The aim of the Global Energy and Water Cycle Experiment Cloud System S
tudy (GCSS) is to promote the description and understanding of key clo
ud system processes, with the aim of developing and improving the repr
esentation of cloud processes in general circulation models. The GCSS
Science Panel identified a need to document important observational ga
ps in the structure of cloud systems inhibiting the development of clo
ud-resolving models as a tool for parameterizing cloud systems in gene
ral circulation models. The nature of precipitating layer clouds aroun
d the world is not well documented. To better quantify this, a synthes
is of observations of these types of clouds made during field experime
nts conducted around the world has been developed. The synthesis draws
on observations made in Australia, Canada, China, Israel, Japan, Russ
ia, the Ukraine, the United States, and several European countries. Th
e survey examines the global variation of the horizontal scales of clo
ud and precipitation, embedded phenomena such as rainbands, conveyor b
elt characteristics, ice crystal and water droplet concentrations, and
raindrop and ice crystal size distributions.