Alexandre Araújo Costa

SST Sensitivities in Multiday TOGA COARE Cloud-Resolving Simulations

A two-dimensional cloud-resolving model (CRM) was used to simulate the evolution of convection over the western Pacific between 19 and 26 December 1992, during the Tropical Ocean Global Atmosphere Coupled Ocean‐Atmosphere Response Experiment. A control simulation (CONTROL) was performed in which observed, time-evolving, spatially homogeneous SSTs were used as a lower boundary condition. It showed that the CRM was able to properly represent the evolution of the cloud systems. Sensitivity experiments were carried out, in which the sea surface temperature was increased (SST1 )o r decreased (SST2 )b y 18C and the same evolving large-scale forcing used in CONTROL. The similarities among all simulations suggested that the large-scale forcing is the dominant mechanism controlling the statistics of the cloud systems, including the total precipitation. However, the convective‐stratiform partition of the cloud systems was altered, the convective part being favored in SST1 and the stratiform part favored in SST2. In terms of the radiative budget, the reduced low-level cloud coverage in SST1 acted to compensate the enhancement of high-cloud coverage produced by more vigorous convection (the opposite occurred in SST2). As a consequence, the surface downward radiation was approximately the same in CONTROL, SST1, and SST2.

Modelagem numérica em alta resolução para previsão de geração de energia eólica no Ceará

Neste trabalho, foi utilizado um modelo de atmosfera de mesoescala para previsao de ventos em curto prazo para aplicacoes em geracao de energia eolica. Diferentes resolucoes espaciais e parametrizacoes foram testadas, sendo a comparacao entre as simulacoes feita com base em uma metodologia estatistica, que se utiliza de um conjunto de indices e medidas de erro amplamente utilizados em estudos meteorologicos e avaliacoes de modelos atmosfericos. Tal metodologia foi aplicada para escolha das melhores opcoes de espacamento de grade horizontal, parametrizacao de turbulencia e peso do relaxamento newtoniano na representacao dos campos de vento do litoral cearense em quatro dias do periodo de transicao entre as estacoes seca e chuvosa. Os testes revelam que, dentre as opcoes testadas, a configuracao que melhor reproduz as observacoes ao longo do litoral, conta com espacamento de grade horizontal de 1 km, turbulencia parametrizada com a versao anisotropica do esquema proposto por Smagorinsky e escala de tempo do relaxamento newtoniano de 12 h.

Moist convection in Amazonia: implications for numerical modelling

A review of the literature on convection in Amazonia, with a focus on it parameterization in numerical models, is presented here. Studies based on observational data obtained during field campaigns are examined. The basic characteristics of deep convection in the Amazon, its temporal and geographical variability are discussed focusing of the difficulties convective parameterizations have in capturing this variability, particularly the diurnal cycle. The role of thermodynamic variables such as CAPE and CIN are argued to be critical in understanding the deficiencies in properly representing the diurnal cycle of convection. Other elements of the model physics relevant to convective parameterization, particularly those related to surface energy fluxes and development of the boundary layer are also considered. The interaction of shallow convection with radiation is presented. Superparameterization, as a tool for explicitly representing convection is reviewed as it is a possible future direction for the simulation of convective effects in numerical models. To conclude, various suggestions are made for future studies in order to better our understanding of convective processes and their parameterizations.

Coupled Ocean-Cloud-Resolving Simulations of the Air–Sea Interaction over the Equatorial Western Pacific

Abstract A cloud-resolving model coupled to an ocean model with high vertical resolution is used to investigate air–sea interactions in 10-day long simulations. Modeled fields showed good agreement with two different convective regimes during the Tropical Ocean Global Atmosphere Coupled Ocean–Atmosphere Research Experiment (TOGA COARE) Intensive Observing Period. The model simulates the formation of precipitation-produced, stable freshwater lenses at the top of the ocean mixed layer, with a variety of horizontal dimensions and lifetimes. The simulated fresh anomalies show realistic features, such as a positive correlation between salinity and temperature, the development of a surface jet in the direction of the wind, and, as a consequence, downwelling (upwelling) on its downwind (upwind) edge. The dataset generated by the coupled model is used to evaluate the contribution from several factors (ocean currents, gustiness, and correlations between wind speed and air temperature, wind speed and water vapor mi...

Um estudo inter-comparativo de previsão sazonal estatística-dinâmica de precipitação no nordeste do Brasil

Despite significant advances of the dynamic atmosphere models over the last decades of the 20th century, the empirical atmospheric models have been widely used due mostly to both its general applicability and its little dependence on the computational resources. This study is show comparison of precipitation simulation to Northeast Brazil (NEB) - 1971-2000 from large scale dynamical modeling and regional model (downscaling) and the forecast of empirical modeling (K-nearest-neighbor (k-NN). Were user the general circulation model ECHAM4.5 together two regional models, the Regional Spectral Model (RSM/97) from the National Centers for Atmospheric Prediction-NCEP and the Regional Atmospheric Model System (RAMS) developed at Colorado State University. The regional models were nested in ECHAM4.5, forced with the observed Sea Surface Temperature as a boundary condition, for the period from February to May. The results show that the empirical model presented a smaller absolute error than the dynamic models for the periods February to April (FMA) and March to May (MAM) in isolated areas of the north of Maranhao and Piaui states, west and south of Ceara, center-south of Piaui and west and northeast of Bahia state. Regarding model biases, ECHAM4.5 and the RSM/97 produced, to a large extent, a humid bias over large areas of NEB, however with an average precipitation for the northern sector of NEB (2oS-12oS and 45oW-37oW) close to the observations. RAMS and the analog method had a dominance of a dry bias over NEB, with precipitation totals below the observed values. The model skills (using the Heidke score) were evaluated for three categories Dry (S), Normal (N), Rainy (C), showed that the analogous method has low skills, between 0,1 and 0,3 in all categories, while dynamic models presented superior skills, with larger values for categories S and C (of the order of 0,4 the 0,5), exceeding 0,6 in some areas of the northern sector of NEB for category C as seen in the models ECHAM4.5 and RSM/97 models.

Verificação das previsões de tempo para precipitação usando ensemble regional para o estado do Ceará em 2009

Este artigo apresenta um estudo de verificacao das previsoes de chuva de um sistema de previsao do tempo por ensemble regional. O conjunto e composto por seis membros, dos quais quatro utilizam o modelo RAMS 6.0 e dois usam o WRF 3.1, inicializados com dados dos modelos globais do CPTEC ou GFS e diferentes parametrizacoes de conveccao. A verificacao foca nas previsoes de chuva de 24, 48 e 72 horas e nos limiares de precipitacao de 1mm, 5mm e 10mm sobre o Estado do Ceara. Os membros do ensemble apresentaram resultados superiores a persistencia em todo o dominio avaliado. O modelo RAMS apresenta maior indice de acerto, principalmente no litoral norte do Estado, porem um maior falso alarme em comparacao com o modelo WRF. O sistema de previsao de chuva diminui sua qualidade com o aumento dos horizontes e a intensidade da chuva que se quer prever.

Estimation of solar radiation by mesoscale atmospheric modeling applied to the northeast Brazil region

A utilizacao de fontes alternativas de energias, como a solar, a eolica e a biomassa, vem crescendo significativamente nos ultimos anos, sendo a energia solar, em particular, uma fonte abundante na regiao Nordeste do Brasil. O conhecimento preciso da radiacao solar incidente e, assim, de grande importância para o planejamento energetico brasileiro, servindo de base para o desenvolvimento de futuros projetos de plantas fotovoltaicas e de aproveitamento da energia solar. Este trabalho apresenta uma metodologia para o mapeamento da energia solar incidente ao nivel do solo para a regiao Nordeste do Brasil, utilizando um modelo atmosferico de mesoescala (Regional Atmospheric Modeling System - RAMS), validado e ajustado por meio dos dados medidos pela rede de plataformas de coleta de dados (PCDs) da Fundacao Cearense de Meteorologia e Recursos Hidricos (FUNCEME). Os resultados mostraram que o modelo apresenta erros sistematicos, sobreestimando a radiacao na superficie, porem apos as devidas correcoes estatisticas, utilizando-se uma relacao entre a fracao de cobertura de nuvens prevista pelo modelo e a radiacao observada na superficie e estimada no topo da atmosfera, encontram-se correlacoes de 0,92 com intervalos de confianca de 13,5 W/m2 para dados com base mensal. Usando essa metodologia, a estimativa do valor medio anual (apos ajustes) da radiacao solar incidente no estado do Ceara e de 215 W/m2 (maximo em outubro: 260 W/m2).

MODELAGEM CLIMÁTICA REGIONAL (DOWNSCALING) E APLICAÇÕES EM ENERGIA EÓLICA: VARIABILIDADE E MUDANÇAS CLIMÁTICAS

Atualmente, os modelos atmosfericos de circulacao geral (AGCMs) apresentam uma resolucao espacial entre 100 e 200 km para previsoes climaticas sazonais (e, eventualmente mais grosseira ainda quando se trata de estudos de mudancas climaticas). Para tomada de decisao ao nivel regional/local, pelo estado ou pela sociedade civil, no entanto, ha uma demanda por uma maior resolucao nas previsoes e cenarios, ja que a variabilidade espacial e temporal da precipitacao associada com processos fisicos nao resolvidos em AGCMs (circulacoes atmosfericas de mesoescala) pode afetar de forma significativa determinada atividade economica. O setor de energias renovaveis, especialmente a energia eolica, cujo crescimento sobre o norte do Nordeste Brasileiro (NEB), especialmente sobre o Ceara, tem sido acentuado, tambem requer informacao de alta resolucao espacial para planejamento de suas acoes na escala da variabilidade climatica sazonal, bem como para avaliacao dos potenciais impactos das mudancas climaticas antropogenicas sobre a disponibilidade dos recursos energeticos renovaveis na regiao.