Strong Far-Away Effects of Local Cloud Seeding. Progress in Technology Depends on Intense Studies of These Phenomena.

: The Public Law 94-490 of 1974 directs the Secretary of Commerce to formulate an appropriate national policy on weather modification. This event stimulated publication of 'A statistician's view of weather modification technology,' (Proc. Natl. Acad. Sci., Vol. 74, 1977). The present Technical Report is similarly motivated. It assembles evidence of an unexpected phenomenon: the seeding of clouds intended to affect the precipitation in a conventional target, perhaps some 50 km across, appears to have strong effects on rain at distances of 140-280 km, 'the far-away effects.' The hypothetical atmospheric physics mechanism described in the Report explains some of the empirical findings, but not all. The particularly interesting unexpected finding refers to the seven year long Arizona experiment: an apparent 74% increase in rain (P=0.047) in far-away localities on the right of the day's wind direction. The statistical methodology used is a combination of 'moving grids' and of optimal C(alpha) tests. (Author)