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Last modified
7/28/2009 2:35:20 PM
Creation date
3/11/2008 11:30:28 AM
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Template:
Weather Modification
Title
Harold D. Orville Symposium - Forty Years of Modeling Clouds and Weather Modification
Date
4/26/2003
Weather Modification - Doc Type
Report
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<br />I <br /> <br />I <br /> <br />JS <br /> <br />ACClJIIII.Arol RAIN <br /> <br />JO <br /> <br />I <br /> <br />A2S <br /> <br /> <br />I <br /> <br />Ela <br />l!: <br />;i I' <br />'" <br />.. <br />i" <br /> <br />I <br /> <br /> <br />to u to " ~ ~ n n N ~ <br />DISTAllCE FIlIlIllEfT llOUIIllMf (_, <br /> <br />I <br /> <br />ACClMll.Altll IlAll <br /> <br />! <br /> <br /> <br />I <br /> <br />iE' <br />~ <br />... <br />co <br /> <br />;il <br />'" <br />~ <br />i <br />I <br /> <br />I <br /> <br />, <br />~ to u to " ~ n n n N 2S <br />DISTANCE .FRll'lltfT lIOUIIIAIlf (_) <br /> <br />I <br /> <br />IS <br /> <br />ACCl.IU.AlED Mill <br /> <br />i <br />-I' <br />'" <br />i <br />i, <br />:f <br /> <br /> <br />o <br />I' <br /> <br />IJ U to I' i!O <br />DISTAIa fIliII lEfT llOUIIllMY (_, <br /> <br />1I <br /> <br />n <br /> <br />ACCIJIlt.ATED HAIL <br /> <br />r.5 <br /> <br /> <br />'" <br />t: <br />:!: I <br /> <br />~ <br />i <br /> <br />, <br />15 <br /> <br />II II " zo <br />DISTAMCE fIliIILEfT IOUIIDARY (hi) <br /> <br />14 <br /> <br />z. <br /> <br />12 <br /> <br />Fig. 12. Comparison of accumulated rain (top panel) and hail (lower panel) deposited at the model suiface <br />between 63 and 81 min as afimction of horizontal position. The solid line gives results for the natural <br />(unseeded) case, the dot-dash line is for the .c02 seeded case, and the dotted line is for the AgI seeded case. <br />Results for the storm complex are shown on the left, that due solely to the feeder cell on right. <br /> <br />I <br /> <br />I <br /> <br />Seeding experiments similar to those conducted in <br />the field in Alberta were simulated for this case. These <br />involved seeding the feeder cell early in its active <br />development phase with dry ice or silver iodide <br />introduced near cloud top (temperature -lOoe). The <br />model simulations of these seeded cases captured some <br />of the observed seeding signatures detected by radar <br />and aircraft. In these model experiments, dry ice <br />seeding produced a slightly stronger response than AgI <br />seeding relative to inhibiting hail formation. In both <br />seeded <br />cases, production of precipitating ice was initially <br />enhanced by the seeding, but retarded in the later <br />stages, as can be seen by comparison of the simulated <br />radar reflectivity fields for the natural case (Fig. 10) <br />with that for the CO2 seeded case (Fig. 11). The net <br />result of seeding on the feeder cell was slightly reduced <br />hail accumulations and modest increases in surface rain <br />as shown in Fig. 12. It should be noted that seeding did <br />not reduce hail from the main storm cell. <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />More recently we have simulated effects of silver <br />iodide seeding on the severe hailstorm case of 28 June <br />1989 from. the North Dakota Thunderstorm Project <br />(NDTP). The series of cells which develop in the <br />simulations reported in Farley et al. (2003) display <br />consider <br /> <br />I <br /> <br />I <br /> <br />I <br /> <br />able variability in hail and precipitation formation and <br />evolution, consistent with the observed character of the <br />convection. The amount of hail produced was <br />dependent on the assumption of the presence of <br />coalescence (a warm rain process) and whether the hail <br />cell was growing in isolation from the other cells in the <br />storm system. Figure 13 illustrates the evolution of the <br />various cells for Case I, which applied an <br />auto conversion threshold of 4 g/kg. Another case (Case <br />II) was run with an unattainably large value of the <br />autoconversion threshold which made the warm rain <br />process inactive. The large-scale features and dynamic <br />characteristics of Case II were very similar to those of <br />Case I. <br /> <br />The largest hail in these simulations was produced <br />from an isolated cell (Cell 3) with a weak warm rain <br />process active (Case I). For Case II, the precipitation <br />from Cell 3 was markedly reduced. These pronounced <br />differences in precipitation production for Cell 3 in the <br />two cases and the anomalous production of large hail <br />from Cell 3 in Case I prompted a number of cloud <br />seeding simulations, most of which were targeted at <br />Cell 3. Dramatic differences were induced by the <br />seeding if it was performed early in the life of Cell 3 at <br />cloud top (near the -lOOC level). <br /> <br />25 <br />
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