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<br />3 <br /> <br />, <br /> <br />from the vanor at me~ium to high altitu~es. coli temneratures and low(sub-water <br /> <br />saturation)6uDersaturations with resnect to ice, We may be able to create <br /> <br />cirrus clou:ls with higher concentrations of smaller crystals which would <br /> <br />be more stable than aircraft contrails. If so. it remains to be seen how <br /> <br />these clou-Is will moJify the raliation balance at the surface comnare! to <br /> <br />aircraft contrails. <br /> <br />" <br />~ <br /> <br />An exneriment will be conducted when ra':!ioson'ieJata and ground observa- <br /> <br />tions of nersistent contrails in:! icate clear ice-sunersatura.!-<:~ regions. The <br /> <br />Schweizer will seek out a region (between 20,000 an'.l 35.000 feet. We eX""ect) <br /> <br />with the nroner conditions. Observations of the contrail laiJ out by its <br /> <br />engine as well as. nerhans. the nucleation of nencil-thin ice crystal trails <br /> <br />from a small cylin-1er of liqui'l carbon :iioxi]e allowe-\ to exhaust slowly through <br /> <br />a small valve. will nrovi:lethe nilot with enough information to fin.] the <br /> <br />area. When he is sure conditions are nroner, he will fly a circle nattern <br /> <br />a..,nroximately three miles in diameter and burn one 285-gram silver ioii,'e flare. <br /> <br />If a cloud is nucleated. the subsequent growth and diffusion will be followe! by <br /> <br />the aircraft and by a ground ocserver(if nossiblelfor as long as is nractical, <br /> <br />nerhans one-half hour. In addition to nucleating our own cloues. we also hone <br /> <br />to stu:y natural cirrus and nersistent jet contrails for' comnarison. With some <br /> <br />goo,l fortune. all three tynes of cloud might be stu:lie \ on one flight. <br /> <br />Clear air seeding from aircraft using known effective artificial ice <br /> <br /> <br />nuclei is" not new. Vincent Schaeffer(using 'iry ice)an'i Bernar:l Vonnegut(using <br /> <br />silver iodi2e)conducted trials during the Project Cirrus studies of the General <br /> <br />Electric Comnany.during the early 1950's. More recently E. K. Bigg(using Jry <br />