Radar Meteorology A First Course

A comprehensive introduction to the current technology and application of radar in meteorology and atmospheric sciences

Written by leading experts in the field, Radar Meteorology, A first Course offers an introduction to meteorological radar systems and applications, with emphasis on observation and interpretation of physical processes in clouds and weather systems. This comprehensive introduction to the subject offers an overview of the quantities essential to radar meteorology including the radar reflectivity factor, and Doppler, dual-polarization, and multi-wavelength radar variables. The authors highlight wind retrieval from single and multiple Doppler radars, precipitation estimation and hydrometeorological applications, with chapters dedicated to interpretation of radar data from warm season mid-latitude severe weather, winter storms, tropical cyclones and more.

In addition, Radar Meteorology highlights research applications of this burgeoning technology, exploring dynamic applications such as space-borne and ground-based vertically pointing radar systems, and cloud, airborne and mobile radars.  As meteorological radars are increasingly used professionally for weather observation, forecasting and warning, this much-needed text: 

•    Presents an introduction to the technical aspects and current application of radar as used in the meteorology and atmospheric sciences

•    Contains full-colour illustrations that enhance the understanding of the material presented

•    Examines the wide-range of meteorological applications of radar

•    Includes problems at the end of each chapter as a helpful review of the contents

•    Provides full instructor support with all illustrations and answers to problems available via the book’s instructor website. 

Radar Meteorology offers a much-needed introductory text to the study of radar as applied to meteorology. The text was designed for a one semester course based on the authors’ own course in Radar Meteorology at the University of Illinois at Urbana-Champaign.

Robert M. Rauber, Professor of Atmospheric Sciences, University of Illinois, Urbana-Champaign, US.

Stephen W. Nesbitt, Professor of Atmospheric Sciences, University of Illinois, Urbana-Champaign, US.

Preface xvii

Acknowledgments xxi

About the Companion Website xxiii

1 Properties of Electromagnetic Waves 1

1.1 Introduction 1

1.2 Electric and magnetic fields 2

1.2.1 The electric field 2

1.2.2 The magnetic field 4

1.2.3 Relating the electric and magnetic fields—a simple dipole antenna 5

1.2.4 Maxwell equations 6

1.3 The nature of electromagnetic radiation 8

1.3.1 The electromagnetic spectrum 8

1.3.2 Electromagnetic wave interactions 9

1.4 Interactions of electromagnetic waves with matter 11

1.4.1 Refraction 12

1.4.2 Reflection 12

1.4.3 Mie scattering 14

1.4.4 Bragg scattering 17

1.4.5 Absorption 18

1.5 Polarization of electromagnetic waves 18

Important terms 20

Review questions 21

Challenge problems 22

2 Radar Hardware 23

2.1 Introduction 23

2.2 Frequency and wavelength 23

2.3 Components of a weather radar system 25

2.3.1 Transmitter section 26

2.3.2 Waveguides, rotary joints, polarization switching devices, and circulators 28

2.3.3 The antenna section 32

2.3.4 The receiver section 36

2.3.5 Magnetron transmitters 38

2.4 Specialized radar systems 40

2.4.1 Phased-array radars 40

2.4.2 Mobile and deployable radars 41

2.4.3 Airborne radars 43

2.4.4 Spaceborne radars 44

Important terms 46

Review questions 47

Challenge problems 47

3 Radar Characteristics 49

3.1 Introduction 49

3.2 Range and range ambiguity 50

3.3 The transmitted and received signal 53

3.3.1 Pulse duration and pulse length 54

3.3.2 Power and the duty cycle 54

3.4 Radar geometry and types of displays 56

3.4.1 Common radar displays in spherical coordinates 56

Important terms 64

Review questions 64

Challenge problems 64

4 The Path of a Radar Ray 66

4.1 Introduction 66

4.2 Ray propagation in an idealized atmosphere 67

4.2.1 Factors influencing radar ray paths 67

4.2.2 The path of a ray in an idealized atmosphere 69

4.2.3 The range and height of a pulse volume in space 72

4.3 Anomalous propagation 74

Important terms 78

Review questions 78

Challenge problems 79

5 Power and the Radar Reflectivity Factor 82

5.1 Introduction 82

5.2 Radar equation for a solitary target 83

5.2.1 Power flux density incident on a target 83

5.2.2 Power flux density scattered back to the radar 85

5.2.3 Backscattered power collected by the radar antenna 86

5.2.4 Implications of the radar equation 87

5.3 Radar equation for a distributed target 89

5.3.1 The contributing volume for distributed targets 89

5.3.2 The radar cross section of distributed targets 91

5.3.3 The radar equation for a distributed target 94

5.4 The weather radar equation 95

5.4.1 Radar cross section of a small dielectric sphere 95

5.4.2 The radar reflectivity factor 96

5.4.3 The weather radar equation 97

5.4.4 The validity of the Rayleigh approximation 98

5.5 Summary 100

Important terms 101

Review questions 101

Challenge problems 102

6 Radial Velocity—The Doppler Effect 104

6.1 Introduction 104

6.2 Measurement of radial velocity 106

6.2.1 Phase measurements and radial velocity retrieval 107

6.2.2 Velocity ambiguities and their resolution 108

6.3 Doppler spectra 115

6.3.1 Doppler spectra of weather and other targets 116

6.3.2 Moments of the Doppler spectrum 117

6.4 Measurement of the Doppler moments 119

6.5 Summary 122

Important terms 123

Review questions 123

Challenge problems 124

7 Dual-Polarization Radar 126

7.1 Introduction 126

7.2 The physical bases for radar polarimetry 127

7.3 Measuring polarimetric quantities 130

7.4 Reflectivity, differential reflectivity, and linear depolarization ratio 132

7.4.1 Reflectivity factor in the dual-polarization framework (ZHH and ZVV) 132

7.4.2 Differential reflectivity (ZDR) 133

7.4.3 Raindrop shapes and sizes 134

7.4.4 ZDR measurements in rain 138

7.4.5 ZDR measurements in ice and mixed-phase precipitation 141

7.4.6 Linear depolarization ratio (LDR) 145

7.5 Polarization and phase 149

7.5.1 Propagation differential phase shift (;;DP) 150

7.5.2 Backscatter differential phase shift (;;) 152

7.5.3 Specific differential phase (KDP) 152

7.5.4 Retrieval of KDP 155

7.5.5 Co-polar correlation coefficient (;;HV) 162

7.5.6 Using polarimetric variables together 168

7.5.7 Covariation of the polarimetric variables: an example at Sand C-band 168

7.5.8 Using dual-polarization variables to discern meteorological versus non-meteorological echo and non-uniform beam filling 170

7.5.9 Hydrometeor classification 172

Important terms 176

Review questions 181

Challenge problems 181

8 Clear Air Echoes 183

8.1 Introduction 183

8.2 Ground clutter 184

8.2.1 Ground clutter characteristics 184

8.2.2 Sea clutter 185

8.2.3 Effects of anomalous propagation 188

8.2.4 Ground clutter mitigation 188

8.3 Echoes from biological sources 191

8.3.1 Insect echo 192

8.3.2 Birds and bats 193

8.4 Debris, dust, and smoke 195

8.5 Aircraft echoes and chaff 196

8.6 Other non-meteorological echo sources 198

8.6.1 The sun 199

8.6.2 Receiver noise 199

8.6.3 Radio interference 200

8.7 Bragg scattering 200

Important terms 203

Review questions 203

Challenge problems 204

9 Propagation Effects: Attenuation and Refractivity 205

9.1 Introduction 205

9.2 Attenuation 206

9.2.1 Attenuation by atmospheric gases and measurement of water vapor 207

9.2.2 Attenuation by cloud droplets and measurement of liquid water content 212

9.2.3 Attenuation by rain and its correction 214

9.2.4 Attenuation by hail 219

9.2.5 Short-wavelength radars and attenuation 224

9.3 Refractivity 225

9.3.1 Basic principles 226

9.3.2 Measurement of the water vapor field 227

Important terms 229

Review questions 229

Challenge problems 230

10 Operational Radar Networks 232

10.1 Introduction 232

10.2 The WSR-88D radar network 233

10.2.1 Network coverage 233

10.2.2 Radar characteristics and data distribution 234

10.2.3 Scanning strategies 236

10.2.4 Ground clutter suppression 240

10.2.5 Super resolution 240

10.2.6 Additional features 242

10.3 Terminal Doppler weather radars 242

10.3.1 Radar characteristics and data distribution 243

10.4 International operational radar networks 246

Important terms 248

Review questions 249

Challenge problems 249

11 Doppler Velocity Patterns and Single-Radar Wind Retrieval 251

11.1 Introduction 251

11.2 Kinematic properties of the wind field 252

11.3 Doppler radial velocity patterns and the wind field 254

11.3.1 Large-scale flow patterns 255

11.3.2 Fronts 257

11.3.3 Convective scale flow patterns 259

11.4 Wind retrieval with profiling radars 261

11.4.1 Wind profilers 261

11.5 Velocity–azimuth display wind retrieval 264

11.5.1 VAD technique 264

11.5.2 Extended VAD analysis 272

Important terms 275

Review questions 276

Challenge problems 277

12 Multiple Doppler Wind Retrieval 279

12.1 Introduction 279

12.2 Network design and deployment 279

12.2.1 Meteorological considerations 281

12.2.2 Sampling limitations 281

12.2.3 Siting and logistics 283

12.3 Characteristics of single Doppler data 284

12.3.1 Geographic location of a range gate 284

12.3.2 Characteristics of raw data 284

12.3.3 Ambiguities and Doppler radar data editing 287

12.4 Procedures for multiple Doppler syntheses 290

12.4.1 Interpolation of data from spherical to Cartesian coordinates 290

12.4.2 Transformation of radial velocities to orthogonal particle motion components 292

12.4.3 Calculation of vertical motion from orthogonal wind components 302

12.4.4 Uncertainty in vertical motion retrievals 304

12.5 Summary 306

Important terms 306

Review questions 307

Challenge problems 308

13 Precipitation Estimation with Radar 310

13.1 Introduction 310

13.2 Measurement of precipitation rate, total precipitation, and particle size distributions 311

13.2.1 Precipitation gauges 311

13.2.2 Disdrometers 313

13.2.3 Optical array probes 315

13.3 Nature of particle size distributions 316

13.3.1 The exponential size distribution 318

13.3.2 The gamma size distribution 319

13.4 Radar remote sensing of precipitation 319

13.4.1 Determining Z–R relationships 322

13.4.2 Challenges in precipitation estimation with radar 323

13.5 Precipitation estimation using dual polarization 326

13.6 Winter precipitation 329

13.7 Measuring precipitation from space 330

13.7.1 Tropical Rainfall Measuring Mission 332

13.7.2 Global Precipitation Mission 332

Important terms 334

Review questions 334

Challenge problems 335

14 Warm Season Convection 338

14.1 Introduction 338

14.2 Mesoscale convective systems 339

14.2.1 Radar-observed life cycle of an MCS 339

14.2.2 Conceptual model of an MCS as observed with a research radar 341

14.2.3 Radar signatures of hazardous weather in MCSs 343

14.2.4 Frontal squall lines 345

14.3 Supercell thunderstorms 349

14.3.1 Tornado detection 352

14.3.2 Radar signatures of supercells 354

14.3.3 Hail detection 356

14.4 Downbursts and wind shear 358

Important terms 358

Challenge problems 359

15 Extratropical Cyclones 361

15.1 Introduction 361

15.2 Radar approaches to monitor cyclone mesostructure 363

15.3 Mesoscale structures observable with radar 366

15.3.1 The comma-cloud tail 367

15.3.2 The comma-cloud head 371

Important terms 381

Review questions 381

Challenge problems 382

16 Tropical Cyclones 383

16.1 Introduction 383

16.2 Airborne and satellite radar systems for tropical cyclone research and operations 386

16.2.1 NOAA WP-3D radar systems 386

16.2.2 Other airborne radars used in hurricane research 388

16.2.3 Satellite radars used in hurricane research 389

16.3 Tropical cyclone structure and kinematics 390

16.3.1 Eyewall and eye radar structure 395

16.3.2 Radar structure of principal band 399

16.3.3 Other bands within the hurricane vortex 404

16.4 Operational use of radar to detect tropical cyclone hazards 405

16.4.1 High winds and storm surge 405

16.4.2 Heavy precipitation and flooding 407

16.4.3 Tornadoes 409

Important terms 411

Review questions 411

Challenge problems 412

17 Clouds and Vertical Motions 413

17.1 Introduction 413

17.2 Cloud radars 414

17.2.1 Advantages and disadvantages of cloud radars 415

17.2.2 Examples of data from cloud radars 417

17.3 Application of cloud radars 421

17.3.1 Determining vertical motions in clouds 421

17.3.2 Determining statistical cloud properties 424

17.3.3 Understanding atmospheric and storm structure 428

17.3.4 Understanding global cloud properties 432

Important terms 432

Review questions 433

Challenge problems 433

Appendix A List of Variables (and Chapters) 435

Appendix B Derivation of the Exact Equation for a Ray Path through a

Spherically Stratified Atmosphere 441

Index 443

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