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<br />13 <br /> <br />Melting <br /> <br />Ice particles falling below the melting level in the atmosphere gradually <br /> <br />develop a I iquid layer and melt into raindrops which continue their fall to the <br /> <br />..; <br /> <br />ground. Some ice particles can (if large enough) reach the ground as ice. Large <br /> <br />" <br /> <br />melting ic:e particles (hail) will develop a liquid layer which then is shed in the <br /> <br />particle's wake as blown off small liquid drops. <br /> <br />At temperatures warmer than 0 oc a falling hailstone will melt at a rate <br /> <br />determined by the balance between the conduction of heat from the air, the transfer <br /> <br />of latent heat by the condensation of water vapor onto the hailstone, and the <br /> <br />accretion of I iquid water drops having temperatures warmer than the hailstone. <br /> <br />Fol lowing the development of Wisner, et al. (1772), the expression for the <br /> <br />rate of mass loss by melting of a falling hailstone in unit time can be written as: <br /> <br />(when T > T , i.e., warmer than freezing) <br />o <br /> <br />;, MO = - [1.6 +O.31/Re"'1 [ ~foH~ (T - To)+lv ~MtC] <br /> <br /> C ~Ma <br /> - ~(T-T) <br /> Lf 0 Tt <br />where MD = mass of hailstone of diameter D <br /> Re = Reynolds number of hailstone <br /> K = thermal conductivity of air <br /> a <br /> T = temperature of air <br /> T = 273.16 OK <br /> 0 <br /> L = latent heat of condensation <br /> v <br /> Lf = latent heat of fusion <br /> <br />(eq. 12) <br /> <br />';.' <br />