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<br />. <br /> <br />7 <br /> <br />. <br /> <br />underestimated. With these data, theoretical results can be examined and <br /> <br /> <br />corrected, and the theoretical basis for microphysical model fonnulation can <br /> <br /> <br />be improved. Furthermore, important quantities such as axial ratios and <br /> <br /> <br />apparent densities, which must be empirically determined, can properly be <br /> <br /> <br />applied to the models. Finally, the experimental data can be used to compare <br /> <br /> <br />with computer output and help critique numerical models. Without these <br /> <br /> <br />data, important checks could not be made and speculation would needlessly <br /> <br /> <br />replace fact. <br /> <br /> <br />Since around 1980, the completions of at least three experimental <br /> <br /> <br />investigations have been carried out to resolve the problems associated with <br /> <br /> <br />this data void. Kowa (1981), Gong and Fukuta (1985) and Takahashi and <br /> <br /> <br />Fukuta (to be published) have performed laboratory experiments in which ice <br /> <br /> <br />crystals were suspended under simulated conditions of natural growth. <br /> <br /> <br />Using a unique supercooled cloud tunnel contructed at the University of <br /> <br /> <br />Utah, these investigators were able to grow crystals for periods up to 30 <br /> <br />minutes. The crystals' growth environment was first prepared in a fog <br /> <br /> <br />chamber. In the chamber, steam was injected into cold air to generate <br /> <br /> <br />supercooled fog at some predetermined number and mass concentration. <br /> <br /> <br />The fog became homogeneous with respect to temperature and moisture <br /> <br />content due of turbulence callSE'd during the fog generation process. Next, the <br /> <br /> <br />resultant fog was sucked into a vertical wind tunnel where the crystal was <br /> <br /> <br />freely suspended without creating unsteady and unstable motion so that the <br /> <br /> <br />particle could remain in the tunnel while growing and falling. Thus, the <br /> <br /> <br />investigators were able to gather basic data such as mass, dimensions and <br /> <br /> <br />terminal velocity for ice crystals that have grown in a controlled, cloud <br /> <br /> <br />simulating environment for extended periods of time. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br />