ANÁLISE DOS DADOS DE PRECIPITAÇÃO PROVENIENTES DE DIFERENTES FONTES SOBRE A AMÉRICA DO SUL COM ÊNFASE NO BRASIL

In this work the potentialities and limitations from different precipitation sources over South America, with emphasis on Brazil were investigated. The regional similarities and differences were analyzed between the precipitation values obtained from ANEEL (National Electrical Energy Agency), and the rain gauge series obtained from the reanalysis of NCEP/NCAR (National Centers for Environmental Prediction/ National Center for Atmospheric Research) and GPCP (Global Precipitation Climatology Project) The analysis considers the annual and seasonal averages and the correlation between the data measured (ANEEL stations) and the rain gauge series obtained from the other sources from the different country regions.RESUMO Neste trabalho foram investigadas as potencialidades e limitações de diferentes fontes de precipitação no Brasil. Foram analisadas as semelhanças e diferenças regionais entre os valores de precipitação obtidos das estações da ANEEL (Agência Nacional de Energia Elétrica), e as séries pluviométricas obtidas da reanálise do NCEP/ NCAR (National Centers for Environmental Prediction/ National Center for Atmospheric Research) e do GPCP (Global Precipitation Climatology Project). A análise levou em conta as precipitações médias anuais e sazonais e as correlações entre as séries pluviométricas de valores medidos (estações da ANEEL) e as séries pluviométricas obtidas das outras fontes nas diferentes regiões do país. Palavras-chave: Precipitação. Fontes de dados. Climatologia. América do Sul. Regiões do Brasil. Estações Pluviométricas. ABSTRACT In this work the potentialities and limitations from different precipitation sources over Brazil were investigated. The regional similarities and differences were analyzed between the precipitation values obtained from ANEEL (National Electrical Energy Agency), and the rain gauge series obtained from the reanalysis of NCEP/NCAR (National Centers for Environmental Prediction/ National Center for Atmospheric Research) and GPCP (Global Precipitation Climatology Project). The analysis considered the average annual and seasonal precipitation and the correlations between the rain gauge series measured data (ANEEL stations) and the rain gauge series obtained from the other sources in different country regions. Keywords: Precipitation. Data Sources. Climatology. South America. Regions of Brazil. Rain Gauge. RESUMEN En este trabajo se investigó el potencial y las limitaciones de diferentes fuentes de precipitación en Brasil. Se analizaron las similitudes y diferencias regionales entre los valores de precipitación obtenidos en las estaciones de ANEEL (agencia Nacional de Energía Eléctrica), y las series pluviométricas obtenidas de reanálisis de NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) y del GPCP (Global Precipitation Climatology Project). El análisis tuvo en cuenta las precipitaciones medias anuales y estacionales y las relaciones entre las series pluviométricas de valores medidos (estaciones de ANEEL) y las series pluviométricas obtenidas de otras fuentes en las diferentes regiones del país. Palabras clave: Precipitación. Fuentes de los datos. Climatología. America del Sur. Regiones de Brasil. Estaciones Pluviométricas

Decadal variation of atmosphere-ocean interaction in the tropical Atlantic and its relationship to the Northeast Brazil rainfall

The moisture budget over the Atlantic Ocean and South America is evaluated for two contrasting 5-year periods, 1985-1989 (wet) and 1990-1994 (dry), of rainfall over Northeast Brazil (NEB) using NCEP/NCAR reanalysis data. The linear correlation coefficients between the 5-year averages of rainfall over NEB and sea surface temperature (SST) anomalies over the Atlantic Ocean show a dipole configuration over the Tropical Atlantic. It is found that evaporation is higher over the Tropical North Atlantic, and lower over the Tropical South Atlantic during the 5-year period of higher rainfall over NEB. Higher evaporation causes lower SST and vice versa. This seems to be the main mechanism which generates dipole configuration in the Atlantic SST. During the rainy season (February through May) in NEB moisture is transported towards NEB and converges, providing the necessary moisture source for the rainfall. This low level convergence is associated with the rising branch of a local meridional circulation cell, which in turn is generated by the SST dipole. This series of interlinked mechanisms seems to fit in a physical picture responsible for the rainfall decadal variation over NEB.Pages: 63-7

Annual mean analysis of the tropical heat balance and associations with the Walker circulation Análise média anual do balanço de calor tropical e associações com a circulação de Walker

The present study presents an analysis of the annual mean tropical heat balance and its association with the Walker circulation (WC) using NCEP/NCAR Reanalysis data. This study shows the relative importance of diabatic data to produce vertical motion in the tropics and for the WC region. It is shown that ascending motion in the WC's upward branch is determined by the joint effect of latent heating and radiative cooling processes while infrared radiation loss is associated to sink motions on the WC's descending branch. In ascending branches of the WC vertical velocity from reanalysis is overestimated when latent heat is taken into account to drive motions. Radiative cooling is indentified as the main physical process yielding sinking motion in the WC's downward branches. In upward branches of the WC, resulting diabatic processes (latent heat release) are balanced by adiabatic expansion (due rising motions). In descending branches of the WC, there is a near balance between radiative cooling (due to longwave emission) and heating (due to sinking motions).Este estudo apresenta uma análise do balanço de calor anual médio da região tropical e sua associação com a Circulação de Walker (CW), a partir das reanálises do NCEP/NCAR. Este estudo mostra a importância relativa do aquecimento diabático para gerar movimentos verticais nos trópicos e na região de atuação da CW. Os resultados mostram que o movimento ascendente nos ramos principais da CW é governado pelo efeito conjunto dos processos de aquecimento latente e resfriamento radiativo, enquanto que a perda de radiação infravermelha produz movimento descendente nos ramos secundários da CW. Mostra-se que o aquecimento latente força movimentos ascendentes sobre os ramos principais da CW, todavia, a velocidade vertical observada é superestimada, se apenas o calor latente é levado em consideração para forçar os movimentos. Além disso, o resfriamento radiativo foi identificado como o principal processo físico que produz movimentos subsidentes nos ramos secundários da CW. Nos ramos ascendentes da CW, o aquecimento resultante entre os processos de liberação de calor latente e de resfriamento radiativo é balanceado pela expansão adiabática, enquanto que em regiões de fraca convecção (ramos secundários da CW) existe um balanço aproximado entre o resfriamento radiativo (devido a emissão de ondas longas) e o aquecimento devido à compressão associado aos movimentos descendentes

Estudos numéricos sobre a migração sazonal da zona de convergência intertropical com um modelo estatístico-dinâmico

A two-layer, global, primitive equation zonally averaged model with diurnal cycle of radiation is used for studying the seasonal variations of the Inter-Tropical Convergence Zone (ITCZ). In order to investigate the mechanism that affects the displacement of the ITCZ over different types of surfaces three numerical experiments were made, considering: a)the earth's surface covered by the actual fractions of land, ocean, ice and snow; b) the earth's surface covered only by ocean ("aqua-planet"); and c) the earth's surface covered only by land ("continental planet"). The results showed that in the case of the "aqua-planet"the seasonal variation of the ITCZ was around 15\ub0, like in the case considering the earth's surface covered by the fractions of the different types of surface; in the case of the "continental planet", the seasonal variationof the ITCZ was larger than in the other cases (around 25\ub0). It was also that in the case of the earth's surface covered by land there was a strong seasonal inversion of the wind from the winter to the summer hemisphere. In the case of the erath's surface covered by ocean the seasonal inversion of the wind was moderate. RESUMO: Um modelo estatistico-dinamico de media zonal, de duas camadas, global, de equacoes primitivas, incluindo uma representacao do ciclo diurno da radiacao solar e utilizado para o estudo das variacoes sazonais da Zona de Convergencia Intertropical (ZCIT). Para investigar os mecanismos que afetam seu deslocamento sobre diferentes tipos de superficie foram realizados tres experimentos, que consideraram a superficie do globo coberta: a)pelas fracoes reais de terra, oceano, gelo e neve; b?somente por oceano ("planeta aquatico"); e c)somente por terra ("planeta continental"). Os resultados mostraram que, no caso do "planeta aquatico", a ZCIT teve um deslocamento sazonal de 15\ub0 de latitude, como no caso de se considerar as fracoes reais dos diferentes tipos de superficie dentro dos cinturoes de latitude; no caso do "planeta continental", a ZCIT teve um deslocamento sazonal maior, cerca de 25\ub0 de latitude. Foi notado, no caso do experimento com a superficie coberta por continente, uma forte inversao sazonal do vento, do hemisferio de inverno para o verao. No caso do experimento com a superficie coberta por oceano, a inversao sazonal do vento foi moderada.Pages: 75-8

Sensitivity tests with a biosphere model based on BATS, suitable for coupling with a simple climatic model

A biosphere model based on the Biosphere Atmosphere Transfer Scheme (BATS) suitable for coupling with a simple climate model is described. In this model the equations of BATS are adapted to the energy flux formulations of the statistical-dynamical model developed by Franchito & Rao (Climatic Change, 22:1-34; 1992). In this work the land surface model was run to perfom sensitivity tests regarding the behaviour of the model variables with respect to prescribed model parameters and contrasting vegetation types, such as evergreen broadleaf forest and short grass. The results show that the soil surface temperature increases with the decrease of the fractional area of vegetation cover due to the lower surface solar radiation flux absorption in both types of vegetation. As the water interception increases the wet foliage air layer prevents the evaporation of the soil water, so that there is an increase of the ground surface temperature. The surface temperature is lower in the forest than in the case of short grass due to the surface roughness effect. In the case of dry soil the available energy increases with the increase of the fractional area of vegetation cover because the latent heat flux increases quickly and the sensible heat flux decreases slowly. In the situation of fully wet soil the available energy dependence on the interception is reduced due to the effect of water evaporation at the ground surface that increases the latent heat flux, even if the interception is small or nil. A factor z is inserted in the expression that gives the fractional area of the leaf canopy cover by water in order to take into account the effect of the part of vegetation predominantly porous. The lower values of z give better results regarding the component terms of the evapotranspiration. However, the total flux of water vapor to atmosphere does not change with z. Sensitivity tests are made with respect to the factor Y introduced in the expression of the water vapor flux to the atmosphere in order to adjust the partitioning of the available energy into latent and sensible heat. The results show that the latent (sensible) heat increases (decreases) with the increase in Y. Although the variation of Y modifies the Bowens ratio there is no change of the evapotranspiration partitioning into its components. RESUMO: Um modelo de biosfera baseado no esquema BATS (Biosphere Atmosphere Transfer Scheme) útil para ser acoplado a um modelo climático simples é descrito. Neste modelo as equações do esquema BATS são adaptadas às formulações dos fluxos de energia do modelo estatístico-dinâmico desenvolvido por Franchito & Rao (Climatic Change, 22: 1-34; 1992). Neste trabalho, o modelo de processos de superfície foi rodado para realizar testes de sensibilidade referentes ao comportamento das variáveis do modelo com respeito a parâmetros prescritos e tipos de vegetação contrastantes, tais como floresta perenifólia e gramíneas. Os resultados mostraram que a temperatura da superfície do solo aumenta com o decréscimo da fração da cobertura vegetal devido à menor absorção do fluxo de radiação solar na superfície em ambos os tipos de vegetação. \uc0 medida que a interceptação aumenta a camada de ar na folhagem úmida impede a evaporação de água no solo, de forma que há um aumento da temperatura da superfície do solo. A temperatura da superficie é menor sob a floresta perenifólia do que sob gramíneas baixas devido ao efeito da rugosidade da superfície. No caso de solo seco a energia disponível aumenta quanto maior for a fração de cobertura vegetal pois o fluxo de calor latente aumenta rapidamente enquanto que o fluxo de calor sensível reduz-se mais lentamente. Na situação de solo plenamente abastecido de água, a dependência da energia disponível em relação à interceptação diminui devido ao efeito da evaporação de água à superfície do solo, a qual aumenta o fluxo de calor latente mesmo que a interceptação é pequena ou nula. Um fator z foi inserido na expressão referente à fração da folhagem coberta pela água interceptada para levar em conta o efeito da parte da vegetação predominantemente porosa. Melhores resultados dos cálculos dos termos componentes da evapotranspiração foram obtidos com menores valores de z. Contudo, o fluxo total de vapor dágua para a atmosfera não se altera com z. Foram realizados testes de sensibilidade com respeito ao fator Y, introduzido na expressão do fluxo de vapor dágua para a atmosfera para ajustar a partição da energia disponível em calor sensível e latente. Os resultados mostraram que o fluxo de calor latente (sensível) aumenta (decresce) quanto maior for Y. Embora a variação de Y modifica a razão de Bowen, não há alteração na partição da evapotranspiração em seus termos componentes.Pages: 191-20

A parameterization of radiative fluxes suitable for use in a statistical-dynamical model

A parameterization of shortwave and longwave radiation fluxes derived from detailed radiative transfer models is included in a global primitive equation statistical-dynamical model (SDM) with two bulk atmospheric layers. The model is validated comparing the model simulations with the observed mean annual and seasonal zonally averaged climate. The results show that the simulation of the shortwave and longwave radiation fluxes matches well with the observations. The SDM variables such as surface and 500hPa temperatures, zonal winds at 250hPa and 750 hPa, vertical velocity at 500 hPa and precipitation are also in good agreement with the observations. A comparison between the results obtained with the present SDM and those with the previous version of the model indicates that the model results improved when the parameterization of the radiative fluxes based on detailed radiative transfer models are included into the SDM. The SDM is used to investigate its response to the greenhouse effect. Sensitivity experiments regarding the doubling of CO2 and the changing of the cloud amount and height an performed. In the case 2xCO(2) the model results are consistent with those obtained from GCMs, showing a warming of the climate system. An enhancement of the greenhouse effect is also noted when the cloud layer is higher. However, an increase of the cloud amount in all the latitude belts provokes an increase of the surface temperature near poles and a decrease in all the other regions. This suggests that the greenhouse effect overcomes the albedo effect in the polar latitudes and the opposite occurs in other regions. In all the experiments the changes in the surface temperature an larger near poles, mainly in the Southern Hemisphere.Pages: 23-3

Análise de textura em produtos de sensoriamento remoto aplicada a energia eólica

Renewable energy sources have been the subject of many studies, due to the increasing world interest in clean energy. The installation of a wind farm depends on several studies related to intensity and direction of the winds and morphometric aspects of land cover. One of the factors considered in wind power assessment is wind speed profile. Frictional forces, related to roughness of the surface layer, play an important role when dealing with wind speed profile. In this paper is proposed the application of the Haralick Method (HM) of texture classification to characterize the roughness over complex surface land cover. The HM was applied to digital elevation model relative to 3 different regions from São Paulo State where anemometric towers were installed. Results show that the HM is able to detect geomorphologic features related to local wind direction prevalence and that these regions have smoother textures.Pages: 1402-140

Monsoonlike circulations in a zonally averaged numerical model with topography

A primitive equation global zonally averaged general circulation model is used to study the effects of the topography on the atmospheric annual cycle. A smoothed zonally averaged topography that has a form similar to that observed was used. The control experiment showed that the model was capable of capturing the zonally averaged behavior of the annual cycle. The model is able to capture some characteristics of the monsoonlike circulation such as the seasonal wind reversal and the easterly jet in the boreal summer. Even in the absence of topography the model was able to reproduce the monsoonlike features. However, the circulation was weak and the position of its components was altered. This suggests that the topography has an important role in modifying the intensity and position of the monsoon circulation. Sensitivity tests were made in order to investigate the effects of high elevation and its steep southern slope. Two experiments were performed: 1) increasing the elevation of orography without changing the steepness of the slope, and 2) increasing both the elevation and the steepness of the slope. The results indicated that the steepness of the southern slope seems to control the monsoonlike flow in the model. The model was also capable of reproducing a monsoonlike response to changed external conditions. When the values of the earth’s orbital parameters (precession, obliquity, and eccentricity) were changed to those of 9000 yr BP, the precipitation and circulation intensified, which seems to agree with paleoclimatic evidencePages: 779-79

Characteristics of quasi-stationary waves in the Southern Hemisphere

Characteristics of quasi-stationary (QS) waves in the Southern Hemisphere are discussed using 51 years of NCEP/NCAR reanalysis data. The amplitude of QS wave 1 has two maxima in the upper atmosphere, one at 30°S and the other at 60°S. QS waves 2 and 3 have much less amplitude. Monthly variation of the amplitude of QS wave 1 shows that it is highest in October particularly in the upper troposphere and stratosphere. RESUMO: Características das ondas quase-estacionárias (QE) no Hemisfério Sul são discutidas usando 51 anos de dados da reanálise do NCEP/NCAR. A amplitude da onda QE 1 tem dois máximos na alta atmosfera, um em 30°S e o outro em 60°S. As ondas QE 2 e 3 têm muito menor amplitudes. Variação mensal da amplitude da onda QE 1 mostra que ela é maior em outubro, particularmente na alta troposfera e estratosfera.Pages: 943-94

Variability of rainfall in the east coast of the North-Eastern Brazil region

Northeast Brazil (NEB) is located in the tropics, approximately between 1°S and 18°S and 35°W and 47°W and, it has an area ofabout 1.5 million square kilometers. Different rainfall regimes are identified in NEB: in the north, the main rainy season is February through April; in the south, rains occur during the period of December through February; and the rainy season of the eastem part is May through July (Strang, 1972). Spatial variations of annual rainfall is highly variable in each region. While portions of the interior dry region receive less than 600 mm of rainfall, the east coast receives around 2000mm (Kousky and Chu, 1978). However, the east coast of NEB deserve special attention since 32% of the northem population lives in this region (Magalhães et al., 1987), having their conditions of life and economy affected by extreme climatic events (drought/flood) which have been observed in some years. There are many factors influencing rainfall variability in the east coast of NEB. The systems which mar have an effect on the rainfall in this region are the cold frontal systems (Kousky, 1979), the cold upper tropospheric cyclonic vortices (Gan, 1983), the Intertropical Convergence Zone (ITCZ) , the high pressure system in the South Atlantic (Strang, 1983), westward propagating cloud systems (Chan, 1990), and the instability lines associated with the sea breeze (Cavalcanti and Kousky, 1982). In addition, other mechanisms involve the EI Nino/Southem Oscillation phenom- enon (ENSO) and the parameter sea surface temperature (SST) in the Tropical Atlantic. The climatological features of rainfall over east of the NEB are studied. It is noted that this region has a typical regime although it is affected by the dynamical mechanisms which affect the north and south parts of NEB. The main rainy season is April through July, which explains 60% of the annual rainfall. The dry season is September through December and this season explains 10 % of the annual rainfall. A remarkable characteristic of this region is the occurrence of extreme years, where the floods are more severe than the droughts. Some of the processes responsible for the annual variation of rainfall of this region are: 1) the position and intensity of the high pressure system in the South Atlantic, as revealed by the surface wind variations over Trindade Island and Abrolhos; 2) the occurrence or absence of EI Nino, as given by the Southem Oscillation Index (Sal); and 3) SST variation over the Subtropical Atlantic. It is found that the sal does not correlate well with the interannual rainfall variation over Bastem Northeast Brazil, but intense EI Nifio years such as 1983 are in general years of drought throughout NEB including the east coast of this region. The surface wind over Trindade Island and Abrolhos correlates well with the interannual variation of rainfall over this region. This shows that the intensity and position of the Subtropical High have a controlling influence on the rainfall of this region. The high values of lagged correlation between the surface wind over these two stations and the rainfall over the Eastem NEB suggests the utility of this parameter for long range forecasting of rainfall over this region. The relationship between the SST over the Tropical Atlantic and the rainfall shows that a dipole type configuration with higher (lower) temperatures in the South (North) Atlantic is favorable for higher (lower) rainfall. Although this is qualitatively similar to that noted by Moura and Shukla (1981), the details ofthe centers of higher correlation are different