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<br />;. <br />, <br /> <br />. <br /> <br />1.2 Wintertime orographic cloud seeding <br /> <br />: .; <br /> <br />l, <br /> <br />Since the Drst conceptual models (Bergeron, 1949; Ludlum, 1955) to increase <br />winter snowpack on mountain ranges by seeding clouds with sUver iodide or dry ice <br />several operational and research orographic cloud seeding programs have been conducted <br />worldwide. The experiments can be divided into two groups, namely statistical <br />and physical experiments (Reynolds, 1988). The earlier experiments emphasized a <br />statistical approach whereby clouds were seeded in a randomized manner and the results <br />were evaluated through statistical analyses of data obtained mainly from precipitation <br />measurements at the sunace. The physical experiments in retrospect were characterized <br />by a greater emphasis on physical measurements in clouds and at the sunace to document <br />the physical chain ol events leading to precipitation !ormation in seeded and unseeded <br />clouds. . Elliott (1986), Reynolds (1988), Reinking and Meitin (1989), and Super (1990) <br />provides & review of these experiments. Although there is general consensue that seeding <br />does increase precipitation under certain favourable conditions (American Meteorological <br />Society AMS, 1985), there is very little agreement on the magnitude and manner or the <br />increases or decreases in precipitation due to cloud seeding. There are still major gaps in <br />our understanding of both the naturally and modified evolution of winter orographic cloud <br />systems. <br /> <br />. <br /> <br />j- <br />i <br />i. <br /> <br />1-'. <br />I <br />I <br />1 <br /> <br />r ' <br /> <br />Several key areas where scientific knowledge is lacking or inadequate are: <br /> <br />\.-, <br /> <br />i) The three-dimensional flow fields over mountainous terrain and its eft'ect on cloud <br />and precipitation development. <br /> <br />, <br />L . <br /> <br />ii) The transport and dispersion olseeding material in both time and space over <br />mountainous regions. <br /> <br /> <br />iii) The temporal and spatial evolution and variability ol CLW (cloud liquid water) <br /> <br />f''-' <br /> <br />. <br /> <br />5 <br />