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<br />1452 <br /> <br />JOURNAL OF APPLIED METEOROLOGY <br /> <br />VOLUME 35 <br /> <br />a. _ 0.20 <br />o.c <br />a.e 0.10 <br />cE <br />C'i - 0.00 <br /> <br />- <br />9 <br />- -4 <br />a. <br />::E <br />w <br />t- -8 <br />- 0.4 <br />('f) <br />E <br />-- <br />S <br />0 0.2 <br />3: <br />...I <br /> 0.0 <br /> 2700 <br />- <br />E <br />- <br />~ 2400 <br /><C <br /> 2100 <br />- 20 <br />t- <br />a. <br />a. <br />co 10 <br />II. <br />U) <br /> 0 <br /> 18.80 <br /> <br /> <br />T <br /> <br /> <br />1850 <br /> <br />h <br /> <br />::::J <br />20~ <br />as <br />Ui <br />>. <br />.... <br />10~ <br />U <br />, <br /> <br />o ~ <br /> <br />1852 <br /> <br />1854 <br /> <br />1856 <br /> <br /> <br /> <br />18.85 18.90 <br />Time (UTe) <br /> <br />18.95 <br /> <br />FIG. 22. Same as Fig. 18 but for 9 February 1993 along-ridge pass for a seeded plume initiated <br />from site 7. The 11-s lag, as was shown in Fig. 18, should be applied to the SF6 trace. <br /> <br />The question arises of whether these enhanced <br />regions of liquid water may be associated with the up- <br />draft portion of the lee wave and the enhanced ice a <br />result of ice multiplication, as both days indicated nee- <br />dle crystals in these regions. The purpose of releasing <br />the tracer SF6 was to avoid any confusion between nat- <br />ural and artificial ice production. The ice crystal sig- <br />nature shown for 17 February has a distinct SF6 tag. It <br />is highly unlikely that at just this location a distinct lee- <br />wave updraft would occur and not appear anywhere <br />else along the flight track. The ice crystal signature <br />shown for 9 February is not as definitive since the SF6 <br />signature is not as distinct. The similarities of the seed- <br />ing effects on two different days, however, suggest that <br />a dynamic seeding effect may be occurring. <br />Following Super and Boe (1988) I-min averages <br />(about 4.8 kIn of flight time) of crystal concentrations <br />and calculated precipitation rates were made for the 17 <br /> <br />February site 9 seeded plumes. These averages were <br />made the minute prior to entering the SF6 plume (non- <br />seeded), the minute centered on the plume (seeded), <br />and the minute following the plume (nonseeded) for <br />all six plumes sampled from site 9. The mean of the <br />six I-min averages centered on the seeding plume <br />showed a 33% increase in ice crystal concentration and <br />an 18% increase in calculated precipitation rate com- <br />pared to the mean of the six I-min averages on either <br />side. <br /> <br />b. GUIDE model plume and crystal trajectory <br />simulations for 17 February <br /> <br />The GUIDE is a simple two-dimensional kine- <br />matic model incorporating Gaussian plume disper- <br />sion (Rauber et al. 1988). The model is used <br />operationally to predict the area of effect from seeding. <br />