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1762 '5.00 JOURNAL OF APPLIED METEOROLOGY VOLUME 17 em =23.20 C BASE=3 km M. R. = 11.3g kg-I 12.00 200JJ.m - E = 9.00 :J: t- o.. W o o ::> o 6.00 ..J U :::t ::> :::t z i 3.00 12.00 18.00 UPDRAFT (m ,-oj 24.00 FIG. 2. Variation of the minimum cloud depth required for a particle to grow large enough to begin to fall through the cloud as a function of updraft speed for initial' hygroscopic drop diameters of 5-400 pm (model computations). high enough to freeze and subsequently grow large enough to fall through the updraft and emerge at the melting level as 1-,3 cm hailstones. However, many more precipitation particles would be produced by the 40 and 100 }Lm seeds, which would undergo drop breakup three and six times, respectively, prior to freezing. - Fig. 1f illustrates the very strong updraft case (25 m S-l). As would be expected, the smaller seeds are all ejected out the top of the cloud, whereas the 100 and 200 }Lm seeds grow large enough to fall back through the updraft as hail. The same general pattern is apparent for higher based clouds such as are found in the Great Plains regions. However, since these clouds have lower liquid water contents, the particles take a higher trajectory above cloud base to grow large enough to fall out, and therefore require a greater cloud depth. Fig. 19 illustrates this point well: The same in-cloud moist adiabatic temperature was used as in the preceding example, but a higher cloud base (3 km) was assumed. Comparing this graph with Fig. 1c (both are for 5 m S-l updrafts), it can be seen that the particles travel 200-700 m higher above cloud base in the high-base situation. Quite a dramatic change is apparent in the high- base situation compared to the low when updraft speeds are 10 m S-l and greater. Since the hydro- meteors travel into colder regions sooner in the high- base clouds, they become ice particles earlier in the growth stage. A large-drop accumulation wne was shown to occur in Fig. 1d for all but the 5 }Lm hy- groscopic seed. However, in the high cloud-base 30.00 situation (as illustrated in Fig. 1h), all seeds of initial size of 40 }Lm or smaller freeze prior to reaching water breakup size. In this case all seeds larger than 100 }Lm initial size would grow large enough to break up and float near a balance level. These characteristics are further accentuated in the colder cloud cases. Figs. 1i and 1j illustrate computer runs for an in-cloud moist adiabatic temperature of 160C, a 3 km cloud base, and updraft speeds of 5 and 15 m s-\ respectively. Notice the much lower liquid water content values and lower temperatures, which account for the absence of a drop breakup' wne in Fig. 1i. It also accounts for all the seeds 5-40 }Lm being blown out the top of the cloud with a 15 m S-l updraft (see Fig. 1j). For the same updraft speed but more moist. cloud conditions these same size particles grew large enough to fall back to cloudbase (see Fig. 1e). b. Syntheses of case studies A large number of graphs were generated by the computer model for various initial conditions. Certain patterns are apparent from which specific conclusions can be drawn: 1) For a given updraft speed, 'the smaller initial- size hygroscopic particles require a greater cloud depth to grow large enough to start falling through the cloud. Fig. 2 illustrates this fact well. For instance, about 2 km more cloud depth is required at 5 m S-l updraft for a 5 }Lm seed compared with a 40 }Lm one. Notice also that the smaller seeds pass through the top of the cloud much more readily. At 15 m S-l updraft speed, a 5 }Lm seed passes through the top (16 km summit), whereas a 40 }Lm seed would start falling through the cloud at 7 km above cloud base. 15.00 - 8m=23.20C BASE=lkm M.R.=IG.2g kg-' 8m=23,20C BASE=3km M.R.=11.3g kg-I ....... 8m = ,Go C BASE= 3 km M.R.= 5.9 9 kg-I 12.00 51'm E .:::. 9.00 :r: I- 0.. W o o :> o 6.00 ..J U :;; :> :;; z i 3.00 '24.00 -.J 30.00 12.00 18.00 UPDRAFT 1m s''i FIG. 3. As in Fig. 2 except for drop diameters of 5 and 40 }.1m and for cloud conditions ranging from cold and relatively dry to warm and moist (model computations).