WMOD00079

• Contract/Permit #: #98-1
• Applicant: Western Kansas Groundwater
• Project Name: Kansas Weather Modification
• Date: 1/1/1998
• Weather Modification - Doc Type: Report

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Although silver iodide produces greater numbers of ice nuclei than does dry ice, gram for
gram, large numbers of ice nuclei can be produced more quickly by dropping comparatively larger .
amounts dry ice directly into the moisture-laden cloud updrafts found in the new-growth cloud towers.
Relatively large amounts of dry ice are needed to produce an equivalent number of ice crystals from
a given mass of silver iodide---roughly 1000 to 2000 grams of dry ice are needed to match one gram
of silver iodide. Supercooled cloud droplets contacting dry ice which is falling through clouds, or those
droplets brought into the wake ofthe falling dry ice, immediately change into ice crystals. Whereas,
silver iodide-based seeding agents, while rising in the cloud, begin activating in droplets to form ice
crystals at temperatures near -4C to -5C---rougWy 2,000 to 2,500 feet above the freezing level.

Dry ice is dispensed from a container auguring dry ice into an opening in the aircraft floor
which lets the dry ice fall directly into the clouds. The container carries about 200 lbs of pelletized dry
ice and is released at a rate of Sibs per minute.

Dispensing ejectable silver iodide flares at cloud top is not done on the WKWMP primarily
because it is a much more expensive form of seeding agent than is dry ice, despite dry ice subliming
while in storage between operational periods.

The cloud systems listed below, and variations of them, are most responsible for producing rain
and hail in Western Kansas:

(1) the air-mass storm complex

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(2) multiple celled storms

(3) the squall line

Air-mass storms often become complex after starting out as an isolated cloud system with a
well-organized cloud base and its new growth updraft area usually visible somewhere around its base.
Multiple cloud turrets often develop around the initial "parent" storm and subsequent storm
movements can become erratic depending upon several factors such as its severity, terrain effects,
dynamic factors within the storm, cloud height, variability of wind speed and direction with height plus
the blocking of steering winds caused by large upwind cloud systems.

Air-mass storm complexes often transition into a large, multi-celled systems. Fig. 2 shows a
"classic" storm with new growth on its upwind (left) side. Updrafts upwind of a storm's direction of
movement are termed "trailing" or "back" side; the "front" side is on its downwind, leading edge side.
Most often, updrafts pertinent to the hail process are found along its trailing edge below cloud base
at some distance behind the precipitation.

Air-mass stonns can transition into a line of storms containing multiple cells showing
characteristics more similar to those of a small squall line. During the gradual development of these
multi-cellular lines, cloud base updrafts frequently shift around although they are still found around
some of the individual cell elements comprising it making proper cloud base treatment quite difficult

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