WMOD00234

• Contract/Permit #: #93-5
• Applicant: Western Kansas Groundwater
• Project Name: Kansas Weather Modification
• Date: 1/1/1993
• Weather Modification - Doc Type: Report

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is employed in which wing-tip generators are filled with a liquid
solution of silver iodide (described below) which produces
trillions of ice nuclei per gram of silver iodide consumed. A
Carley-type generator is mounted in the wing-tip position on each
cloud base seeding plane. Pressurized by air contained in an air
tank built into each generator, the liquid seeding solution is
forced through an aperture producing a fine spray which flows into
a combustion chamber where it is vaporized by burning. As the spray
burns, very pure silver iodide particles are formed and exhaust
freely into the cloud base updrafts to be carried aloft by natural
action into the cloud's supercooled region.

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Since 1987, the liquid seeding agent formulation has been the
same. It contains quantities of the oxidizers sodium perchlorate
and ammonium perchlorate added to a standard 2% silver iodide-
ammonium iodide-acetone-water solution. A ratio of 4 moles sodium
to 1 mole silver results in particles acting initially as strong
hygroscopic condensation nuclei, thereby insuring the formation of
vast numbers of water droplets containing silver iodide nuclei in
the lowest parts of clouds. Most silver iodide ice nuclei not
trapped in the water droplets will be collected later in other
droplets by "contact nucleation". Contact nucleation occurs when
ice nuclei inside moist cloud updrafts collide randomly with water
droplets to become captured in those droplets. This hygroscopic
condensation-contact nucleation process produces more number9 of
ice crystals formed at relatively warmer temperatures wi thin a
cloud than when simply using older seeding formulations dependen"C
only upon contact nucleation. When silver iodide is used only as
a contact nucleant, it lingers within the treated cloud until
either captured by water droplets or until the cloud dissipates.
Usually, silver iodide is preferred for,rain stimulation.

In order to obtain the desired result seeding clouds with
sil ver iodide each cloud must be treated wi thin a proper time
interval, or "window of opportunity", to produce the optimum ice
crystal concentrations in clouds na"Curally deficien"C in them and
promote supercooled water drop freezing within clouds. A cloud
growing to maturity must be treated with enough time allowed so
that the silver iodide ice nuclei can be lifted by natural cloud
action into the appropriate temperature and moisture regime and
kept there for a sufficient time to react with the supercooled
water in that volume. When increasing rainfall is the objective,
if this window is missed, the cloud may collapse prematurely with
the efforc and resources wasted. This "residence" time in the
supercooled cloud volume is critical to the success of both rain
stimulation and hail reduction.

The behavior of weakly and moderately growing cumuli form
clouds can be altered through what is called the "dynamic effect".
Under certain atmospheric. conditions, cumulus clouds may be stimu-
lated to grow larger and rain longer than would be if otherwise
left unseeded. This is accomplished by getting large amounts of

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