CHARACTERISTICS OF RAINFALL AND PRECIPITATION FEATURES DEFINED BY THE TROPICAL RAINFALL MEASURING MISSION OVER SOUTH AMERICA

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

The performance of the Tropical Rainfall Measuring Mission (TRMM) rainfall algorithms was investigated from December 1997 to November 2000 over South America and adjoining oceans. The Precipitation Radar (PR) and the TRMM Microwave Imager (TMI) algorithms are compared with the rainfall estimates of the Geostationary Environmental Satellite (GOES) Precipitation Index (GPI), the gauge analysis of Global Precipitation Climatology Center (GPCC), and an additional dataset (GAUGES) that includes conventional and automatic rain gauges, mainly located over Brazil. The general pattern of PR tends to have qualitative good agreement with the climatologies. However, discrepancies are observed for regional, monthly, and seasonal averages. There appears to be a tendency of PR underestimating (-10%) large rainfall in the tropics and overestimating (18%) in the subtropics compared to GAUGES. TMI (GPI) estimates are generally high in both tropics and subtropics, where the differences from GAUGES are 13% (12%) in the tropics and 42% (21%) in the subtropics. GPCC is 4 and 6% higher than GAUGES in the tropics and subtropics, respectively. High rainfall estimated by the PR in southeast South America could be related to sampling problems, where PR overestimates rainfall from large MCSs, which contribute up to 80% of the total rainfall. Statistical tests of the confidence intervals have shown that small variations in sampling MCSs can lead to discrepancies in the rainfall estimates of PR compared to other algorithms. The characteristics of the precipitation features (PFs) and the diurnal cycle of rainfall were separated by regions to examine the regional differences in the continent and surrounding oceans. Although the largest numbers of PFs with MCSs were observed in the continental tropics, the most intense systems were observed in the Plata Basin, western Colombia, and Gulf of Panama. The diurnal cycle of rainfall over land often has a double peak, one related to an afternoon maximum of sub-MCS PFs and one related to a night-early-morning peak of MCS rain. The diurnal cycle of the rainfall from PFs with MCSs was shown to vary significantly among the regions in South America due to different physiographical and meteorological characteristics. Over the oceanic regions the diurnal cycle of rainfall typically has a weak morning maximum agreeing with previous studies, with the notable exception of the Gulf of Panama, which has the largest amplitude of the diurnal cycle among the regions considered. There, the large-amplitude diurnal cycle is vividly dominated by MCSs forming in the late evening and lasting until early afternoon.

ASSUNTO(S)

rainfall estimates satellite estimates trmm satellite south american rainfall meteorologia climatologia rain gauges sensoriamento remoto da atmosfera tropical rainfall

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