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Design of an Experiment to Suppress Hail in Illinois

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Design of an Experiment to Suppress Hail in Illinois BULLETIN 61 Design of an Experiment to Suppress Hail in Illinois by STANLEY A. CHANGNON, Jr., and GRIFFITH M. MORGAN, Jr. STATE OF ILLINOIS HON. DANIEL WALKER, Governor DEPARTMENT OF REGISTRATION AND EDUCATION RONALD E. STACKLER, J.D., Director BOARD OF NATURAL RESOURCES AND CONSERVATION Ronald E. Stackler, J.D., Chairman Thomas Park, Ph.D., Biology H. S. Gutowsky, Ph.D., Chemistry Robert H. Anderson, B.S., Engineering Stanley K. Shapiro, Ph.D., Forestry Laurence L. Sloss, Ph.D., Geology John C. Guyon, Ph.D., Southern Illinois University William L. Everitt, E.E., Ph.D., University of Illinois STATE WATER SURVEY DIVISION WILLIAM C. ACKERMANN, D.Sc, Chief URBANA 1976 Printed by authority of the State of Illinois-Ch. 127, IRS, Par. 58.29 (3-76-1500) CONTENTS PAGE Introduction 1 Part 1. Results of DESH 5 A. Radar-hail detection and forecasting 5 Introduction 5 3-cm radar studies 5 Surface reflectivities-hail relations 5 Relationship of hail and reflectivities aloft 6 Hail-volume detection 6 Characteristics of hail-producing echoes 7 Summary 7 10-cm radar studies 8 Chill dual wavelength radar and related studies 8 Signal processing 9 Comparison of radar data and hail observations 9 Radar estimates of severe storm properties on 3 April 1974 13 Radar-thermodynamic hail day determination 14 Conceptual framework 15 Data 15 Hail probability as a function of surface dew point temperature .... 15 Hail probability as a function of maximum daily echo heights 16 Hail probability as a function of the maximum daily echo height and the warm layer thickness 18 Diurnal behavior of echo tops 21 Seasonal changes in echo-top heights 25 Radar-derived indications of hail outbreaks 26 B. Estimates from radar for operational planning 29 Factors pertinent to low-level aircraft operations 29 Hail day cloud base heights 29 Visibility 30 Echo-cloud dimensions 31 Duration of network storm periods 33 Frequency of potential hail cells 34 Cell development over the network 36 C. DESH field measurements 37 Radar and support operations 37 Network operations 37 Surface hail results 40 Micro-network study 45 D. Weather analysis and forecasting studies 50 Synoptic climatology of hail in Illinois 50 Hail and severe weather calendar 51 Data and evaluation of data sources 51 Coincidence of hail and severe weather 53 Objective weather analysis 53 Dynamic destabilization as a convective release mechanism 53 Calculation of mesoscale vertical velocities 55 Application of cumulative lift to Illinois thunderstorm data 61 Application of the cumulative lift to short-range storm forecasts 67 Meshing the TFA with surface and upper air thermodynamics 72 Continuing research 73 CONTENTS (Continued) PAGE E. Cloud properties 74 Cloud base updrafts 74 Mid-cloud penetrations 75 F. Suppression hypothesis and seeding technologies 81 Storm structure and airflow 81 Suppression hypothesis 82 Seeding technologies 82 Soviet projects 83 Alberta hail project field program 84 South Africa project 85 National hail research experiment 86 G. Desirability studies 88 Public attitude sampling 88 Silver sampling 92 Economic studies 93 H. Evaluation of hail suppression........................................................................................ 94 South Africa project 94 Data 94 Analysis and results 95 Summary 97 Texas project 100 Hail-day results 100 Crop-hail insurance results 101 Conclusions 105 North Dakota project 105 Illinois sampling requirements 106 Basic data and crop-insurance parameters 106 Experimental design 107 Results 110 Summary and conclusions 114 Summary 115 Part 2. Design of an experiment to suppress hail in Illinois 116 Introduction 116 Experimental goals 116 Design philosophy 117 Application of results 118 Design components 118 Modification hypothesis and seeding techniques 118 Hypothesis choice 118 Conceptual models 119 Basic modification hypothesis 119 Seeding techniques 119 Delivery systems 119 Seeding material and rate of seeding 120 Statistical-physical design and evaluation 120 Proof 120 Detection of effect 121 Experimental unit 121 Summary 123 CONTENTS (Concluded) PAGE Operational aspects 124 Headquarters 124 Forecast system 124 Seeding system 125 Seeding materials 126 Radar 126 Evaluation system 126 Networks 126 Crop loss data 127 Atmospheric data 127 Radar 127 Satellite 128 Data processing and preliminary analysis 128 Impact monitoring and public interactions 128 Interactions 128 Impact monitoring 130 Public attitudes 130 Economic impacts 130 Impacts beyond the project area 130 Ecological impacts 131 Additional issues requiring research 131 Part 3. Advisability of an experiment in Illinois 133 References 135 Appendices 140 A. List of hail-related papers and reports of the Illinois State Water Survey . 140 B. The public view toward weather modification in Illinois: A social assessment 147 C. Statement on planned precipitation modification 173 D. Summary of discussions on hail suppression with operational experts ... 176 E. Distribution of frontal passages in east-central Illinois, 1951-1960 .... 178 F. Summary of activities related to DESH 187 Design of an Experiment to Suppress Hail in Illinois by Stanley A. Changnon, Jr., and Griffith M. Morgan, Jr. INTRODUCTION This report concludes a 2 1/2-year project dealing with the development of an optimum design of a hail suppression experiment in Illinois. The ultimate goal of the project was to advise the Illinois government and citizens as to the desirability of hail suppression in Illinois, and to provide the proper experimental design. Importantly, this project for the Design of an Experiment to Suppress Hail (DESH) was based on data and results from prior hail research that began in 1967, some of which was aimed at this goal. This report serves also as the final report of National Science Foundation (RANN) grants GI-37859 and ERT 73-07770. This effort was funded by the state of Illinois and the Weather Modification Program of the Foundation. The authors were the Co-Principal Investigators of the NSF grants. After 10 years of various kinds of specialized hail research projects (1957-1966), the Illinois State Water Survey began in 1967 a research program aimed partially at developing a de­ sign for a hail suppression experiment in Illinois (figure 1). Such an experiment in Illinois was con­ sidered to have viable prospects within a national framework, since the Illinois hail climate is Figure 1. Flow diagram for Illinois hail suppression program 1 representative of that throughout the Midwest and the crop-hail losses in the Midwest rank second nationally only to those of the Great Plains (Changnon, 1972). More crop-hail insurance is sold in Illinois than in any other state, and Illinois ranks seventh nationally in total hail losses per year. In 1973 Illinois led the nation in crop-hail losses with a total of $40 million. DESH comprised a series of interlocking studies that incorporated a 'building block' and 'stop-go' approach. In the logical sequence of such a program, as shown on figure 1, the initial studies were those critical to answering prime unknowns about midwestern hail, and thus essential to proper planning of the later studies of the current design program. The major initial studies and the years they were pursued were: 1) Ascertaining the potential economic benefits of hail suppression (1969-1972) 2) The gathering of basic surface hail data to understand its time-space variability, suitable size and shape of experimental area, and damage-producing characteristics (1967-1972) 3) Developing instruments to provide desired measures of surface hail (1967-1972) 4) Investigating the utility of 3-cm wavelength weather radars to detect hailstorms in field operations and for suppression evaluation (1967-1969) 5) Analyzing historical hail data to ascertain the optimum statistical design, best evaluation techniques, and the probable length of a well-designed program (1967-1970) 6) Conceptual modeling of hailstorms (1969-1972) All of these initial studies were performed under a combination of state, private industry, and National Science Foundation sponsorship (NSF GA-482, GA-1520, GA-4618, GA-18909, GA-43005, and GA-16917). These studies provided a) the information desired, and b) importantly, the information that indicated that a suppression experiment in Illinois was possible within a scientific framework and desirable within an economic framework. Other important information areas essential to a properly designed experiment were not then available, but became the subjects studied in the 30-month DESH project. These included: 1) Investigation of seeding systems and determination of the technology needed for Illinois types of hailstorms 2) Evaluation of potential adverse side-effects from hail modification (increased severe weather, decreased rainfall) 3) Study of hail forecasting techniques for operational utility 4) Evaluation of 10-cm radar for monitoring of hail production in storms for operational seeding decisions 5) The ascertainment of public attitudes toward weather modification so as to develop a proper social framework for the experiment 6) Chemical monitoring of background amounts of potential seeding materials in Illinois rainwater and hailstones so that measurements during an experiment can be used to evaluate possible effects on the ecosystem, to examine the efficacy of the seeding system, and to discern possible differences in the hailfall characteristics of seeded and nonseeded storms 7) Atmospheric sampling of Illinois hail-producing cloud conditions with respect to their moisture and nuclei
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