WMOD00176

• Project Name: Annual Report
• Title: Seeding Operations & Atmospheric Research, 2005 Annual Report
• Prepared By: Duncan Axisia
• Date: 12/31/2005
• Weather Modification - Doc Type: Report

Type of cloud seeding
employed by SOAR

The ob;ective of a doud seeding program IS to
increase rainfall when rain-beanng clouds are
known 10 have poor rainfall efficiency. Texas
projects use glaciogenic seeding to improve
the efftclency of the cold rain process The
target 01 such seeding operations is the
supercooled water which is found in the cold
part of the cloud aoove the freezing level.

Dunng the Spring and summer of 2005. SOAR
has been pioneering hygroscopic seeding of
douds within and around the Southern
Ogallala target area using milled salt.

The methodology of glaciogenic
seeding

The agent used is silver iodide. which is
released in douds to empower the fannalien of
ice aggregates. The maximum efficiency for
aggregation occurs around -5"C Seedable
douds must have lop heights around this
temperature but warmer than -15"C.

Typically, douds are seeded at-SOC level and
the silver iodide is released in the earty stages
of development and within the first halt-lifetime
Dosages should reach the dynamic mode of
seeding, around 100 ice-nudei per liler of
supercooled volume. Radar volume scans are
used to measure the exact dosage required 10
reach lhe dynamic mode, Clouds thai are
seeded are very carefully chosen in that the in-
doud roalescence of the douds is dosely
monitored using the Index of Coalescence
Activity

There are two methods of glaciogenlC doud
seeding utilized by the SOAR program. 1)
doud base seeding and 2) doud top seeding_

Glaciogenic seeding at cloud base

Glaciogenic seeding at base is accomplished
by injection of 40-gram Silver Iodide
pyrolechnic flares into cloud updrafts in excess
of 200 feet per minute near the bases of douds
along predetermined tracks 10 to 30 miles
upwind of the target area

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FlQUre 10: In a doud ~ see6lng ffilSSion. M a.rcraf!
releasesSilverlodldeftarest1}, ~liquidwaterls
converted Into ice parbcIes (2). releasing Ialent heat
InaeaSlng buoyancy. am Invigoratng cloud upjrafts (3l.

Glaciogentc seeding at cloud top

Glaciogenic seeding at doud top IS
accomplished by an aircraft. flying just above
the freeZIng level that drops up to two ejectable
Silver Iodide pyrotechnic flares. each flare
releasing 20 grams of Silver Iodide smoke. into
the top of the growing cumulus cloud 10 to 30
miles upwind of the target area

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Pyrotechnics used

The pyrotechnics used for seeding at doud
base and on top are manufactured by Concho
Cartridge. Reports from doud chambers show
that the flares are producing about 10^^13 ice-
nudei per liter at 5 "C. and about 2 x 1 O^^ 13 at
-SOC.

The metl1odoIogy of hygroscopic
seeding

Hygroscopic seeding at cloud base IS
accomplished by injection of the hygroscipic
seeding malenal (satt) into doud updrafts In
excess of 200 feet per minute near the bases
of douds along predetermined tracks 10 to 30
miles upwind of the target area

In the summer of 2005. the SOAR crew
conducted several hygroscopic Seeding
experiments using milled salt released from an
agricultural aircraft. SF6 gas was released in
the updraft by the doud-base seeder
simultaneous with the release of the

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