Contents

1 The climate system 1

1.1 Introduction 1

1.2 Solar radiation 2

1.3 The atmosphere 3

1.4 Clouds and aerosols 6

1.5 Radiative equilibrium and radiative forcing 8

1.6 Atmospheric circulation 10

1.7 The hydrosphere and the cryosphere 12

1.7.1 Oceanic circulation 13

1.7.2 El Nino southern oscillation (ENSO) 15

1.7.3 North Atlantic oscillation (NAO) 17

1.7.4 Ice sheets 19

1.8 The land surface and biosphere 20

1.8.1 Land-surface albedo 20

1.8.2 Carbon dioxide sequestering 20

1.9 The climate record 21

1.9.1 Temperature trends 21

1.9.2 Sea-ice extent 21

1.9.3 Extreme events 22

1.9.4 Sea-level trends 24

1.10 Projections of future climate 24

1.10.1 Emission scenarios and global warming 26

1.10.2 Climate projections for the twenty-first century 27

1.11 Bibliography 30

1.11.1 Notes 30

1.11.2 References and further reading 31

2 Atmospheric physics and thermodynamics 33

2.1 Introduction 33

2.2 Atmospheric composition 34

2.2.1 Well-mixed species 34

2.2.2 Water vapour and ozone 35

2.2.3 Trace constituents 37

2.3 Pressure and hydrostatic equilibrium 39

2.4 Vapours and ideal gases 40

2.5 Vertical temperature structure 42

2.6 Thermodynamics of moist air 45

2.7 Condensation processes, clouds and aerosols 48

2.7.1 Criteria for vertical stability 48

2.7.2 Growth of cloud particles 49

2.7.3 Cloud particle size distributions 51

2.7.4 Aerosols 52 2.8 Bibliography 54

2.8.1 Notes 54

2.8.2 References and further reading 54

3 Radiation—transfer theory 56

3.1 Introduction 56

3.2 Basic definitions 56

3.2.1 The inverse square law 56

3.2.2 Radiance 58

3.2.3 Mean radiance and flux 59

3.2.4 Luminosity 60

3.3 Blackbody radiation 60

3.3.1 Planck's law 61

3.3.2 Stefan-Boltzmann law 61

3.3.3 Radiation energy density 62

3.3.4 Wien's displacement law 62

3.4 Absorption, emission and scattering 63

3.4.1 Absorption and emission 63

3.4.2 Scattering 64

3.4.3 The extinction coefficient and optical depth 65

3.4.4 Volume emission and Kirchoff's law 67

3.4.5 The source function and redistribution 68

3.4.6 Limiting forms of the redistribution function 68

3.4.7 Forms of the source function 71

3.5 The equation of radiation transfer 72

3.5.1 General form 72

3.5.2 Plane-parallel atmosphere 73

3.5.3 Solution for pure absorption 74

3.5.4 Solution for thermal emission 75

3.5.5 The diffusivity approximation 75

3.5.6 The Eddington and diffusion approximations 76

3.5.7 The Schuster-Schwarzschild approximation 78

3.5.8 General solutions for upwelling radiation 80

3.5.9 Schwarzschild-Milne equations 81

3.5.10 Grey atmospheres in radiative equilibrium 82

3.6 Bibliography 84

3.6.1 Notes 84

3.6.2 References and further reading 85

4 Thermal infra—red transfer in the atmosphere 86

4.1 Introduction 86

4.2 Spectral lines 86 4.2.1 Line broadening mechanisms 87

4.2.2 The Einstein coefficients 91

4.2.3 Line absorptance or equivalent width 93

4.2.4 The curve of growth 95

4.3 Rotational lines and bands 97 4.3.1 Effect of degeneracy 100

4.4 Vibrational lines and bands 101

4.4.1 The harmonic vibrator 101

4.4.2 The anharmonic vibrator 101

4.4.3 The anharmonic vibrator-rotator 104

4.4.4 Absorption bands of polyatomic molecules 106

4.5 Band absorptance formulations 107

4.5.1 Doppler-broadened rotational lines 107

4.5.2 Collisionally-broadened rotational lines 109

4.5.3 Temperature dependence of absorptance 111

4.6 Important greenhouse gases 114

4.6.1 Bands in the terrestrial infra-red region 114

4.6.2 Water vapour 114

4.6.3 Carbon dioxide 115

4.6.4 Ozone 116

4.6.5 Methane, ammonia and N2O 116

4.7 The HITRAN database 117 4.7.1 Application to N2O 119

4.8 Clear-sky fluxes 119

4.8.1 Upwelling fluxes 121

4.8.2 Downwelling fluxes 121

4.8.3 Outgoing flux at TOA 122

4.9 Cloudy-sky fluxes 122

4.9.1 Outgoing flux above a cloud layer 123

4.9.2 Downwelling flux at the Earth's surface 123

4.10 Computation of fluxes 124

4.10.1 Data requirements 124

4.10.2 Curtis-Godson approximation 125

4.11 Bibliography 126

4.11.1 Notes 126

4.11.2 References and further reading 126

5 Incoming solar radiation 128

5.1 Introduction 128

5.2 The Sun as a main-sequence star 129

5.2.1 Stellar properties 129

5.2.2 Total solar irradiance 131

5.2.3 The solar cycle 132

5.2.4 Solar spectral irradiance 134

5.3 Solar evolution 137

5.3.1 Protostar to main sequence 137

5.3.2 Beyond the main sequence 138

5.4 Solar luminosity evolution 139

5.4.1 The role of mean molecular weight 139

5.4.2 The faint-young-Sun paradox 140

5.5 Solar ultraviolet flux evolution 140

5.5.1 Stellar activity and rotation 140

5.5.2 Rotation with spectral type and age 142

5.5.3 Rossby number with spectral type and age 142

5.5.4 XUV-Lya emission and Rossby number 143

5.5.5 Solar XUV and Ly-a emission flux evolution 147

5.5.6 Solar photospheric irradiance evolution 149

5.6 Solar flux at the Earth's orbit 151

5.6.1 The Earth's elliptical orbit 151

5.6.2 The plane of the ecliptic 151

5.6.3 Sun-Earth distance and solar longitude 152

5.6.4 The equation of time 153

5.6.5 Incoming radiation at TOA 155

5.6.6 Global distribution of incoming radiation 156

5.7 Bibliography 158

5.7.1 Notes 158

5.7.2 References and further reading 159

6 Solar radiation transfer in the atmosphere 163

6.1 Introduction 163

6.2 Atmospheric molecular absorption 164

6.2.1 Ultraviolet-visible absorption 164

6.2.2 Near-infra-red absorption 166

6.3 Particle absorption and scattering 168

6.3.1 Mie scattering 169

6.3.2 The Mie scattering functions 174

6.3.3 Rayleigh scattering 177

6.4 Clouds absorption and scattering 179

6.4.1 Cloud types 179

6.4.2 Visible scattering 180

6.4.3 Near-infra-red absorption and scattering 181

6.5 Aerosol absorption and scattering 181

6.5.1 Aerosol radiative properties 181

6.5.2 Particle size and Angstrom parameter 182

6.5.3 Aerosol fine and coarse modes 184

6.6 Surface reflection 187 6.6.1 Snell and Fresnel laws 187

6.7 Multiple scattering solution for inhomogeneous layers 189 6.7.1 Isotropic scattering solution 190

6.7.2 Thomas algorithm 190

6.7.3 Anisotropic scattering solution 191

6.7.4 Atmospheres with clouds and aerosols 196

6.7.5 Sample computations 197 6.8 Bibliography 198

6.8.1 Notes 198

6.8.2 References and further reading 198

7 Atmospheric photochemistry 201

7.1 Introduction 201

7.2 The continuity equation 202

7.3 Brownian and turbulent diffusion 203

7.3.1 Fick's law 203

7.3.2 Bimolecular diffusion 204

7.3.3 Diffusive flux 205

7.4 Surface deposition 208

7.4.1 Surface deposition loss rate 208

7.4.2 Dry deposition velocities 209

7.5 Surface emission 211

7.6 Photolysis 212

7.6.1 Photolysis rate 212

7.6.2 Quantum yield 213

7.6.3 O2 photolysis 214

7.6.4 O3 photolysis 217

7.6.5 H2O photolysis 218

7.6.6 CO2 photolysis 219

7.6.7 CH4 photolysis 220

7.6.8 Atmospheric photolysis rates 221

7.7 Collisionally induced reactions 222

7.7.1 Types of reactions 222

7.7.2 Bimolecular reactions 223

7.7.3 Termolecular reactions 225

7.8 Ozone photochemistry 226

7.8.1 The Chapman mechanism 226

7.8.2 N2O and NOK photochemistry 227

7.8.3 Water vapour and HOK photochemistry 229

7.8.4 Chlorine and ClOK photochemistry 232

7.8.5 Polar stratospheric clouds 234

7.9 Methane and hydrogen photochemistry 235

7.9.1 H2 in the atmosphere 235

7.9.2 Effects of increasing CH4 emission 236

7.9.3 Effects of increasing CO2 levels 237

7.10 Bibliography 238 7.10.1 Notes 238

7.10.2 References and further reading 239

8 The Earth's radiation budget 245

8.1 Introduction 245

8.2 Model input data 248

8.2.1 Cloud radiative properties 248

8.2.2 Cloud data sets 249

8.2.3 Water vapour and temperature profiles 251

8.2.4 Other greenhouse gases 252

8.2.5 Surface properties 253

8.2.6 Aerosol particles 254

8.3 Validation data 255

8.3.1 Global energy balance archive 256

8.3.2 Baseline radiation network 257

8.3.3 ERBE data 257

8.4 Outgoing solar radiation at TO A 259

8.4.1 Planetary albedo 259

8.4.2 Global distribution 261

8.4.3 Zonal-seasonal variation 262

8.4.4 Mean annual latitudinal variation 263

8.4.5 Seasonal variation 264

8.4.6 Mean annual hemispherical variation 266

8.4.7 Time series of planetary albedo 266

8.5 The shortwave radiation budget at surface 267

8.5.1 Global distribution 267

8.5.2 Zonal-seasonal variation 269

8.5.3 Latitudinal and seasonal variation 270

8.5.4 Validation with observations 270

8.5.5 Mean annual hemispherical variation 271

8.5.6 Long-term anomaly 272

8.5.7 Sensitivity analysis 274

8.6 Shortwave aerosol radiative forcing 275

8.6.1 Aerosol forcing at TOA 276

8.6.2 Aerosol forcing of atmospheric absorption 277

8.6.3 Aerosol forcing at the Earth's surface 278

8.6.4 Mean annual hemispherical aerosol forcings 279

8.7 Longwave radiation budget at TOA 280

8.7.1 Global distribution 281

8.7.2 Zonal-seasonal variation 281

8.7.3 Latitudinal and seasonal variation 282

8.7.4 Log-term hemispherical and global means 282

8.8 Longwave radiation budget at surface 283

8.8.1 Global distribution 284

8.8.2 Zonal, latitudinal and seasonal variations 285

8.8.3 Long-term anomaly 286

8.8.4 Long-term hemispherical and global means 287

8.8.5 Sensitivity analysis 288

8.9 Mediterranean Sea heat budget 290

8.9.1 The heat budget equation 291

8.9.2 Latent and sensible heat flux 292

8.9.3 Sea data for computing heat storage 293

8.9.4 Data for computing turbulent fluxes 294

8.9.5 Radiation fluxes 296

8.9.6 Heat storage 297

8.9.7 Turbulent fluxes 297

8.9.8 Seasonal evaporation rate 299

8.9.9 Annual evaporation rate 299

8.9.10 Comparison with Red and Black Seas 300

8.10 Bibliography 301

8.10.1 Notes 301

8.10.2 References and further reading 302

9 Theory of radiation measurements 310

9.1 Introduction 310

9.2 Detectors 311

9.3 Thermal detectors 314

9.4 Photon detectors 320

9.4.1 Photoconductive detectors 321

9.4.2 Photovoltaic detectors 323

9.5 Detector arrays and charge coupled devices 325

9.6 Properties of IR systems 325

9.6.1 Spectral properties 326

9.6.2 Wavelength calibration 328

9.6.3 Geometrical optical properties 328

9.6.4 Radiometric properties 331

9.7 Radiometric performance 333

9.7.1 Signal-to-noise ratio 333

9.7.2 A generalized radiometer 336

9.7.3 A realistic radiometer 337

9.7.4 Spectrometers and interferometers 340

9.8 Bibliography 343

9.8.1 Notes 343

9.8.2 References and further reading 343

10 Climate observations by radiometry—spectrometry 345

10.1 Introduction 345

10.2 Surface radiation budget: the pyranometer 346

10.3 Solar irradiance: ACRIM 350

10.4 TOA radiation budget: ERB, CERES and GERB 351

10.5 Sea surface temperature: ATSR 355

10.6 Surface properties: Thematic Mapper and MODIS 358

10.7 Atmospheric temperature: HIRS and AIRS 361

10.8 Atmospheric composition: IRIS, ATM OS and TES 366

10.9 Detection of climate change 370 10.10Bibliography 374

10.10.1 Notes 374

10.10.2 References and further reading 374

11 Climate modelling 377

11.1 Introduction 377

11.2 Simple climate models 378

11.2.1 Global energy balance models 378

11.2.2 Simple greenhouse models 380

11.3 Radiative-convective climate models 385

11.3.1 Convective versus radiative equilibrium 385

11.3.2 Convective equilibrium 386

11.3.3 Radiative equilibrium 388

11.3.4 Climatic effects of increasing CO2 levels 389

11.3.5 Climatic effects of increasing CH4 levels 391

11.3.6 Climatic effects of increasing CO levels 392

11.3.7 Climatic effects of increasing H2 levels 393

11.3.8 Climatic effects of cloud-cover feedbacks 393

11.4 General circulation models 393

11.4.1 Types of climate models 395

11.4.2 Solar radiation transfer in GCMs 396

11.4.3 Terrestrial radiation transfer in GCMs 398

11.4.4 Surface albedo and emissivity in GCMs 398

11.5 GCM climate projections 399

11.5.1 SRES emission scenarios 400

11.5.2 Global change in temperature 403

11.5.3 Global change in precipitation 404

11.5.4 Global change in sea level 406

11.6 Bibliography 410

11.6.1 Notes 410

11.6.2 References and further reading 410

12 Planetary evolution and comparative climatology 413

12.1 Introduction 413

12.1.1 Origin of the solar system 415

12.1.2 Evolution of planetary atmospheres 416

12.1.3 Escape processes 417

12.2 The evolution of the Earth's climate 419

12.2.1 The Precambrian atmosphere 420

12.2.2 The faint-young-Sun paradox 420

12.2.3 Greenhouse-weathering evolution model 421

12.2.4 Surface temperature and CO2 evolution 426

12.3 Comparative climatology of the terrestrial planets 427

12.3.1 Mercury 427

12.3.2 Venus 428

12.3.3 Mars 434

12.4 The giant planets 438

12.5 Titan's atmosphere and haze 439

12.5.1 Physical properties 442

12.5.2 Collisionally induced absorption 444

12.5.3 Geometric albedo 445

12.5.4 Laboratory and in-situ measurements 446

12.5.5 Haze formation 447

12.5.6 Thermal structure 453

12.5.7 Atmospheric chemistry 454

12.6 Extrasolar planets 460

12.7 Bibliography 461

12.7.1 Notes 461

12.7.2 References and further reading 461

A Physical constants 467

B Tables of reactions 468

Index 477

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