Study of the horizontal and vertical energy exchanges during SACZ episodes: influence of the resolution of the analyses and the models and the convection parameterization

The horizontal and vertical energy exchanges for a composite of seven South Atlantic Convergence Zone (SACZ) episodes were studied by expansion into three-dimensional normal mode functions (Kasahara and Puri, 1981) using the National Centers for Environmental Prediction (NCEP) analyses with T062L28, T126L28 e T170L42 resolutions. In the first part of this study (observational part), energetics analyses for the SACZ composite were performed with an emphasis on the vertical energy partition between external and internal modes and on the energy interactions within and between various horizontal oscillation modes, such as Rossby, Kelvin, Mixed Rossby-Gravity and West and East Gravity modes. In the second part (modelling experiments), the performance of the CPTEC Global Model in simulating the modal energetics for the SACZ composite was evaluated, emphasizing the influence of the model resolution and the three different deep convection parameterizations: Kuo, Relaxed Arakawa-Schubert (RAS) and Grell. A maximum share of the total energy (about 60%) was found in the 4th to 7th internal modes with equivalent depths between 100 and 600 meters, especially over the great part of the central South America and near equator including the SACZ region. As the latitude increases, the energy is distributed towards the lower order modes (n = 1 to 3) with the external modes category becoming dominant at higher latitudes. For the horizontal energy partition, the most expressive contributions were obtained for the auto-interactions of the Rossby and Kelvin modes and for Rossby-Kelvin cross interactions in all vertical modes categories. The Rossby-Kelvin cross interactions were the main process for constructive energy interferences in the SACZ region. The vertical modes interactions indicated that the percentage of total energy increases from low levels to the stratosphere with maximum positive (negative) interferences in high levels (stratosphere), in the 4th to 7th internal modes. The results from the modelling experiments showed that the model predictions using the Kuo, RAS and Grell deep convection schemes were similar with each other, and had a good agreement with the patterns obtained in the observational part. The use of different deep convection schemes did not present significant impact in the partition and interaction of energy between vertical and horizontal modes. A greater impact was obtained increasing the vertical resolution of the analyses and the model from 28 to 42 levels. A greater number of internal modes shows a relevant role in the horizontal and vertical energy exchanges, in terms of representing the observed characteristics.Pages: 1833-183

Analise do balanco de vorticidade no modelo global do CPTEC/COLA para previsao de tempo durante um episodio de ZCAS e alta da Bolivia

The large scale vorticity budget is studied during a SACZ and Bolivian High Episode for a NCEP analyses and CPTEC Global Model forecasts. It is analyzed the predominant components and interpreted the vorticity sources and sinks based on residuals. The results indicate that the vertical advection terms play an important contribuation to the residuals especially in the regions with intense convective activity. The best performance of CPTEC Global Model is obtained in the 24, 48 and 72 hours forecasts.Pages: 3655-366

Analise dos balancos de calor e umidade no modelo global do CPTEC/COLA para previsao previsao de tempo durante um episodio de ZCAS e alta da Bolivia

The large scale heat and moisture budgets are studied during a SACZ and Bolivian High Episode for a NCEP analyses and CPTEC Global Model forecasts. It is analyzed the predominant components and interpreted the heat and moisture sources and sinks based on residuals. The results indicate that the vertical advection terms play an important contribuation to the residuals specially in the regions with intense convective activity. The best performance of CPTEC Global Model is obtained in the 24, 48 and 72 hours forecasts.Pages: 3646-365

Impacto da utilização de previsões "defasadas" no sistema de previsão de tempo por conjunto do CPTEC/INPE The impact of using lagged forecasts on the CPTEC/INPE ensemble prediction system

Neste trabalho é descrita a aplicação da técnica de previsões defasadas no sistema de previsão de tempo por conjuntos do Centro de Previsão de Tempo e Estudos Climáticos (EPS-CPTEC/INPE). Os dados do CPTEC/INPE consistem em uma amostra de dois meses com previsões de 15 dias para as variáveis: altura geopotencial em 500 hPa, temperatura do ar no nível de 850 hPa, e pressão atmosférica ao nível médio do mar. O estudo consiste em investigar: 1) o desempenho do EPS-CPTEC/INPE utilizando a técnica de previsões defasadas comparado àquele do conjunto operacional; 2) a relação entre o espalhamento e o desempenho da previsão, a fim de avaliar o uso da dispersão como preditor do desempenho. Os resultados indicam que a utilização de previsões defasadas em 12h, melhora o desempenho do conjunto operacional, contribuindo para aumentar o espalhamento do conjunto e, conseqüentemente, reduzir a sub-dispersão do sistema. Também foi observado que o conjunto defasado tem desempenho comparável àquele do conjunto operacional e que há uma tendência de desempenho alto quando o espalhamento é baixo, para os prazos de 5 e 7 dias de previsão. Estes resultados servem como base para a implementação operacional desta técnica, que apresenta baixo custo computacional, e contribui para a utilização mais eficiente das previsões por conjunto do CPTEC/INPE.<br>In this work we report the application of the lagged average forecasting technique to CPTEC/INPE ensemble forecast. The CPTEC/INPE data consist of two months samples of 15 days forecast for the variables: geopotential height at 500 hPa, air temperature at 850 hPa and mean sea level atmospheric pressure. We focus on the following: 1) Does the lagged averaged ensemble forecast improve forecast skill compared to the CPTEC/INPE operational ensemble? 2) Is the dispersion of the ensemble useful in predicting forecast skill? The results indicate that the utilization of 12h-lagged average forecasts improves the performance of the operational ensemble contributing to increase the ensemble spreading and, consequently, to reduce the under-dispersion of the system. Also we observed that lagged average forecast (LAF) shows similar performance of the operational EPS-CPTEC/INPE and that there is a tendency to higher performance when spread forecast is low, for 5 and 7 day forecast. These results provide the basis for the operational implementation of the LAF technique, which has low computational cost, and contribute to a more efficient utilization of the CPTEC/INPE ensemble predictions

Estudo da energética modal para episódios de ZCAS. Parte I: análise observacional Study of the modal energetics for SACZ episodes. Part I: observational analyses

As trocas horizontais e verticais de energia para um composto de sete episódios de Zona de Convergência do Atlântico Sul (ZCAS), foram estudadas a partir da decomposição em modos normais, considerando-se a partição vertical de energia entre os modos externo e internos, e as interferências entre os modos horizontais de oscilação Rossby, Kelvin, Misto Rossby-Gravidade, Gravidade Oeste e Leste. Um máximo de porcentagem de energia total (aproximadamente 60%) é observado para os modos internos 4 a 7, com alturas equivalentes entre 100 e 600 metros, especialmente sobre grande parte da América do Sul central e próximo ao equador, incluindo a região da ZCAS. À medida que a latitude aumenta, a energia é distribuída para os modos mais externos (n=1 a 3). Para a partição horizontal de energia, as maiores contribuições foram obtidas para as auto-interações dos modos Rossby e Kelvin e interações cruzadas Rossby-Kelvin, em todas as categorias de modos verticais, sendo estas últimas responsáveis pelas interferências construtivas de energia na região da ZCAS. As interações entre modos verticais mostraram um aumento da porcentagem de energia dos Baixos Níveis para a Estratosfera, com máxima interferência positiva (negativa) de energia em Altos Níveis (Estratosfera), para os modos internos 4 a 7.<br>The horizontal and vertical energy exchanges for a composite of seven South Atlantic Convergence Zone (SACZ) episodes were studied by expansion into normal mode functions, with an emphasis on the vertical energy partition between external and internal modes and on the energy interactions within and among various horizontal oscillation modes: Rossby, Kelvin, Mixed Rossby-Gravity and West and East Gravity. A maximum share of the total energy (about 60%) was found in the 4th to 7th internal modes at equivalent highs between 100 and 600 meters, especially over large part of the central South America and near the equator including the SACZ region. As the latitude increases, the energy is distributed towards the lower order modes (n = 1 to 3). For the horizontal energy partition, the most expressive contributions were obtained for the self-interactions of the Rossby and Kelvin modes and for Rossby-Kelvin cross interactions in all vertical mode categories. The Rossby-Kelvin cross interactions constituted the main process for constructive energy interferences in the SACZ region. The vertical mode interactions indicated that the percentage of total energy increases from low levels to the stratosphere with maximum positive (negative) interferences in high levels (stratosphere), for the 4th to 7th internal modes

Estudo da energética modal para episódios de ZCAS. Parte II: impacto da resolução do modelo e da parametrização de convecção Study of the modal energetics for SACZ episodes. Part II: Impact of the model resolution and the convection parameterization

O desempenho do Modelo Global do Centro de Previsão de Tempo e Estudos Climáticos (CPTEC) em simular a energética modal para um composto de sete episódios de Zona de Convergência do Atlântico Sul (ZCAS) é avaliado, enfatizando-se a influência da resolução espacial do modelo e de três diferentes parametrizações de convecção profunda: Kuo, Relaxed Arakawa-Schubert (RAS) e Grell na partição vertical de energia entre os modos externos e internos, e as trocas de energia entre os modos horizontais de oscilação Rossby, Kelvin, Misto Rossby-Gravidade, Gravidade Oeste e Leste. Os resultados mostraram que as previsões utilizando os esquemas de convecção profunda Kuo, RAS e Grell foram semelhantes entre si e apresentaram uma boa concordância em relação aos padrões obtidos na parte observacional (Parte I deste artigo). O emprego de diferentes esquemas de convecção profunda não apresentou impactos significativos na partição e interação de energia entre os modos verticais e horizontais. Um impacto maior foi obtido com o aumento da resolução vertical das análises e do modelo, de 28 para 42 níveis, em que um maior número de modos internos apresenta um papel relevante nas trocas horizontais e verticais de energia.<br>The performance of the CPTEC Global Model in simulating the modal energetics for a composite of seven South Atlantic Convergence Zone (SACZ) episodes was evaluated, emphasizing the influence of the model resolution and the three different deep convection parameterizations: Kuo, Relaxed Arakawa-Schubert (RAS) and Grell on the vertical energy partition between external and internal modes and on the energy interactions within and between various horizontal oscillation modes: Rossby, Kelvin, Mixed Rossby-Gravity and West and East Gravity. The results showed that the model predictions using the Kuo, RAS and Grell deep convection schemes were similar with each other, and had a good agreement with the patterns obtained in the observational part (Part I of this paper). The use of different deep convection schemes did not present significant impact in the partition and interaction of energy between vertical and horizontal modes. A greater impact was obtained when increasing the vertical resolution of the analyses and the model from 28 to 42 levels. A greater number of internal modes show a relevant role in the horizontal and vertical energy exchanges, in terms of representing the observed characteristics