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<br />RECEIVED <br /> <br />SEP 1 1 1996 <br />WESTERN KANSAS WEATHER MODIFICATION PROGRJ\M CcI0rad0WllIer <br />e-mail: hailman@pl.d. com Conservation Bollld <br />Internet: http://www.pld.com/users/hailman/master.html <br /> <br />~) <br /> <br />I f^i S' <br /> <br />.',. <br />..... <br /> <br />WEEKLY NEWSLETTER <br />96-21 <br /> <br />FOR THE PERIOD AUGUST 31 - SEPTEMBER 6, 1996 <br /> <br />General Interest: The following article presents information which <br />may have the most significant implication for precipitation <br />enhancement in Western Kansas, Eastern Colorado arid the Oklahoma <br />Panhandle since weather modification began here 22 sea~ons ago. <br /> <br />Attempts at precipitation enhancement, rain sti~ul~tion, rain <br />augmentation' Q:~::i, :r...in im:::t'ease all mean the' eame tF},',,','J; ,!,", ;l:lloud <br />seeders are trying to increase the amount of rainfail v~lich would <br />naturally fall from a cloud system. At this moment few, if any, <br />farmers want anymore rainfall, but the time will come when we will <br />be moisture-short again and interest in it will inc,;e;a"lE:. <br /> <br />Some readers may recall an article in this cOlHllUl (!, few weeks <br />ago in which I discussed the rainfall stimulation experihlents being <br />conducted in Mexico by NCAR (the National Center for Atmospheric <br />Research). In that article I mentioned the principal seeding agent <br />was going to be hygroscopic in nature. Here' s an oversimplified <br />explanation how the precipitation process works and what we mean <br />when we talk about hygroscopic seeding: <br /> <br />Visible clouds are formed out of water droplets formed by <br />water vapor collecting on, or being attracted to Cloud ~ondensation <br />Nuclei (CCN). Many of these same little particles are the same <br />ones you see floating in the air when sunshine pours through a <br />window into a darkened room. It's natural for these particles to <br />, exist in great abundance. It is only when water droplets rise above <br />the freezing level that Ice Nuclei (IN), perhaps more'correctly <br />called Ice Forming Nulei (IFN), are important in the precipitation <br />pr'oce~!, < . ('Jmvis usually, are deficient in cont",ining s\l,fficient <br />numbers, of IFN. The,few IFN which are captured in water clropiet:;; <br />will begin to freeze first, becoming ice crystals which can grow <br />larger by several means and/or collide with other drops and ice <br />crystals whiCh than shatter, grow larger, etc., in a repeating <br />process until the ice (or ice/water) particles fall from the cloud <br />and land as rain, sleet, graupel, drizzle, hail or snow. When this <br />ice forming process is absent, or lacking, clouds can form but not <br />produce rainfall before it evaporates back into the atmosphere. <br /> <br />On the Western Kansas Weather Modification Pro.gram we use <br />seeding agents which produce IFN. The design of our program is <br />centered around this seeding agent. <br /> <br />Out over the oceans air is much cleaner having fewer of the <br />same kinds of CCN available as are found over the ~ontinents. So, <br />why does it rain so much over the oceans? Largely, the answer is <br />