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<br />1170 <br /> <br />JOURNAL OF APPLIED METEOROLOGY <br /> <br />VOLUME 27 <br /> <br />~~ <br />~E <br />(l)m <br />40 <br /> <br />~ <br /> <br />I <br /> <br />~- <br /> <br />ENE <br /> <br />"II <br /> <br />z <br />o <br />fi <br />a:: <br />... <br />z <br />w <br />o <br />z <br />o <br />o <br />~20 <br />o <br />~ <br />a:: <br />: <br />w <br />2 <br />z 10 <br />>C <br />W <br />2 <br /> <br />860319 <br />1159-1310 mst <br />FIRST 6 PASSES <br /> <br />-. <br />I <br /> <br />~- <br />\~SW <br /> <br />~ <br /> <br />I~ <br /> <br />1" <br /> <br />1 <br /> <br /> <br /> <br />o <br /> <br />5 10 <br />'DISTANCE WSW FROM SNOW LA8 IN KM <br /> <br />15 <br /> <br />FIG. 4. Mean IPCs and SLW contents recorded on six crosswind passes through the seeding plume during the ground-based <br />seeding experiment of 19 Mar 1986. AgI plume edges are noted by vertical lines at the top of the IPC plot. <br /> <br />the experiment. No precipitation gages were located <br />under the seeded zone, and the closest crosswind gage <br />recorded no snowfall. <br />Figure 3 shows buffer-by-buffer IPC (discussed in <br />Part I) and 1 Hz SL W observations for the sixth pass <br />at 3.8 km. The width of the seeded zone is 0.8 km, <br />near the median of the seven passes. The fine-scale <br />structure in the essentially instantaneous sample is well <br />illustrated. No definite SLW reduction was observed <br />in association with the seeded zone on this or the other <br />six passes, though there was some suggestion of it. <br />The mean IPC and SLW for the first six 3.8 km <br />passes are shown on Fig. 4, along with the AgI plume <br />edge positions estimated for the four passes having suf- <br />ficient ice nucleus counts. In general, less SL W was <br />observed to the WSW. The seeded zone is quite evident, <br />but it meandered over 3.2 km (from 5.1 to 8.3 km <br />WSW of the Snow Lab) during the course of the ex- <br />periment. <br />Comparison of the microphysical characteristics <br />within the seeded zone with those of nearby natural <br />cloud was accomplished by defining 2 km-wide cross- <br />wind control zones to the ENE and WSW of the seeded <br />zone. One km-wide buffer zones separated the seeded <br /> <br />and control zones. Ice particle sizes, concentrations and <br />habits were calculated for each zone and pass by the <br />method in Holroyd (1987). The means for each seeded, <br />buffer and control zone for passes 1, 2, 3 and 6 are <br />shown in Fig. 5. (Passes 4 and 5 were excluded due to <br />their extremely narrow plume widths and low AgI <br />counts, which suggests that they were nearer to plume <br />top than the other passes.) Ice particle concentrations <br />of about 3 L -1 were found in the control zones (ENEC, <br />WSWC) and buffer zones (ENEB, WSWB), while IPC <br />averaged 26 L -1 in the seeded zone (SZ). Most of the <br />increases arose from ice particles with a maximum di- <br />mension of less than 1 mm. (Note: The length limits <br />were chosen to provide a logarithmic scale; log 0.10 <br />= -1.0, logO. 16 = -0.8, logO.25 = -0.6, etc.) Most ice <br />particles within the seeded zone were classified as <br />spherical, hexagonal or irregular, with a lesser increase <br />in dendritic crystals. The mean temperature at the <br />sampling level was -140C, so that dendritic crystals <br />would be expected with SL W present (Magono and <br />Lee 1966). <br />The sampling line was only 6.3 km downwind of <br />the generator, and the generator itselfwas not in cloud. <br />The aircraft-measured wind speed was 14 m S-I over <br />