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

immediately suspected. The problem was determined to be an aerosol sample plumbing problem inside
the instrument. In spite of the aircraft aerosol inlet being connected to the CCN instrument sample line,
the manufacturer had not connected the aerosol sample line inside the CCN counter case to the inlet
manifold upstream of the CCN column. This created a problem because although the air sample was
entering the instrument, the “leak” prevented the aerosol from entering the CCN column inside the
instrument. This “leak” also affected the TDMA data since the TDMA pumps were downstream of the
CCN counter, drawing residual aerosol from the CCN instrument into the DMA. This issue was resolved
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on the 17 August 2004. During SPECTRA 1, the supersaturation settings that were operative inside the
CCN instrument during the research mission were usually set to cycle through a supersaturation of 0.1%
for 3 minutes, 0.25% for 2 minutes, 0.5% for 2 minutes and 1% for 2 minutes. In this case, the cycle time
of one supersaturation cycle is approximately 9 minutes. The instrument works best when the
temperature in the column is stable (not changing), so the data in between the supersaturation settings
cannot be viewed as being an absolute CCN concentration that corresponds to that exact calculated
supersaturation value.
The problem with the aircraft position data was due to an error in the new DAQ Factory data acquisition
software. The Differential Global Positioning System (DGPS) was accurately broadcasting the position
data and this data was being displayed correctly in real time. The problem occurred when the latitude
data was logged. This data was logged incorrectly even though the data was being displayed accurately
in real time. When the problem was diagnosed, the data acquisition software code was changed to
resolve the issue. The latitude data for each of the 8 flights was retrieved from project TITAN data and
from the aircraft telemetry GPS board. This was an intermittent problem and the issue was resolved
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completely on 21 September 2004.
The most disappointing error for the duration of the project was the performance of the Cloud Droplet
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Probe (CDP) during the last 12 flights. On 10 September 2004, DMT recalled the CDP unit to change
the firmware to improve the CDP accuracy and decrease the instrument sensitivity to droplet coincidence.
A firmware “upgrade” was installed at DMT and measurements resumed. This “upgrade” resulted in the
CDP undercounting by about a factor of 4 when compared to previous measurements in similar clouds,
while still providing comparable CDP liquid water content to hot wire liquid water content. DMT was
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approached with this problem and a resolution is still pending. The CDP data from 16 September
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through the 1 October is therefore not reliable. The SOAR group had an opportunity to fly an FSSP in
tandem with a CDP in a subsequent project. This allowed for the inter-comparison of the performance of
the two probes. These tests are described in detail in Appendix A. This has allowed for a correction factor
to be applied to the CDP data to observe relative concentrations of cloud droplet concentrations after the
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10 September 2004. The corrected CDP concentrations, although indicative of the droplet
concentrations, should not be inferred as absolute values.
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To summarize, the cloud physics data between 7 August and 5 September are of good quality. Out of
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this data set, CCN data were available after 19 August and TDMA data after 20 August. A summary of
the data quality during the SPECTRA 1 project is included in table 4 (unless stated in the ‘Known
problems column’ all instrumentation was functional).
DateData system
Brief description of research flight Known problems
(Local)time (GMT)
Ignore CCN due to a leak in the
DSD to 25000 ft in former HP project area (north of
080704 2242 - 0041 counter. PCASP not operational.
Lubbock area).
Problem creating ASCII file.
Ignore CCN. PCASP not
Flight from Plains to College Station. DSD of shallow Cu
080804 2225 – 0051 operational. Problem creating ASCII
along the flight path.
file.
Ignore CCN. PCASP not
081004 2131 – 2334 Flight from College Station to Plains. No DSD. operational. Problem creating ASCII
file.
System time problem. Ignore CCN.
081304 2245 - 0116 DSD to 11000 ft around Tolk power plant.
PCASP not operational. Problem
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