by Doreen Wachner

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• historical developments of the artificial weather

• important kind of weather influencing

• hail-suppression

• effects of the artificial weather

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>>> basis of the experiments of weather-influencing is the basis-research of cloud-physics

1. step: ( 1911 – 1945 )

- theories of precipitation formation

2. step: ( 1946 – 1947 )

- discovery of chemicals to dissolve the ice-formation

3. step: ( 1947 – 1954 )

- some experiments of weather-influencing

4. step: ( 1955 to now )

- economic applicability

.

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• creation of artificial rain

• influencing / dissolution of fog

• hail-suppression

.

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hail-damage:

• 14,5 million €/a hail-damage in Steiermark

• 300 million $/a harvest-damage and 25 million $/a damage to property in USA

• example for Germany: 1984 in München

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green: low hail-risk

red: heavy hail-risk

Quelle: Risikostatistik

Hagel 1980-1998

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• microphysics of rain drops

• microphysics of ice particles

.

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microphysics of ice particles

thermometric scale thermometric scale

[ °C ][ °C ]

from undercooled water from undercooled water drops to ice particlesdrops to ice particles

0 to -120 to -12 undercooled water dropsundercooled water drops

-13 to -20-13 to -20 water drops and ice crystals water drops and ice crystals

-20 to -40-20 to -40 outweigh ice crystalsoutweigh ice crystals

< -40< -40 only ice crystalsonly ice crystals

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microphysics of ice particles

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basis of the formation of hail:

1) existence of ice particles ( freezing nuclear )

2) existence of undercooled water ( T< 0°C )

.

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formation of hail:

________ • a new cloud area forms

• these particles acts as nuclear of the growth of hail

___________ • the nuclear with undercooled water drops grow to hailstone

>>> conditions of the two-stage process are dynamical

operations in the clouds !!!

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• “single cell thunderstorm”

• “more cell thunderstorm”

• “super cell thunderstorm”

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picture: “single cell thunderstorm”

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picture: “more cell thunderstorm”

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picture: “super cell thunderstorm”

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1) competition principle

2) cloud seeding with airplane

3) conception of the accelerate growth of drops in the principal prevailing of wind

4) conception of the path reduction of hail grains

5) ice formation hypothesis

7) conception of artificial influencing of cloud dynamics

6) conception of early precipitate of hail-embryos

.

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1947 >>> first step of the scientific weather influencing

(B. Vonnegut)

chemical properties of AgI :

• three modifications

- AgI

(cubic room-centers ) - AgI

(hexagonal

“wurtzit-grating” )

- AgI

(cubic “zinkblende”)

.

1919

chemical properties of AgI :

• -4,5°C ( -5,2°C completed) >>> AgI – efficiency

• affinity to hexagonal snow crystals

• no toxicity

• AgI disintegrates photochemically to silver and iodine (UV-light)

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• AgI >>> freezing nucleus

• use of -AgI

• combination of seed substance:

>>> four parts of AgI and one part of NaI

• nuclear action of AgI based of:

>>> heterogeneous ice nucleation ( homogeneous ice nucleation : < -40°C )

>>> hexagonal structure favors the nuclear action of AgI

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• effect of AgI starts at -7°C

• AgI distribution in the cloud = principle of the Gauss-distribution:

>>> AgI amount: 8 g

>>> AgI density of all particles in the cloud: 10-15 g/cm3

.

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distribution of AgI in the clouds

• ice nucleus number ( activation temperature: -7°C ) = 1013 ice nucleuses/ kg AgI

• ice nucleus concentration ( -7°C) = 10-2 l-1

>>> -10°C = 10 l-1

>>> -20°C = 100 – 1000 l-1

AgI-seeding ( temperature: -20°C ) produces 100

more ice nucleus per liter in the

cloud as in a natural cloud ! ! !

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AgI – NaI

Lösung

AgI

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( >>> values from the “Steierischen Hagelabwehrgenossenschaft”

1991 - 2002 )

solution combination:

• 1 liter acetone ~ 1000g

• four parts AgI ( 62,5 g )

• flow volume: 5 – 6 l/h

• to released AgI amount: 300 – 400 g/h per generator

• one part NaI ( solvent )

.

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1) enough “artificial nucleuses” to yield in the cloud

2) these nucleuses must not be too long and must not stay too high in the updraft

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• “single cell thunderstorm”:

>>> number of hits at seeding = 90 – 100 %

• “super cell thunderstorm”:

>>> number of hits at seeding = 50 %

• “more cell thunderstorm”:

>>> number of hits at seeding = between single- and super cell thunderstorm

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number of hits to seeding per airplane:

time of development (exist) of the hail clouds:

• “single cell thunderstorm”: 10 – 15 min.

• “more cell thunderstorm”: 20 – 90 min.

• “super cell thunderstorm”: >30 min.

general: 80 % of the clouds will be real seeding

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• more application of sodium chloride

• new seeding substance:

>>> complex of AgClI*0,5 NaCl

• aim of the new seeding substances is:

>>> improvement of the rain dissolution

>>> improvement of the hail suppression

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flood disaster from Lynmounth ( 1952 )

weather influencing in Vietnam-war

artificial rain prevented aridity in Chonburi

.

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[1] E. Heyer, Witterung und Klima – Eine allgemeine Klimatologie, B.G. Teubner Verlagsgesellschaft, 9. Aufl., Leipzig, 1993.

[2] W. Atkinson, Wetterforschung – Analyse, Vorhersagen und Beeinflussung des Wetter, Deutsche Verlags-Anstalt Stuttgart, 1.Aufl., Stuttgart, 1970.

[3] P.D. Jones, History and Climate – Memories of the Future?, Kluwer Academic/Plenum Plublisher, 1.Aufl.,New York, 2001.

[4] J. Bendix, Geländeklimatologie, Gebrüder Borntraeger Verlagsbuchhandlung, 1. Aufl., Stuttgart, 2004.

[5] http://www.klimaforschung.net/silberjodid/index.htm

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[7] http://www.hagelabwehr.at/brenner.asp

[8] http://www.bayercropscience.de/

[9] http://www.chinadaily.com.cn/english/doc/2004-07/13/content_348065.htm

[10] http://www.sonnenseite.com/fp/archiv/Art-Zukunft/regenmacher.php

[11] www.guardian.co.uk/china/story/0,7369,1261697,00.html

[6] http://www.wetter-zentrale.de/cgi-bin/wetterchronik/home.pl

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• principle of the Gauss-distribution