Overview: Precipitation characteristics and sensitivities to environmental conditions during GoAmazon2014/5 and ACRIDICON-CHUVA
Authors: Machado Luiz A. T. , Calheiros Alan J. P. , Biscaro Thiago , Giangrande Scott , Silva Dias Maria A. F. , Cecchini Micael A. , Albrecht Rachel , Andreae Meinrat O. , Araujo Wagner F. , Artaxo Paulo , Borrmann Stephan , Braga Ramon , Burleyson Casey , Eichholz Cristiano W. , Fan Jiwen , Feng Zhe , Fisch Gilberto F. , Jensen Michael P. , Martin Scot T. , Pöschl Ulrich , Pöhlker Christopher , Pöhlker Mira L. , Ribaud Jean-François , Rosenfeld Daniel , Saraiva Jaci M. B. , Schumacher Courtney , Thalman Ryan , Walter David , Wendisch Manfred 
Published: May 2018

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.