• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 624
  • 453
  • 136
  • 93
  • 46
  • 24
  • 14
  • 12
  • 7
  • 6
  • 5
  • 3
  • 2
  • 2
  • 2
  • Tagged with
  • 1796
  • 751
  • 477
  • 259
  • 211
  • 183
  • 164
  • 151
  • 144
  • 143
  • 142
  • 120
  • 119
  • 113
  • 112
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
361

Análise do impactos econômicos da territorialização do setor sucroenergético e suas consequências para o desenvolvimento social na microrregião de São José do Rio Preto : o caso dos municípios de José Bonifácio, Planalto e Ubarana /

Pauli, Lucas January 2019 (has links)
Orientador: Eduardo Paulon Girardi / Resumo: Na presente dissertação partimos da identificação de que, a partir de 2003, o governo brasileiro retomou o incentivo ao setor sucroenergético via Banco Nacional de Desenvolvimento Econômico e Social - BNDES no contexto da produção das agroenergias, especificamente o etanol. Isso provocou um intenso processo de expansão dos canaviais e de usinas no Brasil e principalmente no estado de São Paulo. A partir de 2006 a expansão da cana-de-açúcar no estado de São Paulo orientou-se para novas áreas do estado, já que as regiões tradicionais chegavam ao limite de expansão da atividade sucroenergética. Buscou-se incorporar novas terras para o setor sucroenergético no oeste de São Paulo, com grande concentração no Pontal do Paranapanema e no noroeste paulista. A microrregião de São José do Rio Preto está dentre as que receberam usinas e onde houve maior aumento da área plantada de cana-de-açúcar. Dessa forma, selecionamos para análise os municípios de José Bonifácio, Planalto e Ubarana, localizados na microrregião em questão e que estão inseridos neste contexto de expansão. Nesse sentido, a territorialização do setor sucroenergético, com as grandes plantas industriais, alavancou intensas alterações e impactos econômicos e sociais nos municípios elencados. Frente a este quadro, a questão na qual está centrada a pesquisa é: como essas alterações econômicas e sociais podem ou não ter contribuído para o desenvolvimento nesses municípios, tendo em vista toda a discussão e contradições que env... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In this dissertation, we start from the identification that, as of 2003, the Brazilian government has resumed encouraging the sugar-energy sector through the National Economic and Social Development Bank - BNDES in the context of agroenergy production, specifically ethanol. This led to an intense process of expansion of sugarcane plantations and mills in Brazil and especially in the state of São Paulo. As of 2006, the expansion of sugarcane in the state of São Paulo was oriented towards new areas of the state, since the traditional regions reached the limit of the expansion of the sugar-energy activity. The aim was to incorporate new lands for the sugar-energy sector in western São Paulo, with a high concentration in Pontal do Paranapanema and in the northwest of São Paulo. The micro-region of São José do Rio Preto is among those that received mills and where there was the greatest increase in planted area of sugarcane. Thus, we selected for analysis the municipalities of José Bonifácio, Planalto and Ubarana, located in the microregion in question and which are inserted in this context of expansion. In this sense, the territorialization of the sugar-energy sector, with the large industrial plants, has leveraged intense changes and economic and social impacts in the municipalities listed. Faced with this situation, the question on which the research is focused is: how may or may not these economic and social changes have contributed to development in these municipalities, give... (Complete abstract click electronic access below) / Mestre
362

The challenges of tax administration in Somaliland Ministry of Finance: a critical analysis of institutional perspective

Haginour, Faisal January 2018 (has links)
Masters in Public Administration - MPA / This research focuses on the challenges of tax administration in Somaliland Ministry of Finance (MOF). The study analyses existing challenges in the MOF-Tax Administration, causes of these challenges, the impact of these challenges on domestic revenue collection as well as the country’s economic growth and development. In order to obtain a desirable, comprehensive, and in-depth understanding of the research problem, the researcher applied a mixed method approach, thereby limiting the weaknesses of using the quantitative or qualitative research approach alone. The sample size consisted of 63 staff members. The research included 57 questionnaires for 57 employees and lower level managers as well as 6 interviews for top and middle-level managers in Somaliland Inland Revenue Department. The data was analyzed using Statistical Package for Social Science (SPSS), Ms. Excel, and conceptual analysis, where themes were developed and analyzed. The key findings of the research were that Somaliland tax administration faces immense challenges that can be broadly grouped into three categories: institutional challenges, attitudinal challenges as well as political and economic challenges. These challenges are mainly due to the absence of professional staff, the lack of taxpayers’ education, outdated tax laws, non-compliance behavior of taxpayers, rigidity of the tax system, and poor public trust amongst others. These challenges restrained tax revenue collection, public service provision, investments, and economic growth issues. Therefore, the recommendations, accordingly made in this thesis, include, amongst others, the need to establishing a professional training center for staff, automating tax procedure, implementing effective performance appraisal system, and the regular updating of tax policies to establish a transparent, accountable and equitable tax system in Somaliland.
363

Epidemiologické a ekologické dopady povodní v okrese Český Krumlov / Epidemiological and ecological impacts of floods in the Cesky Krumlov district

PAPOUŠKOVÁ, Michala January 2019 (has links)
The topic of my diploma thesis are Epidemiological and ecological impacts of floods in the Cesky Krumlov district. In the theoretical part I deal, from the perspective of epidemiology, with infectious diseases that may occur due to floods, I explain what information system was used by the regional hygiene stations in order to carry out the obligatory report, records, and analysis of occurrence of infectious diseases, and I would like to point out that from 1 January 2018 on, a new system started working for regional hygiene stations in the Czech Republic. Further, I deal with ecological impacts, and explain ecology in terms of Nature Conservation Act. Last but not least, I mention floods as such in the theoretical part, I define flood legislation, what administrative authorities work if such a crisis situation occurs, and what flood affected the region of Cesky Krumlov. The practical part analyses Epidat and the ISIN information system data using metaanalysis, searching for a link between them and infectious diseases during floods. I focused on infectious diseases that ma occur in connection to floods, such as Leptospirosis, Shigelosis, Cryptosporidiosis, Gastroenteritis caused by Campylobacteria and Norovirus, Virus Hepatitis type A, and Virus Hepatitis type E. The Discussion part evaluates the questionnaire aimed at the citizens of Cesky Krumlov region, also at the primary school pupils. What is their image of consequences of floods, and what may bet he cause. The results are then discussed in the conclusion of my diploma thesis. Creating an information leaflet meant for the lay public is another output of my diploma thesis.
364

THE INFLUENCE OF MUSIC FESTIVAL EXPERIENCE ON DESTINATION IMAGE AND FESTIVAL IMAGE.pdf

Matthew Corey Mosley (7027583) 15 August 2019 (has links)
<p>The purpose of this study is to explore how attending a blues music festival can influence an attendees image of the destination, the image of the festival and their intention to return. Predicting attendee behavior intentions have been a constant focus of academics and festival organizers. It has been shown that the festival environment (venue and facilities) are influential, that positive interactions with festival staff and vendors affect attendee satisfaction and depending on the study the aspect surrounding the musical performance can influence future behavior. This study has incorporated an area previously found to be important to attendee satisfaction but so far has not been studied with the other aspects of how a festival performs. This study investigated the influence of those four factors (venue, services, core product and safety) on attendees’ perception of their satisfaction with the festival and the subsequent influence on their image of the destination and festival. </p>
365

Artificial intelligence impacts on organizations and work: a Delphi study with brazilian experts / Impactos da inteligência artificial nas organizações e no trabalho: um estudo Delphi com especialistas brasileiros

Pauli, Sergi 07 June 2019 (has links)
We are living a new and emerging technological wave that is mainly based on Artificial Intelligence. It is being led by the great IT corporations and could potentially bring transformation and disruption in large scale to the economy, industries, businesses, organizations, and people in the years to come. Frey & Osborne (2017)\'s research was an important milestone in evaluating the impact of AI and automatization in the future of employment and their key conclusion that 47% of total U.S. employment was at risk of being potentially extinguished in a decade or two had an enormous impact on the mass media. Therefore, the objective of this study is to evaluate what could be the key impacts of Artificial Intelligence on Organizations and Work. In doing so, we scrutinize the authors\' research and propose an alternate ranking of occupation\'s susceptibility based on a different method and grounded on experts\' opinions. We also evaluate Frey & Osborne (2017)\'s key finding regarding to employment impact by technologies and identify key positive and negative qualitative impacts of AI on organizations and work, occupations and labor market. Taking into account the nature of this research, which is forward-looking, experimental and propositional, focused on current and future implications of Artificial Intelligence, we performed field research with experts supported by a Delphi Method, which is complemented by other techniques. Delphi is a robust and proven method commonly used in future research to assess the direction of long-range trends, with special emphasis on science and technology, and their probable effects on our society and our world. Among our key conclusions, we evaluate bottlenecks applied in to the occupation context and compare them to those identified by Frey & Osborne (2017). We also create our susceptibility ranking that takes into account an integration complexity factor, derived from Metcalfe\'s Law, which shows that occupations with less integration complexity, like clerks and assistant positions, are more likely of being replaced, while the ones that demand higher integration of abilities are practically not at risk. These results help in elucidating the current and future situation of this theme and allow us to suggest some possible suppositions. One of the most important is that no occupation will reach the 100% susceptibility index in twenty years, contrary to Frey & Osborne (2017)\'s research, which means that few occupations can be entirely replaced with acceptable quality by machines that combine Artificial Intelligence, Robotics, and related technologies. Yet, our most relevant finding is this research is related to complexity and integration of occupations. Technologies may emulate individual abilities to a higher extent in the future, but more important than that is being able to harmonically combine these capabilities and make them work together with synergy to achieve even basic tasks of occupations. This integration challenge in association with Autor (2015)\'s Polanyi\'s paradox corroborates the fact that no matter how advanced technology might be in a specific ability, it takes more than that for machines to successfully replace humans in an occupation, which we understand confirms the future scenario of collaboration, complementation and synergy between humans and machines, rather than the replacement and displacement / Vivemos uma nova e emergente onda tecnológica que é principalmente baseada em Inteligência Artificial. Ela está sendo liderada pelas grandes corporações de TI e pode trazer transformação e rupturas em grande escala para a economia, indústrias, empresas, organizações e pessoas nos próximos anos. A pesquisa de Frey & Osborne (2017) foi um marco importante na avaliação do impacto da IA e da automatização no futuro do emprego e sua conclusão fundamental de que 47% do emprego dos EUA está em risco de ser potencialmente extinto em uma década ou duas, teve um enorme impacto nos meios de comunicação de massa. Assim, o objetivo deste estudo é avaliar quais podem ser os principais impactos da Inteligência Artificial sobre as organizações e o trabalho. Ao fazer isso, examinamos a pesquisa dos autores e propomos um ranking alternativo da suscetibilidade das ocupações com base em um método distinto e fundamentado em opiniões de especialistas. Também avaliamos as principais conclusões de Frey & Osborne (2017) em relação ao impacto no emprego pelas tecnologias e identificamos os principais impactos qualitativos positivos e negativos da IA em organizações e trabalho, ocupações e mercado de trabalho. Levando em conta a natureza desta pesquisa, prospectiva, experimental e proposicional, focada nas implicações atuais e futuras da Inteligência Artificial, realizamos uma pesquisa de campo com especialistas apoiados pelo método Delphi, que é complementado por outras técnicas. O Delphi é um método robusto e comprovado, comumente usado em pesquisas com orientação futura para avaliar a direção de tendências de longo prazo, com especial ênfase em ciência e tecnologia, e seus prováveis efeitos em nossa sociedade e em nosso mundo. Entre nossas principais conclusões, avaliamos os gargalos aplicados no contexto das ocupação e comparamos com aqueles identificados por Frey & Osborne (2017). Também elaboramos nosso próprio ranking que leva em conta um fator de complexidade de integração, derivado da Lei de Metcalfe, que mostra que ocupações com menor complexidade de integração, como assistentes, têm maior probabilidade de serem substituídas, enquanto as que exigem maior integração entre habilidades estão praticamente fora de risco. Estes resultados ajudam a elucidar a situação atual e futura deste tema e nos permitem sugerir algumas possíveis suposições. Uma das mais importantes é que poucas ocupações atingirão o índice de suscetibilidade de 100% em vinte anos, contrariamente à pesquisa de Frey & Osborne (2017), o que significa que nem uma única ocupação pode ser totalmente substituída com um nível de qualidade aceitável por máquinas que combinem Inteligência Artificial, Robótica e outras tecnologias. No entanto, nosso achado mais relevante nesta pesquisa está relacionado à complexidade e integração de habilidades para ocupações. As tecnologias podem emular habilidades individuais em maior escala no futuro, mas mais importante do que isso, é poder combinar harmonicamente essas capacidades e fazê-las trabalhar em sinergia para alcançar tarefas básicas de ocupações. Este desafio de integração associado ao Paradoxo de Polanyi de Autor (2015) corrobora o fato de que não importa quão avançada seja a tecnologia em uma habilidade específica, é preciso mais do que isso para que máquinas substituíam com sucesso humanos em uma ocupação, o que entendemos que confirma o cenário futuro de colaboração, complementação e sinergia entre humanos e máquinas, ao invés de substituição e deslocamento
366

Comment mesurer l'influence de l'information préventive sur les risques majeurs ? : L'intérêt de la mise en situation sur maquette / How to assess preventive information on major risks? : The interest of role play on a 3D platform

Borelly, Audrey 27 May 2019 (has links)
Depuis 1987, l’information préventive sur les risques majeurs est un droit accordé aux populations. Elle est transmise sous diverses modalités : des documents règlementaires (DICRIM, brochure PPI etc.) et une variété de supports et formes d’expressions alternatives (pièces de théâtre, clips, expositions etc.). L’efficacité et l’impact de la première catégorie d’information préventive est déjà évaluée par des questionnaires réalisés auprès des populations. Cependant, ces évaluations ne permettent pas de vérifier si ces informations induisent effectivement des comportements adaptés en condition de stress que procure un évènement extrême. L’impact de la seconde catégorie d’information apparait comme très peu étudiée, alors qu’elle se caractérise par des méthodes et outils originaux, empruntés aux arts et à la pédagogie, et produisant une certaine participation des populations et l’activation du corps, des sens et des émotions. Or les sciences de la communication ont montré que la mobilisation des sens et des émotions favorise la mémorisation des messages.Devant ce constat, cette thèse propose d’évaluer l’influence des différentes formes d’information préventive sur les comportements en situation de crise fictive, par la création et l’expérimentation d’une nouvelle méthode inspirée des arts et des jeux de rôle. Ce faisant, l’étude compare d’une part cette nouvelle méthode à celle par questionnaire, et d’autre part les modalités d’informations réglementaires aux informations alternatives. En se focalisant sur les risques d’inondation, de séisme et d’émanation de gaz toxique, cette comparaison est mise en place sur trois terrains d’étude en Isère : Grenoble, Jarrie et Saint-Egrève. En mettant les enquêtés en situation sur une maquette, en les confrontant à des dilemmes que peut faire émerger l’urgence de la crise, la thèse met en exergue des réactions qui n’apparaissent pas dans les questionnaires : des réactions réflexes, contraires aux connaissances des enquêtés, des hésitations, etc. Les apports et limites des informations préventives sont alors précisées, selon les contextes et profils sociogéographiques des enquêtés. Les résultats montrent l’intérêt de multiplier les modalités d’informations et de les adapter sur des publics particuliers en favorisant l’échange et la contextualisation de la crise. / Since 1987, populations have been granted access to preventive information about major risks. It is passed down through a variety of methods, from regulatory documents (DICRIM, PPI brochure etc.) to original supports and alternative expression forms (plays, video clips, exhibitions etc.). Direct questionnaires to populations already assess the efficiency and impact of first category preventive information. However, these assessments do not check whether the information has actually induced adapted behaviors when confronted to stressful conditions, as is the case with extreme events. On the other hand, the impact of second category information appears under-studied, while it is characterized by original methods and tools. These methods, borrowed from arts and pedagogy, generate an interesting popular response, by activating emotions and resorting to sensory stimulation. As a matter of fact, communication science has shown that mobilizing sense and emotions helps with message memorization.In the face of these observations, this thesis proposes to assess how different ways to pass down preventive information influence behavior in a fictional crisis situation. To that end, a new method inspired from arts and role play has been created and experimented upon.Therefore, the study first compares this new method to the classic questionnaire method, and secondly, it opposes regulatory documents to alternative information. By focusing on floods, earthquakes and gas emanation risks, the comparison has been set up and studied on three different sites in Isère in France: Grenoble, Jarrie et Saint-Egrève. The respondents were presented a 3D model as the operating stage, and then confronted to typical dilemmas that can stem from emergency situations. Here, this thesis has highlighted reactions that surveys cannot reveal: reflex actions sometimes contradicting the respondents’ knowledge, hesitations, etc. Benefits and limits of preventive information are thereby more accurate, and depend on circumstances as well as on the respondents’ sociogeographic profiles. The results demonstrate how necessary it is to multiply and diversify the modes of information transmission, and to adapt them to specific audiences, through experience sharing and crisis contextualization.
367

Electronic medical records: an empirical study of South African health workers' attitudes, use and perceptions of impacts

Katsande, Tinashe 19 August 2014 (has links)
Thesis (M.Com. (Information Systems))--University of the Witwatersrand, Faculty of Commerce, Law and Management, School of Economic and Business Sciences, 2014. / Successful implementation of electronic medical record systems (EMRs) can result in many benefits. However, the adoption and use of EMRs by health workers is often problematic. Understanding the perceptions and attitudes of health workers towards the use of these systems is therefore important. This study has contributed by examining (a) perceptions of health workers towards the characteristics of EMR systems, (b) perceptions of the impacts of EMR use on healthcare delivery and other workplace outcomes (i.e. individual work performance and job satisfaction), (c) their intentions to continue using EMRs. The DeLone and McLean Information System Success model and the Information Systems Continuance model were used to underpin the study and to hypothesize inter-relationships amongst these perceptions and attitudes. The empirical context of the study was Tygerberg Hospital in Cape Town, South Africa. A survey was carried out and 142 responses were obtained from the nurses at the hospital. Results showed that system characteristics, namely, system quality, information quality and service quality were significant predictors of user satisfaction, which in turn was found to be a significant predictor of EMR use. Satisfaction together with perceptions of individual impacts and healthcare impacts was found to lead to continuance intention. Users reported statistically significantly higher levels of job satisfaction than non-users. Healthcare impact perceptions was positively associated with job satisfaction. Based on the results of the study, it is recommended that decision makers, policy makers and EMR vendors pay close attention to the service quality and the system quality of EMRs as these are the key determinants of user satisfaction. It is also recommended that managers ensure that all healthcare workers be given access to and encouraged to use EMRs to perform their work related task as EMR users have been shown to have higher levels of job satisfaction than non-users.
368

Radioaktivita hornin a ovzduší ve vybraných podzemních prostorách a jejich zdravotní dopady / Radioactivity of the rock and the environment in selected underground areas and its impact on human health

Thinová, Lenka January 2013 (has links)
The thesis is focused on measurement and assessment of absorbed doses of radiation in caves of the Czech Republic, out of which some exhibit high activity concentration of radon in air. This thesis presents an analysis and recommendations based on measurement results obtained in the underground caves over the past 10 years. The focus is on defining the sources of irradiation within the cave environment (and in areas used for speleotherapy), considering their potential health effect, including the variable dependence of external and internal irradiation influences. All of the measurements had as an objective to verify, and where possible improve, the existing methodology for assessing and calculating the dose from radon in underground spaces. The main issue that had to be resolved was whether a numerically specified cave factor value is applicable to all underground areas. The research measurements were carried out in all available show caves and in several underground areas, and were based on the initial results from an aerosol measurement campaign. Two caves (the Bozkov Dolomite Caves and the Zbrašov Aragonite Caves) were selected for advanced long-term measurements. A large number of long-term and short-term studies were carried out. The most important results for cave environments were: the...
369

Le littoral méditerranéen entre l'oued Kiss et le Cap des Trois Fourches (NE du Maroc) : évolution naturelle et impact des aménagements / The Mediterranean coastline between l'wadi Kiss and the Cap of the Three Fourches (of NE Morocco) : natural evolution and impact of installation

Bouabdallah, Mostafa 27 June 2008 (has links)
Le littoral méditerranéen oriental du Maroc compris entre l’oued Kiss et le Cap des Trois Fourches s’étire sur près de 120 km. Ce littoral, objet de notre étude, est caractérisé par des unités morphologiques variées : embouchure, baies, lagune, plages, flèches sableuses, tombolo, falaises (vives et mortes). C’est une zone particulièrement intéressante pour l’étude et la compréhension de l’influence des processus naturels et anthropiques sur la dynamique sédimentaire. L’augmentation des activités industrielles et l’urbanisation croissante ont conduit ces dernières années à la construction de nombreux ouvrages le long de la côte, conduisant à des modifications dans la distribution des sédiments et à une dégradation de l’environnement naturel de certaines plages. L’étude sédimentologique couplée à l’analyse des photos aériennes de plusieurs missions a permis de caractériser les différents environnements de ce littoral, de reconstituer la dynamique des différents environnements sédimentaires et de souligner les facteurs, les processus hydrologiques et hydrographiques qui contrôlent ce littoral méditerranéen. Les analyses minéralogiques, en particulier l’étude des minéraux lourds, nous ont fourni des indications sur l’origine des sédiments, la nature du bassin versant fournisseur, également ont permis de mettre évidence deux secteurs morphosédimentaires de part et d’autre de l’embouchure de la Moulouya. Á l’Est, on trouve un secteur en démaigrissement et un secteur en accrétion est situé dans la partie Ouest de l’embouchure de la Moulouya. L'évolution morphodynamique de chacun de ces deux secteurs résulte des interactions entre les facteurs naturels et l’impact des aménagements réalisés sur cette portion de littoral / The Eastern Mediterranean coastline of Morocco ranging between Kiss and the Cap of the Three Fourches is stretched along nearly 120 km. This littoral, the object of our study, is characterized by varied morphological units: mouth, bays, lagoon, beaches, sand, tombolo, cliffs (formed and dead). It is a particularly interesting zone for the study and the comprehension of the influence of the natural and anthropic processes and sedimentary dynamics. During the last few years the increase in the industrial activities and the increasing urbanization led to the construction of many works along the coast, leading to modifications in the distribution of the sediments and to a degradation of the natural environment of certain beaches. The sedimentological study coupled with the analysis of aerial photographs (of several missions) made it possible to characterize the various environments of this littoral, to reconstitute the dynamics of the various sedimentary environments and to underline the factors, the hydrological and hydrographic processes which control this Mediterranean coastline. The mineralogical analysis, the study of heavy minerals in particular, provided indications on the origin of the sediments, the nature of the catchment supplier area and made it possible to put two morphosedimentary sectors obvious on both sides of the mouth of Moulouya. The morphodynamic evolution of each one of these two sectors results from the interactions between the natural factors and the impact from the installations carried out on this portion from littoral
370

Les nuages de mi-niveau en Afrique de l'Ouest : observation, caractérisation, modélisation

Bourgeois, Elsa 07 December 2017 (has links) (PDF)
Les nuages jouent un rôle important dans le cycle de l'eau et de l'énergie au sein de l'atmosphère. De plus, ils représentent l'une des principales sources d'incertitudes dans les projections des modèles de climat en raison notamment de la difficulté à paramétrer les processus qui leurs sont associés ainsi que leurs interactions avec l'environnement. Dans cette thèse nous étudions les nuages de mi-niveau qui ont été beaucoup moins étudiés que les nuages bas et les nuages hauts, en se focalisant sur l’Afrique de l'Ouest. L'Afrique de l'Ouest se caractérise par une forte saisonnalité des précipitations survenant au Sahel de juin à septembre durant la période dite de mousson. Cette période coïncide également avec le maximum annuel de la couverture nuageuse. Au travers du déploiement de la station mobile ARM (Atmospheric Radiation Measurement) durant une année en 2006 à Niamey (Niger), Bouniol et al. (2012) ont documenté les différents types de nuages observés pendant la mousson et ont montré la présence récurrente de nuages vers 6 km d'altitude dont l’impact radiatif est important dans les domaines du visible et de l'infrarouge. Dans le prolongement de cette étude, l'objectif de cette thèse est donc d'analyser plus en détails ces nuages de mi-niveau en documentant leur occurrence, leur cycle diurne et leurs caractéristiques macro- et microphysiques. Nous analysons également l'environnement thermodynamique dans lequel ces nuages sont observés ainsi que leurs effets radiatifs. D’autre part, en analysant les simulations effectuées dans le cadre du projet CMIP5, Roehrig et al. (2013) ont montré une sous-estimation de ce type de nuages dans les modèles de climat. Nous documentons plus précisément ici comment les modèles de climat et les modèles à aire limitée simulent ces nuages de mi-niveau. Afin de documenter ces nuages, des observations obtenues à partir d'instruments de télédétection active déployés sur deux sites sols : Niamey au Sahel et Bordj Badji Mokhtar au Sahara ont été combinées avec les données satellites de CloudSat et CALIPSO. Ces observations ont révélé une occurrence de ces nuages tout au long de l'année avec une prédominance durant la période de mousson. Ces nuages sont majoritairement observés dans le Sud et l'Ouest de l'Afrique de l'Ouest mais s’étendent jusqu’au cœur du Sahara. Leur présence dans cette zone désertique pourrait s’expliquer par la dynamique de la dépression thermique saharienne (Saharan Heat Low). Ces nuages sont généralement fins (la plupart ont une épaisseur inférieure à 1000 m) et sont principalement composés d'eau liquide. Une méthode de clustering appliquée à ces données nous a permis d'identifier trois types de nuages : le premier avec des bases plus basses, le deuxième avec des bases plus hautes et le dernier avec de plus fortes épaisseurs. Les radiosondages et les mesures de rayonnement nous ont permis de déterminer la stratification thermodynamique dans laquelle ces nuages sont observés ainsi que d’estimer leur impact radiatif. On observe généralement des inversions de température potentielle au sommet des nuages des deux premières familles. Dans les modèles de climat, nous avons mis en évidence une forte dispersion des occurrences des nuages de mi-niveau en termes de fréquence, de position et d’extension sur la verticale et de cycle saisonnier. L'analyse des simulations régionales indique aussi une influence de la résolution spatiale et de la paramétrisation de la convection sur la modélisation des nuages de mi-niveau simulés au Sahel et sur le Sahara.

Page generated in 0.0356 seconds