HAII. 



sens gives a 22.6 percent decrease of 

 hail falls as an average over the eight- 

 year period since the experiment be- 

 gan. The French scientists are using 

 surface Agl-acetone generators, of 

 which 240 are distributed over 70,000 

 square kilometers. The generators are 

 lighted 6V2 hours before the expected 

 outbreak of hailstorm activity in or- 

 der to load the air sufficiently with 

 good freezing nuclei, which may not 

 normally be possible. 



The operations in Switzerland 

 (GROSSVERSUCH III) can be re- 

 lated to those in France in regard to 

 the density of the generator network. 

 The results for GROSSVERSUCH III 

 show an increase of the number of 

 days of hail (and an increase of rain 

 amount per seeded day), while Des- 

 sens reports a decrease in hail dam- 

 age. Of course, "days of hail" and 

 "hail damage" are two parameters 

 that need not be directly proportional. 



Hail Suppression: Kenya 



Final results are available for the 

 hail-suppression experiment carried 

 out from 1963 to 1967 in Kericho, 

 Kenya. It was based on the firing 

 of Italian antihail rockets from 13 

 firing positions within the Kitumbe 

 Estate. In 1968 the rocket network 

 was expanded to neighboring estates 

 to a total of more than 30 stations. 

 The rockets contain 800 grams of 

 TNT and no Agl; their burst occurs 

 at 2,000 to 2,400 meters above 

 ground or at about the +2° cen- 

 tigrade level. Rocket-firing begins 

 when hail starts falling and continues 

 until hail stops. In Kitumbe nearly 

 5,000 rockets were fired during 60 

 hail storms. 



Because of the consistency of the 

 reduction of damage on Kitumbe dur- 

 ing both periods, it seems unlikely 

 that this was due to chance. (See 

 Figure V-12) Five mechanisms have 

 been suggested to explain why the 

 experiment should work: (a) cavita- 

 tion, (b) shock-induced freezing, (c) 

 freezing due to adiabatic expansion, 



(d) introduction of ice nuclei, and 



(e) introduction of hygroscopic nuclei. 



Continuing Experimentation — Pre- 

 liminary results have been obtained 

 from continued experiments over tea 

 estates in Kericho. Seeding was done 

 at cloud base with pyrotechnic de- 

 vices dispersing between 6 and 30 

 grams of Agl per minute; 247 seed- 

 ing flights were carried out on 225 

 operational days. In the first season, 

 58 hail reports from within the tea 

 groves were obtained from 670 

 seeded cells, against a historical 

 background of 360 hail reports from 

 686 nonseeded cells. Damage per hail 

 instance was 2,929 pounds with seed- 

 ing and 7,130 pounds without seed- 

 ing. The great frequency of storms 

 seems to make this area an excellent 

 natural laboratory. 



Hail Suppression: Italy 



The effort in Italy proceeds along 

 two avenues. The first approach is 

 scientific in character and entails a 

 study of the hail phenomenon rather 

 than of hail prevention. The project 

 is carried out by the Institute for 

 Atmospheric Physics of the National 

 Research Council. The second ap- 

 proach has been developed by farmer 

 associations and the Ministry of 

 Agriculture and Forests. The largest 

 effort is that of exploding rockets 

 inside the clouds when the hailstorm 

 is overhead. The rockets carry 800 

 grams of TNT to altitudes of 1,000, 



1,500, or 2,000 meters. In 1968, 

 96,000 of these rockets were fired 

 in Italy. Plans are being made 

 through the National Bureau of Elec- 

 trical Energy for a project employing 

 ground-based silver iodide burners of 

 the type used by Dessens in France. 



Hail Suppression: United States 



In the United States, plans for a 

 National Hail Suppression Field Test 

 proceed slowly, while theoretical and 

 applied research on the structure of 

 hailstorms and the hailstone mech- 

 anism progresses more rapidly. Proj- 

 ect HAILSWATH, a loosely coordi- 

 nated field experiment, was organized 

 in the summer of 1966 in Rapid City, 

 South Dakota. Twenty-three institu- 

 tions participated in this endeavor, 

 whose outstanding purpose was to 

 explore the feasibility of a large joint 

 operation involving, at times, as 

 many as 12 aircraft. Hailstorms were 

 seeded with dry ice and silver iodide 

 according to a target-control area 

 approach on 10 experimental days, 

 but the results lack statistical sig- 

 nificance. 



A review of various hail-suppres- 

 sion projects in the United States 

 makes it apparent that American 

 hail-suppression activities can hardly 

 be called successful. 



Figure V-12 — HAIL SUPPRESSION AT KERICHO, KENYA 



The table shows the decrease in the average loss per hailstorm in kilograms per 

 hectare at Kitumbe estate compared with other estates in the nearby area. 



153 



