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<br />000951 <br /> <br />,'lir4" <br />~ <br />t~ ," <br />-, , <br />.- '." <br />~i~t~~i <br />t"~f.4:~;'~{' <br />i{&~ta(~ <br />~1~*1'J~1 <br /> <br /> <br />The following discussion of the technical aspects of precipitation <br />modification will clarify such terms as "seedability'i' and explain the <br />emphasis placed on cloud seeding, <br /> <br />Weather phenomena, including precipitation, involve large exchanges <br /> <br /> <br />of energy. Man's efforts to alter the weather have the greatest chance <br /> <br /> <br />of success if the comparatively meager amounts of energy which he <br /> <br /> <br />can selectively introduce are applied to unstable atmospheric situations <br /> <br /> <br />where relatively small amounts of energy can serve as a trigger for <br /> <br /> <br />the release of much larger anlounts through natural processes, Nature <br /> <br /> <br />offers at least four types of instability important to weather modifi- <br /> <br /> <br />cation: <br /> <br /> <br />1. Phase instability in which supercooled liquid water may be <br /> <br /> <br />changed to ice with a resulting liberation of the heat of fusion <br /> <br /> <br />to form a heat source <br /> <br /> <br />2. Colloidal instability in which small cloud droplets may be <br /> <br /> <br />encouraged to give up their water to form snowflakes <br /> <br /> <br />3. Vertical instability in which accumulations of heat at low ele- <br /> <br /> <br />vations may be released to higher levels with accompanying <br /> <br /> <br />transformations of the types that are observed in thunder- <br /> <br /> <br />storms <br /> <br /> <br />4. Horizontal instability in the large-scale circulation in which <br /> <br /> <br />energy imbalances between the equator and the poles are <br /> <br /> <br />relieved by the formation of cyclonic storms <br /> <br />II <br /> <br />I'o..~~,..$: <br /> <br /> <br />-.-,- ~ - ", . <br /> <br />;f':~.; ~~~::-~~:t <br />">' .,- <br /> <br />10 <br /> <br />\:>- <br />. ...-. <br />