Laserfiche WebLink
<br />~ <br /> <br />ADDENDUM TO COMMENTS ON ''WEATHER MODIFICATION <br />IN ARIZONA, 1971" BY HERBERT B. OSBORN <br /> <br />By <br />Wallace E. Howell, Chief <br />Research and Development Branch <br />Division of Atmospheric Water Resources Management <br />Bureau of Reclamation <br />U.S. Department of the Interior <br />Denver, Colorado <br /> <br />This addeudW'G deals with inferences that have been drawn from the <br />results of Project Whitetop bearing on the possibility of negative <br />effects of cloud seeding in Arizona using the Flagstaff treatment <br />model. The comments to which this is an addendum dealt with infer- <br />ences drawn from the Santa Catalina experiments; the reaSQn for <br />the addendum is that the Whitetop results have been conjoined itl <br />many references with the Santa Catalina results as implying a <br />negative outcome from cloud seeding. <br /> <br />Inference from Whitetop is even more questionable. In the first <br />place, besides being relatively remote from Arizona in terms of <br />airmass and frontal conditions for cloud and precipitation devel.op- <br />ment, the White top experiment suffered the same drawbacks with <br />respect to seeding materials, selection of clouds for seeding, <br />and placement of the seeding materials that affected the Catalina <br />experiment, with the same physical rationale for rain decrease. <br />It has the additional feature that the failure of the seeding <br />material to mix into the water-rich layer of air near the ground <br />and so enter the updraft cores was confirmed by on-the-spot meas- <br />urements that showed no significant increases in ice nucleus con- <br />centration near the ground at the radar site during cloud seeding <br />operations (Bourquard, 1963). <br /> <br />In the second place, analysts of Whitetop have had to cope from <br />the beginning with the finding that rainfall was lighter outside <br />the seeded plume, as well as inside it, on the operational days <br />that were randomly selected for seeding. Respecting this finding, <br />Decker and Schickedanz (1967) noted: <br /> <br />'~his appears to indicate that in spite of randomization, <br />the no-treatment days were meteorologically favored with <br />rain. This meteorological difference is confounded with <br />any treatment effects." <br /> <br />Flueck (1971) uses the term "uncontrolled background effects" to <br />describe the same phenomenon. <br /> <br />Neyman and Scott (1967) took sharp issue with the notion that this <br />background effect was meteorological: <br /> <br />I <br />_n_"~_"_J <br />