EXPERIMENTAL METEOROLOGY 303 
TABLE 1 
Flight Seeding 
No. Date Agent Results 
45 October 1948 CO./AgI Development of large storm. 
106 July 1949 CO; Removal of large cloud from line of 
cumulus 
108 July 1949 CO, Towering, followed by consolidated rain- 
storm. 
Ke) July 1949 AgICO, Development of large storm. 
168 July 1950 CO, Development of cirrus overcast. 
172 July 1950 CO, Towering, followed by consolidated rain- 
storm. 
total vertical thickness was between 8,000 and g,0o0o feet, and 
thickness of supercooled cloud was 4,000 to 5,000 feet. Seeding 
was effected at the top of the clouds with temperatures of about 
—12°C. Crushed dry ice fragments with no particles larger than 
I cubic centimeter were scattered through the top portion ot the 
cloud at a rate of about 2 pounds per mile. 
6. Under these conditions initial radar echoes followed the 
seeding operation by 14 to 21 minutes. The echoes invariably 
brightened rapidly and showed close relationship to the upper air 
motions related to the areas seeded. 
7. Heavy rains occurring with a sparsity or complete absence 
of lightning were the most striking effects observed after dry ice 
seeding. Observations of the appearance of the cloud tops asso- 
ciated with the experiments showed regions where spectacular 
towering occurred, followed by a rounding off and consolidation 
of the ice crystal tops, especially where rains persisted for 2 to 4 
hours. 
8. The largest effects followed combined seeding of dry ice and 
silver iodide with the latter introduced either by airborne or 
ground-based generators. 
g. When cumulus cloud developments started in the afternoon, 
cloud dissipation was the common result of seeding activities. 
10. Large cumulus clouds which do not develop to the precipi- 
tation stage are of relatively common occurrence in regions like 
New Mexico and Arizona. When precipitation fails to occur, 
