OCR Text |
Show of 1 and a crystal capture area equivalent to half a solid disc, (7T r 2 / 2 ). resulting rimmg rates ar e also shown in T able Al. His The abo ve calculations show that when crystals are small, and the collection efficiency is small, growth is by diffusion. But as soon as the crystal achieves a radius of about 100 µ, accretion growth becomes predominant. 4. Fall Ve locity of Rimed Crystals Empiricai data of Nakaya and Terada (1935) show that rimed crystals fall at velocities of about 1 m sec -1, and graupel pellets considerably faster. The fall velocity of rimed dendrites can be given as, v=kd 0. 3 m ( 11) wh e re k varies with snow flake type (K = 210 for dendrites), and d is melted m crystal diameter. Assuming dm ?:' r, thus, V = k r 0. 3 ( 12) The general velocity equation in differential form is: (13) dZ = vdt with substitution yields, 4 0. 3 2. 48 x 10 k r dr dZ or z = (14) 4 ( 1. 3 - r 1. 91 x 10 k r Z 0 (15) -6 (16) 8. 15 t z = X 10 Z 0. 202Z 0.77 o. 77 (1 7) ( 18) · h' d b ·ming after falling a cloud This equation set gives the size r Z ac 1eve Y ri · 1 1 ·t t point Z. Table A2 distance Z in time t , as well as the termma ve oci Y a 2 · g· en above It can be seen presents results obtained from the expre ss1ons 1v · 345 |