Synoptic-dinamic study of cyclogenesis using potential vorticity / Estudo sinotico-dinamico de ciclogenese usando vorticidade potencial

AUTOR(ES)
DATA DE PUBLICAÇÃO

1999

RESUMO

A case study of cyclogenesis that occured on 9-10 of July, 1996 over Uruguay was performed. The data utilized consists on the daily temperature, geopotential, pressure at mean sea level, vertical velocity and wind fields, at 17 isobaric levels, from NCEP. The study was based on isobaric and isentropic analysis of those meteorological parameters, and also on potential vorticity perspective. The extratropical cyclone formed from the propagation of a pre-existent cut-off low in the Pacific Ocean, which reached the surface, and crossed the Andes Cordillera. The synoptic analysis of this case revealed that this event can be classified as a lee cyclogenesis, since the existence of the mountain barrier was fundamental for the intensification of the surface baroclinicity, which, in turn, brougth to the formation of the extratropical cyclone. Also, the Andes Cordillera defined the vertical tilt of the system to the east, favoring the cyclonic vorticity advection at higher levels, above the warm thermal advection at low levels, and it defined the final baroclinic configuration that fed the system in its greater development stage. The numerical inversion of total and perturbation potential vorticity was also undertaken. The results revealed that the evolution of the system can be recovered by the dinamically balanced part of the flow. It was also accessed the relative contributions of three distinct anomalies to this cyclogenesis event: lower boundary temperature perturbation and high and low-levels potential vorticity perturbations. It was found that at low levels, the most significant contribution (concerning intensity) to surface cyclogenesis was related to the low-level potential vorticity perturbation. But the position of the system was defined by the jointed contribution of low-level potential vorticity and lower boundary temperature anomalies. At upper levels, the ciclonic circulation was mostly due to the upper-level potential vorticity perturbation.

ASSUNTO(S)

efeito de montanha estudos do tempo e clima principio da invertibilidade ciclogeneses vorticidade instabilidade baroclinica

ACESSO AO ARTIGO

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