WMOD00289 ‎(2)‎

• Title: Observations and Numerical Simulations of Precipitation Mechanisms in Natural and Seeded Convective Clouds
• Prepared By: Lroen D. Nelson
• Date: 3/1/1979
• State: IL
• Weather Modification - Doc Type: Report

10

where K(x' ,x) dx = the number of drops of mass x to x-fdx found by

breakup of one drop of mass x'

P(x) =the probability of breakup of a drop of mass x

in unit time.

Drop Freezing

Drops of liquid water at supercooled temperatures are allowed tel freeze

stochastically to ice spheres according to the formulation of Bigg (1953).

P = 1.0 - EXP [-5.2 E-10(V/ALFA)[EXP(A TS) - 1.0l}

(eq. 8)

where

P = cumulative freezing probability of a drop

v = drop volume in cc

ALFA= cooling rate in degree/second

A= 1.0

TS = degrees supercooling ('C)

Ice Nucleation

Ice crystals are nucleated from the vapor according to the relationship

given by Fletcher (1966).

n(TS) = NZERO*EXP(BETA-TS)

(eq. 9)

where

TS = degrees supercool ing

n(TS) = cumulative number of nuclei active at supercoolings
less than TS

NZERO = typically about 1.0E-S/liter
BETA = typically about 0.67