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<br />. <br /> <br />0fAP1'ER 3: Plm:IPITATION PROCESSES <br /> <br />. <br /> <br />3.1: Ice nucleation. Filter samples of ice nuclei were collected <br /> <br />during the flights in Montana, am most were processed in the Wyoming <br /> <br />. <br /> <br />filter processor (described by Gordon and Vali, 1976). The resulting <br /> <br />concentrations for the samples from one year (1979) are shown in Fig. <br /> <br />3 . 1. The samples were exposed at a var iety of fl ight al ti tudes, but <br />emphasized the boundary layer air and the air near the -lOoC level. For <br /> <br />.. <br /> <br />most of the samples, the volume collected on the filters was about 100 <br /> <br />L, but there were a few extreme samples of from 30-900 L. The <br /> <br /> <br />processing in each case was perfonned at a temperature 10C colder than <br /> <br />. <br /> <br />that plotted, but at 99% relative humidity; the activity of filter <br /> <br />. <br /> <br />10.00 <br /> <br /> <br />1...J 1.00 . <br />W <br />...J <br />U 0.10 <br />:J <br />Z <br />W . <br />U <br /> 0.01 <br /> <br />0.00 <br />-10.00 <br /> <br />-15.00 <br /> <br />-20.00 <br /> <br />. <br /> <br />TEMPERATURE (OC) <br /> <br />Fig. 3.1: Concentration of ice nuclei as a function of temperature. Each <br />point represents the results fran one membrane filter exposed during <br />the 1979 HIPLEX (Montana) field season. The filters were processed in a <br />conventional filter processing chamber, as described in the text. <br /> <br />. <br /> <br />36 <br /> <br />. <br />