THE TEXTURE OF CLOUDS

Using a precise definition of clustering, it is shown that in two trop ical cumulus clouds, droplets appear to be bunched over distances rang ing from at least a kilometer or more down to several centimeters. A s tatistical framework is proposed for quantifying clustering in terms o f a Poisson probability mixture. While these observations require furt her substantiation in many different clouds, droplet clustering may pl ay a role in diverse phenomena from the coalescence growth of raindrop s to the scattering of radiation by clouds.