Laserfiche WebLink
<br />Table 1 lists the results of each of the seven flights. Table 2 <br />aggregates the flights into each of the discrete monthly "seasons" that were <br />selected for the field programs; March, 1983, December, 1983 and February, <br />1984. The data in Table 2 are the arithmetic averages of the one-second values <br />used in the total flight results of Table 1. Cumulative frequency plots of all <br />the one-second liquid water and and ice crystal values are presented in Figures <br />2 and 3 for each of the combined "seasonal" field programs. <br /> <br />The results suggest that liquid water values in excess of 0.1 g m-3, <br />are relatively frequent. Figure 2 indicates that over 50% of values exceed this <br />value for all three seasons. The March cases have the highest values, with an <br />average of 0.23 g m-3 and with almost 20% of the values exceeding 0.5 g m-3 <br /> <br />Average ice crystal concentrations for all flights are consistently <br />less than 10 L-1 for most cases. Figure 3 shows that for all data sampled, less <br />than 25% exceed thi s val ue. March measurements show the hi ghest ice crystal <br />values, with February cases showing average values of less than 2 L-1. <br /> <br />This combination of relative high liquid water values compared to ice <br />crystal concentrations yields high "seedibil ity" ratios as indicated in the <br />tables. Average values for these are on the order of a few hundred, suggesting <br />a notable "seeding potential" using a minimum benchmark of ten (Heggli, et al, <br />1983). Further analysis of this data will involve assessment of the <br />precipitation efficiency of these clouds. (Krauss et al, 1983). <br /> <br />The preliminary results of a more detailed analysis of aircraft data <br />collected on 9 February 1984 have al so been examined. A total of 17 cloud <br />penetrations were made during flights on this day. These measurements were made <br />near the upper edge of a stratocumulus deck that extended across the divide and <br />became mostly broken to the east. Cloud bases were approximately ten thousand <br />feet with tops just above twelve thousand feet. <br /> <br />The absolute amount of liquid cloud water is a major consideration for <br />seeding assessment. The presence of sufficient liquid water, with the <br />concurrent absence of natural ice crystals, indicate that a potential for <br />seeding exists. The distribution of the relative frequency of occurrence of <br />one-second averages of in-cloud liquid water contents is given in Figure 4. <br />Over 55% of the values exceed the 0.1 g m-3 minimum for a seeding potential <br />cited for the Sierra Mountains (Marwitz and Stewart, 1981). Ice crystal <br />concentrations were all less than 10 L-1, commonly around 1 L-1. This <br />combination of available liquid water and low ice would suggest that many of <br />these clouds would meet the criteria for being "seedable" (Heggl i et al., <br />1983 ) . <br /> <br />Cloud liquid water values were also measured during flights on 15 and <br />27 March, 9 and 10 December, 1983 and 1 and 8 February, 1984. The average <br />liquid water values were generally 0.1 to 0.2 g m-3 with peak values <br />approaching 0.9 g m-3. Analysis of these flights is continuing. <br /> <br />1 <br /> <br />52 <br />