A Look at Amazon Basin Seasonal Dynamics with the Biophysical ...

Observation and numerical simulation of the river breeze circulationin the vicinity of the Tapajós and Amazon riversMaria A. F. Silva Dias (1)Marcos Longo(1)Pedro L. Silva Dias(1)David R. Fitzjarrald (2)A. Scott Denning(3)Priscila Brier D'Auria(1)(1) Departamento de Ciências Atmosféricas, Universidade de São Paulo(2) Atmospheric Science Research Center, State University of New York at Albany(3) Department of Atmospheric Sciences, Colorado State UniversityRua do Matão, 1226 - 05508-900 São Paulo - SP - mafdsdia@usp.brDuring the beginning of the dry season of 2001 in the Amazon Region, basically from middle Julyto middle August, an atmospheric intensive field campaign called CIRSAN/LBA (Circulation inSantarém) was carried out close to Santarém as part of the LBA. Boundary layer and upper airmeasurements were carried out in both margins of the Tapajós rivers and on the southern margin ofthe Amazon with the objective of studying the local circulation. This paper presents preliminarydata on the local circulation evolution close to the Tapajós and Amazon rivers intersection,embedded in weak trade winds during an event of “friagem” in the Amazon region. Numericalsimulations of the river circulation with 2 km resolution are presented and used to help theunderstanding of the observations. The preliminary analysis of the observations taken duringCIRSAN/LBA indicate that the margins of the Tapajós and Amazon rivers, close to the city ofSantarém in Eastern Amazon, are influenced by river induced thermal circulations; the localcirculation is more evident during periods of light large scale winds. A "friagem" event reachingwestern Amazon during CIRSAN produced the ideal conditions for the development of riverinduced circulations in Santarém. The effect of the river breeze is basically to lower the mixed layerheight and enhance cumulus cloud at the river margin. The effect of these on the venting of mixedlayer trace gases may be an important feature in the interpretation surface measurement in the area.The numerical simulations show the coupling of the circulation on both sides of the river and theadvection of the circulation cell to the west, thus inducing cloudless skies in the western margin ofthe Tapajós.