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<br />APRIL 1990 <br /> <br />DESHLER, REYNOLDS AND HUGGINS <br /> <br />295 <br /> <br /> <br /> <br />o. <br /> <br />MESO'IET:LWC Sigrcl Peak <br /> <br />MESO'IET:LWC Squaw Peak <br /> <br /> <br />-v <br /> <br />UQUlD (MMl AT KlNGVALE <br /> <br /> <br />~.~J <br /> <br />o.~ <br />1200 <br /> <br />1400 1600 <br /> <br />i ..1; <br />= ;; <br />I 5i <br />,{ ~^ w7vf;~~J \P~"'vv.. <br /> <br />1800 <br /> <br />2000 <br /> <br />2200 <br /> <br />0000 <br /> <br />TIME (GMT) <br /> <br />FIG. 4. Liquid water measurements from the radiometer at KGV, and the icing rate meters <br />at Signal Peak and Squaw Peak. <br /> <br />below aircraft altitudes. The cloud was classified as <br />seedable based on liquid-water measurements by the <br />radiometer. <br /> <br />2) FIXED TARGET EXPERIMENT 1, 1800-1900 UTC <br /> <br />The seed1ine location for targeting KGV was deter- <br />mined with the OTM targeting model, using soundings <br />from SHR and KGV at 1500 and the aircraft ascent <br />sounding. A nucleation time lag of 5 min was assumed <br />for the crystal targeted to fall at KGV. The seeder air- <br />craft flew the seeding pattern, three 37 km long lines, <br />from 1744 to 1801, but no seeding material was re- <br />leased. Thus these seed1ines were placebos (P 1-P3 ). <br />The cloud physics aircraft sampled these lines from <br />1803 to 1837. The first four penetrations of P3 were <br />accomplished using the aircraft pointer, which indi- <br />cated that P3 advected from 1960 at 17.3 m S-I. Using <br />this advection and comparing seedline motion with <br />the aircraft flight track indicated that P3 was penetrated <br />an additional five times after the pointer information <br />was lost. The first two lines were not sampled. <br />Time series plots of the aircraft measurements during <br />these penetrations are shown in Fig. 5. Wind tunnel <br />tests have shown the CSIRO liquid water probe to be <br />accurate to within 10 percent of icing cylinder mea- <br />surements (King et. al. 1985), and to be sensitive to <br />droplets> 40 ~m as well as smaller droplets (King et <br />al. 1981). Measurements from the FSSP on the aircraft <br />have been corrected according to the method of Cerni <br />( 1983). This corrects sizing errors to <0.5 ~m, although <br />the instrument still artifically broadens the cloud drop <br />spectra by several micrometers. Both uncorrected and <br />corrected particle concentrations are shown for the 2D- <br />C and 2D-P. The corrected concentrations are obtained <br />by removing "zero area" images, and images created <br />by particles shattering on the probe or water streaming <br />from the probe tips. For the SCPP measurements zero <br /> <br />area images are the primary source of the difference <br />between the corrected and uncorrected particle con- <br />centrations. The statistical sampling error for all of the <br />particle probes (FSSP, 1D-C, 2D-C, 2D-P) is No.5. <br />Since concentrations are generally> 10 per unit volume <br />the counting errors are generally <30 percent of the <br />particle concentration, although this error can exceed <br />50 percent for low concentrations measured by the 2D- <br />P. The display of the FSSP, 2D-C, and 2D-P data as a <br />cumulative size distribution is quite useful to see re- <br />gions of new ice (high concentration of predominantly <br />small particles) and mature ice (even distribution of <br />all particle sizes), as well as liquid cloud characterized <br />by evaporation, growth, or regions oflarge water drops. <br />Note that with this display, errors in the FSSP data <br />caused by ice (Gardiner and Hallett 1985) can be di- <br />rectly observed since they would produce a flat size <br />distribution in the FSSP data. As can be seen this is <br />not a problem for any of the data presented here. <br />The lack of ice nuclei concentrations in the aircraft <br />data (Fig. 5) indicates clearly that this cloud was not <br />seeded. The following discussion will focus on the ice <br />particle measurements to show that they are generally <br />consistent with a non seeded cloud, although ICC were <br />increasing at the seedline. At time to no liquid water <br />was observed at the seedline, although there was a small <br />region of ice with ICC > 20 L -1. At this time the re- <br />search aircraft was 300 m above the seeder aircraft ma- <br />neuvering for descent to 3 km, the treatment level. As <br />the research aircraft descended and made its pass <br />through P3 5 min downwind, liquid water up to 0.25 <br />g m -3 was observed near the seedline. The mean drop- <br />let diameter was 1 0 ~m. The ICC was minimal although <br />a few irregular crystals were observed. At the 8 min <br />pass liquid water had increased in areal extent. In close <br />proximity to P3, ICC were increasing and the drop size <br />distribution broadening. Line P3 was then penetrated <br />