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Project Objectives |
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The
Southern Plains Experiment in Cloud Seeding of
Thunderstorms for Rainfall Augmentation (SPECTRA)
Project was designed to study convective clouds in
Texas, southeastern New Mexico and Oklahoma where
advertent and/or inadvertent weather modification
occurs. The objectives of the SPECTRA project were to
document microphysical signatures produced by
glaciogenic base seeding, document the Cloud
Condensation Nuclei (CCN) distribution and their
effect on the cloud Drop Size Distribution (DSD), test
hygroscopic seeding using milled salt and finally,
conduct model simulations of seeded and non-seeded
clouds. In order to achieve these objectives, a field
program was designed starting initially with Phase 1
(2004) which focused on the collection of CCN number
concentrations and CCN size distributions at cloud
base and measurement of the DSD spectra of convective
clouds at various levels from cloud base to cloud top.
Phase 2 resumed in 2005 and focused on hygroscopic
seeding using milled salt.
To attain the fundamental purpose of SPECTRA, specific
objectives related to field
work, and subsequent analysis, were pursued for each
phase of the project.
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SPECTRA Phase I |
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1. |
The identification of types, and frequency of
occurrence, of cloud condensation nuclei (CCN) within
and in the vicinity of growing convective cloud
towers. |
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2. |
Observations of cloud-droplet spectrum, liquid water
contents and hydrometeor sizes and types, as well as
inferences about cloud updrafts, to determine the
impact of the CCN particulates on in-cloud processes,
most notably coalescence.
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SPECTRA Phase II |
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1. |
To disperse hygroscopic material (finely milled salts)
into the updraft regions of growing convective towers
and, then, to observe and document cloud behavior in
response to the seeding using ground-based radar and
cloud-physics data obtained with the SOAR research
aircraft; the treated cloud volumes were identified by
the release, and detection, of sulfur hexafluoride
(SF6) gas. |
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2. |
To study and document seeding signatures in convective
towers using glaciogenic materials dispensed from
cloud base at one, or more, rain enhancement project
areas in south Texas.
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Instrumentation during SPECTRA |
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The SOAR research
aircraft, leased to the TDLR for up to 130 hours of
flight time, equipped with cloud-physics
instrumentation and aerosol instruments. The cloud
physics instruments used were the DMT CIP and DMT CDP.
In addition, the DMT CCN counter, the DMT modified
PCASP and the Texas A&M University DMA/TDMA were used
during this campaign. For phase 2, the aircraft was
equipped with the University of Washington SF6
detector.
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An agricultural-type
single-engine aircraft for up to 40 hours, with a
capability of dispensing seeding material (milled
salt) and SF6 gas at cloud base;
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5-centimeter wavelength
radar (known as a WSR 100/2/77) with a volume scan
equipped with Thunderstorm Identification, Tracking,
Analysis, and Nowcasting (TITAN).
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NEXRAD weather radar
data feed (from Lubbock and Midland NWS sites) run
through TITAN;
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An Emergency Managers
Weather Information Network (EMWIN), a satellite
networking system that retrieves information issued
from the National Weather Service (NWS) within a few
seconds of time of issuance;
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Radio communication
equipment to direct pilots of both seeder and research
aircraft in, and among, convective towers.
Geostationary Positioning Satellite (GPS) latitude and
longitude data from each of the two aircraft will be
collected and viewed with the TITAN software.
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