Article

On the El-Niño Teleconnection to Spring Precipitation In Europe

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Abstract

In a statistical analysis of more than a century of data we find a strong connection between strong warm El Nino winter events and high spring precipitation in a band from Southern England eastwards into Asia. This relationship is an extension of the connection mentioned by Kiladis and Diaz (1989), and much stronger than the winter season teleconnection that has been the subject of other studies. Linear correlation coefficients between DJF NINO3 indices and MAM precipitation are higher than r=0.3 for individual stations, and as high as r=0.49 for an index of precipitation anomalies around 50N from 5W to 35E. The lagged correlation suggests that south-east Asian surface temperature anomalies may act as intermediate variables.

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... We have described but a small part of the substantial progress that has been achieved in understanding the ENSO impact on NAE climate, but there are still many unsettled questions related to the strength, pattern, stationarity, and the underpinning physical mechanisms of the ENSO-NAE teleconnection Hardiman et al. 2019;Lorenzo et al. 2011;Moron and Ward 1998;van Oldenborgh et al. 2000). In this study we look into the possible variation of ENSO and NAO co-occurrence to test the theory that the total ENSO influence on the NAE area projects onto the NAO pattern in late winter. ...
... As highlighted in van Oldenborgh and Burgers (2005), the relatively short period of observations, weak ENSO signal and large atmospheric noise in the extratropics are all limiting factors for investigating the strength and long-term variations of ENSO teleconnections. The modulations of ENSO teleconnections can be small compared to the effects of atmospheric internal variability and it is often challenging to demonstrate high statistical confidence (Sterl et al. 2007;van Oldenborgh et al. 2000). However, the presented analysis of the ENSO-NAE teleconnection, together with the consistent results of targeted model experiments, supports our hypothesis that sea-ice concentration and SST climatology are important factors in the modulation of the ENSO-NAE teleconnection. ...
Article
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New observational evidence for variability of the atmospheric response to wintertime El Niño-Southern Oscillation (ENSO) is found. Using different approaches and datasets, a weakening in the recent ENSO teleconnection over the North Atlantic-European (NAE) region is demonstrated. Changes in both pattern and strength of the teleconnection indicate a turning point in the 1970s with a shift from a response resembling the North Atlantic Oscillation (NAO) to an anomaly pattern orthogonal to NAO with very weak or statistically non-significant values; and to nearly non-existent teleconnection in the most recent decades. Results shows the importance of the background sea surface temperature (SST) state and sea-ice climatology having opposite effects in modulating the ENSO-NAE teleconnection. As indicated with targeted simulations, the recent change in the SST climatology in the Atlantic and Arctic has contributed to the weakening of the ENSO effect. The findings of this study can have implications on our understanding of modulations of ENSO teleconnections and ENSO as a source of predictability in the NAE sector.
... The strong links between ENSO and MAM precipitation also existed in the region 47.5°-52.5°N, 35°E-5°W of Europe from 1851 to 1993 (Van Oldenborgh et al., 2000). During summer and fall increased precipitation over southern Europe occurs when El Nino conditions prevail in the equatorial Pacific (Park, 2004). ...
... These ENSO teleconnections to seasonal precipitation can provide an approach to predict the precipitation at regional and global scales (Van Oldenborgh et al., 2000;Chiodi and Harrison 2015), and obviously can be applied to the seasonal precipitation over Central Asia. Moreover, according to the composite analyses of our results, Mariotti (2007) suggested that enhanced precipitation in southwest Central Asia during warm ENSO events results from an anomalous southwesterly water vapor flux across the Arabian Peninsula coming from the Arabian Sea and tropical Africa, which is generated along the northwestern flank of the high pressure anomaly over the Indian and western Pacific Oceans, part of the ENSO see pressure anomalies. ...
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The vulnerable ecosystem of the arid and semiarid region in Central Asia is sensitive to precipitation variations. Long-term changes of the seasonal precipitation can reveal the evolution rules of the precipitation climate. Therefore, in this study, the change of the seasonal precipitation over Central Asia has been analyzed during the last century (1901–2013) based on the latest global monthly precipitation dataset Global Precipitation Climatology Centre (GPCC) Full Data Reanalysis Version 7, as well as their relations with El Nino- Southern Oscillation (ENSO). Results show that the precipitation in Central Asia is mainly concentrated in spring and summer seasons, especially in spring. For the whole study period, increasing trends were found in spring and winter, while decreasing trends were detected in summer and fall. Inter-annual signals with 3–7 years multi-periods were derived to explain the dominant components for seasonal precipitation variability. In terms of the dominant spatial pattern, Empirical orthogonal function (EOF) results show that the spatial distribution of EOF-1 mode in summer is different from those of the other seasons during 1901–2013. Moreover, significant ENSO-associated changes in precipitation are evident during the fall, winter, spring, and absent during summer. The lagged associations between ENSO and seasonal precipitation are also obtained in Central Asia. The ENSO-based composite analyses show that these water vapor fluxes of spring, fall and winter precipitation are mainly generated in Indian and North Atlantic Oceans during El Nino. The enhanced westerlies strengthen the western water vapor path for Central Asia, thereby causing a rainy winter.
... While the NAO predominantly influences climate variability in the Northern Hemisphere (Hurrell and Deser 2010;Manola et al. 2013;Luo et al. 2018), it also causes variations in precipitation, surface temperature, and wind patterns in various regions worldwide (Pinto and Raible 2012). Its teleconnection with ENSO seemingly lacks a simple correlation (Van Oldenborgh et al. 2000;Hu et al. 2013), but the dependency of its relationship on ENSO diversity has been identified (Zhang et al. 2015(Zhang et al. , 2018Zhang and Wu 2023), as well as boreal winter modulation, mainly during January-March (JFM) (Brönnimann et al. 2007;Mezzina et al. 2020;Geng et al. 2023) and vice versa during December and January (Alexander et al. 2002). EP and CP El Niño events are typically accompanied by a negative NAO phase, while EP La Niña events are associated with a positive phase; and the difference between the two types is most evident during JFM (Zhang et al. 2015). ...
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The Central-Pacific (CP) and Eastern-Pacific (EP) types of El Niño-Southern Oscillation (ENSO) and their ocean–atmosphere effect cause diverse responses in the hydroclimatological patterns of specific regions. Given the impact of ENSO diversity on the North Atlantic Oscillation (NAO), this study aimed to determine the relationship between the ENSO-NAO teleconnection and the ENSO-influenced precipitation patterns in Colombia during the December–February period. Precipitation data from 1981 to 2023, obtained from the Climate Hazards Group (CHIRPS), were analyzed using nine ENSO and NAO indices spanning from 1951 to 2023. Using Pearson’s correlation and mutual information (MI) techniques, nine scenarios were devised, encompassing the CP and EP ENSO events, neutral years, and volcanic eruptions. The results suggest a shift in the direction of the ENSO-NAO relationship when distinguishing between the CP and EP events. Higher linear correlations were observed in the CP ENSO scenarios (r > 0.65) using the MEI and BEST indices, while lower correlations were observed when considering EP events along with the Niño 3 and Niño 1.2 indices. MI show difference in relationships based on the event type and the ENSO index used. Notably, an increase in the non-linear relationship was observed for the EP scenarios with respect to correlation. Both teleconnections followed a similar pattern, exhibiting a more substantial impact during CP ENSO events. This highlights the significance of investigating the impacts of ENSO on hydrometeorological variables in the context of adapting to climate change, while acknowledging the intricate diversity inherent to the ENSO phenomenon.
... The large-scale pressure anomalies (climate signals/ teleconnections) are recurring modes, controlling the spatiotemporal variability of the precipitation systems happening over a given region during a specific period (Irannezhad et al. 2017). Several studies have investigated the correlation of climate signals and the precipitation variabilities at far distances (e.g., Araghi et al. 2017;Casanueva et al. 2014;Duzenli et al. 2018;Oldenborgh et al. 2000;Yuan et al. 2016) in order to improve our understanding of the current and future conditions of the local/regional bio-hydroclimatic variables (Wise et al. 2015). The possible influences of teleconnections on the seasonal and monthly precipitation amounts in Iran have been reported in several studies. ...
Article
This study was aimed at evaluating the application of the canonical correlation analysis (CCA) to predict monthly precipitation amounts (predictands) by benefitting from 17 large-scale climate indices (predictors) in Iran. Monthly precipitation data, covering the period of 1987–2017, were collected from 100 weather stations across the country. Monthly precipitations were predicted using the multiple linear regression (MLR) models, based on the 1- to 6-month lead times of the original and canonical predictors. The cross-validation was conducted to compare the prediction skills of the two sets of MLR models constructed on the basis of the original predictors (MLOrigPr) and the canonical predictors (MLCCAPr). The analyses revealed the dominant teleconnections and that there are the interannual variations in responses of precipitation to them suggesting that a signal only is not sufficient to achieve a robust understanding of the associations. At the 1-month lead time, the MLR models based on the canonical predictors outperformed those based on the original predictors. However, the skill of both models was reduced by increasing the lead times up to 6 months. Averaging on all stations, around 61.4% and 26.3% of the observed values, falls into the cross-validated 95% prediction intervals of the MLCCAPr and MLOrigPr models, respectively. Furthermore, the MLCCAPr models were found to be more spatially universal than the MLOrigPr ones and decrease multicollinearity symptoms strengthening the predictions. These findings corroborated the advantage of using the CCA in improving the teleconnective predictability of precipitation in Iran.
... Li et al. (2022) studied up to a 2-year lag between several teleconnection patterns and terrestrial water storage and observed an approximately 5-month lag for most surface components. However, in this study, a lagged effect of teleconnection indices on SM was considered for up to 6 months, as in similar studies (Runge et al., 2019b;Silva et al., 2021;van Oldenborgh et al., 2000). Once the 7 R values were obtained for each pixel, the maximum absolute value of R (R max ) was obtained, considering only those with statistical significance. ...
Article
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Soil moisture (SM) plays a key role in the water cycle, and its variability is intimately linked to coupled land-atmosphere processes. Having a good knowledge of soil-atmospheric interactions is thus essential to assess the impact of climate change on SM; however, many aspects of how water and energy exchanges occur in the soil-atmosphere continuum are still uncertain. In particular, it is known that atmospheric circulation patterns influence climate conditions over Europe but their impact on SM has only rarely been studied. This study provides insight into how atmospheric patterns influence soil moisture dynamics in Europe, where an increase in temperature and agricultural droughts are expected as an impact of climate change. To do so, we analysed the influence of the North Atlantic Oscillation (NAO), the Arctic Oscillation (AO), and the El Niño Southern Oscillation (ENSO) on European SM, including lagged responses, for the period 1991–2020 at a monthly scale. Two methods have been used: a lagged correlation analysis and a more sophisticated causality approach using the PCMCI (PC method combined with the momentary conditional independence (MCI) test). SM series from two different databases were considered: the hydrological model LISFLOOD and the reanalysis dataset ERA5-Land. The results from the correlation analysis showed a significant, predominantly negative relationships of SM with NAO and AO over almost all of Europe and no significant relation with ENSO. With the causality analysis, similar patterns are obtained for NAO and AO; however, the PCMCI analysis revealed clear patterns of ENSO influencing SM with a delayed response of one-to-two months in central and northwest Europe. The results obtained in this work highlight that there are causal relations between the main modes of interannual climate oscillations and SM variations in Europe, underlining the importance of accounting for global atmospheric circulations to study current changes in regional soil water-related processes.
... Ainsi, les régions subsahariennes ne montrent aucune dépendance distincte vis-à-vis de la trajectoire des dépressions dans l'Atlantique Nord et de la NAO et les mécanismes de génération de précipitations semblent plus complexes (Knippertz et al., 2003a). Si les recherches climatologiques ont accordées une grande importance à la variabilité des précipitations hivernales en relation avec la NAO (Lamb and Peppler, 1987), peu d'études ont abordé la question de cette variabilité avec la phénomène ENSO (Knippertz et al., 2003b;Rodo et al., 1997;Oldenborgh et al., 2000;Van Loon et Madden, 1981). Ce lien entre la variabilité ENSO en hiver boréal représenté par l'indice NINO3, à savoir les anomalies de température de surface de an Pacifique Est et les conditions météorologiques au printemps en Europe et en Afrique du Nord-Ouest a été examiné par Knippertz et al (2003b). ...
Article
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Variability of spring precipitations in relation to ENSO in morrocan oasis. The purpose of this work is to study the rainy atmospheric conditions of the spring season in Moroccan oasis in relation to the temperature of the oceanic surface of the Pacific in the winter season (NINO3 index). Indeed, the link between the variability of the NINO3 index and the standardized mean spring rainfall (SAI index), has shown that during the warm phases of the ENSO, the spring rainfall of the oasis decreases; it coincides with the zonal extension of the Azores high pressure ridge over Morocco which is favorable to the establishment of a NAO + phase. On other hand, the cold phases are concomitant with the lengthening of the high pressure ridge of the Azores towards the northeast of the Atlantic and there is a decrease in spring rainfall. During this wet spring phase, we also witness a deepening of the Saharan depression in comparison with the dry phase of the same season.
... Some of the teleconnections modulating the climate variability over Eurasia can be caused by tropical forcing, which causes an atmospheric response that propagates polewards (e.g., Hoskins and Ambrizzi 1993;Van Oldenborgh et al. 2000;Ding et al. 2011, Gastineau and Frankignoul 2015, Wulff et al. 2017, O'Reilly et al. 2018, Neddermann et al. 2019, for example, the circumglobal teleconnection pattern (CGT, Barnstator et al. 2002). Particularly for Europe, Wulff et al (2017) showed some evidence that the summer east Atlantic mode, which modulates the precipitation over the North Atlantic west of the British Isles, is forced by diabatic heating anomalies of opposing signs in the tropical Pacific and Caribbean. ...
Article
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The influence of Rossby waves emitted in the northeastern Pacific Ocean on the Northern Hemisphere’s atmosphere during summer is analysed using ERA5 reanalysis and a new large ensemble performed with the EC-Earth3 model. The Rossby Wave Sources (RWS) trigger wave-like patterns arising from the upper troposphere of the north-eastern Pacific region, causing a response around the Northern Hemisphere with alternating regions of positive and negative correlation values between RWS and geopotential height at 500 hPa. Increased RWS intensity during summer is related to negative temperature anomalies over western North America, and positive temperature anomalies over eastern North America, concurrently with increased precipitation over the western subtropical Atlantic and Northern Europe during summer. Colder than normal conditions on the North Pacific Ocean intensify the RWS and its impact on the global atmospheric circulation. Different warm or cold states in the Pacific and Atlantic Oceans modify the atmospheric response to RWS, showing a change in the middle troposphere (500 hPa) towards a more-wavy structure with cold Pacific conditions, and towards a less-wavy structure with a warm Pacific Ocean. Furthermore, the North Atlantic plays a very important role in hindering (in the case of warm water) or permitting (cold water) that Rossby waves generated in the Pacific modulate the atmospheric conditions over Europe.
... The large-scale pressure anomalies (climate signals/ teleconnections) are recurring modes, controlling the spatiotemporal variability of the precipitation systems happening over a given region during a specific period (Irannezhad et al. 2017). Several studies have investigated the correlation of climate signals and the precipitation variabilities at far distances (e.g., Araghi et al. 2017;Casanueva et al. 2014;Duzenli et al. 2018;Oldenborgh et al. 2000;Yuan et al. 2016) in order to improve our understanding of the current and future conditions of the local/regional bio-hydroclimatic variables (Wise et al. 2015). The possible influences of teleconnections on the seasonal and monthly precipitation amounts in Iran have been reported in several studies. ...
Preprint
Full-text available
This study aimed to evaluate the application of the canonical correlation analysis (CCA) to predict monthly precipitation amounts (predictands) by benefitting from 17 large-scale climate indices (predictors) in Iran. Monthly precipitation data, covering the period of 1987–2017, were collected from 100 weather stations across the country. Monthly precipitations were predicted using the multiple linear regression (MLR) models, based on the 1- to 6-month lead times of the original and canonical predictors. The cross-validation was conducted to compare the prediction skills of the two sets of MLR models constructed on the basis of the original predictors (MLOrigPr) and the canonical predictors (MLCCAPr). The analyses revealed the dominant teleconnections and that there are the interannual variations in responses of precipitation to them suggesting that a signal only is not sufficient to achieve a robust understanding of the associations. At the 1-month lead time, the MLR models based on the canonical predictors outperformed those based on the original predictors. However, the skill of both models was reduced by increasing the lead times up to 6 months. Averaging on all stations, around 61.4% and 26.3% of the observed values falls into the 95% prediction intervals of the MLCCAPr and MLOrigPr models, respectively. Furthermore, the MLCCAPr models were found to be more spatially universal than the MLOrigPr ones. These findings corroborated the advantage of using the CCA in improving the teleconnective predictability of precipitation in Iran.
... Some of the teleconnections modulating the climate variability over Eurasia can be caused by tropical forcing, which causes an atmospheric response that propagates polewards (e.g., Hoskins and Ambrizzi, 1993;Van Oldenborgh et al., 2000;Ding et al, 2011, Gastineau and Frankignoul 2015, Wulff et al. 2017, O'Reilly et al. 2018, Neddermann et al. 2019, for example, the circumglobal teleconnection pattern (CGT, Barnstator et al. 2002). ...
Preprint
Full-text available
The influence of Rossby wave sources (RWS) emitted on the Northeastern Pacific Ocean in the Northern Hemisphere during summer is analysed in the ERA5 reanalysis and new large ensemble performed with the EC-Earth3 model. Using extreme years composites of precipitation, surface temperature, geopotential height, we found a causal influence of the Rossby waves generated over the Northeastern Pacific Ocean, on a global climate response. Both the reanalysis ERA5 and the EC-Earth3 model show that RWS triggers wave-like patterns arising from the upper troposphere Northeastern Pacific region. We show that an increased Rossby wave sources intensity is related with negative temperature anomalies over western North America, and positive temperature anomalies over eastern North America concurrently increased precipitation over Northern Europe during summer and sea-ice concentration decrease in the Arctic. We also show that the North Atlantic plays a very important role hindering or permitting that Rossby waves generated in the Pacific reach the Atlantic and modulate the atmospheric conditions over Europe. Such conditions were found in ERA5 and SMHI-LENS during colder and icier conditions over the North Atlantic.
... Apart for NAO, other predefined teleconnection patterns have been linked with anomalous precipitation across Europe, such as the Scandinavian pattern (SCA), which is mainly related to high-latitude blocking over Scandinavia 19 , and the East Atlantic pattern 20 , or the East Atlantic/Western Russia pattern 21 . On a global scale, European precipitation has been linked with the El Niño-Southern Oscillation (ENSO), especially in spring 22 . However, the relationship between European precipitation and ENSO is non-stationary and varies with both season and region 23,24 . ...
Article
Full-text available
Central Europe has experienced a severe drought almost every April for the last 14 years consecutively, driven by record high temperatures, low flows, high evapotranspiration, and high soil moisture deficit. The dynamic of this recent and recurrent midspring dryness is not yet understood. Here we show that the period 2007–2020 was characterized by a reduction of ~50% of the usual April rainfall amount over large areas in central Europe. The precipitation deficit and the record high temperatures were triggered by a multiyear recurrent high-pressure system centered over the North Sea and northern Germany and a decline in the temperature gradient between the Arctic region and the mid-latitudes, which diverted the Atlantic storm tracks northward. From a long-term perspective, the precipitation, temperature, and soil moisture anomalies observed over the last 14 years have reached the highest amplitudes over the observational record. Our study provides an in-depth analysis of the hydroclimate extremes in central Europe over the last 140 years and their atmospheric drivers, enabling us to increase our dynamical understating of longterm dry periods, which is vital to enhance forecasting and mitigation of such events.
... Its accompanying atmospheric component, Southern Oscillation, is the principal mode of pressure variability in the tropics, which affects the climate of many regions worldwide (Allan et al., 1996). The connections between the stated patterns and the climate parameters throughout different regions have been observed in many studies, e.g., Tyson (1987), Oldenberg et al. (2000), Gong and Ho (2003), Pozo-Vazquez et al. (2005), Canon (2007), and Gaughan and Waylen (2012). A well-known pattern is North Atlantic Oscillation (NAO), that in winter its station-based index is the climate variability mode in North Atlantic Ocean and is defined as the difference in normalized mean winter (December to March of the next year) sea level pressure (SLP) anomalies between Iceland and Portugal (Hurrell, 1995). ...
Article
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global warming is one of the most complicated challenges of our time causing considerable tension on our societies and on the environment. The impacts of global warming are felt unprecedentedly in a wide variety of ways from shifting weather patterns that threatens food production, to rising sea levels that deteriorates the risk of catastrophic flooding. Among all aspects related to global warming, there is a growing concern on water resource management. This field is targeted at preventing future water crisis threatening human beings. The very first stage in such management is to recognize the prospective climate parameters influencing the future water resource conditions. Numerous prediction models, methods and tools, in this case, have been developed and applied so far. In line with trend, the current study intends to compare three optimization algorithms on the platform of a multilayer perceptron (MLP) network to explore any meaningful connection between large-scale climate indices (LSCIs) and precipitation in the capital of Iran, a country which is located in an arid and semi-arid region and suffers from severe water scarcity caused by mismanagement over years and intensified by global warming. This situation has propelled a great deal of population to immigrate towards more developed cities within the country especially towards Tehran. Therefore, the current and future environmental conditions of this city especially its water supply conditions are of great importance. To tackle this complication an outlook for the future precipitation should be provided and appropriate forecasting trajectories compatible with this region’s characteristics should be developed. To this end, the present study investigates three training methods namely backpropagation (BP), genetic algorithms (GAs), and particle swarm optimization (PSO) algorithms on a MLP platform. Two frameworks distinguished by their input compositions are denoted in this study: Concurrent Model Framework (CMF) and Integrated Model Framework (IMF). Through these two frameworks, 13 cases are generated: 12 cases within CMF, each of which contains all selected LSCIs in the same lead-times, and one case within IMF that is constituted from the combination of the most correlated LSCIs with Tehran precipitation in each lead-time. Following the evaluation of all model performances through related statistical tests, Taylor diagram is implemented to make comparison among the final selected models in all three optimization algorithms, the best of which is found to be MLP-PSO in IMF.
... The El Niño-Southern Oscillation (ENSO) teleconnection to North Atlantic-European (NAE) region is an active field of current research (e.g., van Loon and Madden 1981;Kiladis and Diaz 1989;Halpert and Ropelewski 1992;Rodó et al. 1997;Moron and Ward 1998;Van Oldenborgh et al. 2000;Brönnimann 2007;Lorenzo et al. 2011;Herceg-Bulić et al. 2012. This teleconnection is much weaker than the ENSO teleconnection to the Pacific-North American (PNA) region, but is nevertheless the major source for seasonal predictability in the Euro-Atlantic region (e.g., Domeisen et al. 2015;Scaife et al. 2017). ...
Article
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In this study the role of an Indian Ocean heating dipole anomaly in the transition of the North Atlantic European (NAE) circulation response to El Niño-Southern Oscillation (ENSO) from early to late winter is analyzed using 20th century reanalysis and simulations from the fifth Coupled Model Intercomparison Project (CMIP5). It is shown that in early winter a warm (cold) ENSO event is connected through an atmospheric bridge with positive (negative) rainfall anomalies in the western and negative (positive) anomalies in the eastern Indian Ocean. The early winter heating dipole, forced by a warm (cold) ENSO event, can set up a wave train emanating from the subtropical South Asian jet (SAJET) region that reaches the North Atlantic and leads to a response that spatially projects onto the positive (negative) phase of the North Atlantic Oscillation (NAO). The Indian Ocean heating dipole is partly forced as an atmospheric teleconnection by ENSO, but can also exist independently and is not strongly related to local Indian Ocean sea surface temperature (SST) forcing. The Indian Ocean heating dipole response to ENSO is much weaker in late winter (February and March) and not able to force significant signals in the North Atlantic region. CMIP5 multi-model ensemble reproduces the early winter Indian Ocean heating dipole response to ENSO and its transition in the North Atlantic region to some extent, but with weaker amplitude. Generally, models that have a strong early winter ENSO response in the subtropical SAJET region along with Tropical Indian Ocean heating dipole also reproduce the North Atlantic response.
... Meddi et al. (2010), based on the canonical analysis of correlations, revealed a link between the SOI, NINA4, and NAO climate indices and rainfall in northwestern Algeria both before and after 1975. In addition, many studies have shown that variations in precipitation variability in the Mediterranean basin are related to general atmospheric circulation patterns such as the El Niño Southern Oscillation (ENSO) (Kiladis and Diaz 1989;Meddi et al. 2010;Rodo et al. 1997;Knippertz et al. 2003;Lloyd-Hughes and Saunders 2002;Van Oldenborgh et al. 2000), the Mediterranean Oscillation (MO) (Conte et al. 1989), and the Western Mediterranean Oscillation (WeMO) (Martín-Vide and Lopez-Bustins 2006). For Algeria, Meddi et al. (2010) showed that the temporal variability of annual precipitation in the west is influenced by ENSO, but no other studies have reported the influence of general atmospheric circulation patterns on dry sequences in northern Algeria. ...
Article
The decrease in rainfall and the decrease in rainy days are also accompanied by a poor distribution of rainfall especially during the period of growth of the rain crops which usually extends from October to May. The Cheliff is under the influence of a semi-arid climate with precipitation that ranges from about 600 mm year−1 to the northeast and 300 mm year−1 to the west and south of the basin. The daily rainfall data used in this study concern eleven stations covering varying periods representative of different rainfall regimes in the Cheliff basin. The results obtained showed that the monthly dry sequences encountered during the rainy season decrease when the number of dry days increases, and the maximum values have been observed for the number of 1 to 7 consecutive dry days and the values were observed for a number greater than or equal to 21 consecutive dry days. It is important to say that the month of February recorded the lowest value of consecutive dry days for all stations. Also, the western stations of the study area display the largest values of the lengths of the dry sequences. Most of the stations are more correlated with the MO and AMO climatic indices than the other indices. These are the stations located west of the study area that are strongly correlated with AMO. It also appears that the total number of dry days of the stations located west of the study area is negatively correlated with SOI.
... Les effets sur le climat méditerranéen peuvent être constatés pendant la même saison ou avec un décalage de quelques mois selon le mécanisme de transport du signal d'ENSO. Des corrélations ont été observées entre ENSO et les précipitations de l'ouest de la Méditerranée pour l'automne et le printemps mais avec des signes opposés : en phase El Niño (phase chaude de ENSO) les précipitations de printemps sont plus faibles (Rodó et al., 1997, Van Oldenborgh et al., 2000, Mariotti et al., 2002, alors que les précipitations d'automne précédant la phase mature d'El Niño sont plus fortes d'environ 10% (Mariotti et al., 2005, Shaman et Tziperman, 2011 1931et 1960(Knippertz et al., 2003. Pour les précipitations d'hiver, Pozo-Vázquez et al. (2005) ont identifié un signal de La Niña (phase négative d'ENSO) dans des anomalies négatives dans le sud de l'Europe (plus prononcé dans le sud-ouest de la péninsule ibérique) du fait de trajectoires plus zonales des dépressions des moyennes latitudes et par conséquent moins de dépressions dans la Méditerranée. ...
Thesis
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L’étude du cycle de l’eau est d’une importance cruciale pour toutes les sociétés et plus particulièrement pour celles du pourtour méditerranéen qui souffrent à la fois de sécheresses en été et d’inondations dues à des événements de précipitations extrêmes survenant en automne et en hiver. La température est l’un des principaux facteurs qui gouvernent l’intensité maximale des précipitations via la relation de Clausius-Clapeyron (CC). Cette loi exprime la quantité maximale de vapeur d’eau que peut contenir l’atmosphère à une température donnée. À l’aide de simulations climatiques régionales et d’observations, nous avons montré que les relations température-précipitations extrêmes du bassin méditerranéen présentent une forme en crochet avec une augmentation des précipitations extrêmes proche de CC aux basses températures puis une augmentation moins forte (voire une diminution) aux hautes températures. Présents en grande quantité sur le pourtour méditerranéen, les aérosols absorbent et réfléchissent une partie du rayonnement, ce qui contribue à refroidir les basses couches de l’atmosphère. Par leur action sur la température de surface, les aérosols réduisent les précipitations. L’étude de simulations numériques montre également une modification de la relation température-précipitations par les aérosols (leur effet sur les nuages) dans la région euro-méditerranéenne. En plus de faire baisser le contenu en vapeur d'eau disponible, les aérosols stabilisent l’atmosphère en refroidissant davantage les basses couches de l’atmosphère par rapport aux couches supérieures. On étudie souvent la relation température-précipitations d’un climat donné dans le but de prédire l’évolution des précipitations dans un climat futur plus chaud. Cependant cette extrapolation suppose que la relation entre la température et les précipitations ne change pas entre le climat présent et le climat futur, une hypothèse qui s’avère fragile au vu de la sensibilité de cette relation au contenu en aérosols de l’atmosphère, mais aussi au vu du changement de la disponibilité en vapeur d’eau dans un climat futur. Au cours de cette thèse, nous avons ainsi montré que pour plusieurs stations côtières les projections dans le futur de plusieurs modèles de climat régionaux suggèrent que les précipitations extrêmes devraient augmenter proportionnellement à l’augmentation des températures selon la loi de CC. Un phénomène que nous n’avons pas pu observer pour des régions plus isolées de la mer et où l’afflux de vapeur d’eau serait moindre.
... Several studies correlate rainfall variability in the Mediterranean basin with the influence of general atmospheric circulation (van Oldenborgh et al., 2000;Lloyd-Hughes and Saunders, 2002;Knippertz et al., 2003;Xoplaki et al., 2004;López and Frances, 2010;Brandimarte et al., 2011). Meddi et al. (2010) and Taibi et al. (2017) highlighted a relationship between El Niño Southern Oscillation (ENSO) and annual rainfall variability over northwestern Algeria. ...
Article
Particular attention has been given in recent years to precipitation and variations in climate change scenarios by modeling these phenomena at different timescales. Regional climate models enable assessing the impact of climate change at the regional and local scales. This study aims, firstly, to analyze the rainfall variability in northern Algeria, and secondly, to evaluate future seasonal rainfall variability using regional climate models of the ENSEMBLE project. Statistical tests and the bias method have been used for this study. Analysis of rainfall variability using statistical tests during the reference period (1961-1990) reveals a significant decrease of rainfall since the 1970s at the Tenes and Oran stations, located in the northwest of Algeria. This decrease occurs during the months of December and January (in winter), and March and April (in spring), and is associated to a reduction of 10-20 and 20-50 mm of daily rainfall, respectively, while the rainfall increases in the eastern region. Simulated data of 12 regional climate models have been compared to observations carried out during the reference period (1961-1990) using the bias method. Future seasonal rainfall variability was analyzed for two projection periods: 2021-2050 and 2070-2099. Most often, models underestimate the wet seasons and overestimate the dry seasons during the reference period. The models simulated a significant decrease of future rainfall in winter and spring over the two projected periods. Further investigations must be conducted to explain the underestimation of the models. It is also important to reconsider uncertainties that affect the results of this study.
... Brönnimann (2007) noted that despite the large interevent and seasonal variability, the impact of ENSO on the European climate is robust. Most consistent signals of El Niño on the climatic features of Europe include a decrease in surface temperature over northeastern Europe (Brönnimann 2007 and references therein) and an increase in precipitation over central Europe (Van Oldenborgh et al. 2000;Brönnimann 2007). ...
Article
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The El Niño–Southern Oscillation (ENSO) is one of the dominant climate forcings affecting the interannual climate variability in many regions worldwide. Using the ERA-Interim monthly data for the period 1980–2016, for the first time the impact of the eastern Pacific (EP) and central Pacific (CP) El Niños on the climate of Iran is investigated. Results indicate that the ENSO cycle contributes to the interannual climate variability over Iran. Indeed, about 26% (23%) of the variance in annual precipitation over Iran is explained by annual SST changes in the Niño 3.4 region (annual changes of the Southern Oscillation Index). In spite of the seasonality of the ENSO signal and its interevent variability, annually all regions of Iran are anomalously wet during the EP El Niño, and dry during La Niña events. The CP El Niño events result in anomalously wet conditions over northwestern, northern, northeastern and western Iran, but dry conditions over central, eastern, southwestern, southern and southeastern Iran. However, the impact of the CP El Niño on the annual precipitation of Iran is not statistically significant, in contrast to the statistically significant impact of both La Niña and the EP El Niño. An equatorward displacement of the subtropical jet stream over Southwest Asia is found during the EP El Niño, while strengthening of the jet is found during La Niña, and they are statistically significant at the 95%95\% level. These changes in the position and intensity of the subtropical jet stream alter the position of the troughs and ridges of the Rossby waves and their speed, which contribute to the interannual climate variability over Iran. Equatorward displacement of the jet during the EP El Niño leads to the equatorward displacement of the Mediterranean storm track, while the intensified jet during La Niña weakens the quasi-stationary mid-tropospheric planetary waves.
... On seasonal timescales, anomalous atmospheric conditions are often linked with seasonal variations in the rivers streamflow, via variations in precipitation and temperature [Dettinger and Diaz, 2000;Cullen et al., 2002]. For example, spring and summer rainfall and temperatures anomalies across Europe may be forecasted from prior knowledge of varying boundary conditions such as anomalous sea surface temperature (SST) in the North Atlantic Ocean [Colman, 1997;Colman and Davey, 1999;Wilby, 2001] and/or the tropical Pacific Ocean [Kiladis and Diaz, 1989;Lloyd-Huges and Saunders, 2002;van Oldenborgh et al., 2000]. Spring precipitation over central Europe is higher than normal average following warm El Niño events combined with lower SSTs west of Ireland [Lloyd-Huges and Saunders, 2002]. ...
... This would indicate that USATOUR would increase during less rain events on Aruba, while HOLTOUR would increase during more rain events on Aruba. Previous research has shown that strong El Nino's could increase rain in the Netherlands during spring and that La Nina had no influence on the rain pattern on Holland [61]. This would indicate that a La Nina event would not act as a push factor on tourism demand from Holland, but more like a pull factor from Aruba. ...
Article
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This study estimates the influence of long cyclical climate patterns of pull and push climate elements (rainfall, temperature, wind) on cyclical fluctuations in tourism demand from the United States, the Netherlands and Venezuela on a small island state. Two important atmospheric variabilities, the El Niño Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO), were also included. Wavelet analysis was used because meteorological and economical time-series are typically noisy, complex and strongly non-stationary. Results show that both pull and push cyclical climate factors had an influence on tourism demand from the USA, the Netherlands and Venezuela. Furthermore, ENSO and NAO had also an influence on tourism demand from the USA and the Netherlands. The finding of a statistical relationship between atmospheric variabilities and tourism suggests that that they should be taken into account when developing tourism demand models, in order to create simpler econometric models.
... Then the westerly is blocked by the High Pressure belt and cold air accumulates. It becomes cold in Europe and in West Pacific Warm Pool because of their teleconnection[53]. The Qinghai-Tibet Plateau is also a vast refrigerator[54]. ...
Conference Paper
As the latest abrupt cold event, the study on the Younger Dryas event is important to forecast the change of future climate, especially to present global warming. So that what caused the event and how the event worldly spread is crucial to anticipate anything like that. Spatial distribution and relative timing of the Younger Dryas event are central for our understanding of causes and transferring mechanism of it. From the large numbers of the published works on the late Quaternary paleoclimatic research, the evidences of the Younger Dryas event were summarized and the accurate coordinates of these sites were put on the world map with Mapinfo software From more than 200 sites which have the event records, the onset, the termination and duration trend of it are figured and analyzed. The onset time of the event is different from 11.8 cal. ka B.P. to 13.7 cal. ka B.P. The mean value is 12.72 cal. ka B.P. The contour line of 12.8 cal. ka B.P. circle more than half of the earth, from Europe to Qinghai-Tibet Plateau, southwest Pacific, east Antarctica, South Africa, South Atlantic Ocean and South America. The earliest site is 13.7 cal. ka B.P. at MD01-2386 core, West Pacific Warm Pool and at AD91-17, South Adriatic Sea, not at Arctic region. The end time of the event is 7.8-12.53 cal. ka B.P., mean is 11.52 cal. ka B.P. The contour line of 11.5 cal. ka B.P. covers almost north Hemisphere except North Africa and west Pacific, from north to south total tread of the terminative time is younger. The terminative time of the event at continents is earlier than around oceans. The duration of the Younger Dryas event is 0.25-4.46 cal. ka, the mean value is 1.20 cal. ka. The areas more than 1.2 cal. ka is most in low latitude. At the North Africa and the West Pacific Warm Pool the duration is longer than at other places. While at high latitude it is shorter. The results indicate that the origin of the Younger Dryas event is at West Pacific Warm Pool. The trigger is Qinghai-Tibet Plateau. The changing of the atmosphere general circulation is the reason of the beginning and the ending of the event. And the signs of the event are transferred by the air circulation and ocean-air exchanging. Because special factors the local responses of the Younger Dryas event are diversity in different places.
... Although the climatological onset dates vary with regions, the inter annual variability of regional monsoon onset over most of Asia is partly affected by the ENSO . The European continent is located far from the tropical Pacific Ocean; however, climatic teleconnections of ENSO can still be sensed (Wilby, 1993;Fraedrich, 1994;Van Oldenborgh et al., 2000). During a typical El Niño, the Asian monsoon usually weakens and is pushed towards equator, often bringing summer drought to north-west and central regions of India and heavy rainfall in the north-east. ...
Article
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El Niño events are large climate disturbances which are originated in the equatorial Pacific Ocean, and occur in every 2 to 8 years. The developed phase of El Niño is characterized by unusual warm waters at the ocean surface, from the coasts of Peru and Ecuador to the center of the equatorial Pacific Ocean. This phenomenon is caused by strange weakening of the trade winds blowing westward, which allows warm surface waters to reverse their direction eastward. The climatic impacts of El Niño are amplifying throughout the world which can show several effects on regional weather. It is related with wide-ranging changes in the climate system and can lead to prominent socioeconomic impacts affecting infrastructure, agriculture, health and energy sectors. Even though El Niño appears in the region of tropical Pacific; it has impact on the global climate and weather phenomena such as drought/flooding and tropical storms. The normal status in the equatorial Pacific is changed due to the raise in greenhouse gases which in turn results in El Niño Southern Oscillation (ENSO) changes. We can assure that ENSO variations will endure and influence the global climatic conditions in the coming decades and centuries. Hence, forecasting and interpreting ENSO conditions are essential to both the scientists and the public. In this paper, the occurrence of El Niño and its impact on global climate and socioeconomic status has been studied and reviewed from literature.
... Thompson and Wallace, 1998) and due to a poten-tial ENSO (El Niño-Southern Oscillation) influence on Europe (e.g. Pozo-Vázquez et al., 2001;Halpert and Ropelewski, 1992;Fraedrich, 1994;Van Oldenborgh et al., 2000;Knippertz et al., 2003), we include also the Southern Oscillation (SO, e.g. Walker and Bliss, 1932). ...
Article
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The link between the indices of twelve atmospheric teleconnection patterns (mostly Northern Hemispheric) and gridded European temperature data is investigated by means of multiple linear regression models for each grid cell and month. Furthermore index-specific signals are calculated to estimate the contribution to temperature anomalies caused by each individual teleconnection pattern. To this extent, an observational product of monthly mean temperature (E-OBS), as well as monthly time series of teleconnection indices (CPC, NOAA) for the period 1951-2010 are evaluated. The stepwise regression approach is used to build grid cell based models for each month on the basis of the five most important teleconnection indices (NAO, EA, EAWR, SCAND, POLEUR), which are motivated by an exploratory correlation analysis. The temperature links are dominated by NAO and EA in Northern, Western, Central and South Western Europe, by EAWR during summer/autumn in Russia/Fenno-Scandia and by SCAND in Russia/Northern Europe; POLEUR shows minor effects only. In comparison to the climatological forecast, the presented linear regression models improve the temperature modelling by 30-40 % with better results in winter and spring. They can be used to model the spatial distribution and structure of observed temperature anomalies, where two to three patterns are the main contributors. As an example the estimated temperature signals induced by the teleconnection indices is shown for February 2010.
... Furthermore, many studies have shown that changes in rainfall variability in the Mediterranean Basin are related to general atmospheric circulation patterns such as the North Atlantic Oscillation (NAO) (Salameh 2008;Xoplaki et al. 2004;Lopez and Frances 2010;Brandimarte et al. 2011;Maheras et al. 1999;Dünkeloh and Jacobeit 2003), the El Niño Southern Oscillation (ENSO) (Kiladis and Diaz 1989;Meddi et al. 2010;Rodo et al. 1997;Knippertz et al. 2003b;Lloyd-Hughes and Saunders 2002;Van Oldenborgh et al. 2000), the Mediterranean Oscillation (MO) (Conte et al. 1989), and the Western Mediterranean Oscillation (WeMO) (Martín-Vide and Lopez-Bustins 2006). ...
Article
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This work aims, as a first step, to analyze rainfall variability in Northern Algeria, in particular extreme events, during the period from 1940 to 2010. Analysis of annual rainfall shows that stations in the northwest record a significant decrease in rainfall since the 1970s. Frequencies of rainy days for each percentile (5th, 10th, 25th, 50th, 75th, 90th, 95th, and 99th) and each rainfall interval class (1–5, 5–10, 10–20, 20– 50, and ≥50 mm) do not show a significant change in the evolution of daily rainfall. The Tenes station is the only one to show a significant decrease in the frequency of rainy days up to the 75th percentile and for the 10–20-mm interval class. There is no significant change in the temporal evolution of extreme events in the 90th, 95th, and 99th percentiles. The relationships between rainfall variability and general atmospheric circulation indices for interannual and extreme event variability are moderately influenced by the El Niño-Southern Oscillation and Mediterranean Oscillation. Significant correlations are observed between the Southern Oscillation Index and annual rainfall in the northwestern part of the study area, which is likely linked with the decrease in rainfall in this region. Seasonal rainfall in Northern Algeria is affected by the Mediterranean Oscillation and North Atlantic Oscillation in the west. The ENSEMBLES regional climate models (RCMs) are assessed using the bias method to test their ability to reproduce rainfall variability at different time scales. The Centre National de Recherches Météorologiques (CNRM),
... Furthermore, many studies have shown that changes in rainfall variability in the Mediterranean Basin are related to general atmospheric circulation patterns such as the North Atlantic Oscillation (NAO) (Salameh 2008;Xoplaki et al. 2004;Lopez and Frances 2010;Brandimarte et al. 2011;Maheras et al. 1999;Dünkeloh and Jacobeit 2003), the El Niño Southern Oscillation (ENSO) (Kiladis and Diaz 1989;Meddi et al. 2010;Rodo et al. 1997;Knippertz et al. 2003b;Lloyd-Hughes and Saunders 2002;Van Oldenborgh et al. 2000), the Mediterranean Oscillation (MO) (Conte et al. 1989), and the Western Mediterranean Oscillation (WeMO) (Martín-Vide and Lopez-Bustins 2006). ...
Article
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This work aims, as a first step, to analyze rainfall variability in Northern Algeria, in particular extreme events, during the period from 1940 to 2010. Analysis of annual rainfall shows that stations in the northwest record a significant decrease in rainfall since the 1970s. Frequencies of rainy days for each percentile (5th, 10th, 25th, 50th, 75th, 90th, 95th, and 99th) and each rainfall interval class (1–5, 5–10, 10–20, 20– 50, and ≥50 mm) do not show a significant change in the evolution of daily rainfall. The Tenes station is the only one to show a significant decrease in the frequency of rainy days up to the 75th percentile and for the 10–20-mm interval class. There is no significant change in the temporal evolution of extreme events in the 90th, 95th, and 99th percentiles. The relationships between rainfall variability and general atmospheric circulation indices for interannual and extreme event variability are moderately influenced by the El Niño-Southern Oscillation and Mediterranean Oscillation. Significant correlations are observed between the Southern Oscillation Index and annual rainfall in the northwestern part of the study area, which is likely linked with the decrease in rainfall in this region. Seasonal rainfall in Northern Algeria is affected by the Mediterranean Oscillation and North Atlantic Oscillation in the west. The ENSEMBLES regional climate models (RCMs) are assessed using the bias method to test their ability to reproduce rainfall variability at different time scales. The Centre National de Recherches Météorologiques (CNRM), Czech Hydrometeorological Institute (CHMI), Eidgenössische Technische Hochschule Zürich (ETHZ), and Forschungszentrum Geesthacht (GKSS) models yield the least biased results.
... ENSO influences on the Mediterranean are linked to different stages of the ENSO cycle, depend on the season, occur within the same season or with a time lag amounting to several months to seasons, and differ in the particular mechanisms of large-scale signal transport. Correlations between ENSO and western Mediterranean rainfall have been found for spring and autumn, but with opposite signs: spring rainfall following ENSO warm events is decreased (Rodó et al., 1997;van Oldenborgh et al., 2000;Mariotti et al., 2002), whereas autumn rainfall preceding the mature warm phase of ENSO is increased (Mariotti et al., 2005). There is also evidence for decadal changes of such links during the twentieth century. ...
... Elsewhere in Africa, drier than normal conditions persisted in the Mediterranean states, but a below-normal similar signal is evident for La Niña (Fig. 6b) and so may be spurious. In northeastern Europe areas of significantly high frequencies of above-normal precipitation remained patchy (Fraedrich 1994;Rodo et al. 1999;van Oldenborgh et al. 2000). The stronger signal in the Kazakhstan area shifted southward reaching into northern India. ...
Article
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Extreme phases of the El Niño-Southern Oscillation (ENSO) phenomenon have been blamed for precipitation anomalies in many areas of the world. In some areas the probability of above-normal precipitation may be increased during warm or cold events, while in others below-normal precipitation may be more likely. The percentages of times that seasonal precipitation over land areas was above, near, and below normal during the eight strongest El Niño and La Niña episodes are tabulated, and the significance levels of the posterior probabilities are calculated using the hypergeometric distribution. These frequencies may provide a useful starting point for probabilistic climate forecasts during strong ENSO events. Areas with significantly high or low frequencies or above-or below-normal precipitation are highlighted, and attempts are made to estimate the proportion of land areas with significant ENSO-related precipitation signals. There is a danger of overstating the global impact of ENSO events because only about 20%-30% of land areas experience significantly increased probabilities of above-or below-normal seasonal precipitation during at least some part of the year. Since different areas are affected at different times of the year, the fraction of global land affected in any particular season is only about 15%-25%. The danger of focusing on the impact of only warm-phase events is emphasized also: the global impact of La Niña seems to be at least as widespread as that of El Niño. Furthermore, there are a number of notable asymmetries in precipitation responses to El Niño and La Niña events. For many areas it should not be assumed that the typical climate anomaly of one ENSO extreme is likely to be the opposite of the other extreme. A high frequency of above-normal precipitation during strong El Niño conditions, for example, does not guarantee a high frequency of below-normal precipitation during La Niña events, or vice versa. On a global basis El Niño events are predominantly associated with below-normal seasonal precipitation over land, whereas La Niña events, result in a wider extent of above-normal precipitation.
... Par ailleurs, de nombreuses études ont montré que les variations du régime pluviométrique dans le bassin méditerranéen sont liées à la circulation atmosphérique générale tels que: l'Oscillation Nord Atlantique NAO (Salameh, 2008;Xoplaki et al., 2004;Lopez and Frances, 2010;Brandimarte et al., 2011) El Nino South Oscillation (ENSO) (Meddi et al., 2010;Kiladis and Diaz 1989;Rodo et al., 1997;Van Oldenborgh et al., 2000;Lloyd-Hughes and Saunders, 2002;Knippertz et al., 2003), MO (Mediterranean oscillation) (Conte et al., 1989) et WeMO (West Mediterranean Oscilation) (Martín-Vide and Lopez-Bustins, 2006). ...
Article
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Une analyse des pluies journalières extrêmes du bassin du Chéliff (plus grand bassin du Nord de l’Algérie) a été établie sur la période 1971–2010. Pour cela 13 stations pluviométriques ont été sélectionnées et recueillies auprès de l’Agence Nationale des Ressources Hydrauliques (ANRH). Six indices de pluies journalières ont été analysés pour caractériser l’évolution temporelle de la fréquence et l’intensité des pluies journalières sur la période d’étude. Ces indices correspondent à la pluie totale annuelle des jours de pluies ( ≥ 1 mm), aux percentiles 90, 95, 99 et 99.5% et à l’intensité journalière des jours de pluie (≥ 1 mm). Le test de Mann–Kendall indique une tendance générale à la baisse significative pour les pluies totales et l’intensité journalière de certaines stations. La fréquence des fortes pluies ne montre pas de changement significatif de son évolution temporelle pour la majorité des stations. La recherche de relation entre les indices de pluies journalières et les différents modes de circulation atmosphérique a mis en évidence l’influence de l’oscillation méditerranéenne sur la variabilité des précipitations journalières du Chéliff, particulièrement pour les stations qui ont connu une baisse significative de leur indice de pluies journalières.
... Greater incidence of ENSO exists on the temperature of the country. Key words: Climate variability, ENSO, Climate Explorer riables de ENOS, en escalas anual y trimestral, utilizando principalmente el software Climate Explorer [10], [11], disponible en: http://climexp.knmi. nl; todo esto, a fin de facilitar futuros estudios que puedan ser incluidos en los procesos de planificación de los recursos naturales ante los riesgos climáticos en el país. ...
Article
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El conocimiento de El Niño-Oscilación del Sur (ENOS) aún es parcial; las variaciones del clima colombiano y de eventos ENOS dificultan su entendimiento y la predicción de sus impactos. Esta investigación utilizó el Climate Explorer para establecer relaciones lineales entre la precipitación y la temperatura media del aire (anual y trimestral) de Colombia con variables asociadas a ENOS, entre 1975-2000. Se concluye que al centro, norte y occidente del país, El Niño (fase cálida) trae disminución de lluvias e incrementa la temperatura, lo contrario sucede durante La Niña. Mayores correlaciones significativas se obtuvieron con períodos trimestrales (principalmente en DEF) y rezagos alrededor de cero; éstas decaen en el trimestre MAM de las variables climatológicas; entre la precipitación y el índice IMENSO se obtuvieron mayores coeficientes en DEF (r=-0.44). Existe mayor incidencia de ENOS sobre la temperatura del país.
... En cap cas aquestes relacions apareixen -com succeeix amb la NAO-amb les pluges d'hivern (Quadrelli et al., 2001), sinó que estan centrades principalment a la primavera i la tardor, exactament aquelles èpoques on en conjunt les precipitacions són més abundants i importants de cara a la vegetació i els conreus. De forma similar, altres estudis recents (van Oldenborgh et al., 2000i Mariotti et al., 2002 també constaten aquestes respostes a l'ENSO en la precipitació i les temperatures, tant a la tardor com a la primavera, en la mateixa línia descrita anteriorment. A més, l'es-tudi de Mariotti et al. (2002) permet entendre una mica més quines són les estructures atmosfèriques que es formen durant aquests episodis sobre la península i la Mediterrània, així com a l'Atlàntic adjacent (figura A4.32). ...
... Positive values of winter PC2 of SPEI3 are also associated with negative SST anomalies in the central tropical Pacific flanked by positive SST anomalies in the central north Pacific and central south Pacific (Fig. 5e). This pattern resembles the SST pattern associated to the cold phase of El Niño-Southern Oscillation (ENSO) and it is consistent with the results of previous studies which showed that ENSO has a strong influence on the river streamflow in Europe (Rimbu et al. 2004;Ionita et al. 2008Ionita et al. , 2011Ionita et al. , 2012b, on precipitation over Europe (Mariotti et al. 2002;van Oldenborgh et al. 2000) and on diurnal temperature range over Europe (Ionita et al. 2012c). It is also consistent with the results presented in Sect. 3 showing that the time series of standardized coefficients of winter PC2 of SPEI3 is significantly correlated with the winter Niño 4 index (r = −0.22, ...
Article
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The relationship between the seasonal modes of interannual variability of a multiscalar drought index over Europe and the large-scale atmospheric circulation and sea surface temperature (SST) anomaly fields is investigated through statistical analysis of observed and reanalysis data. It is shown that the seasonal modes of dryness and wetness variability over Europe and their relationship with the large-scale atmospheric circulation and global SST anomaly fields differ from one season to another. During winter, the dominant modes of dryness and wetness variability are influenced by the Arctic Oscillation (AO)/North Atlantic Oscillation (NAO), the Scandinavian pattern, the East Atlantic pattern and the East Atlantic/Western Russia pattern. The spring dryness/wetness modes are influenced mainly by the AO, Polar/Eurasian patterns and the Atlantic Multidecadal Oscillation conditions. The phases (positive or negative) and the superposition of these large scale variability modes play a significant role in modulating the drought conditions over Europe. During summer, the atmospheric blocking is one of the main drivers of dryness and wetness conditions, while during autumn dryness/wetness conditions variability can be related to the NAO or with a wave train like pattern in the geopotential height at 850mb, which develops over the Atlantic Ocean and extends up to Siberia. It is also found that the response of the dryness and wetness conditions to global SST is more regional in summer, compared to the other seasons, when local processes may play a more important role.
... Together with the responses over the Pacific/America, the impact of ENSO over the North Atlantic and European regions has also been investigated by many researchers (van Loon and Madden, 1981;Rogers, 1984;Fraedrich, 1990;Huang et al., 1998;van Oldenborgh et al., 2000;Pozo-Vazquez et al., 2001). However, the statistical relationship seems to be not simple, with the results depending on the data period and season. ...
Article
The present study suggests that the off-equatorial North Atlantic (NATL) SST warming plays a significant role in modulating El Niño teleconnection and its impact on the North Atlantic and European regions. The El Niño events accompanied by NATL SST warming exhibit south-north dipole pattern over the Western Europe to Atlantic, while the ENSO teleconnection pattern without NATL warming exhibits a Rossby wave-like pattern confined over the North Pacific and western Atlantic. Especially, the El Niño events with NATL warming show positive (negative) geopotential-height anomalies over the North Atlantic (Western Europe) which resemble the negative phase of the NAO. Consistently, it is shown using a simple statistical model that NATL SSTA in addition to the tropical Pacific SSTA leads to better prediction on regional climate variation over the North Atlantic and European regions. This role of NATL SST on ENSO teleconnection is also validated and discussed in a long term simulation of coupled global circulation model (CGCM).
... Over the last few years, the quality of seasonal forecasts for average temperature conditions and precipitation totals have significantly improved, with our capacity to anticipate mean temperatures over land being higher in spring both in North America and in Europe [29,30]. The quality of seasonal climate forecasts increases during the development of El Niño events, particularly in the tropics. ...
Article
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The impact of climate change on human health is a serious concern. In particular, changes in the frequency and intensity of heat waves and cold spells are of high relevance in terms of mortality and morbidity. This demonstrates the urgent need for reliable early-warning systems to help authorities prepare and respond to emergency situations. In this study, we evaluate the performance of a climate-driven mortality model to provide probabilistic predictions of exceeding emergency mortality thresholds for heat wave and cold spell scenarios. Daily mortality data corresponding to 187 NUTS2 regions across 16 countries in Europe were obtained from 1998-2003. Data were aggregated to 54 larger regions in Europe, defined according to similarities in population structure and climate. Location-specific average mortality rates, at given temperature intervals over the time period, were modelled to account for the increased mortality observed during both high and low temperature extremes and differing comfort temperatures between regions. Model parameters were estimated in a Bayesian framework, in order to generate probabilistic simulations of mortality across Europe for time periods of interest. For the heat wave scenario (1-15 August 2003), the model was successfully able to anticipate the occurrence or non-occurrence of mortality rates exceeding the emergency threshold (75th percentile of the mortality distribution) for 89% of the 54 regions, given a probability decision threshold of 70%. For the cold spell scenario (1-15 January 2003), mortality events in 69% of the regions were correctly anticipated with a probability decision threshold of 70%. By using a more conservative decision threshold of 30%, this proportion increased to 87%. Overall, the model performed better for the heat wave scenario. By replacing observed temperature data in the model with forecast temperature, from state-of-the-art European forecasting systems, probabilistic mortality predictions could potentially be made several months ahead of imminent heat waves and cold spells.
... With regard to spring, connections have been found between La Niña and the droughts in the north-west of the Peninsula, although it appears that El Niño does not bring wet spring seasons [Lorenzo et al., 2010]. Mariotti et al. [2002] The ENSO is also related to winter precipitation in the east of the Peninsula [ van Oldenborgh et al., 2000], and surface pressure at the south-western IP is oppositely related to the Southern Oscillation index [Trenberth et al., 2007, see Fig. 3.27]. This relationship is explained by some authors on the basis of the NAO [Pozo-Vázquez, 2005a and b], establishing that there is a trend towards relative high Azores pressure in winter coincidence with La Niña events, causing a significant decrease of winter precipitation (December-January-February) over the IP. ...
... Greater incidence of ENSO exists on the temperature of the country. Key words: Climate variability, ENSO, Climate Explorer riables de ENOS, en escalas anual y trimestral, utilizando principalmente el software Climate Explorer [10], [11], disponible en: http://climexp.knmi. nl; todo esto, a fin de facilitar futuros estudios que puedan ser incluidos en los procesos de planificación de los recursos naturales ante los riesgos climáticos en el país. ...
Article
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The knowledge of the phenomenon El Niño Southern Oscillation (ENSO) still is partial, the variations in the Colombian climate and the ENSO events make difficult its understanding and the prediction of its impacts. This research used the Climate Explorer, to establish linear relations between the precipitation and the average temperature of the air (annual and quarterly) with associated variables to ENSO, between 1975 and 2000. It is concluded that in the center, north and west of the country, El Niño (warm phase) brings rain diminution and increases the temperature, the opposite happens during La Niña. Greater significant correlations obtained with quarterly periods (mainly in DJF) and lags around zero; which decay in trimester MAM of the climatological variables; between the precipitation and index IMENSO greater coefficients in DJF were obtained (r=-0.44). Greater incidence of ENSO exists on the temperature of the country.
... El ENSO también está relacionado con la precipitación de invierno en el este peninsular [van Oldenborgh et al., 2000]; de forma que la presión en superficie en el suroeste de la PI y el índice de la Oscilación del Sur están opuestamente relacionados [Trenberth et al., 2007, ver Fig. 3.27]. Esta relación es explicada por algunos autores a partir de la NAO [Pozo-Vázquez, 2005a y b], determinando que existe una tendencia hacia las altas presiones relativas durante el invierno en la zona de Azores en coincidencia con los eventos La Niña, ocasionando la disminución alrededor de un 25% en la precipitación de invierno (diciembreenero-febrero) en la PI. ...
Article
El Niño events are large climate disturbances which are originated within the equatorial Pacific, and occur in every 2 to eight years. The developed phase of El Niño is characterized by unusual warm waters at the ocean surface, from the coasts of Peru and Ecuador to the middle of the equatorial Pacific. This phenomenon is caused by strange weakening of the trade winds blowing westward, which allows warm surface waters to reverse their direction eastward. The climatic impacts of El Niño are amplifying throughout the planet which may show several effects on regional weather. it’s related with wide-ranging changes within the climate system and may cause prominent socio-economic impacts affecting infrastructure, agriculture, health and energy sectors. albeit El Niño appears within the region of tropical Pacific; it’s impact on the worldwide climate and weather phenomena like drought/flooding and tropical storms. the traditional status within the equatorial Pacific is modified due to the raise in greenhouse gases which in turn leads to El Niño Southern Oscillation (ENSO) changes. we are able to assure that ENSO variations will endure and influence the worldwide climate within the coming decades and centuries. Hence, forecasting and interpreting ENSO conditions are essential to both the scientists and therefore the public. during this paper, the occurrence of El Niño and its impact on global climate and socio-economic status has been studied and reviewed from literature.
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We investigate the climate signature of δ18O tree-ring records from sites distributed all over Europe covering the last 400 years. An empirical orthogonal function (EOF) analysis reveals two distinct modes of variability on the basis of the existing δ18O tree-ring records. The first mode is associated with anomaly patterns projecting onto the El Niño–Southern Oscillation (ENSO) and reflects a multi-seasonal climatic signal. The ENSO link is pronounced for the last 130 years, but it is found to be weak over the period from 1600 to 1850, suggesting that the relationship between ENSO and the European climate may not be stable over time. The second mode of δ18O variability, which captures a north–south dipole in the European δ18O tree-ring records, is related to a regional summer atmospheric circulation pattern, revealing a pronounced centre over the North Sea. Locally, the δ18O anomalies associated with this mode show the same (opposite) sign with temperature (precipitation). Based on the oxygen isotopic signature derived from tree rings, we argue that the prevailing large-scale atmospheric circulation patterns and the related teleconnections can be analysed beyond instrumental records.
Article
The impact of the wintertime El Niño-Southern Oscillation (ENSO) on European late spring climate is examined using an atmospheric general circulation model of intermediate complexity. The analysis is focused on the response of the lower stratosphere/upper troposphere, downward propagation of the ENSO signal detected in temperature, zonal wind and geopotential height and contribution of the North Atlantic to the persistence of the associated surface anomalies. It is found that the stratosphere responds to El Niño (La Niña) events with substantial warming (cooling) occurring in the polar area accompanied by a corresponding modification of upper-level geopotential heights and zonal winds resembling the pattern of the Northern Annular Mode. The atmospheric response is detected in the upper troposphere as well as at the surface where it interacts with the North Atlantic. In this way, the footprint of atmospheric wintertime ENSO signal is preserved in the ocean persisting until the following spring when it is transmitted back into the atmosphere through the sea–air interaction. Furthermore, it is showed here that the late springtime ENSO signal over Europe may be considered as a result of two contributing processes: one is a direct (spring-to-spring) ENSO influence and the other is a delayed (winter-to-spring) ENSO influence. Two processes enable the delayed ENSO impact: the persistence of the wintertime ENSO signal in the stratosphere and the atmosphere–ocean interaction in the North Atlantic. Numerical simulations indicate that the memory of the ocean mixed layer is stronger than that of the stratosphere. In this manner, the presented results emphasize the extratropical Atlantic as a contributing factor for climate variability linking wintertime atmospheric circulation associated with ENSO forcing and European climate during the following spring.
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Preparing for episodes with risks of anomalous weather a month to a year ahead is an important challenge for governments, non-governmental organisations, and private companies and is dependent on the availability of reliable forecasts. The majority of operational seasonal forecasts are made using process-based dynamical models, which are complex, computationally challenging and prone to biases. Empirical forecast approaches built on statistical models to represent physical processes offer an alternative to dynamical systems and can provide either a benchmark for comparison or independent supplementary forecasts. Here, we present a simple empirical system based on multiple linear regression for producing probabilistic forecasts of seasonal surface air temperature and precipitation across the globe. The global CO2-equivalent concentration is taken as the primary predictor; subsequent predictors, including large-scale modes of variability in the climate system and local-scale information, are selected on the basis of their physical relationship with the predictand. The focus given to the climate change signal as a source of skill and the probabilistic nature of the forecasts produced constitute a novel approach to global empirical prediction. Hindcasts for the period 1961–2013 are validated against observations using deterministic (correlation of seasonal means) and probabilistic (continuous rank probability skill scores) metrics. Good skill is found in many regions, particularly for surface air temperature and most notably in much of Europe during the spring and summer seasons. For precipitation, skill is generally limited to regions with known El Niño–Southern Oscillation (ENSO) teleconnections. The system is used in a quasi-operational framework to generate empirical seasonal forecasts on a monthly basis.
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The extreme precipitation that would result in historic flooding across areas of northeastern France and southern Germany began on May 26th when a large cut-off low spurred the development of several slow moving low pressure disturbances. The precipitation took different forms in each country. Warm and humid air from the south fueled sustained, large-scale, heavy rainfall over France resulting in significant river flooding on the Seine and Loire (and their tributaries), whereas the rain came from smaller clusters of intense thunderstorms in Germany triggering flash floods in mountainous areas. The floods left tens of thousands without power, caused over a billion Euros in damage in France alone, and are reported to have killed at least 18 people in Germany, France, Romania, and Belgium. The extreme nature of this event left many asking whether anthropogenic climate change may have played a role. To answer this question objectively, a rapid attribution analysis was performed in near-real time, using the best available observational data and climate models. In this rapid attribution study, where results were completed and released to the public in one week and an additional week to finalise this article, we present a first estimate of how anthropogenic climate change affected the likelihood of meteorological variables corresponding to the event, 3-day precipitation averaged over the Seine and Loire basins and the spatial maximum of 1-day precipitation over southern Germany (excluding the Alps). We find that the precipitation in the Seine basin was very rare in April–June, with a return time of hundreds of years in this season. It was less rare on the Loire, roughly 1 in 50 years in April–June. At a given location the return times for 1-day precipitation as heavy as the highest observed in southern Germany is 1 in 3000 years in April–June. This translates to once roughly every 20 years somewhere in this region and season. The probability of 3-day extreme rainfall in this season has increased by about a factor 2.3 (> 1.6) on the Seine a factor 2.0 (> 1.4) on the Loire, with all four climate models that simulated the statistical properties of the extremes agreeing. The observed trend of heavy 1-day precipitation in southern Germany is significantly negative, whereas the one model that has the correct distribution simulates a significant positive trend, making an attribution statement for these thunderstorms impossible at this time.
Article
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.
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Preparing for episodes with risks of anomalous weather a month to a year ahead is an important challenge for governments, NGOs and companies and relies on the availability of reliable forecasts. The majority of operational seasonal forecasts are made using process-based dynamical models, which are complex, computationally challenging and prone to biases. Empirical forecast approaches built on statistical models to represent physical processes offer an alternative to dynamical systems and can provide either a benchmark for comparison or independent supplementary forecasts. Here, we present a simple empirical system based on multiple linear regression for producing probabilistic forecasts of seasonal surface air temperature and precipitation across the globe. The global CO2-equivalent concentration is taken as the primary predictor; subsequent predictors, including large-scale modes of variability in the climate system and local-scale information, are selected on the basis of their physical relationship with the predictand. The focus given to the climate change signal as a source of skill and the probabilistic nature of the forecasts produced constitute a novel approach to global empirical prediction. Hindcasts for the period 1961–2013 are validated using correlation and skill scores. Good skill is found in many regions, particularly for surface air temperature and most notably in much of Europe during the spring and summer seasons. For precipitation, skill is generally limited to regions with known ENSO teleconnections. The system is used in a quasi-operational framework to generate empirical seasonal forecasts on a monthly basis.
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The daily rainfall extremes have been analyzed for 5 stations of Northern Algeria, over seventy years. The choice of these stations is based on the availability of long and complete daily rainfall series. Two classification methods have been used to analyze daily rainfall. Eight Percentiles indices of daily rainfall are considered in the first method: 5th, 10th, 25th, 50th, 75th, 90th, 95th and 99th. The second method is evaluated the number of wet day into five interval class of rainfall: 1-5 mm, 5-10 mm, 10-20 mm, 20-50mm, ≥ 50 mm. Theilsen slope and the linear regression show a general decreasing trend of the number of extreme events, but it is not significant. At each station the Kendall correlation has been used to search for correlations between the frequency of extreme rainfall events and climatic indices time series. The results show that the frequency of extreme rainfall events in Algiers are correlated with the Mediterranean Oscillation Index (MOI), while the stations of Annaba and Oran are better correlated with the Southern Oscillation Index (SOI).
Article
The relationship between the seasonal modes of interannual variability of a multiscalar drought index over Europe and the large-scale atmospheric circulation and sea surface temperature (SST) anomaly fields is investigated through statistical analysis of observed and reanalysis data. It is shown that the seasonal modes of dryness and wetness variability over Europe and their relationship with the large-scale atmospheric circulation and global SST anomaly fields differ from one season to another. During winter, the dominant modes of dryness and wetness variability are influenced by the Arctic Oscillation (AO)/North Atlantic Oscillation (NAO), the Scandinavian pattern, the East Atlantic pattern and the East Atlantic/Western Russia pattern. The spring dryness/wetness modes are influenced mainly by the AO, Polar/Eurasian patterns and the Atlantic Multidecadal Oscillation conditions. The phases (positive or negative) and the superposition of these large scale variability modes play a significant role in modulating the drought conditions over Europe. During summer, the atmospheric blocking is one of the main drivers of dryness and wetness conditions, while during autumn dryness/wetness conditions variability can be related to the NAO or with a wave train like pattern in the geopotential height at 850mb, which develops over the Atlantic Ocean and extends up to Siberia. It is also found that the response of the dryness and wetness conditions to global SST is more regional in summer, compared to the other seasons, when local processes may play a more important role.
Thesis
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The skill of seasonal precipitation forecasts is assessed worldwide —grid point by grid point— for the forty-year period 1961-2000, considering the ENSEMBLES multi-model hindcast and applying a tercile-based probabilistic approach in terms of the ROC Skill Score (ROCSS). Although predictability varies with region, season and lead-time, results indicate that 1) significant skill is mainly located in the tropics —20 to 40% of the total land areas,— 2) overall, SON (MAM) is the most (least) skillful season, and 3) the skill weakens (with respect to the one-month lead case) at four-month lead —especially in JJA,— although the ROCSS spatial patterns are broadly preserved —particularly in northern South America and the Malay archipelago.—[2] The contribution of ENSO events to this forty-year skill is also analyzed, based on the idea that the seasonal predictability may be mainly driven by El Niño and La Niña precipitation teleconnections and, consequently, limited by the ability of the different seasonal forecasting models to accurately reproduce them. Results show that the ROCSS spatial patterns for 1) the full period 1961-2000 and 2) El Niño and La Niña events are highly correlated –over 0.85.— Moreover, the observed teleconnection patterns are properly simulated (predicted) —with spatialcorrelations around 0.8— by most of the models at both one and four months lead-time.
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One of the major concerns with detecting global climate change is the quality of the data. Climate data are extremely sensitive to errant values and outliers. Prior to analysis of these time series, it is important to remove outliers in a methodical manner.This study provides statistically derived bounds for the uncertainty associated with surface temperature and precipitation measurements and yields a baseline dataset for validation of climate models as well as for a variety of other climatological uses. A two-step procedure using objective analysis was used to identify outliers. The first step was a temporal check that determines if a particular monthly value is consistent with other monthly values for the same station. The second step utilizes six different spatial interpolation techniques to estimate each monthly time series. Each of the methods is ranked according to its respective correlation coefficients with the actual time series, and the technique with the highest correlation coefficient is chosen as the best estimator. For both temperature and precipitation, a multiple regression scheme was found to be the best estimator for the majority of records. Results from the two steps are merged, and a combined set of quality control flags are generated.
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We present global fields of decadal annual surface temperature anomalies, referred to the period 1951-1980, for each decade from 1881-1890 to 1981-1990 and for 1984-1993. In addition, we show decadal calendar-seasonal anomaly fields for the warm decades 1936-1945 and 1981-1990. The fields are based on sea surface temperature (SST) and land surface air temperature data. The SSTs are corrected for the pre-World War II use of uninsulated sea temperature buckets and incorporate adjusted satellite-based SSTs from 1982 onward. The generally cold end of the nineteenth century and start to the twentieth century are confirmed, toegether with the substantial warming between about 1920 and 1940. Slight cooling of the northern hemisphere took place between the 1950s and the mid-1970s, although slight warming continued south of the equator. Recent warmth has been most marked over the northern continents in winter and spring, but the 1980s were warm almost everywhere. -from Authors
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Pressure data from Indonesia and Tahiti for years before 1866 are used to extend the Southern Oscillation index (SOI) back to 1841, with a gap between 1861 and 1865. Further extension is possible using an index of Jakarta rainday counts back to 1829. Rainday counts correlate (r = 0.60) with average Jakarta pressure for the June-November dry season over the 1876-1944 period. Although low, this correlation is still better than the correlation of tree rings with pressure or SOI. After 1950 the rainday count-pressure relationship alters, and by the 1990s 18% more raindays (an increase of seven per dry season) occur than the pressure would indicate. The dramatic increase in the size and population of Jakarta since 1950 is considered the most likely reason.
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We describe the global correlations between a measure of the S Oscillation and sea level pressure and surface air temperature in the northern winter. The stability of these correlations were tested on the N Hemisphere for an 80-yr period, and it turned out that most stable correlation coefficients were found over India, the N Pacific Ocean, the Rocky Mountains, and the central and western N Atlantic Ocean. On the S Hemisphere most records are too short for a similar test.-from Authors
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Composite temperature and precipitation anomalies during various stages of an event in the Southern Oscillation (SO) have been computed for several hundred stations across the globe. Large regions of coherent, significant signals are shown to exist for both extremes of the SO, with warm event signals generally opposite to those during cold events. In addition, during the year preceding the development of an event in the SO (year 1), climatic anomalies tend to be opposite to those during the following year (year 0). This confirms that the biennial tendency of the SO over the Pacific/Indian ocean sectors is also present in more remote regions with climatic signals related to the SO. Many of the signals are consistent enough from event to event to be useful for extended range forecasting purposes.
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An extension of the Tahiti minus Darwin Southern Oscillation Index (SOI) from 1882 back to 1876 is reported following the recovery of early Darwin mean sea-level pressure data spanning the period 1865-81. As a result, we are able to compare, for the first time, the major 1877-78 and 1982-83 ENSO events on the basis of this commonly used index. Early Darwin and Jakarta data are also examined in terms of a measure of the Australian response to documented El Niño and/or ENSO events in 1866, 1868, 1871, 1873, 1874 and 1875.The SOI during the 1877-78 ENSO event has a similar temporal response to that in 1982-83, but the index is slightly weaker than in the recent event. Examination of documentary evidence confirms the severity of the drought conditions that affected the Australian continent during the 1877-78 ENSO, and shows that this response is in line with the wider Indo-Pacific impacts reported in the literature. Earlier El Niño phases in 1868 and 1873 are not resolved distinctly in either the Darwin or Jakarta pressure data. This appears to illustrate that El Niño event histories do not always indicate wider ENSO influences in the Indo-Pacific basin, particularly during weak to moderate phases.
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Global analyses of monthly sea surface temperature (SST) anomalies from 1856 to 1991 are produced using three statistically based methods: optimal smoothing (OS), the Kaiman filter (KF) and optimal interpolation (OI). Each of these is accompanied by estimates of the error covariance of the analyzed fields. The spatial covariance function these methods require is estimated from the available data; the timemarching model is a first‐order autoregressive model again estimated from data. The data input for the analyses are monthly anomalies from the United Kingdom Meteorological Office historical sea surface temperature data set (MOHSST5) [ Parker et al. , 1994] of the Global Ocean Surface Temperature Atlas (GOSTA) [ Bottomley et al ., 1990]. These analyses are compared with each other, with GOSTA, and with an analysis generated by projection (P) onto a set of empirical orthogonal functions (as in Smith et al . [1996]). In theory, the quality of the analyses should rank in the order OS, KF, OI, P, and GOSTA. It is found that the first four give comparable results in the data‐rich periods (1951–1991), but at times when data is sparse the first three differ significantly from P and GOSTA. At these times the latter two often have extreme and fluctuating values, prima facie evidence of error. The statistical schemes are also verified against data not used in any of the analyses (proxy records derived from corals and air temperature records from coastal and island stations). We also present evidence that the analysis error estimates are indeed indicative of the quality of the products. At most times the OS and KF products are close to the OI product, but at times of especially poor coverage their use of information from other times is advantageous. The methods appear to reconstruct the major features of the global SST field from very sparse data. Comparison with other indications of the El Niño‐Southern Oscillation cycle show that the analyses provide usable information on interannual variability as far back as the 1860s.
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Measurements of temperature at the ocean surface are an indispensible part of the Global Climate Observing System (GCOS). We describe the varying coverage of these measurements from the mid-nineteenth century through to the present era of satellite data, along with ongoing attempts to augment the available digitized data base. We next survey attempts to remove systematic biases from both sea surface temperature (SST) and marine air temperature (MAT) data and to combinein situ and satellite SSTs in a consistent manner. We also describe new or planned geographically complete climatologies of SST and night MAT for 1961-90. These are expected to be more reliable than existing climatologies in the Southern Ocean and other sparsely-observed areas. The new SST climatology has been used in the construction of an improved geographically-complete data set of sea ice and SST: the techniques used are briefly reviewed, as are other methods of analysis and assessment of worldwide SST. We present global and regional time series of anomalies (i.e. deviations from reference climatology) of SST and night MAT for 1856 to 1994 constructed using the most complete data and best-estimate bias-corrections hitherto available. These series are compared with earlier published series, and are validated by means of comparisons with anomalies of air temperature from coastal and island stations. The sensitivity of the time series to imperfect coverage is assessed by means of frozen grid experiments. The results underscore the need for ongoing development of SST and MAT data bases within GCOS for the detection of climatic change, and for improved methods of analysis to optimally isolate the signals from incomplete data.
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Analysis of data from seventeen rainfall stations in the Iberian Peninsula, Balearic Islands and Northern Africa has revealed significant El Niño-Southern Oscillation (ENSO) signals in Europe. Both North Atlantic Oscillation (NAO) and Southern Oscillation (SO) exert an influence on Iberian climate, but at different temporal and spatial scales. Though most of the peninsula is under NAO influence in winter, some stations in the eastern region show no connection with this phenomenon. The same is found for ENSO, with a positively correlated region appearing in the eastern part of Spain, while the rest of the peninsula remains insensitive. The correlation between ENSO and Iberian rainfall has increased towards the end of the present century, with strong positive signals spanning over half of the area studied. The percentage of springtime variability due to ENSO has similarly increased, reaching up to 50% in certain areas. We also show how there are outstanding climatic sensors of these phenomena such as Lake Gallocanta, which manifests a positive response to ENSO while appears insensitive to NAO. Common long-term patterns are observed between SOI and an inferred lake level series, suggesting a constant influence of the low-frequency component of ENSO throughout the period considered. Lake drying phases every 14 years reflect the impact of this signal, approximately every four ENSO events.
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The possible influence of the El Nino/Southern Oscillation (ENSO) warm and cold extremes on mid-latitude circulation regimes in the North Atlantic/European sector is described in terms of a phenomenological, statistical and physical analysis of observational data. (1) The European circulation patterns (after Hess-Brezowsky, 1977) are combined to a binary set of cyclonic and anticyclonic (low and high pressure) centres of action. They reveal a regional ENSO response with predominantly cyclonic (anticyclonic) Grosswetter for warm (cold) ENSO events in winters at the peak of the episode. (2) Standard climate statistics of the same winter seasons (surface pressure, temperature and precipitation anomalies) supplement the Grosswetter phenomenology. They suggest a shift of the tail end of the cross Atlantic storm track and its rainbearing frontal systems from a more northern route (during warm events) to a more zonal orientation (in cold events). (3) Finally, the transient and stationary eddy–mean flow interaction is diagnosed from daily hemispheric 500 mb geopotential height fields. They are composited about most extreme anomalies in Europe (independent of ENSO) defined by the amplitude of the first simultaneous EOF of normalized monthly mean pressure, temperature and precipitation at 40 stations. Thus (upstream location and intensity of) dynamic sources of wave activity flux in the western North-Atlantic cyclogenesis area can be identified. They are associated with European climate anomalies and may represent the connection linking ENSO and Europe under favourable conditions. DOI: 10.1034/j.1600-0870.1994.00015.x
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The `typical' global and large-scale regional temperature patterns associated with the low (warm) and high (cold) phases of the Southern Oscillation (SO) are investigated. A total of 12 separate regions were found to have consistent temperature patterns associated with low phase of the SO, while 11 areas were found to have temperature patterns associated with the high phase. Of these areas, 9 have expected temperature patterns during both phases of the SO. In the tropics, temperature anomalies are of the same sign as the SO-related sea surface temperature (SST) anomaly in all land regions except for one area in the west Pacific. Three extratropical responses to the low phase of the SO are found over North America and one is found in Japan. High SO-temperature patterns were found in the extratropies for Japan, western Europe, and northwestern North America. The identified temperature responses are more consistent in tropical regions than in the extratropies. The SO can influence the estimation of global surface temperature anomalies.
Article
This is the first of two papers on Atlantic seasonal hurricane frequency. In this paper, seasonal hurricane frequency as related to El Nino events during 1900-82 and to the equatorial Quasi-Biennial Oscillation (QBO) of stratospheric zonal wind from 1950 to 1982 is discussed. It is shown that a substantial negative correlation is typically present between the seasonal number of hurricanes, hurricane days and tropical storms, and moderate or strong (15 cases) El Ninos off the South American West Coast. El Nino events are shown to be related to an anomalous increase in upper tropospheric westerly winds over the Carribean basin and the equatorial Atlantic. Such anomalous westerly winds inhibit tropical cyclone activity by increasing tropospheric vertical wind shear and giving rise to a regional upper level environment which is less anticyclonic and consequently less conducive to cyclone development and maintenance. The seasonal frequency of hurricane activity in storm basins elsewhere is much less affected by El Nino events and the QBO. Seasonal hurricane frequency in the Atlantic and the stratostrophic QBO is hypothesized to be associated with the trade wind nature of Atlantic cyclone formation. Tropical cyclone formation in the other storm basins is primarily associated with monsoon trough conditions which are absent in the Atlantic. Quasi Biennial Oscillation induced influences do not positively enhance monsoon trough region vorticity fields as they apparently do with cyclone formations within the trade winds. (from author's abstract)
Article
The primary focus of this review is tropical-extratropical interactions and especially the issues involved in determining the response of the extratropical atmosphere to tropical forcing associated with sea surface temperature (SST) anomalies. The review encompasses observations, empirical studies, theory and modeling of the extratropical teleconnections with a focus on developments over the Tropical Oceans-Global Atmosphere (TOGA) decade and the current state of understanding. In the tropical atmosphere, anomalous SSTs force anomalies in convection and large-scale overturning with subsidence in the descending branch of the local Hadley circulation. The resulting strong upper tropospheric divergence in the tropics and convergence in the subtropics act as a Rossby wave source. The climatological stationary planetary waves and associated jet streams, especially in the northern hemisphere, can make the total Rossby wave sources somewhat insensitive to the position of the tropical heating that induces them and thus can create preferred teleconnection response patterns, such as the Pacific-North American (PNA) pattern. However, a number of factors influence the dispersion and propagation of Rossby waves through the atmosphere, including zonal asymmetries in the climatological state, transients, and baroclinic and nonlinear effects. Internal midlatitude sources can amplify perturbations. Observations, modeling, and theory have clearly shown how storm tracks change in response to changes in quasi-stationary waves and how these changes generally feedback to maintain or strengthen the dominant perturbations through vorticity and momentum transports. The response of the extratropical atmosphere naturally induces changes in the underlying surface, so that there are changes in extratropical SSTs and changes in land surface hydrology and moisture availability that can feedback and influence the total response. Land surface processes are believed to be especially important in spring and summer. Anomalous SSTs and tropical forcing have tended to be strongest in the northern winter, and teleconnections in the southern hemisphere are weaker and more variable and thus more inclined to be masked by natural variability. Occasional strong forcing in seasons other than winter can produce strong and identifiable signals in the northern hemisphere and, because the noise of natural variability is less, the signal-to-noise ratio can be large. The relative importance of tropical versus extratropical SST forcings has been established through numerical experiments with atmospheric general circulation models (AGCMs). Predictability of anomalous circulation and associated surface temperature and precipitation in the extratropics is somewhat limited by the difficulty of finding a modest signal embedded in the high level of noise from natural variability in the extratropics, and the complexity and variety of the possible feedbacks. Accordingly, ensembles of AGCM runs and time averaging are needed to identify signals and make predictions. Strong anomalous tropical forcing provides opportunities for skillful forecasts, and the accuracy and usefulness of forecasts is expected to improve as the ability to forecast the anomalous SSTs improves, as models improve, and as the information available from the mean and the spread of ensemble forecasts is better utilized.
Article
Land-based compilations of gridded monthly surface air temperature anomalies, averaged into hemispheric values for the last 140 years, have been available for climatological analyses for the last 10 years or so. The analysis techniques used in their construction, particularly the need for a common reference period, mean that it is difficult to include, retrospectively, any of the new temperature datasets now available for some countries. So, despite data availability improvements in some areas, the number of stations used has fallen since 1970, both in the hemispheric averages and in their constituent grid-box datasets. The present study is a reanalysis of both the existing and the newly available temperature datasets to produce a grid-box dataset of 5{degrees} x 5{degrees} temperature anomalies. The reanalysis not only uses over 1000 more stations (2961 in total), principally covering the period from the 1920s to about 1990, but also arrests the decline of stations incorporated in real time for the latest years. Two hundred and fifty-two more stations are used in this analysis for the 1991-1993 period, compared with earlier analyses. The purpose of the reanalysis, however, is not just to calculate hemispheric averages. The improvements in station numbers used mean that the grid-box dataset should better estimate time series for small subcontinental scales. Despite the dramatic improvements in the numbers of stations used, the results change little from earlier analyses for the Northern Hemisphere average, indicating the robustness of the earlier time series. Similar results could have been achieved with as few as 109 stations. Over the Southern Hemisphere, comparisons of the results indicate larger (but still relatively small) differences with earlier analyses, particularly over continental-scale regions. 22 refs., 10 figs., 5 tabs.
Article
The possible influence of the El Niño/Southern Oscillation (ENSO) warm and cold extremes on mid-latitude circulation regimes in the North Atlantic/European sector is described in terms of a phenomenological, statistical and physical analysis of observational data. (1) The European circulation patterns (after Hess-Brezowsky, 1977) are combined to a binary set of cyclonic and anticyclonic (low and high pressure) centres of action. They reveal a regional ENSO response with predominantly cyclonic (anticyclonic) Grosswetter for warm (cold) ENSO events in winters at the peak of the episode. (2) Standard climate statistics of the same winter seasons (surface pressure, temperature and precipitation anomalies) supplement the Grosswetter phenomenology. They suggest a shift of the tail end of the cross Atlantic storm track and its rainbearing frontal systems from a more northern route (during warm events) to a more zonal orientation (in cold events). (3) Finally, the transient and stationary eddy–mean flow interaction is diagnosed from daily hemispheric 500 mb geopotential height fields. They are composited about most extreme anomalies in Europe (independent of ENSO) defined by the amplitude of the first simultaneous EOF of normalized monthly mean pressure, temperature and precipitation at 40 stations. Thus (upstream location and intensity of) dynamic sources of wave activity flux in the western North-Atlantic cyclogenesis area can be identified. They are associated with European climate anomalies and may represent the connection linking ENSO and Europe under favourable conditions.
Article
Reconstructions of monthly mean sea-level grid-point pressure from station pressure data over the Arctic region using an objective technique have revealed two serious errors in the gridded data. First, all gridded data (from the U.S. Historical Weather Map series) for the Arctic Ocean area away from the North Atlantic sector appears to be between 4 and 6 mb too high before about 1931. The semi-permanent Arctic high produced in the early historical map series was the result of a lack of basic station data, and the belief amongst many North American meteorologists of the 1920s and 1930s of the existence of a polar or glacial anticyclone. The second error affects only north-western North America for the years 1899–1909. Here pressure is again too high compared with reconstructed data. The cause of this error is not immediately apparent, but is probably the result of an erroneous correction to sea level for stations in the region. Both errors seriously affect the homogeneity of the gridded Arctic series. The objective scheme used to reveal the errors, can also be used to derive correction factors for the gridded data prior to 1931.
Article
The new NOAA operational global sea surface temperature (SST) analysis is described. The analyses use 7 days of in situ (ship and buoy) and satellite SST. These analyses are produced weekly and daily using optimum interpolation (OI) on a 1° grid. The OI technique requires the specification of data and analysis error statistics. These statistics are derived and show that the SST rms data errors from ships are almost twice as large as the data errors from buoys or satellites. In addition, the average e-folding spatial error scales have been found to be 850 km in the zonal direction and 615 km in the meridional direction. The analysis also includes a preliminary step that corrects any satellite biases relative to the in situ data using Poisson's equation. The importance of this correction is demonstrated using recent data following the 1991 eruptions of Mt. Pinatubo. The OI analysis has been computed using the in situ and bias-corrected satellite data for the period 1985 to present.
De6elopment of the Global Mean Sea Le6el Pressure Data Set GMSLP2, Climatic Research Technical Note 79 Hadley Centre Meteorological Office, Bracknell, UK. 16 pp plus Appendices
  • T A Basnett
  • D E Parker
Basnett, T.A. and Parker, D.E. 1997. De6elopment of the Global Mean Sea Le6el Pressure Data Set GMSLP2, Climatic Research Technical Note 79 Hadley Centre Meteorological Office, Bracknell, UK. 16 pp plus Appendices. Data are available from http://www.cru.uea.ac.uk/cru/data/pressure.htm
A further extension of the Tahiti-Darwin SOI, early SOI results and Darwin pressure', J. Climate, 4, 743{749. The series can be
  • R J Allan
  • N Nicholls
  • P D Jones
  • I J Butterworth
Allan, R. J., Nicholls, N., Jones, P. D., and Butterworth, I. J. 1991.`A further extension of the Tahiti-Darwin SOI, early SOI results and Darwin pressure', J. Climate, 4, 743{749. The series can be found at http://www.cru.uea.ac.uk/ cru/data/soi.htm.
The quality control of long-term climatological data using objective data analysis
  • C B Baker
  • J K Eischeid
  • T R Karl
  • H F Diaz
Baker, C. B., Eischeid, J. K., Karl, T. R., and Diaz, H. F. 1995.`The quality control of long-term climatological data using objective data analysis', in Preprints of AMS Ninth Conference on Applied Climatology Dallas TX, January 15{20 1995. American Meteorological Society, Boston, MA. The data are available from http://www.ncdc.noaa.gov/onlinedata/climatedata/ grid.prcp.seasanom.html.
Development of the global mean sea level pressure data set GMSLP2', Climatic Research Technical Note 79 Hadley Centre Meteorological O ce
  • T A Basnett
  • D E Parker
Basnett, T. A. and Parker, D. E. 1997.`Development of the global mean sea level pressure data set GMSLP2', Climatic Research Technical Note 79 Hadley Centre Meteorological O ce, Bracknell, U. K. 16pp plus Appendices. Data are available from http://www.cru.uea.ac.uk/cru/data/pressure.htm.