Dissertations / Theses on the topic 'CMIP6 simulations'
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Ouhechou, Amine. "Analyse de la variabilité multi-échelles du rayonnement solaire incident sur la façade atlantique de l'Afrique Centrale : observations in-situ, estimations satellitaires, et simulations climatiques CMIP6." Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALU007.
Western Central Africa, home to the densest forests of the Congo Basin - the second largest tropical forest massif after Amazonia - is characterized by an equatorial climate with high temperatures, a bimodal rainfall pattern and, a long and cloudy dry season from June to September. Despite its ecological importance, the climate variability of this region has been less studied compared with other parts of the African continent, mainly because of the scarcity of in-situ observations.Recognizing these challenges posed by the lack of in-situ data, this study explores the climate variability in Western Central Africa through the lens of surface solar radiation, a key parameter for the functioning of tropical forests. In this context, this thesis aims to establish an initial climatology of surface solar radiation for the region, to document its variability, particularly during the cloudy dry season from June to September, and to assess the performance of satellite products, reanalyses and CMIP6 climate model simulations.In the first part, an evaluation of eight satellite products for estimating solar radiation (CERES-EBAF, CERES-SYN1deg, TPDC, CMSAF SARAH-2, CMSAF CLARA-A2, CAMS-JADE, WorldClim 2 and ERA5 reanalysis) reveals differences in the spatiotemporal fields. While successfully capturing mean annual solar radiation cycles, the products show regional variations, highlighting the impact of atmospheric parameters on the accurate estimation of solar radiation. In addition, all the products except WorldClim 2 agree that the Atlantic coast receives less solar radiation than the other regions of Central Africa. The performance of these products is also assessed against in-situ measurements based on four types of solar radiation diurnal cycle - Obscure, Obscure AM (morning), Obscure PM (afternoon) and Bright days. The products correctly represent the shape of these four types, but with a larger amplitude.The second part focuses on studying the interannual variability and trends in solar radiation during the June-September cloudy dry season, highlighting notable differences between CMSAF SARAH-2 satellite product and ERA5 reanalysis. The study also made it possible to identify the onset and cessation dates of the dry season based on solar radiation, and establishing a significant relationship between surface temperatures of the equatorial Atlantic ocean and the onset of the dry season.In the final part, the capacity of CMIP6 global climate models to reproduce average levels of solar radiation in the region was assessed. The results highlight sub-regional disparities in model performance. The models used in this study underestimate solar radiation in the south-west of Gabon-Congo, while they overestimate it in the north-east, mainly from april to december. The largest differences were observed during the october-november rainy season. These disparities seem to be caused by cloud cover, in particular low- and medium-level clouds, which have a significant influence on solar radiation, although the relationship varies according to the models. This section also highlights the teleconnection between the surface temperature of the equatorial Atlantic ocean and solar radiation in the models, which varies between the coastal and inland areas of Gabon, underlining the need to use regional climate models
Monerie, Paul-Arthur. "Le changement climatique en région de mousson africaine : évolution des champs pluviométriques et atmosphériques dans les simulations CMIP3 et CMIP5 sous scénario A1B et rcp45 (1960-1999, 2031-2070)." Phd thesis, Université de Bourgogne, 2013. http://tel.archives-ouvertes.fr/tel-00955371.
Mitchell, D. M., S. Misios, L. J. Gray, K. Tourpali, K. Matthes, L. Hood, H. Schmidt, et al. "Solar signals in CMIP-5 simulations: the stratospheric pathway." Royal Meteorological Society, 2015. http://hdl.handle.net/10150/623311.
Parsons, Luke A., Garrison R. Loope, Jonathan T. Overpeck, Toby R. Ault, Ronald Stouffer, and Julia E. Cole. "Temperature and Precipitation Variance in CMIP5 Simulations and Paleoclimate Records of the Last Millennium." AMER METEOROLOGICAL SOC, 2017. http://hdl.handle.net/10150/626270.
Sumi, Selina Jahan. "Eco-Hydrology Driven Evaluation of Statistically Downscaled Precipitation CMIP5 Climate Model Simulations over Louisiana." Thesis, University of Louisiana at Lafayette, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1594512.
Statistically downscaled CMIP5 precipitation data are available at higher spatial resolution compared to global climate models. The downscaled climate models have been used in many hydrological applications. However, limited numbers of studies focused on downscaled CMIP5 precipitation data for Louisiana. Statistically downscaled precipitation data for Louisiana is critically needed for various water resources engineering, planning and design purposes. This study has focused on assessing the skill of CMIP5 climate models in reproducing observed precipitation of Louisiana and application of CMIP5 precipitation data to analyze the impact of precipitation on hydrology (salinity and water level). Assessment of CMIP5 precipitation showed that statistically downscaled and bias corrected precipitation data reproduce observed average annual precipitation. But for other statistics (standard deviation), model data are not the same as observation data. The bias correction procedure ensured that models would reproduce the observed average precipitation. The maps of correlation distance for the models do not match with that of observation. This may be an indication that bias correction does not force the model to perform better in all statistics except annual average. Based on the analysis over climate divisions, it can be stated that spatial and temporal aggregation enables the models to perform better than gridded dataset. Application of CMIP5 precipitation data indicates that precipitation has a significant effect on salinity and almost zero effect on water level. Different salinity variables control the hydrologic and habitat suitability indices in coastal Louisiana. The cell-based analysis shows that different variables have different degrees of effect on vegetation and species (brown shrimp and oyster). Some species thrive in a high salinity environment while some others in low salinity. The uncertainty in the salinity and water level may occur due to insufficient data and boundary conditions provided in the Eco-hydrology model environment.
Santolaria, Otín María. "Le rôle de la couverture de neige de l'Arctique dans le cycle hydrologique de hautes latitudes révélé par les simulations des modèles climatiques." Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAU027/document.
Snow is a critical component of the Arctic climate system. Over Northern Eurasia and North America the duration of snow cover is 7 to 10 months per year and a maximum snow extension is over 40% of the Northern Hemisphere land each year. Snow affects a variety of high latitude climate processes and feedbacks. High reflectivity of snow and low thermal conductivity have a cooling effect and modulates the snow-albedo feedback. A contribution from terrestrial snow to the Earth’s radiation budget at the top of the atmosphere is close to that from the sea ice. Snow also prevents large energy losses from the underlying soil and notably the ice growth and the development of seasonal permafrost. Being a natural water storage, snow plays a critical role in high latitude hydrological cycle, including evaporation and run-off. Snow is also one of the most variable components of climate system. With the Arctic warming twice as fast as the globe, the present and future variability of snow characteristics are crucially important for better understanding of the processes and changes undergoing with climate. However, our capacity to observe the terrestrial Arctic is limited compared to the mid-latitudes and climate models play very important role in our ability to understand the snow-related processes especially in the context of a warming cryosphere. In this respect representation of snow-associated feedbacks in climate models, especially during the shoulder seasons (when Arctic snow cover exhibits the strongest variability) is of a special interest.The focus of this study is on the representation of the Arctic terrestrial snow in global circulation models from Coupled Model Intercomparison Project (CMIP5) ensemble during the melting (March-April) and the onset (October-November) season for the period from 1979 to 2005. Snow characteristics from the general circulation models have been validated against in situ snow measurements, different satellite-based products and reanalyses.We found that snow characteristics in models have stronger bias in spring than in autumn. The annual cycle of snow cover is well captured by models in comparison with observations, however, the annual cycles of snow water equivalent and snow depth are largely overestimated by models, especially in North America. There is better agreement between models and observations in the snow margin position in spring rather than in autumn. Magnitudes of interannual variability for all snow characteristics are significantly underestimated in most CMIP5 models compared to observations. For both seasons, trends of snow characteristics in models are primarily negative but weaker and less significant than those from observations. The patterns of snow cover trends are relatively well reproduced in models, however, the spatial distribution of trends for snow water equivalent and snow depth display strong regional heterogeneities.Finally, we have concluded CMIP5 general circulation models provides valuable information about the snow characteristics in the terrestrial Arctic, however, they have still limitations. There is a lack of agreement among the ensemble of models in the spatial distribution of snow compared to the observations and reanalysis. And these discrepancies are accentuated in regions where variability of snow is higher in areas with complex terrain such as Canada and Alaska and during the melting and the onset season. Our goal in this study was to identify where and when these models are or are not reproducing the real snow characteristics in the Arctic, thus we hope that our results should be considered when using these snow-related variables from CMIP5 historical output in future climate studies
Chavaillaz, Yann. "La vitesse du changement climatique et ses implications sur la perception des générations futures." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLV021/document.
In most climate studies, climate change is approached by focusing on the evolution between a fixed current baseline and a future period, emphasizing stronger warming as we move further over the 21st century. Under climate conditions that are continuously evolving, human and natural systems might have to constantly adapt to a changing climate. This thesis proposes an alternative approach to climate projections. Here, I consider and analyze indicators of the pace of changes relative to temperature, precipitation and vegetation in order to be relevant for both urban and rural populations. An ensemble of CMIP5 simulations from 18 climate models is selected. The pace is represented by differences between two subsequent 20-year periods. Considering the pace of change would be beneficial for climate impacts and adaptation analyses.The models predict that the warming rate strongly increases without any mitigation policies (RCP8.5 scenario). It is twice as high by the end of the century compared to the current period, and even three times higher in some regions. Significant shifts in temperature distributions between two subsequent 20-year periods are projected to involve almost half of all land surfaces and most tropical areas by 2060 onwards (i.e. at least four times as many regions than currently). In these regions, an extremely warm year with a return period of about 50 years would become quite common only 20 years later. The fraction of the world population exposed to such shifts might reach about 60% (6 billion people, i.e. seven times more than currently). Low mitigation measures (RCP6.0) allow the warming rate to be kept at current values, and reduce the fraction of the world population exposed to significant shifts of temperature distributions by one third.Under RCP8.5, rainfall moistening and drying rates both increase by 30-40% above current levels. As we move further over the century, their patterns become geographically stationary and the trends become persistent. The stabilization of the geographical rate patterns that occurs despite the acceleration of global warming can be physically explained: it results from the increasing contribution of thermodynamic processes compared to dynamic processes in the control of precipitation change. The combination of intensification and increasing persistence of precipitation rate patterns may affect the way human societies and ecosystems adapt to climate change, especially in the Mediterranean basin, Central America, South Asia and the Arctic. Such an evolution in precipitation has already become noticeable over the last few decades, but it could be reversed if strong mitigation policies were quickly implemented (RCP2.6).Changes in vegetation could be visual landmarks of climate change. In mid- and high-latitudes of the Northern Hemisphere, the phenology of grass and trees follows the warming rate. Without any mitigation policies, the start of spring occurs earlier, and its duration is extended faster as we move over the century. The vegetation cover becomes denser, regardless of the selected pathway, in proportion to the temperature rise. The seasonal cycle of mid-latitude crops also depends on the temperature, and the seasonal cycle of tropical crops directly follows the features of the wet season. In all other latitudes, no robust evolution of the seasonal cycle is projected. The pace of change of vegetation cover since 1880 already doubled before 1950, mainly due to a strong change in land use. This pace is then projected to be stable over the entire 21st century if the vegetation dynamically interacts with the climate system in the models. This corresponds to a reduction of land-use change and to the acceleration of changes of vegetation cover under climate change
Dars, Ghulam Hussain. "Climate Change Impacts on Precipitation Extremes over the Columbia River Basin Based on Downscaled CMIP5 Climate Scenarios." PDXScholar, 2013. https://pdxscholar.library.pdx.edu/open_access_etds/979.
Chavaillaz, Yann. "La vitesse du changement climatique et ses implications sur la perception des générations futures." Electronic Thesis or Diss., Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLV021.
In most climate studies, climate change is approached by focusing on the evolution between a fixed current baseline and a future period, emphasizing stronger warming as we move further over the 21st century. Under climate conditions that are continuously evolving, human and natural systems might have to constantly adapt to a changing climate. This thesis proposes an alternative approach to climate projections. Here, I consider and analyze indicators of the pace of changes relative to temperature, precipitation and vegetation in order to be relevant for both urban and rural populations. An ensemble of CMIP5 simulations from 18 climate models is selected. The pace is represented by differences between two subsequent 20-year periods. Considering the pace of change would be beneficial for climate impacts and adaptation analyses.The models predict that the warming rate strongly increases without any mitigation policies (RCP8.5 scenario). It is twice as high by the end of the century compared to the current period, and even three times higher in some regions. Significant shifts in temperature distributions between two subsequent 20-year periods are projected to involve almost half of all land surfaces and most tropical areas by 2060 onwards (i.e. at least four times as many regions than currently). In these regions, an extremely warm year with a return period of about 50 years would become quite common only 20 years later. The fraction of the world population exposed to such shifts might reach about 60% (6 billion people, i.e. seven times more than currently). Low mitigation measures (RCP6.0) allow the warming rate to be kept at current values, and reduce the fraction of the world population exposed to significant shifts of temperature distributions by one third.Under RCP8.5, rainfall moistening and drying rates both increase by 30-40% above current levels. As we move further over the century, their patterns become geographically stationary and the trends become persistent. The stabilization of the geographical rate patterns that occurs despite the acceleration of global warming can be physically explained: it results from the increasing contribution of thermodynamic processes compared to dynamic processes in the control of precipitation change. The combination of intensification and increasing persistence of precipitation rate patterns may affect the way human societies and ecosystems adapt to climate change, especially in the Mediterranean basin, Central America, South Asia and the Arctic. Such an evolution in precipitation has already become noticeable over the last few decades, but it could be reversed if strong mitigation policies were quickly implemented (RCP2.6).Changes in vegetation could be visual landmarks of climate change. In mid- and high-latitudes of the Northern Hemisphere, the phenology of grass and trees follows the warming rate. Without any mitigation policies, the start of spring occurs earlier, and its duration is extended faster as we move over the century. The vegetation cover becomes denser, regardless of the selected pathway, in proportion to the temperature rise. The seasonal cycle of mid-latitude crops also depends on the temperature, and the seasonal cycle of tropical crops directly follows the features of the wet season. In all other latitudes, no robust evolution of the seasonal cycle is projected. The pace of change of vegetation cover since 1880 already doubled before 1950, mainly due to a strong change in land use. This pace is then projected to be stable over the entire 21st century if the vegetation dynamically interacts with the climate system in the models. This corresponds to a reduction of land-use change and to the acceleration of changes of vegetation cover under climate change
Peings, Yannick. "Influence de la couverture de neige de l'hémisphère nord sur la variabilité interannuelle du climat." Phd thesis, Université Paul Sabatier - Toulouse III, 2010. http://tel.archives-ouvertes.fr/tel-00562496.
Tang, Chao. "Model estimations of possible climate changes of surface solar radiation at regional scales over Southern Africa and the South West Indian Ocean." Thesis, La Réunion, 2017. http://www.theses.fr/2017LARE0055/document.
Changes in Surface Solar Radiation (SSR) have the potential to significantly impact diverse aspects of the climate system, and notably the socio-economic development of any nation. To identify the possible impacts of climate change on SSR at regional scales (~50 km) over Southern Africa and the South West Indian Ocean (SA-SWIO; 0-40°S ; 0- 100°E) up to the end of the 21st century, a slice downscaling experiment consisting of simulations covering three temporal windows: a) the present 1996-2005; b) the future 2046-2055 and 2090-2099 conducted with the Regional Climate Model (RCM) RegCM version 4, driven by the European Center for Medium-range Weather Forecasting (ECMWF) ERA-Interim reanalysis (ERAINT, only present) and 2 Global Climate Model (GCMs: HadGEM2-ES and GFDL-ESM2M) from the Coupled Model Intercomparison Project Phase 5 (CMIP5) under RCP8.5 scenario, are performed and evaluated. Since the slice simulation is of limited temporal coverage, number of regional and driven global models and climate change forcings, mainly because of the limit of available computational resources, the study towards a comprehensive knowledge of SSR changes in context of climate change is thus extended: an ensemble consisting of outputs from 20 regional climate downscaling realisations based on 5 RCMs that participated in the Coordinated Regional Downscaling Experiment (CORDEX) program (CORDEX-Africa) along with their 10 driving GCMs from CMIP5 covering southern Africa (0-40°S; 0- 100°E) during the period of 1990-2099 is analyzed under RCP4.5 and RCP8.5 up to 2099.The slice experiment indicates that 1) RegCM4 simulates present-day seasonal climatology, (surface air temperature, precipitation and SSR) quite well, but has a negative total cloud cover bias (about -20% in absolute percentage) when forced by the ERAINT and the two GCMs. 2) Internal variability of RegCM4-simulated annual means SSR (about 0.2 W/m2) is of one order smaller than the model bias compared with reference data. 3) RegCM4 simulates SSR changes in opposite signs when driven by the different GCMs under RCP8.5 scenario. 4) Electricity potential calculated using first-order estimation based on the RegCM simulations indicates a change less then 2% to 2099 with respect on present level.It is also found from the ensemble study that: 1) GCMs ensemble generally overestimates SSR by about 1 W/m2 in austral summer (December, January, and February, short as DJF) and 7.5 W/m2 in austral winter (June, July and August, short as JJA), while RCMs ensemble mean shows underestimations of SSR by about -32 W/m2 and -14 W/m2 in summer and winter seasons respectively when driven by GCMs. 2) Multi-model mean projections of SSR change patterns simulated by the GCMs and their embedded RCMs are fairly consistent. 3) GCMs project, in their multi-model means, a statistically significant increase of SSR of about 8 W/m2 in RCP4.5 and 12 W/m2 in RCP8.5 by 2099 over Centre Southern Africa (SA-C) and a highly confident decreasing SSR over Eastern Equatorial Africa (EA-E) of about -5 W/m2 in RCP4.5 and -10 W/m2 in RCP8.5 during the DJF season. RCMs simulate SSR change with statistical confidence over SA-C and EA-E area as well with a little spatial extension compared to GCMs. However, in the JJA season, an increase of SSR is found over EA-E of about 5 W/m2 by 2099 under RCP4.5 and 10 W/m2 under RCP8.5, of similar amplitudes in both the GCMs and RCMs simulations. 4) Significant cloudiness decrease (about -6 % to 2099) is found over continent of SA for GCMs and also shown in RCMs. 5) Larger SSR changes are found in the RCP8.5 scenario than in the RCP4.5 scenario in 2099, with about 2.5 W/m2 enhanced changes in GCMs and about 5 W/m2 in RCMs. 6) Either the biases or the changes pattern of SSR are overall correlated with the patterns of total cloud cover from RCMs in CORDEX-Africa program (for RegCM4 as well). The slice experiment indicates that
Ribu, Cherian, and Johannes Quaas. "Trends in AOD, Clouds, and Cloud Radiative Effects in Satellite Data and CMIP5 and CMIP6 Model Simulations Over Aerosol Source Regions." 2020. https://ul.qucosa.de/id/qucosa%3A72473.
Wu, Ren-Jie, and 吳仁傑. "The simulation of decadal variability in CMIP5." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/52499006156584821429.
國立臺灣大學
大氣科學研究所
100
Decadal variability is an oscillation for more than ten years, usually appears in the ocean. In the Atlantic, AMO is the main multi-decadal variability. There are several decadal oscillations in the Pacific, which we call Pacific decadal variability (PDV). These decadal structures may impact on regional climate. IPCC will take decadal variability as an important issue and publish the result in the fifth assessment report (AR5). This study uses Rotated-EOF (REOF) method, analyzes decadal variability in observation data and CMIP5 models. In observation data, AMO structure appears in REOF1. Decadal variability of Nino region, north Pacific and Indian Ocean are the 2nd mode in REOF analysis. SPDO, PDO and decadal variability in central Pacific appear in REOF3. The rotated principal components (RPCs) also match with the previous study. In CMIP5 models, we use three different model experiment designs: (1) Pre-industrial, refer as the internal variability in models. (2) Historical run, with the observation record from 1850 to 2005. (3) RCP8.5 identifies a concentration pathway that approximately results in a radiative forcing of 8.5 W/m2 at year 2100. In the pre-industrial run, most of the CMIP5 models show the decadal variability of El-Nino region, but the AMO structure which consider as a nature mode in decadal variability, does not appear in model’s pre-industrual run. In the Historical run, decadal structure shows variety types in each model. In the model’s RCP8.5 run, main decadal structure shows large region in global, with an upward parabola time series. We use pattern correlation analysis, and choose the models which are similar with observation data. In this study, historical run in HadGEM2-CC models are similar with the observation data. On the analysis of variance, we separate total variance to three different time scales: annual, decadal and trend. We compute the ratio of the three time scales and the total variance. The smallest ratio of trend variance is model’s pre-industrial run, but most significant in RCP8.5 run which the mean is more than 80% in box-plot analysis. In variance map, decadal variance ratio is most significant in North Hemisphere Ocean in observation data; it can be simulated in some model’s historical run. In RCP8.5 run, the decadal variability ratio is less than 10% in most regions. We find that the total mass of CO2 in RCP8.5 run, ascending with a parabolic curve. We remove the linear trend of total mass of CO2, the residual forcing could project on decadal variability and affect the RPC performance. Keywords: Decadal variability, Atlantic Multi-decadal Oscillation, pacific decadal variability, rotated-EOF, pattern correlation
"Evaluation of CMIP5 historical simulations in the Colorado River Basin." Master's thesis, 2018. http://hdl.handle.net/2286/R.I.49105.
Dissertation/Thesis
Masters Thesis Civil, Environmental and Sustainable Engineering 2018
Lemos, Gil Ramos Lopes Gonçalves. "Wave climate in a global warming scenario: simulations with a CMIP5 ensemble." Master's thesis, 2016. http://hdl.handle.net/10451/24664.
As ondas gravíticas geradas pelo vento na superfície do oceano são as mais energéticas do espectro, sendo responsáveis por mais de metade da energia presente em todas as ondas nesta superfície (Kinsman, 1965). São geradas pela transferência de momento do vento para a água e dominam o espectro de ondas oceânicas, ultrapassando a contribuição das marés, das “storm surges”, dos tsunamis, etc. (Munk, 1951). Pela sua prevalência no oceano e influência nas actividades humanas, o seu estudo deve ser aprofundado, e as potenciais alterações no seu regime devem ser tidas em conta. Porém, apesar da sua relevância, não existe ainda nenhum modelo teórico preciso de geração e crescimento das ondas, dado que os mecanismos presentes nestes fenómenos não são ainda totalmente compreendidos por forma a serem correctamente quantificados. Quando o vento sopra sobre a superfície do oceano, ondas são formadas pela transferência de momento no sentido da água. Esta perturbação inicial pode desenvolver-se se o vento continuar a soprar de forma constante, sendo que as ondas irão crescer até atingirem o seu nível de saturação. Os dois principais tipos de ondas à superfície do oceano são denominados “wind sea” ou apenas “sea”, e “swell”. As ondas de “sea” detêm alta frequência e curtos comprimentos de onda, estando directamente associadas ao campo de vento sobrejacente, crescendo rapidamente e depressa atingindo o nível de saturação. Por sua vez, as ondas de “swell”, com frequências mais baixas e comprimentos de onda maiores, crescem lentamente e podem propagar-se com velocidades de fase superiores à velocidade do vento, uma vez que também extraem energia de ondas com mais alta frequência, devido a interações não lineares entre as ondas. Estas ondas podem propagar-se por milhares de quilómetros (Barber and Ursell, 1948; Munk et al., 1963; Snodgrass et al., 1966) com muito ligeira atenuação (Ardhuin et al., 2009). Assim sendo, é possível assumir que existe uma ligação causal entre, por exemplo, um evento local de erosão costeira e uma tempestade que ocorreu “do outro lado” do mundo (em outro hemisfério). Este é apenas um dos factores interessantes que motivam a execução deste trabalho de análise das futuras alterações no clima de ondas global, uma vez que as alterações climáticas atmosféricas locais no vento podem propagar-se sob a forma de ondas à superfície do oceano, e gerar impactos a longas distâncias. Até recentemente, o impacto das alterações climáticas no clima de ondas futuro tinha recebido muito pouca atenção. Nos últimos anos, alguns estudos foram realizados, sob os auspícios do COWCLIP (Coordinated Ocean Wave Climate Project), utilizando um único modelo e um único cenário de concentração de gases de efeito estufa (CMIP3), recebendo atenção moderada por parte do IPCC-AR5 (Intergovernmental Panel for Climate Change - Fifth Assessment Report). No presente estudo, o impacto do aquecimento global no clima de ondas global é investigado, através de um “ensemble” composto por 2 membros (simulações do modelo de ondas WAM) de um conjunto maior, composto por 8 simulações dinâmicas e 20 simulações estatísticas, denominado GLOWAVES-2, e pertencente ao projecto COWCLIP. O (único) forçamento destas duas simulações (em termos de velocidade do vento e cobertura oceânica de gelo) provém do modelo climático EC-Earth, seguindo um cenário de elevadas emissões de gases de efeito estufa (RCP8.5). Ambas as simulações cobrem um período total de 130 anos (1971-2100), no entanto, para efeitos de análise comparativa, dois períodos mais curtos são utilizados como referência: o “clima presente” (PC20: média das duas simulações (PC20-1 e PC20-4); 1971-2000) e o “clima futuro” (projectado; FC21: média das duas simulações (FC21-1 e FC21-4); 2071-2100). O período de referência histórico (1971-2005) foi validado através da comparação com a reanálise ERA-Interim, do ECMWF (European Centre for Medium-Range Weather Forecasts) e com dados observacionais de bóias, revelando que o modelo WAM, com forçamento do EC-Earth, é capaz de produzir cenários realistas do clima de ondas global no final do século XX, fornecendo a confiança necessária na capacidade de simular uma alteração climática igualmente credível até ao final do século XXI. Os resultados (alterações futuras no clima de ondas como projectado pelas simulações) são obtidos através da comparação entre as médias de PC20 e FC21, para quatro variáveis diferentes: (altura significativa; m), (período médio da onda; s), (direcção média da frente de onda; º), (potência das ondas; W/m, = , como em Young, 1999). Para complementar os resultados destas variáveis, os impactos da alteração climática no campo do vento ( ; velocidade do vento a 10 metros de altura; m/s) foram também analisados. Os resultados expõem médias a nível anual e sazonal (estações extremas de Inverno e Verão: DJF (Dezembro, Janeiro e Fevereiro) e JJA (Junho, Julho e Agosto)). Como forma de complemento, são também apresentadas as tendências lineares ao longo do período 2006-2100, para a altura significativa e para a potência (fluxo de energia) das ondas. Devido às alterações climáticas, as projecções indicam alterações estatisticamente significativas em todas as variáveis analisadas, que poderão referir-se a aumentos ou decréscimos na sua intensidade, gradiente espacial ou mudanças na localização geográfica de determinados valores. No que toca à altura significativa, , os aumentos nesta variável dominam as projecções, essencialmente a nível anual, e durante o período JJA (verificando-se em 73.93% do oceano global), sendo no Oceano Antárctico (“Southern Ocean”) que os maiores aumentos se verificam, estando esta situação directamente relacionada com uma intensificação projectada a nível da velocidade do vento ( ) na mesma área. A região onde os decréscimos projectados se mostram mais prevalecentes é no Oceano Atlântico Norte, em particular durante DJF. A tendência linear de altura significativa projectada durante o período 2006-2100 estabelece-se, a nível anual, em 0.41 cm/década. No que toca ao período médio, , são esperados aumentos nos seus valores anuais e sazonais em praticamente todo o oceano global, excepto no Atlântico Norte e Pacífico Oeste durante DJF, e em maior extensão no verão boreal (JJA), em 87.48% da área de oceano global, em média. Tendo em conta os resultados para esta variável e para a altura significativa, uma vez que a potência das ondas ( ) depende destes, é esperado que o seu comportamento não se diferencie muito dos anteriormente referidos. É efectivamente o que acontece nas projecções de , onde se verifica um padrão de alterações muito semelhante ao da altura significativa, uma vez que as diferenças de apresentam valores reduzidos. Aumentos projectados de potência das ondas (que se observam em 81.43% do oceano global) alcançam os 30% no sector Índico do Oceano Antárctico (a sudoeste da Austrália), durante o inverno austral (JJA), sendo que o valor médio de incremento a nível global para esta estação se situa nos 7.18%. A tendência linear de potência das ondas projectada durante o período 2006-2100 estabelece-se, a nível anual, em 0.36 cm/década. Relativamente à direcção média da frente de onda ( ), as projecções indicam a prevalência de rotações anti-horárias (contra os ponteiros do relógio) nas latitudes médias e altas de ambos os hemisférios, associadas ao deslocamento latitudinal positivo das tempestades para latitudes mais elevadas (Arblaster et al., 2011). Nas regiões tropicais e subtropicais, rotações positivas (no sentido dos ponteiros do relógio) são consistentes com uma maior contribuição de “swell” proveniente do Oceano Antárctico, especialmente durante o inverno austral (JJA), quando a sua “produção” é maior. A análise de EOFs (“Empirical Orthogonal Functions”) para os campos de e no Oceano Atlântico Norte, em termos de alterações entre o clima presente (PC20) e o projectado para o futuro (FC21), relevou que é esperado um ligeiro enfraquecimento dos principais centros de acção de ambos os campos (redução da variabilidade), a nível anual. A nível sazonal, comportamento similar foi detectado para a altura significativa, porém, a nível de potência, um ligeiro fortalecimento dos seus centros de acção é esperado, com um deslocamento latitudinal positivo associado, de cerca de 2º. No entanto, deslocamentos da posição dos valores climatológicos máximos para latitudes mais elevadas não se verificam para o Atlântico Norte, apenas em algumas regiões do Oceano Antárctico.
Ocean surface wind waves are of outmost relevance for practical and scientific reasons. On the one hand, waves have a direct impact in coastal erosion, but also in sediment transport and beach nourishment, in ship routing and ship design, as well as in coastal and offshore infrastructures, just to mention the most relevant. On the other hand waves are part of the climate system, and modulate most of the exchanges that take place at the atmosphere-ocean interface. In fact waves are the “ultimate” air-sea interaction process, clearly visible and noticeable. Up until recently, the impact of climate change in future wave climate had received very little attention. Some single model single scenario global wave climate projections, based on CMIP3 scenarios, were pursued and received some attention in the IPCC (Intergovernmental Panel for Climate Change) AR5 (Fifth Assessment Report). In the present study the impact of a warmer climate in the global ocean future wave climate is investigated through a 2-member “coherent” ensemble of wave climate projections: single-model, single-forcing, and single-scenario. The two ensemble members were produced with the wave model WAM, forced with wind speed and ice coverage from EC-Earth projections, following the representative concentration pathway with a high emissions scenario 8.5 (RCP8.5). The ensemble historic period has been set for 1971 to 2005. The projected changes in the global ocean wave climate are analyzed for the 2071-2100 period. The ensemble historical period is evaluated trough the comparison with the European Centre for medium-range weather forecasts (ECMWF) ERA-Interim reanalysis, and buoy observations.
蔡鴻鵬. "Analysis of the summer ISO simulation in CMIP-5 AGCMs and CGCMs." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/94816415105236989027.
"Climate Variability and Trend on Interannual-to-Centennial timescales from Global Observations and Atmosphere-Ocean Model Simulations." Doctoral diss., 2013. http://hdl.handle.net/2286/R.I.17718.
Dissertation/Thesis
Ph.D. Mechanical Engineering 2013