Experimentos com o modelo regional eta em diferentes configurações durante o período salljex e mecanismos de mesoescala associados ao desenvolvimento de scm / Experiments with the regional eta model in different settings during the salljex period and mesoescale mechanisms associated with MCS development

AUTOR(ES)

José Roberto Rozante

DATA DE PUBLICAÇÃO

2008

RESUMO

The rainfall regime over southern Brazil, Uruguay and northern Argentina is strongly influenced by Mesoscale Convective Complexes (MCCs) that develop during night time associated with the Low Level Jet (LLJ) to the east of Andes. As they are mesoscale systems, their predictability depends on the model resolution and ability in representing the main features associated with their development. This study aimed to find the best configuration of the regional Eta model applied to the region of frequent MCS development to the east of Andes, and to analyze the atmospheric conditions associated with the development of these systems in a high resolution model results. Three experiments were performed, considering the South American Low Level Jet Experiment (SALLJEX) period, to test some features of the model: Hydrostatic (H) vs Nonhydrostatic (NH), convection scheme (Betts-Miller-Janjic (BMJ) vs Kain Fritsch) and soil moisture (Estimated (EM) vs Climatological (CM). The best configuration (NH,KF,EM) was applied to study the atmospheric circulation and local influences associated with the MCCs development. The position and intensity of convection associated with the MCCs were related to the regions of upper and low level jets and to the available atmospheric humidity. The model was able to simulate, 72 hours in advance, the precipitation and the associated mechanisms of MCCs occurrence. The diurnal cycle and local circulation were also well represented by the model with closer values to observations in KF than in BMJ. The mountain-vale circulation to the east of Andes due to the diferential heating and the inertial circulation due to the Coriolis force which strengthened the LLJ, contributed to the development of convection associated with the MCCs. Results of simulation and forecasting of a MCC case, (using analyses and forecasting from a GCM), indicated that the model is able to predict well this system if the lateral boundary conditions are appropriated. The errors in the forecasting were related to dynamic fields provided by the AGCM, mainly in the southern boundary conditions at the upper level jet region, and in the northern boundary conditions related to the low level northerlies that were introduced inside the domain.

ASSUNTO(S)

eta model jatos de baixos níveis sistemas de convectivos de mesoescala (scm) mesoescale convective systems (mcs) scheme of convection esquema de convecção circulação local local circulation low level jet modelo eta

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