WMOD00269

• Title: The Southern Plains Experiment in Cloud Seeding of Thunderstorms for Rainfall Augmentation Phase I ‎(SPECTRA 1)‎
• Prepared For: Texas Department of Licensing and Regulation
• Prepared By: Duncan Axisa, Seeding Operations and Atmospheric Research
• Date: 3/1/2006
• State: TX
• Weather Modification - Doc Type: Report

Executive Summary
SPECTRA 1 plans, objectives and resources
In 2003 the Texas Department of Licensing & Regulation (TDLR) was awarded a grant from the U. S.
Bureau of Reclamation to participate in a collaborative effort known as the Weather Damage Modification
S
Program (WDMP). The research, which was to be supported by the grant was known as the outhern
PECTRASPECTRA
lainsxperiment in loud-seeding of hunderstorms for ain ugmentation (), was to
evaluate the physical mechanisms in the atmosphere, particularly within convective cloud towers leading
to losses from hail and drought and to identify and administer appropriate cloud seeding materials that
might mitigate these losses.
The original plan called for the research to be conducted in two phases in the Texas-Oklahoma portion of
the southern U. S. Great Plains region during the spring and summer of 2004. Unforeseen delays in the
bid solicitation process allowed only the initial phase of the research to be accomplished during the late
summer of 2004. This effort, which came to be known as SPECTRA I, focused on the documentation of
the size distributions of cloud condensation nuclei (CCN) throughout Texas and measurement of the Drop
Size Distribution (DSD) spectra of convective clouds at various levels from cloud base to cloud top.
to document the Cloud Condensation Nuclei (CCN) distribution at
The main goal of SPECTRA 1 is
the cloud bases and their effect on the cloud Drop Size Distribution (DSD) and precipitation
forming mechanisms.
To achieve this goal, the operational plan was to focus the measurement program
on 3 tasks:
1. To measure the CCN concentration and the aerosol concentration below cloud base level of
growing towering cumulus.
2. To measure the cloud droplet concentrations and size distributions of droplets from the cloud
bases to the cloud tops of young and growing convective towers.
3. To measure the onset of precipitation and identify the predominant precipitation forming
mechanism within young and growing convective towers.
In order to achieve these tasks, and to increase the measurement capability of the region, a new Texas
based cloud physics aircraft was equipped specifically as part of this project. The Seeding Operations &
Atmospheric Research (SOAR) program Piper Cheyenne II was equipped with instrumentation purchased
by the Texas Department of Licensing and Regulation (TDLR) through the WDMP grant.
During the SPECTRA Phase 1 campaign, 34 research flights were flown totaling 75 flight hours from the
thst
period 7 August 2004 to 1 October 2004. It was determined that extending the measurement program
into October was not desirable due to the remarked climatological decline in convective activity in Texas,
southeastern New Mexico and Oklahoma. As with every field research program, fair shares of
instrumentation problems were encountered. The field research crew was very persistent in maintaining
the high quality of the data for the duration of the field program. This resulted in an excellent data set of
cloud physics and CCN measurements within the boundaries of the Texas weather modification
programs.
The equipment used in SPECTRA 1 included:
A high-performance twin-engine turboprop aircraft (Cheyenne II) owned by SOAR and leased to
the TDLR for up to 80 hours of flight time. The capabilities of this aircraft are addressed in
Appendix A;
An instrument package carried onboard the cloud physics aircraft (Cheyenne II), consisting of
sensors having the capability to measure in situ microphysical properties of clouds and their
thermodynamic environment, for documenting the composition of clouds, and for diagnosing the
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