Littérature scientifique sur le sujet « Seasonal precipitation teleconnection »
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Articles de revues sur le sujet "Seasonal precipitation teleconnection"
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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.
Thèses sur le sujet "Seasonal precipitation teleconnection"
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Sakian, Nicholas A. « Seasonal Trends and Variability of Temperature, Precipitation, and Diurnal Temperature Range in U.S. Climate Divisions ». The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1440428134.
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Zamboni, Laura. « Seasonal variability of precipitation over South Eastern South America : its relationship with upper level circulation as physical base for predictions ». Doctoral thesis, Università degli studi di Trieste, 2009. http://hdl.handle.net/10077/3212.
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2007/2008At the interannual timescale Sea Surface Temperature (SST) associated with El Niño Southern Oscillation (ENSO) have been identified as modulators of rainfall over South America. The proposed mechanism responsible for anomalies over northern South America involves the modification of the Walker circulation, while the generation (or excitement) of the Pacific-South American (PSA) modes would represent the teleconnection to the subtropics. However, the latter is present even in seasons in which ENSO is not at its peak. In this study our aim is to investigate the interannual variability of seasonal precipitation over South Eastern South America (SESA), which comprises southern Brazil, Uruguay, Paraguay and northeastern Argentina, and its dynamical dependence from ENSO and the PSA modes. We have shown the existence of a pervasive mode of upper level atmospheric variability which dominates the circulation over South America in all seasons. The mode consists of a continental scale vortex and resembles the eastern end of the leading Pacific-South American mode (PSA1). Differences in the structure and intensity of the vortex and the effects of orography affect the transport and convergence of moisture into SESA thus creating rainfall anomalies there. Motivated by and to test further the reported relationship between the upper level wind and precipitation anomalies, we developed a method to predict precipitation over SESA in which the upper level wind is the predictor. The method has a high potential in all seasons, but limited skill in forecast mode due to limitations of Coupled General Circulation Model performances. In exploring the predictability of the vortex, we assessed to what extent each connection of the schematic chain ENSO->PSA1->vortex->rainfall holds. The latter relationship between the vortex over SA and rainfall in SESA holds in spring, summer and fall. The vortex is, at least partially, an internal mode of variability in all seasons. In spring the whole chain of elements is observed: the vortex appears as a mode forced by ENSO via excitement of the leading PSA mode. In summer the vortex is uncoupled from the circulation over the Pacific Ocean, supporting the interpretation that regional effects dominate during the monsoon season. No connection with SSTs, and thus predictability, is found for this season. In fall the PSA1 pattern and the vortex are partially linked as for the spring season. However, the connection with SSTs is more puzzling and further analysis is required to clarify the nature of the leading PSA mode and its predictability. In view of our results, we underline that the leading Pacific-South American pattern properly comprehends centers of anomalies over the Southern Pacific Ocean only but not those over the South American sector.
XXI Ciclo
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Luciani, Riccardo. « Study of Europe-ENSO teleconnection in an El Niño index phase analysis framework ». Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/18807/.
Texte intégralRésumé :
El Niño/Southern Oscillation (ENSO) is the most important coupled ocean-atmosphere phenomenon to cause global climate variability on seasonal to interannual time scales. Therefore understanding some of its most important features may help to shed light on the field of climate predictions. Here the focus is put on the seasonal precipitation patterns which respond to persistent thermal forcing happening thousands of kilometers far away.
The first objective of this work is to look for and describe the correlation patterns between seasonal rainfall anomalies over Northern Italy and global seasonal Sea Surface Temperature anomalies (SSTA). Tri-monthly means of precipitation and tri-monthly means of SSTA from observational datasets are used in an anomaly correlation study in order to explore this teleconnection. The study is developed in the Nino Index Phase Analysis (NIPA) framework, as presented by Zimmerman et al., which consists in separating the positive and negative ENSO phase years in the computation of the anomaly correlation.
The second objective of the work is to check if the correlations found are consistent with the shift of the circulation pattern which is due to a non-weak ENSO state. The anomaly means of the main ocean-atmospheric variables are examined in order to characterise the way in which the circulation works when the system is under El Niño or La Niña conditions and when the precipitation over the basins is higher or lower.
Then, a Rossby waves simulation software is used to show that the propagation of a Rossby wave train, in a basic state with zonally varying middle latitude or low latitude jet, may be the cause of the correlations in the area under exam and for the seasons chosen, and how. This is an indication of the fact that the ENSO state and its spatial features can influence the tropospheric pathways through which planetary waves can propagate and this, in turn, could have an effect on midlatitudes large-scale circulation.
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Bonsal, Barrie Richard. « Teleconnections between ENSO events and growing season precipitation on the Canadian Prairies ». Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq24052.pdf.
Texte intégralLivres sur le sujet "Seasonal precipitation teleconnection"
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Goswami, B. N., et Soumi Chakravorty. Dynamics of the Indian Summer Monsoon Climate. Oxford University Press, 2017. http://dx.doi.org/10.1093/acrefore/9780190228620.013.613.
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Lifeline for about one-sixth of the world’s population in the subcontinent, the Indian summer monsoon (ISM) is an integral part of the annual cycle of the winds (reversal of winds with seasons), coupled with a strong annual cycle of precipitation (wet summer and dry winter). For over a century, high socioeconomic impacts of ISM rainfall (ISMR) in the region have driven scientists to attempt to predict the year-to-year variations of ISM rainfall. A remarkably stable phenomenon, making its appearance every year without fail, the ISM climate exhibits a rather small year-to-year variation (the standard deviation of the seasonal mean being 10% of the long-term mean), but it has proven to be an extremely challenging system to predict. Even the most skillful, sophisticated models are barely useful with skill significantly below the potential limit on predictability. Understanding what drives the mean ISM climate and its variability on different timescales is, therefore, critical to advancing skills in predicting the monsoon. A conceptual ISM model helps explain what maintains not only the mean ISM but also its variability on interannual and longer timescales.The annual ISM precipitation cycle can be described as a manifestation of the seasonal migration of the intertropical convergence zone (ITCZ) or the zonally oriented cloud (rain) band characterized by a sudden “onset.” The other important feature of ISM is the deep overturning meridional (regional Hadley circulation) that is associated with it, driven primarily by the latent heat release associated with the ISM (ITCZ) precipitation. The dynamics of the monsoon climate, therefore, is an extension of the dynamics of the ITCZ. The classical land–sea surface temperature gradient model of ISM may explain the seasonal reversal of the surface winds, but it fails to explain the onset and the deep vertical structure of the ISM circulation. While the surface temperature over land cools after the onset, reversing the north–south surface temperature gradient and making it inadequate to sustain the monsoon after onset, it is the tropospheric temperature gradient that becomes positive at the time of onset and remains strongly positive thereafter, maintaining the monsoon. The change in sign of the tropospheric temperature (TT) gradient is dynamically responsible for a symmetric instability, leading to the onset and subsequent northward progression of the ITCZ. The unified ISM model in terms of the TT gradient provides a platform to understand the drivers of ISM variability by identifying processes that affect TT in the north and the south and influence the gradient.The predictability of the seasonal mean ISM is limited by interactions of the annual cycle and higher frequency monsoon variability within the season. The monsoon intraseasonal oscillation (MISO) has a seminal role in influencing the seasonal mean and its interannual variability. While ISM climate on long timescales (e.g., multimillennium) largely follows the solar forcing, on shorter timescales the ISM variability is governed by the internal dynamics arising from ocean–atmosphere–land interactions, regional as well as remote, together with teleconnections with other climate modes. Also important is the role of anthropogenic forcing, such as the greenhouse gases and aerosols versus the natural multidecadal variability in the context of the recent six-decade long decreasing trend of ISM rainfall.
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Cook, Kerry H. Climate Change Scenarios and African Climate Change. Oxford University Press, 2018. http://dx.doi.org/10.1093/acrefore/9780190228620.013.545.
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Accurate projections of climate change under increasing atmospheric greenhouse gas levels are needed to evaluate the environmental cost of anthropogenic emissions, and to guide mitigation efforts. These projections are nowhere more important than Africa, with its high dependence on rain-fed agriculture and, in many regions, limited resources for adaptation. Climate models provide our best method for climate prediction but there are uncertainties in projections, especially on regional space scale. In Africa, limitations of observational networks add to this uncertainty since a crucial step in improving model projections is comparisons with observations. Exceeding uncertainties associated with climate model simulation are uncertainties due to projections of future emissions of CO2 and other greenhouse gases. Humanity’s choices in emissions pathways will have profound effects on climate, especially after the mid-century.The African Sahel is a transition zone characterized by strong meridional precipitation and temperature gradients. Over West Africa, the Sahel marks the northernmost extent of the West African monsoon system. The region’s climate is known to be sensitive to sea surface temperatures, both regional and global, as well as to land surface conditions. Increasing atmospheric greenhouse gases are already causing amplified warming over the Sahara Desert and, consequently, increased rainfall in parts of the Sahel. Climate model projections indicate that much of this increased rainfall will be delivered in the form of more intense storm systems.The complicated and highly regional precipitation regimes of East Africa present a challenge for climate modeling. Within roughly 5º of latitude of the equator, rainfall is delivered in two seasons—the long rains in the spring, and the short rains in the fall. Regional climate model projections suggest that the long rains will weaken under greenhouse gas forcing, and the short rains season will extend farther into the winter months. Observations indicate that the long rains are already weakening.Changes in seasonal rainfall over parts of subtropical southern Africa are observed, with repercussions and challenges for agriculture and water availability. Some elements of these observed changes are captured in model simulations of greenhouse gas-induced climate change, especially an early demise of the rainy season. The projected changes are quite regional, however, and more high-resolution study is needed. In addition, there has been very limited study of climate change in the Congo Basin and across northern Africa. Continued efforts to understand and predict climate using higher-resolution simulation must be sustained to better understand observed and projected changes in the physical processes that support African precipitation systems as well as the teleconnections that communicate remote forcings into the continent.
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Rosenzweig, Cynthia, et Daniel Hillel. Climate Variability and the Global Harvest. Oxford University Press, 2008. http://dx.doi.org/10.1093/oso/9780195137637.001.0001.
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The Earth's climate is constantly changing. Some of the changes are progressive, while others fluctuate at various time scales. The El Niño-la Niña cycle is one such fluctuation that recurs every few years and has far-reaching impacts. It generally appears at least once per decade, but this may vary with our changing climate. The exact frequency, sequence, duration and intensity of El Niño's manifestations, as well as its effects and geographic distributions, are highly variable. The El Niño-la Niña cycle is particularly challenging to study due to its many interlinked phenomena that occur in various locations around the globe. These worldwide teleconnections are precisely what makes studying El Niño-la Niña so important. Cynthia Rosenzweig and Daniel Hillel describe the current efforts to develop and apply a global-to-regional approach to climate-risk management. They explain how atmospheric and social scientists are cooperating with agricultural practitioners in various regions around the world to determine how farmers may benefit most from new climate predictions. Specifically, the emerging ability to predict the El Niño-Southern Oscillation (ENSO) cycle offers the potential to transform agricultural planning worldwide. Biophysical scientists are only now beginning to recognize the large-scale, globally distributed impacts of ENSO on the probabilities of seasonal precipitation and temperature regimes. Meanwhile, social scientists have been researching how to disseminate forecasts more effectively within rural communities. Consequently, as the quality of climatic predictions have improved, the dissemination and presentation of forecasts have become more effective as well. This book explores the growing understanding of the interconnectedness of climate predictions and productive agriculture for sustainable development, as well as methods and models used to study this relationship.
Chapitres de livres sur le sujet "Seasonal precipitation teleconnection"
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Rosenzweig, Cynthia, et Daniel Hillel. « Links to Agroecosystems : Processes and Productivity ». Dans Climate Variability and the Global Harvest. Oxford University Press, 2008. http://dx.doi.org/10.1093/oso/9780195137637.003.0008.
Texte intégralRésumé :
The climate teleconnections related to El Niño–Southern Oscillation (ENSO) events described in chapter 1 have global implications regarding agriculture. In many locations, ENSO events appear to account for a significant part of the climate variability that governs the responses of crops and livestock on a range of temporal and spatial scales. Teleconnections affect variations in production both within growing seasons and from one season or year to another. Precipitation, temperature, and other climate variables are key determinants of crop growth and livestock health, affecting all aspects of agroecosystems, including the survival and reproduction of both beneficial and damaging insects. An understanding of ENSO teleconnections may help farmers and regional planners assess changes in probable yield levels before the growing season and thus provide guidance for improved management. In this chapter we introduce agricultural responses to climate extremes in general and to ENSO climate teleconnections in particular. Subsequent chapters describe methods of analysis, use of ENSO predictions for agriculture, and regional aspects in more detail. Variability in agricultural production affects risk on at least five levels: individual farms, farming regions within nations, nations, groups of nations, and the global food system. Contributing factors and consequences of variability at successive levels differ in type and scale. Perhaps the most relevant example of these differences is the contrast between the effect of variability on a single farm and its effect at the national level for any country in which the agricultural sector plays a significant role in the overall economy. At the individual farm level, the aim is generally to produce high yields as consistently as possible. Hence, the main concern regarding climate is the occurrence of seasons with low yield levels that threaten subsistence or income. When regional or national yields are very low, overall food security may be threatened, necessitating relief efforts by donor countries and agencies. At the national level, however, problems may be caused not only by low yields but also by the opposite—unusually high yields. Whereas low national yields may cause food shortages and high food prices, high overall yields tend to lower commodity prices paid to farmers and create excessive surpluses that necessitate government intervention. High variability in food production at the national level thus can destabilize domestic prices, farm income, and national budgets.
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Goodin, Douglas G. « Introductory Overview ». Dans Climate Variability and Ecosystem Response in Long-Term Ecological Research Sites. Oxford University Press, 2003. http://dx.doi.org/10.1093/oso/9780195150599.003.0022.
Texte intégralRésumé :
Timescale is the organizing framework of this volume. In various sections, we consider the effects of climate variability on ecosystems at timescales ranging from weeks or months to centuries. In part III, we turn our attention to interdecadal-scale events. The timescales we consider are not absolutely defined, but for our purposes we define the interdecadal scale to encompass effects occurring with recurring cycles generally ranging from 10 to 50 years. A recurring theme in many of the chapters in this section is the effect on ecosystem response of teleconnection patterns associated with recognized quasi-periodic atmospheric circulation modes. These circulation modes include the well-known El Niño– Southern Oscillation (ENSO) phenomenon, which is generally thought to recur at shorter, interdecadal timescales but also includes some longer-term periodicities. Several other climate variability modes, including the Pacific North American index (PNA), North Atlantic Oscillation (NAO), Pacific Decadal Oscillation (PDO), and North Pacific index (NP) also show strong interdecadal scale signatures and figure prominently in the chapters of part III. McHugh and Goodin begin the section by examining the climate record at several North American LTER sites for evidence of interdecadal-scale fluctuation. They note that interdecadal-scale contributions to climate variability can best be described in terms of two types of variation: (1) discontinuities in mean value, and (2) the presence of trends in the data. Evaluation of interdecadal periodicities in LTER data is complicated by the relatively short time series of observations available. McHugh and Goodin approach the problem mainly through the use of power spectrum analysis, a widely used tool for evaluating the periodicity in a time series of data. Principal components analysis is used to decompose the time series of growing-season climate data for each of the LTER sites into their principal modes of variability. These modes are then subjected to power spectrum analysis to evaluate the proportions of the variance in the data occurring at various timescales. McHugh and Goodin’s results suggest that significant effects on precipitation and temperature at interdecadal timescales are uncommon in these data, although significant periodicities at both shorter and longer frequencies do emerge from the data (a finding of relevance to other sections of this volume).