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<br />1. The liquid water content in many of the HIPLEX-1 clouds decayed ra- <br />pidly due to entrainment, accounting for their low natural precipitation <br />efficiency. The liquid water depleted faster by entrainment than <br />seeding could exploit it to develop precipitation. In this respect, the <br />cloud selection criteria had failed to provide the intended sample of <br />clouds whose liquid water would persist at least 30 min after treat- <br />ment as required by the physical hypothesis. <br /> <br />2. Precipitation development in most of the seeded clouds did not <br />proceed via the graupel process as hypothesized. Primarily because of <br />the high ice concentrations produced by the seeding, a combination of <br />aggregation and low-density accretion onto the loose aggregates was the <br />dominant precipitation process. Only small raindrops were produced in <br />this way, which were insignificant in comparison to those produced by <br />the natural accretional growth process. In this respect, the seeding <br />operation failed to produce the target concentrations of 10 per liter <br />without penalty. <br /> <br />3. Precipitation development proceeded as hypothesized in those clouds <br />with sustained updrafts such that the main precipitation growth occurred <br />at temperatures colder than -10 oC (above the seeding level). These <br />results are supported by calculations (Cooper and Lawson, 1984; Cooper, <br />1984) which show that accretional growth is more rapid and more effi- <br />cient at about -12 and -20 oC. In this respect, the seeding hypothesis <br />which emphasized the warm temperature region of the cloud was in error <br />and the choice of seeding levE~l was, perhaps, too low since it failed to <br />take advantage of the region of rapid development of graupel from ice <br />crystals in most cases. <br /> <br />29 <br />