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<br />. <br /> <br />. <br /> <br />e <br /> <br />CHAPTER I I <br /> <br />. <br /> <br />LITERATURE REVIEW <br /> <br />2.1 REVI~ OF DIFFUSIONAL AND AOCRETIONAL GRafl'H KDELS <br /> <br />. <br /> <br />e <br /> <br />The theory of growth of ice particles by diffusion and <br /> <br /> <br />accretion in a cloud of supercooled droplets was reviewed by <br /> <br /> <br />Houghton (1950). He showed that ice crystal growth by diffusion <br /> <br /> <br />was more rapid than accr:etion in the early stages of precipitation <br /> <br />development. The diffusional process was most rapid when the <br /> <br />atmosphere was water saturated at -15oC and the crystals were of <br /> <br />dendri tic form. The rate of growth by accretion was dependent on <br /> <br /> <br />the mass of the particle, the liquid water content (LOC) of the <br /> <br /> <br />cloud, the maJian cloud droplet diameter and the dispersion of the <br /> <br /> <br />cloud drop-size distribution. <br /> <br /> <br />Koenig (1971) and Jayaweera (1971) developed theories on lce <br /> <br /> <br />crystal growth by using enpirical relationships to distribute the <br /> <br /> <br />mass into crystalline shapes. The growth rate equations were <br /> <br />based on Fick's law of diffusion. For nonspherical ice crystals <br /> <br />the analogy between an electrostatic potential field surrounding a <br /> <br /> <br />charged body and the vapor density field surrounding a similarly <br /> <br />shaped ice crystal was utilized. The equations allowed for the <br /> <br /> <br />effects of forced convection ("ventilation") caused by the fall <br /> <br />.e <br /> <br />. <br /> <br />.e <br /> <br />. <br /> <br />'. <br /> <br />. <br /> <br />I- <br />