Relationships between cloud properties and precipitation amount over the Amazon basin

Comparisons between the precipitation amount, P, and monthly averaged cloud properties (optical depths of low-level water clouds, τlow, and “total clouds”, τtot, effective particle radius, re, and columnar-integrated droplet number of low-level water clouds, Nc) over the Amazon basin elucidated the effect of precipitation on low cloud properties and the relationship between precipitation and “total cloud” cover. The relationship between re and P was positive, while the relationship between Nc and P was negative. Since low clouds in this region generally produce little precipitation, these relationships may reflect the scavenging of aerosols by precipitation and suggest the aerosol indirect effect of the first kind. The relationship between τtot and P was positive because the “total clouds” included actual precipitating clouds.