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Lenssen, Nathan J. L., Lisa Goddard et Simon Mason. « Seasonal Forecast Skill of ENSO Teleconnection Maps ». Weather and Forecasting 35, no 6 (décembre 2020) : 2387–406. http://dx.doi.org/10.1175/waf-d-19-0235.1.
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AbstractEl Niño–Southern Oscillation (ENSO) is the dominant source of seasonal climate predictability. This study quantifies the historical impact of ENSO on seasonal precipitation through an update of the global ENSO teleconnection maps of Mason and Goddard. Many additional teleconnections are detected due to better handling of missing values and 20 years of additional, higher quality data. These global teleconnection maps are used as deterministic and probabilistic empirical seasonal forecasts in a verification study. The probabilistic empirical forecast model outperforms climatology in the tropics demonstrating the value of a forecast derived from the expected precipitation anomalies given the ENSO phase. Incorporating uncertainty due to SST prediction shows that teleconnection maps are skillful in predicting tropical precipitation up to a lead time of 4 months. The historical IRI seasonal forecasts generally outperform the empirical forecasts made with the teleconnection maps, demonstrating the additional value of state-of-the-art dynamical-based seasonal forecast systems. Additionally, the probabilistic empirical seasonal forecasts are proposed as reference forecasts for future skill assessments of real-time seasonal forecast systems.
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Zhao, Tongtiegang, Haoling Chen, Quanxi Shao, Tongbi Tu, Yu Tian et Xiaohong Chen. « Attributing correlation skill of dynamical GCM precipitation forecasts to statistical ENSO teleconnection using a set-theory-based approach ». Hydrology and Earth System Sciences 25, no 11 (8 novembre 2021) : 5717–32. http://dx.doi.org/10.5194/hess-25-5717-2021.
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Abstract. Climate teleconnections are essential for the verification of valuable precipitation forecasts generated by global climate models (GCMs). This paper develops a novel approach to attributing correlation skill of dynamical GCM forecasts to statistical El Niño–Southern Oscillation (ENSO) teleconnection by using the coefficient of determination (R2). Specifically, observed precipitation is respectively regressed against GCM forecasts, Niño3.4 and both of them, and then the intersection operation is implemented to quantify the overlapping R2 for GCM forecasts and Niño3.4. The significance of overlapping R2 and the sign of ENSO teleconnection facilitate three cases of attribution, i.e., significantly positive anomaly correlation attributable to positive ENSO teleconnection, attributable to negative ENSO teleconnection and not attributable to ENSO teleconnection. A case study is devised for the Climate Forecast System version 2 (CFSv2) seasonal forecasts of global precipitation. For grid cells around the world, the ratio of significantly positive anomaly correlation attributable to positive (negative) ENSO teleconnection is respectively 10.8 % (11.7 %) in December–January–February (DJF), 7.1 % (7.3 %) in March–April–May (MAM), 6.3 % (7.4 %) in June–July–August (JJA) and 7.0 % (14.3 %) in September–October–November (SON). The results not only confirm the prominent contributions of ENSO teleconnection to GCM forecasts, but also present spatial plots of regions where significantly positive anomaly correlation is subject to positive ENSO teleconnection, negative ENSO teleconnection and teleconnections other than ENSO. Overall, the proposed attribution approach can serve as an effective tool to investigate the sources of predictability for GCM seasonal forecasts of global precipitation.
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Carpenedo, Camila Bertoletti, et Carlos Batista Da Silva. « Teleconnections influence on Precipitation of Brazilian Cerrado ». Revista Brasileira de Climatologia 30 (16 février 2022) : 26–46. http://dx.doi.org/10.55761/abclima.v30i18.14607.
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Teleconnections are remote connections, which explain the relationship between anomalies distant from each other, typically on the order of 1,000 km, covering large geographic areas. Thus, the objective of this study is to evaluate how teleconnections influence precipitation in the Brazilian Cerrado. Through seasonal linear correlation analysis (between summer 1980 and spring 2019) with precipitation (CPC/NOAA), the tropic-tropic teleconnection (SST anomalies in El Niño regions) shows that each El Niño region and season affect differently the precipitation in the Cerrado. The tropic-subtropic teleconnection (South Atlantic Dipole) shows a predominance of positive correlations in the northern Cerrado and negative (positive) correlations in the southern Cerrado, during winter and spring (summer and autumn). The tropic-extratropic teleconnection (Southern Annular Mode - SAM) shows a predominance of positive correlations in relation to negative correlations. The stochastic model suggests that about 30% of the precipitation in the Cerrado, in autumn and winter, is associated with SAM and SST anomalies in the El Niño regions.
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Liess, Stefan, Arjun Kumar, Peter K. Snyder, Jaya Kawale, Karsten Steinhaeuser, Frederick H. M. Semazzi, Auroop R. Ganguly, Nagiza F. Samatova et Vipin Kumar. « Different Modes of Variability over the Tasman Sea : Implications for Regional Climate* ». Journal of Climate 27, no 22 (4 novembre 2014) : 8466–86. http://dx.doi.org/10.1175/jcli-d-13-00713.1.
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Abstract A new approach is used to detect atmospheric teleconnections without being bound by orthogonality (such as empirical orthogonal functions). This method employs negative correlations in a global dataset to detect potential teleconnections. One teleconnection occurs between the Tasman Sea and the Southern Ocean. It is related to El Niño–Southern Oscillation (ENSO), the Indian Ocean dipole (IOD), and the southern annular mode (SAM). This teleconnection is significantly correlated with SAM during austral summer, fall, and winter, with IOD during spring, and with ENSO in summer. It can thus be described as a hybrid between these modes. Given previously found relationships between IOD and ENSO, and IOD’s proximity to the teleconnection centers, correlations to IOD are generally stronger than to ENSO. Increasing pressure over the Tasman Sea leads to higher (lower) surface temperature over eastern Australia (the southwestern Pacific) in all seasons and is related to reduced surface temperature over Wilkes Land and Adélie Land in Antarctica during fall and winter. Precipitation responses are generally negative over New Zealand. For one standard deviation of the teleconnection index, precipitation anomalies are positive over Australia in fall, negative over southern Australia in winter and spring, and negative over eastern Australia in summer. When doubling the threshold, the size of the anomalous high-pressure center increases and annual precipitation anomalies are negative over southeastern Australia and northern New Zealand. Eliassen–Palm fluxes quantify the seasonal dependence of SAM, ENSO, and IOD influences. Analysis of the dynamical interactions between these teleconnection patterns can improve prediction of seasonal temperature and precipitation patterns in Australia and New Zealand.
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Langenbrunner, Baird, et J. David Neelin. « Analyzing ENSO Teleconnections in CMIP Models as a Measure of Model Fidelity in Simulating Precipitation ». Journal of Climate 26, no 13 (1 juillet 2013) : 4431–46. http://dx.doi.org/10.1175/jcli-d-12-00542.1.
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Abstract The accurate representation of precipitation is a recurring issue in climate models. El Niño–Southern Oscillation (ENSO) precipitation teleconnections provide a test bed for comparison of modeled to observed precipitation. The simulation quality for the atmospheric component of models in the Coupled Model Intercomparison Project (CMIP) phase 5 (CMIP5) is assessed here, using the ensemble of runs driven by observed sea surface temperatures (SSTs). Simulated seasonal precipitation teleconnection patterns are compared to observations during 1979–2005 and to the ensemble of CMIP phase 3 (CMIP3). Within regions of strong observed teleconnections (equatorial South America, the western equatorial Pacific, and a southern section of North America), there is little improvement in the CMIP5 ensemble relative to CMIP3 in amplitude and spatial correlation metrics of precipitation. Spatial patterns within each region exhibit substantial departures from observations, with spatial correlation coefficients typically less than 0.5. However, the atmospheric models do considerably better in other measures. First, the amplitude of the precipitation response (root-mean-square deviation over each region) is well estimated by the mean of the amplitudes from the individual models. This is in contrast with the amplitude of the multimodel ensemble mean, which is systematically smaller (by about 30%–40%) in the selected teleconnection regions. Second, high intermodel agreement on teleconnection sign provides a good predictor for high model agreement with observed teleconnections. The ability of the model ensemble to yield amplitude and sign measures that agree with the observed signal for ENSO precipitation teleconnections lends supporting evidence for the use of corresponding measures in global warming projections.
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Shaman, Jeffrey. « The Seasonal Effects of ENSO on European Precipitation : Observational Analysis ». Journal of Climate 27, no 17 (28 août 2014) : 6423–38. http://dx.doi.org/10.1175/jcli-d-14-00008.1.
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Abstract An analysis and characterization of seasonal changes in the atmospheric teleconnection between ENSO and western European precipitation, as well as atmospheric conditions over the North Atlantic and Europe, are presented. Significant ENSO-associated changes in precipitation are evident during the boreal spring and fall seasons, marginal during boreal summer, and absent during boreal winter. The spring and fall precipitation anomalies are accompanied by statistically significant ENSO-related changes in large-scale fields over the North Atlantic and Europe. These seasonal teleconnections appear to be mediated by changes in upper tropospheric conditions along the coast of Europe that project down to the lower troposphere and produce onshore or offshore moisture flux anomalies, depending on the season. Some ENSO-related changes in storm activity are also evident during fall and winter. Analyses during boreal winter reveal little effect of coincident ENSO conditions on either European precipitation or upper tropospheric conditions over Europe.
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Yang, Xiaosong, et Timothy DelSole. « Systematic Comparison of ENSO Teleconnection Patterns between Models and Observations ». Journal of Climate 25, no 2 (15 janvier 2012) : 425–46. http://dx.doi.org/10.1175/jcli-d-11-00175.1.
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Abstract This paper applies a new field significance test to establish the existence and consistency of ENSO teleconnection patterns across models and observations. An ENSO teleconnection pattern is defined as a field of regression coefficients between an index of the tropical Pacific sea surface temperature and a field of variables such as surface air temperature or precipitation. The test is applied to boreal winter and summer in six continents using observations and hindcasts from the Development of a European Multimodel Ensemble System for Seasonal-to-Interannual Prediction (DEMETER) and the ENSEMBLE-based predictions of climate changes and their impacts (ENSEMBLES) projects. This comparison represents one of the most comprehensive and up-to-date assessments of the extent to which ENSO teleconnection patterns exist and can be reproduced by coupled models. Statistically significant ENSO teleconnection patterns are detected in both observations and models and in all continents and in both winter and summer seasons, except in two cases: 1) Europe (both seasons and variables), and 2) North America (both variables in boreal summer). Despite many ENSO teleconnection patterns being significant, however, the patterns do not necessarily agree between observations and models. The degree of agreement between models and observations is characterized as “robust,” “moderate,” or “low.” Only Australia and South America are found to have robust agreement between ENSO teleconnection patterns, and then only for limited seasons and variables. Although many of our conclusions regarding teleconnection patterns conform to previous studies, there are exceptions, including the fact that the teleconnection for boreal winter precipitation is generally accepted to exist in Africa but in fact has only low agreement with model simulations, while that in Asia is not widely recognized to exist but is found to be significant and in moderate agreement with model teleconnections.
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Wise, Erika K., Melissa L. Wrzesien, Matthew P. Dannenberg et David L. McGinnis. « Cool-Season Precipitation Patterns Associated with Teleconnection Interactions in the United States ». Journal of Applied Meteorology and Climatology 54, no 2 (février 2015) : 494–505. http://dx.doi.org/10.1175/jamc-d-14-0040.1.
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AbstractSeasonal climate forecasts are regularly published to provide decision makers with insights on upcoming climate conditions. Precipitation forecasts, in particular, are useful for fields such as agriculture and water resources. Projections frequently cite a single climate oscillation such as El Niño–Southern Oscillation (ENSO) or the North Atlantic Oscillation (NAO) when suggesting whether a region will be wetter or drier than normal. The complex climate system is composed of a multitude of simultaneous oceanic and atmospheric oscillations, however. Through the study of five atmospheric-pressure-based oscillations, their interactions, and associated precipitation values, this research demonstrates the wide variety of precipitation patterns that can arise when different phases of prominent climate modes occur. Results show that incorporating other Northern Hemisphere teleconnections can dampen or shift expected ENSO and NAO impact patterns. These results indicate that seasonal precipitation projections may be improved by incorporating multiple, regionally important teleconnection indices into the forecast.
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Baek, Seung H., Jason E. Smerdon, Sloan Coats, A. Park Williams, Benjamin I. Cook, Edward R. Cook et Richard Seager. « Precipitation, Temperature, and Teleconnection Signals across the Combined North American, Monsoon Asia, and Old World Drought Atlases ». Journal of Climate 30, no 18 (8 août 2017) : 7141–55. http://dx.doi.org/10.1175/jcli-d-16-0766.1.
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Abstract The tree-ring-based North American Drought Atlas (NADA), Monsoon Asia Drought Atlas (MADA), and Old World Drought Atlas (OWDA) collectively yield a near-hemispheric gridded reconstruction of hydroclimate variability over the last millennium. To test the robustness of the large-scale representation of hydroclimate variability across the drought atlases, the joint expression of seasonal climate variability and teleconnections in the NADA, MADA, and OWDA are compared against two global, observation-based PDSI products. Predominantly positive (negative) correlations are determined between seasonal precipitation (surface air temperature) and collocated tree-ring-based PDSI, with average Pearson’s correlation coefficients increasing in magnitude from boreal winter to summer. For precipitation, these correlations tend to be stronger in the boreal winter and summer when calculated for the observed PDSI record, while remaining similar for temperature. Notwithstanding these differences, the drought atlases robustly express teleconnection patterns associated with El Niño–Southern Oscillation (ENSO), the North Atlantic Oscillation (NAO), the Pacific decadal oscillation (PDO), and the Atlantic multidecadal oscillation (AMO). These expressions exist in the drought atlas estimates of boreal summer PDSI despite the fact that these modes of climate variability are dominant in boreal winter, with the exception of the AMO. ENSO and NAO teleconnection patterns in the drought atlases are particularly consistent with their well-known dominant expressions in boreal winter and over the OWDA domain, respectively. Collectively, the findings herein confirm that the joint Northern Hemisphere drought atlases robustly reflect large-scale patterns of hydroclimate variability on seasonal to multidecadal time scales over the twentieth century and are likely to provide similarly robust estimates of hydroclimate variability prior to the existence of widespread instrumental data.
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Nieto, Susana, et Concepción Rodríguez-Puebla. « Comparison of Precipitation from Observed Data and General Circulation Models over the Iberian Peninsula ». Journal of Climate 19, no 17 (1 septembre 2006) : 4254–75. http://dx.doi.org/10.1175/jcli3859.1.
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Abstract In this paper, the ability of model outputs from the Intergovernmental Panel on Climate Change (IPCC) to describe the natural internal variability of precipitation observations is evaluated. The analysis is focused on the Iberian Peninsula for December–February (DJF). The study was performed with observed data from National Meteorological Institutes, reanalysis data from the National Centers for Environmental Prediction–National Center for Atmospheric Research, teleconnection indices, and model simulations. First, the seasonal cycle, mean winter pattern, and tendency for nine model simulations were evaluated. Then, four models were selected to obtain interannual variability and to diagnose the links between precipitation and large-scale circulation. This intercomparison is based on the modes obtained by the empirical orthogonal function (EOF) and spectral analyses to investigate the temporal properties of the most significant spatial patterns. The models well reproduce the observed seasonal cycle and the mean winter pattern; however, they poorly capture the interannual variability found in observed data. To ascertain the reasons for these results, features affecting the precipitation process are considered by analyzing the relationships with the dominant modes of large-scale atmospheric fields, such as sea level pressure, storm activity, jet stream, moisture flux, and teleconnection indices. The precipitation response to the mean flow suggests signs of potential seasonal predictability in DJF.
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Lu, Riyu, et Zhongda Lin. « Role of Subtropical Precipitation Anomalies in Maintaining the Summertime Meridional Teleconnection over the Western North Pacific and East Asia ». Journal of Climate 22, no 8 (15 avril 2009) : 2058–72. http://dx.doi.org/10.1175/2008jcli2444.1.
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Abstract The meridional teleconnection patterns over the western North Pacific and East Asia (WNP–EA) during summer have a predominant role in affecting East Asian climate on the interannual time scale. A well-known seesaw pattern of tropical–subtropical precipitation is associated with the meridional teleconnection, and the subtropical precipitation anomaly has been previously viewed as a result of anomalous circulations associated with the teleconnection. In this study, however, the authors suggest that subtropical precipitation anomalies, in turn, can significantly affect large-scale circulations and may be crucial for maintenance of the meridional teleconnection. Diagnosis by using observational and reanalysis data indicates that the meridional teleconnection patterns are clearer in summers when the subtropical rainfall anomalies are greater. The simulated results by a linear baroclinic model indicate that a subtropical heat source, which is equivalent to the diagnosed positive subtropical precipitation anomaly, induces zonally elongated zonal wind anomalies that resemble the diagnosed ones in both the upper and lower troposphere over the extratropical WNP–EA. The simulated results also indicate that the horizontal and vertical structures of circulation responses are insensitive to the locations and shapes of imposed subtropical heat anomalies, which implies the important role of basic flow in circulation responses. This study suggests that, for confidential dynamical seasonal forecasting in East Asia, general circulation models should be required to capture the features of interannual subtropical rainfall variability and basic-state flows in WNP–EA.
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Hoell, Andrew, Mathew Barlow et Roop Saini. « Intraseasonal and Seasonal-to-Interannual Indian Ocean Convection and Hemispheric Teleconnections ». Journal of Climate 26, no 22 (29 octobre 2013) : 8850–67. http://dx.doi.org/10.1175/jcli-d-12-00306.1.
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Abstract Deep tropical convection over the Indian Ocean leads to intense diabatic heating, a main driver of the climate system. The Northern Hemisphere circulation and precipitation associated with intraseasonal and seasonal-to-interannual components of the leading pattern of Indian Ocean convection are investigated for November–April 1979–2008. The leading pattern of Indian Ocean convection is separated into intraseasonal and seasonal-to-interannual components by filtering an index of outgoing longwave radiation at 33–105 days and greater than 105 days, yielding Madden–Julian oscillation (MJO)- and El Niño–Southern Oscillation (ENSO)-influenced patterns, respectively. Observations and barotropic Rossby wave ray tracing experiments suggest that Indian Ocean convection can influence the ENSO-related hemispheric teleconnection pattern in addition to the regional Asian teleconnection. Equivalent barotropic circulation anomalies throughout the Northern Hemisphere subtropics are associated with both seasonal-to-interannual Indian Ocean convection and ENSO. The hemispheric teleconnection associated with seasonal-to-interannual Indian Ocean convection is investigated with ray tracing, which suggests that forcing over the Indian Ocean can propagate eastward across the hemisphere and back to Asia. The relationship between the seasonal-to-interannual component of Indian Ocean convection and ENSO is investigated in terms of a gradient in sea surface temperatures (SST) over the equatorial western Pacific Ocean. When the western Pacific SST gradient is strong during ENSO, strong Maritime Continent precipitation extends further westward into the Indian Ocean, which is accompanied by enhanced tropospheric Asian circulation, similar to the seasonal-to-interannual component of Indian Ocean convection. Analysis of the three strongest interannual convection seasons shows that the strong Indian Ocean pattern of ENSO can dominate individual seasons.
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Garaboa-Paz, Daniel, Nieves Lorenzo et Vicente Pérez-Muñuzuri. « Influence of finite-time Lyapunov exponents on winter precipitation over the Iberian Peninsula ». Nonlinear Processes in Geophysics 24, no 2 (24 mai 2017) : 227–35. http://dx.doi.org/10.5194/npg-24-227-2017.
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Abstract. Seasonal forecasts have improved during the last decades, mostly due to an increase in understanding of the coupled ocean–atmosphere dynamics, and the development of models able to predict the atmosphere variability. Correlations between different teleconnection patterns and severe weather in different parts of the world are constantly evolving and changing. This paper evaluates the connection between winter precipitation over the Iberian Peninsula and the large-scale tropospheric mixing over the eastern Atlantic Ocean. Finite-time Lyapunov exponents (FTLEs) have been calculated from 1979 to 2008 to evaluate this mixing. Our study suggests that significant negative correlations exist between summer FTLE anomalies and winter precipitation over Portugal and Spain. To understand the mechanisms behind this correlation, summer anomalies of the FTLE have also been correlated with other climatic variables such as the sea surface temperature (SST), the sea level pressure (SLP) or the geopotential. The East Atlantic (EA) teleconnection index correlates with the summer FTLE anomalies, confirming their role as a seasonal predictor for winter precipitation over the Iberian Peninsula.
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Guérémy, J. F., N. Laanaia et J. P. Céron. « Seasonal forecast of French Mediterranean heavy precipitating events linked to weather regimes ». Natural Hazards and Earth System Sciences 12, no 7 (25 juillet 2012) : 2389–98. http://dx.doi.org/10.5194/nhess-12-2389-2012.
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Abstract. Seasonal predictability of local precipitation is rather weak in the mid-latitudes. This is the case when assessing the skill of the seasonal forecast of Heavy Precipitating Event (HPE) extreme occurrence over the French Mediterranean coast during the fall season. Tropics to extra-tropics teleconnection patterns do appear when averaging analyzed fields over the years characterised by a frequency of HPE occurrence in the upper 17% of the distribution. A methodology taking weather regime occurrence into account as an intermediate step to forecast HPE extreme occurrence is presented. For the period 1960 to 2001 and four different sets of seasonal forecast, the Economical Value is doubled, compared to the score obtained with the simulated local precipitation data, when using a linear model (Linear Discriminant Analysis in this case) taking simulated 200 hPa velocity potential–stream function regime occurrences as predictors. Interestingly, larger scores are shown for this couple of fields over a large-scale domain including the tropics than for the 500 hPa geopotential height over an Euro–Atlantic domain, despite a tighter link of the latter field to the local precipitation.
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Caloiero, T., R. Coscarelli, E. Ferrari et M. Mancini. « Precipitation change in Southern Italy linked to global scale oscillation indexes ». Natural Hazards and Earth System Sciences 11, no 6 (15 juin 2011) : 1683–94. http://dx.doi.org/10.5194/nhess-11-1683-2011.
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Abstract. This study investigates precipitation variability in five regions of Southern Italy (Campania, Apulia, Basilicata, Calabria and Sicily) using a homogeneous database of about 70 rain gauges with more than 50 years of observation. First, a statistical analysis was performed through the Mann-Kendall non-parametric test in order to determine rainfall the trend on both yearly and seasonal scales. Then, the relationship between the rainfall and some teleconnection pattern indexes was investigated using Spearman's test. The results show remarkable statistically significant negative trends for annual and winter aggregations in most part of the series. Moreover, a strong correlation has emerged between the teleconnection patterns and precipitation in Southern Italy, particularly in winter and on the Tyrrhenian side of the study area.
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Ajjur, Salah Basem, et Sami G. Al-Ghamdi. « Variation in Seasonal Precipitation over Gaza (Palestine) and Its Sensitivity to Teleconnection Patterns ». Water 13, no 5 (1 mars 2021) : 667. http://dx.doi.org/10.3390/w13050667.
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The seasonal precipitation (SP) trend and its sensitivity to teleconnection patterns over the East Mediterranean (EM) region remain inconsistent. Based on rainfall records during 1974–2016 at seven meteorological stations in the Gaza region, this study aims to (1) analyze the observed SP trend over the Gaza region, and (2) examine the SP sensitivity to climate indices. Pearson and Spearman correlations between climate indices and SP in the current and following years were calculated, and the seasonal period (particular month) with the highest correlation was identified. Results show that the climate indices, with greater impact on SP over the Gaza region in the autumn and spring, were in the order; El Niño-Southern Oscillation (ENSO) > East Atlantic/Western Russia (EAWR) > North Atlantic Oscillation (NAO) > Arctic Oscillation (AO). The indices’ impact was minimal in the winter precipitation. ENSO types’ correlations (Southern Oscillation Index-SOI and Niño 3.4) were moderate and significant at α = 0.05. Rainfall at most stations positively correlates with AO and EAWR in spring and autumn. During the study period, warm phases of ENSO (i.e., El Niño) intensified autumn precipitation. Simultaneously with warm phases of EAWR or AO, more influence on autumn precipitation is exerted. Cold phases of ENSO (i.e., La Niña) have an adverse impact compared to El Niño. EAWR co-variation was evident only with the ENSO. Regarding AO, a non-meaningful action was noticed during the neutral phases of ENSO and EAWR. The findings of this study help understand and predict the seasonal trend of precipitation over the Gaza region. This is essential to set up climate change mitigation and adaptation strategies in the EM region.
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Strazzo, Sarah, Dan C. Collins, Andrew Schepen, Q. J. Wang, Emily Becker et Liwei Jia. « Application of a Hybrid Statistical–Dynamical System to Seasonal Prediction of North American Temperature and Precipitation ». Monthly Weather Review 147, no 2 (24 janvier 2019) : 607–25. http://dx.doi.org/10.1175/mwr-d-18-0156.1.
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Abstract Recent research demonstrates that dynamical models sometimes fail to represent observed teleconnection patterns associated with predictable modes of climate variability. As a result, model forecast skill may be reduced. We address this gap in skill through the application of a Bayesian postprocessing technique—the calibration, bridging, and merging (CBaM) method—which previously has been shown to improve probabilistic seasonal forecast skill over Australia. Calibration models developed from dynamical model reforecasts and observations are employed to statistically correct dynamical model forecasts. Bridging models use dynamical model forecasts of relevant climate modes (e.g., ENSO) as predictors of remote temperature and precipitation. Bridging and calibration models are first developed separately using Bayesian joint probability modeling and then merged using Bayesian model averaging to yield an optimal forecast. We apply CBaM to seasonal forecasts of North American 2-m temperature and precipitation from the North American Multimodel Ensemble (NMME) hindcast. Bridging is done using the model-predicted Niño-3.4 index. Overall, the fully merged CBaM forecasts achieve higher Brier skill scores and better reliability compared to raw NMME forecasts. Bridging enhances forecast skill for individual NMME member model forecasts of temperature, but does not result in significant improvements in precipitation forecast skill, possibly because the models of the NMME better represent the ENSO–precipitation teleconnection pattern compared to the ENSO–temperature pattern. These results demonstrate the potential utility of the CBaM method to improve seasonal forecast skill over North America.
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Wilby, RL. « Statistical downscaling of daily precipitation using daily airflow and seasonal teleconnection indices ». Climate Research 10 (1998) : 163–78. http://dx.doi.org/10.3354/cr010163.
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Räsänen, T. A., V. Lindgren, J. H. A. Guillaume, B. M. Buckley et M. Kummu. « On the spatial and temporal variability of ENSO precipitation and drought teleconnection in mainland Southeast Asia ». Climate of the Past Discussions 11, no 6 (10 novembre 2015) : 5307–43. http://dx.doi.org/10.5194/cpd-11-5307-2015.
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Abstract. The variability in the hydroclimate over mainland Southeast Asia is strongly influenced by the El Niño–Southern Oscillation (ENSO) phenomenon, which has been linked to severe drought and floods that profoundly influence human societies and ecosystems alike. However, the spatial characteristics and long-term stationarity of ENSO's influence in the region are not well understood. We thus aim to analyse seasonal evolution and spatial variations in the effect of ENSO on precipitation over the period of 1980–2013, and long-term variation in the ENSO-teleconnection using tree-ring derived Palmer Drought Severity Indices (PDSI) that span from 1650–2004. We found that the majority of the study area is under the influence of ENSO, which has affected the region's hydroclimate over the majority (96 %) of the 355 year study period. Our results further indicate that there is a pattern of seasonal evolution of precipitation anomalies during ENSO. However, considerable variability in the ENSO's influence is revealed: the strength of ENSO's influence was found to vary in time and space, and the different ENSO events resulted in varying precipitation anomalies. Additional research is needed to investigate how this variation in ENSO teleconnection is influenced by other factors, such as the properties of the ENSO events and other ocean and atmospheric phenomena. In general, the high variability we found in ENSO teleconnection combined with limitations of current knowledge, suggests that the adaptation to extremes in hydroclimate in mainland Southeast Asia needs to go beyond "predict-and-control" and recognise both uncertainty and complexity as fundamental principles.
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Misra, Vasubandhu. « Coupled Air, Sea, and Land Interactions of the South American Monsoon ». Journal of Climate 21, no 23 (1 décembre 2008) : 6389–403. http://dx.doi.org/10.1175/2008jcli2497.1.
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Abstract The dominant interannual variation of the austral summer South American monsoon season (SAM) is associated with El Niño–Southern Oscillation (ENSO). Although this teleconnection provides a basis for the seasonal predictability of SAM, it is shown that the conventional tier-2 modeling approach of prescribing observed sea surface temperature (SST) is inappropriate to capture this teleconnection. Furthermore, such a forced atmospheric general circulation model (AGCM) simulation leads to degradation of the SAM precipitation variability. However, when the same AGCM is coupled to an ocean general circulation model to allow for coupled air–sea interactions, then this ENSO–SAM teleconnection is reasonably well simulated. This is attributed to the role of air–sea coupling in modulating the large-scale east–west circulation, especially associated with Niño-3 SST anomalies. It is also shown that the land–atmosphere feedback in the SAM domain as a result of the inclusion of air–sea coupling is more robust. As a consequence of this stronger land–atmosphere feedback the decorrelation time of the daily rainfall in the SAM region is prolonged to match more closely with the observed behavior. A subtle difference in the austral summer seasonal precipitation anomalies between that over the Amazon River basin (ARB) and the SAM core region is also drawn from this study in reference to the influence of the air–sea interaction. It is shown that the dominant interannual precipitation variability over the ARB is simulated both by the uncoupled and coupled (to OGCM) AGCM in contrast to that over the SAM core region in southeastern Brazil.
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Zhao, Tongtiegang, Haoling Chen, Yu Tian, Denghua Yan, Weixin Xu, Huayang Cai, Jiabiao Wang et Xiaohong Chen. « Quantifying overlapping and differing information of global precipitation for GCM forecasts and El Niño–Southern Oscillation ». Hydrology and Earth System Sciences 26, no 16 (17 août 2022) : 4233–49. http://dx.doi.org/10.5194/hess-26-4233-2022.
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Abstract. While El Niño–Southern Oscillation (ENSO) teleconnection has long been used in statistical precipitation forecasting, global climate models (GCMs) provide increasingly available dynamical precipitation forecasts for hydrological modeling and water resources management. It is not yet known to what extent dynamical GCM forecasts provide new information compared to statistical teleconnection. This paper develops a novel set operations of coefficients of determination (SOCD) method to explicitly quantify the overlapping and differing information for GCM forecasts and ENSO teleconnection. Specifically, the intersection operation of the coefficient of determination derives the overlapping information for GCM forecasts and the Niño3.4 index, and then the difference operation determines the differing information in GCM forecasts (Niño3.4 index) from the Niño3.4 index (GCM forecasts). A case study is devised for the Climate Forecast System version 2 (CFSv2) seasonal forecasts of global precipitation in December–January–February. The results show that the overlapping information for GCM forecasts and the Niño3.4 index is significant for 34.94 % of the global land grid cells, that the differing information in GCM forecasts from the Niño3.4 index is significant for 31.18 % of the grid cells and that the differing information in the Niño3.4 index from GCM forecasts is significant for 11.37 % of the grid cells. These results confirm the effectiveness of GCMs in capturing the ENSO-related variability of global precipitation and illustrate where there is room for improvement of GCM forecasts. Furthermore, the bootstrapping significance tests of the three types of information facilitate in total eight patterns to disentangle the close but divergent associations of GCM forecast correlation skill with ENSO teleconnection.
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Lee, June-Yi, Bin Wang, Kyong-Hwan Seo, Jong-Seong Kug, Yong-Sang Choi, Yu Kosaka et Kyung-Ja Ha. « Future Change of Northern Hemisphere Summer Tropical–Extratropical Teleconnection in CMIP5 Models* ». Journal of Climate 27, no 10 (9 mai 2014) : 3643–64. http://dx.doi.org/10.1175/jcli-d-13-00261.1.
Texte intégralRésumé :
Abstract Two dominant global-scale teleconnections in the Northern Hemisphere (NH) extratropics during boreal summer season (June–August) have been identified: the western North Pacific–North America (WPNA) and circumglobal teleconnection (CGT) patterns. These teleconnection patterns are of critical importance for the NH summer seasonal climate prediction. Here, how these teleconnections will change under anthropogenic global warming is investigated using representative concentration pathway 4.5 (RCP4.5) experiments by 20 coupled models that participated in phase 5 of the Coupled Model Intercomparison Project (CMIP5). The six best models are selected based on their performance in simulation of the two teleconnection patterns and climatological means and variances of atmospheric circulation, precipitation, and sea surface temperature. The selected models capture the CGT and its relationship with the Indian summer monsoon (ISM) reasonably well. The models can also capture the WPNA circulation pattern but with striking deficiencies in reproducing its associated rainfall anomalies due to poor simulation of the western North Pacific summer monsoon rainfall. The following changes are anticipated in the latter half of twenty-first century under the RCP4.5 scenario: 1) significant weakening of year-to-year variability of the upper-level circulation due to increased atmospheric stability, although the moderate increase in convective heating over the tropics may act to strengthen the variability; 2) intensification of the WPNA pattern and major spectral peaks, particularly over the eastern Pacific–North America and North Atlantic–Europe sectors, which is attributed to the strengthening of its relationship with the preceding mature phase of El Niño–Southern Oscillation (ENSO); and 3) weakening of the CGT due to atmospheric stabilization and decreasing relationship with ISM as well as weakening of the ISM–ENSO relationship.
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Yin, Zhi-Yong, Hongli Wang et Xiaodong Liu. « A Comparative Study on Precipitation Climatology and Interannual Variability in the Lower Midlatitude East Asia and Central Asia ». Journal of Climate 27, no 20 (7 octobre 2014) : 7830–48. http://dx.doi.org/10.1175/jcli-d-14-00052.1.
Texte intégralRésumé :
Abstract This study examines precipitation climatology and interannual variability in two regions in the lower midlatitude Asia to the east and west of the Tibetan Plateau, one located in monsoonal East Asia (the M region) and the other in semiarid central Asia (the W region). The focus is on the 5-month summer half year (May–September) for the M region and the winter half year (December–April) for the W region, corresponding to their respective rainy seasons. The main mechanism of moisture transport for the M region is the summer lower-tropospheric southerly winds, whereas the winter midtropospheric westerly circulation between 25° and 45°N is responsible for conducting moisture fluxes to the W region. It is further discovered that the winter precipitation series are positively correlated between the two regions (r = 0.47). There is also a weak cross-seasonal correlation between the winter W region precipitation and summer M region precipitation (r = 0.27). Winter westerly circulation over the W region is influenced by both the east Atlantic–western Russia and the polar–Eurasia extratropical teleconnection patterns, while El Niño–Southern Oscillation influences regional circulation patterns in both regions through teleconnections via the Indo-Pacific warm pool convection in winter and its lagged impact on the western North Pacific anticyclone over the Philippine Sea. In the meantime, responses of the regional winter circulation in the M region to the upstream westerly circulation intensity cause the correlation in winter precipitation between the two regions. Such linkages form the basis of the concurrent and cross-seasonal correlations in precipitation between the two remote regions.
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Rana, Sapna, James Renwick, James McGregor et Ankita Singh. « Seasonal Prediction of Winter Precipitation Anomalies over Central Southwest Asia : A Canonical Correlation Analysis Approach ». Journal of Climate 31, no 2 (janvier 2018) : 727–41. http://dx.doi.org/10.1175/jcli-d-17-0131.1.
Texte intégralRésumé :
Central southwest Asia (CSWA; 20°–47°N, 40°–85°E) is a water-stressed region prone to significant variations in precipitation during its winter precipitation season of November–April. Wintertime precipitation is crucial for regional water resources, agriculture, and livelihood; however, in recent years droughts have been a notable feature of CSWA interannual variability. Here, the predictability of CSWA wintertime precipitation is explored based on its time-lagged relationship with the preceding months’ (September–October) sea surface temperature (SST), using a canonical correlation analysis (CCA) approach. For both periods, results indicate that for CSWA much of the seasonal predictability arises from SST variations in the Pacific related to El Niño–Southern Oscillation (ENSO) and the Pacific decadal oscillation (PDO). Additional sources of skill that play a weaker predictive role include long-term SST trends, North Atlantic variability, and regional teleconnections. CCA cross-validation skill shows that the regional potential predictability has a strong dependency on the ENSO phenomenon, and the strengthening (weakening) of this relationship yields forecasts with higher (lower) predictive skill. This finding is validated by the mean cross-validated correlation skill of 0.71 and 0.38 obtained for the 1980/81–2014/15 and 1950/51–2014/15 CCA analyses, respectively. The development of cold (warm) ENSO conditions during September–October, in combination with cold (warm) PDO conditions, is associated with a northward (southward) shift of the jet stream and a strong tendency of negative (positive) winter precipitation anomalies; other sources of predictability influence the regional precipitation directly during non-ENSO years or by modulating the impact of ENSO teleconnection based on their relative strengths.
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Shaman, Jeffrey. « The Seasonal Effects of ENSO on Atmospheric Conditions Associated with European Precipitation : Model Simulations of Seasonal Teleconnections ». Journal of Climate 27, no 3 (24 janvier 2014) : 1010–28. http://dx.doi.org/10.1175/jcli-d-12-00734.1.
Texte intégralRésumé :
Abstract The seasonal upper-tropospheric teleconnection between ENSO and the North Atlantic/European sector is explored through a series of model experiments. A barotropic vorticity equation model is linearized about climatological conditions for each season of the year, and divergence forcing is applied over the equatorial Pacific to mimic El Niño–related convective activity. During boreal fall, winter, and spring, this forcing similarly excites a northeastward-propagating stationary barotropic Rossby wave train that extends across the North Atlantic to the European coast. Strong anomalies develop over the British Isles in the vicinity of the North Atlantic jet exit. Solutions during boreal summer produce no clear wave train; however, evidence exists for a North Atlantic response because of both eastward- and westward-propagating signals. These direct responses over the Atlantic and Europe are qualitatively similar to observed ENSO-associated anomalies during boreal spring and fall, but differ structurally during summer and winter. Further experiments with the vorticity equation model using full Rossby wave source forcing, which included vorticity advection, increase the amplitude of the response over Europe during some seasons; however, structural differences persist. Finally, experiments with the Community Atmosphere Model (CAM), version 4, reveal that the basic northeastward-propagating response is modulated by downstream feedbacks. These changes are most profound during boreal winter and engender an arching wave train pattern that, matching observations, reflects off the jet over North America, propagates southeastward over the North Atlantic, and fails to reach the European coast. Overall, the simulations with CAM correctly depict observed seasonal changes in the magnitude of the ENSO–North Atlantic/European teleconnection by producing a strong fall and winter response but a weaker spring and summer response. The CAM experiments also indicate that the seasonal response is not dependent on antecedent conditions; however, CAM simulations fail to project the upper-tropospheric anomalies appropriately to the lower troposphere.
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Yuan, Jiacan, Benkui Tan, Steven B. Feldstein et Sukyoung Lee. « Wintertime North Pacific Teleconnection Patterns : Seasonal and Interannual Variability ». Journal of Climate 28, no 20 (13 octobre 2015) : 8247–63. http://dx.doi.org/10.1175/jcli-d-14-00749.1.
Texte intégralRésumé :
Abstract The teleconnections of the wintertime North Pacific are examined from the continuum perspective with self-organizing map (SOM) analysis. Daily ERA-Interim data for the 1979–2011 period are used. It is found that most of the North Pacific teleconnections can be grouped into several Pacific–North American (PNA)-like, western Pacific (WP)-like, and east Pacific (EP)-like SOM patterns. Each of the SOM patterns has an e-folding time scale of 7–10 days. The WP-like SOM patterns undergo a decline in their frequency from early to late winter, and vice versa for the EP-like SOM patterns, corresponding to an eastward seasonal shift of the North Pacific teleconnections. This seasonal shift is observed for both phases of the WP and EP patterns, and is only weakly sensitive to the phase of El Niño–Southern Oscillation. It is shown that the interannual variability of the PNA, WP, and EP can be interpreted as arising from interannual changes in the frequency of the corresponding SOM patterns. The WP- and EP-like SOM patterns are found to be associated with statistically significant sea ice cover anomalies over the Sea of Okhotsk and the Bering Sea. The low-level wind and temperature anomalies associated with these patterns are consistent with the changes in sea ice arising from both wind-driven sea ice motion and freezing and/or melting of sea ice due to horizontal temperature advection. Furthermore, widespread precipitation anomalies over the North Pacific are found for all three patterns.
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Pompa-García, Marín, et Xanat Antonio Némiga. « ENSO index teleconnection with seasonal precipitation in a temperate ecosystem of northern Mexic ». Atmósfera 28, no 1 (1 janvier 2015) : 43–50. http://dx.doi.org/10.20937/atm.2015.28.01.04.
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Pompa-García, Marín, et Xanat Antonio Némiga. « ENSO index teleconnection with seasonal precipitation in a temperate ecosystem of northern Mexico ». Atmósfera 28, no 1 (janvier 2015) : 43–50. http://dx.doi.org/10.1016/s0187-6236(15)72158-2.
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Lin, Jia-Lin, Toshiaki Shinoda, Taotao Qian, Weiqing Han, Paul Roundy et Yangxing Zheng. « Intraseasonal Variation of Winter Precipitation over the Western United States Simulated by 14 IPCC AR4 Coupled GCMs ». Journal of Climate 23, no 11 (1 juin 2010) : 3094–119. http://dx.doi.org/10.1175/2009jcli2991.1.
Texte intégralRésumé :
Abstract This study evaluates the intraseasonal variation of winter precipitation over the western United States in 14 coupled general circulation models (GCMs) participating in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). Eight years of each model’s twentieth-century climate simulation are analyzed. The focus is on the two dominant intraseasonal modes for the western U.S. precipitation: the 40-day mode and the 22-day mode. The results show that the models tend to overestimate the northern winter (November–April) seasonal mean precipitation over the western United States and Canada. The models also tend to produce overly strong intraseasonal variability in western U.S. wintertime precipitation, in spite of the overly weak tropical intraseasonal variability in most of the models. All models capture both the 40-day mode and the 22-day mode, usually with overly large variances. For the 40-day mode, models tend to reproduce its deep barotropic vertical structure and three-cell horizontal structure, but only 5 of the 14 models capture its northward propagation, and only 2 models simulate its teleconnection with the Madden–Julian oscillation in the tropical Pacific. For the 22-day mode, 8 of the 14 models reproduce its coherent northward propagation, and 9 models capture its teleconnection with precipitation in the tropical Pacific.
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Buric, Dragan, Vladan Ducic, Jovan Mihajlovic, Jelena Lukovic et Jovan Dragojlovic. « Relationship between the precipitation variability in Montenegro and the Mediterranean oscillation ». Glasnik Srpskog geografskog drustva 94, no 4 (2014) : 109–20. http://dx.doi.org/10.2298/gsgd1404109b.
Texte intégralRésumé :
This study investigates the influence of atmospheric circulation in the Mediterranean region on the precipitation in Montenegro. Nine precipitation parameters have been used in the analysis and the relationship has been investigated by the Mediterranean and West Mediterranean Oscillation change index (MO and WeMO). According to a 60 - year observed period (1951-2010), the research results show that nothing characteristic happens with seasonal and annual precipitation sums because the trend is mainly insignificant. However, precipitation extremes are getting more extreme, which corresponds with a general idea of global warming. Negative consequences of daily intensity increase and frequency of precipitation days above fixed and percentile thresholds have been recorded recently in the form of torrents, floods, intensive erosive processes, etc., but it should be pointed out that human factor is partly a cause of such events. The estimate of the influence of teleconnection patterns primarily related to the Mediterranean Basin has shown that their variability affects the observed precipitation parameters on the territory of Montenegro regarding both seasonal and annual sums and frequency and intensity of extreme events shown by climate indices.
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King, Martin P., Ivana Herceg-Bulić, Ileana Bladé, Javier García-Serrano, Noel Keenlyside, Fred Kucharski, Camille Li et Stefan Sobolowski. « Importance of Late Fall ENSO Teleconnection in the Euro-Atlantic Sector ». Bulletin of the American Meteorological Society 99, no 7 (juillet 2018) : 1337–43. http://dx.doi.org/10.1175/bams-d-17-0020.1.
Texte intégralRésumé :
AbstractRecent studies have indicated the importance of fall climate forcings and teleconnections in influencing the climate of the northern mid- to high latitudes. Here, we present some exploratory analyses using observational data and seasonal hindcasts, with the aim of highlighting the potential of the El Niño–Southern Oscillation (ENSO) as a driver of climate variability during boreal late fall and early winter (November and December) in the North Atlantic–European sector, and motivating further research on this relatively unexplored topic. The atmospheric ENSO teleconnection in November and December is reminiscent of the east Atlantic pattern and distinct from the well-known arching extratropical Rossby wave train found from January to March. Temperature and precipitation over Europe in November are positively correlated with the Niño-3.4 index, which suggests a potentially important ENSO climate impact during late fall. In particular, the ENSO-related temperature anomaly extends over a much larger area than during the subsequent winter months. We discuss the implications of these results and pose some research questions.
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Ferreira, Glauber W. S., Michelle S. Reboita et Anita Drumond. « Evaluation of ECMWF-SEAS5 Seasonal Temperature and Precipitation Predictions over South America ». Climate 10, no 9 (29 août 2022) : 128. http://dx.doi.org/10.3390/cli10090128.
Texte intégralRésumé :
Nowadays, a challenge in Climate Science is the seasonal forecast and knowledge of the model’s performance in different regions. The challenge in South America reflects its huge territory; some models present a good performance, and others do not. Nevertheless, reliable seasonal climate forecasts can benefit numerous decision-making processes related to agriculture, energy generation, and extreme events mitigation. Thus, given the few works assessing the ECMWF-SEAS5 performance in South America, this study investigated the quality of its seasonal temperature and precipitation predictions over the continent. For this purpose, predictions from all members of the hindcasts (1993–2016) and forecasts (2017–2021) ensemble were used, considering the four yearly seasons. The analyses included seasonal mean fields, bias correction, anomaly correlations, statistical indicators, and seasonality index. The best system’s performance occurred in regions strongly influenced by teleconnection effects, such as northern South America and northeastern Brazil, in which ECMWF-SEAS5 even reproduced the extreme precipitation anomalies that happened in recent decades. Moreover, the system indicated a moderate capability of seasonal predictions in medium and low predictability regions. In summary, the results show that ECMWF-SEAS5 climate forecasts are potentially helpful and should be considered to plan various strategic activities better.
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Schwitalla, Thomas, Kirsten Warrach-Sagi, Volker Wulfmeyer et Michael Resch. « Near-global-scale high-resolution seasonal simulations with WRF-Noah-MP v.3.8.1 ». Geoscientific Model Development 13, no 4 (21 avril 2020) : 1959–74. http://dx.doi.org/10.5194/gmd-13-1959-2020.
Texte intégralRésumé :
Abstract. The added value of global simulations on the convection-permitting (CP) scale is a subject of extensive research in the earth system science community. An increase in predictive skill can be expected due to advanced representations of feedbacks and teleconnections in the ocean–land–atmosphere system. However, the proof of this hypothesis by corresponding simulations is computationally and scientifically extremely demanding. We present a novel latitude-belt simulation from 57∘ S to 65∘ N using the Weather Research and Forecasting (WRF)-Noah-MP model system with a grid increment of 0.03∘ over a period of 5 months forced by sea surface temperature observations. In comparison to a latitude-belt simulation with 45 km resolution, at CP resolution the representation of the spatial-temporal scales and the organization of tropical convection are improved considerably. The teleconnection pattern is very close to that of the operational European Centre for Medium Range Weather Forecasting (ECMWF) analyses. The CP simulation is associated with an improvement of the precipitation forecast over South America, Africa, and the Indian Ocean and considerably improves the representation of cloud coverage along the tropics. Our results demonstrate a significant added value of future simulations on the CP scale up to the seasonal forecast range.
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Lin, Hai, William J. Merryfield, Ryan Muncaster, Gregory C. Smith, Marko Markovic, Frédéric Dupont, François Roy et al. « The Canadian Seasonal to Interannual Prediction System Version 2 (CanSIPSv2) ». Weather and Forecasting 35, no 4 (1 août 2020) : 1317–43. http://dx.doi.org/10.1175/waf-d-19-0259.1.
Texte intégralRésumé :
AbstractThe second version of the Canadian Seasonal to Interannual Prediction System (CanSIPSv2) was implemented operationally at Environment and Climate Change Canada (ECCC) in July 2019. Like its predecessors, CanSIPSv2 applies a multimodel ensemble approach with two coupled atmosphere–ocean models, CanCM4i and GEM-NEMO. While CanCM4i is a climate model, which is upgraded from CanCM4 of the previous CanSIPSv1 with improved sea ice initialization, GEM-NEMO is a newly developed numerical weather prediction (NWP)-based global atmosphere–ocean coupled model. In this paper, CanSIPSv2 is introduced, and its performance is assessed based on the reforecast of 30 years from 1981 to 2010, with 10 ensemble members of 12-month integrations for each model. Ensemble seasonal forecast skill of 2-m air temperature, 500-hPa geopotential height, precipitation rate, sea surface temperature, and sea ice concentration is assessed. Verification is also performed for the Niño-3.4, the Pacific–North American pattern (PNA), the North Atlantic Oscillation (NAO), and the Madden–Julian oscillation (MJO) indices. It is found that CanSIPSv2 outperforms the previous CanSIPSv1 system in many aspects. Atmospheric teleconnections associated with the El Niño–Southern Oscillation (ENSO) are reasonably well captured by the two CanSIPSv2 models, and a large part of the seasonal forecast skill in boreal winter can be attributed to the ENSO impact. The two models are also able to simulate the Northern Hemisphere teleconnection associated with the tropical MJO, which likely provides another source of skill on the subseasonal to seasonal time scale.
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Jan van Oldenborgh, Geert, Magdalena A. Balmaseda, Laura Ferranti, Timothy N. Stockdale et David L. T. Anderson. « Evaluation of Atmospheric Fields from the ECMWF Seasonal Forecasts over a 15-Year Period ». Journal of Climate 18, no 16 (15 août 2005) : 3250–69. http://dx.doi.org/10.1175/jcli3421.1.
Texte intégralRésumé :
Abstract Since 1997, the European Centre for Medium-Range Weather Forecasts (ECMWF) has made seasonal forecasts with ensembles of a coupled ocean–atmosphere model, System-1 (S1). In January 2002, a new version, System-2 (S2), was introduced. For the calibration of these models, hindcasts have been performed starting in 1987, so that 15 yr of hindcasts and forecasts are now available for verification. The main cause of seasonal predictability is El Niño and La Niña perturbing the average weather in many regions and seasons throughout the world. As a baseline to compare the dynamical models with, a set of simple statistical models (STAT) is constructed. These are based on persistence and a lagged regression with the first few EOFs of SST from 1901 to 1986 wherever the correlations are significant. The first EOF corresponds to ENSO, and the second corresponds to decadal ENSO. The temperature model uses one EOF, the sea level pressure (SLP) model uses five EOFs, and the precipitation model uses two EOFs but excludes persistence. As the number of verification data points is very low (15), the simplest measure of skill is used: the correlation coefficient of the ensemble mean. To further reduce the sampling uncertainties, we restrict ourselves to areas and seasons of known ENSO teleconnections. The dynamical ECMWF models show better skill in 2-m temperature forecasts over sea and the tropical land areas than STAT, but the modeled ENSO teleconnection pattern to North America is shifted relative to observations, leading to little pointwise skill. Precipitation forecasts of the ECMWF models are very good, better than those of the statistical model, in southeast Asia, the equatorial Pacific, and the Americas in December–February. In March–May the skill is lower. Overall, S1 (S2) shows better skill than STAT at lead time of 2 months in 29 (32) out of 40 regions and seasons of known ENSO teleconnections.
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Small, David, Shafiqul Islam et Mathew Barlow. « The Impact of a Hemispheric Circulation Regime on Fall Precipitation over North America ». Journal of Hydrometeorology 11, no 5 (1 octobre 2010) : 1182–89. http://dx.doi.org/10.1175/2010jhm1273.1.
Texte intégralRésumé :
Abstract While there is growing evidence that the main contribution to trends in U.S. precipitation occurs during fall, most studies of seasonal precipitation have focused on winter or summer. Here, the leading mode of fall precipitation variability over North America is isolated from multiple data sources and connected to a hemispheric-scale circulation pattern. Over North America, the leading mode of fall precipitation variability in both station-based and satellite-blended data is a tripole that links fall precipitation anomalies in southern Alaska, the central United States, and eastern Canada. This mode is part of a larger pattern of alternating wet and dry anomalies stretching from the western Pacific to the North Atlantic. Dynamically, the precipitation anomalies are closely associated with changes to regional-scale moisture transport that are, in turn, linked to two independently identified hemispheric-scale wave patterns that are one-quarter wavelength out of phase (i.e., in quadrature) and resemble the circumglobal teleconnection.
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Nag, Bappaditya, V. Misra et S. Bastola. « Validating ENSO Teleconnections on Southeastern U.S. Winter Hydrology ». Earth Interactions 18, no 15 (1 janvier 2014) : 1–23. http://dx.doi.org/10.1175/ei-d-14-0007.1.
Texte intégralRésumé :
Abstract In this study, the authors contrast four century-long meteorological datasets comprising of two sets of observations [Climate Research Unit (CRU) and Parameter–Elevation Regressions on Independent Slopes Model (PRISM)] and two atmospheric reanalyses [Twentieth Century Reanalysis (20CR) and Florida Climate Institute–Florida State University Land–Atmosphere Regional Reanalysis version 1.0 (FLAReS1.0)] to diagnose the El Niño–Southern Oscillation (ENSO) forced variations on the streamflow in 28 watersheds spread across the southeastern United States (SEUS). The datasets are used to force three different lumped (calibrated) hydrological models with precipitation from these four sources of century-long datasets separately to obtain the median prediction from 1800 (=3 models × 600 simulations per model per watershed per season) multimodel estimates of seasonal mean streamflow across the 28 watersheds in the SEUS for each winter season from 1906 to 2005. The authors then compare and contrast the mean streamflow and its variability estimates from all three of the century-long climate forcings. The multimodel strategy of simulating the seasonal mean streamflow is to reduce the hydrological model uncertainty. The authors focus on the boreal winter season when ENSO influence on the SEUS climate variations is well known. The authors find that the atmospheric reanalysis over the SEUS is able to reasonably capture the ENSO teleconnections as depicted in the CRU and PRISM precipitation datasets. Even the observed decadal modulation of this teleconnection by Atlantic multidecadal oscillation (AMO) is broadly captured. The streamflow in the 28 watersheds also show similar consistency across the four datasets in that the positive correlations of the boreal winter Niño-3.4 SST anomalies with corresponding anomalies of streamflow, the associated shift in the probability density function of the streamflow with the change in phase of ENSO, and the decadal modulation of the ENSO teleconnection by the AMO are sustained in the streamflow simulations forced by all four climate datasets (CRU, PRISM, 20CR, and FLAReS1.0). However, the ENSO signal in the streamflow is consistently much stronger in the southern watersheds (over Florida) of the SEUS across all four climate datasets. During the negative phase of the AMO, however, there is a clear shift of the ENSO teleconnections with streamflow, with winter streamflows in northern watersheds (over the Carolinas) exhibiting much stronger correlations with the ENSO Niño-3.4 index relative to the southern watersheds of the SEUS. This study clearly indicates that the proposed methodology using FLAReS1.0 serves as a viable alternative to reconstruct twentieth-century SEUS seasonal winter hydrology that captures the interannual variations of ENSO and associated decadal variations forced by the AMO. However, it is found that the FLAReS1.0 forced streamflow is far from adequate in simulating the streamflow dynamics of the watershed over the SEUS at a daily time scale.
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Wang, Huaijun, Yingping Pan et Yaning Chen. « Impacts of regional climate and teleconnection on hydrological change in the Bosten Lake Basin, arid region of northwestern China ». Journal of Water and Climate Change 9, no 1 (25 octobre 2017) : 74–88. http://dx.doi.org/10.2166/wcc.2017.140.
Texte intégralRésumé :
Abstract This investigation examined effects of climate change, measured as annual, seasonal, and monthly air temperature and precipitation from 1958 to 2010, on water resources (i.e., runoff) in the Bosten Lake Basin. Additionally, teleconnections of hydrological changes to large-scale circulation indices including El Nino Southern Oscillation (ENSO), Arctic Oscillation (AO), North Atlantic Oscillation (NAO), Tibetan High (XZH), westerly circulation index (WI), and northern hemisphere polar vortex area index (VPA) were analyzed in our study. The results showed the following. (1) Annual and seasonal air temperature increased significantly in the Bosten Lake Basin. Precipitation exhibited an increasing trend, while the significance was less than that of temperature. Abrupt changes were observed in 1996 in mountain temperature and in 1985 in plain temperature. (2) Runoff varied in three stages, decreasing before 1986, increasing from 1987 to 2003, and decreasing after 2003. (3) Precipitation and air temperature have significant impacts on runoff. The hydrological processes in the Bosten Lake Basin were (statistically) significantly affected by the northern hemisphere polar vortex area index (VPA) and the Tibetan High (XZH). The results of this study are good indicators of local climate change, which can enhance human mitigation of climate warming in the Bosten Lake Basin.
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Athanasiadis, Panos J., Alessio Bellucci, Adam A. Scaife, Leon Hermanson, Stefano Materia, Antonella Sanna, Andrea Borrelli, Craig MacLachlan et Silvio Gualdi. « A Multisystem View of Wintertime NAO Seasonal Predictions ». Journal of Climate 30, no 4 (7 février 2017) : 1461–75. http://dx.doi.org/10.1175/jcli-d-16-0153.1.
Texte intégralRésumé :
Abstract Significant predictive skill for the mean winter North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) has been recently reported for a number of different seasonal forecasting systems. These findings are important in exploring the predictability of the natural system, but they are also important from a socioeconomic point of view, since the ability to predict the wintertime atmospheric circulation anomalies over the North Atlantic well ahead in time will have significant benefits for North American and European countries. In contrast to the tropics, for the mid latitudes the predictive skill of many forecasting systems at the seasonal time scale has been shown to be low to moderate. The recent findings are promising in this regard, suggesting that better forecasts are possible, provided that key components of the climate system are initialized realistically and the coupled models are able to simulate adequately the dominant processes and teleconnections associated with low-frequency variability. It is shown that a multisystem approach has unprecedented high predictive skill for the NAO and AO, probably largely due to increasing the ensemble size and partly due to increasing model diversity. Predicting successfully the winter mean NAO does not ensure that the respective climate anomalies are also well predicted. The NAO has a strong impact on Europe and North America, yet it only explains part of the interannual and low-frequency variability over these areas. Here it is shown with a number of different diagnostics that the high predictive skill for the NAO/AO indeed translates to more accurate predictions of temperature, surface pressure, and precipitation in the areas of influence of this teleconnection.
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da Rocha Júnior, Rodrigo Lins, David Duarte Cavalcante Pinto, Fabrício Daniel dos Santos Silva, Heliofábio Barros Gomes, Helber Barros Gomes, Rafaela Lisboa Costa, Marcos Paulo Santos Pereira, Malaquías Peña, Caio Augusto dos Santos Coelho et Dirceu Luís Herdies. « An Empirical Seasonal Rainfall Forecasting Model for the Northeast Region of Brazil ». Water 13, no 12 (8 juin 2021) : 1613. http://dx.doi.org/10.3390/w13121613.
Texte intégralRésumé :
The Northeast region of Brazil (NEB) is characterized by large climate variability that causes extreme and long unseasonal wet and dry periods. Despite significant model developments to improve seasonal forecasting for the NEB, the achievement of a satisfactory accuracy often remains a challenge, and forecasting methods aimed at reducing uncertainties regarding future climate are needed. In this work, we implement and assess the performance of an empirical model (EmpM) based on a decomposition of historical data into dominant modes of precipitation and seasonal forecast applied to the NEB domain. We analyzed the model’s performance for the February-March-April quarter and compared its results with forecasts based on data from the North American Multi-model Ensemble (NMME) project for the same period. We found that the first three leading precipitation modes obtained by empirical orthogonal functions (EOF) explained most of the rainfall variability for the season of interest. Thereby, this study focuses on them for the forecast evaluations. A teleconnection analysis shows that most of the variability in precipitation comes from sea surface temperature (SST) anomalies in various areas of the Pacific and the tropical Atlantic. The modes exhibit different spatial patterns across the NEB, with the first being concentrated in the northern half of the region and presenting remarkable associations with the El Niño-Southern Oscillation (ENSO) and the Atlantic Meridional Mode (AMM), both linked to the latitudinal migration of the intertropical convergence zone (ITCZ). As for the second mode, the correlations with oceanic regions and its loading pattern point to the influence of the incursion of frontal systems in the southern NEB. The time series of the third mode implies the influence of a lower frequency mode of variability, probably related to the Interdecadal Pacific Oscillation (IPO). The teleconnection patterns found in the analysis allowed for a reliable forecast of the time series of each mode, which, combined, result in the final rainfall prediction outputted by the model. Overall, the EmpM outperformed the post-processed NMME for most of the NEB, except for some areas along the northern region, where the NMME showed superiority.
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Ma, Lan, Qiang Huang, Shengzhi Huang, Dengfeng Liu, Guoyong Leng, Lu Wang et Pei Li. « Propagation dynamics and causes of hydrological drought in response to meteorological drought at seasonal timescales ». Hydrology Research 53, no 1 (10 décembre 2021) : 193–205. http://dx.doi.org/10.2166/nh.2021.006.
Texte intégralRésumé :
Abstract According to the widely accepted definition of drought, meteorological and hydrological droughts originally develop from rainfall and runoff deficits, respectively. Runoff deficit is mainly derived from rainfall deficit, and the propagation from meteorological drought to hydrological drought is critical for agricultural water management. Nevertheless, the characteristics and dynamics of drought propagation in the spatiotemporal scale remain unresolved. To this end, the characteristics and dynamics of drought propagation in different seasons and their linkages with key forcing factors are evaluated. In this study, meteorological and hydrological droughts are characterized by the Standardized Precipitation Index (SPI) and the Standardized Runoff Index (SRI), respectively. Propagation time is identified by the corresponding timescale of the maximum correlation coefficient between the SPI and the SRI. Then, a 20-year sliding window is adopted to explore the propagation dynamic in various seasons. Furthermore, the multiple linear regression model is established to quantitatively explore the influence of meteorological factors, underlying surface features and teleconnection factors on the propagation time variations. The Wei River Basin, a typical Loess Plateau watershed in China, is selected as a case study. Results indicate the following: (1) the propagation time from meteorological to hydrological drought is shorter in summer (2 months) and autumn (3 months), whereas it is longer in spring (8 months) and winter (13 months). Moreover, the propagation rates exhibit a decreasing trend in warm seasons, which, however, show an increasing trend in cold seasons; (2) a significant slowing propagation in autumn is mainly caused by the decreasing soil moisture and precipitation, whereas the non-significant tendency in summer is generally induced by the offset between insignificant increasing precipitation and significant decreasing soil moisture; (3) the replenishment from streamflow to groundwater in advance prompts the faster propagation from meteorological to hydrological drought in spring and winter and (4) teleconnection factors have strong influences on the propagation in autumn, in which Arctic Oscillation, El Niño-Southern Oscillation and Pacific Decadal Oscillation mainly affect participation, arid index and soil moisture, thereby impacting drought propagation.
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Warren, Robert J., et Mark A. Bradford. « Seasonal Climate Trends, the North Atlantic Oscillation, and Salamander Abundance in the Southern Appalachian Mountain Region ». Journal of Applied Meteorology and Climatology 49, no 8 (1 août 2010) : 1597–603. http://dx.doi.org/10.1175/2010jamc2511.1.
Texte intégralRésumé :
Abstract The North Atlantic Oscillation (NAO) is a large-scale climate teleconnection that coincides with worldwide changes in weather. Its impacts have been documented at large scales, particularly in Europe, but not as much at regional scales. Furthermore, despite documented impacts on ecological dynamics in Europe, the NAO’s influence on North American biota has been somewhat overlooked. This paper examines long-term temperature and precipitation trends in the southern Appalachian Mountain region—a region well known for its biotic diversity, particularly in salamander species—and examines the connections between these trends and NAO cycles. To connect the NAO phase shifts with southern Appalachian ecology, trends in stream salamander abundance are also examined as a function of the NAO index. The results reported here indicate no substantial long-term warming or precipitation trends in the southern Appalachians and suggest a strong relationship between cool season (November–April) temperature and precipitation and the NAO. More importantly, trends in stream salamander abundance are best explained by variation in the NAO as salamanders are most plentiful during the warmer, wetter phases.
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Peings, Y., Y. Lim et G. Magnusdottir. « Potential Predictability of Southwest U.S. Rainfall : Role of Tropical and High-Latitude Variability ». Journal of Climate 35, no 6 (15 mars 2022) : 1697–717. http://dx.doi.org/10.1175/jcli-d-21-0775.1.
Texte intégralRésumé :
Abstract This study explores the potential predictability of Southwest U.S. (SWUS) precipitation for the November–March season in a set of numerical experiments performed with the Whole Atmospheric Community Climate Model. In addition to the prescription of observed sea surface temperature and sea ice concentration, observed variability from the MERRA-2 reanalysis is prescribed in the tropics and/or the Arctic through nudging of wind and temperature. These experiments reveal how a perfect prediction of tropical and/or Arctic variability in the model would impact the prediction of seasonal rainfall over the SWUS, at various time scales. Imposing tropical variability improves the representation of the observed North Pacific atmospheric circulation, and the associated SWUS seasonal precipitation. This is also the case at the subseasonal time scale due to the inclusion of the Madden–Julian oscillation (MJO) in the model. When additional nudging is applied in the Arctic, the model skill improves even further, suggesting that improving seasonal predictions in high latitudes may also benefit prediction of SWUS precipitation. An interesting finding of our study is that subseasonal variability represents a source of noise (i.e., limited predictability) for the seasonal time scale. This is because when prescribed in the model, subseasonal variability, mostly the MJO, weakens the El Niño–Southern Oscillation (ENSO) teleconnection with SWUS precipitation. Such knowledge may benefit S2S and seasonal prediction as it shows that depending on the amount of subseasonal activity in the tropics on a given year, better skill may be achieved in predicting subseasonal rather than seasonal rainfall anomalies, and conversely. Significance Statement Subseasonal and seasonal predictability of precipitation over the Southwest United States (SWUS) during the wet season is challenging, and long-range forecasts from climate models still exhibit poor skill over this region. In this study we use numerical experiments with constrained tropical and/or Arctic atmospheric variability to explore how climate processes in these two regions impact the SWUS precipitation. Our results highlight how much forecast skill in SWUS precipitation may be gained from better predictions in tropical and high latitudes, from subseasonal to multiyear time scales.
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Jiang, Rengui, Yinping Wang, Jiancang Xie, Yong Zhao, Fawen Li et Xiaojie Wang. « Multiscale characteristics of Jing-Jin-Ji’s seasonal precipitation and their teleconnection with large-scale climate indices ». Theoretical and Applied Climatology 137, no 1-2 (30 octobre 2018) : 1495–513. http://dx.doi.org/10.1007/s00704-018-2682-3.
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Siqueira, L., B. P. Kirtman et L. C. Laurindo. « Forecasting Remote Atmospheric Responses to Decadal Kuroshio Stability Transitions ». Journal of Climate 34, no 1 (janvier 2021) : 379–95. http://dx.doi.org/10.1175/jcli-d-20-0139.1.
Texte intégralRésumé :
AbstractBased on observational estimates and global ocean eddy-resolving coupled retrospective initialized predictions, we show that Kuroshio Extension variability affects rainfall variability along the west coast of North America. We show that the teleconnection between the current undulations and downstream rainfall can lead to improved subseasonal to seasonal predictions of precipitation over California, and we demonstrate that capturing these teleconnections requires coupled systems with sufficient ocean resolution (i.e., eddy-resolving), especially over time scales longer than one season. The improved forecast skill is diagnosed in terms of 35 years of retrospective initialized ensemble forecasts with an ocean eddy-resolving and an ocean eddy-parameterized coupled model. Not only does the ocean eddy-resolving model show sensitivity to Kuroshio Extension variability in terms of western North America precipitation, but the ocean eddy-resolving forecasts also show improved forecast skill compared to the ocean eddy-parameterized model. The ocean eddy-parameterized coupled model shows no sensitivity to Kuroshio Extension variability. We also find near-decadal variability associated with a progression of a lower-tropospheric height dipole around the North Pacific and how these height anomalies lead to wind-driven Rossby waves that affect the eddy activity in the Kuroshio Extension with a time lag on the order of four years. This decadal-scale variability (~10 years) opens the possibility of multiyear predictability of western North American rainfall.
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O’Reilly, Christopher H., Tim Woollings, Laure Zanna et Antje Weisheimer. « The Impact of Tropical Precipitation on Summertime Euro-Atlantic Circulation via a Circumglobal Wave Train ». Journal of Climate 31, no 16 (août 2018) : 6481–504. http://dx.doi.org/10.1175/jcli-d-17-0451.1.
Texte intégralRésumé :
The influence of tropical precipitation variability on summertime seasonal circulation anomalies in the Euro-Atlantic sector is investigated. The dominant mode of the maximum covariance analysis (MCA) between the Euro-Atlantic circulation and tropical precipitation reveals a cyclonic anomaly over the extratropical North Atlantic, contributing to anomalously wet conditions over western Europe and dry conditions over eastern Europe and Scandinavia (in the positive phase). The related mode of tropical precipitation variability is associated with tropical Pacific SST anomalies and is closely linked to the El Niño–Southern Oscillation (ENSO). The second MCA mode consists of weaker tropical precipitation anomalies but with a stronger extratropical signal that reflects internal atmospheric variability. The teleconnection mechanism is tested in barotropic model simulations, which indicate that the observed link between the dominant mode of tropical precipitation and the Euro-Atlantic circulation anomalies is largely consistent with linear Rossby wave dynamics. The barotropic model response consists of a circumglobal wave train in the extratropics that is primarily forced by divergence anomalies in the eastern tropical Pacific. Both the eastward and westward group propagation of the Rossby waves are found to be important in determining the circulation response over the Euro-Atlantic sector. The mechanism was also analyzed in an operational seasonal forecasting system, ECMWF’s System 4. While System 4 is well able to reproduce and skillfully forecast the tropical precipitation, the extratropical circulation response is absent over the Euro-Atlantic region, which is likely related to biases in the Asian jet stream.
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Zeng, Z., W. W. Hsieh, A. Shabbar et W. R. Burrows. « Seasonal prediction of winter extreme precipitation over Canada by support vector regression ». Hydrology and Earth System Sciences 15, no 1 (6 janvier 2011) : 65–74. http://dx.doi.org/10.5194/hess-15-65-2011.
Texte intégralRésumé :
Abstract. For forecasting the maximum 5-day accumulated precipitation over the winter season at lead times of 3, 6, 9 and 12 months over Canada from 1950 to 2007, two nonlinear and two linear regression models were used, where the models were support vector regression (SVR) (nonlinear and linear versions), nonlinear Bayesian neural network (BNN) and multiple linear regression (MLR). The 118 stations were grouped into six geographic regions by K-means clustering. For each region, the leading principal components of the winter maximum 5-d accumulated precipitation anomalies were the predictands. Potential predictors included quasi-global sea surface temperature anomalies and 500 hPa geopotential height anomalies over the Northern Hemisphere, as well as six climate indices (the Niño-3.4 region sea surface temperature, the North Atlantic Oscillation, the Pacific-North American teleconnection, the Pacific Decadal Oscillation, the Scandinavia pattern, and the East Atlantic pattern). The results showed that in general the two robust SVR models tended to have better forecast skills than the two non-robust models (MLR and BNN), and the nonlinear SVR model tended to forecast slightly better than the linear SVR model. Among the six regions, the Prairies region displayed the highest forecast skills, and the Arctic region the second highest. The strongest nonlinearity was manifested over the Prairies and the weakest nonlinearity over the Arctic.
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Zeng, Z., W. W. Hsieh, A. Shabbar et W. R. Burrows. « Seasonal prediction of winter extreme precipitation over Canada by support vector regression ». Hydrology and Earth System Sciences Discussions 7, no 3 (16 juin 2010) : 3521–50. http://dx.doi.org/10.5194/hessd-7-3521-2010.
Texte intégralRésumé :
Abstract. For forecasting the maximum 5-d accumulated precipitation over the winter season at lead times of 3, 6, 9 and 12 months over Canada from 1950 to 2007, two nonlinear and two linear regression models were used, where the models were support vector regression (SVR) (nonlinear and linear versions), nonlinear Bayesian neural network (BNN) and multiple linear regression (MLR). The 118 stations were grouped into six geographic regions by K-means clustering. For each region, the leading principal components of the winter extreme precipitation were the predictands. Potential predictors included quasi-global sea surface temperature anomalies and 500 hPa geopotential height anomalies over the Northern Hemisphere, as well as six climate indices (the Niño-3.4 region sea surface temperature, the North Atlantic Oscillation, the Pacific-North American teleconnection, the Pacific Decadal Oscillation, the Scandinavia pattern, and the East Atlantic pattern). The results showed that in general the two robust SVR models tended to have better forecast skills than the two non-robust models (MLR and BNN), and the nonlinear SVR model tended to forecast slightly better than the linear SVR model. Among the six regions, the Eastern Prairies region displayed the highest forecast skills, and the Arctic region the second highest. The strongest nonlinearity was manifested over the Eastern Prairies and the weakest nonlinearity over the Arctic.
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Stephan, Claudia Christine, Nicholas P. Klingaman, Pier Luigi Vidale, Andrew G. Turner, Marie-Estelle Demory et Liang Guo. « Interannual rainfall variability over China in the MetUM GA6 and GC2 configurations ». Geoscientific Model Development 11, no 5 (8 mai 2018) : 1823–47. http://dx.doi.org/10.5194/gmd-11-1823-2018.
Texte intégralRésumé :
Abstract. Six climate simulations of the Met Office Unified Model Global Atmosphere 6.0 and Global Coupled 2.0 configurations are evaluated against observations and reanalysis data for their ability to simulate the mean state and year-to-year variability of precipitation over China. To analyse the sensitivity to air–sea coupling and horizontal resolution, atmosphere-only and coupled integrations at atmospheric horizontal resolutions of N96, N216 and N512 (corresponding to ∼ 200, 90 and 40 km in the zonal direction at the equator, respectively) are analysed. The mean and interannual variance of seasonal precipitation are too high in all simulations over China but improve with finer resolution and coupling. Empirical orthogonal teleconnection (EOT) analysis is applied to simulated and observed precipitation to identify spatial patterns of temporally coherent interannual variability in seasonal precipitation. To connect these patterns to large-scale atmospheric and coupled air–sea processes, atmospheric and oceanic fields are regressed onto the corresponding seasonal mean time series. All simulations reproduce the observed leading pattern of interannual rainfall variability in winter, spring and autumn; the leading pattern in summer is present in all but one simulation. However, only in two simulations are the four leading patterns associated with the observed physical mechanisms. Coupled simulations capture more observed patterns of variability and associate more of them with the correct physical mechanism, compared to atmosphere-only simulations at the same resolution. However, finer resolution does not improve the fidelity of these patterns or their associated mechanisms. This shows that evaluating climate models by only geographical distribution of mean precipitation and its interannual variance is insufficient. The EOT analysis adds knowledge about coherent variability and associated mechanisms.
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Räsänen, Timo A., Ville Lindgren, Joseph H. A. Guillaume, Brendan M. Buckley et Matti Kummu. « On the spatial and temporal variability of ENSO precipitation and drought teleconnection in mainland Southeast Asia ». Climate of the Past 12, no 9 (21 septembre 2016) : 1889–905. http://dx.doi.org/10.5194/cp-12-1889-2016.
Texte intégralRésumé :
Abstract. The variability of the hydroclimate over mainland Southeast Asia is strongly influenced by the El Niño–Southern Oscillation (ENSO), which has been linked to severe droughts and floods that profoundly influence human societies and ecosystems alike. Although the significance of ENSO is well understood, there are still limitations in the understanding of its effects on hydroclimate, particularly with regard to understanding the spatio-temporal characteristics and the long-term variation of its effects. Therefore we analysed the seasonal evolution and spatial variations in the effect of ENSO on precipitation over the period of 1980–2013 and the long-term variation in the ENSO teleconnection using tree-ring-derived Palmer drought severity indices (PDSIs) for the March–May season that span over the time period 1650–2004. The analyses provided an improved understanding of the seasonal evolution of the precipitation anomalies during ENSO events. The effects of ENSO were found to be most consistent and expressed over the largest areal extents during March–May of the year when the ENSO events decay. On a longer timescale, we found that ENSO has affected the region's March–May hydroclimate over the majority (95 %) of the 355-year study period and that during half (52 %) of the time ENSO caused a significant increase in hydroclimatic variability. The majority of the extremely wet and dry March–May seasons also occurred during ENSO events. However, considerable variability in ENSO's influence was revealed: the spatial pattern of precipitation anomalies varied between individual ENSO events, and the strength of ENSO's influence was found to vary through time. Given the high variability in ENSO teleconnection that we described and the limitations of the current understanding of the effects of ENSO, we suggest that the adaptation to ENSO-related extremes in hydroclimate over mainland Southeast Asia needs to recognise uncertainty as an inherent part of adaptation, must go beyond "predict and control", and should seek adaptation opportunities widely within society.