Atmospheric mass is transported in and out of the stratospheric polar cap region by a wave-driven meridional circulation. Using composites of polar cap pressure anomalies, defined as deviations from the average annual cycle, it is shown that this stratospheric mass flux is accompanied by a similar mass flux near the surface. This 'tropospheric amplification' of the stratospheric signal is introduced as a new way to quantify stratosphere-troposphere coupling. Regression analysis is used to create a vertical profile of atmospheric pressure during a tropospheric amplification event, and the regression slope profile is used as a tool to quantify the amplification. Using data from 5 reanalysis datasets and 11 climate models, it is shown that high-top models, with a model lid of above 1 hPa, are significantly better at reproducing tropospheric amplification than low-top models, due to having more detailed parameterisations of stratospheric processes. However, the regression slope profiles of all models, bar one, are significantly different to the profile of reanalysis data at a 95% confidence level. Tropospheric amplification is also investigated in historical and future simulations from these models, and it is concluded that there is not expected to be a large change in the phenomenon over the next 100 years. The processes needed to reproduce tropospheric amplification can be identified by comparing idealised models of different complexity. A simple dry-core model is not able to reproduce tropospheric amplification, while a model with a comprehensive radiation scheme does produce the basic regression slope profile under certain configurations. The associations between pressure change and mass flux are further investigated using primitive equations. It is found that vertical and horizontal contributions to mass flux act to mostly cancel each other out, leaving a poorly-conditioned residual, and that the horizontal mass flux across the polar cap boundary has both geostrophic and ageostrophic components.

Atmosphere-Ocean General Circulation Models (AOGCMs) are the primary tool for modelling global climate change in the future. However, their coarse spatial resolution does not permit direct application for local scale impact studies. Therefore, either dynamical or statistical downscaling techniques are used for translating AOGCM outputs to local scale climatic variables. The main goal of this study was to improve our understanding of the historical and future climate change at local-scale in the Canadian Prairie Provinces (CPPs) of Alberta, Saskatchewan and Manitoba, comprising 47 diverse watersheds. Given the vast nature of the study area and paucity of recorded data, a novel approach for identifying homogeneous regions for regionalization of precipitation characteristics for the CPPs was proposed. This approach incorporated information about predictors ― large-scale atmospheric covariates from the National Center for Environmental Prediction (NCEP) Reanalysis-I, teleconnection indices and geographical site attributes that impact spatial patterns of precipitation in order to delineate homogeneous precipitation regions using a combination of multivariate approaches. This resulted in the delimitation of five homogeneous climatic regions which were validated independently for homogeneity using statistics computed from observations recorded at 120 stations across the CPPs. For multisite multivariate statistical downscaling, an approach based on the Generalized Linear Model (GLM) framework was developed to downscale daily observations of precipitation and minimum and maximum temperatures from 120 sites located across the CPPs. First, the aforementioned predictors and observed daily precipitation and temperature records were used to calibrate GLMs for the 1971–2000 period. Then the calibrated GLMs were used to generate daily sequences of precipitation and temperatures for the 1962–2005 historical (conditioned on NCEP predictors), and future period (2006–2100) using outputs from six CMIP5 (Coupled Model Intercomparison Project Phase-5) AOGCMs corresponding to Representative Concentration Pathway (RCP): RCP2.6, RCP4.5, and RCP8.5 scenarios. The results indicated that the fitted GLMs were able to capture spatiotemporal characteristics of observed climatic fields. According to the downscaled future climate, mean precipitation is projected to increase in summer and decrease in winter while minimum temperature is expected to warm faster than the maximum temperature. Climate extremes are projected to intensify with increased radiative forcing.

This study investigated the impact of changing climate and growing population on water supply and demand in one of the most rapidly growing cities in the semi-arid regions of western US, Las Vegas Valley (LVV), Nevada. Future scenarios of supply and demand using climate and hydrological models of Coupled Model Intercomparison Project phase 3 (CMIP3) and a more recent CMIP5 have been evaluated and a comparison of their results has been made. A system dynamics model for LVV was developed with a period of study from 1989 to 2049. For the study area, climate and hydrological data projections for the future period (2013-2049) were obtained from the outputs of 16 Global Climate Models (GCMs) of CMIP3 model ensemble with 3 emission scenarios and that from 37 GCMs of CMIP5 model ensemble with 4 Representative concentration pathways. Population growth forecast by Center for Business and Economic Research (CBER) and prevalent conservation practices by Southern Nevada Water Authority (SNWA) were used for the model. The water availability scenario in the future for LVV in the form of Lake Mead elevation was assessed and the water demand was also predicted. This study found that mean lake elevation for the future period (2013-2049) can go as low as 21.8% lesser than that for the historical period (1989-2012). 59 of 97 projections of CMIP5 models against 27 of 48 projections of CMIP3 models indicated that the future mean lake elevation would be lower than the historical mean. Demand forecasts showed Southern Nevada Water Authority conservation goal for 2035 could be met under prevalent conservation practices. This study can be very useful for the water managers and planners to predict the future water budget, plan accordingly, and make decisions to achieve water sustainability. This study has been performed as a part of the Thriving Earth Exchange (TEX) program to assess the current vulnerability of LVV to drought, and the impact on supply and demand of water resources for the future climate scenarios.

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2016-05-04T00:12:48Z No. of bitstreams: 1 NaurineteDeJesusDaCostaBarreto_TESE.pdf: 20476602 bytes, checksum: ddf29db5dc57738de84c8009f0e93e2b (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2016-05-06T19:50:50Z (GMT) No. of bitstreams: 1 NaurineteDeJesusDaCostaBarreto_TESE.pdf: 20476602 bytes, checksum: ddf29db5dc57738de84c8009f0e93e2b (MD5) / Made available in DSpace on 2016-05-06T19:50:50Z (GMT). No. of bitstreams: 1 NaurineteDeJesusDaCostaBarreto_TESE.pdf: 20476602 bytes, checksum: ddf29db5dc57738de84c8009f0e93e2b (MD5) Previous issue date: 2015-02-06 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior (CAPES) / A variabilidade intrassazonal ? uma importante componente do sistema clim?tico da Terra, apresenta intera??o com diversos fen?menos meteorol?gicos, sendo um elo entre os sistemas de tempo e clima, tornando-se uma ferramenta essencial para previs?o e proje??o do clima. O objetivo principal deste trabalho ? avaliar o comportamento intrassazonal da precipita??o sobre o Brasil Tropical e poss?veis altera??es ocasionadas nos cen?rios de simula??o clim?tica: ?Historical? que representa o clima atual (1979 -2005) e ?RCP8.5? representando as proje??es de mudan?as clim?ticas com o aumento da for?ante radioativa da atmosf?rica em 8,5 W/m? para o per?odo de 2070 at? 2100. Entre os resultados obtidos est?o: na primeira etapa ? elabora??o de um ?ndice multivariado intrassazonal para o Brasil Tropical, por meio da aplica??o da an?lise de m?xima covari?ncia, associada ? proje??o dos modos dominantes em eixos ortogonais. Desta forma ? poss?vel caracterizar os padr?es resultantes em oitos fases, cujas composi??es representam a evolu??o da intrassazonalidade sobre a regi?o de estudo. Na segunda Etapa foi realizada uma avalia??o da sensibilidade dos modelos do ?Coupled Model Intercomparison Project Phase 5?(CMIP5) ? variabilidade semanal de precipita??o durante os meses de ver?o e outono austal, dos dezesseis modelos avaliados, observou-se que apenas seis foram capazes de representar de forma significativa o padr?o de precipita??o, e dentre estes o modelo MRI-CGCM3 foi o que obteve o melhor resultado. A terceira e ultima etapa consistiu na aplica??o da metodologia empregada na etapa 1 no modelo que melhor representou o padr?o de precipita??o, encontrado na Etapa 2, ou seja no MRI-CGCM3, num contexto geral notou-se que este modelo ? capaz de representar bem o padr?o de variabilidade espacial e ciclo evolutivo, entretanto do ponto de vista regional, ainda h? necessidade de melhorias na representatividade dos sistemas. / The intraseasonal variability is an important component of Earth?s climate system, shows interaction with various meteorological phenomena, being a link between weather and climate systems, making it an essential tool for forecasting and climate projection. The aim of this study is to evaluate the behavior of intraseasonal precipitation over Brazil Tropical and possible changes caused in climate simulation scenarios, Historical that represents the current climate (1979 -2005) and Representative Concentration Pathways (RCP8.5) representing projections of climate change with increasing radioactive forcing of air at 8.5W/m2 for the period 2070 to 2100. Among the results are: the ?rst step to the establishment of a intraseasonal multivariate index for Brazil Tropical, by applying the maximum covariance analysis, associated with the projection ofthedominantmodesinorthogonalaxes.Thusitispossibletocharacterizetheresulting patterns in eight phases, whose compositions represent the evolution of intrassazonalidade on the study region. In the second step was carried out an assessment of the sensitivity of the models Coupled Model Intercomparison Project Phase 5 (CMIP5) theweeklyvariabilityofrainfallduringthemonthsofsummerandfallAustal,thesixteen models evaluated, it was observed that only six were able to represent signi?cantly the pattern of rainfall, and of these MRI-CGCM3 model was the one that obtained the best result. The third and ?nal step was the application of the methodology used in step 1 in the model that best represented the rainfall pattern, found in Step 2, ie in MRI-CGCM3 in a general context it was noted that this model is able to represent well the pattern of spatial variability and evolutionary cycle, however the regional point of view, there is still need for improvement in the representation of systems.

abstract: The numerical climate models have provided scientists, policy makers and the general public, crucial information for climate projections since mid-20th century. An international effort to compare and validate the simulations of all major climate models is organized by the Coupled Model Intercomparison Project (CMIP), which has gone through several phases since 1995 with CMIP5 being the state of the art. In parallel, an organized effort to consolidate all observational data in the past century culminates in the creation of several "reanalysis" datasets that are considered the closest representation of the true observation. This study compared the climate variability and trend in the climate model simulations and observations on the timescales ranging from interannual to centennial. The analysis focused on the dynamic climate quantity of zonal-mean zonal wind and global atmospheric angular momentum (AAM), and incorporated multiple datasets from reanalysis and the most recent CMIP3 and CMIP5 archives. For the observation, the validation of AAM by the length-of-day (LOD) and the intercomparison of AAM revealed a good agreement among reanalyses on the interannual and the decadal-to-interdecadal timescales, respectively. But the most significant discrepancies among them are in the long-term mean and long-term trend. For the simulations, the CMIP5 models produced a significantly smaller bias and a narrower ensemble spread of the climatology and trend in the 20th century for AAM compared to CMIP3, while CMIP3 and CMIP5 simulations consistently produced a positive trend for the 20th and 21st century. Both CMIP3 and CMIP5 models produced a wide range of the magnitudes of decadal and interdecadal variability of wind component of AAM (MR) compared to observation. The ensemble means of CMIP3 and CMIP5 are not statistically distinguishable for either the 20th- or 21st-century runs. The in-house atmospheric general circulation model (AGCM) simulations forced by the sea surface temperature (SST) taken from the CMIP5 simulations as lower boundary conditions were carried out. The zonal wind and MR in the CMIP5 simulations are well simulated in the AGCM simulations. This confirmed SST as an important mediator in regulating the global atmospheric changes due to GHG effect. / Dissertation/Thesis / Ph.D. Mechanical Engineering 2013

The effect of wind changes on aircraft routing has been identified as a potential impact of climate change on aviation. This is of particular interest for trans-Atlantic flights, where the pattern of upper-level winds over the north Atlantic, in particular the location and strength of the jet stream, strongly influences both the optimal flight route and the resulting flight time. Eastbound trans-Atlantic flights can often be routed to take advantage of the strong tailwinds in the jet stream, shortening the flight time and reducing fuel consumption. Here we investigate the impact of climate change on upper-level winds over the north Atlantic, using five climate model simulations from the Fifth Coupled Model Intercomparison Project, considering a high greenhouse-gas emissions scenario. The impact on aircraft routing and flight time are quantified using flight routing software. The climate models agree that the jet stream will be on average located 1° further north, with a small increase in mean strength, by 2100. However daily variations in both its location and speed are significantly larger than the magnitude of any changes due to climate change. The net effect of climate change on trans-Atlantic aircraft routes is small; in the annual-mean eastbound routes are 1 min shorter and located further north and westbound routes are 1 min longer and more spread out around the great circle. There are, however, seasonal variations; route time changes are larger in winter, while in summer both eastbound and westbound route times increase.

No description available.

The meridional temperature gradient between mid and high latitudes decreases by Arctic amplification. Following this decrease, the circulation in the mid latitudes may change and, therefore, the meridional flux of heat and moisture increases. This might increase the Arctic temperatures even further. A proxy for the vertically integrated atmospheric horizontal energy flux was analyzed using the self-organizing-map (SOM) method. Climate Model Intercomparison Project Phase 5 (CMIP5) model data of the historical and Representative Concentration Pathway 8.5 (RCP8.5) experiments were analyzed to extract horizontal flux patterns. These patterns were analyzed for changes between and within the respective experiments. It was found that the general horizontal flux patterns are reproduced by all models and in all experiments in comparison with reanalyses. By comparing the reanalysis time frame with the respective historical experiments, we found that the general occurrence frequencies of the patterns differ substantially. The results show that the general structure of the flux patterns is not changed when comparing the historical and RCP8.5 results. However, the amplitudes of the fluxes are decreasing. It is suggested that the amplitudes are smaller in the RCP8.5 results compared to the historical results, following a greater meandering of the jet stream, which yields smaller flux amplitudes of the cluster mean.

No description available.

Sur les effets du changement climatique aux échelles globale et régionale. Il montre en particulierqu’aucun consensus ne peut être trouvé pour ce qui concerne l’évolution future de lapluviométrie — et de la dynamique atmosphérique associée — en région de mousson africaine.Ce mémoire revisite cette question à la lumière des nouvelles données disponibles et selon uneapproche évitant toute surreprésentation du nombre de simulations disponibles pour un type demodèle donné, tout en prenant en compte la diversité des modèles ainsi que leur évolution dansle temps : sorties de vingt modèles de circulation générale (MCGs) ayant participé aux exercicesCMIP3 (douze MCGs) et CMIP5 (huit MCGs) sous les scénarios d’émissions A1B et rcp4.5,respectivement. Les sorties sont analysées principalement sur deux fenêtres de quarante ans —périodes actuelle (1960-1999) et future (2031-2070) — et les résultats discutés au regard de leurvraisemblance selon une approche permettant à la fois de quantifier les différences futur moinsactuel, de mesurer les significativités et les robustesses statistiques et d’associer une probabilitémesurant le consensus des modèles en fonction des échelles et des variables considérées.Les analyses menées sur CMIP3 et CMIP5 montrent qu’un consensus sur l’effet du changementclimatique en Afrique de l’Ouest peut être obtenu si l’on ne fait pas de l’ensemble de labande sahélienne une entité homogène et qu’on raisonne à des échelles spatiales inférieures. Lesrésultats révèlent une évolution contrastée entre le centre et l’ouest du Sahel avec, pour le futur(i) une hausse des précipitations au centre s’expliquant surtout par une plus grande convergencedes flux dans les basses couches, ainsi qu’une pénétration plus au nord de la mousson ;(ii) une baisse des précipitations à l’ouest s’expliquant par le renforcement de la circulation detype Walker, du Jet d’Est Africain (JEA) et de la subsidence dans les couches moyennes. Parailleurs, on peut s’attendre à une modification du cycle annuel moyen avec un retrait retardé dela mousson. Ce retard est notamment lié aux apports supplémentaires d’humidité depuis l’Atlantique,dus au renforcement des contrastes thermiques et d’humidité entre océan et continent,mais aussi et surtout aux apports tardifs d’humidité depuis la Méditerranée et au renforcementdes flux de nord en septembre et octobre en direction du Sahel / The fourth IPCC report in 2007 established the synthesis of previously published work onthe effects of climate change on global and regional scales. It shows in particular that no consensuscan be found with regard to the future of rainfall — and atmospheric dynamics- associatedwith region — African monsoon. This dissertation revisits this issue in the light of new dataand using an approach avoiding over-representation of the number of simulations available forone type of model and taking into account the diversity of models and their evolution in time :twenty general circulation models (GCMs) participating in the exercises CMIP3 (twelve GCMs)and CMIP5 (eight GCMs) under the A1B emissions scenario and rcp4.5, respectively. Outputsare analyzed on two 40-year periods, — ‘Present’ (1960-1999) and ‘Future’ (2031-2070) — anddiscussed in terms of likelihood, through an approach allowing us to both quantify differences‘future’ minus ‘present’, measure robustness and statistical significances and associate a probabilitymeasuring the model consensus as a function of scales and variables.Analyzes conducted on CMIP3 and CMIP5 show that consensus on the effect of climatechange in West Africa can be achieved if we do not consider the Sahel as a whole and homogeneousentity but at lower scales. The results show contrasted responses over the centraland western Sahel, with for the future, (i) an increase in precipitation in the central regionexplained primarily by a greater convergence of flow in the lower layers and a most northerlymonsoon penetration over the continent, (ii) a rainfall decrease in the western Sahel explainedby increased Walker-type circulation, African easterly jet and mid-level subsidence. Moreover,we can expect a change in the mean annual cycle of the monsoon season with a delayed withdrawallinked to additional inputs of moisture from the Atlantic due to increasing thermal andmoisture contrasts between ocean and continent but also to a stronger contribution of moisturefluxes in September and October from the Mediterranean into the Sahel