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Doctoral Thesis
DOI
10.11606/T.14.2019.tde-24052018-115441
Document
Author
Full name
Meiry Sayuri Sakamoto
E-mail
Institute/School/College
Knowledge Area
Date of Defense
Published
São Paulo, 2009
Supervisor
Committee
Ambrizzi, Tercio (President)
Gan, Manoel Alonso
Herdies, Dirceu Luís
Pereira Filho, Augusto Jose
Salio, Paola Veronica
Title in Portuguese
Sistemas convectivos de mesoescala observados na Região Subtropical da América do Sul durante o SALLJEX
Keywords in Portuguese
SALLJEX
sistemas convectivos de mesoescala
Abstract in Portuguese
Neste estudo sao analisados os sistemas convectivos de mesoescala (SCMs) subtropicais, de origem continental e oceanica, observados na America do Sul durante o South American Low Level Experiment (SALLJEX), realizado no verao de 2002/2003. Nesta analise sao avaliadas a distribuicao espacial, variabilidade diurna, ciclo de vida, deslocamento e parametros morfologicos dos SCMs continentais e oceanicos, sendo tambem investigadas as origens das fontes de umidade que contribuem para a genese desses sistemas. Outros aspectos explorados sao a caracterizacao das condicoes sinoticas com atencao a identificacao dos fatores pre-condicionantes e mecanismos de gatilho a conveccao; a avaliacao das condicoes dinamicas e termodinamicas observadas durante a genese do sistema convectivo e sua evolucao ao longo do ciclo de vida. Alem disso, sao realizadas simulacoes numericas dos SCMs com enfoque na verificacao da qualidade da previsao de precipitacao em funcao da capacidade do modelo em reproduzir as condicoes atmosfericas essenciais a geracao da conveccao. Os resultados mostram que os sistemas convectivos continentais sao mais numerosos que os oceanicos, e em ambas as regioes, SCMs com maior duracao apresentam taxas de expansao maiores nas primeiras horas do seu ciclo de vida. O jato de baixos niveis (JBN) afeta a formacao de sistemas continentais, porem, seu efeito sobre os SCMs oceanicos e minimo. O oceano Atlantico tropical, a regiao Amazonica e o oceano Pacifico subtropical, sao as principais regioes de origem da umidade para a genese dos sistemas convectivos, contudo, a atuacao dessas fontes depende da regiao de formacao do sistema e das condicoes sinoticas. O aquecimento diurno da camada limite convectiva, o jato de baixos niveis, o cavado em 500 hPa e a circulacao transversa sao os pre-condicionantes identificados na formacao dos SCMs continentais noturnos. Em relacao aos mecanismos de gatilho, os principais fatores sao os sistemas frontais e o fluxo catabatico dos Andes. Sistemas convectivos que apresentam ciclo de vida mais longo sao gerados em um ambiente em que se identificam mais de um fator pre-condicionante e de gatilho atuando de forma conjunta. Alem disso, o cisalhamento vertical do vento em baixos niveis parece ser um dos diferenciais na fase inicial dos SCMs de maior duracao. Os resultados das simulacoes numericas sugerem que quando as caracteristicas sinoticas e de mesoescala que atuam como pre-condicionantes ou mecanismos de gatilho sao mais bem definidas, o desempenho do modelo melhora sensivelmente, pois a simulacao consegue reproduzir com mais precisao as condicoes ambientais observadas durante a genese do sistema convectivo. Assim, sistemas com maior duracao tendem a ser mais bem simulados.
Title in English
Mesoscale convective systems observed in subtropics of South America during SALLJEX
Keywords in English
mesoscale convective systems
SALLJEX
Abstract in English
In this study, we analyze continental and oceanic mesoscale convective systems (MCS's) observed in the subtropics of South America during the South American Low Level Experiment (SALLJEX), held in the summer of 2002/2003. This analysis evaluated the spatial distribution, diurnal variability, life cycle, displacement and morphological parameters of the continental and oceanic MCSs, and also investigated the origins of moisture sources that contribute to these systems genesis. Other issues considered are the characterization of the synoptic conditions and the identification of preconditioning and trigger mechanisms, and evaluation of dynamic and thermodynamic conditions observed during the convective system genesis and its evolution over the life cycle. Moreover, MCSs numerical simulations are made focused on the model capability to replicate the essential atmospheric conditions to the convection generation. The results show that the continental convective systems are more numerous than the oceanic ones, and in both regions, MCS's with longer duration have higher growth rates in the early hours of their life cycle. The low level jet (LLJ) affects the formation of the continental systems, but its effect on oceanic MCS's is minimal. The tropical Atlantic Ocean, the Amazon region and the subtropical Pacific Ocean, are the main moisture source to the genesis of convective systems, however, the incidence of these sources depends on the convective system genesis area and the synoptic conditions. The daytime heating of convective boundary layer, the low level jet, the trough at 500 hPa and transverse circulation are the preconditioning processes identified in the formation of nocturnal MCS's with continental origin. For trigger mechanisms, the main factors are the frontal systems and the katabatic flow from the Andes Mountain. Convective systems with longer life cycles are generated in an environment in which several preconditioning and trigger mechanisms act jointly. Moreover, the vertical wind shear at low levels appears to be one of the differences in the initial phase of long living MCSs. The results of numerical simulations suggest that when the characteristics of synoptic and mesoscale that act as pre-conditions or triggering mechanisms are better defined, the model's performance improves significantly, because the simulation can more accurately reproduce the environmental conditions observed during the genesis of the convective system. Thus, systems with longer duration tend to be better simulated.
 
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Publishing Date
2019-01-22
 
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