ANÁLISE DOS DADOS DE PRECIPITAÇÃO PROVENIENTES DE DIFERENTES FONTES SOBRE A AMÉRICA DO SUL COM ÊNFASE NO BRASIL

In this work the potentialities and limitations from different precipitation sources over South America, with emphasis on Brazil were investigated. The regional similarities and differences were analyzed between the precipitation values obtained from ANEEL (National Electrical Energy Agency), and the rain gauge series obtained from the reanalysis of NCEP/NCAR (National Centers for Environmental Prediction/ National Center for Atmospheric Research) and GPCP (Global Precipitation Climatology Project) The analysis considers the annual and seasonal averages and the correlation between the data measured (ANEEL stations) and the rain gauge series obtained from the other sources from the different country regions.RESUMO Neste trabalho foram investigadas as potencialidades e limitações de diferentes fontes de precipitação no Brasil. Foram analisadas as semelhanças e diferenças regionais entre os valores de precipitação obtidos das estações da ANEEL (Agência Nacional de Energia Elétrica), e as séries pluviométricas obtidas da reanálise do NCEP/ NCAR (National Centers for Environmental Prediction/ National Center for Atmospheric Research) e do GPCP (Global Precipitation Climatology Project). A análise levou em conta as precipitações médias anuais e sazonais e as correlações entre as séries pluviométricas de valores medidos (estações da ANEEL) e as séries pluviométricas obtidas das outras fontes nas diferentes regiões do país. Palavras-chave: Precipitação. Fontes de dados. Climatologia. América do Sul. Regiões do Brasil. Estações Pluviométricas. ABSTRACT In this work the potentialities and limitations from different precipitation sources over Brazil were investigated. The regional similarities and differences were analyzed between the precipitation values obtained from ANEEL (National Electrical Energy Agency), and the rain gauge series obtained from the reanalysis of NCEP/NCAR (National Centers for Environmental Prediction/ National Center for Atmospheric Research) and GPCP (Global Precipitation Climatology Project). The analysis considered the average annual and seasonal precipitation and the correlations between the rain gauge series measured data (ANEEL stations) and the rain gauge series obtained from the other sources in different country regions. Keywords: Precipitation. Data Sources. Climatology. South America. Regions of Brazil. Rain Gauge. RESUMEN En este trabajo se investigó el potencial y las limitaciones de diferentes fuentes de precipitación en Brasil. Se analizaron las similitudes y diferencias regionales entre los valores de precipitación obtenidos en las estaciones de ANEEL (agencia Nacional de Energía Eléctrica), y las series pluviométricas obtenidas de reanálisis de NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research) y del GPCP (Global Precipitation Climatology Project). El análisis tuvo en cuenta las precipitaciones medias anuales y estacionales y las relaciones entre las series pluviométricas de valores medidos (estaciones de ANEEL) y las series pluviométricas obtenidas de otras fuentes en las diferentes regiones del país. Palabras clave: Precipitación. Fuentes de los datos. Climatología. America del Sur. Regiones de Brasil. Estaciones Pluviométricas

Theoretical and synoptic study of western disturbance

The theoretical part of the papel deals with the stability characteristics of the observed mean zonal current over lndia and neighbourhood in winter. The analysis shows that the mean zonal current is unstable with respect to a small perturbation superimposed on it. The synoptic part deals with a case study of a westem disturbance which developed into a depression. The developrnent of the westem disturbance is similar to the development of a baro- clinically unstable disturbance. Power spectral analysis of the meridional component of wind shows a periodicity of 8-10 days for westem disturbances. The estimated wavelength of the westem disturbance is in good agreement with the theoretically determined most unstable wavelength.Pages: 193-20

Annual cycle of precipitation and moisture characteristics over Brazil

Convective precipitation over tropical Brazil is characterized by strong annual variation of precipitation. This precipitation is associated with large scale features such as Intertropical Convergence Zone (ITCZ) over the northeast Brazil in austral autumn, and with South Atlantic Convergence Zone (SACZ) over the region from northwestem Brazil to the southeast. Over these regions convective activity begins in spring, at its peak in summer and seldom appears in winter. This sequence of events seen in the present study using the upper tropospheric wind data and the moisture parameters

Case studies of cyclogenies over South America

A detailed case study of cyclogenesis over South America during the period 5-9 June 1981 is undertaken. The intensification of the cyclone occurred first in the upper troposphere. The disturbance showed several characteristics found in baroclinic disturbances, such as eastward tJropagation, intensification with westward vertical tilt and barotropic decay. However, the vertical tilt was confined to upper levels only and the surface temperature gradient was low. This suggests ~hat the mechanism of development might be somewhat different than the usual cases of baroclinic :nstability associated with 10w-Ievel vertical inclination. Internal baroclinic instability is suggested as t plausible mechanism of development. Cases of intense cyclogenesis are also studied during the leriod 1979 to 1988 using the Laplacian of the sea-Ievel pressure criterion in the autumn, winter md spring seasons. The case which occurred on 19 September 1984 over Uruguay and southern ~razil is presented; the pressure drop was 12 hPa in 24 hours over Paraguay and South Brazil.Pages: 359-36

Comments on Climatology of Cyclogenesis for the Southern Hemisphere

In a recent paper Sinclair (1995, hereafter SI) made a climatological study of cyclogenesis in the Southern Hemisphere using seven years (.1980-86) of European Centre for Medium-Range Forecasts (ECMWF) data. Geostrophic yorticity at 1000 hPa is used to locate cy- clones and determine their intensity. In an earlier study Gan and Rao (1991, hereafter GR91) also exarnined the cyclogenesis using the surface pressure charts for four hours an each day for the period January 1979- December 1988. Their study was for South America (the area enclosed by 15\ub0-50\ub0S and 30\ub0-90\ub0W). In GR91, the method used to manually identify surface cyclogenesis was that at least oneclosed isobar around a low pressure center should be found for an analysis of 2-hPa intervals. The purpose of this comment is to compare the results of these two studies for the South American region.Pages: 2614-261

The influence of the Andes Cordillera on transient disturbances

The influence of the Andes Cordillera on transient disturbances is investigated in this study using a lag-correlation analysis. This analysis shows that the unfiltered geopotential height data have a wavelike pattern moving to the east while tilting to the west in the vertical. When the wave approaches the Andes Cordillera, it exhibits orographic effects such as anticyclonic turning of a low-level disturbance trajectory, a zonal trajectory in the upper levels, distortions of the isolines of correlation, and an elongation of maximum correlation on the lee side of the Andes. The anticyclonic turning of the trajectory in the low-altitude levels and a zonal trajectory in upper levels implies a decrease in the vertical tilt of the system on the windward side and an increase in the tilt on the lee side. The increase of baroclinicity on the lee side results in baroclinic development as predicted from a linearly obtained normal-mode solution in the presence of mountains. A cross-correlation analysis of the high-pass-filtered disturbances shows an eastward phase propagation and a westward vertical tilt with height on the order of one-quarter wavelength between 1000- and 300-hPa levels. The horizontal structure and phase propagation show characteristics similar to the fastest-growing baroclinic normal mode in a two-layer, quasigeostrophic, beta-plane, linear model with a mountain placed in the north-south direction. This shows that the high-pass-filtered anomalies over the South American region are associated with baroclinic disturbances influenced by the Andes Cordillera. The results further show that the interaction of these anomalies with the Andes Cordillera is responsible for lee cyclogenesis. The composite maps show that the positive and negative high-pass-filtered anomalies have the same structure and paths of phase propagation. These anomalies intensify over the Pacific Ocean near the South American continent.Pages: 1141-115