46 MALKUS AND RONNE 
stirring with an almost infinite extent of homo- 
geneous sea surface. One might expect, @ priori, 
uniform or random bunching of tropical Cumulus 
clouds, with Cumulonimbus build-ups and _ pre- 
cipitation distributed here, there, and every- 
where, and cloud patterns which statistically 
show little diurnal, weekly or even seasonal varia- 
tions. The organization, if any, might be ex- 
pected to be the hexagonal or roll convection 
typical of laboratory experiments over a heated 
surface. 
This classical picture of tropical convection 
has gradually faded. The first blow came with 
the Wyman-Woodcock trade-wind expedition, 
discussed by Bunker and others [1949] and the 
entrainment theory of Stommel [1947] evolved 
from its data. Clouds were found to exchange 
air with their surroundings and consequently the 
degree of instability of the temperature lapse 
rate lost its unique significance in determining 
cloud growth. The moisture distribution of the 
ambient air was found to affect m-cloud para- 
meters, and most tropical Cumuli lost buoyancy 
by drying out well below the level where a stable 
layer was reached. Cumulonimbus towers reach- 
ing the high troposphere were, to be sure, oc- 
casionally observed but conditions permitting 
their growth proved rare. The evolution of the 
Woods Hole Studies (during the period 1947— 
1957) further emphasized the controlling effects 
of the environment and the inhibitory factors 
against penetrative development. Runaway cloud 
growth to the Cumulonimbus stage has been 
found to require special circumstances. Among 
these are a deep moist layer, a large horizontal 
dimension, and probably synoptic-scale conver- 
gence in the low levels. The correlation between 
vertical development and degree of conditional 
instability proves not just to be low but generally 
inverse; a more unstable lapse rate is found 
where our films show a sky of widely separated 
stunted trade Cumulus, than in easterly wave 
and hurricane, when Cumulonimbi are rampant. 
The classical convection picture collapsed en- 
tirely with the work of Riehl and collaborators 
which carried tropical meteorology both upward 
and equatorward from the lower trades, where 
the synoptic disturbance is least evident. In con- 
trast to the steadiness of the lower trades, the 
upper tropical atmosphere is characterized by 
extreme restlessness. Even in the upstream in- 
version-dominated portions, the constancy van- 
ishes above the moist layer, and large space and 
time variations in wind, humidity, and stability 
aloft — governed by the dynamics and_ther- 
modynamics of phenomena on the synoptic 
scale. Equatorward from the trades, the in- 
version weakens and disappears and inconstancy 
at all levels becomes pronounced; the steady 
trade flow becomes perturbed into the deepening 
waves and vortices characteristic of the equa- 
torial trough zone, which itself operates in a 
fluctuating manner. Throughout the tropics, over 
land and sea the reputed clockwork regularity 
of showers proved an erroneous myth. Nothing 
could be more unreliable than tropical rain. In 
fact, tropical rainfall studies revealed an enor- 
mously skewed distribution, with the major 
fraction of monthly precipitation falling on two 
or three days and being almost entirely concen- 
trated in major disturbances, again pointing the 
finger toward a high degree of cloud, especially 
precipitating cloud, organization on the synoptic 
seale. 
Our study was designed to pursue this point 
in terms of specific questions, for which it was 
hoped to gain quantitative answers. Three cir- 
cuits of the North Pacific area were accom- 
plished in July and August 1957 and 8000 ft of 
film suecessfully exposed, only about one-third 
of which has been analyzed to date because of 
the exorbitant labor involved. The three overall 
conclusions of most pertinence to cloud physics 
are: 
(1) The degree of regulation and control upon 
cloud forms exerted by the synoptic scale of 
motion, which must be considered in its entire 
three-dimensional extent throughout the tropo- 
sphere (including up to, at least, the 200 mb 
level). 
(2) The extreme rarity and concentration of 
Cumulus and Cumulonimbus 
clouds, which on the first flight (which has been 
completely analyzed) never occurred except in a 
precipitating 
disturbance or a region where low-level syn- 
optic-seale convergence could be readily inferred 
from the charts. 
(3) The organization of Cumulus clouds into 
rows parallel to the low-level flow. On the 6300 
km of Fhlght I, such organization was de- 
tected (and the angle determined by quantitative 
measurement on the films) 91% of the time; 
it was coded as moderate or strong 62% of the 
time. Organization was only absent in trade-in- 
version dominated circumstances and became 
more pronounced as the degree of disturbance 
increased. We have measured the orientation of 
