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<br />~ <br /> <br />. . <br /> <br />The development of the target versus control cOlllparison ~s based on <br />the selection of a variable that \",ould be affected by seeding (usually <br />precipitation) . Records of the variable to be tested are, acquired for <br />an historical period (usually over several years) to represent condi- <br />tions which might be expected to occur "naturally" (without seeding). <br />These records are divided into those that lie within the designated <br />"target" area of the project and those in a nearby "control" area. The <br />control area is selected in an area which \vould be unaffected by the <br />seed.ing. <br /> <br /> <br />These two sets of data are then analyzed mathematically to develop <br />an equation which predicts the amount of target area precipitation based ' <br />on precipitation in the control area. This equation is then used during <br />the seeded period to esttmate what the target area precipitation should <br />have been based on that observed in the control area. A comparison can, <br />then be made between the predicted target area precipitation and that <br />which actually occurred. Any resulting difference can be tested for its <br />significance through statistical tests. This target and control tech- <br />nique works well \ihen a good correlation can be found between target and <br />control area precipitation. Generally, the closer the two areas are <br />together the higher will be the correlation. Areas selected too close <br />together, however, can be subject to contamination of the control area <br />by the seeding activities which can have the effect of underestimating <br />the seeding effect. <br /> <br />4.1 Evaluation of Storm Precipitation <br />In the Santa Barbara research project an evaluation of seeding effect <br />on individual convection bands was made as well as an evaluation of the <br />effect of seeding on whole storms. Whole storm periods \iere designated as <br />all the precipitation that fell within a 48 hour period and usually would <br />contain several convection bands. Within this 48 hour period all of the <br />convection bands would either be seeded or not be seeded depending upon a <br />rand{)m decision made in advance. <br /> <br />4-2 <br />