A Project for a Formation of Cumulonimbus 
by Artificial 
Convection 
Henri Dessens 
Observatowe du Puy de Déme, Clermont-Ferrand, France 
Abstract—The researches on the weather control should not be restricted to the 
nucleation of the clouds. The convection 
the formation of the precipitation. After several experiments with great brush fires 
process plays a first importance part in 
’ 
an experimental installation capable of modifying the local system of convection suf- 
ficiently to produce rain has been planned. This installation called ‘meteotron’ will 
consist of a pump serving 100 burners with fuel oil, so that the total consumption 
will be of the order of one ton per minute. The results of the experiments with great 
brush fires indicate that the formation of 
obtained, at least in equatorial regions, by 
Historical introduction—At the conference in 
Tueson, in April 1956, Byers recalled the sug- 
gestions made by Hspy [1841] that it would be 
possible to stimulate the formation of rain-giv- 
ing Cumulus clouds by means of large fires. In 
1938, 100 years later, Gorog and Rovo [1938], on 
the bases of some observational data, proposed 
that gasoline could be burned in large quantities 
with the same effect. In 1930, Dessoliers [1930] 
showed how the men should be able to increase 
rainfall progressively in arid regions ‘‘en créant 
et multiphant au milieu des terres et des eaux 
des aires de surchauffe solaire de quelque cent 
hectares destinées 4 provoquer l’appel, la con- 
vergence d’énormes masses d’air et leur ascension 
vers le zénith ou, plus briévement, en créant et 
multiphant les centres de coordination atmos- 
phériques.” 
Preliminary experiments—The first experi- 
mental trial for the stimulation of convective as- 
cending air currents consisted in clearing in the 
equatorial forest a surface of 0.2 km’. In effect, 
in the surrounding forest the thermal capacity 
of the vegetation and the high evaporation 
tended to reduce the daily variation of tempera- 
ture, in particular to reduce the daily maximum 
temperature. Over the cleared area, the solar 
radiation heated the soil to high temperature 
and the air temperature is also raised. In fact, it 
was observed that Cumulus clouds did tend to 
form over the cleared area and the study of 
these clouds has allowed a theory called that of 
‘coupled convection’ [Dessens, 1956]. But it ap- 
pears that to obtain Cumulus clouds sufficiently 
developed to give rain, there were also the fol- 
lowing requirements: (1) the cleared area should 
artificial thunderstorms will probably be 
working with the meteotron. 
be at least 1 km* in extent; (2) it is not sufficient 
really to clear or to burn the vegetation, but it 
would be necessary to make use of an uniform 
artificial covering for the area; and (3) the con- 
vective effect is only noticeable when low winds 
are very light. 
To cover the terrain will be an expensive 
proposition and the results at least uncertain. 
For these reasons, instead of following the idea 
to use only the solar energy, we preferred to 
have recourse to another source of energy, very 
much cheaper, for short series of experiments: 
the energy liberated by the burning of the vege- 
tation. We were immediately struck by the ease 
with which, in the equatorial regions, large Cu- 
mulus clouds can be obtained by this method, 
on a condition solely that the fire should be 
started at a suitable time in the day. These fires 
should be made with careful regard to the me- 
teorological conditions. When these are favor- 
able, large Cumulus clouds can easily be stimu- 
lated. These observations confirm entirely the 
ideas expressed in the last century by Espy 
[1841]. 
Artificial cloud seeding or artificial convection 
—Since 1955 we have made experiments to at- 
tempt to increase precipitation on an area of 
the Congo Basin at Lukolela (1°S, 17°E). Two 
methods have been employed: (1) the use of 
rockets to send large sodium chloride particles 
up to cloud base; and (2) the use of silver iodide 
emitted by burners situated at ground level. Be- 
ginning in 1956, we have undertaken these si- 
multaneously with experiments of artificial con- 
vection. The preliminary conclusion which we 
have reached after these two series of experi- 
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