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<br />. <br />. <br />. <br />. <br />. <br />. <br />t <br />t <br />t <br />t <br />t <br />t <br />t <br />t <br />t <br />t <br />t <br />t <br />t <br />t <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />~ <br />~ <br />~ <br />~ <br />I <br />I <br />I <br />I <br />. <br />I <br />. <br />I <br />I <br />I <br />I <br /> <br /> <br />SOAR Research Activities and Opportunities <br />Moving towards a better understanding of the clouds we seed <br /> <br />SOAR's participation in atmospheric research <br /> <br />The SPECTRA project <br /> <br />The Southern Plains Experiment in Cloud <br />seeding of Thunderstorms fOf Rainfall <br />Augmentation, or SPECTRA, is a mutli- <br />organizational collaborative research effort <br />formed to gain a better understanding of the <br />microphysical processes in seeded and noo- <br />seeded convective douds across the south <br />central United States. The SOAR program <br />headquarters has served as the focal point for <br />this research project. In addition to SOAR's <br />involvement. other organizations or person(s) <br />contributing to this research effort are Texas <br />A&M University, Woodley Weather Consultants. <br />the Texas Department of Licensing and <br />Regulation, and Dr. Daniel Rosenfeld of the <br />Hebrew University of Jerusalem. To attain the <br />fundamental purpose of SPECTRA.. specific <br />objectives related to fieldwork, and subsequent <br />analysis. were pursued for each phase of the <br />project <br /> <br />1. The identification of types. and frequency of <br />oca.mence. of cloud condensation nuclei <br />(CCN) within and in the vicinity of growing <br />convective cloud towers. <br />2. Observations of doud-droplet spectl\Jm, <br />liquid water contents and hydrometeor sizes <br />and types. as well as inferences about cloud <br />updrafts, to determine the impact of the CCN <br />particulates on in-doud processes, most <br />notably coalescence. <br />3 To disperse hygroscopic material (finely <br />milled salts) into the updraft regions of <br />growing convective lowers and. then. to <br />observe and document cloud behavior in <br />response to the seeding using ground-based <br /> <br />radar and cloud-physics data obtained with <br />the SOAR research aircraft: the treated cloud <br />volumes were identified by the release, and <br />detection, of sulfur hexafluoride (SF6) gas. <br />4 . To study and document seeding signatures <br />in convective towers using glaciogenic <br />materials dispensed from cloud base at one. <br />or more. rain enhancement project areas in <br />south Texas. <br /> <br />In order to achieve these objectives, a field <br />program was designed starting initially with <br />Phase 1 (2004) which focused on the collection <br />of CCN number concentrations and CCN size <br />distnbutions at cloud base and measurement of <br />the drop size distribution (DSD) spectra of <br />convective clouds at various levels from cloud <br />base to cloud top. Phase 2 resumed in 2005 and <br />focused on hygroscopic seeding using milled <br />sail. <br /> <br />CCN Sizes and their Effect on Cloud <br />Microstructure <br /> <br />As stated earlier, recent work by Rosenfeld <br />(2004) has elucidated the effect that anomalous <br />CCN concentrations of a particular size might <br />have on rainfall processes. The Southem <br />Ogallala region is located within a continental <br />regime as many of the air masses that traverse <br />the region originate over arid topography. The <br />CCN characteristics of such air masses are <br />distinctly different from oceanic maritime air <br />masses typically found along the Gulf Coast. <br />These maritime air masses ingest large amounts <br />of salt nuclei from sea spray which subsequently <br />serve as giant cloud nuclei. In contrast, the <br />