WMOD00317

• Contract/Permit #: 14-06-D-6999
• Project Name: CAWRP
• Title: Cascades Atmosphere Water Resources Program - Volume I
• Prepared For: US Department of the Interior Bureau of Reclaimation
• Date: 7/1/1970
• Weather Modification - Doc Type: Report

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Mountains, and to predict the effects which changes in the concentrations of
ice particles (which may be accomplished, for example, by artificial seeding)
will have on the trajectories of precipitation particles and the distribution
of snowfall on the ground.
The trajectory of a cloud or precipitation particle can be determined if
at each point in space the terminal fall speed of the particle and the
magnitude and direction of the wind field is known. The latter is predicted
by the airflow model previously described. In this section we present the
equations which are used to determine the rates of increase in the masses and
the fall speeds of ice particles. The particles are assumed to grow by
diffusion from the vapor phase and by collecting supercooled cloud droplets
(riming). Growth by aggregation with other ice particles is not considered at
this time.
3.3.l Growth by Diffusion from the Vapor Phase
The rate of increase in the mass M of an ice particle due to deposition
from the vapor phase is given by

dM
dt = 4'1\'CGSi

(3.64)

where, C is the electrostatic capacity of the ice particle, S. the
1
supersaturation of the air relative to ice and

Dpv
G = - (1 +
Ps

DL2 M
Pv 0
RT2t(

(3.65)

-1
)

where, D is the diffusion coefficient of water vapor in air, L the latent heat

of deposition, pv and Ps the densities of water vapor and ice respectively,

)

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