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Binod Pokharel, Bart Geerts, and Xiaoqin Jing

1. Introduction Water is vital for humanity and the environment. Water availability is limited yet demand is expected to continue to rise. Limited resources and increasing demand have prompted an interest in the feasibility of augmenting the water supply by means of cloud seeding. The most researched and widely practiced method of advertent weather modification aimed at precipitation enhancement in the western United States is the glaciogenic seeding of cold-season orographic clouds (e

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Anthony E. Morrison, Steven T. Siems, Michael J. Manton, and Alex Nazarov

1. Introduction The practice of cloud seeding has remained a point of contention in the scientific community for over half of a century. Early laboratory experiments were able to readily demonstrate precipitation enhancement mechanisms through the conversion of supercooled water to ice by the introduction of suitable ice nuclei ( Schaefer 1946 ), and these laboratory experiments were followed by a field demonstration on individual clouds by Kraus and Squires (1947) . However, the extension of

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Robert M. Rauber, Bart Geerts, Lulin Xue, Jeffrey French, Katja Friedrich, Roy M. Rasmussen, Sarah A. Tessendorf, Derek R. Blestrud, Melvin L. Kunkel, and Shaun Parkinson

1. Introduction The U.S. population more than doubled from 1950 to 2010 and shifted from rural to urban areas ( U.S. Census Bureau 2010 ). Southern and western states experienced the greatest population increase, resulting in concurrent expansion of public water supply systems. In response to increased demands and limits on water supplies, western communities have sought additional water sources through technologies such as cloud seeding, and/or have instituted water-conservation measures to

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Daniel Rosenfeld, Duncan Axisa, William L. Woodley, and Ronen Lahav

1. Introduction This study examines the spreading and dilution of seeded hygroscopic aerosols from two perspectives—their impacts on cloud drop size distribution (DSD) and how that might affect the precipitation forming processes. Before describing the experiments, we briefly state the physical background. Hygroscopic seeding for rain enhancement in convective clouds is aimed at accelerating autoconversion (i.e., the conversion of cloud water to precipitation). This was reviewed extensively by

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Lulin Xue, Akihiro Hashimoto, Masataka Murakami, Roy Rasmussen, Sarah A. Tessendorf, Daniel Breed, Shaun Parkinson, Pat Holbrook, and Derek Blestrud

1. Introduction Freshwater is becoming one of the most stressed and in-demand natural resources given the rapidly increasing human population. The need for water provides motivation to find solutions other than drilling wells, digging canals, and building reservoirs. Cloud seeding is one method being pursued in many locations around the world. Since the first proof-of-concept experiment on glaciogenic seeding of nonprecipitating supercooled stratus clouds by dry ice ( Schaefer 1946 ) and the

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Sarah A. Tessendorf, Kyoko Ikeda, Courtney Weeks, Roy Rasmussen, Jamie Wolff, and Lulin Xue

1. Introduction Since the seminal work on glaciogenic cloud seeding in the late 1940s ( Schaefer 1946 ; Vonnegut 1947 ), a number of programs have investigated whether seeding winter orographic clouds with silver iodide (AgI) could produce additional snow. Evaluation of this hypothesis has been attempted over the last half century using randomized statistical experiments, observational studies, and numerical modeling of both natural and seeded clouds, but most programs to date have yielded

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Xia Chu, Bart Geerts, Lulin Xue, and Binod Pokharel

particles that activate at a relatively high temperature can be injected in supercooled liquid water (SLW) cloud. Silver iodide (AgI) nuclei are suitable for this purpose ( Vonnegut 1947 ) at temperatures below approximately −8°C ( DeMott 1997 ; Breed et al. 2014 ). Many projects have been staged to study the impact of ground-based or airborne AgI seeding on precipitation. Many of these targeted relatively shallow winter orographic clouds, because SLW is common in such clouds. Several projects focused

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Xiaoqin Jing, Bart Geerts, and Bruce Boe

1. Introduction Intentional weather modification efforts normally define a target area where the impact of seeding is expected and analyzed. Usually this seeding area is within 50 km from the source of artificial nuclei (e.g., Breed et al. 2014 ). There have long been concerns about the downwind effect of cloud seeding activities (e.g., Long 2001 ; DeFelice et al. 2014 ). The general public often raises concerns about how precipitation enhancement in a close-fetch target area may result in

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Lulin Xue, Sarah A. Tessendorf, Eric Nelson, Roy Rasmussen, Daniel Breed, Shaun Parkinson, Pat Holbrook, and Derek Blestrud

( Xue et al. 2013 , hereinafter Part I ), we demonstrated that a silver iodide (AgI) cloud-seeding parameterization coupled with the Thompson micropyhysics scheme ( Thompson et al. 2004 , 2008 ) reasonably simulated glaciogenic seeding effects of orographic clouds from ground-based generators and aircraft in an idealized two-dimensional (2D) model setup. The results indicated that, for stably stratified orographic clouds, AgI particles nucleated ice crystals mainly through deposition and enhanced

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Bart Geerts, Qun Miao, Yang Yang, Roy Rasmussen, and Daniel Breed

1. Introduction In a 2008 editorial column in Nature , it was argued that “… weather modification is one of those areas in which science can have an immediate and obvious benefit for society” ( Nature 2008 ). Cloud seeding probably has been the most widely practiced method of intentional weather modification for the last few decades (e.g., Bruintjes 1999 ; Qiu and Cressey 2008 ). It is remarkable that notwithstanding a series of targeted field campaigns and the stronger experimental control

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