This thesis examines the structure of the Tropical Easterly Jet (TEJ) in a General Circulation Model (GCM). The TEJ is observed only during the Indian summer monsoon period and is strongest during July and August. The jet structure simulated by an atmospheric GCM (CAM-3.1) in July has been compared with reanalysis data. The simulated TEJ was displaced westward by ~ 25◦ when compared to observations. The removal of orography had no impact on the jet structure. This demonstrated that the Tibetan Plateau did not play an important role in the location and structure of the jet. The changes in cumulus scheme in the GCM had a large influence on the location of the jet maxima. To examine the factors which control the location and structure of the jet, a series of experiments were conducted using an aqua-planet version of the model. The impact of different sea surface temperature (SST) profiles was studied. The rainfall in the GCM was primarily in the regions where the SST attained a maximum. By altering the location of SST maximum (and hence the rainfall maximum), the impact of location of rainfall maximum on the location and structure of the jet was studied. When the rainfall maximum was located close to the equator, it did not generate a strong jet but had an influence on the vertical structure of the jet. A large number of simulations were conducted with multiple rainfall maxima and the need for these was demonstrated since only then was the observed jet structure well simulated. Based on the simulations, it was concluded that the simulation of the TEJ by CAM-3.1 was unrealistic because of large unrealistic rainfall over Saudi Arabia in this GCM. Equatorial heating has been shown to be important to simulate proper jet structure. The zonal structure of the jet was also influenced by rainfall in the Pacific Ocean. Although the aqua-planet configuration of the CAM-3.1 GCM provided several useful insights, the simulation was not perfect on account of errors in the simulation of the temperature profile in the lower troposphere. An ideal-physics configuration of the GCM was used. This removed the cumulus physics and instead imposed the observed heating pro-files. Both upper tropospheric friction and radiative-convective atmospheric temperatures were required to simulate the TEJ. The problems with the simulation of structure in the jet exit region was corrected by using radiative-convective atmospheric temperatures that were qualitatively similar to those observed in northern hemisphere summer time. The ideal-physics configuration reconfirmed that the Saudi Arabian rainfall was responsible for the westward shift of the TEJ in the simulations. The ideal-physics simulations showed that the simple analytical model proposed by Gillin1980 was not suitable for the simulation of TEJ. The above the simulations indicate that a shift in the location of the jet is related to a shift in the rainfall pattern. Based on this insight one would expect that the jet location will be different in good and bad monsoon periods. This is indeed the case. In July 2002 the Indian monsoon failed after beginning well in June. In June the TEJ is consequently located west ward compared to July. The same situation prevails even in good and poor monsoon years. In a good monsoon year (July 1988) the jet maximum is located westward when compared to a bad monsoon year (July 2002). In this thesis we have clearly demonstrated the role of anomalous rainfall on the location of the TEJ. This thesis has shown that an accurate simulation of the TEJ depends upon the accurate simulation of various rainfall centers that act as multiple heat sources in the atmosphere. The rainfall in the equatorial region does not influence the strength of the TEJ but alters the vertical structure of the jet. The strength the jet is dependent on the intensity of rainfall and the latitudinal distance from the equator. The complex vertical structure of the jet is not simulated by simple analytical models of the jet.

This paper is concerned with the efficiency of aid in Masaka, Uganda which is about 140 km from the capital city Kampala. It uses the results of 300 surveys and several interviews to gather data, and a causal methodology to define results. Much of the methodology is based on theories from William Easterly, Andrew Mwenda, Dambisa Moyo, Jeffrey Sachs, and Amartya Sen. It has been concluded that there are several problems in the Masaka area. One is Uganda's federal government, which is inefficient and unaccountable. There is also lack of easily accessible health care for rural citizens, and a lack of local development due to poor governance. Conversely, the residents of Masaka are quite developed in terms of employment and education, and have rated themselves as quite free and satisfied with life. There is also a quite adequate level of gender equality, especially in terms of education.

African easterly waves (AEWs) are known precursors to tropical cyclone (TC) formation, although it is not always clear which AEWs will develop and which AEWs will not. To investigate AEW evolution, this study examines novel observations from the geostationary Advanced Baseline Imager (ABI) during July-September 2019. Case studies are conducted for two AEWs: one that became Hurricane Dorian, the strongest and most devastating hurricane of the 2019 Atlantic hurricane season, and a long-lived September AEW that did not become a TC. Lower-level moisture and flow, and the strength and spatial distribution of convective activity, differed between these two waves. By then exploring these characteristics for additional developing and non-developing AEWs, ABI observations show that developing AEWs are associated with low-level moist air ahead of the wave combined with enhanced convective activity, while non-developing AEWs tend to encounter drier air and exhibit a persistently broader structure with less-organized convection.

<p>The aim of this dissertation is to examine and compare William Easterly’s and PGU’s (Shared Responsibility: Sweden's Policy for Global Development) different views on development and international development cooperation. The methodological approach chosen in this study is an analysis of ideas based on the following questions:</p><p>1. Which principles should be applied to development and international development cooperation?</p><p>2. Which are the central actors in development and international development cooperation and what should their roles be in the development process?</p><p>3. Between which levels in society should the international development cooperation take place?</p><p>The result shows that Easterly and PGU agree that the receiving society should be responsible for the development process and that the poor are important actors in this process. In spite of their common view on the importance of national ownership their strategies and views on development and international development cooperation differ from one another. The main differences are based on their different views on how social changes should be done. Easterly suggests a piecemeal social engineering in contrast to PGU who suggests a holistic social engineering.</p>

Uma climatologia de 21 anos dos Distúrbios Ondulatórios de Leste (DOLs) sobre a região NEB foi realizada com o intuito de obter um melhor entendimento dos processos dinâmicos e sinóticos do ciclo de vida destes sistemas, incluindo gênese, crescimento/decaimento, trajetória e dissipação. Adicionalmente, foi avaliada a eficiência do modelo de mesoescala WRF em simular este tipo de sistema. A identificação dos DOLs foi obtida de forma subjetiva através de imagens de satélite no canal infravermelho e campos de linhas de corrente e vorticidade relativa nos níveis de 1000, 850, 700, 500 e 200 hPa da reanálise do ERA-Interim. Neste período foram identificados 518 eventos de DOLs, onde 97% (3%) dessas ondas atingiram (não atingiram) a região do NEB, 64% (36%) foram convectivas (não convectivas) e 14% (86%) atingiram a região da Amazônia. Os principais sistemas que deram origem aos DOLs foram: Zona de Convergência Intertropical (ZCIT), Vórtice Ciclônico de Altos Níveis (VCAN), Frentes Frias (FF) e conglomerados convectivos provenientes da costa oeste da África (AF). Além destes, a interação entre os sistemas AF/FF, AF/ZCIT, AF/VCAN e ZCIT/FF estiveram associadas a sua formação. Em média, foram observadas aproximadamente 25 ondas por ano, com máxima (mínima) frequência compreendida entre os meses de Março a Agosto (Setembro a Fevereiro) e, com pronunciada variabilidade interanual. O ciclo de vida dos DOLs foi avaliado de forma objetiva a partir de um método automático de identificação e rastreio (TracKH), onde dos 518 eventos identificados na análise subjetiva, conseguiu capturar 342 ondas ( ~ 66%). A partir desta detecção, uma análise foi feita no nível 850 hPa para determinar as características típicas do seu ciclo de vida, que mostra um pico proeminente entre as longitudes de 35°W e 15°W e latitudes de 20°S e 5°N associado a densidade de gênese. A trajetória e dissipação se concentraram sobre a costa leste do NEB, entre os estados de Alagoas e Rio Grande do Norte, porém a dissipação diminuía a medida que adentrava ao continente. Os padrões sinóticos associados aos DOLs foram analisados através da anomalia de composição durante o período de máxima (úmido) e mínima (seco) frequência desde 3 dias antes até um dia após os DOLs atingirem a costa do NEB. Durante o período úmido, a circulação associada aos DOLs apresentou anomalia ciclônica e confluente, vorticidade negativa e convergência até médios níveis, enquanto que em 200 hPa apresentou apenas a característica do cavado. Por outro lado, para o período seco, estas características foram observadas somente em baixos níveis. Anomalias negativas de movimentos verticais e temperatura e positivas de umidade foram observadas associadas aos DOLs nas duas estações, porém atingindo maiores altitudes durante o período seco. A composição de precipitação indicou que os DOLs são responsáveis por um acréscimo de 16% (4%) durante a estação úmida (seca). As características típicas dessas ondas foram: período médio de 8 (73) dias, comprimento de onda de aproximadamente 4500 (5500) km e velocidade de fase da ordem de 6,5 (0,9) m.s-1, para o período úmido (seco). O modelo WRF simulou os padrões sinóticos, a precipitação e as características típicas associadas aos DOLs de forma coerente, sendo comparado aos resultados do Climate Forecast System Reanalysis (CFSR), porém com maior intensidade, para os eventos de 11 e 17 de junho de 2006. / A 21-year climatology of Easterly Wave Disturbances (EWDs) over NEB region was constructed in order to obtain a better understanding of dynamic and synoptic processes life cycle of these systems, including genesis, growth / decay, trajectory and dissipation. Moreover, we evaluated the efficiency of WRF mesoscale model to simulate this type of system. The identification of EWDs was obtained subjectively through satellite images in infrared channel and fields of streamlines and relative vorticity at the levels 1000, 850, 700, 500 and 200 hPa from ERA-Interim reanalysis. During this period, 518 EWDs were identified, where 97% (3%) of these waves hit (not hit) the NEB region, 64% (36%) were convective (non-convective) and 14% (86%) reached the Amazon region. The main systems that gave rise to DOLs were: Intertropical Convergence Zone (ITCZ), Upper-Tropospheric Cyclonic Vortices (UTCV), Cold Fronts (FF) and convective clusters from the west coast of Africa (AF). In addition, the interaction between systems AF/FF, AF/ITCZ, AF/UTCV and ITCZ/FF were associated with their formation. On average, we observed approximately 25 waves per year, with maximum (minimum) frequency between the months of March to August (September to February) and, with pronounced interannual variability. The life cycle of EWDs was evaluated objectively using an automatic method for the identification and tracking (TracKH). From the 518 events identified in the subjective analysis, TracKH was able to capture 342 waves (~ 66%). From this detection, an analysis was made at 850 hPa level to determine the characteristics of their life cycle, which shows a prominent peak around of 35°W-15°W and 20°S-5°N associated with density genesis. The trajectory and dissipation have concentrated over east coast of the NEB, between the states of Alagoas and Rio Grande do Norte, but the dissipation decreased once the systems enter the continent. The synoptic patterns associated with EWDs were analyzed by composing anomaly during the period of maximum (wet) and minimum (dry) frequency from 3 days before until one day after the EWDs reaching the NEB coast. During the wet period, the circulation presented cyclonic and confluent anomaly, negative vorticity and convergence at all levels except at 200 hPa which only showed a trough characteristic while for the dry season, this feature was only observed at low levels. Negative anomalies of vertical movements and temperature and positive humidity associated with EWDs were observed in both seasons, but reaching higher elevations during the dry period. The precipitation composition indicated that the EWDs are responsible for an increase of 16% (4%) during the wet season (dry). Typical characteristics of these waves were: mean period of 8 (73) days, wavelength of about 4500 (5500) km and phase velocity of about 6.5 (0.9) m.s-1 for the wet period (dry). The WRF model simulated the synoptic patterns, precipitation and the typical features associated with EWDs in a coherently manner when compared to the results of the Climate Forecast System Reanalysis (CFSR), but with greater intensity to the events of 11 and 17 June 2006.

It has been proposed that the Asian-Australasian monsoon system is influenced by large-scale sea-surface temperature (SST) variability in the three tropical oceans although how this influence is manifested has remained a largely open question. Closure of this issue is important because it is needed to explain trends in monsoon precipitation and circulation that have occurred in the last 30 years. Using an atmospheric general circulation model, we run a series of experiments with different configurations of global SST relating to various epochs occurring during the last century to evaluate their influence on the monsoon. Comparisons of circulation fields show that a colder SST configuration generates a weaker large-scale monsoonal circulation. On the other hand, warmer SST states generate stronger large scale circulations with more vigorous centers of divergence and convergence. Warmer SST configurations are associated with positive anomalies of precipitation in the eastern Bay of Bengal, Eastern Indian Ocean and South East Asia. Cooler SST configurations are associated with negative anomalies of precipitation in the Arabian Sea and Indian peninsula, especially at the beginning of the summer. Since SST gradients determine, to a large degree, the low level flow, they are also going to influence the transport of atmospheric moisture. Comparison of vertically integrated moisture transport fields between the different experiments show that cold SST configuration favors an increased inter-hemispheric flow of moisture but decreases in the westerly moisture flow in to the Bay of Bengal and India. Warm SST configurations, on the other hand, strengthens westerly flow into the eastern Indian Ocean. An increasing availability of moisture in a region of stronger convergence constitutes a favorable environment for the production of monsoonal precipitation. African easterly waves (AEW) constitute an important component of the African and tropical Atlantic Ocean climate during the boreal summer. An understanding of this component is essential since AEW are closely related with tropical Atlantic storm activity. We adopt an idealized modeling approach using the WRF model initialized with ERA-40 reanalysis data to study the mechanisms that trigger the formation and maintenance of AEW. The model domain includes the African continent, central and eastern Atlantic Ocean and the western Indian Ocean. Experiments are designed to test the relative importance of the thermal effect of the eastern African topography and the influence of the cross-equatorial pressure gradient, induced by the sea surface temperature (SST) on the origins and maintenance of AEW. Topography and SST variation are selectively added and removed. The control experiment shows that the model reproduces many of the mean features observed during the boreal summer. Westward propagating disturbances of 3-8 day period that originate between 30 and 40E at the surface levels and in the mid troposphere are well depicted. In addition, the model provides a reasonable representation of the AEJ. When all topographic features are removed, there is a weakening of the AEJ over land and ocean, however, longitude-time sections of meridional velocity still exhibit westward propagating disturbances that reach the western African coast at the surface and at the jet level with the same 3-8 day period. Spectral analysis of meridional velocity show that the variability associated with AEWs is reduced over East Africa and West Africa at 850-hPa and is reduced west of 20E along the southern flank of the jet and over northern Africa at the jet level. Maximum amplitude of the disturbances occurs right at the coast. The spatial distribution of barotropic and baroclinic energy conversions explains the reduction in AEWs over land and the intensification of these features at the coast. When the zonal SST gradient is removed, a weaker AEJ displaces southward and a weaker monsoon flow ensues. Spectral analysis of meridional velocity displays a variance reduction in the 3-8 day band at the 850-hP a level in western and eastern Africa and at the coast. At the 650-hPa level significant changes are not observed at the latitude of the AEJ (15N), however, a decrease in the variance associated with AEW occurs at the southern flank of the jet. A southward displacement of the jet favors a weakening of the baroclinic energy conversions. Barotropic conversions also appear to be weaker when the SST gradient is removed. The present study suggests that orography plays an important role in determining the variability of meridional wind associated with AEW over Eastern Africa at the lower levels. Further, zonal SST gradients over the Atlantic favor intensification of waves when they reach the coast and the maintenance of disturbances across the Ocean. Also, results could suggest that SST gradients support genesis of AEW just off the coast of Africa.

Earth's radiation budget is directly influenced by aerosols through the absorption of solar radiation and subsequent heating of the atmosphere. Aerosols modulate the hydrological cycle indirectly by modifying cloud properties, precipitation and ocean heat storage. In addition, polluting aerosols impose health risks in local, regional and global scales. In spite of recent advances in the study of aerosols variability, uncertainty in their spatial and temporal distributions still presents a challenge in the understanding of climate variability. For example, aerosol loading varies not only from year to year but also on higher frequency intraseasonal time scales producing strong variability on local and regional scales. An assessment of the impact of aerosol variability requires long period measurements of aerosols at both regional and global scales. The present dissertation compiles a large database of remotely sensed aerosol loading in order to analyze its spatio-temporal variability, and how this load interacts with different variables that characterize the dynamic and thermodynamic states of the environment. Aerosol Index (AI) and Aerosol Optical Depth (AOD) were used as measures of the atmospheric aerosol load. In addition, atmospheric and oceanic satellite observations, and reanalysis datasets is used in the analysis to investigate aerosol-environment interactions. A diagnostic study is conducted to produce global and regional aerosol satellite climatologies, and to analyze and compare the validity of aerosol retrievals. We find similarities and differences between the aerosol distributions over various regions of the globe when comparing the different satellite retrievals. A nonparametric approach is also used to examine the spatial distribution of the recent trends in aerosol concentration. A significant positive trend was found over the Middle East, Arabian Sea and South Asian regions strongly influenced by increases in dust events. Spectral and composite analyses of surface temperature, atmospheric wind, geopotential height, outgoing longwave radiation, water vapor and precipitation together with the climatology of aerosols provide insight on how the variables interact. Different modes of variability, especially in intraseasonal time scales appear as strong modulators of the aerosol distribution. In particular, we investigate how two modes of variability related to the westward propagating synoptic African Easterly Waves of the Tropical Atlantic Ocean affect the horizontal and vertical structure of the environment. The statistical significance of these two modes is tested with the use of two different spectral techniques. The pattern of propagation of aerosol load shows good correspondence with the progression of the atmospheric and oceanic synoptic conditions suitable for dust mobilization over the Atlantic Ocean. We present extensions to previous studies related with dust variability over the Atlantic region by evaluating the performance of the long period satellite aerosol retrievals in determining modes of aerosol variability. Results of the covariability between aerosols-environment motivate the use of statistical regression models to test the significance of the forecasting skill of daily AOD time series. The regression models are calibrated using atmospheric variables as predictors from the reanalysis variables. The results show poor forecasting skill with significant error growing after the 3rd day of the prediction. It is hypothesized that the simplicity of linear models results in an inability to provide a useful forecast.

The spatial and temporal complexity of tropical cyclones (TCs) raises a number of scientific questions regarding their genesis, movement, intensification, and variability. In this dissertation, the principal goal is to determine the current state of predictability for each of these processes. To quantify the current extent of tropical cyclone predictability, we assess probabilistic forecasts from the most advanced global numerical weather prediction system to date, the ECMWF Variable Resolution Ensemble Prediction System (VarEPS). Using a new false alarm clustering technique to maximize the utility of the VarEPS, the ensemble system is shown to provide well-calibrated probabilistic forecasts for TC genesis through a lead-time of one week, and pregenesis track forecasts with similar skill compared to the VarEPS's postgenesis track forecasts. To quantify the predictability of TCs on intraseasonal time scales, forecasts from the ECMWF Monthly Forecast System (ECMFS) are examined for the North Atlantic Ocean. From this assessment, dynamically based forecasts from the ECMFS provide forecast skill exceeding climatology out to weeks three and four for portions of the southern Gulf of Mexico, western Caribbean and the Main Development Region. Forecast skill in these regions is traced to the model's ability to capture correctly the variability in deep-layer vertical wind shear, the relative frequency of easterly waves moving through these regions, and the intraseasonal modulation of the Madden-Julian Oscillation. On interannual time scales, the predictability of TCs is examined by considering their relationship with tropical Atlantic easterly waves. First, a set of easterly wave climatologies for the CFS-R, ERA-Interim, ERA-40, and NCEP/NCAR Reanalysis are developed using a new easterly wave-tracking algorithm. From the reanalysis-derived climatologies, a moderately positive and statistically significant relationship is seen with tropical Atlantic TCs. In relation to large-scale climate modes, the Atlantic Multidecadal Oscillation (AMO) and Atlantic Meridional Mode (AMM) exhibit the strongest positive covariability with Atlantic easterly wave frequency. Besides changes in the number of easterly waves, the intensification efficiency of easterly waves has also been evaluated. These findings offer a plausible physical explanation for the recent increase in the number of NATL TCs, as it has been concomitant with an increasing trend in both the number of tropical Atlantic easterly waves and intensification efficiency. The last component of this dissertation examines how the historical variability in U.S. landfalling TCs has impacted the annual TC tornado record. To reconcile the inhomogeneous, historical tornado record, two statistical tornado models, developed from a set of a priori predictors for TC tornado formation, are used to reconstruct the TC tornado climatology. While the synthetic TC tornado record reflects decadal scale variations in association with the AMO, a comparison of the current warm phase of the AMO with the previous warm phase period shows that the median number of tornadoes per Gulf TC landfall has significantly increased. This change likely reflects the increase in median TC size (by 35%) of Gulf landfalling TCs along with an increased frequency of large TCs at landfall.

We examine the eastern Pacific Ocean Intertropical Convergence Zone (ITCZ) both in its mean state and transient phases using a combined diagnostic, theoretical and numerical modeling approach. We note that the ITCZ is perpetually in a transient state with strong variability occurring on 4-8 day time scales. Transients, about half the amplitude of the mean ITCZ, propagate northwards from the near-equatorial southern hemisphere eventually increasing the convection in the vicinity of the mean ITCZ convection. It is argued that the mean ITCZ is continually inertially unstable with incursions of anticyclonic vorticity advected across the equator resulting in the creation of a divergence-convergence doublet. The low-level convergence generates convection and vortex tube stretching which generates cyclonic vorticity counteracting the northward advection of anticyclonic vorticity. During a cycle, the heating in the mid-troposphere near 10°N oscillated between 6 and 12 K/day at the inertial frequency of the latitude of the mean convection. The shallow meridional circulation, noted in the mean field in other studies, appears to be a result of the transient nature of the ITCZ. It is hypothesized that westward propagating equatorial waves result from the inertial oscillation of the ITCZ. To test that the waves are formed in situ in the eastern Pacific and not remnants of waves propagating from the Atlantic or promoted by the Central and South American orography, several numerical experiments are undertaken using a high-resolution regional model spanning the western Atlantic Ocean and the eastern Pacific. In the control case, the model is initialized at all boundaries with full high-frequency observations. In two additional experiments, these transients are filtered out, and a third experiment is run with the topography over a large part of Central and South America removed. In all experiments, westward propagating waves are formed in the region of high CEPG suggesting that the hypothesis of in situ development may be correct.

Uma climatologia de 21 anos dos Distúrbios Ondulatórios de Leste (DOLs) sobre a região NEB foi realizada com o intuito de obter um melhor entendimento dos processos dinâmicos e sinóticos do ciclo de vida destes sistemas, incluindo gênese, crescimento/decaimento, trajetória e dissipação. Adicionalmente, foi avaliada a eficiência do modelo de mesoescala WRF em simular este tipo de sistema. A identificação dos DOLs foi obtida de forma subjetiva através de imagens de satélite no canal infravermelho e campos de linhas de corrente e vorticidade relativa nos níveis de 1000, 850, 700, 500 e 200 hPa da reanálise do ERA-Interim. Neste período foram identificados 518 eventos de DOLs, onde 97% (3%) dessas ondas atingiram (não atingiram) a região do NEB, 64% (36%) foram convectivas (não convectivas) e 14% (86%) atingiram a região da Amazônia. Os principais sistemas que deram origem aos DOLs foram: Zona de Convergência Intertropical (ZCIT), Vórtice Ciclônico de Altos Níveis (VCAN), Frentes Frias (FF) e conglomerados convectivos provenientes da costa oeste da África (AF). Além destes, a interação entre os sistemas AF/FF, AF/ZCIT, AF/VCAN e ZCIT/FF estiveram associadas a sua formação. Em média, foram observadas aproximadamente 25 ondas por ano, com máxima (mínima) frequência compreendida entre os meses de Março a Agosto (Setembro a Fevereiro) e, com pronunciada variabilidade interanual. O ciclo de vida dos DOLs foi avaliado de forma objetiva a partir de um método automático de identificação e rastreio (TracKH), onde dos 518 eventos identificados na análise subjetiva, conseguiu capturar 342 ondas ( ~ 66%). A partir desta detecção, uma análise foi feita no nível 850 hPa para determinar as características típicas do seu ciclo de vida, que mostra um pico proeminente entre as longitudes de 35°W e 15°W e latitudes de 20°S e 5°N associado a densidade de gênese. A trajetória e dissipação se concentraram sobre a costa leste do NEB, entre os estados de Alagoas e Rio Grande do Norte, porém a dissipação diminuía a medida que adentrava ao continente. Os padrões sinóticos associados aos DOLs foram analisados através da anomalia de composição durante o período de máxima (úmido) e mínima (seco) frequência desde 3 dias antes até um dia após os DOLs atingirem a costa do NEB. Durante o período úmido, a circulação associada aos DOLs apresentou anomalia ciclônica e confluente, vorticidade negativa e convergência até médios níveis, enquanto que em 200 hPa apresentou apenas a característica do cavado. Por outro lado, para o período seco, estas características foram observadas somente em baixos níveis. Anomalias negativas de movimentos verticais e temperatura e positivas de umidade foram observadas associadas aos DOLs nas duas estações, porém atingindo maiores altitudes durante o período seco. A composição de precipitação indicou que os DOLs são responsáveis por um acréscimo de 16% (4%) durante a estação úmida (seca). As características típicas dessas ondas foram: período médio de 8 (73) dias, comprimento de onda de aproximadamente 4500 (5500) km e velocidade de fase da ordem de 6,5 (0,9) m.s-1, para o período úmido (seco). O modelo WRF simulou os padrões sinóticos, a precipitação e as características típicas associadas aos DOLs de forma coerente, sendo comparado aos resultados do Climate Forecast System Reanalysis (CFSR), porém com maior intensidade, para os eventos de 11 e 17 de junho de 2006. / A 21-year climatology of Easterly Wave Disturbances (EWDs) over NEB region was constructed in order to obtain a better understanding of dynamic and synoptic processes life cycle of these systems, including genesis, growth / decay, trajectory and dissipation. Moreover, we evaluated the efficiency of WRF mesoscale model to simulate this type of system. The identification of EWDs was obtained subjectively through satellite images in infrared channel and fields of streamlines and relative vorticity at the levels 1000, 850, 700, 500 and 200 hPa from ERA-Interim reanalysis. During this period, 518 EWDs were identified, where 97% (3%) of these waves hit (not hit) the NEB region, 64% (36%) were convective (non-convective) and 14% (86%) reached the Amazon region. The main systems that gave rise to DOLs were: Intertropical Convergence Zone (ITCZ), Upper-Tropospheric Cyclonic Vortices (UTCV), Cold Fronts (FF) and convective clusters from the west coast of Africa (AF). In addition, the interaction between systems AF/FF, AF/ITCZ, AF/UTCV and ITCZ/FF were associated with their formation. On average, we observed approximately 25 waves per year, with maximum (minimum) frequency between the months of March to August (September to February) and, with pronounced interannual variability. The life cycle of EWDs was evaluated objectively using an automatic method for the identification and tracking (TracKH). From the 518 events identified in the subjective analysis, TracKH was able to capture 342 waves (~ 66%). From this detection, an analysis was made at 850 hPa level to determine the characteristics of their life cycle, which shows a prominent peak around of 35°W-15°W and 20°S-5°N associated with density genesis. The trajectory and dissipation have concentrated over east coast of the NEB, between the states of Alagoas and Rio Grande do Norte, but the dissipation decreased once the systems enter the continent. The synoptic patterns associated with EWDs were analyzed by composing anomaly during the period of maximum (wet) and minimum (dry) frequency from 3 days before until one day after the EWDs reaching the NEB coast. During the wet period, the circulation presented cyclonic and confluent anomaly, negative vorticity and convergence at all levels except at 200 hPa which only showed a trough characteristic while for the dry season, this feature was only observed at low levels. Negative anomalies of vertical movements and temperature and positive humidity associated with EWDs were observed in both seasons, but reaching higher elevations during the dry period. The precipitation composition indicated that the EWDs are responsible for an increase of 16% (4%) during the wet season (dry). Typical characteristics of these waves were: mean period of 8 (73) days, wavelength of about 4500 (5500) km and phase velocity of about 6.5 (0.9) m.s-1 for the wet period (dry). The WRF model simulated the synoptic patterns, precipitation and the typical features associated with EWDs in a coherently manner when compared to the results of the Climate Forecast System Reanalysis (CFSR), but with greater intensity to the events of 11 and 17 June 2006.