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Over the last 20 years, developments in climatology have provided an amazing array of explanations for the pattern of world climates. This textbook, first published in 2006, examines the earth's climate systems in light of this incredible growth in data availability, data retrieval systems, and satellite and computer applications. It considers regional climate anomalies, developments in teleconnections, unusual sequences of recent climate change, and human impacts upon the climate system. The physical climate forms the main part of the book, but it also considers social and economic aspects of the global climate system. This textbook has been derived from the authors' extensive experience of teaching climatology and atmospheric science. Each chapter contains an essay by a specialist in the field to enhance the understanding of selected topics. An extensive bibliography is included and lists of websites for further study. This textbook will be invaluable to advanced students of climatology and atmospheric science.

Seasonal mean atmospheric circulation in Europe can vary substantially from year to year. This diversity of conditions impacts many socioeconomic sectors. Teleconnection indices can be used to characterize this seasonal variability, while seasonal forecasts of those indices offer the opportunity to take adaptation actions a few months in advance. For instance, the North Atlantic Oscillation has proven useful as a proxy for atmospheric effects in several sectors, and dynamical forecasts of its evolution in winter have been shown skillful. However the NAO only characterizes part of this seasonal circulation anomalies, and other teleconnections such as the East Atlantic, the East Atlantic Western Russia or the Scandinavian Pattern also play an important role in shaping atmospheric conditions in the continent throughout the year. This paper explores the quality of seasonal forecasts of these four teleconnection indices for the four seasons of the year, derived from five different seasonal prediction systems. We find that several teleconnection indices can be skillfully predicted in advance in winter, spring and summer. We also show that there is no single prediction system that performs better than the others for all seasons and teleconnections, and that a multi-system approach produces results that are as good as the best of the systems. ; The research leading to these results has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement n° 776787 (S2S4E). ; Peer Reviewed ; Postprint (published version)

This study investigates how teleconnections linking tropical rainfall anomalies and wintertime circulation in the northern extra-tropics are represented in historical simulations for the period 1950–2010 run by partners of the EU-funded PRIMAVERA project, following the HighResMIP protocol of CMIP6. The analysis focusses on teleconnections from the western/central Indian Ocean in mid-winter and from the NINO4 region in both the early and the late part of winter; this choice is justified by a substantial change in the relationship between ENSO and the North Atlantic Oscillation (NAO) in the two parts of the season. Model results for both coupled integrations and runs with prescribed sea-surface temperature (SST) are validated against data from the latest ECMWF 20th-century re-analysis, CERA20C. Simulations from six modelling groups are considered, comparing the impact of increasing atmospheric resolution in runs with prescribed SST, and of moving from uncoupled to coupled simulations in the high-resolution version of each model. Single runs were available for each model configurations at the time of writing, with one centre (ECMWF) also providing a 6-member ensemble. Results from this ensemble are compared with those of a 6-member multi-model ensemble (MME) formed by including one simulation from each model. Using only a single historical simulation from each model configuration, it is difficult to detect a consistent change in the fidelity of model-generated teleconnections when either atmospheric resolution is increased or ocean coupling is introduced. However, when simulations from six different models are pooled together in the MME, some improvements in teleconnection patterns can be seen when moving from uncoupled to coupled simulations. For the ECMWF ensemble, improvements in the coupled simulations are only apparent for the late-winter NINO4 teleconnection. While the Indian Ocean teleconnection and the late-winter NINO4 teleconnection appear equally robust in the re-analysis record, the latter is well simulated in the majority of both uncoupled and coupled runs, while the former is reproduced with (generally) much larger errors, and a high degree of variability between individual models and ensemble members. Most of the simulations with prescribed SST fail to produce a realistic estimate of multi-decadal changes between the first and the second part of the 60-year record. This is (at least partially) due to their inability to simulate an Indian Ocean rainfall change which, in observations, has a zonal gradient out of phase with SST changes. In coupled runs, at least one model run with both realistic teleconnections and a good simulation of the inter-decadal pattern of Indian Ocean rainfall also shows a realistic NAO signal in extratropical multi-decadal variability. ; The simulations and diagnostics described in this paper have been funded by the European Union Horizon 2020 PRIMAVERA project, grant agreement no. 641727. Model output from the PRIMAVERA simulations can be accessed from the archive of the Centre for Environmental Data Analysis (CEDA). Re-analysis data from CERA20C is available from the European Centre for Medium-Range Weather Forecasts (ECMWF). ; Peer Reviewed ; Postprint (published version)

The goal of this analysis is the better understanding of how the large-scale atmospheric patterns affect the renewable resources over Europe and to investigate to what extent the dynamical predictions of the large-scale variability might be used to formulate empirical prediction of local climate conditions (relevant for the energy sector). The increasing integration of renewable energy into the power mix is making the electricity supply more vulnerable to climate variability, therefore increasing the need for skillful weather and climate predictions. Forecasting seasonal variations of energy relevant climate variables can help the transition to renewable energy and the entire energy industry to make better informed decision-making. At seasonal timescale climate variability can be described by recurring and persistent, large-scale patterns of atmospheric pressure and circulation anomalies that interest vast geographical areas. The main patterns of the North Atlantic region (Euro Atlantic Teleconnections, EATCs) drive variations in the surface climate over Europe. We analyze reanalysis dataset ERA5 and the multi-system seasonal forecast service provided by Copernicus Climate Change Service (C3S). We found that the observed EATC indices are strongly correlated with surface variables. However, the observed relationship between EATC patterns and surface impacts is not accurately reproduced by seasonal prediction systems. This opens the door to employ hybrid dynamical-statistical methods. The idea consists in combining the dynamical seasonal predictions of EATC indices with the observed relationship between EATCs and surface variables. We reconstructed the surface anomalies for multiple seasonal prediction systems and benchmarked these hybrid forecasts with the direct variable forecasts from the systems and also with the climatology. The analysis suggests that hybrid methodology can bring several improvements to the predictions of energy relevant Essential Climate Variables. ; This work was supported by the European Union's Horizon 2020 research and innovation programme [Grant Numbers. No 776787, H2020 S2S4E] and by the National Italian project PAR 2019–2021 1.8 'Energia dal Mare'. ; Peer Reviewed ; Postprint (published version)

Climate variability, predictability, and change : an introduction -- Overview : thermal regimes -- Global climate change impact on the midwestern USA--a summer cooling trend -- Historical and projected changes in the length of the frost-free season -- Long-term midwestern USA summer equivalent temperature variability -- Estimating changes in temperature variability in a future climate -- Wisconsin's changing climate : temperature -- Overview : hydrologic regimes -- Did precipitation regimes change during the twentieth century? -- Climate change and streamflow in the upper Mississippi River Basin -- The influence of land cover type on surface hydrology in Michigan -- Wisconsin's changing climate : hydrologic cycle -- Spatial and temporal dimensions of extreme rainfall in the Twin Cities metropolitan area -- Overview : North American atmospheric circulation effects on midwestern USA climate -- Historical trends in near-surface wind speeds -- Variability of wind speed regimes in Minnesota -- Teleconnections and circulation patterns in the midwestern USA -- Regional synoptic classification: a midwestern USA example -- Overview : climate hazards -- Severe storms in the midwestern USA -- Climate sensitivity of Great Lakes-generated weather systems -- Severe weather hazards in the Twin Cities metropolitan area -- Where is climate science in the midwestern USA going?

El Niño Southern Oscillation (ENSO) represents the major driver of interannual climate variability at global scale. Observational and model-based studies have fostered a long-standing debate on the shape and intensity of the ENSO influence over the Euro-Mediterranean sector. Indeed, the detection of this signal is strongly affected by the large internal variability that characterizes the atmospheric circulation in the North Atlantic–European (NAE) region. This study explores if and how the low-frequency variability of North Pacific sea surface temperature (SST) may impact the El Niño-NAE teleconnection in late winter, which consists of a dipolar pattern between middle and high latitudes. A set of idealized atmosphere-only experiments, prescribing different phases of the anomalous SST linked to the Pacific Decadal Oscillation (PDO) superimposed onto an El Niño-like forcing in the tropical Pacific, has been performed in a multi-model framework, in order to assess the potential modulation of the positive ENSO signal. The modelling results suggest, in agreement with observational estimates, that the PDO negative phase (PDO−) may enhance the amplitude of the El Niño-NAE teleconnection, while the dynamics involved appear to be unaltered. On the other hand, the modulating role of the PDO positive phase (PDO+) is not reliable across models. This finding is consistent with the atmospheric response to the PDO itself, which is robust and statistically significant only for PDO−. Its modulation seems to rely on the enhanced meridional SST gradient and the related turbulent heat-flux released along the Kuroshio–Oyashio extension. PDO− weakens the North Pacific jet, whereby favoring more poleward propagation of wave activity, strengthening the El Niño-forced Rossby wave-train. These results imply that there might be conditional predictability for the interannual Euro-Mediterranean climate variability depending on the background state. ; This work has been performed in the framework of the MEDSCOPE (MEDiterranean Services Chain based on climate PrEdictions) ERA4CS project (grant agreement no. 690462) funded by the European Union. J.G.-S. was supported by the "Ramón y Cajal" programme (RYC-2016-21181). F.M.P. was partially supported by the Spanish DANAE (CGL2015-68342-R) and GRAVITOCAST (ERC2018-092835) projects. We greatly thank the two anonymous reviewers for the insightful and constructive comments and suggestions. ; Postprint (published version)

All aspects of human life are, directly or indirectly, affected by climatic processes. This effect is especially noticeable in such fields as agriculture, irrigation, economy, telecommunications, transportation, traffic, air pollution and military industries (Haltiner & Williams 1980). A number of researchers have studied the possibility of forecasting rainfall several months in advance using climate indices such as SOI, PDOI and NPI (e.g. Silverman and Dracup 2000). A well-known atmospheric phenomenon is the Southern Oscillation (SO). The SO is an atmospheric see-saw process in the tropical Pacific sea level pressure between the eastern and western hemispheres associated with the El Niño and La Niña oceanographic features. The oscillation can be characterized by a simple index, the Southern Oscillation Index (SOI). (Kawamura et al., 1998). The Pacific Decadal Oscillation index (PDOI) is the leading principal component of monthly sea surface temperature (SST) anomalies in the North Pacific Ocean north of 20°N (Zhang et al., 1997; Mantua et al., 1997). Trenberth and Hurrell (1994) have defined the North Pacific Index (NPI) as the area-weighted sea level pressure over the region 30°N to 65°N, 160°E to 140°W to measure the decadal variations of atmosphere and ocean in the north Pacific. ; https://digitalcommons.usu.edu/modern_climatology/1013/thumbnail.jpg

Abstract. The link between winter (December-January-February) precipitation events at 15 Mediterranean coastal locations and synoptic features (cyclones and Northern Hemisphere teleconnection patterns) is analyzed. A list of precipitation events has been produced; q percentile thresholds (Thq) and corresponding frequency Nq (for q equal to 25, 50, 90 and 98) have been considered. A negative trend has been detected in total precipitation and N50 at many locations, while no significant trend in N25, N90 and N98 has been found. The negative phase of the North Atlantic Oscillation (NAO) and the East Atlantic/West Russia pattern (EAWR) compete for exerting the largest influence on the frequency of the 25th, 50th and 90th percentiles, with EAWR and NAO exerting their largest influence in the central and western Mediterranean areas, respectively. All percentiles show a similar behavior except for the 98th percentile, which shows no convincing link to any teleconnection pattern. The cyclone tracks that are associated with precipitation events have been selected using the ERA-40 reanalysis data, and a strong link between intense precipitation and cyclones is shown for all stations. In general, the probability of detecting a cyclone within a distance of 20° from each station increases with the intensity of the precipitation event and decreases with the duration of a dry period. The origin and track of cyclones producing intense precipitation differ among different areas. When precipitation occurs in the northwestern Mediterranean, cyclones are generally either of Atlantic origin or secondary cyclones associated with the passage of major cyclones north of the Mediterranean Basin, while they are mostly generated inside the region itself for events at the eastern Mediterranean coast. An important fraction of intense events in the southern areas is produced by cyclones that are generated over northern Africa. The analysis of sea level pressure and geopotential height at 500 hPa highlights the important role of cyclone depth, circulation strength, surrounding synoptic condition, and of slow speed of the cyclone center for producing intense precipitation events.

European winter weather is dominated by several low-frequency teleconnection patterns, the main ones being the North Atlantic Oscillation, East Atlantic, East Atlantic/Western Russia, and Scandinavian patterns. We analyze the century-long ERA-20C reanalysis and ASF-20C seasonal hindcast data sets and find that these patterns are subject to decadal variability and fluctuations in predictive skill. Using indices for determining periods of extreme cold or warm temperatures, we establish that the teleconnection patterns are, for some regions, significantly correlated or anti-correlated to cold or heat waves. The seasonal hindcasts are however only partly able to capture these relationships. There do not seem to be significant changes to the observed links between large-scale circulation patterns and extreme temperatures between periods of higher and lower predictive skill. ; The authors have received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 776787 (S2S4E). The authors thank three anonymous reviewers for their comments, which helped us to improve and clarify this manuscript. ; Peer Reviewed ; Postprint (published version)

El Niño-Southern Oscillation (ENSO) is the dominant mode of climate variability, affecting climate conditions over large areas of the globe. There are, however, substantial differences in how ENSO teleconnections with regional climate variability are represented in different datasets such as gridded observations and climate models. Here we examine the global responses of temperature and precipitation over land to ENSO within a hierarchy of datasets with different levels of observational constraints. Anomaly maps of observed El Niño and La Niña responses are compared to reanalysis, atmospheric models driven by observed sea surface temperature (SST), and coupled atmosphere–ocean general circulation models. There is a gradual decline in anomaly pattern agreement relative to observations moving down the dataset hierarchy to lower observational constraints. We find a positive relationship between the models' fidelity in representing ENSO temperature and precipitation, though the relationship is stronger for El Niño teleconnections than La Niña. The models also reproduce El Niño response patterns with greater fidelity than La Niña patterns. Additionally, the fidelity of model-simulated responses to El Niño is related to the magnitude of SST variability in the tropical Pacific, but no such relationship could be found for La Niña responses. This comprehensive evaluation highlights the importance of realistically simulating atmospheric circulation and SST variability to better capturing the patterns of regional climate variability in response to ENSO in climate models. ; This study was supported by funding from the Australian Research Council Centre for Climate Extremes and Climate Change Research Centre, University of New South Wales, Sydney, Australia. This project was undertaken with the assistance of resources and services from the National Computational Infrastructure (NCI), which is supported by the Australian Government. AST is supported by the Australian Research Council (FT160100465). We thank the reviewers for their constructive comments and suggestions that contributed to the improvement of this study. ; Peer Reviewed ; Postprint (author's final draft)

The impact of El Niño-Southern Oscillation (ENSO) on the late-winter extra-tropical stratosphere (January–March) is assessed in a multi-model framework. Three state-of-the-art atmospheric models are run with prescribed SST anomalies representative of a strong ENSO event, with symmetric patterns for El Niño and La Niña. The well-known temperature perturbation in the lower stratosphere during El Niño is captured by two models, in which the anomalous warming at polar latitudes is accompanied by a positive geopotential height anomaly that extends over the polar cap. In the third model, which shows a lack of temperature anomalies over the pole, the anomalous anticyclone is confined over Canada and does not expand to the polar cap. This anomalous center of action emerges from the large-scale tropospheric Rossby wave train forced by ENSO, and shrinking/stretching around the polar vortex is invoked to link it to the temperature response. No disagreement across models is found in the lower stratosphere for La Niña, whose teleconnection is opposite in sign but weaker. In the middle-upper stratosphere (above 50 hPa) the geopotential height anomalies project on a wavenumber-1 (WN1) pattern for both El Niño and, more weakly, La Niña, and show a westward tilt with height up to the stratopause. It is suggested that this WN1 pattern arises from the high-latitude lower-stratospheric anomalies, and that the ENSO teleconnection to the polar stratosphere can be interpreted in terms of upward propagation of the stationary Rossby wave train and quasi-geostrophic balance, instead of wave breaking. ; This work was supported by the MEDSCOPE project. MEDSCOPE is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by AEMET (ES), ANR (FR), BSC (ES), CMCC (IT), CNR (IT), IMR (BE) and Météo-France (FR), with co-funding by the European Union (Grant 690462). B.M. and J.G.-S. were supported by the "Contratos Predoctorales para la Formación de Doctores" (BES-2016-076431) and "Ramón y Cajal" (RYC-2016-21181) programmes, respectively. F.M.P. was partially supported by the Spanish DANAE (CGL2015-68342-R) and GRAVITOCAST (ERC2018-092835) projects. Technical support at BSC (Computational Earth Sciences group) is sincerely acknowledged. We also thank the two anonymous reviewers for their helpful feedback. ; Peer Reviewed ; Postprint (published version)

The Madden–Julian oscillation (MJO), a prominent feature of the tropical atmospheric circulation at subseasonal time scales, is known to modulate atmospheric variability in the Euro-Atlantic region. However, current subseasonal prediction systems fail to accurately reproduce the physical processes involved in these teleconnection mechanisms. This paper explores the observed impact of strong MJO events on surface wind speed over Europe. It is found that some MJO phases are accompanied by strong wind anomalies in Europe. After showing that this teleconnective mechanism is not present in the predictions of the ECMWF monthly forecasting system, a methodology to reconstruct forecasts of daily mean wind speed in the continent weeks ahead is proposed. This method combines MJO forecasts from the S2S project database and the observed teleconnection impacts in the historical records. Although it is found that strong MJO events cannot be skillfully predicted more than 10 days ahead with current prediction systems, a theoretical experiment shows that this method can effectively transform a dynamical MJO forecast into a probabilistic wind speed prediction in Europe. ; The research leading to these results has received funding from the European Union's Horizon 2020 research and innovation program under Grant 776787 (S2S4E) and from the Ministerio de Ciencia, Innovación y Universidades (MICINN) as part of the CLINSA project (CGL2017-85791-R). The authors acknowledge Australian Bureau of Meteorology for providing the MJO RMM historical indices, and the S2S project for providing the MJO indices from ECMWF MFS forecasts and ERA-Interim. The authors want to thank Nicolau Manubens for technical support with the startR R package, which allows processing big memory arrays by chunks in a cluster and then merges the results back together. Many analyses would have not been possible without this package. The CSTools R package was also used to produce some figures. Pierre-Antoine Bretonnière and Margarida Samsó helped downloading and formatting the surface wind datasets. The authors want to thank Frederic Vitart and Laura Ferranti for helping with the interpretation of some results, and Verónica Torralba for helping to structure the material. ; Peer Reviewed ; Postprint (published version)

El Niño-Southern Oscillation (ENSO) is known to affect the Northern Hemisphere tropospheric circulation in late-winter (January–March), but whether El Niño and La Niña lead to symmetric impacts and with the same underlying dynamics remains unclear, particularly in the North Atlantic. Three state-of-the-art atmospheric models forced by symmetric anomalous sea surface temperature (SST) patterns, mimicking strong ENSO events, are used to robustly diagnose symmetries and asymmetries in the extra-tropical ENSO response. Asymmetries arise in the sea-level pressure (SLP) response over the North Pacific and North Atlantic, as the response to La Niña tends to be weaker and shifted westward with respect to that of El Niño. The difference in amplitude can be traced back to the distinct energy available for the two ENSO phases associated with the non-linear diabatic heating response to the total SST field. The longitudinal shift is embedded into the large-scale Rossby wave train triggered from the tropical Pacific, as its anomalies in the upper troposphere show a similar westward displacement in La Niña compared to El Niño. To fully explain this shift, the response in tropical convection and the related anomalous upper-level divergence have to be considered together with the climatological vorticity gradient of the subtropical jet, i.e. diagnosing the tropical Rossby wave source. In the North Atlantic, the ENSO-forced SLP signal is a well-known dipole between middle and high latitudes, different from the North Atlantic Oscillation, whose asymmetry is not indicative of distinct mechanisms driving the teleconnection for El Niño and La Niña. ; This work was supported by the MEDSCOPE project. MEDSCOPE is part of ERA4CS, an ERA-NET initiated by JPI Climate, and funded by AEMET (ES), ANR (FR), BSC (ES), CMCC (IT), CNR (IT), IMR (BE) and Météo-France (FR), with co-funding by the European Union (Grant 690462). B.M. and J.G.-S. were supported by the "Contratos Predoctorales para la Formación de Doctores" (BES-2016-076431) and "Ramón y Cajal" (RYC-2016-21181) programmes, respectively. F.M.P. was partially supported by the Spanish DANAE (CGL2015-68342-R) and GRAVITOCAST (ERC2018-092835) projects. Technical support at BSC (Computational Earth Sciences group) is sincerely acknowledged. We also thank four anonymous reviewers for their valuable insights. ; Peer Reviewed ; Postprint (published version)

Atlantic multidecadal variability (AMV) has been linked to the observed slowdown of global warming over 1998–2012 through its impact on the tropical Pacific. Given the global importance of tropical Pacific variability, better understanding this Atlantic–Pacific teleconnection is key for improving climate predictions, but the robustness and strength of this link are uncertain. Analyzing a multi-model set of sensitivity experiments, we find that models differ by a factor of 10 in simulating the amplitude of the Equatorial Pacific cooling response to observed AMV warming. The inter-model spread is mainly driven by different amounts of moist static energy injection from the tropical Atlantic surface into the upper troposphere. We reduce this inter-model uncertainty by analytically correcting models for their mean precipitation biases and we quantify that, following an observed 0.26 °C AMV warming, the equatorial Pacific cools by 0.11 °C with an inter-model standard deviation of 0.03 °C. ; Y.R.-R. was founded by the European Union's Horizon 2020 Research and Innovation Program in the framework of the Marie Skłodowska-Curie grant INADEC (Grant agreement 800154). E.M.-C. acknowledges funding from the European Commission's Horizon 2020 projects PRIMAVERA (Grant Agreement 641727). X.L. has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement H2020-MSCA-COFUND-2016-754433. A.B. and D.N. acknowledge funding from the European Commission's Horizon 2020 project EUCP (Grant agreement 776613). F.C. and G.D. were supported by the US National Science Foundation (NSF) under the Collaborative Research EaSM2 Grant OCE-1243015 to NCAR and by the US National Oceanic and Atmospheric Administration (NOAA) Climate Program Office under the Climate Variability and Predictability Program Grant NA13OAR4310138. NCAR is a major facility sponsored by the US NSF under Cooperative Agreement 1852977. Acknowledgments are made for the use of ECMWF's computing and archive facilities in this research, in particular, P.D. thanks ECMWF for providing computing time in the framework of the special project SPITDAVI. R.E., N.D., L.H., and D.S. were supported by the Met Office Hadley Center 522 Climate Program funded by BEIS and Defra and by the European Commission Horizon 2020 EUCP 523 project (GA 776613). J.L.-P. was funded by the European Union's Horizon 2020 Research and Innovation Program in the framework of the PRIMAVERA project (Grant Agreement 641727). J.R. and D.H. were funded by NERC via NCAS and the ACSIS project (NE/N018001/1), and JR was also funded by the NERC SMURPHS project (NE/N006054/1). M.M.-R. was funded by the European Union's Horizon 2020 Research and Innovation Program in the framework of the Marie Skłodowska-Curie grant FESTIVAL (Grant agreement 797236). E.T. has received funding from the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No. 748750 (SPFireSD project). The analysis and plots of this paper were performed with the NCAR Command Language (Version 6.6.2; 2019)67. ; Peer Reviewed ; "Article signat per 25 autors/es: Yohan Ruprich-Robert, Eduardo Moreno-Chamarro, Xavier Levine, Alessio Bellucci, Christophe Cassou, Frederic Castruccio, Paolo Davini, Rosie Eade, Guillaume Gastineau, Leon Hermanson, Dan Hodson, Katja Lohmann, Jorge Lopez-Parages, Paul-Arthur Monerie, Dario Nicolì, Said Qasmi, Christopher D. Roberts, Emilia Sanchez-Gomez, Gokhan Danabasoglu, Nick Dunstone, Marta Martin-Rey, Rym Msadek, Jon Robson, Doug Smith & Etienne Tourigny " ; Postprint (author's final draft)

Mountain systems within the Mediterranean region, e.g., the Pyrenees, are very sensitive to climate change. In the present study, we quantified the magnitude of extreme precipitation events and the number of days with torrential precipitation (daily precipitation ≥ 100 mm) in all the rain gauges available in the Pyrenees for the 1981-2015 period, analyzing the contribution of the synoptic scale in this type of event. The easternmost (under Mediterranean influence) and north-westernmost (under Atlantic influence) areas of the Pyrenees registered the highest number of torrential events. The heaviest events are expected in the eastern part, i.e., 400 mm day−1 for a return period of 200 years. Northerly advections over the Iberian Peninsula, which present a low zonal index, i.e., implying a stronger meridional component, give rise to torrential events over the western Pyrenees; and easterly advections favour extreme precipitation over the eastern Pyrenees. The air mass travels a long way, from the east coast of North America, bringing heavy rainfall to the western Pyrenees. In the case of the torrential events over the eastern Pyrenees, the trajectory of the air mass causing the events in these areas is very short and originates in the Mediterranean Basin. The North Atlantic Oscillation (NAO) index has no influence upon the occurrence of torrential events in the Pyrenees, but these events are closely related to certain Mediterranean teleconnections such as the Western Mediterranean Oscillation (WeMO) ; The present study was conducted within the framework of the Climatology Group of the University of Barcelona (2017 SGR 1362, Catalan Government) and the Spanish CLICES project (CGL2017-83866-C3-2-R, AEI/FEDER, UE). M.L.-C. was awarded a pre-doctoral FPU Grant (FPU2017/02166) from the Spanish Ministry of Science, Innovation and Universities. R.S.-N. and J.M.C. are partially supported by the Government of Aragón through the "Program of research groups" (group H38, "Clima, Agua, Cambio Global, y Sistemas Naturales")