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I I I I I I I I I I I I I I I I I I I 3. Obsenations within the Seeding Plumes Prior to the start of seeding on 26 January the mobile radiometer ascended the plateau, tra\'eling from HQ to RRS (Fig. 1) between 0910 and 1020. Data from this traverse are shO\..n in Fig. 41. During this period most of the liquid water was observed over the Sanpete Valley and the lower foothills of the plateau. Along the edge of the top of the Plateau and at RRS very little liquid water was observed. Between 1045 and 1245 six passes were made with the mobile radiometer between RRS and the Junction of Highways 31 and 264 (Fig. 1). The temperature at the surface ranged from -6'" to -8". Liquid water depths rarely exceeded 0.04 mm on these passes, and only occasional light sno\\fall was noted. This is consistent with the very weak radar echo (Figs. 38-40) over the plateau prior to 1100. Beginning at about 1250, and continuing through 1600, the mobile radiometer made ten passes in tandem with the Ctah instrumented van (called Starship) bet\veen RRS and Jet. 311264. The Starship monitored SF", ice nuclei and re{;{)rded 2D-C images along the route. Figure 42 shows data from the first two passes between 1250 and 1328. Radar returns over the highway were increasing during this time, and light to moderate sno\\:fall was observed. On both passes SF 6 and ice nuclei plumes were encountered at about the same location (1.5-3.0 Ian northwest of RRS) \vithin a region of slightly enhanced liquid water. On the first pass the SF 6 plume was coincident with a small scale liquid maximum, while the second plume interception matched a liquid water minimum, so it is not clear from these two passes if seeding was depleting the cloud liquid. The temperatures at the surface were near the threshold of activation for the AgI solution in use. Also between 1314 and 1317 the research aircraft, flying at about 3250 m on its west track, encountered SF(jand ice nuclei plumes. The locations of the Starship and aircraft plumes are shown in plan view in Fig. 43. With the southwest to west-southwest flow detected at HAS and RRS, it is apparent that the Starship plume originated from the HA.S generator. The aircraft, however. was apparently detecting mainly the AHS generator plume, although some SF 6 values slightly above detectable background were noted 4-9 kIn north ofRRS, and these might have been the plume from HAS. Although the aircraft flew its east and we~t tracks numerous times between 1124 and 1400, the plume encountered shortly after 1300 was the most definitive and accounted for nearly all of the SFfdetected on this flight. On its t\\l0 stops at RRS bet\\leen 1248 and 1328 the van detected no SF6 54