Abstract
Standard Amazonian rainfall climatologies rely on stations preferentially located near river margins. River breeze circulations that tend to suppress afternoon rainfall near the river and enhance it inland are not typically considered when reporting results. Previous studies found surprising nocturnal rainfall maxima near the rivers in some locations. We examine spatial and temporal rainfall variability in the Santarém region of the Tapajós-Amazon confluence, seeking to describe the importance of breeze effects on afternoon precipitation and defining the areal extent of nocturnal rainfall maxima.We used three years of mean S band radar reflectivity from Santarém airport with a Z-R relationship appropriate for tropical convective conditions. These data were complemented by TRMM satellite rainfall estimates. Nocturnal rainfall was enhanced along the Amazon River, consistent with the hypothesis that these are associated with the passage of instability lines, perhaps enhanced by local channeling and by land breeze convergence. In the daytime, two rainfall bands appear in mean results, along the east bank of the Tapajós River and to the south of the Amazon River, respectively.
Highlights
In the Amazon Basin in situ climate data comes from a sparse network of automatic and conventional weather stations selectively located near communities sustained by river transport
Seasonal and diurnal precipitation variability near the Tapajós-Amazon confluence using the
Results clearly establish the geographical extent of the river breeze influences on rainfall
Summary
In the Amazon Basin in situ climate data comes from a sparse network of automatic and conventional weather stations selectively located near communities sustained by river transport. Fitzjarrald et al (2008) analyzed data obtained from a network with automatic weather stations deployed during the LBA-ECO Project (http://www.lbaeco.org) near the confluence of the Tapajós and Amazon Rivers near Santarém, Pará, Brazil. They found an interesting difference in the diurnal rainfall pattern as one goes inland from the rivers. In this paper we use precipitation data estimated using the Santarém meteorological radar to clarify the importance of river breezes and the early morning passage of instability lines on spatial distribution of rainfall near the Tapajós-Amazon confluence, extending the efforts of Fitzjarrald et al (2008) who had only automatic weather stations at the surface.
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