Infrared satellite images of the oceanic warm-pool region (80-degrees-
E-160-degrees-W) have been objectively processed to reveal tropical ''
cloud clusters'' with temperatures colder than a given threshold. Clou
d clusters span a somewhat lognormal distribution of sizes. The cloudi
ness per unit size interval peaks at small size, but half of the very
cold (<208 K) cloudiness is contributed by cloud clusters greater than
20 000 km2 in size, while half of the moderately cold (<235 K) cloudi
ness is contributed by cloud clusters greater than 100 000 km2 in size
. The diurnal cycle of cold cloudiness is primarily a sun-synchronous
process within large and giant clusters, not a modulation of populatio
ns of isolated convective clouds. Deep convection in these clusters pe
aks before dawn and decreases through the morning; then the moderately
cold cloud area expands suddenly in the afternoon. Over the maritime
continent, an additional diurnal cycle of small clusters is present, w
ith an afternoon pulse of convection over land and a lesser peak in sm
all-cluster convection over the surrounding seas at night.The eastward
-propagating intraseasonal variation (ISV) is apparent in fractional c
old cloudiness integrated across the entire tropical latitude belt. Th
e ISV modulates cloud clusters of all sizes, but larger clusters are p
roportionately more affected than smaller clusters. Cloud clusters hav
e been tracked in time to reveal ''time clusters,'' which spatially ov
erlap from one frame of imagery to the next. In some cases, convection
is so gregarious and interconnected that these time clusters last for
more than two days. These cases are called ''superclusters.'' Althoug
h they may exist at any given instant as several distinct cloud cluste
rs, these superclusters are apparently real physical entities, as defi
ned by space-time continuity of very cold-topped cloud (proxy for prec
ipitation) area.