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Subsequently, ice formed faster and the KSLWC (King supercooled liquid water content) decayed more rapidly in these clouds.” On the other hand, “clouds that were relatively isolated during their growth phases retained their KSLWC longer than clustered clouds. Rain drops were rare during the initial cloud passes and increased only slightly late.” This readily illustrates the importance of the exchange of hydrometeors in the development of precipitation in clouds that could not otherwise develop precipitation on their own (Woodley and Rosenfeld, 2002). TEXARC was supported by the National Oceanic and Atmospheric Administration (NOAA) and the Texas Natural Resource Conservation Commission (TNRCC) through a cooperative agreement with the TNRCC, a participant in NOAA’s Atmospheric Modification Program. Although these results are encouraging, the sample of cloud physics cases is still too small to justify a claim that the effect of AgI seeding on in-cloud structure and circulations has been demonstrated. Additional cases should be qualified and analyzed to strengthen further the physical basis for the cloud seeding experiments. 1.4 The need for a research aircraft based in Texas As is noted above, Texas and Oklahoma has been involved in the past in several research efforts where cloud physics aircraft were brought in from out-of-state to fulfill the contractual needs and meet the research objectives in a timely way. Several hundreds of thousands of dollars have been spent on aircraft operational costs and data collection. Although the scientific community and the state consortium of Texas, New Mexico and Oklahoma have undoubtedly benefited from these data and their analysis, the importation of outside cloud physics aircraft has not increased the measurement capabilities of the region. Regional leadership has decided, therefore, to develop its own cloud physics capabilities. When subsequent funding is available for a new research program or field project, out-of-state aircraft need not be brought in for cloud physics in-situ measurements and data collection. It was proposed to the Bureau of Reclamation by the TDLR in January 2003 that an adequate aircraft based in Texas be leased for cloud physics measurements and that the Bureau of Reclamation participate in the purchase of airborne instrumentation. This approach has promoted greater flexibility in the deployment of the research aircraft and in the quality of the research effort. 1.5 The cloud physics platform during SPECTRA 1 1.5.1 The SOAR research aircraft The SOAR research aircraft is a Piper PA-31T Cheyenne II cloud penetrating aircraft. The Cheyenne has -1-1 a research airspeed of 85 ms to 110 msand when performing climbing penetrations, the research ceiling is 25000 feet. The research aircraft has the capability of measuring the size distribution of aerosols ranging from 0.1 µm to 3 µm and hydrometeors from 2 µm to 1.55 mm in diameter. The platform of the SOAR research aircraft during SPECTRA consisted of the Particle Measuring Systems’ (PMS) Passive Cavity Aerosol Spectrometer Probe (PCASP SPP-200), the Droplet Measurement Technologies (DMT) Cloud Droplet Probe (CDP) and the DMT Cloud Imaging Probe (CIP). This range gives the scientists a spectrum of measurements in the temporarily suspended aerosol range and in the cloud hydrometeor range. In addition, inferences on the cloud composition and the particles that act as CCN can be achieved by DMT’s airborne CCN counter. The SOAR research aircraft was also equipped with Texas A&M University’s aircraft-based high flow rate Differential Mobility Analyzer (DMA)/Tandem Differential Mobility Analyzer (TDMA) for sequential measurement of the hygroscopic growth of particles and measurements of the aerosol concentrations as a function of size to determine the critical supersaturation spectrum of aerosols. 13