1. The climate system .......................................... 1
1.1. Introduction: A definition of climate ................. 1
1.2. Solar radiation and the energy budget of
the Earth ............................................. 3
1.3. Atmosphere and climate ................................ 6
1.3.1. Evolution of the atmosphere .................... 6
1.3.2. Temperature structure .......................... 6
1.3.3. Pressure, composition, and temperature
variations and dynamics ........................ 7
1.4. Ocean and climate ..................................... 9
1.4.1. Heat storage and transport ..................... 9
1.4.2. Hydrological cycle ............................ 10
1.4.3. Carbon dioxide exchange with the oceans ....... 11
1.4.4. Dynamical coupling between the atmosphere
and the ocean ................................. 12
1.5. Radiative transfer in the atmosphere ................. 12
1.6. The greenhouse effect ................................ 14
1.7. The ozone layer and ozone depletion .................. 17
1.8. Climate observations ................................. 19
1.9. The stability of the climate ......................... 21
1.9.1. Data on past fluctuations ..................... 21
1.9.2. Origin of the observed fluctuations ........... 22
1.10. Climate modelling .................................... 23
1.11. Climate on other planets ............................. 26
Further reading ............................................ 28
Questions .................................................. 28
2. Solar radiation and the energy budget of the earth ......... 29
2.1. Sun and climate ...................................... 29
2.2. Solar physics ........................................ 30
2.3. Source of the Sun's energy ........................... 30
2.4. The radiation laws ................................... 31
2.5. The solar constant ................................... 32
2.6. The solar spectrum ................................... 33
2.7. Solar observations ................................... 34
2.8. Absorption of solar radiation in the atmosphere ...... 35
2.9. The balance between incoming solar and outgoing
thermal radiation .................................... 36
Further reading ............................................ 39
Questions .................................................. 39
3. Atmosphere and climate ..................................... 40
3.1. Introduction ......................................... 40
3.2. Atmospheric composition .............................. 41
3.3. Units of pressure .................................... 41
3.4. The variation of pressure with height ................ 42
3.5. Vertical temperature structure ....................... 43
3.5.1. Tropospheric temperature profile .............. 44
3.5.2. Stratospheric temperature profile ............. 46
3.5.3. Observed temperature profiles ................. 47
3.6. The general circulation of the atmosphere ............ 49
Further reading ............................................ 51
Questions .................................................. 51
4. Clouds and aerosols ........................................ 52
4.1. Introduction ......................................... 52
4.2. Potential temperature and entropy .................... 52
4.3. Potential energy and available potential energy ...... 55
4.4. Humidity ............................................. 56
4.5. Thermodynamics of moist air .......................... 58
4.6. Condensation processes and cloud formation ........... 60
4.7. Growth of cloud droplets ............................. 62
4.8. Growth of ice crystals ............................... 64
4.9. Collision and coalescence ............................ 65
4.10. Aerosols ............................................. 65
Further reading ............................................ 67
Questions .................................................. 67
5. Ocean and climate .......................................... 68
5.1. Introduction ......................................... 68
5.2. Ocean measurements ................................... 69
5.3. Composition of the ocean: Salinity ................... 72
5.4. Vertical and latitudinal structure of the ocean ...... 73
5.5. The oceanic equation of state ........................ 75
5.6. The general circulation of the ocean ................. 76
5.6.1. The Coriolis Force ............................ 77
5.6.2. Deep ocean dynamics: the thermohaline
circulation ................................... 78
5.6.3. Near surface dynamics: Ekman transport
Sverdrup balance .............................. 81
5.7. Ocean circulation and climate change ................. 85
Further reading ............................................ 85
Questions .................................................. 86
6. Radiative transfer ......................................... 87
6.1. Introduction ......................................... 87
6.2. Black body or cavity radiation ....................... 88
6.3. Atmospheric absorption and emission .................. 89
6.4. Atmospheric radiative transfer ....................... 90
6.5. The radiative transfer equation ...................... 91
6.6. Integration over wavelength .......................... 93
6.7. Spectral properties of atmospheric gases ............. 93
6.7.1. Spectral lines ................................ 94
6.7.2. Vibration-rotation bands ...................... 94
6.7.3. Band absorption formulations and band
models ........................................ 95
6.8. Radiative equilibrium models for the temperature
profile .............................................. 97
6.9. Temperature sounding and weighting functions ......... 99
6.10. The inverse problem ................................. 101
Further reading ........................................... 103
Questions ................................................. 103
7. Earth's energy budget: The 'Greenhouse' effect ............ 104
7.1. Introduction ........................................ 104
7.2. Is the atmosphere a 'Greenhouse'? ................... 104
7.3. The 'Greenhouse' gases .............................. 105
7.4. Energy balance calculations ......................... 108
7.5. A simple physical greenhouse model .................. 109
7.6. A better greenhouse model ........................... 110
7.6.1. The radiative-dynamical equilibrium profile
revisited .................................... 110
7.6.2. Surface temperature versus absorber amount ... 112
7.6.3. Effect of changing albedo on surface
temperature .................................. 114
7.7. A simple model with feedback ........................ 116
7.8. Conclusions ......................................... 117
Further reading ........................................... 118
Questions ................................................. 118
8. The ozone layer ........................................... 119
8.1. Introduction ........................................ 119
8.2. Ultraviolet radiation in the atmosphere ............. 120
8.3. Photochemistry of ozone production .................. 121
8.4. Variation of ozone concentration with altitude ...... 123
8.5. Catalytic cycles .................................... 123
8.6. Ozone measurements .................................. 125
8.7. The Antarctic ozone hole ............................ 126
8.8. The global distribution of ozone .................... 127
Further reading ........................................... 128
Questions ................................................. 129
9. Climate observations by remote sensing .................... 130
9.1. Introduction ........................................ 130
9.2. Ground-based measurements ........................... 130
9.1. Satellite measurements .............................. 132
9.4. Infrared instruments for remote sounding ............ 134
9.4.1. Calibration .................................. 134
9.4.2. Modulation ................................... 135
9.4.3. Radiometer optics ............................ 136
9.4.4. Interference filters ......................... 136
9.4.5. Thermal infrared detectors ................... 138
9.4.6. Photon detectors ............................. 138
9.4.7. Electronics and telemetry .................... 139
9.5. Radiometric performance .............................. 139
9.5.1. Signal ....................................... 139
9.5.2. Noise ........................................ 140
9.5.3. Signal to noise ratio ........................ 141
9.6. Limb viewing instruments ............................ 142
9.7. Contemporary satellites and instruments: Three
examples ............................................ 143
9.7.1. Weather satellites: The Geostationary
Operational Environmental Satellite .......... 143
9.7.2. Environmental satellites: ENVISAT ............ 145
9.7.3. Research satellites: UARS and EOS ............ 145
9.8. Applications of remote sensing to climate studies ... 148
9.8.1. Earth's radiation budget ..................... 148
9.8.2. Atmospheric temperature sounding ............. 150
9.8.3. Atmospheric composition and chemistry ........ 151
9.8.4. Clouds, aerosols, and polar stratospheric
clouds ....................................... 153
9.8.5. Doppler wind measurements .................... 153
9.8.6. Surface properties ........................... 154
9.8.7. Detection of climate change .................. 156
9.9. The future .......................................... 157
Further reading ........................................... 157
Questions ................................................. 158
10. Climate sensitivity and change ............................ 160
10.1. Introduction ........................................ 160
10.2. Astronomical changes ................................ 161
10.2.1.The Milankovich cycles ....................... 161
10.2.2.The ice ages ................................. 163
10.2.3.Current changes .............................. 165
10.3. Variations in solar output .......................... 165
10.4. Changes in atmospheric composition .................. 167
10.4.1.Greenhouse gases ............................. 167
10.4.2.Aerosols ..................................... 168
10.4.3.Cloud and albedo variations .................. 169
10.5. Ocean circulation variations ........................ 170
10.5.1.Changes in the thermohaline circulation ...... 170
10.5.2.Rapid climate change ......................... 170
10.5.3.Ocean-atmosphere coupling:
The El Nino-Southern Oscillation (ENSO) ...... 172
10.6. Natural temperature fluctuations .................... 173
10.7. Summary ............................................. 175
Further reading ........................................... 176
Questions ................................................. 176
11. Climate models and predictions ............................ 177
11.1. Introduction ........................................ 177
11.2. Current models and predictions ...................... 179
11.3. Multiple climate equilibria and sudden climate
change .............................................. 182
11.3.1.A simple radiative model ..................... 183
11.3.2.Box models of the ocean ...................... 184
11.3.3.Complex models ............................... 187
11.4. Problems of detection, attribution, and
prediction .......................................... 189
Further reading ........................................... 192
Questions ................................................. 193
12. Climate on other planets .................................. 194
12.1. Introduction ........................................ 194
12.2. Mercury ............................................. 195
12.3. Venus ............................................... 196
12.4. Mars ................................................ 199
12.5. Titan ............................................... 201
12.6. The Jovian planets .................................. 202
12.7. Planets of other stars .............................. 204
12.8. Planets without stars ............................... 205
Further reading ........................................... 205
Questions ................................................. 205
13. Epilogue .................................................. 207
Index ......................................................... 211
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