Spatial and temporal rainfall variability near the Amazon‐Tapajós confluence

Abstract

[1] Do the influences of river breezes or other mesoscale effects lead to a systematic river proximity bias in Amazon rainfall data? We analyzed rainfall for a network of 38 rain gauges located near the confluence of the Tapajós and Amazon rivers in the eastern Amazon Basin. Tipping bucket rain gauges worked adequately in the Amazon rainfall regime, but careful field calibration and comparison with collocated conventional rain gauges were essential to incorporate daily totals from our array into regional maps. Stations very near the large rivers miss the afternoon convective rain, as expected if a river breeze promotes subsidence over the river, but paradoxically, this deficiency is more than compensated by additional nocturnal rainfall at these locations. The NOAA Climate Prediction Center (CPC) Morphing technique (CMORPH) passive infrared inferred rainfall data do an adequate job of describing medium scale variability in this region, but some localized breeze effects are not resolved at 0.25°resolution. For areas inland from the rivers, nocturnal rainfall contributes less than half of total precipitation. A large-scale rainfall increase just to the west of Santarém manifests itself locally as a 'tongue' of enhanced rain from along the wide area of open water at the Tapajós-Amazon confluence. The Amazon River breeze circulation affects rainfall more than does the Tapajós breeze, which moves contrary to the predominant wind. East of the riverbank, the effects of the Tapajós breeze extend only a few kilometers inland. Rainfall increases to the north of the Amazon, possibly the result of uplift over elevated terrain. Dry season rainfall increases by up to 30% going away from the Amazon River, as would be expected given breeze-induced subsidence over the river.

Carbon exchange in an Amazon forest: from hours to years

“…Our synthetic decade-long rainfall record corresponded closely with the nearby INMET Belterra measurements, although INMET Belterra had on average 220 mm of rainfall more per year, likely due to differences in circulation and convection between the km67 forest and Belterra pasture land surface (Fitzjarrald et al, 2008). Annual rainfall (Fig.…”

“…We discarded site-based data and calculated a distance-weighted synthetic hourly rainfall time series from a network of nearby meteorological stations, with locations ranging from 10 to 110 km away from km67. More information on the meteorological network is available in Fitzjarrald et al (2008). Detailed information about the subsequent calculations of the synthetic precipitation data set and PAR drift correction are available in Longo (2014).…”

Overview: Precipitation characteristics and sensitivities to environmental conditions during GoAmazon2014/5 and ACRIDICON-CHUVA

“…Dos Santos et al (2014) used satellite rainfall products to define the features of river breezes associated with the Negro, Solimões, and Amazon rivers. Fitzjarrald et al (2008) have described the effect of the Tapajos River on rainfall, and Silva have shown how wind structure favours cloud formation on the upwind side of the Tapajós River during daytime. Negri et al (2000) used passive microwave radiances to construct a 10-year climate related to the Amazonas rainfall patterns.…”

“…The diurnal convection cycle is strongly linked to underlying surface features Silva Dias et al, 2002), including its topography , deforestation (Saad et al, 2010), and large rivers (Dos Santos et al, 2014;Silva Dias et al, 2004). Additionally, large rivers impact the evolution of rainfall through the convergence of river breezes with ambient air flow (Fitzjarrald et al, 2008). Adams et al (2015) have shown that one central problem of the climate model related to the Amazon's diurnal convection and rainfall variability is the transition from shallow to deep convection, which occurs on a timescale of a few hours.…”

Overview: Precipitation Characteristics and Sensitivities to the Environmental Conditions during GoAmazon2014/5 and ACRIDICON-CHUVA

“…The diurnal cycle of convection has a strong link to the underlying surface: its topography (Laurent et al 2002), deforestation (Saad et al 2010) and large rivers , demonstrating a link to surface features . Additionally, large rivers impact rainfall evolution through the convergence of the river breeze with ambient flow (Fitzjarrald et al 2008). Adams et al (2016) showed that one 25 of the climate models central problem related to Amazon diurnal variability of convection and rainfall is the transition from shallow to deep convection, which occurs on a time scale of approximately three hours.…”