WMOD00132

• Contract/Permit #: #95-5
• Applicant: Western Kansas Groundwater
• Project Name: Kansas Weather Modification
• Date: 1/1/1995
• Weather Modification - Doc Type: Report

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

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 I 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 and become captured in those,droplets. This hygroscopic
condensation-contact nucleation process forms greater numbers of
ice crystals at relatively warmer temperatures within a cloud than
does the older seedingforrnulation (silver iodide-ammonium iodlde-
acetone-water) which depended solely 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.

In order to obtain the desired result from seeding clouds with
silver iodide each cloud must be treated within a proper time
interval, Le., "a window of ,opportunity", if it is wished to
produce the optimum ice crystal concentrations in clouds naturally
deficient in them to 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 effort 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 many weakly and moderately growing cumuliform
clouds can be altered through what is called the "dynamic effect".
Under certain atmospheric conditions, cumulus clouds may be stimu-

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