David Mendes

Avaliação do modelo regional eta utilizando as análises do CPTEC e NCEP

Os modelos numericos de tempo sao ferramentas essenciais para a previsao de curto e longo prazo, permitindo realizar a previsao com varios dias de antecedencia. O conhecimento do desempenho dos modelos e dos erros sistematicos a eles associados, e de suma importância, pois permite avaliar a capacidade dos mesmos em captar os processos fisicos da atmosfera. Com intuito de melhorar a qualidade da previsao de tempo na America do Sul, disponibilizada no Centro de Previsao de Tempo e Estudos Climaticos (CPTEC), este trabalho avaliou as previsoes de precipitacao e pressao ao nivel medio do mar para o prazo de ate 120 horas, utilizando o erro medio (EM) e a raiz do erro medio quadratico (REMQ) no periodo de dezembro de 2007 a fevereiro de 2008. O modelo utilizado foi o ETA (40 km), com duas entradas distintas de dados, as analises do Physical-space Statistical Analysis System (PSAS) (ETA-I) e do National Centers for Environmental Predictions (NCEP) (ETA-II). Os resultados mostraram, para ambas as analises, uma tendencia de superestimativa (valores positivos do erro medio) da precipitacao sobre a Regiao Norte do Brasil, principalmente para 24 horas de previsao. Em relacao a pressao ao nivel medio do mar (PNMM) foi possivel verificar claramente que o ETA-I apresenta melhores resultados em comparacao com o ETA-II, cujos valores de pressao se aproximaram bastante do observado, principalmente nas primeiras horas de integracao.

Climatology of cyclones, anticyclones and storm tracks: revision of concepts

This paper has the finality of describe climatology of extratropical cyclones, anticyclones and storm tracks for the NH and SH. There is a long history of studies on the characteristics of synoptic systems, beginning with classical work on mid-latitude cyclones. For the SH, analyses of pressure data provide extensive statistics of the climatology of synoptic systems. Interestingly, the anticyclones mean central pressure at 38oS in JJA and 44oS in DJF. SH cyclones are characterized in frequency maximum in the circumpolar trough between about 50oS and 70oS. For the NH cyclones, the principal findings of the analysis are as follows: In January the primary maxima are in the western North Atlantic, with a peak about 45o - 50oN, where there is a secondary peak, over the north-central Mediterranean; These characteristics are similar in April but with decrease in the frequency of centers; In July the frequencies are further reduced and the hemisphere maximum is over eastern Canada at 55oN; The October pattern resembles that of winter, except that the Atlantic maximum is off southeast Greenland.

Refinement of the daily precipitation simulated by the CMIP5 models over the north of the Northeast of Brazil

The ability of the Artificial Neural Network (ANN) and the Multiple Linear Regression (MLR) in reproducing the area-average observed daily precipitation during the rainy season (Feb-Mar-Apr) over the north of the Northeast of Brazil (NEB) is examined. For the present climate of Dec-Jan-Feb from 1963 to 2003 period these statistical models are developed and validated using the observed daily precipitation and simulated from the historical outputs of 4 models of the fifth phase of the Coupled Model Intercomparison Project (CMIP5). The simulations from all the models during DJF and FMA seasons show an anomalous intensification of the ITCZ and southward displacement in comparison with the climatology. Correlations of 0.54, 0.66 and 0.66 are found between the simulated daily precipitation of the CCSM4, GFDL_ESM2M and MIROC_ESM models during DJF season and the observed values during FMA season. Only the CCSM4 model displays a slightly reasonable agreement with the observations. A comparison between the statistical downscaling using the nonlinear (ANN) and linear model (MLR) to identify the one most suitable for the analysis of daily precipitation was made. The ANN technique provides more ability to predict the present climate when compared to MLR technique. Based on this result, we examined the accuracy of the ANN model in project the changes for the future climate period from 2055 to 2095 over the same study region. For instance, a comparison between the daily precipitation changes projected indirectly from the ANN during Feb-Mar-Apr with those projected directly from the CMIP5 models forced by RCP 8.5 scenario is made. The results suggest that ANN model weights the CMIP5 projections according to the each model ability in simulating the present climate (and its variability). In others, the ANN model is a potentially promising approach to use as a complementary tool to improvement of the seasonal numerical simulations.

Downscaling statistical model techniques for climate change analysis applied to the Amazon region

The Amazon is an area covered predominantly by dense tropical rainforest with relatively small inclusions of several other types of vegetation. In the last decades, scientific research has suggested a strong link between the health of the Amazon and the integrity of the global climate: tropical forests and woodlands (e.g., savannas) exchange vast amounts of water and energy with the atmosphere and are thought to be important in controlling local and regional climates. Consider the importance of the Amazon biome to the global climate changes impacts and the role of the protected area in the conservation of biodiversity and state-of-art of downscaling model techniques based on ANN Calibrate and run a downscaling model technique based on the Artificial Neural Network (ANN) that is applied to the Amazon region in order to obtain regional and local climate predicted data (e.g., precipitation). Considering the importance of the Amazon biome to the global climate changes impacts and the state-of-art of downscaling techniques for climate models, the shower of this work is presented as follows: the use of ANNs good similarity with the observation in the cities of Belem and Manaus, with correlations of approximately 88.9% and 91.3%, respectively, and spatial distribution, especially in the correction process, representing a good fit.

Estudo de caso de ciclone extratropical sobre a América do Sul: sensibilidade das análises

The trajectory and the energetic of extratropical cyclones are analyzed using the NCEP/NCAR reanalysis in comparison with the model outputs CPTEC/COLA (T126L28) with GPSAS analysis. The analysis of the energetic and path of the cyclone formed over East Argentina on 23 August 2005 showed significant differences between the reanalysis and the model, especially in its track and magnitude. The comparison of the extratropical cyclone evolution, between reanalysis and the model, showed some considerable results such as: greater difference in the central pressure intensity of the extratropical cyclones; larger differences in kinetic energy after maximum cyclone intensity and a striking difference in the extratropical cyclone position.

COMPARAÇÃO ENTRE OS MODELOS DE CMIP5 E A CLIMATOLOGIA DA PRECIPITAÇÃO SEMANAL SOBRE O BRASIL TROPICAL

Este estudo apresenta uma visao geral do desempenho dos modelos climaticos globais que participam do Projeto de Intercomparacao de Modelos Acoplados Fase 5 (CMIP5) na simulacao da variabilidade semanal da precipitacao pluvial sobre o Brasil Tropical (BrT). As medias semanais calculadas para regioes especificas de chuva do BrT foram comparadas com as simuladas por oito modelos do CMIP5. As analises mostram que os modelos geralmente sao capazes de simular o sinal do padrao semanal medio tanto do ponto de vista espacial e como temporal, porem alguns apresentam pouca sensibilidade a magnitude.