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<br />Oklahoma, but remain airborne in Arizona. The reasonableness of <br />this hypothesis can be checked readily by making field measurements. <br /> <br />Natural ice nuclei in Oklahoma seemed capable of showing glaciation <br />around cumulus tops at rather warm temperatures - probably often in <br />the range of -4C to -8C. However, the seeding of such clouds with <br />AgI flares was able to produce dramatic additional glaciation. Evidently <br />nature provided some natural nuclei and crystals, but so few that there <br />was still considerable supercooled water available for an artificial <br />seeding effect. My observation of seeded glaciation vs natural was <br />circumstantial, not conclusive. However, the location, timing, and <br />characteristic "isolated feather" appearance of the glaciation makes <br />me confident that I was observing a distinct nuclei seeding effect on <br />several occasions. <br /> <br />As to the cloud dynamics and cloud environment aspects of seedability in <br />Oklahoma, we should note the cloud temperatures and dimensions are often <br />such as to give a good potential for seeding. Cloud bases are generally <br />warm, say +14C, and so hygroscopic seeding can have many kilometers of <br />depth of cloud to work in before ice nuclei .can start having an effect. <br />When clouds do tower above the -4C level, and have diameters in the 2-5 km <br />range, the one dimensional cumulus model predictions as used by the <br />Bureau of Reclamation usually indicated that seeding with AgI should be <br />effective in stimulating growth and increasing precipitation. In summary, <br />medium size convective clouds in Oklahoma are generally seedable, and <br />both seeding methods are usually employable. <br /> <br />The larger clouds and storm systems can certainly have their characteristics <br />altered by seeding, but the complexity of interacting mechanisms and factors <br />makes it impossible to say just what net effect the seeding will have on <br />area-wide precipitation. The simple model calculations are not appropriate <br />for large, complex systems. One can hypothesize mechanisms which would <br />give increases from seeding and others that would result in decreases. I feel <br />increases would be most common, but there cannot be definite answers <br />without careful research on the large scale storms. One thing is certainly <br />obvious to an observer in Oklahoma, however; the medium size storms are <br />very inefficient, leaving huge amounts of condensed moisture aloft. In the <br />absence of excessive amounts 'of natural nuclei, some form of seeding should <br />be able to increase the efficiency. <br /> <br />34 <br />