No description available.

No description available.

<p>Light rainfall is the baseline input to the annual water budget in mountainous landscapes through the tropics and at mid-latitudes. In the Southern Appalachians, the contribution from light rainfall ranges from 50-60% during wet years to 80-90% during dry years, with convective activity and tropical cyclone input providing most of the interannual variability. The Southern Appalachians is a region characterized by rich biodiversity that is vulnerable to land use/land cover changes due to its proximity to a rapidly growing population. Persistent near surface moisture and associated microclimates observed in this region has been well documented since the colonization of the area in terms of species health, fire frequency, and overall biodiversity. The overarching objective of this research is to elucidate the microphysics of light rainfall and the dynamics of low level moisture in the inner region of the Southern Appalachians during the warm season, with a focus on orographically mediated processes. The overarching research hypothesis is that physical processes leading to and governing the life cycle of orographic fog, low level clouds, and precipitation, and their interactions, are strongly tied to landform, land cover, and the diurnal cycles of flow patterns, radiative forcing, and surface fluxes at the ridge-valley scale. The following science questions will be addressed specifically: 1) How do orographic clouds and fog affect the hydrometeorological regime from event to annual scale and as a function of terrain characteristics and land cover?; 2) What are the source areas, governing processes, and relevant time-scales of near surface moisture convergence patterns in the region?; and 3) What are the four dimensional microphysical and dynamical characteristics, including variability and controlling factors and processes, of fog and light rainfall? The research was conducted with two major components: 1) ground-based high-quality observations using multi-sensor platforms and 2) interpretive numerical modeling guided by the analysis of the in situ data collection. Findings illuminate a high level of spatial – down to the ridge scale - and temporal – from event to annual scale - heterogeneity in observations, and a significant impact on the hydrological regime as a result of seeder-feeder interactions among fog, low level clouds, and stratiform rainfall that enhance coalescence efficiency and lead to significantly higher rainfall rates at the land surface. Specifically, results show that enhancement of an event up to one order of magnitude in short-term accumulation can occur as a result of concurrent fog presence. Results also show that events are modulated strongly by terrain characteristics including elevation, slope, geometry, and land cover. These factors produce interactions between highly localized flows and gradients of temperature and moisture with larger scale circulations. Resulting observations of DSD and rainfall patterns are stratified by region and altitude and exhibit clear diurnal and seasonal cycles.</p> / Dissertation

Orography plays a major role in the general circulation and climate of the tropics. Although many works have been done on the impact of global orography on summer monsoon, the previous studies have examined the impact on seasonal mean scale or only during the first half of the season. Role of orography on intra-seasonal variability has not been addressed previously. Also, the proximate and remote impacts of orography have not been studied. In this thesis an atmospheric General Circulation Model (GCM) has been used to investigate the impact of global and regional orography on monsoon climate. Two different cumulus schemes have been used to study the sensitivity of the results to the cumulus parameterization scheme. The model was forced with seasonally varying sea surface temperature (SST) for the year 1998. An ensemble simulation of 5 members were performed for each experiment. The simulations showed that the removal of Himalayas or orography over the entire earth caused a delay of about one month in the onset of the monsoon. The delay in monsoon onset was on account of a more stable atmosphere due to intrusion of mid-latitude cold air into the Indian region in the absence of Himalayas. After the onset, the precipitation rate was comparable in control and no-mountain simulations. The seasonal mean (June-September) precipitation over this region decreased by 25% in the no-mountain case as compared to control. A comparison of the impact of east and west Himalaya orography showed that orography west of 80E has more impact on the phase and intensity of summer monsoon precipitation over the Indian region than orography east of 80E. The onset of summer monsoon over the Indian region was delayed by about one month with the removal of Himalaya orography west of 80E, but was delayed by just about one week with the removal of Himalaya orography east of 80E. This is because, the cold air intrusion was more when Himalaya orography west of 80E was removed. Seasonal mean precipitation decreased by 22% and 12% with the removal of orography west and east of 80E respectively. Himalaya orography east of 80E showed more influence on precipitation over the north-east Indian region and East Asia. The removal of orography from the African continent increased the summer monsoon precipitation over the Indian region. This was on account of an increase in the zonal mass flux from the African continent in the absence of East African mountains. This mass flux brings more moisture into the south Asian region and increases precipitation over the Indian region and Bay of Bengal. A higher precipitation over the Bay of Bengal leads to higher wind over the Somalia coast and this acts as a positive feedback to enhance the summer monsoon precipitation by about 28% over the Indian region. The presence of orography only over the African continent resulted in the largest delay in the monsoon onset (by 50 days) and the lowest amount of seasonal precipitation (decrease by 36%) over the Indian region among all the simulations. This is due to further reduction in zonal mass (and hence, moisture) flux toward the Indian subcontinent with the inclusion of African orography when compared with no-global orography simulation. The seasonal mean precipitation decreased by 19% over the Indian region with the removal of American orography. The onset of monsoon was delayed by about 3 weeks in this experiment as compared to control. This delay was due to a relative downward motion in the upper troposphere on account of the shift of the Rossby wave with the removal of American mountains. In this thesis, a new theory has been proposed for monsoon onset based on thermodynamic conditioning (necessary condition) and mechanical trigger (sufficient condition) of the atmosphere. This theory was able to explain the large variation in monsoon onset dates (maximum spread 57 days) in different simulations. The low level circulation was affected more by Himalaya orography west of 80E, which had a profound influence on precipitation over the Indian region. However, upper level circulation was affected more by Himalaya orography east of 80 E. The northward shift of the upper tropospheric westerly jet during the Northern Hemispheric summer was sudden in presence of the Tibetan Plateau and gradual in its absence. This shift was not related to the onset of monsoon over the Indian region. Northward propagation of convection was found to be present even in the absence of global orography. But northward extent of this propagation was delayed without orography on account of the absence of a favorite meridional gradient of moist static energy in the lower troposphere in the early summer season due to intrusion of mid-latitude cold air. Space-time spectral analysis showed that the intensity of eastward moving convectively coupled atmospheric waves, known as Madden-Julian oscillation (MJO), decreased in absence of global orography. Moreover, the presence of orography favor the higher zonal wave number for MJO propagation.

L'impact dynamique des montagnes sur la circulation de grande échelle de l'atmosphère passe généralement par des forces : pour cette raison, la partie de l'orographie qui n'est pas résolue par les modèles de circulation générale est prise en compte par la paramétrisations des forces qu'elle applique à l'atmosphère. Dans cette thèse , nous nous attacherons à comprendre l'impact des forces appliquées par les montagnes des moyennes latitudes, en particulier le Plateau tibétain, sur la circulation de l'atmosphère. Pour ce faire, nous utiliserons notamment le concept de couple appliqué par les montagnes sur l'atmosphère, traduction des forces à l'échelle globale. Les chaînes de montagnes les plus importantes des moyennes latitudes génèrent, à l'échelle synoptique, d'importantes vagues de froid appelées cold surges dans la littérature anglophone, un terme que nous traduirons littéralement par crues froides. L'importance du couple équatorial des montagnes dans l'initiation des crues froides sur l'Asie de l'Est (impact du Plateau tibétain), l'Amérique du Nord (impact des montagnes Rocheuses) et l'Amérique du sud (impact de la cordillère des Andes) est mise en évidence par une étude statistique. À l'aide d'un modèle dynamique simple, une interprétation du mécanisme sous-jacent à ce forçage est proposée, montrant que les forces de portance appliquées par la montagne à l'atmosphère dans la phase initiale des crues froides suffisent à leur déclenchement. L'impact dynamique du plateau tibétain sur la mousson d'hiver est-asiatique est important, en particulier sur les événements de convection en hiver sur la Mer de Chine Méridionale. Une séquence d'événements montrant cet impact a été identifiée statistiquement : un forçage dynamique de la circulation atmosphérique par le Plateau tibétain, se traduisant par un fort signal sur le couple des montagnes équatorial appliqué à l'atmosphère, est suivi par le déclenchement d'une crue froide puis, après quelques jours, par un renforcement de la convection profonde sur la Mer de Chine Méridionale. Cet effet dynamique du Plateau tibétain sur la mousson d'hiver s'étend au sud jusqu'à l'Indonésie et à l'ouest jusqu'à la Baie du Bengale. L'utilisation du modèle de circulation générale du Laboratoire de Métérorologie Dynamique, LMDz, permet de compléter les résultats observationnels décrits auparavant. Ce modèle ferme de manière satisfaisante le bilan de moment angulaire et permet de montrer que l'orographie sous-maille joue un rôle important sur la phase finale de l'évolution des crues froides. Des résultats nouveaux sont présentés sur le bilan de moment angulaire de l'atmosphère, en particulier en ce qui concerne l'impact du couple équatorial des montagnes et de la contribution du Plateau tibétain. Il est en particulier montré que le couple équatorial appliqué par le Plateau tibétain joue un rôle faible dans l'évolution temporelle du moment angulaire équatorial, mais un rôle significatif dans sa répartition spatiale / Mountains have an impact on the large scale circulation of the atmosphere, this impact being predominantly a consequence of the forces they exert on the atmosphere : for this reason, the part of the orography which is not resolved explicitly by the general circulation models is taken into account through parametrisations of the forces it applies to the atmosphere. This PhD thesis is focused on understanding the impact of the forces applied by the midlatitude mountains, particularly the Tibetan Plateau, on the atmosphere. For that purpose, we will consider the mountain torque applied by the mountains on the atmosphere, a global scale counterpart of the mountain forces.The major midlatitude mountain ranges can trigger massive synoptic scale cold surges on their eastern flanks. This thesis uncovers the importance of the equatorial mountain torque in triggering the cold surges over east-Asia (impact of the Tibetan Plateau), north-America (impact of the Rockie Mountains) and south-America (impact of the Andes cordillera). Using a simple dynamical model, an interpretation of the mechanism underlying the forcing of the cold surges by the equatorial mountain torque is proposed, showing that the existence of a lift force applied by the mountain on the atmosphere is sufficient for the triggering of cold surges.The dynamical impact of the Tibetan plateau on the east-asian winter monsoon, more specifically on the wintertime convection events on the South China Sea, is important. A typical sequence of events showing this dynamical impact has been identified statistically : a dynamical forcing of the atmospheric circulation by the Tibetan Plateau, materialized by a strong signal on the equatorial mountain torque on the atmosphere is followed quickly by the occurence of a cold surge and, a few days later, by an outburst of deep convection over the South China Sea. This dynamical effect of the Tibetan Plateau on the winter monsoon extends as far south as Indonesia, and westward to the Bay of Bengal. The use of the general circulation model of the Laboratoire de Météorologie Dynamique general circulation model, LMDz, makes it possible to extend the observational results described above. This model closes properly the budget of atmospheric angular momentum, and will be used to show that that sub-grid sale orography plays an important role in the terminal phase of the evolution of cold surges. New results are presented concerning the equatorial atmospheric angular momentum budget are presented, adressing specifically the impact of the equatorial mountain torque and that of the contribution of the Tibetan Plateau. It is shown that the equatorial mountain torque applied by the Tibetan Plateau has only a weak role in the temporal evolution of the equatorial angular momentum, but a significant role concerning its spatial repartition

Unidades climáticas são determinadas áreas da superfície terrestre que apresentam características climáticas relativamente homogêneas ao longo do tempo e do espaço. Sua existência, a priori, depende da relação única entre a superfície terrestre e a dinâmica atmosférica, quando a primeira exerce controle sobre a segunda, influenciando tais características. Essas características climáticas, sob a forma da variação temporal da temperatura, umidade, chuvas, entre outros, são espacialmente melhor percebidas de acordo com a escala de trabalho da pesquisa adotada e podem realçar a existência de ambientes diferenciados (daqueles conhecidos em escalas mais generalistas) - os climas locais e os topoclimas, que são a base climatológica mais complexa dos planos de ordenação territorial. O município de Ilhabela reflete as transformações socioeconômicas e ambientais que vem ocorrendo na região do Litoral Norte do estado de São Paulo, essencialmente no período posterior a 1970, com a inauguração da Rodovia Rio-Santos (BR101/SP55), que pressupõem, por conta do aporte migratório, transformações nas paisagens locais e regionais. Entretanto, a Ilha de São Sebastião (a maior e sede do município) resguarda 75% de seu território sob a forma de unidade de conservação Parque Estadual de Ilhabela (PEIb). Desta forma, a essência do estudo aqui proposto é a identificação das unidades climáticas naturais da ilha, por meio da análise da variação de temperatura, umidade relativa e precipitações identificadas em diferentes localidades deste ambiente ilhéu e avaliar possíveis influências da urbanização sobre este processo. O método utilizado nesta pesquisa está assentado na instalação de equipamentos sensores da temperatura do ar, umidade relativa e da precipitação líquida como os termo-higrômetros (eletrônicos) e os pluviômetros (totalizadores e registradores, manuais e eletrônicos, respectivamente), dentro do período de um ano. A análise dos dados considerou aspectos geográficos e climatológicos de ordem local, assim como aqueles de ordem regional (meteorológicos sinóticos) resultando em informações quantitativas e qualitativas, que sob a luz da análise rítmica e da heurística possibilitaram sua análise crítica. Os resultados, quando observados individualmente, representam a situação geoclimática dos sítios de instalação da instrumentação meteorológica; por outro lado, a variabilidade espacial dos atributos em sua relação com os sistemas atmosféricos atuantes, considerados então como representativos dos meso e topoclimas, permite a identificação, individualização e definição de unidades climáticas da ilha no período da coleta de dados. Foram então definidos 12 ambientes topoclimaticamente diferenciados com a clara percepção de heterogeneidade entre si, organizados sob 5 mesoclimas conforme a insolação, os fluxos de ar predominantes, a orientação geral das vertentes e das bacias hidrográficas e a variação dos atributos do clima. O setor norte: quente e pouco chuvoso. A vertente leste: mais ensolarada e úmida. O sul sudoeste: barlavento dos sistemas frontais. O setor central: urbano é sujeito a atividade convectiva intensa. / Climate units are certain areas of the Earth\'s surface that have relatively homogeneous climatic characteristics over time and space. Its existence, in principle, depends on the unique relationship between the ground surface and the atmospheric dynamics, where the first exercises control over the second influencing such features. These climatic characteristics in the form of temporal variation of temperature, humidity, rainfall, among others, are spatially better perceived according to the adopted research work schedule and can highlight the existence of different environments (those known in more general scales) - local climates and topoclimas, which are the most complex climatological basis of territorial development plans. The municipality of Ilhabela reflects the socioeconomic and environmental changes that have occurred in the North Coast region of the state of São Paulo, mainly in the period to 1970, with the inauguration of the Rio-Santos highway (BR101 / SP55), which require, due to the migratory contribution, changes in local and regional landscapes. However, Sao Sebastiao Island (the largest and county seat) protects 75% of its territory in the form of conservation unit - Ilhabela State Park (PEIb). Thus, the essence of the herein proposed study is to identify the natural climate units of the island, through the analysis of the variation of temperature, relative humidity and precipitation identified in different locations of the islet environment and to evaluate the possible influence of urbanization on this process. The method used in this research is seated in the installation of sensor equipment of the air temperature, relative humidity and liquid precipitation as the thermo-hygrometers (electronic) and rain gauges (totalizers and registers, manual and electronic, respectively) within the period of one year. Data analysis considered geographical and climatological aspects of local order, as well as those of regional order (synoptic weather) resulting in quantitative and qualitative information, which in the light of rhythmic analysis and heuristics enabled critical analysis. The results, when viewed individually, represent the geoclimática situation of installation sites of meteorological instrumentation; on the other hand, the spatial variability of the attributes in its relation to the active atmospheric systems, considered then as representative of meso and topoclimas allows the identification, individualization and definition of climate units of the island in the period of data collection. They were then set 12 topoclimaticamente different environments with a clear perception of heterogeneity among themselves, organized under 5 mesoclimas as heatstroke, prevailing air flows, the general orientation of the slopes and river basins and the change of climate attributes. The northern sector: hot and slightly rainy. The east side: more sunny and humid. The south southwest: windward of frontal system. The central sector: Urban is subject to intense convective activity.

Unidades climáticas são determinadas áreas da superfície terrestre que apresentam características climáticas relativamente homogêneas ao longo do tempo e do espaço. Sua existência, a priori, depende da relação única entre a superfície terrestre e a dinâmica atmosférica, quando a primeira exerce controle sobre a segunda, influenciando tais características. Essas características climáticas, sob a forma da variação temporal da temperatura, umidade, chuvas, entre outros, são espacialmente melhor percebidas de acordo com a escala de trabalho da pesquisa adotada e podem realçar a existência de ambientes diferenciados (daqueles conhecidos em escalas mais generalistas) - os climas locais e os topoclimas, que são a base climatológica mais complexa dos planos de ordenação territorial. O município de Ilhabela reflete as transformações socioeconômicas e ambientais que vem ocorrendo na região do Litoral Norte do estado de São Paulo, essencialmente no período posterior a 1970, com a inauguração da Rodovia Rio-Santos (BR101/SP55), que pressupõem, por conta do aporte migratório, transformações nas paisagens locais e regionais. Entretanto, a Ilha de São Sebastião (a maior e sede do município) resguarda 75% de seu território sob a forma de unidade de conservação Parque Estadual de Ilhabela (PEIb). Desta forma, a essência do estudo aqui proposto é a identificação das unidades climáticas naturais da ilha, por meio da análise da variação de temperatura, umidade relativa e precipitações identificadas em diferentes localidades deste ambiente ilhéu e avaliar possíveis influências da urbanização sobre este processo. O método utilizado nesta pesquisa está assentado na instalação de equipamentos sensores da temperatura do ar, umidade relativa e da precipitação líquida como os termo-higrômetros (eletrônicos) e os pluviômetros (totalizadores e registradores, manuais e eletrônicos, respectivamente), dentro do período de um ano. A análise dos dados considerou aspectos geográficos e climatológicos de ordem local, assim como aqueles de ordem regional (meteorológicos sinóticos) resultando em informações quantitativas e qualitativas, que sob a luz da análise rítmica e da heurística possibilitaram sua análise crítica. Os resultados, quando observados individualmente, representam a situação geoclimática dos sítios de instalação da instrumentação meteorológica; por outro lado, a variabilidade espacial dos atributos em sua relação com os sistemas atmosféricos atuantes, considerados então como representativos dos meso e topoclimas, permite a identificação, individualização e definição de unidades climáticas da ilha no período da coleta de dados. Foram então definidos 12 ambientes topoclimaticamente diferenciados com a clara percepção de heterogeneidade entre si, organizados sob 5 mesoclimas conforme a insolação, os fluxos de ar predominantes, a orientação geral das vertentes e das bacias hidrográficas e a variação dos atributos do clima. O setor norte: quente e pouco chuvoso. A vertente leste: mais ensolarada e úmida. O sul sudoeste: barlavento dos sistemas frontais. O setor central: urbano é sujeito a atividade convectiva intensa. / Climate units are certain areas of the Earth\'s surface that have relatively homogeneous climatic characteristics over time and space. Its existence, in principle, depends on the unique relationship between the ground surface and the atmospheric dynamics, where the first exercises control over the second influencing such features. These climatic characteristics in the form of temporal variation of temperature, humidity, rainfall, among others, are spatially better perceived according to the adopted research work schedule and can highlight the existence of different environments (those known in more general scales) - local climates and topoclimas, which are the most complex climatological basis of territorial development plans. The municipality of Ilhabela reflects the socioeconomic and environmental changes that have occurred in the North Coast region of the state of São Paulo, mainly in the period to 1970, with the inauguration of the Rio-Santos highway (BR101 / SP55), which require, due to the migratory contribution, changes in local and regional landscapes. However, Sao Sebastiao Island (the largest and county seat) protects 75% of its territory in the form of conservation unit - Ilhabela State Park (PEIb). Thus, the essence of the herein proposed study is to identify the natural climate units of the island, through the analysis of the variation of temperature, relative humidity and precipitation identified in different locations of the islet environment and to evaluate the possible influence of urbanization on this process. The method used in this research is seated in the installation of sensor equipment of the air temperature, relative humidity and liquid precipitation as the thermo-hygrometers (electronic) and rain gauges (totalizers and registers, manual and electronic, respectively) within the period of one year. Data analysis considered geographical and climatological aspects of local order, as well as those of regional order (synoptic weather) resulting in quantitative and qualitative information, which in the light of rhythmic analysis and heuristics enabled critical analysis. The results, when viewed individually, represent the geoclimática situation of installation sites of meteorological instrumentation; on the other hand, the spatial variability of the attributes in its relation to the active atmospheric systems, considered then as representative of meso and topoclimas allows the identification, individualization and definition of climate units of the island in the period of data collection. They were then set 12 topoclimaticamente different environments with a clear perception of heterogeneity among themselves, organized under 5 mesoclimas as heatstroke, prevailing air flows, the general orientation of the slopes and river basins and the change of climate attributes. The northern sector: hot and slightly rainy. The east side: more sunny and humid. The south southwest: windward of frontal system. The central sector: Urban is subject to intense convective activity.

Stable isotopes of oxygen (O18) and hydrogen (H2) are used as proxies of past climates when ice preserved in the polar icecaps. The main assumption when doing paleoclimatic reconstructions using these isotopes is that the isotopic composition of the snow that turned into ice reflect the present temperature of the planet during deposition. In this study, I investigate to what extent the composition of O18 and H2 varies as a function of precipitation. I tested the following hypotheses: i) δO18 and δH2 decreases due to fractionation during orographic fallout, and ii) the electric conductivity in the snow decreases with distance from sea due to fading marine inputs. The hypotheses were tested with field samples gathered along a precipitation gradient from the Norwegian coast to Kiruna, Northern Sweden. To support my first hypothesis, I found a decrease from -9.32% δO18 (-54.85% δH2) to -25.48% δO18 (-109.54 % δH2) due to orographic deposition over the Scandes with a drastic drop in Abisko caused by a rain shadow. Similarly, I found a considerable variation and decreasing trend of conductivity along the precipitation gradient. My study raises awareness that δO18 in snow is in fact dependent on precipitation regimes rather than temperature regimes in this area, which should be considered when interpreting environmental records of δO18 in a paleoclimatic context. Lastly, I suggest further studies targeting the effects of post-depositional processes (melting, sublimation, and anthropogenic influence) on the isotopic composition and conductivity, especially with a changing climate.

Thermodynamic characteristics analysis of 80 MCC events during 10 years (1999-2009) in the Brazilian Northeast was the principal goal of this study. CCM events were observed more frequently (66%) in the dry season (January March). Reanalysis data showed SST temperatures above 27°C in adjacent ocean, and a 180° wind variation in relation to lower and higher levels. MCC development (declining) stage was associated more frequently with upslope (downslope) trajectory. K ant TT indexes showed more instability of the upslope air parcels in the majority of the events. In development stage, Convective Inhibition (CIN) values showed a decrease in its values and in the declining stage an increase were seen. Radiosonde data presented average values in consistency with reference data. Potential Instability showed influence in most of the cases, especially in the upslope events in the development stage. The influence of dynamical aspects on the instability took place in a better way for the MCC than the convective forcing / A análise termodinâmica de 80 eventos de CCM ocorridos entre 1999 e 2009 é o objetivo deste estudo. Foi visto que 66% dos eventos de CCM ocorreram entre janeiro e março, estação seca na região leste do Nordeste Brasileiro. Foi verificado com dados de reanálises valores de TSM acima de 27°C no litoral adjacente e variação de 180° no vento entre baixos e altos níveis. A maioria dos casos apresentou trajetória ascendente à montanha na fase de desenvolvimento do sistema. Na fase de decaimento, a maioria das trajetórias foram descendentes. Os índices K e TT mostraram instabilização das parcelas ascendentes na maioria dos eventos. O potencial de inibição da convecção (CIN) apresentou diminuição de seus valores no desenvolvimento e aumento no decaimento. Dados de radiossondagem obtidos em Recife-PE, dentro da área de estudo, mostraram valores dos índices termodinâmicos condizentes com os valores de referência na literatura. A instabilidade potencial esteve presente na maioria dos casos, especialmente nos casos com trajetória ascendente no desenvolvimento. No período de decaimento, a influência da montanha se deu na estabilização das parcelas. A instabilidade convectiva não foi o principal fator contribuinte na instabilidade associada aos CCM, uma vez que a variação de temperatura durante o ciclo diurno foi pequena, tendo seus valores de temperatura máxima com pequena diferença com relação aos valores reais

Submitted by (ana.araujo@ufrpe.br) on 2016-08-01T19:24:52Z No. of bitstreams: 1 Leda Valeria Ramos Santana.pdf: 2437098 bytes, checksum: f1ab02f82d16ec8b95e0800f78ab7585 (MD5) / Made available in DSpace on 2016-08-01T19:26:38Z (GMT). No. of bitstreams: 1 Leda Valeria Ramos Santana.pdf: 2437098 bytes, checksum: f1ab02f82d16ec8b95e0800f78ab7585 (MD5) Previous issue date: 2014-02-17 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Wind speed distribution depends on relief of a certain region, in the case of Brazilian Northeast (NE) there are four subregions with different characteristics of relief: Atlantic Rainforest zone, Agreste, North-Eastern Backlands and Northeast Mid North. Among probability distributions that were proposed for wind data, Weibull, General-ized Gamma and Rayleigh distributions were found to be most appropriate to model wind speed variability in many locations. In this work we analyze ERA-40 data, during the period 1958-2001, to evaluate which probability distribution is most suitable to describe temporal variability of wind speed in NE. ERA-40 is a re-analysis of meteor-ological observations from September 1958 to August 2002 produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) in collaboration with many institutions. The data were produced using different sources such as radiosondes, ocean buoys, satellites and meteorological stations, and have temporal resolution of 6h and spatial resolution of 2.5ox2.5º. The two parameter Weibull distribution is found to be the best for modeling frequency distribution of wind speed data for most of the NE. The coastal zone is characterized by strongest winds and smallest temporal variability. These results can be used to evaluate the wind energy potential at NE and the influence of wind on various environmental phenomena as soil erosion, rainfall, dune formation and dispersion of seeds and poluents. / A distribuição da velocidade do vento depende do relevo de uma determinada região, no caso do Nordeste brasileiro são quatro sub-regiões com características de relevo distintas: Meio Norte, Sertão, Agreste e Zona da Mata. Entre as distribuições de probabilidade que foram propostas para dados de vento, a distribuição Weibull, Gama Generalizada e a Rayleigh são consideradas as mais apropriadas para modelar a variabilidade da velocidade do vento em muitos locais. Neste trabalho foram analisados dados da ERA-40, durante o período 1958-2001, para verificar que distribuição de probabilidade é mais adequada para descrever a variabilidade temporal da velocidade do vento no NE. A ERA-40 é uma re-análise de observações meteoro-lógica de Setembro de 1958 a Agosto de 2002 produzida pelo European Centre for Medium-Range Weather Forecasts (ECMWF) em colaboração com muitas institui-ções. Os dados são produzidos usando diferentes fontes tais como radiossondas, boias oceânicas, satélites e estações meteorológicas. E tem resolução temporal é de 6 h e espacial de 2.5º x 2.5º. A distribuição Weibull de dois parâmetros é considera-da a melhor para modelar a distribuição de frequência dos dados da velocidade do vento para a maior parte do NE. A faixa litorânea é caracterizada por altas velocidades e baixa variabilidade temporal. Estes resultados podem ser usados para avaliar o potencial eólico do NE e, a influência do vento sobre vários fenômenos ambientais como erosão do solo, precipitação, formação de dunas, dispersão de sementes e poluentes.