WMOD00576

• Title: Summary of Weather Modification Activities Reported in 1979
• Date: 7/1/1980
• Weather Modification - Doc Type: Report

CY 1978.

Duration of Modification Activities

The total number of days on which weather modification was attempted
varied from year to year as did the number of days devoted to attempts to
increase precipitation or to disperse fog. However, for both types of
weather modification activity, the trend in the number of days per year
after CY 1977 is downward.

The hours during which fog or cloud seeding was carried out from air-
craft indicated no certain trend over the reporting period. However, the
hours of ground-based operation showed a definite increasing trend until
CY 1979.

Seeding Agents

The use of dry ice (C02) to increase airport visibility in periods of
supercooled fog, to create clearings in stratus clouds, or to increase
precipitation in other cloud formations generally was greater until
CY 1978 when usage dropped abruptly. The peak year for seeding with silver
iodide was 1975. The Air Force relied on liquid propane vented to the
atmosphere in order to alleviate supercooled fog at two of its airbases
in the United States; however, no obvious trend was observed in the data.
The peak year for using polyelectrolytes to dissipate warm fog was 1976.

CONCLUDING REMARKS

CY 1979 had less weather modification activity than any year since the
reporting program began in CY 1973. In comparison with CY 1978, the
number of activities in CY 1979 was 20 percent lower; community sponsor-
ship was 63 percent less; target area was decreased by 47 percent; total
modification days were 26 percent fewer; the amount of silver iodide used
was 40 percent less; and the number of hours of ground generator operation
was diminished by 80 percent. There were increases in the number of
commercial modifiers., municipal sponsors, and fog modification days.

Seven years of data on reported weather modification activities in the
United States do not allow reliable conclusions about the trend in
Federal and nonfederal experiments or operations. In particular, all
estimates of trends in the data were clouded by the data by CY 1977, a
year of maximum activity in weather modification. However, a comparison
of CY 1979 data with the average of the six prior years shows that 1979
activities were 29 percent less; the target area was 35 percent less; the

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