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

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effect on precipitation development through
either of two distinct mechanisms:

1. introduction of embryos on which
raindrops form: or
2. broadening of the initial droplet sIZe
distribution resulting in acceleration of all
stages of the coalescence process.

In 1990. G. Mather reported a case of
inadvertent seeding of douds by hygrosa:>pic
partides emitted from a Kraft paper mill in
South Africa This observation led to further
doud seeding experiments in South Africa
(Mather et at.. 1997), Mexico (Bruinljes, 1999)
and in Thailand (Silverman, 2002) with highly
encouraging results.

Planned research with hygroscopic seeding in
Texas was conducted in 2005 utilizing the
SOAR research aircraft and its O"ew. Prof.
Daniel Rosenfeld and Dr. William Woodley
identified a patented means of processing
common salt (NaCI) to virtually any desired
size as verified after production by analysis
with an electron microscope (Figure 11). A
desiccant was added to the salt powder during
its production to prevent its dumping. The
mcx:lel simulations of Segal et al. (2004)
indicated that 3 to 5 microns diameter would be
the optimal size range and partides of this size
were produced for initial experiments to be
conducted in Texas (SPECTRA II).

Inadvertent anthropogenic seeding
and its implications for operational
cloud seeding

Studies conducted by Rosenfeld (1999.2000)
using satellite data reveal qualitative evidence
suggesting that industrial plumes change the
composition of CCN in sum a way as to have
an adverse effect on precipitation processes
downwind of industrial centers. A later study
by Boryn (2003) would lend credence to these
findings by quantifying decreases of up to 50%
in orographic snowfall rates over Colorado due
to the addition of tiny anthropogenic sulfate
aerosols. Building off of Boryo's work, Givati
and Rosenfeld (2004) constructed trend
analyses of rain gauges downwind of industrial
centers in Califomia and Israel to ascertain the
effect of concentrated plumes of tiny CCN on

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orographic precipitation formation. After
comparing the long-range trends of rainfall
upwind of the mountainous regions to rain
gauge trends in situ of orographicaUy favored
regions for precipitation it was found that
regions along the coast experienced static to
even positive trends in precipitation whereas
those regions downwind of industrial centers
experienced negative trends. During the same
time period. it was found that although air
pollution is decreasing in these regions, the
production of very small CCN is increasing due
to factors such as greater diesel consumption
among others Further substantiating the
causative evidence is the observation that no
such difference in rainfall trends were seen in
high elevation rain gauge data downwind of
pristine areas devoid of large industrial centers.

The implications for these results are of great
importance in regards to the question of
operational doud seeding and its viability.
These results qualitatively and quantitatively
illustrate the ability of anthropogenic sources to
inadvertently modify the weather in such a way
as to distort natural precipitation processes in a
statistically significant manner. In his review on
the current state of weather modification
Roland List (2004) states:

Weather mcxJification Vv'C:tks beyond any doubl Ndxxty
else but nature itself is doing weather mcxJification on a
grand scale: c:kuds and cloud systems, unable to yield
rain over con~nents due to heavy loads of small-sized
cloud coodensabon nuclei (CCN; many prtxluced by
bi<rnass burning) are revitalized, while moving back over
!he oreans, by !he ingestion of sea sa~ nudei, and can
yield rain again {Rosenfeld (2003), confirmed by R.
Bruinljes (2003. pe=la1 COf1'mJnicaIiooII.

Therefore. the use of anthropogenic material in
a deliberate manner to augment precipitation
processes remains a viable altemative to other
water conservation efforts. [n addition. these
studies reveal the need for operational seeding
programs to have an understanding of typical
CCN sizes and concentrations in their
respective water districts so as to deliver
scientifically sound treatments of CCN to
clouds for rainfall augmentation.

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