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Despite our lack of understanding of the process by which seeding with salts enhances the natural rain- <br />production process within convective towers, there is reason to expect that hygroscopic seeding as done in <br />South Africa and Mexico can be replicated successfully in Texas, with the consequence being quantifiable <br />increases from treated towers. Confirming various aspects of the South African results and addressing the <br />remaining uncertainties now has high scientific priority in a systematic research program having the potential to <br />be applied later on an area-wide basis. <br /> Planned research with salts in Texas in 2005 may also yield some significantly new insight into the <br />impact that seeding has on convective storms with potential to produce hail. It is conceivable that hygroscopic <br />seeding will transform continental clouds to those that have a more maritimemicrophysical structure, <br />characterized by an active coalescence process with early glaciation and increased rainwater. Because <br />maritime clouds rarely produce hail of note, if the goal of transforming continental clouds into more maritime <br />clouds can be promoted, then some important strides in hail suppression might be realized. <br /> Regions of Texas where hygroscopic seeding may be best suited were inferred from satellite <br />representations of cloud structure using the method of Rosenfeld and Lensky (1998). These were made on <br />every day that AVHRR imagery was available in 1999 and 2000 for seeding target areas in Texas. Cloud- <br />structure classifications ranged in value between 1 and 5, with 1 corresponding to clouds that do not become <br />0 <br />completely glaciated until T<-25C and whose effective radii do not reach the 15-micron precipitation threshold <br />00 <br />until T<-15C and a 5 corresponds to clouds that glaciate at temperatures warmer than -10C and whose <br />0 <br />effective radii reach the 15-micron precipitation threshold at T>15C. Thus, clouds with a classification of 1 <br />are highly continental with small drops, no coalescence, and delayed glaciation, sometimes to the point of <br />0 <br />homogeneous nucleation (i.e. at -38C) (Rosenfeld and Woodley, 2000), while those with a classification of 5 <br />are highly maritime with intense coalescence and raindrop formation and full glaciation at warm temperatures. <br />4.0INITIAL PLANS FOR SPECTRA II <br /> The primary aim of SPECTRA II wasto improve and evaluate the physical mechanisms in the <br />atmosphere, and particularly within convective cloud towers, in order to identify, for later application during <br />operational cloud seeding, the appropriate seeding protocol(s) that will lead to the reduction of damage and loss <br />from drought and hail. It was expected that the understanding gained from this endeavor would enhance the <br />efforts of the water-resource management community in the semi-arid Southwest to apply a regional weather <br />modification program systematically for both precipitation enhancement and hail suppression. The research <br />will develop methods and procedures for documenting the efficacy of opportunistic cloud seeding. Very <br />importantly, this research will contribute significantly to a more thorough understanding, and validation, of the <br />“working” hypothesis now in use in the southern U. S. Great Plains region for increasing rainfall and <br />suppressing hail. <br />4.1Goals and Objectives <br />To attain the fundamental purpose of SPECTRA II, specific objectives related to field <br />work, and subsequent analysis, were pursued: <br />(4) To disperse hygroscopic material (finely milled salts) into the updraft regions of growing <br />convective towers and, then, to observe and document cloud behavior in response to the seeding <br />using ground-based radar and cloud-physics data obtained with a “chase” aircraft especially <br />14 <br />