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In this paper, we report on the frequency of false onsets of wet season rainfall in the case of the Northern Australian wet season and investigate the role of large‐scale tropical climate processes such as the El Niño–Southern Oscillation, Indian Ocean Dipole (IOD) and Madden–Julian Oscillation. A false onset occurs when a wet season rainfall onset criterion is met, but follow‐up rainfall is not received for weeks or months later. Our analysis of wet season rainfall data from 1950 through 2020 shows a false onset occurs, on average, between 20 and 30% of wet seasons across all of northern Australia. This increases at a regional and local level such as at Darwin, the Northern Territory (NT), and parts of Queensland's north coast to over 50%. Seasonal climate influences, such as a La Niña pattern and a negative IOD that typically expedite the wet season rainfall onset, also increase the likelihood of a false onset over northern Australia. Our analysis also finds that periods of false onsets can sometimes, but not always, coincide with periods of rapid soil moisture depletion. The false rainfall onsets that develop into flash drought can be potentially disruptive and costly and are of potential significance for agriculture and fire management in northern Australia, and in other monsoonal climates that also typically experience a slow build‐up to the seasonal monsoon. In conclusion, effective rainfall indicates that many seasons experience 'false onsets' with dry conditions after early rainfall. We propose that false onsets are a physical characteristic of the climate of northern Australia which occurs with relatively high frequency. In addition, these false onsets may sometimes co‐occur with a flash drought. [ABSTRACT FROM AUTHOR]

Southeastern South America is subject to considerable precipitation variability on seasonal to decadal timescales and has undergone very heavy land‐cover changes (LCCs) since the middle of the past century. The influence of local LCC and precipitation as drivers of regional evapotranspiration (ET) long‐term trends and variability remains largely unknown in the region. Here, ensembles of stand‐alone dynamic global vegetation models (DGVMs) with different atmospheric forcings are used to disentangle the influence of those two drivers on austral summer ET from 1950 to 2010. This paper examines the influence of both the El Niño‐Southern Oscillation (ENSO) and the dipole‐like first‐mode of southeastern South American precipitation variability (EOF1) on regional ET. We found that in the lower La Plata Basin, ET was driven by precipitation variability and showed a positive summer trend. Moreover, the region showed marked seasonal anomalies during El Niño and La Niña summers but mainly during EOF1 phases. On the contrary, in the upper La Plata Basin, LCCs forced the negative summer ET trend and particularly reduced the summer anomalies of the late 1990s, a period of ENSO and EOF1‐positive phases. In the South Atlantic Convergence Zone region, the high ET uncertainty across ensemble members impeded finding robust results, which highlights the importance of using multiple DGVMs and atmospheric forcings instead of relying on single model/forcing results. [ABSTRACT FROM AUTHOR]

Seasonal prediction of extreme precipitation has long been a challenge especially for the East Asian Summer Monsoon region, where extreme rains are often disastrous for the human society and economy. This paper introduces a decision‐tree (DT) method for predicting extreme precipitation in the rainy season over South China in April–June (SC‐AMJ) and the North China Plain in July–August (NCP‐JA). A number of preceding climate indices are adopted as predictors. In both cases, the DT models involving ENSO and NAO indices exhibit the best performance with significant skills among those with other combinations of predictors and are superior to their linear counterpart, the binary logistic regression model. The physical mechanisms for the DT results are demonstrated by composite analyses of the same DT path samples. For SC‐AMJ, an extreme season can be determined mainly via two paths: the first follows a persistent negative NAO phase in February–March; the second goes with decaying El Niño. For NCP‐JA, an extreme season can also be traced via two paths: the first is featured by "non El Niño" and an extremely negative NAO phase in the preceding winter; the second follows a shift from El Niño in the preceding winter to La Niña in the early summer. Most of the mechanisms underlying the decision rules have been documented in previous studies, while some need further studies. The present results suggest that the decision‐tree approach takes advantage of discovering and incorporating various nonlinear relationships in the climate system, hence is of great potential for improving the prediction of seasonal extreme precipitation for given regions with increasing sample observations. [ABSTRACT FROM AUTHOR]

The present paper investigates the impact of El Niño‐Southern Oscillation (ENSO) on the Bay of Bengal tropical cyclone (TC) activity and associated alterations in environmental conditions during post‐monsoon (October–December) season for a period of 44 years (1972–2015). The analysis reveals that the post‐monsoon season TCs frequency, accumulated cyclone energy (ACE) and power dissipation index (PDI) values are negatively correlated with the Niño 3.4 sea surface temperature (SST) anomalies (significant at the 95% confidence level). La Niña years are characterized by more frequent and intense cyclonic events compared with El Niño years. The mean ACE and PDI values are approximately two times higher in La Niña than El Niño years. The mean number of TC days per year is also higher in La Niña (7.64 days) than El Niño (3.68 days) years (significant at 95% confidence level). In addition, a significant shift in genesis locations, tracks and landfalling locations of TCs has been observed under different ENSO phases. The mean genesis location of TCs have shifted eastward with tendency of more recurving tracks in La Niña than El Niño years. The presence of strong convective activity, reduced vertical wind shear, high SST (≥28°C), enhanced mid‐tropospheric relative humidity and low‐level cyclonic circulation aids the TCs formation and strengthening during La Niña and vice‐versa in El Niño conditions. [ABSTRACT FROM AUTHOR]

The paper tests if the two La Niña (LN) types can be distinguished from each other using their climate impacts on northeastern Brazil (NEB). To this end, all LN events during the 1901–2010 period followed by a wet or dry rainy season (from February to April) in NEB are classified into two categories: WET‐LN and DRY‐LN. The global and regional anomalous atmospheric circulation patterns and the rainfall anomaly patterns in South America associated with the two cases are analysed. The WET‐LN and DRY‐LN events present, respectively, the eastern Pacific LN and central Pacific LN sea surface temperature (SST) anomaly features in the tropical Pacific. On the other hand, the WET‐LN features an interhemispheric SST dipole pattern in the tropical Atlantic, and the DRY‐LN, colder‐than‐normal surface waters in the tropical South Atlantic (TSA) and equatorial Atlantic during MAM(+1). The two analysed cases show regional differential circulation patterns in all seasons. The anomalous wetness over northern and northwestern South America occurs for the WET‐LN type during JJA(0)–DJF(+1) and for the DRY‐LN type, during DJF(+1)–MAM(+1). The anomalous dryness over SESA is more evident for the WET‐LN during JJA(0) and MAM(+1), and for the DRY‐LN, during SON(0). Anomalous dryness occurs in central and eastern South America noted during JJA(0) and DJF(+1) for both cases analysed. The precipitation anomalies in northern South America during DJF(+1) are stronger and more extensive for the DRY‐LN than for the WET‐LN events due to the action of both the anomalous (double) Walker and Hadley cells for the DRY‐LN, in contrast with the exclusive action of an anomalous Walker cell for the WET‐LN case. Also, a double Walker cell drives the dry–wet dipole between northern South America and NEB during MAM(+1) for the DRY‐LN. Our results might be useful mainly for climate monitoring purposes. The two La Niña (LN) types were distinguished from each other using their climate impacts on northeastern Brazil (NEB) and classified in two categories WET‐LN (LN events followed by a wet rainy season in NEB) and DRY‐LN (LN events followed by a dry rainy season in NEB) that present, respectively, the eastern Pacific LN and central Pacific LN sea surface temperature (SST) anomaly features in the tropical Pacific. The illustration shows the LN‐related SST and precipitation anomaly patterns evolutions associated with the two LN types. [ABSTRACT FROM AUTHOR]

This paper investigates the factors affecting the annual number of tropical cyclones (TCs) passing within 100 km of the coast of Korea and Japan (KJ). Using a training set consisting of the coefficients of empirical orthogonal functions of these factors between 1965 and 2005, equations are derived to predict the annual number of these TCs over the whole season in April, and to update this prediction for the July-November (JN) season in June. Results show that the El Niño-Southern Oscillation (ENSO) plays a key role in determining the behaviour of TCs affecting KJ, with more TCs affecting the region during El Niño and less during La Niña. This difference can be attributed to ENSO modifying the flow patterns, which in turn affects TC behaviour. The prediction equations suggest that the 500-hPa geopotential height is more important in determining the number of TCs affecting KJ in the whole season, while both the 850-hPa geopotential height and 850-hPa vorticity play a role in the JN season. Both prediction schemes are able to produce acceptable results, with forecast skills of 42.3 and 33.3% over climatology for the whole, and JN seasons, respectively. The predicted TC number for 2006, 2007, and 2008 are also mostly accurate to within one standard deviation of the observed number. Copyright © 2010 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Extreme events contribute significantly to rainfall variability in semi‐arid regions like South Africa. Here, following the definition of a novel typology of rainfall extremes, disentangling large‐ and small‐scale events in Part I, we use quality‐controlled observational databases in South Africa, the ERA5 reanalysis and satellite estimates TRMM‐3B42 to examine the relationship between these two types of rainfall extremes and different modes of climate variability at various timescales. At low frequencies, rainfall extremes are assessed at interannual (IV: 2–8 years) and quasi‐decadal (QDV: 8–13 years) timescales, which are primarily associated with the El Niño–Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO), respectively. At subseasonal timescales, the typology of rainfall extremes is analysed depending on the synoptic configurations, as inferred by seven convective regimes including tropical temperate troughs (TTTs: 3–7 days), and the intraseasonal variability associated with the Madden–Julien Oscillation (MJO: 30–60 days). At the IV timescale, the occurrence of large‐scale extremes is substantially higher during its wet phases thereby suggesting a 400% rise in the occurrence of large‐scale extremes as compared to its dry phases. At the QDV timescale, variability mostly relates to the modulation of small‐scale extremes during its wet phases. Teleconnections with global sea surface temperature (SST) confirm that La Niña conditions favour overall wet conditions and extremes in South Africa. The numbers of large‐scale extremes are consistently related to warmer SSTs in the North Atlantic, while their link with warmer Indian and tropical South Atlantic oceans is found to be statistically independent of the state of ENSO. At the subseasonal timescales, large‐scale extremes largely occur during three out of the seven convective regimes identified in the southern African region whereas small‐scale extremes are nearly equiprobable during all convective regimes. The occurrence of large‐scale extremes during continent‐rooted TTT is further enhanced during the locally wet phases of the MJO and is symmetrically weakened during its dry phases. [ABSTRACT FROM AUTHOR]

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

In this study, we focus on the features and predictability of winter 2‐m air temperature (t2m) over China under different intensities of La Niña events. The seasonal and intraseasonal prediction skills of winter t2m over China are examined by four state‐of‐art seasonal climate forecast models. The results show that the China winter t2m anomaly is sensitive to the intensity of La Niña. Strong and moderate (S/M) La Niña events are often accompanied by cold winter over China, while a positive anomaly of mean t2m over China frequently occurs in the weak La Niña events. The intensity difference of the East Asian winter monsoon (EAWM) results in this discrepancy. All models have a slightly higher anomaly correlation coefficient (ACC) for the S/M La Niña than that for the weak La Niña in leading 1 month (LT1). Both individual models and MME exhibit higher skills of anomaly sign consistency rate (ASCR) for the S/M La Niña, which implies that models predict t2m anomaly over China more accurately in the S/M La Niña events. Furthermore, the winter t2m over China presents larger intraseasonal variability for the S/M La Niña than that for the weak La Niña. Models can capture the t2m anomaly over China more accurately when the temperature varies gently with small intraseasonal variability during winter for the S/M La Niña. [ABSTRACT FROM AUTHOR]

The Pacific‐Japan (PJ) pattern is the dominant teleconnection over East Asia, closely related to the summer precipitation on various time scales. However, studies on the connection between the interdecadal variations of the PJ pattern and sea surface temperature (SST) forcing are still limited. This study indicates that the relationship between the PJ pattern and ENSO presents a pronounced interdecadal change around 1997/1998. The PJ pattern shows a baroclinic structure over the northwest Pacific and a barotropic structure near Japan during 1979–1997, while its baroclinic structure in the tropics weakens remarkably during 1998–2021, with a southward shift of its midlatitude barotropic structure. As a result, the connection between the PJ pattern and summer precipitation over East Asia exhibits an interdecadal transition in the late 1990s. In the slow La Niña decaying summer of 1979–1997, the cold SST anomalies in the tropical Indian Ocean (TIO) excite an eastward‐propagating Kelvin wave that enhances convection over the northwest Pacific, resulting in the formation of the PJ pattern. In contrast, the cold SST anomalies in the Maritime Continent rather than the TIO yield a zonally confined Kelvin wave in the rapid La Niña decaying summer of 1998–2021. The elongated Kelvin wave penetrating the central Pacific weakens convective anomalies over the northwest Pacific, thereby weakening the baroclinic structure of the PJ pattern in the tropics. Meanwhile, the warm SST anomalies in the Kuroshio Extension (KE) induce a northward shift of the East Asian subtropical westerly jet, with the anomalous anticyclonic circulation over the KE significantly affecting summer precipitation along the Meiyu belt. Therefore, the midlatitude barotropic structure of the PJ pattern shifts southward after the late 1990s. [ABSTRACT FROM AUTHOR]

This study examines the climatology, variability, and trends of tropical cyclones (TCs) affecting the Solomon Islands (SI) territory, in the wider southwest Pacific (SWP), using the South Pacific Enhanced Archive for Tropical Cyclones (SPEArTC) database. During the period 1969/1970–2018/2019, 168 TCs were recorded in the SI territory. A cluster analysis is used to objectively partition these tracks into three clusters of similar TC trajectories to obtain better insights into the effects of natural climate variability, particularly due to the El Niño–Southern Oscillation (ENSO) phenomenon, which otherwise is not very apparent for TCs when considered collectively in the SI region. We find that TCs in clusters 1 and 3 show enhanced activity during El Niño phase, whereas TCs in cluster 2 are enhanced during La Niña and neutral phases. In addition to being modulated by ENSO, TCs in clusters 2 and 3 show statistically significant modulation at an intraseasonal timescale due to the Madden–Julian Oscillation (MJO) phenomenon. There are also some indications through sophisticated Bayesian modelling that TCs in clusters 2 and 3 are slightly influenced by the Interdecadal Pacific Oscillation (IPO). These results can have substantial implications for cluster‐specific development of TC prediction schemes for the SI region. [ABSTRACT FROM AUTHOR]

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

Positive/negative Indian Ocean Dipole (IOD) tends to co‐occur with El Niño/La Niña. Five positive IODs, however, are observed under La Niña condition in 1961, 1966, 1967, 2007, and 2011. This study uses the monthly ocean temperature and atmospheric reanalysis datasets from ECMWF to investigate how these positive IOD events occurred. It is found that the five positive IODs are consistently accompanied by a moderately strong positive subsurface IOD (Sub‐IOD) event that initiated earlier. The Sub‐IOD‐related oceanic dynamical processes including oceanic Kelvin and Rossby waves help to promote the development of the positive IODs. More specifically, the equatorial easterly anomalies in the Tropical Indian Ocean (TIO) that are crucial for the development of the positive Sub‐IODs and IODs in 1961/2011 are triggered by an anticyclonic curl over South Indian Ocean that is induced by a Southern Hemispheric Indian Ocean Subtropical Dipole mode. The crucial equatorial easterly anomalies in 1967 are triggered by a thermocline warming in the southwestern TIO induced by westward downwelling oceanic Rossby waves, while in 1966/2007, the equatorial easterly anomalies are connected with the anomalous Walker circulation resulting from the certain sea surface temperature anomaly pattern over the equatorial Pacific. On the other hand, the remote effects of La Niña on TIO are relatively weaker, being overwhelmed by the above triggering processes. [ABSTRACT FROM AUTHOR]

Through a set of observational analyses and baroclinic model experiments, we show that during La Niña conditions a wave train in North Pacific propagates eastwards along the Asian jet, crosses the equator and interacts with the SACZ through an equatorial window in the East Pacific. Composites of active SACZ for November–March of 1979–2013 are used, drawn from the full dataset and also from just the La Niña years. The data are filtered in two‐time bands: 20–90 days (intraseasonal) and >200 days (interannual). Interhemispheric waveguides are identified in the anomalous SACZ composites during La Niña years. A similar wave pattern is simulated by a baroclinic atmospheric model with a fixed La Niña basic state where a thermal forcing anomaly is added on Southeast Asia. This La Niña basic state favours anomalous westerly equatorial flow at high levels, enabling a connection between Asia and South America around 15 days. [ABSTRACT FROM AUTHOR]

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

Using both observations and ensemble hindcasts of Nanjing University of Information Science and Technology Climate Forecast System (NUIST‐CFS1.0) for the period of 1983–2020, the leading modes of sea surface temperature anomalies (SSTAs) over the tropical Atlantic in boreal spring and summer (March–April–May–June–July–August, MAM‐JJA) and their connections with El Niño‐Southern Oscillation (ENSO) are investigated with Empirical Orthogonal Function (EOF), partial‐correlation, and composite analyses. In both observations and hindcasts, the first EOF mode is characterized by a basin‐wide SSTA pattern, and the second mode features a meridional dipole pattern. The meridional dipole mode cannot trigger ENSO, while the basin‐wide SST warming mode contributes to a subsequent La Niña via both north‐tropical and equatorial pathways. The north‐tropical pathway involves a low‐level anomalous anticyclone over North Pacific as a Matsuno‐Gill‐type response to the basin‐wide SST warming, related to a North Pacific Meridional Mode characterized with a cold SSTA and north‐easterly wind coupling over the northeast tropical Pacific, and finally triggers La Niña via the seasonal footprinting mechanism. This pathway is less important in the hindcasts than in observations. The equatorial pathway is tightly linked to the Kelvin wave, characteristic of an eastward propagation of the coupled pattern of SST and low‐level winds and a wedge‐like 500‐hPa air temperature anomaly over the tropical Indian and western equatorial Pacific Oceans, which is more significant in the hindcasts than in observations. Further composite analyses confirm that, even without the effect of the preceding ENSO, a basin‐wide tropical Atlantic SST warming favours the development of La Niña. [ABSTRACT FROM AUTHOR]

This study assesses the intensity, spatial distribution and temporal variability of extreme precipitation events (EPEs) on different time scales relevant to agriculture and water resources during the 1901–2016 period over Argentina's Austral Chaco (ACh). EPEs were identified using a nonparametric approach for the Standardized Precipitation Index (SPI). The leading modes of SPI's variability were detected using the Singular Spectrum Analysis. We also compile and control the quality of precipitation observations in a scarcely monitored region. The limited number of stations conditions the interpolation of the GPCC v2018 database here used, mainly during the early twentieth century. The EPEs characterized by SPI at a 24‐month time scale, which favour long‐lasting water excesses or deficits with hydrological impacts, underwent two differentiated long‐term periods: a dry one before 1960 and a wet one from 1960 to 2005. Consistently, seasonal wet EPEs were more frequent during the wet period while seasonal droughts were more frequent and with larger spatial extent during the dry period. Seasonal EPEs, represented by the SPI at 3‐month time scale, can impact agriculture during the crops' critical growth period. Since 2006, the long‐term wetting trend has been reversed. If this behaviour continues into the coming decades, more droughts and less wetness might be expected. The EPEs present a large interannual variability with 6.3‐ and 9‐year significant cycles that, combined with long‐term trends, favoured extremely wet/dry EPEs. Most of the wet/dry EPEs occurred during El Niño/La Niña events. Although this relationship is not straightforward, we found a discriminant ENSO signal between October of the year when an ENSO event starts and February of the next year. Finally, severely dry/wet EPEs tend to have large spatial extent in the ACh region. The central‐eastern ACh region experiences the most extreme wet and dry conditions, which makes this area more prone to extreme EPEs. [ABSTRACT FROM AUTHOR]

The 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. [ABSTRACT FROM AUTHOR]

The Okavango River Basin (ORB) is a highly sensitive and biodiverse region in southern Africa whose climate, vegetation and river discharge characteristics are not well understood. This study investigated relationships between rainfall, temperature, Normalized Difference Vegetation Index (NDVI) and river discharge over the region as well as their trends and interannual variability. It is found that spatial patterns of NDVI are closely related to those of rainfall, but less so with temperature at monthly and seasonal time scales. The relationships between NDVI and rainfall/temperature differ north of 18.9°S where rainfall is higher than to its south. Typically, there are lags of 1–2‐months between NDVI and either rainfall or temperature. Also, there are large areas across the region that show significant warming trends in all seasons as well as wetting (mainly in the north). This increasing trend in surface temperature may act to worsen the impacts of extreme events such as severe drought and fire in the region. There is also pronounced interannual variability with significant correlations found with El Niño‐Southern Oscillation (ENSO), the subtropical South Indian Ocean Dipole and the Botswana High for rainfall and temperature, and for NDVI with ENSO. For the Southern Annular Mode, significant correlations were found with rainfall and temperature only in December and April. On longer time scales, focus was also placed on the wet 2006–2013 period relative to much drier 1999–2005 epoch for October–December. The wetter conditions during 2006–2013 appear related to La Niña Modoki conditions and warmer sea surface temperature near Angola as well as regional circulation differences. [ABSTRACT FROM AUTHOR]

This study aimed to analyse the spatio‐temporal variability of wet and drought events in the Paraná River Basin and their association with the El Niño—Southern 20 Oscillation (ENSO) phenomenon. A dataset of daily precipitation from 953 pluviometric stations from 1982 to 2016 was used. Anomalies of sea surface temperature (SST) from the four Niño regions of the Equatorial Pacific were also used. Homogeneous rainfall regions were defined using cluster analysis and principal component analysis (PCA). To describe the drought or wet conditions the standardized precipitation index (SPI) for 1‐, 3‐, and 12‐months time scales were used. The relationship between the ENSO and the wet and drought conditions were also analysed. The results suggest that two regions are enough to represent the whole Paraná River Basin during different rainfall patterns. In the 1‐month SPI, the precipitation extremes of the region that is mainly composed of the state of Paraná and southern region of Mato Grosso do Sul (Region 2), showed a statistically significant correlation at the level of 1% with ENSO events. In the 12‐month SPI, the most intense drought and wet events and with greater spatial coverage, in general, were observed in years with ENSO occurrences. In general, it is observed that although the ENSO phenomenon is not the main factor that causes the drought and wet events in the region, El Niño contributes to the rainfall excess and La Niña to the rainfall deficit in the Paraná River Basin. [ABSTRACT FROM AUTHOR]

Precipitation in the outer tropical Andes is highly seasonal, exhibits considerable interannual variability, and is vital for regulating freshwater availability, flooding, glacier mass balance, and droughts. The primary driver of interannual variability is El Niño Southern Oscillation (ENSO), with most investigations reporting that the El Niño (La Niña) results in negative (positive) precipitation anomalies across the region. Recent investigations, however, have identified substantial spatiotemporal differences in ENSO‐precipitation relationships. Motivated by the dissimilarity of these findings, this study examines a carefully selected data set (≥ 90% completeness) of ground‐based precipitation observations from 75 high‐elevation (≥ 2,500 m above sea level) meteorological stations in the tropical Andes of southern Peru and Bolivia for the period 1972–2016. Distinct groups of stations and associated variability in precipitation characteristics (e.g., total seasonal precipitation, wet season onset, and wet season length) are identified. Using no spatial constraints, the K‐Means algorithm optimally grouped stations into five easily identifiable groups. The groups farthest from the Amazon basin had significant negative (positive) precipitation anomalies (p <.05) during El Niño (La Niña), aligning with the traditional view of ENSO‐precipitation relationships while groups closest to the Amazon had opposite relationships. Additionally, though studies have reported delays in the wet season, years characterized by El Niño had an earlier wet season onset in all five groups. These findings may aid in improving seasonal climate prediction and managing water resources, and could allow for improved interpretation of tropical Andean ice cores. [ABSTRACT FROM AUTHOR]

The present study investigates how the 20th‐century atmospheric reanalyses (ERA‐20C and NOAA‐20CR) reproduce the known impacts of El Niño–Southern Oscillation (ENSO) on the tropical North Atlantic (TNA) atmospheric circulation from the boreal winter to spring and the consequences on northeastern Brazil (NEB) precipitation during its rainy season (boreal spring). For the period 1979–2010, comparisons of atmospheric patterns associated with ENSO events are made through the use of anomaly composites of variables provided by ERA‐20C, NOAA‐20CR and satellite‐era reanalyses (ERA‐Interim and NCEP‐Reanalysis 2). We also evaluate the ability of the reanalyses to reproduce the interannual variability of precipitation during the boreal spring over Ceará state (located in NEB) by statistically comparing them with Funceme rain‐gauge and Global Precipitation Climatology Center (GPCC) datasets. As the main result, both 20th‐century reanalyses capture the major features in the tropical Pacific representing the climatic system during ENSO years as well as its impacts on the tropical Atlantic, in agreement with previous studies. However, some differences are noted, such as (a) NOAA‐20CR differs from the other reanalyses since it indicates stronger (weaker) near‐surface (upper levels) wind anomalies over the central‐western equatorial Pacific in both El Niño and La Niña composites; (b) over the tropical Atlantic, all reanalyses indicate the existence of an omega anomalies dipole between 10°N and 10°S for both ENSO phases although a weaker signal is seen in NOAA‐20CR; (c) NOAA‐20CR underestimates the intensity of the precipitation anomalies over the NEB during El Niño and La Niña years, and this is associated with the weaker vertical velocity anomalies. These results indicate that ERA‐20C is the most appropriate 20th‐century reanalysis to study the long‐term interannual variability in the tropical Atlantic associated with ENSO and its impacts on precipitation in northeastern Brazil. [ABSTRACT FROM AUTHOR]

The predictability of El Niño and La Niña is investigated. In this case, the recently discovered so‐called global atmospheric oscillation (GAO) is considered. Assuming GAO to be the main mode of short‐term climatic variability, this study defines an index that characterizes the dynamics and relationships of the extratropical components of the GAO and El Niño – Southern Oscillation (ENSO). Due to the general propagation of the GAO's spatial structure from west to east, another index – predictor of ENSO is defined. The cross‐wavelet analysis between both of these indices and the Oceanic Niño Index (ONI) is performed. This analysis reveals a range of timescales within which the closest relationship between the GAO and ONI takes place. Using this relationship, it is possible to predict El Niño and La Niña with a lead‐time of approximately 12 months. [ABSTRACT FROM AUTHOR]

Present study investigates the dominant modes of interannual variability in precipitation over the Hengduan Mountains (HM) during rainy seasons. The leading two empirical orthogonal function (EOF) modes of HM precipitation explain 28.4 and 13.9% of the total variance, respectively. Positive EOF1 phase features enhanced precipitation anomalies over the southern HM, and a dipole structure with wet anomalies occupying large areas from the YunGui plateau to Tibetan Plateau is observed in positive EOF2 phase. Analysis of moisture budget and omega equation indicate the importance of leading EOF modes related circulation anomalies, which bring the horizontal warm advection to the HM, favouring the anomalous upward motions and precipitation increase there. For EOF1, the HM is controlled by an anomalous quasi‐barotropic cyclone. This cyclone is one part of a zonally oriented barotropic wave‐like pattern highly resembling the Silk Road pattern. Besides, the SST anomalies over the Indo‐Pacific sector are similar to the decaying phase of La Niña, which induces the wet anomalies and further triggers the anomalous lower‐level cyclone as a Rossby wave response. For EOF2, an anomalous cyclone appears over the Northeast Asia from lower to upper levels, and southerly wind anomalies prevail over the HM. The North Atlantic Oscillation and its coupled tripole SST pattern trigger a zonal wave‐like pattern at middle and high latitudes emanating from the Central Europe, across Mongolia to Northeast Asia. Moreover, the SST anomalies over the Indo‐Pacific sector resemble the developing phase of El Niño, which induces the meridional Pacific‐Japan/East Asia‐Pacific teleconnection from tropical NWP to Northeast Asia. [ABSTRACT FROM AUTHOR]

The present study detected an obvious interdecadal change in the relationship of Indochina Peninsula (ICP) May precipitation to El Niño‐Southern Oscillation (ENSO). During the 1950s through the late‐1970s, more (less) ICP precipitation tends to occur in May of La Niña (El Niño) developing years, whereas after the late‐1990s, more (less) ICP precipitation tends to appear in May of La Niña (El Niño) decaying years. During the late‐1970s through the late‐1990s, more (less) ICP precipitation occurs in May of La Niña (El Niño) persisting years. The interdecadal change in the ICP May precipitation‐ENSO relationship is related to two factors. One factor is the developing time of ENSO events. During the 1950s through the late‐1970s, ENSO events develop earlier with larger equatorial central‐eastern Pacific sea surface temperature (SST) anomalies in May. SST‐induced lower‐level wind anomalies extend northwestward from the equatorial central Pacific to the ICP. After the late‐1990s, ENSO events develop later with smaller equatorial central‐eastern Pacific SST anomalies in May. SST‐induced lower‐level wind anomalies are confined to the Pacific region. The other factor is the tropical Indo‐Pacific SST anomaly pattern. During the ENSO decaying years after the late‐1990s, opposite SST anomalies in the North Indian Ocean and central North Pacific work together to induce stronger wind anomalies over the ICP in May. In contrast, during the ENSO decaying years during the 1950s through the late‐1970s, wind anomalies are weaker over the ICP in May under the sole influence of the North Indian Ocean SST anomalies. [ABSTRACT FROM AUTHOR]

Using the standardized precipitation evapotranspiration index, this study examines the combined effects of El Niño‐Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) on global droughts in terms of magnitude, timing, and duration. The ENSO‐affected drought hotspots are identified based on drought magnitude and probability of occurrence: five hotspots for El Niño (Amazon, India, central China, Indonesia, and eastern Australia) and four hotspots for La Niña (southeastern United States, southern South America, East Africa, and Southwest Asia). When ENSO and PDO are in phase, most of the hotspots exhibit an intensification and expansion of drought, more clearly at longer time scales (6–12 months), supporting previous studies. Interestingly, the in‐phase PDO advances El Niño‐induced drought onset by early summer of the previous year, whereas it delays the withdrawal of La Niña‐induced drought until the end of the event year. This asymmetric response is found to be in part associated with the earlier start and later end of El Niño itself during warm PDO, which does not hold for the La Niña/cold PDO composites. Further analyses of the responses of precipitation (P) and potential evapotranspiration (PET) to different ENSO‐PDO combinations suggest the important role of P reduction in determining drought magnitude and timing over most of the hotspots, with some contribution of enhanced PET to drier conditions over a few La Niña hotspots. It is also found that the PDO modulation of El Niño‐induced drought occurs primarily through the eastern Pacific El Niño with a limited influence on the central Pacific El Niño. [ABSTRACT FROM AUTHOR]

The number of tropical cyclones (TCs) over the western North Pacific (WNP) during spring (March–May) has a significant inverse correlation with concurrent El Niño‐Southern Oscillation (ENSO) conditions during the period from 1979 to 2018. This relationship is different from the previously‐documented weak relationship between TC frequency and ENSO during the climatologically most active portion of the TC season. In general, TCs seldom occur in El Niño years during March–May, whereas they frequently form over the western part of the WNP, particularly to the southeast of the Philippines, in La Niña years. This difference can be largely explained by ENSO‐driven differences in the genesis potential index as derived from environmental variables. In La Niña years, the abnormally moist mid‐troposphere, which relates to the strengthened vertical transport of water vapour induced by the enhanced Walker Circulation, primarily favours TC development, while increased sea surface temperatures and positive low‐level relative vorticity anomalies appear to play a lesser role in impacting TC formation. [ABSTRACT FROM AUTHOR]

Local‐level understanding of within‐season rainfall variability and its relationship with the El Niño Southern Oscillation (ENSO) can shed light on crop yield variations and establish appropriate cropping calendars in rainfed systems. This requires information on the growing season, including its length, the total rainfall, the onset and cessation of rainfall, the number of wet and dry days, and the optimal sowing window. The objective of this study was to examine the onset and cessation of both the rainy and growing seasons using historical daily rainfall datasets (1980–2013) from 50 weather stations distributed across the main grain production region of Brazil. We then correlated the interannual variability of the climate variables and crop water availability with ENSO (using the Oceanic Niño Index, ONI). Across the study region, the onset of the rainy period ranged from late September to early November, and the cessation period ranged from late March to mid‐April. The onset of the growing season followed that of the rainy season, beginning across central and northern Mato Grosso in mid‐October, followed by Goiás and Tocantins, and finally Rondônia by the end of October. The length of the sowing window was reduced, and the mean optimal sowing date was delayed during La Niña years for most weather stations in the study region. Our results infer the need to adjust the cropping calendars for specific ENSO phases only in regions that conduct crop rotations. Based on rice crop model simulations of water availability, we propose a mean optimal crop sowing calendar for annual crops in Central Brazil. Highlights: We analysed the impact of El Niño Southern Oscillation (ENSO) on the growing season characteristics of Central Brazil.The length of the sowing period is markedly reduced during La Niña years across the region. We propose a mean optimal crop sowing calendar for Central Brazil based on crop modelling results of ENSO effects. [ABSTRACT FROM AUTHOR]

Earth's weather and climate are strongly influenced by synoptic scale systems such as extratropical cyclones. From this point of view, investigating the mechanisms associated with cyclogenesis, such as baroclinic instability (BI), which are defined by the thermal gradient and wind shear, are extremely important. However, atmospheric teleconnection patterns such as the El Niño‐Southern Oscillation (ENSO) phenomenon may affect BI in the preferred region of extratropical cyclones, known as the storm track (ST) region. Therefore, the present study shows the impact of ENSO on BI and STs in the Southern Hemisphere. BI is determined by means of the Eady growth rate method, while the STs are calculated from the kinetic energy and by means of the meridional heat transport. In general, the results show that STs calculated from the BI and the kinetic energy show seasonal variability during ENSO events. This results in Southern Hemisphere extratropical cyclones being more intense with trajectories towards lower (higher) latitudes during El Niño (La Niña) summers. In contrast, little difference is seen in El Niño and La Niña winters. For the calculation of the meridional heat transport at 500 hPa, the Climate Forecast System Reanalysis produced weaker transport relative to ERA‐Interim and previous studies. [ABSTRACT FROM AUTHOR]

The eastern Pacific (EP) El Niño‐Southern Oscillation (ENSO) is an important impact factor for the East Asian trough (EAT) variability during boreal winter. However, not all ENSO events can result in anomalous EAT events, which indicates that there could be some other factors modulating the relationship between ENSO and the EAT. The analysis of atmospheric circulations indicates that the intensity of the Asian Polar vortex (PV) plays an important role in the El Niño‐EAT connection. The strengthened Asian PV favours the wave‐train triggered by El Niño events propagates eastward from the North Pacific to East Asia and finally weakens the EAT. In contrast, during El Niño years with the weakened Asian PV, El Niño's influences are confined over western Siberia and the wave activity flux over Eurasia is weak, which consequently leads to a weak response of the EAT. For the La Niña‐EAT connection, the North Pacific Oscillation (NPO) is a potential modulating factor. The La Niña and negative‐phase NPO have a strengthened effect on the EAT, resulting in a strong response of the EAT to La Niña events. In contrast, the effects of La Niña and positive‐phase NPO on the EAT are offset, leading to a weak response of the EAT to La Niña events. The above results are further confirmed by a numerical simulation of the pre‐industrial Control experiment. Therefore, the simultaneous occurrence of the Asian PV and NPO should be a great concern when understanding and predicting the EAT based on ENSO information. [ABSTRACT FROM AUTHOR]

The zonal shift in the western North Pacific subtropical high (WNPSH) is closely associated with moisture transport in East Asia and is thus an important factor that determines the amount of summer precipitation in the region. Climatologically, the WNPSH retreats eastward from early to late summer. However, there is high variability in the early to late summer shift in the WNPSH from year to year. Thus, the interannual variability in the intraseasonal zonal displacement of WNPSH from early to late summer was examined in this study. The results showed that the intraseasonal shift in the WNPSH from early to late summer was almost unrelated to the El Niño‐Southern Oscillation (ENSO) signal, although previous studies have claimed that ENSO can modulate the variation in the summer mean WNPSH. More specifically, the El Niño or La Niña years were not predictive of how the WNPSH would shift zonally from early to late summer. Otherwise, the zonal displacements of the WNPSH were more of mid‐latitude origin. In the strongly retreating years (SRY), the mid‐latitude wave train was much more significant than that in the weakly retreating years (WRY). The mid‐latitude wave train was reminiscent of the Silk Road teleconnection pattern (SRP). In the SRY, the centres of the wave trains had opposite signs in early and late summer, which resulted in the opposite features of the WNPSH between early and late summer. The consistency of the three reanalysis datasets confirmed the robustness of our results. [ABSTRACT FROM AUTHOR]

This study revealed the modulation of the impacts of Madden–Julian Oscillation (MJO) on winter rainfall in China by El Niño‐Southern Oscillation (ENSO) using reanalysis data and statistical analysis. When MJO is active over the Indian Ocean, its impacts are strengthened by El Niño, leading to enhanced positive rainfall anomalies in eastern China. However, the effects of MJO are counteracted by La Niña; thus, significant positive rainfall anomalies exist only in Zhejiang Province and adjacent areas. MJO activity over the western Pacific induces opposite rainfall anomalies in South China between El Niño and La Niña winters; rainfall in South China increases (decreases) in El Niño (La Niña) winters. Such differences in rainfall anomalies are closely related to anomalous circulation and moisture transport. Anomalous southwesterlies in eastern China are enhanced in El Niño winters when MJO is active over the Indian Ocean, which leads to increased moisture transport towards China and stronger ascending motion in eastern China. But the anomalous southwesterlies are weakened in La Niña winters, thereby resulting in less moisture transport and convergence. When MJO is active over the western Pacific, anomalous northeasterlies in mainland China are enhanced (weakened) in La Niña (El Niño) winters, which strengthens (weakens) the moisture divergence and descending motion in China. Moisture convergence anomalies that explain the rainfall anomalies in ENSO winters are mainly attributed to the effects of low‐frequency background state (LFBS) moisture and meridional winds. It was found that ENSO modulates the impacts of MJO by two main ways. First, ENSO can regulate the intensity and distribution of MJO activity. Therefore, MJO in the same phase will lead to different circulation and moisture transport anomalies in China. Second, ENSO‐induced LFBS circulation and moisture anomalies can also influence the moisture convergence in China, which will strengthen or weaken the effects of MJO. [ABSTRACT FROM AUTHOR]

An intercomparison of three regional climate models (RCMs) (PRECIS‐HadRM3P, RCA4, and RegCM4) was performed over the Coordinated Regional Dynamical Experiment (CORDEX)—Central America, Caribbean, and Mexico (CAM) domain to determine their ability to reproduce observed temperature and precipitation trends during 1980–2010. Particular emphasis was given to the North American monsoon (NAM) and the mid‐summer drought (MSD) regions. The three RCMs show negative (positive) temperature (precipitation) biases over the mountains, where observations have more problems due to poor data coverage. Observations from the Climate Research Unit (CRU) and ERA‐Interim show a generalized warming over the domain. The most significant warming trend (≥0.34°C/decade) is observed in the NAM, which is moderately captured by the three RCMs, but with less intensity; each decade from 1970 to 2016 has become warmer than the previous ones, especially during the summer (mean and extremes); this warming appears partially related to the positive Atlantic Multidecadal Oscillation (+AMO). CRU, GPCP, and CHIRPS show significant decreases of precipitation (less than −15%/decade) in parts of the southwest United States and northwestern Mexico, including the NAM, and a positive trend (5–10%/decade) in June–September in eastern Mexico, the MSD region, and northern South America, but longer trends (1950–2017) are not statistically significant. RCMs are able to moderately simulate some of the recent trends, especially in winter. In spite of their mean biases, the RCMs are able to adequately simulate inter‐annual and seasonal variations. Wet (warm) periods in regions affected by the MSD are significantly correlated with the +AMO and La Niña events (+AMO and El Niño). Summer precipitation trends from GPCP show opposite signs to those of CRU and CHIRPS over the Mexican coasts of the southern Gulf of Mexico, the Yucatan Peninsula, and Cuba, possibly due to data limitations and differences in grid resolutions. [ABSTRACT FROM AUTHOR]

By using the observation, reanalysis data and numerical simulation, the inter‐decadal variations in El Niño–Southern Oscillation (ENSO) impacts on the eastern China (EC) precipitation during its developing autumn in the past 65 years have been investigated. Results show that ENSO is related to the significant dipole precipitation anomalies in EC in the early decades (1951–1981); El Niño/La Niña introduces more/less precipitation in the southern EC, but less/more in the northern EC. However, the significant dipole pattern disappears in the recent decades (1985–2015), mainly owing to loss of the significant positive influences of La Niña on the northern EC precipitation. Comparison of the atmospheric circulation anomalies in East Asia related to La Niña in the two periods shows that there are anticyclonic circulation anomalies in the northeastern Asia near Japan in the first period, while they shift to Mongolia in the second period. Hence, in the first period, the northern EC is under the influences of anomalous southwesterlies along the southwestern flank of the anticyclonic circulation anomalies that advect more moisture from the south to the northern EC and lead to more precipitation there. In contrast, in the second period, the northern EC is under the influences of anomalous northeasterlies along the southeastern edge of the anticyclonic circulation anomalies near Mongolia that impede the northwards transport of moisture and are not conducive to surplus precipitation. The westwards shift of the anticyclonic circulation anomalies may be closely related to the higher SST and thus convective anomalies related to La Niña in the tropical western North Pacific (WNP) east of the Philippines in the second than the first periods. The sensitivity experiment forced by the positive SST anomalies in the tropical WNP comparable to the observed in an atmospheric general circulation model can successfully simulate the anticyclonic circulation anomalies around Mongolia. [ABSTRACT FROM AUTHOR]

El Niño–Southern Oscillation (ENSO) plays an important role in modulating the location of tropical cyclone (TC) genesis over the western North Pacific (WNP). This study evaluated the simulation of the ENSO's impact on WNP TC genesis in 10 CMIP5 models based on a TC detection method, and projected its changes under global warming using the historical and the representative concentration pathway 8.5 (RCP8.5) simulations. The observed southeast–northwest shift role of ENSO in the WNP TC genesis location can be well reproduced in most of the models, although the strength of the ENSO's impact is underestimated as the underestimated climatological TC genesis frequency in these models. Moreover, we found the WNP TC during both El Niño and La Niña events shows an apparent eastwards shift under global warming. However, this eastwards shift of WNP TC genesis could be associated with the changes in climatological TC genesis but not the changes in the ENSO's impact. The projected changes in the ENSO's impact on WNP TC genesis is not as certain as we expected based on the previous conclusions of the robust changes in ENSO's impact on large‐scale environment. As a result, we suggest that both the TC genesis climatology and ENSO's impact on TC genesis simulated in the models need improvement in future to project the changes in ENSO's impact under global warming, and more models with 6‐hourly outputs used to detect TCs are needed to increase the confidence of multi‐model ensemble projections. [ABSTRACT FROM AUTHOR]

The impact of the strongest central Pacific (CP) El Niño event 2009/2010 and CP La Niña event 1998/1999 from 1979 to 2010 on the precipitation in eastern China has been analysed. During the 2009/2010 CP El Niño event, it is rainy in northern China during maturing winter and decaying spring, but dry during decaying summer. The rainfall centre is located in south China during maturing period and gradually moves northwards, remaining over the Yellow‐Huai River valley during decaying summer. When the 1998/1999 CP La Niña event occurs, northern China is in a state of drought throughout. In south China, dry periods gradually evolve into rainy ones from maturing winter to decaying summer. The two strongest events also have notable impact on the extreme rainfall, and they mainly affect the total rainfall by influencing the extreme precipitation in eastern China. When the 2009/2010 CP El Niño event occurs, the Western Pacific Subtropical High (WPSH) is stronger with a northwards shift, and there is an obvious anticyclonic circulation near the South China Sea and Philippines. Furthermore, during decaying summer, the Pacific–Japan (PJ) wave train shows an eastwards shift comparing to the typical PJ wave train locating from low latitudes to high latitudes, associating with clearly northwardly spreading wave activity fluxes (WAFs) from the equator. When the 1998/1999 CP La Niña event occurs, the WPSH is weaker and retreats eastwards, and there is a noticeable cyclonic circulation around the South China Sea. In decaying spring, the convective activity in the South China Sea is strong, and there are correspondingly significant WAFs spreading from southeastern Asia to north. In decaying summer, northern (southern) China is controlled by anomalous anticyclones (cyclones) with weak (strong) convection, and the WAFs extend northwards to the Yangtze and Huai River valleys. [ABSTRACT FROM AUTHOR]

Using composite analysis, the timing and extent of El Niño–Southern Oscillation (ENSO) impacts on maximum (Tmax) and minimum temperatures (Tmin) during austral summer are investigated for South Africa over the period 1940–2016. Pearson correlation coefficients determined between temperature data at stations within regions indicate that temperature records are coherent. During austral summer, composite analysis exhibits positive Tmax/Tmin anomalies for El Niño years while negative anomalies are recorded during La Niña years across all regions of South Africa. Statistical significance of composite average temperature anomalies was determined using the Student's t‐test. Tmax for El Niño years are significantly different from the neutral years over the central interior of South Africa for the period 1940–2016. The most notable finding of this study is that El Niño events have had a stronger warming effect during austral summer over many regions in South Africa after the late 1970s, than before. Such an impact has been most prominent over the northern and central interior regions, where, respectively, associated Tmax record an average of 1.1 °C and 0.73 °C higher values for the period 1979–2016 compared to the earlier period (1940–1978). Chi‐squared statistics indicate that ENSO phases exert a stronger influence on temperatures over the interior of South Africa than along the coast. During austral summer, composite analysis exhibits positive Tmax/Tmin anomalies for El Niño years and negative Tmax/Tmin anomalies during La Niña years across all regions of South Africa. Student's t‐test exhibits a significantly strong and consistent relationship between El Niño and Tmax over the central interior for the period 1940–2016. The most notable finding of this study is that El Niño events have had a stronger warming effect over many regions in South Africa after the late 1970s, than before. [ABSTRACT FROM AUTHOR]

This study investigates the El Niño-Southern Oscillation (ENSO)-related seasonal variations in precipitation extremes based on the observed daily precipitation dataset of 23 meteorological stations in Malaysia, spanning a period of 46 years from 1966 to 2011. The extreme indices were a subset of the Expert Team for Climate Change Detection and Indices (ETCCDI) that covers the duration, frequency and intensity aspects of precipitation extremes. Seasonal composites of 'El Niño minus neutral' and 'La Niña minus neutral' years of these indices were computed based on El Niño and La Niña occurrences during the period. The results showed that the ENSO-related variations in precipitation extremes were generally coherent with the variations in total precipitation. Generally, dry (wet) precipitation extremes tended to enhance during El Niño (La Niña); however, this was dependent on season and location. The El Niño and La Niña influences on precipitation extremes were not entirely linear. While the impacts of El Niño and La Niña were generally opposite for most locations and seasons, there were cases where both exerted in-phase influences. The impacts were also dependent on the intensity of the event itself. While the El Niño impacts were generally coherent across different intensities, La Niña can have entirely different impacts among different categories. During December–January–February (DJF), strong (moderate) La Niña caused a significant decrease (increase) in wet precipitation extremes over the Peninsular Malaysia. This was related to the broadening (narrowing and westward displacement) of the anomalous cyclonic circulation over the western north Pacific during strong (moderate) La Niña. Hence, the likelihood for widespread flooding over the east coast of the Peninsular Malaysia during DJF increases during moderate but not during strong La Niña events. [ABSTRACT FROM AUTHOR]

The diverse influences of the El Niño Southern Oscillation (ENSO) on wintertime precipitation over the Maritime Continent are herein investigated using observational data. The ENSO events are divided into four categories -- strong El Niño, strong La Niña, moderate El Niño and moderate La Niña -- according to their amplitudes. Significant negative Maritime Continent precipitation anomalies are observed during strong El Niño events, whereas wet conditions occur during strong La Niña events. In the case of moderate La Niña events, the Maritime Continent rainfall anomalies are similar in spatial structure and comparable in amplitude to strong La Niña events, whereas almost no significant rainfall anomalies are observed in moderate El Niño years. Further analysis shows that strong El Niño (strong/moderate La Niña) events are associated with a significant anticyclone (cyclone) surface response over the western tropical Pacific and related to a significant descending (ascending) branch of the Walker circulation around the Philippines. However, during moderate El Niño events, both the central-eastern and the western tropical sea surface temperature anomalies (SSTA) are weak and cannot significantly change the Walker circulation over the tropical Pacific. Therefore, the descending branch anomalies of the Walker circulation associated with moderate El Niño events around the Philippines are quite weak and cannot cause significant negative precipitation anomalies in that location. In addition, there is large case-to-case variance in the tropical Pacific SSTA associated with moderate El Niño events, which also contributes to the weak Maritime Continent rainfall response in the composite analysis. [ABSTRACT FROM AUTHOR]

ABSTRACT El Niño phenomenon is the leading mode of sea surface temperature interannual variability. It can affect weather patterns worldwide and therefore crop production. Crop models are useful tools for impact and predictability applications, allowing to obtain long time series of potential and attainable crop yield, unlike to available time series of observed crop yield for many countries. Using this tool, crop yield variability in a location of Iberia Peninsula ( IP) has been previously studied, finding predictability from Pacific El Niño conditions. Nevertheless, the work has not been done for an extended area. The present work carries out an analysis of maize yield variability in IP for the whole 20th century, using a calibrated crop model at five contrasting Spanish locations and reanalyses climate datasets to obtain long time series of potential yield. The study tests the use of reanalysis data for obtaining only climate-dependent time series of crop yield for the whole region, and to use these yield to analyse the influences of oceanic and atmospheric patterns. The results show a good reliability of reanalysis data. The spatial distribution of the leading principal component of yield variability shows a similar behaviour over all the studied locations in the IP. The strong linear correlation between El Niño index and yield is remarkable, being this relation non-stationary on time, although the air temperature-yield relationship remains on time, being the highest influences during grain filling period. Regarding atmospheric patterns, the summer Scandinavian pattern has significant influence on yield in IP. The potential usefulness of this study is to apply the relationships found to improving crop forecasting in IP. [ABSTRACT FROM AUTHOR]

ABSTRACT Despite the many improvements that have been achieved in prediction methods, considerable uncertainties in the models and the observing systems remain in El Niño Southern Oscillation predictions. One of the uncertainties is the definition of El Niño and La Niña years. Because academia has accepted too many indexes, there is much confusion among scientists regarding whether El Niño and La Niña events have occurred. In the view of this author, the oceans on this planet can be vividly called 'ocean stabilization machines' (OSMs). When some part of an OSM loses control for unknown reasons, other parts of the OSM function stabilize the atmospheric circulation. As a result, El Niño or La Niña events occur. In this study, we use a most-recognized principle to determine El Niño (La Niña) years based on a K-line diagram technique. This technique not only focuses on the anomaly of five accepted indexes, but also aims at the signals of an on-going crash downward or a dramatic upward tendency of the sea-surface temperature. To achieve this purpose, a new terminology, 'suspected El Niño (La Niña) years' and an Ocean Stabilization Index (OSI) expressing the state of the Pacific are proposed. The results indicate that there were only 10 El Niño years and 12 La Niña years from 1950 to 2012. Significant statistical relationships between the annual OSI and 14 indexes are also found. [ABSTRACT FROM AUTHOR]

ABSTRACT Indian Summer Monsoon Rainfall ( ISMR) experiences quasi-periodic drought and excess rainfall. In this study we examined the contribution of individual month's (June-September) rainfall in the seasonal excess (deficit). Analysis of 110 years (1901-2010) of observed precipitation and 20th century reanalysis data highlights the importance of subseasonal variations of rainfall in modulating Indian summer monsoon. A month which contributes to seasonal excess (deficit) is primarily controlled by large-scale La Niña (El Niño) forcing but with favourable local conditions from the tropical Indian Ocean. On the other hand excess (deficit) rainfall of an individual month which is not contributing to seasonal excess (deficit) is controlled mainly by the local forcing. Such local forcing however is short lived and does not persist more than a month. Our analysis reveals that June is not contributing considerably to the seasonal excess rainfall in the recent years. On the other hand contribution of September rainfall to the seasonal extremes is more frequent in the recent years. During September enhanced El Niño (La Niña) conditions and the local forcing contribute to the seasonal ISMR deficit (excess). It is important to note that none of the above 110 years experienced excess (deficit) rainfall during all the four monsoon months except 1972. This study advocates the need of subseasonal (or monthly) rainfall prediction for better socio-economic benefits. [ABSTRACT FROM AUTHOR]

Sea surface temperature (SST) anomalies in the Pacific Ocean during El Niño-Southern Oscillation (ENSO) episodes exhibit different spatial patterns from year to year. In most ENSO studies, SST anomalies have been analysed in the 3.4 or 3.0 El Niño regions. Recent analyses have considered different SST anomalies areas in the Pacific, such as ENSO Modoki, which takes into account anomalies in the central Pacific which are bounded by opposite anomalies in the eastern and western Pacific. In order to analyse the influence of different Pacific spatial patterns on South American precipitation and on the Southern Hemisphere atmospheric circulation, composites obtained from Canonical ENSO were compared with those from ENSO Modoki in cases when strong anomalies were present in the Central Pacific. During the Canonical El Niño (La Niña), there tends to be a precipitation increase (decrease) in the La Plata Basin (LPB, 45°W-65°W, 15°S-35°S) and a decrease (increase) over northern South America during all seasons. In ENSO Modoki exhibiting strong anomalies in the Central Pacific, these typical patterns are not observed, and in some regions the anomalies even show opposite signs. Precipitation anomaly differences or similarities over South America between the two cases occur in different areas and different seasons. In both cases, differences in tropical South American precipitation during both ENSO types are related to differences in the Walker circulation. In extra-tropical South America, the precipitation differences are due to differences in the Pacific wavetrains and differences in moisture flux intensity over the continent. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Using predictions for the sea surface temperature (SST) generated by a Flexible Global Ocean-Atmosphere-Land System model of IAP/LASG (FGOALS-g), the season-dependent predictability of SST anomalies for El Nino/La Nina events is investigated by analyzing the forecast error growth in an imperfect model scenario. The results indicate that, for the predictions through the spring season in the growth phase of El Nino events, the prediction errors induced by both initial errors and model errors tend to have a prominent season-dependent evolution and yield a prominent spring predictability barrier (SPB). For the decay-phase predictions of El Nino events, a less prominent season-dependent evolution of prediction errors and then a less prominent SPB are observed. For the growth- and decay-phase predictions of La Nina events, the prediction errors do not exhibit a significant season-dependent evolution and yield a less prominent SPB phenomenon. These results indicate that the SPB phenomenon depends remarkably on the ENSO events themselves, particularly the phases of the El Nino/La Nina events. We also report that the initial SST errors that correspond to a significant SPB for El Nino events tend to have the dominant modes in a large-scale dipolar pattern with negative anomalies in the equatorial central-western Pacific and positive anomalies in the eastern Pacific, or vice versa. We further demonstrate that the error growth related to a significant SPB for El Nino prediction generated by the FGOALS-g model can result from two dynamical mechanisms: in one case, the prediction errors grow in a manner similar to El Niño; in the other, the prediction errors develop with a tendency opposite to El Niño. Copyright © 2012 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Whereas the impact of ENSO on the African summer rainfall regions is largely documented and still regularly investigated, little is known about its impact on the winter rainfall regions located at the southwestern and northwestern tips of Africa. Yet, these regions are densely inhabited and are net exporters of high-quality agricultural products. Here we analyze the relationship between El Niño Southern Oscillation (ENSO) and South Africa austral winter rainfall using a 682 raingauges daily rainfall database documenting the period 1950-1999. The May, June and July (MJJ) seasonal rainfall amount shows a positive correlation with the Niño3.4 index that becomes significant since the so-called 1976/1977 climate regime shift. Wet spells properties (length, frequency and intensity) at the raingauge scale indicate that high (low) MJJ seasonal rainfall amounts recorded during El Niño (La Niña) events are the result of longer (shorter) wet spells in the Cape Town area and more (less) frequent wet spells north of 33°S. Wet spells with daily rainfall amounts ranging between 10 and 50 mm are also more (less) frequent. Atmospheric dynamics fields during wet spells feature lower (higher) pressure and northwesterly (southerly) wind anomalies in the troposphere over the region. This suggests that rain-bearing systems are deeper (thinner) and larger (smaller) in extent, and located farther north (south) during El Niño (La Niña) events. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

Land use change and climate change have been increasingly contributing to loss or reduction of biological and economic productivity of arid lands. The dry climate and physiographic characteristics of the Peninsula of La Guajira on the Colombian Caribbean coast are considered to be crucial drivers of the loss of vegetative cover and soil erosion; however, little knowledge exists on long-term changes in climate in the area. This study presents a tree-ring chronology from Parkinsonia praecox (18 trees, 45 radii) that allows the reconstruction of local and global climate drivers spanning the last 63 years. Tree-ring width was strongly correlated with rainfall and wind data, indicating that annual tree growth was closely related to local climatic variability. The chronology also strongly correlated with an index of ENSO severity (El Niño Southern Oscillation), suggesting that large-scale climatic phenomenon also have important influence on Parkinsonia growth. To further investigate rainfall-growth relationships, climate data series of annual rainfall and rainfall from September to November (SON), the rainiest months, were reconstructed using transfer functions. These data series did not exhibit a clear trend of change in rainfall over the last 63 years. The transfer functions reconstructed the total annual rainfall ( R2 = 0.8), and SON ( R2 = 0.7). This study constitutes the first attempt to reconstruct climatic patterns in Colombia with techniques of dendrochronology, and demonstrates the potential of Parkinsonia praecox for studying climatic patterns along the American subtropics, ranging from Mexico to Argentina. Copyright © 2011 Royal Meteorological Society [ABSTRACT FROM AUTHOR]

The article presents a study concentrating on the frequency of extreme rainfall events in Southern Brazil. It highlights two vital areas relating to the impact of El Niño (EN) to the frequency such as the recorded extreme events during EN and decrease during La Niña. Principal Component Analysis has disclosed the most recurrent precipitation patterns during extreme rainfall events.

The article investigates the spatial correction in annual rainfall anomalies in Suriname using principal component analysis, and measures the influence of sea-surface temperature anomalies (SSTAs) in the tropical Atlantic (TA) and the tropical Pacific Ocean in Suriname's seasonal rainfall using composites and cross correlation analysis. Findings show that the meridional movement of the inter-tropical convergence zone (ITCZ) determine the spatial and time variability in rainfall. It was also found out that the highest correlation with SSTAs in the tropical South Atlantic region happened during the end of the long wet season, from June-August rainfall.

While examining the atmospheric structure and dynamics through which the El Niño-Southern Oscillation phenomenon is associated with east African rainfall, it was discovered that circulation variability in the subtropical South Pacific Ocean has a significant but seasonally varying influence on east African rainfall receipt on interannual timescales. Enhanced equatorial east African rainfall receipt associated with El Niño events is well known to occur during the long rains from October to December, but rainfall deficits during the same season are typical of La Niña events. South Pacific circulation variability is found to enhance rainfall receipt during the October to December period, but is associated with significant east African rainfall deficits during the March to May rainy period. It is demonstrated here that outbreaks of moist South Atlantic westerly flows that are often associated with anomalous rainfall receipt over east Africa are enhanced (weakened) during El Niño (La Niña) periods. An empirical orthogonal function analysis is performed to extract the principal mode of sea level pressure variability in the tropical and subtropical South Pacific region. The time series associated with the principal mode of South Pacific circulation variability is correlated with circulation, atmospheric humidity, and outgoing longwave radiation fields during the short rains (October-December) and long rains (March-May). It is shown that South Pacific circulation variability is positively associated with east African rainfall receipt ( r = 0.42, significant at the 99% confidence interval). Strengthened inflows of moist South Atlantic westerlies are associated with enhanced low-level moisture convergence, decreased lower tropospheric stability, increased cloudiness, and increased precipitable water anomalies observed during OND. Reverse circulation and hydroclimatic anomalies observed during MAM are consistent with a negative association with east African rainfall during that season; r = −0.33, significant at the 98% confidence interval. The temporal stability of these associations was tested during periods in which the principal interannual signal associated with El Niño was either very strong or very weak, and it was demonstrated that the correlations strengthened slightly (weakened markedly) during the period when the 5-year signal was very strong (weak). Copyright © 2006 Royal Meteorological Society [ABSTRACT FROM AUTHOR]