WMOD00303

• Title: Observational and Numerical Studies of Cloud and Precipitation Development with a View to Rainfall Enhancement
• Date: 4/1/1992
• Weather Modification - Doc Type: Report

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In the Drst and second regime only growth by vapor clliFusion occurs because too little
liquid water is available lor riming growth ((qc+C!R).S S x 10-2 gm m-S, Regime A-E),
or particles are still small (m; > S x lO-1 gm (< SOJ.'m), Regime A-B). The change in
mass per time step in these regimes are

6m; = 6t (q. - qft. ) ex (mjt
q.. - q.i.

(16)

where q.. and q.i. are the saturation water vapor mixing ratios lor water and ice
respectively. a and fJ are t'unctions ol temperature that determine the growth rate ol ice
particles (see Koenig(1972), Table 2). The sublimation olice particles is treated clliFerently
!rom the K-M approach who used an analogy to raindrop evaporation ol Kessl~r (1969).
The present approach lor sublimation is to also use (16) when q. < q"i..

In the third regime (Fig. 3, Regime B-C), clliFusional and accretional growth occurs
simultaneously when (qc+C!R) > 5 x 10-2 gm m-s and S x10-1 < mj S 10-4 gm (sizes
approximately between 50 and 600 pm diameter assuming a sphere) . Following K-M (see
also Koenig (1972), equations 2 and 3) let

tan,p = 1 + !n[P(q;o+ qR)]

(17)

and

7 = 6t ex (S x 10-1).8 .

(18)

where ,p is the angle between BC and the horizontal from B (Fig. 3, determined from the
liquid water content), and 7 is the mass growth rate due to clliFusion. Then

( _ ) taD.
6mj = 7 S X~~-I .

(19)

A h.cl . b .. th . t. . ,:I. . l .
s t e parti es are groWUlg y 1'1JD111g, e m..YttnUD1 0 tnlft1",um '"'~81on 0 an lce

particle decreases. Eventually the particles tend to a spherical shape and riming growth
starts to dominate. Therefore, only riming growth occurs in the fourth regime (Regime

34