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<br />.' .. <br />~. ,....,.. <br />Be ..... <br />;,: <br />;... . ~ - , <br />I <br />, <br />~ I ~~~~;.:\ <br /> <br />WESTERN KANSAS ~EATHER MODIFIChTION <br />RaSLETTER 94 - 5 <br />FOR THE PERIOD MAY 29 - JUNE 4, 1994 <br /> <br /> <br />" <br /> <br />~~u I"l~"'~C.;,r: Recently we receilted an "Executive SUlllml!lry' of an <br />article in the December 1993 Journal of hpplied Meteorology entitled, " <br />Effect$ of Cloud Seeding in West Texas: Additional Results and New <br />Insights", It vas sent to us by the Mr, George ScaM'. Senior <br />Techni=l Specialist of the lJatershed Management DiV'ision at the 1elXllS <br />Natural Resource Conserltation Commission, The study Vas conducted over <br />portions of the summers of 1987. 1989 and 1990 in the vicinity of Big <br />Spring. Texas, using silver iodide to seed convective clouds, <br /> <br />HI', Bomar states, "A total of 183 convec::tlve cells (93 seeded and <br />90unseeciedj was collected during the three su,,:.e:!'!!! of e!!pedmentation , <br />The analYl!lis of the data revealed that seeded convective cells lived 36 <br />percent longer than the unseeded variety, and the rain volu.es of seeded <br />cells exceeded that of unseeded cells by 130 percent, llso. the seeded <br />cells merged wi th surrounding clouds twice as often as the unseeded <br />ceUs, <br /> <br />In fact . the re~earL::h fQund that seeded cloud systems continued to <br />produce lIlore rainfall than unseeded clouds for periods as long as 2,5 <br />hours after $l!leding vas initiated. Throughout the two and one-half hours <br />fOllowing the onset of seeding. the seeded clouds produced between 126 <br />and 137 pe=ent lIIore rainfall than the clouds not treated with silver <br />iodide. <br />, <br /> <br />another intriguing aspect of the research findings vas that seeding <br />did not substantially increase the height of convective clouds. In fact. <br />seeded clouds grew only 7 percent taller than the unseeded variety, This <br />would appear to alleviate the conCE;lrn, expressed ,"y skeptiC$, that <br />seeding might turn a benign cumulus cloud into a raging severe star.." <br /> <br />Finallv. Mr, Bomar states. "In conclusion, the evidence points to <br />s~ing as having incr_sed rain volum.e primarily by inducing largelr. <br />longer-lasting cells, which showed a greater tendency to aerge with <br />neighboring o~lls, Seedins affects a number of important cloud dyna.ical <br />and microphysical processes in \Jest Texas cloude, leading ultilU.teIy to <br />increosed precipitation,' <br /> <br />It '81 instructive to' note that the study was done u$ing a PoppleI' <br />radar systelll vbich could per-form "volume scans", Volullle scans are <br />nothing very new, The National ieather Service new Nexrad doppler <br />radar systems do it continuously and havs done it for years. even 011 <br />some of their older (non-Doppler) radar systems which were hooked up to <br />CQIIlputers, essentially doing the S-al/ll!l thing, While scanning. <br />reflectivity changes are able to be detected from level to level ~ the <br />radar antenna rises slowly with each rotl!ltion, Using correlations <br />between radar intensities and rainfall ~ates., precipitation OJO.ounts <br />= be inferred. When volume scans ore done on seeded l!lnd unseeded <br />clouds. the usual use of statistics can be employed to find changes <br />and determine effects. This is a much better technique than using <br />rainfall data co_pared to an historical rainfl!lll average for both a <br />"target" and 'control." In the future I predict this Itethod , or <br />variations of it', undoubtedly will become a standard way ill 1/hich to <br />.easure cause and effect from cloud seeding: <br />..~~=#~*.=~~=~~~#.ca~~.,....g.~3&=..~~~~~C~~~~~.*==~~~~AQR._....=a.~~g... <br /> <br />. <br />