Synoptic analysis of an intense rainfall event in Paraíba do Sul river basin in southeast Brazil

Abstract

ABSTRACT:The aim of this study was to analyse the characteristics of an intense rainfall event that occurred in the Paraíba do Sul river basin, southeast Brazil, in early 2000. Rainfall data from conventional meteorological stations and automatic weather stations, satellite images and datasets from the Climate Forecast System Reanalysis, National Centers for Environmental Prediction, were employed. After the arrival of a cold front in the state of São Paulo on 1 January, the first episode of the South Atlantic convergence zone (SACZ) of the year was established, lasting for 8 days. A dipole blocking pattern over the state of Rio Grande do Sul and Uruguay, with a cold core cyclone and a warm core anticyclone in the upper troposphere, weakened the westerly flow from the Pacific, favouring slow displacement of the SACZ. Intense moisture fluxes from the southern Amazon and tropical South Atlantic converged over southeast Brazil providing copious amounts of moisture for convective activity during the first 4 days of January 2000. The most notable aspect of this event was the development of a cyclonic vortex embedded in the SACZ (CVES) in the Atlantic Ocean, with a warm core in the lower troposphere and a cold core at higher levels, which intensified rain in the study region. After the weakening of the blocking on 4 January, the CVES moved southeastward in the Atlantic. The symmetry of the CVES and conditions of the thermal gradient in the lower and higher troposphere suggest that the system presented subtropical characteristics during the first few days and became an extratropical cyclone later.

Automated Detection Algorithm for SACZ, Oceanic SACZ, and Their Climatological Features

“…During SACZOCN episodes the trough near Uruguay coast closes into a cyclonic vortex and moves northward, near the southeast coast of Brazil (compare Figure 4D with Figure 8C). Brasiliense et al (2018) named this closed cyclonic circulation as cyclonic vortex embedded in the SACZ (CVES). From Figures 8A,C it is clear that the CVES is not embedded in the SACZ, but southwest of it, near the RJ coast (see the location of RJ in Figure 5A).…”

Subtropical cyclones over the oceanic basins: a review

“…Recent analysis presented by Brasiliense et al . associated a cyclonic vortex with subtropical characteristics to the occurrence of an extreme precipitation event over Paraíba do Sul river basin (in southeastern Brazil) occurring in January 2000.…”

“…Recent analysis presented by Brasiliense et al 67 associated a cyclonic vortex with subtropical characteristics to the occurrence of an extreme precipitation event over Paraíba do Sul river basin (in southeastern Brazil) occurring in January 2000. For this event, Sugahara et al 68 classified the observed accumulated rainfall during 5 days (which in one rain gauge station reached up to 522 mm) as an extremely rare event for the region, that is, with probability of occurrence less than 1% for most rain gauge stations.…”

A comparative study of intense surface cyclones off the coasts of southeastern Brazil and Mozambique

“…A recent study by Brasiliense et al () analysed an intense cyclone near the southeastern coast of Brazil in January 2000 and the SLP analysis presented in their study resembles the field given in Figure c, except that the central closed isobar value in their case was 1,006 hPa. In the present study the field shown is the composite of 80 cases and therefore the cyclone is less intense.…”

“…The cyclogeneses over these small areas are focused because they impart precipitation and weather changes to adjacent coastal regions. One example of a cyclone development which imparted excessive precipitation in the coastal regions of southeastern Brazil is presented by Brasiliense et al ().…”