A 10-yr Climatology of Amazonian Rainfall Derived from Passive Microwave Satellite Observations

Abstract

In this study, a satellite-derived precipitation ?climatology? (climate description) over northern South America using a passive microwave technique, the Goddard Profiling algorithm, is presented. The results are statistically adjusted to have the same probability distribution as a rain gauge dataset. The climatologies take the form of the mean estimated rainfall for a 10-yr+ period, with subdivisions by month and meteorological season. For the 6-yr period 1992?97, when two satellites were in operation, diurnal variability (to the extent it is discerned by four unequally spaced observations) is presented. In the mean, dramatic patterns of alternating morning and evening maxima are seen stretching from the northeast (Atlantic coast) across the continent to the Pacific. The effects of local circulations caused by topography, coastlines, and geography (river valleys) on the rainfall patterns are evident, particularly in the region around Manaus, Brazil, where the Negro and Solimoes Rivers merge. The interannual variability of the 10-yr rainfall estimate is examined by computing the deviations of yearly and warm-season (December?February) rainfall from their respective long-term means. Rainfall anomalies associated with El Niño and La Niña events then become apparent. This gauge-adjusted satellite climatology enhances existing (gauge based) climatologies by increasing the spatial resolution and providing a common, spaceborne platform for assessing interannual variability. It maintains the same first- and second-order statistics as does the gauge dataset, and allows a first attempt at examining the diurnal cycles by utilizing passive microwave observations (up to) four times per day.