Abstract
Abstract. This study provides an overview of precipitation processes and their sensitivities to environmental conditions in the Central Amazon Basin near Manaus during the GoAmazon2014/5 and ACRIDICON-CHUVA experiments. This study takes advantage of the numerous measurement platforms and instrument systems operating during both campaigns to sample cloud structure and environmental conditions during 2014 and 2015; the rainfall variability among seasons, aerosol loading, land surface type, and topography has been carefully characterized using these data. Differences between the wet and dry seasons were examined from a variety of perspectives. The rainfall rates distribution, total amount of rainfall, and raindrop size distribution (the mass-weighted mean diameter) were quantified over both seasons. The dry season generally exhibited higher rainfall rates than the wet season and included more intense rainfall periods. However, the cumulative rainfall during the wet season was 4 times greater than that during the total dry season rainfall, as shown in the total rainfall accumulation data. The typical size and life cycle of Amazon cloud clusters (observed by satellite) and rain cells (observed by radar) were examined, as were differences in these systems between the seasons. Moreover, monthly mean thermodynamic and dynamic variables were analysed using radiosondes to elucidate the differences in rainfall characteristics during the wet and dry seasons. The sensitivity of rainfall to atmospheric aerosol loading was discussed with regard to mass-weighted mean diameter and rain rate. This topic was evaluated only during the wet season due to the insignificant statistics of rainfall events for different aerosol loading ranges and the low frequency of precipitation events during the dry season. The impacts of aerosols on cloud droplet diameter varied based on droplet size. For the wet season, we observed no dependence between land surface type and rain rate. However, during the dry season, urban areas exhibited the largest rainfall rate tail distribution, and deforested regions exhibited the lowest mean rainfall rate. Airplane measurements were taken to characterize and contrast cloud microphysical properties and processes over forested and deforested regions. Vertical motion was not correlated with cloud droplet sizes, but cloud droplet concentration correlated linearly with vertical motion. Clouds over forested areas contained larger droplets than clouds over pastures at all altitudes. Finally, the connections between topography and rain rate were evaluated, with higher rainfall rates identified at higher elevations during the dry season.
Highlights
1.1 The Amazon Forest climateThe Amazon Forest spans more than 3000 km in the east– west direction and approximately 2000 km from north to south
Approximately 4 times less accumulated rainfall was recorded during the dry season than the wet season, the average rainfall event during the dry season produced a greater amount of rain
Total rainfall in the wet season is 4.2 times larger than that in the dry season, but RRs observed during the dry season are approximately 22 % higher than those that occur in the wet season
Summary
The Amazon Forest spans more than 3000 km in the east– west direction and approximately 2000 km from north to south. The complex physico-chemical interactions observed in the Amazon Basin include rainfall formation processes, diurnal, seasonal, and inter-annual cycles, the spatial organization of clouds, the mechanisms controlling cloud condensation nuclei (CCN), and the interactions between the vegetation, atmospheric boundary layer, clouds, and upper troposphere These processes are all in perfect sync, resulting in a stable equilibrium climate that produces rainfall equivalent to 2.3 m throughout the 6.1 million km of the Amazon Basin, or the equivalent of an average 27 trillion metric tonnes of rainfall each year. A recent study illustrates and quantifies (Fu et al, 2013) how this stable environment can be disturbed and the point of equilibrium shifted far from the one that produces abundant fresh water, keeps the forest alive, and plays a primary role in controlling global atmospheric circulation and energy distribution
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