the results of earlier studies that show spatially coherent trends that tended to reverse in the vicinity of the South Pacific Convergence Zone (SPCZ). We infer that the difference is due to the Interdecadal Pacific Oscillation switching to a negative phase from about 1999, largely reversing earlier rainfall changes. Trend analyses for 1981–2011 show wetter conditions in the West Pacific Monsoon (WPM) region and southwest of the mean SPCZ position. In the tropical North Pacific it has become wetter west of 160°E with the Intertropical Convergence Zone/WPM expanding northwards west of 140°E. Northeast of the SPCZ and in the central tropical Pacific east of about 160°E it has become drier. Our findings for the South Pacific subtropics are consistent with broader trends seen in parts of southern and eastern Australia towards reduced rainfall. The relationship between total and extreme rainfall and Pacific basin sea surface temperatures (SSTs) has been investigated with a focus on the influence of the El Nino-Southern Oscillation (ENSO). We substantiate a strong relationship between ENSO and total rainfall and establish similar relationships for the threshold extreme indices. The percentile-based and absolute extreme indices are influenced by ENSO to a lesser extent and in some cases the influence is marginal. Undoubtedly, larger-scale SST variability is not the only influence on these indices.

This study examines the impact of the cold tongue (CT) El Nino and the warm pool (WP) El Nino on tropical cyclone (TC) genesis over the South China Sea (SCS) from 1965 to 2010. During Sept-Oct-Nov (SON), the TC genesis exhibits clear interannual variability. SON TC genesis is significantly related with the WP Nino index, but not with the CT Nino index. It is found that in the past two decades the SCS TC genesis varies coherently with the WP Nino index on a timescale of approximately 4years, which is in accordance with the recent increase in WP El Nino events. The distinctly different atmospheric teleconnection patterns related to the CT and WP El Nino over the SCS are responsible for these relationships. CT El Nino can induce anticyclone anomalies over the SCS and the western tropical Pacific WP. However, WP El Nino can result in dipolar patterns with anticyclone anomalies over the SCS and cyclone anomalies over the western tropical Pacific WP at low- and mid-level. These WP El Nino-related large-scale circulation anomalies enlarge the low-level northerlies over the SCS. This in turn enhances the vertical wind shear and thus suppresses TC genesis over the SCS.

We develop a climatology of the Amundsen Sea low (ASL) covering the period 1979–2008 using ECMWF operational and reanalysis fields. The depth of the ASL is strongly influenced by the phase of the Southern annular mode (SAM) with positive (negative) mean sea level pressure anomalies when the SAM is negative (positive). The zonal location of the ASL is linked to the phase of the mid-tropospheric planetary waves and the low moves west from close to 110°W in January to near 150°W in June as planetary waves 1 to 3 amplify and their phases shift westwards. The ASL is deeper by a small, but significant amount, during the La Nina phase of El Nino-Southern Oscillation (ENSO) compared to El Nino. The difference in depth of the low between the two states of ENSO is greatest in winter. There is no statistically significant difference in the zonal location of the ASL between the different phases of ENSO. Over 1979–2008 the low has deepened in January by 1.7 hPa dec−1 as the SAM has become more positive. It has also deepened in spring and autumn as the semi-annual oscillation has increase in amplitude over the last 30 years. An increase in central pressure and eastward shift in March has occurred as a result of a cooling of tropical Pacific SSTs that altered the strength of the polar front jet.

The asymmetry of El Nino-La Nina, one of the well-known characteristics of the El Nino-Southern Oscillation (ENSO), is suggested to produce a non-zero residual effect that could rectify the background state, and thereby generates the low-frequency variability in the tropical Pacific. So far, this rectification effect has been hardly quantified apart from the low-frequency variability because the low-frequency variability captured via conventional methods represents the mixture of both the residual effects of ENSO and the no-ENSO-related natural decadal variability. Here we separate the residual effects of ENSO from the natural decadal variability that appears in four historical sea surface temperature datasets during the last century by applying a long-term moving average. A significant correlation between the computed residual effect and the decadal change in the ENSO skewness (i.e. the measure of the El Nino-La Nina asymmetry) confirmed the applicability of our computational method. Quantitatively, the residual effects of ENSO consistently account for at least 15% of the total low-frequency variability in four datasets, especially over the eastern and central tropical Pacific. This implies that the asymmetry of ENSO enhances the tropical Pacific decadal variability for the last century. Copyright © 2012 Royal Meteorological Society

n n Improving El Nino/Southern Oscillation (ENSO) forecast remains a g reat challenge in the climate-predicting community. Previously, an improved solution to sea surface temperature (SST) anomaly simulations in the tropical Pacific was obtained by explicitly embedding into an ocean general circulation model (OGCM) a separate SST anomaly submodel with an empirical parameterisation for the temperature of subsurface water entrained into the ocean mixed layer (Te). In the present work, the benefit of the approach is explored and demonstrated in terms of ENSO prediction. A hybrid coupled ocean-atmosphere model (HCM) is utilized to perform two retrospective ENSO forecasts, differing in the way SST anomaly fields are taken for their coupling to the atmosphere, one directly from the OGCM (referred to as a standard coupling, HCMstd), and another from the embedded SST anomaly submodel with optimized Te parameterisation (referred to as an embedded coupling, HCMembed). The results indicate that ENSO forecasts can be effectively improved using the embedded approach; the predicted Nino-3.4 SST anomaly correlation is higher by 0.1-0.2 at a 12-month lead time in the HCMembed than in the HCMstd, and the corresponding root-mean-square (RMS) error is lower by 0.1-0.2 degrees C. Further improvements and applications are discussed.n

The connection between Tropical Pacific and North Pacific variability is investigated in a state-of-the-art coupled ocean-atmosphere model, comparing two 20th century simulations at T30 and T106 atmospheric horizontal resolutions. Despite a better simulation of the frequency and the spatial distribution of the Tropical Pacific anomalies associated with the El Nino Southern Oscillation (ENSO) in the high-resolution experiment, the response in the North Pacific is scarcely different from the low-resolution experiment where the ENSO variability is weaker and at higher than observed frequency. In the North Pacific, the response of surface atmospheric fields to the variability in the Tropical Pacific appears to be affected by local coupling processes significantly different in the two experiments. The coupling between sea level pressure (SLP) and sea surface temperature (SST) in the North Pacific as well as the influence of the Tropical Pacific SST has been measured here by means of the coupled manifold technique. In the low-resolution case the SLP variances linked to the fraction of North Pacific SST not influenced by the Tropical Pacific are weak suggesting that the remote influence is strong, consistently with the observations. On the contrary, in the high-resolution experiment the fractions and the patterns of the SLP variances due to the Tropical Pacific SST and those linked to the North Pacific SST are comparable. In the latter case, model systematic errors in the northwestern Pacific influences the local coupling processes thus triggering the remote response. We conclude that an increased atmospheric horizontal resolution does not reduce the coupled model systematic errors in the representation of the teleconnection between the North and the Tropical Pacific and that the validation of coupled models has to consider both remote and local processes. Copyright (c) 2011 Royal Meteorological Society

The variability of seasonal precipitation anomalies over Europe displays significant spectral peaks at quasi-quadrennial periods, appearing in power spectra of the two leading principal components of the field. Band-pass filtering of these time series reveals the presence of two different signals within the quadrennial band, each associated to distinct precipitation, sea level pressure (SLP) and sea surface temperature (SST) patterns, obtained here by means of linear regression and composite analysis. One of the quadrennial components seems to be connected with the impact of El Nino-Southern Oscillation (ENSO) over Europe, that leads to anomalous SLP over the North Sea, southwestern Scandinavia and central Europe, along with precipitation anomalies of the same sign in a wide band extending from the British Isles into eastern Europe, fringed by anomalies of the opposite sign along the Norwegian coast and in the western Mediterranean area. The other quadrennial component bears no correlation with the Tropical Pacific SST anomalies, and seems connected with SST anomalies in the equatorial Atlantic, and in the Mediterranean, North and Norwegian Seas. The precipitation anomalies feature a contrast between the northern and southern regions of Europe akin to that associated with the North Atlantic Oscillation (NAO). The SLP pattern resembles the NAO structure, but with a marked eastward shift of its two centres of action towards central Europe and the Barents Sea, respectively. Copyright © 2011 Royal Meteorological Society

El Nino/Southern Oscillation (ENSO) remains the most important coupled ocean–atmosphere phenomenon to cause global climate variability on seasonal to interannual time scales. This paper addresses the need for a reliable ENSO index that allows for the historical definition of ENSO events in the instrumental record back to 1871. The Multivariate ENSO Index (MEI) was originally defined as the first seasonally varying principal component of six atmosphere–ocean (COADS) variable fields in the tropical Pacific basin. It provides for a more complete and flexible description of the ENSO phenomenon than single variable ENSO indices such as the SOI or Nino 3.4 SST. Here we describe our effort to boil the MEI concept down to its most essential components (based on SLP, SST) to enable historical analyses that more than double its period of record to 1871–2005. The new MEI.ext confirms that ENSO activity went through a lull in the early- to mid-20th century, but was just about as prevalent one century ago as in recent decades. We diagnose strong relationships between peak amplitudes of ENSO events and their duration, as well as between their peak amplitudes and their spacing (periodicity). Our effort is designed to help with the assessment of ENSO conditions through as long a record as possible to be able to differentiate between ‘natural’ ENSO behaviour in all its rich facets, and the ‘Brave New World’ of this phenomenon under evolving GHG-related climate conditions. So far, none of the behaviour of recent ENSO events appears unprecedented, including duration, onset timing, and spacing in the last few decades compared to a full century before then. Copyright © 2011 Royal Meteorological Society

The present paper reexamines the relative role of the tropical Pacific and tropical South Atlantic (TSA) on the rainfall over Northeast Brazil (NEB). For several variables, El Nino-Southern Oscillation (ENSO) and TSA-related anomalous patterns are obtained. These patterns are then compared to the combined ENSO and TSA-related patterns to infer the relative importance of the two oceanic basins on the rainfall over NEB. Analyses are done for austral summer and autumn seasons. Considering the composite technique, six cases are examined: El Nino and neutral conditions in the TSA, La Nina and neutral conditions in the TSA, ENSO neutral conditions and warm TSA, ENSO neutral conditions and cold TSA, El Nino and warm TSA, and La Nina and cold TSA. The most important result comes from the cases with competing influences of the tropical Pacific and the TSA. In some of these cases, the SST variability in the TSA is the determining factor of the NEB climate. The result of this study might be useful mainly for regional climate monitoring purposes. Copyright © 2006 Royal Meteorological Society.

Singular value decomposition (SVD) techniques are used to deduce a relationship between rainfall over the Caribbean basin and oppositely signed sea-surface temperature anomalies in the Pacific and Atlantic. The analysis is done for four 3 month seasons. The first two seasons: November–January (NDJ) and February–April (FMA) encompass the Caribbean dry period, and the other two, May–July (MJJ) and August–October (ASO), include the early and late Caribbean rainy seasons. The first SVD mode for all seasons represents variability due to El Nino–southern oscillation (ENSO) and, with the exception of the later wet season, the second SVD mode represents variability due to tropical North Atlantic sea-surface temperatures. ENSO has the greatest impact during the late rainfall season (ASO) and the early dry season (NDJ), whereas the tropical Atlantic controls variability in the early rainfall season (MJJ). The configuration of concurrent but oppositely signed sea-surface temperature anomalies in the tropical Pacific and Atlantic basins is only associated with rainfall modification in the late Caribbean rainfall season (ASO) and the early Caribbean dry season (NDJ). Copyright © 2004 Royal Meteorological Society

This paper presents a study of variability of climate indices and rainfall in southeast Queensland (SE Qld). Using high-resolution gridded rainfall data for all of Australia and global sea surface temperatures (SST), the relationship between rainfall Australia-wide and in SE Qld in particular with SST indices and the Southern Oscillation Index (SOI) have been investigated. It is found that SE Qld is more subject to the breakdown of correlations between the SOI and rainfall than any other part of Australia. Model predictions suggest that this is probable in the future. Considering only timescales longer than interannual, it was found that SSTs in the central tropical Pacific Ocean (TPO) (represented by the Nino-4 index) correlated best with SE Qld rainfall. Eastern TPO (Nino-3) SSTs and the SOI produced successively weaker correlations. The time series of the second modes of variability of SSTs over the Pacific and Indian Oceans were shown to have limited impact on SE Qld rainfall variability. The data was split into periods before and after 1946, when Australian mean rainfall changed (Pittock, 1975). While the SOI correlations with rainfall in SE Australia were similar in both periods, in SE Qld the correlations were very weak in the earlier period (0.06) but very strong in the latter (0.72). The Nino-4 index correlated better than the Nino-3 index in both periods, but they showed smaller changes from the earlier to the latter periods than the SOI.

The seasonal modulation of the relationship between the sea-level pressure anomalies (SLPAS) over the North Atlantic region (100 °W–50 °E; 20–70 °N) and the sea surface temperature anomalies (SSTAS) in the tropical Pacific (120–290 °E; 20 °N–20 °S) is investigated in the northern winter (October to March) from 1873 to 1996, using singular-value decomposition and composite analyses. Both methods show that the pattern of the North Atlantic SLPA associated with the tropical Pacific SSTA in November–December is different from that found in January–March. The surface covered by a significant SLPA is larger in November–December and February–March than in January. In November–December, the warm El Ni˜ no–southern oscillation (ENSO) events are associated with negative SLPAS extending from the Hudson Bay to Scandinavia and positive SLPAS over the Azores high. The cold ENSO events are associated with a positive SLPA between Greenland and western Europe. In January, and mainly in February–March, the warm ENSO events are associated with a positive SLPA north of 50 °N and a negative SLPA extending from the southeastern USA toward western and central Europe. The cold ENSO events exhibit almost reversed SLPA patterns. The change between November–December and January–March is also observed at the hemispheric scale. In November–December, the SLPAS associated with the warm minus cold ENSO composite form a hemispheric north–south dipole pattern with positive (negative) anomalies south (north) of 40–45 °N. In January–March, the SLPA pattern associated with the warm minus cold ENSO composite is close to the tropical Northern-Hemisphere pattern. Copyright  2003 Royal Meteorological Society.

This study shows that above-(below-)normal winter snow depth over European Russia and corresponding below-(above-)normal snow depth over central Siberia is associated with reduced (increased) summer monsoon rainfall over southern and western India and eastern Pakistan, and above-(below-)normal sea-surface temperatures (SSTs) over the eastern and central tropical Pacific Ocean during the following winters. The connection is slightly stronger when snow depth over European Russia is above normal than below normal. These results are derived from an examination of 60 years (1936–1995) of winter snow depth data and SSTs, and 45 years (1951–1995) of summer precipitation records. The results of this study suggest that winter snow depth over the western rather than the eastern portion of Eurasia is critical to Southeast Asian summer monsoon rainfall and eastern tropical Pacific SSTs during the following seasons. Copyright © 2001 Royal Meteorological Society

Thirty-year rainfall records for seven coastal locations in Papua New Guinea were analysed to assess the spatial and temporal characteristics of rainfall anomalies and the general response of coastal rainfall to the Southern Oscillation (SO). Spatial and temporal variability of rainfall anomalies are a distinct feature of the coastal locations analysed. Despite the spatial variability of rainfall anomaly behaviour, an all Papua New Guinea rainfall anomaly index shows significant concurrent and lag inverse associations with the Southern Oscillation Index of Wright. Anomalously high (low) pressure in the Papua New Guinea region leads to low (high) rainfall in the concurrent and ensuing season. Rainfall anomaly periodicities of 7–8 years lie within the time-scale of 2–10 years for ENSO events, but individual locations demonstrate a variable response to ENSO events. Study results fill an important geographical gap in the understanding of the spatial and temporal characteristics of rainfall variability in the western tropical Pacific.

The magnitude of spatial and lagged correlation between the sea-surface temperature anomalies of the eastern tropical Pacific Ocean (El NinMo) and corn yield in the USA is presented. The record is not homogeneous in that the correlation level varies quite strongly over time. The period between 1910 and 1950 shows completely uncorrelated behaviour. In the most recent 40 years the correlation is found to be strongest in the region just south of the Great Lakes in the states of Illinois, Iowa, and Indiana. Correlation maps are presented that show the degree of association for the corn yield in those 41 states for which records are available. For the entire record the highest correlations occur with the sea-surface temperature anomalies appearing after the corn is harvested in September to February of the following year. Since corn yields are a proxy for summer agricultural drought in the central part of the USA, the droughts during the period 1910 to 1950 must have had some other cause.