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Section <br />1 <br />1.Introduction <br />1.1 Background <br />In May 2004, the Texas Department of Licensing and Regulation (TDLR), solicited bids for work and <br />services in support of a weather modification research program in Texas during 2004 and 2005. <br />Specifically, the bids identified a source, and associated costs, for an aircraft (and essential personnel) to <br />serve as an airborne platform from which an assortment of measurements of cloud properties was made. <br />The aircraft carried a sizeable instrument payload for use in detecting and measuring the distribution of <br />Cloud Condensation Nuclei (CCN) and cloud Drop Size Distribution (DSD) during Phase I of the planned <br />research. During Phase 2 the research aircraft was used in detecting a tracer gas used during <br />experimental hygroscopic seeding. TDLR and other project participants provided the instrument payload <br />on the aircraft. The research program was designed to provide insights into the cloud seeding techniques <br />that best mimic the rain-producing processes of large (tall) cloud towers that are responsible for the bulk <br />of the rainwater produced in semi-arid West and South Texas in the warm season each year. Weather <br />modification research activities were conducted between August 7, 2004and October 1, 2004 (Phase I) <br />and between May 5, 2005 and August 19, 2005 (Phase II). This research program was named the <br />Southern Plains Experiment in Cloud Seeding of Thunderstorms for Rainfall Augmentation (SPECTRA) <br />Project. <br />During the SPECTRA Phase 1 campaign, 34 research flights were flown totaling 75 flight hours from the <br />thst <br />period 7 August 2004 to 1 October 2004. It was determined that extending the measurement program <br />into October was not desirable due to the remarked climatological decline in convective activity in Texas, <br />southeastern New Mexico and Oklahoma. As with every field research program, fair shares of <br />instrumentation problems were encountered. The field research crew was very persistent in maintaining <br />the high quality of the data for the duration of the field program. This resulted in an excellent data set of <br />cloud physics and CCN measurements within the boundaries of the Texas weather modification <br />programs. <br />1.2 Objectives of SPECTRA Phase 1 <br />SPECTRA was designed to study convective clouds in the southern plains, specifically areas in Texas, <br />southeastern New Mexico and Oklahoma where weather modification programs have been in place at <br />some point in time in the last decade. The objectives of the SPECTRA project are to document <br />microphysical signatures produced by glaciogenic base seeding, document the Cloud Condensation <br />Nuclei (CCN) distribution and their effect on the cloud Drop Size Distribution (DSD), test hygroscopic <br />seeding using milled salt and finally, conduct model simulations of seeded and non-seeded clouds. In <br />order to achieve these objectives, the field program started initially with Phase 1 and continued with <br />Phase 2. This document is a technical report that details the outcome of SPECTRA Phase 1. <br />The goals of SPECTRA phase 1 focused on the collection of CCN number concentrations and CCN size <br />distributions at cloud base and measurement of the Drop Size Distribution (DSD) spectra of convective <br />to <br />clouds at various levels from cloud base to cloud top. Ultimately, the main goal of SPECTRA 1 is <br />document the Cloud Condensation Nuclei (CCN) distribution at the cloud bases and their effect on <br />the cloud Drop Size Distribution (DSD) and precipitation forming mechanisms. <br />To achieve this goal, <br />the operational plan was to focus the measurement program on 3 tasks: <br />10 <br />