Energetics of cyclogenesis events over the southern coast of Brazil

Energética de eventos de ciclogêneses na costa sul do Brasil

An analysis of 58 cyclogenesis cases occurred from 2003 to 2011 over the southern Brazilian coast is presented focusing on the energy cycle proposed. For this analysis the National Centers for Environmental Prediction (NCEP) data was utilized to create the composite fields of all selected days as also to that of transitional seasons (austral spring and autumn), when it was verified a high number of cyclones. In the analysis, a deepening of a pre-existing surface trough over Paraguay was observed two days (D-2) before the surface pressure had reached its minimum over the southern Brazilian coast. Typically, the cyclogenetic process begins on the southern Brazil coast and spreads in a NW-SE direction, strengthening along its path. On D-2 the jet stream is almost zonally oriented and then when the cyclone is completely formed (D0), this acquire a cyclonic curvature, with two cores: one strongest in the SE and the other one in the NW direction. As soon as the geopotential anomaly for short waves (Gh) is in phase with anomaly for long waves (Gl) on D-1, the PhKh term increases in magnitude, becoming the dominant one. During all evolution stages, the dominant terms were the baroclinic (PlPh and PhKh), followed by the barotropic (KlKh) term. The friction term (RKh) had a secondary role and the source/sink of non conservative energy and flux of the available potential energy (RPh) did not contributed to the deepening of the surface low, which is not depending of the convective activity inside it. Significant differences were not observed in the mechanisms of cyclogenesis development and maintenance during the transition months, except for a greater availability of kinetic (Kh) and potential (Ph) energy and baroclinic and barotropic conversion terms during the austral autumn.

energética; ciclogênese; baroclínia

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