ASCE Standard ASCE/EWRI 42-04 Standard Practice for the Design and Operation of Precipitation Enhancement Projects

CONTENTS

FOREWORD v

LIST OF FIGURES x

SECTION 1.0 INTRODUCTION TO PRECIPITATION ENHANCEMENT

PROJECTS 1

1.1 Historical Perspective 1

1.1.1 Orographic Clouds 1

1.1.2 Convective Clouds 2

1.1.3 Summary 3

1.2 Status of Precipitation Enhancement Technology 3

1.2.1 American Society of Civil Engineers 3

1.2.2 Weather Modification Association 4

1.2.3 American Meteorological Society 4

1.2.4 World Meteorological Organization 5

SECTION 2.0 SCIENTIFIC BASIS OF NATURAL PRECIPITATION EFFICIENCY AND ITS MODIFICATION 7

2.1 Cloud Condensate 7

2.1.1 Properties of Cloud Condensate 7

2.1.2 Destination of Cloud Condensate 7

2.2 Growth of Precipitation-Sized Particles from Cloud Condensate 7

2.2.1 Direct Collision and Coalescence 8

2.2.2 Supercooled Cloud Droplets and Ice Crystals 8

2.3 Precipitation Augmentation Concepts 9

2.3.1 Cloud Seeding to Increase Precipitation Efficiency (Static Seeding Process) 9

2.3.2 The Role of Cloud Seeding to Enhance Cloud Development (Dynamic Seeding) 10

2.3.2.1 Seeding to Enhance Development of an Individual Convective Cloud 10

2.3.2.2 Complexities of the Dynamic Seeding Concepts 11

2.3.2.3 Expansion of Dynamic Seeding Concepts to Cloud Clusters and Mesoscale Systems 13

SECTION 3.0 THE DESIGN OF PRECIPITATION ENHANCEMENT RESEARCH AND OPERATIONAL PROJECTS 13

3.1 Definition of Project Scope 14

3.1.1 Basic Target Area Concepts 15

3.1.2 Initial Design Considerations 16

3.1.3 Climatology 16

3.2 Targeting and Delivery Methods 16

3.2.1 Aerial Applications 17

3.2.2 Ground Applications 19

3.2.3 Advantages and Disadvantages of Aerial and Ground Systems 21

3.3 Seeding Agent Selection 22

3.3.1 Silver Iodide 22

3.3.2 Dry Ice 24

3.3.3 Other Ice Nucleants 24

3.3.4 Hygroscopic Agents 24

3.3.5 Quality Control 25

3.4 Meteorological Data Collection and Instrumentation 25

3.4.1 Real-Time Decision-Making and Monitoring Instrumentation 26

3.4.1.1 Available National Weather Service Data 26

3.4.1.2 Special Project Precipitation Gauges 27

3.4.1.3 Special Project Weather Radar 28

3.4.1.4 Computer-Based Radar Storm Tracking 29

3.4.1.5 Special Project Rawinsondes 29

3.4.1.6 Real-Time Liquid Water Observations 30

3.4.1.7 Special Project Cloud Physics Instrumentation 31

3.4.1.8 Other Instrumentation and Equipment 32

3.4.2 Measurements of Potential Value in Post-Project Assessments 33

3.4.2.1 Precipitation Gauge Data 33

3.4.2.2 Remote Sensor Data 33

3.4.2.3 Cloud Physics Data 34

3.4.2.4 Streamflow Data 34

3.4.2.5 Snow Course Data 34

3.4.2.6 Snow Sample Data 35

3.4.2.7 Numerical Cloud Modeling 35

3.5 Choice and Siting of Cloud Seeding Equipment 36

3.5.1 Dispersion Rates of Cloud Seeding Materials in Wintertime Clouds 37

3.5.2 Aerial Cloud Seeding Modes 38

3.5.3 Ground-Based Cloud Seeding Modes 38

3.6 Legal Issues 39

3.6.1 Potential for Litigation 39

3.6.2 Regulation 39

3.7 Environmental Concerns 40

3.7.1 Redistribution of Precipitation 40

3.7.2 Seeding Agent Safety 40

SECTION 4.0 OPERATIONS OF PRECIPITATION ENHANCEMENT PROJECTS 40

4.1 The Operations Manual 41

4.2 Personnel Requirements 41

4.2.1 Meteorological Staff 41

4.2.2 Cloud-System Treatment Pilots 41

4.2.3 Direction of Operations 41

4.2.4 Support Personnel 42

4.3 Operational Decision-Making 42

4.3.1 Chronology 42

4.3.2 Opportunity Recognition 42

4.3.2.1 Aircraft Right Crews 42

4.3.2.2 IN Treatment by Ground-Based Generators 43

4.4 Communications 43

4.5 Safety Considerations 44

4.5.1 Safety of Field Personnel 44

4.5.1.1 Radar Safety 44

4.5.1.2 Use, Handling, and Storage of Seeding Agents 44

4.5.1.3 Severe Weather Hazards 44

4.5.1.4 Aircraft Safety 45

4.5.2 Seeding Suspension Criteria 45

4.6 Public Relations, Information, and Involvement 46

SECTION 5.0 EVALUATION OF PRECIPITATION ENHANCEMENT PROJECTS 46

5.1 Project Design Constraints 46

5.1.1 Randomized versus Nonrandomized Projects 47

5.1.2 Selection of Target and Control Areas 47

5.1.2.1 Precipitation Patterns 47

5.1.2.2 Storm Frequency 47

5.1.2.3 Contamination 47

5.2 Evaluation Measures 47

5.2.1 Evaluations Using Direct Evidence 48

5.2.1.1 Precipitation Data 48

5.2.1.2 Radar Data 48

5.2.2 Evaluation through Indirect Evidence 48

5.2.2.1 Crop Yield Data 48

5.2.2.2 Runoff Data 48

5.2.2.3 Chemical Analyses 49

5.3 Dissemination of Results 49

SECTION 6.0 GLOSSARY OF TERMS AND ACRONYMS 49

SECTION 7.0 REFERENCES 53

SECTION 8.0 CONVERSION OF UNITS 58

Index 61

FIGURES

3-1 Precipitation enhancement project areas 15

3-2 Cloud base seeding aircraft with wing-tip ice nuclei generators 17

3-3 Wing rack for bum-in-place cloud seeding flares 18

3-4 Example of a droppable Agl pyrotechnic rack 18

3-5 Example of a dry ice dispenser mounted in an aircraft 19

3-6 Ground-based ice nuclei generators 20

3-7 Example of a ground-based Agl pyrotechnic dispenser 21

3-8 Example of a propane dispenser 21

3-9 Acetone-based seeding solutions may be mixed as needed in the field, or delivered to field sites premixed 23

3-10 Dry ice, in extruded pellet form 24

3-11 Hygroscopic flares on wing-rack 25

3-12 Example of a weighing bucket recording precipitation gauge 28

3-13 Example of a self-contained weather radar installation in the field 29

3-14 Example of a rawinsonde receiver system 30

3-15 Example of a microwave radiometer and Lidar 31

3-16 University of Wyoming King Air cloud physics aircraft 32

3-17 The observed maximum temperature for each day of the North Dakota Thunderstorm Project, and the corresponding model-predicted temperature 36

3-18 Depiction of cloud and precipitation at 285 min 37

3-19 Graphical depiction of three seed lines produced from airborne Agl seeding 38