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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />2 <br /> <br />cOl1ditions. These results were sufficiently unexpected and important that <br /> <br />an additional field investigation was justified. <br /> <br />Our purposes in studying these storms ,vere to investigate the dynamical <br /> <br />and microphysical processes in both natural and seeded storm situations, to <br /> <br />evaluate the seeding potential of these storms, and to search for seeding <br /> <br />effects. We utilized both the Wyoming Queen Air (NIOUW) and an NCAR Queen <br /> <br />Air (304D) for airborne observations of these storms. The Hyoming Q/A had a <br /> <br />ne,vly ins taIled cloud physics package, while the NCAR Q/ A had recently been <br /> <br />equipped ,vith an inertial navigation system and air sensing probe for detailed <br /> <br />,vind and turbulence measurements. <br /> <br />The effort directed at assessing the possibility of seeding these storms <br /> <br />assumed the folloHing necessary conditions for successful seeding to increase <br /> <br />precipitation: <br /> <br />1. The presence of supercooled ,\'ater. It is assumed that the seeding <br /> <br />process operates by producing ice in a cloud consisting mostly of supercooled <br /> <br />water, and that the precipitation develops through the conversion of this <br /> <br />Hater to precipitation-size ice particles. Supercooled water may also be <br /> <br />important for the nucleation process itself, since AgI is apparently most <br /> <br />effective as a contact nucleus. <br /> <br />2. Relatively 10\07 ice crystal c~ncentratic:.~s. It has generally been <br /> <br />assumed that for efficient precipitation to occur ice crystal concentrations <br /> <br />on the order of 1-10 per liter are sufficient. The optimum concentration <br /> <br />depends on updraft, temperature, and liquid water content of the clouds as <br /> <br />,,,ell as the relative importance of vapor growth vs. accretional grmvt:lt of the <br /> <br />precipitation elements. Although the optimum concentration :is uncertain,- <br /> <br />there is some point at vlhich further increase of the i.ce crY~J l:a1 corccntraU 011 <br /> <br />would only lead to oversecding and a reducti.on of precipitation. <br />