WMOD00057

• Contract/Permit #: #90-3
• Applicant: Western Kansas Groundwater
• Project Name: Kansas Weather Modification
• Date: 9/13/1990
• Weather Modification - Doc Type: Report

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cloud vtllume 1s critical to the success of both rain stimulation
and hail reduction.

In both weakly and modera"tely growing cUIllullform clouds their
behavior can be altered through what is called the "dynamic
effecttt. When atmospheric conditions are right, cumulus clouds may
be stimulated to grow larger and precipitation persist longer than
would be the case if lef~ unseeded. This 1s done by placing the
seeding agent <dry ice or silver iodide) into the super cooled part
of the cloud to promote the rapid conversion of water droplets into
ice crystals. When this water-to-1ce conversion process occurs
rapidly within a cloud, latent heat of fusion 1s released on such
a scale that the cloud becomes slightly warmer and more buoyant,
thus causing the cloud to grow. As the cloud grows, it draws in
greater amounts of air with the water vapor in it supplying
considerably more moisture to the precipitation-making process.
This allows the cloud to I1process" more water over a longer period
of time and to do so more efficiently than if unseeded.

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Although silver iodide produces the dynamic effect very well,
it is produced more rapidly by dry ice. OP the WKWM Program dry ice
is dispensed through an opening in an aircraft capable of flying
well above freezing level---into the supercooled region of the
clouds. The dry ice dispenser carries about 200 lbs and has been
designed to automatically release dry ice pellets at a rate of 5
lbs a minute of flight. Dry ice dropped into supercooled clouds
immediately converts the supercooled water drops it makes contact
with, or in its "waken, into ice crystals. Silver iodide only
starts becoming increasingly effective at temperatures below -5C---
which translates into approximately 1,500 feet to 3,000 feet above
the freezing level. In this respect, dry ice is much quicker and
mare effective than silver iodide 1n producing ice crystals in the
supercooled part of the claud, even down to the freezing level.
However, relatively large quantities of dry ice are needed to
produce an equal~nd equivalent number of ice crystals from a given
mass of silver iodide---approximately 1000 - 2000 grams dry ice to
one gram silver iodide.

Dispensing silver iodide, using the cloud top delivery
technique is more expensive than-using dry ice. Silver iodide first
has to be manufactured into an ej ectable cartridge that can be
expelled from a rack mounted to an aircraft. Manufacturing costs of
ejectable cartridges, or flares, is much greater than dry ice when
compared to an equivalent amount of ice crystal production.

The following cloud systems and variations of them are roost
responsible for producing rain and hail here in Western Kansas:

(1) air-mass
(2) multiple cell
(3) squall line

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