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

I

Major model results and hypotheses resulting from the study indicate that:

1. There is an exceptionally strong coupling and feedback be-

tween ice-phase and liquid-phase microphysics. In many cases,

the presence or absence of large liquid drops aloft is found to

dominate the subsequent ice-phase behavior of the cloud.

2. Natural clouds can be divided into two microphysical types:

those that are warm-based, efficient, and form frozen-drop pre-

cipitation embryos as opposed to those that are cold-based, in-

efficient 1 and form graupel precipitation embryos aloft.

3. These two cloud types tend to respond in opposite ways to

attainabl.e seeding rates of artificial ice-phase seeding agents.

Seeding increases total precipitation in cold-based clouds and

tends to decrease it in warm-based clouds.

4. In general, rainfall and hailfall are positively coupled and

ice-phase seeding tends to cause them to both increase and

decrease together.

5. Dry ice is a preferred seeding agent for summertime rainfall

augmentation in the High Plains of the West Central United States.

6. Hail suppression and rain augmentation techniques are not

directly transferrable from one geographical and climatological

area to another.

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