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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hygroscopic salt powder. The SOAR cloud
physics research aircraft detected the gas
during the seeding trials. The detection of the
gas indicated that the aircraft had penetrated
the seeded plume.

Quantifying a seedable cloud

The scientific basis to identify a seedable cloud
has been prompted by the Israeli experiments
and the World Meteorological Organization
Precipitation Enhancement Project (WMO
PEP). Clouds are considered to be seedable
tor increasing precipitation according to the
static-mode seeding concept if 1) the coIlision-
coalescence process is inefficient. 2) the rate
of formation of supercooled condensate
exceeds or is comparable to the rate of
depletion of supercooled water, and 3) if there
is sufficient time to grow seeding-induced
precipitation particles that can reach the
ground (Silverman, 2001). These seedable
criteria specified by the static-mode definition
are difficult to apply practically because of the
lack of quantification.

Seedab!e clouds are observed by pilots to be
optically dense growing clouds whose tops at
the time of treatment had risen to at least the
height of 6-8 kilometers (cloud top
temperatures between -1Q"C and -15OC) and
have cloud top diameters between 2 and 5
kilometers.

Extensive use of TITAN to quantify a
seedable cloud

Operations for weather modification field
programs are highly dependent on timely and
accurate radar information. The operational
doud seeding programs of Texas since the
late 1990s, have made extensive use of
TITAN-equipped C-band radars to conduct
project operations and for subsequent
evaluation. This changed when NEXRAD radar
was made available. The TITAN software
processes volume scan data from the Lubbock
and Midland NEXRAD radar. The data allows
analysis of different variables such as storm
identification. location. area. volume. mass of
precipitation. Vertically Integrated Liquid (VIL)
as well as rates of variation of these
parameters.

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Figure 11. t.1ethodology of hygroscopic seeding.

TITAN provides a tool for an appropriately
trained meteorologist to quantify a seedable
cloud appropriately. The meteorologist usually
undergoes a series of decisions that may be
best characterized as: Nowcasting, decision
time, qualification, treatment. maintenance and
termination.

1) Nowcasting is when the meteorologist is
monitoring the atmospheric conditions
desirable for deep convection and seedable
clouds to form. This decision is taken after
studying the meteorological model output that
forecast the prevailing thermodynamic
conditions. This process is usually a routine
analysis of upper air conditions and surface
conditions. Nowcasting of the possibility of
thunderstorms follows and weather
modification pilots are briefed accordingly.

2) Decision time is when the meteorologist
decides to launch a seeding operation based
on his/her observations of the current and
forecast atmospheric conditions. This decision

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