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CRITICAL ISSUES IN WEATHER MODIFICATION RESEARCH Committee on the Status of and Future Directions in U.S. Weather Moclification Research and Operations Board on Atmospheric Sciences and Climate Division on Earth and Life Studies NATIONAl RESEARCH COlJbJCll OF Tf-fE NATIONAL ACADEMfES : yip #X*^ ~ 'l-d W]~ ~ -fir .~ f ~# . ~ ~ .

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THE NATIONAL ACADEMIES PRESS 500 Fifth Street, NW Washington, DC 20001 NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. Support for this project was provided by the National Oceanic and Atmospheric Administration under Contract No. 50-DGNA-1-90024-T0006. Any opinions, findings, and conclusions, or recommendations expressed in this publication are those of the authorts) and do not necessarily reflect the views of the organizations or agencies that provided support for the project. International Standard Book Number 0-309-09053-9 (Book' International Standard Book Number 0-309-518520-0 (PDF) Library of Contress Control Number 2003115099 Additional copies of this report are available from the National Academies Press, 500 Fifth Street, N.W, Lockbox 285, Washington, D.C. 20055; (800) 624-6242 or (202) 334-3313 (in the Washington metropolitan area); Internet, http://www.nap.edu. Cover: Photograph taken by Dr. William L. Woodley at 7:39 pm CDT on August 11, 2001, from a Texas seeder aircraft flying at 20,000 ft. The cloud shown reaching cumulonimbus stature had been seeded near its top 10 minutes earlier with ejectable silver iodide pyrotechnics. Copyright 2003 by the National Academy of Sciences. All rights reserved. Printed in the United States of America

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THE NATIONAL ACADEMIES Advisers to the Nation on Science, Engineering, and Medirine The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M.-Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Wm. A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. ~ ' ' ' ' ' ' ' ' ~ unct~on~ng In accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. Wm. A. Wulf are chair and vice chair, respectively, of the National Research Council. www. national-academies. ore

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COMMITTEE ON THE STATUS OF AND FUTURE DIRECTIONS IN U.S. WEATHER MODIFI CATION RE SEARCH AND OPERATIONS MICHAEL GARSTANG (chair), University of Virginia, Charlottesville ROSCOE R. BRAHAM, JR., North Carolina State University, Raleigh ROELOF T. BRUINTJES, National Center for Atmospheric Research, Boulder, Colorado STEVEN F. CLIFFORD, University of Colorado, Boulder ROSS N. HOFFMAN, Atmospheric & Environmental Research, Inc., Lexington, Massachusetts DOUGLAS K. LILLY, University of Oklahoma, Norman ROLAND LIST*, University of Toronto, Ontario, Canada ROBERT J. SERAFIN, National Center for Atmospheric Research, Boulder, Colorado PAUL D. TRY, Science & Technology Corporation, Silver Spring, Maryland JOHANNES VERLINDE, Pennsylvania State University, University Park NRC Staff LAURIE GELLER, Study Director (until 7/3 1/03) VAUGHAN C TUREKIAN, Study Director (until 8/31/02) ELIZABETH A. GALINIS, Project Assistant JULIE DEMUTH, Research Associate * Resigned 9/02 v

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BOARD ON ATMOSPHERIC SCIENCES AND CLIMATE ERIC J. BARRON, (chair", Pennsylvania State University, University Park RAYMOND J. BAN, The Weather Channel, Inc., Atlanta, Georgia ROBERT C. BEARDSLEY, Woods Hole Oceanographic Institution, Massachusetts ROSINA M. BIERBAUM, University of Michigan, Ann Arbor HOWARD B. BLUESTEIN*, University of Oklahoma, Norman RAFAEL L. BRAS, Massachusetts Institute of Technology, Cambridge STEVEN F. CLIFFORD*, University of Colorado/CIRES, Boulder CASSANDRA G. FESEN, Dartmouth College, Hanover, New Hampshire GEORGE L. FREDERICK*, Vaisala Inc., Boulder, Colorado JUDITH L. LEAN*, Naval Research Laboratory, Washington, D.C. MARGARET A. LEMONE, National Center for Atmospheric Research, Boulder, Colorado MARIO J. MOLINA, Massachusetts Institute of Technology, Cambridge MICHAEL J. PRATHER*, University of California, Irvine WILLIAM J. RANDEL, National Center for Atmospheric Research, Boulder, Colorado RICHARD D. ROSEN, Atmospheric & Environmental Research, Inc., Lexington, Massachusetts THOMAS F. TASCIONE*, Sterling Software, Inc., Bellevue, Nebraska JOHN C. WYNGAARD, Pennsylvania State University, University Park Ex officio Members EUGENE M. RASMUSSON, University of Maryland, College Park ERIC F. WOOD, Princeton University, New Jersey NRC SfaJ0f CHRIS ELFRING, Director ELBERT W. (JOE) FRIDAY, JR., Senior Scholar LAURIE GELLER, Senior Program Officer AMANDA STAUDT, Program Officer SHELDON DROBOT, Program Officer JULIE DEMUTH, Research Associate ELIZABETH A. GALINIS, Project Assistant ROB GREENWAY, Project Assistant DIANE GUSTAFSON, Administrative Associate ROBIN MORRIS, Financial Associate * Term ended 2128103 Vl

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Preface The growing evidence that human activities can affect the weather on scales ranging from local to global has added a new and important dimension to the place of weather modification in the field of atmospheric sciences. There is a need, more urgent than ever, to understand the fundamental processes related to intentional and unintentional changes in the atmosphere. The question of how well current technology, practice, and theory are equipped to meet these broader goals of weather modification is central to this report. The challenge to find the right balance between assured knowledge and the need for action is one which must guide the future actions of both scientists and administrators concerned with weather modification. Difficulties demonstrating repeatability of weather modification experiments, providing convincing scientific evidence of success, and overcoming serious social and legal problems led to the moderation of the early predictions of success in weather modification by the late 1970s. The need to understand the fundamental physical and chemical processes underlying weather modification became obvious, thus a dedicated research effort was repeatedly recommended by successive national panels. Failure to devote significant public and private resources to basic research polarized both the support agencies and scientific community, generating serious feelings of ambivalence within these communities toward weather modification. Despite significant advances in computational capabilities to deal with complex processes in the atmosphere and remarkable advances in observing technology, little of this collective power has been applied in any coherent way to weather modification. The potential for progress in weather modification as seen by this Committee is dependent upon an improved fundamental understanding of crucial cloud, precipitation, and larger- scale atmospheric processes. The Committee believes that such progress is now within reach should the above advances be applied in a sustained manner to answer fundamental outstanding questions. While the Committee acknowledges the prospect of achieving significant advances in the ability of humans to exercise a degree of control over the weather, we caution that such progress is not possible without a concerted and sustained effort at understanding basic processes in the atmosphere. Furthermore, such results are as likely to lead to viable weather modification methodologies as they are to indicate that intentional modification of a weather system is neither currently possible nor desirable. . . V11

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. ~ . V111 PREFACE A significant part of the advances projected from applying the current intellectual and technological tools to solving critical uncertainties in weather modification will produce results well beyond the initial objective and will lead to applications in totally unexpected areas. For example, the ability to make useful precipitation forecasts, particularly from convective storms, may be a valuable by-product of weather modification research. The Committee is also acutely conscious of the fact that, particularly in modifying severe weather, researchers may be required to have, before attempting treatment, a reliable and proven ability to predict what would have taken place had the system not been modified. As a chaotic system, the atmosphere is inherently predictable only for a limited time, with the time limit shorter for smaller spatial scales. Thus, predictions must be couched in probabilistic terms that may not satisfy the user community that a reliable prediction has been made. This report is the latest in a series of assessments of weather modification carried out by the National Academies, which produced reports in 1964, 1966, and 1973, aimed at guiding weather modification research and policy development. The last National Academies report is nearly three decades old and, despite more recent assessments by other bodies such as the American Meteorological Society and the World Meteorological Organization, a need was seen for an evaluation of weather modification research and operations in the United States. In November 2000, the National Academies' Board on Atmospheric Sciences and Climate (BASCJ organized a program development workshop to assess whether it would be useful to take a fresh look at the scientific underpinnings of weather modification. A year later, a study committee was convened, and four committee meetings were held over eight months. The Committee received input from individuals in federal and state agencies, scientists who have or are conducting relevant research, and professionals active in operational weather programs. The charge to the Committee explicitly excluded consideration of the complex social and legal issues associated with weather modification. This part of the question is of such importance in any weather modification effort that the Committee did go so far as to note, but not elaborate upon, the most critical questions in this area. Also in accordance with its charge, the Committee did not address inadvertent global-scale modification of climate and weather (e.g., global warming). However, the potential local and regional impacts of both intentional and inadvertent weather modification are considered. The report is addressed primarily to Administration officials and funding agencies who determine the direction of atmospheric research through budget decisions. The Committee recognizes, however, that weather modification has a wide audience. The Preface and the Executive Summary are directed at this wider audience, while a greater level of technical detail is contained within the body of the report. Michael Garstang, Chair Committee on the Status of and Future Directions in U.S. Weather Modification Research and Operations

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Acknowledgments This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the National Research Council's Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their review of this report: Richard Anthes, University Corporation for Atmospheric Research Rafael Bras, Massachusetts Institute of Technology Stanley A. Changnon, Illinois State Water Survey William Cotton, Colorado State University John Hallett, Desert Research Institute Daniel Rosenfeld, Hebrew University Joanne Simpson, NASA Goddard Space Flight Center Gabor Vali, University of Wyoming Francis Zwiers, University of Victoria Although the reviewers listed above have provided constructive comments and suggestions, they were not asked to endorse the report's conclusions or recommendations, nor did they see the final draft of the report before its release. The review ofthis report was overseen by John A. Dutton, The Pennsylvania State University. Appointed by the National Research Council, he was responsible for making certain that an independent examination ofthis report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution. ix

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Contents EXECUTIVE SUMMARY 1 INTRODUCTION Motivation, 9 Cloud Physics, 13 First Experiments and First Controversies, 15 An Emerging Industry and Developing Public Concern, 16 The Pioneering Experiments, 17 The Need for Impartial Assessment of Seeding Results, 18 2 CURRENT STATUS OF WEATHER MODIFICATION OPERATIONS AND RESEARCH Current Operational Efforts, 23 Current Scientific Efforts, 24 Other Results, 35 Recognition of Key Uncertainties in Weather Modification, 36 EVALUATION REQUIREMENTS FOR WEATHER MODIFICATION Physical Evaluation, 39 Statistical Evaluation, 40 Measurement Uncertainties, 42 Uncertainties in Defining and Tracking the Target, 42 Uncertainties in Reaching the Target, 43 Assessing the Area Affecte d, 44 4 TOOLS AND TECHNIQUES FOR ADVANCING OUR UNDERSTANDING Measurement and Observing Technologies, 45 Modeling and Data Assimilation, 54 Laboratory Studies, 61 Field Studies, 63 Xl 1 9 23 39 45

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. . X11 CONCLUS IONS AND RE COMM ENDATIONS Conclusions, 67 Recommendations, 72 REFERENCES APPENDIXES B C D Glaciogenic and Hygroscopic Seeding: Previous Research and Current Status, 89 Modern Statistical Methods and Weather Modification Research, 107 Glossary, 1 14 Acronyms, 118 E Community Participation, 1 19 F Committee Member B fog raphies, 1 2 1 CONTENTS 67 75 89