Environmental Physics Climate Dynamics aspects Arnaud Czaja Space
![Solar spectr um Lean (1991) [adapted by Lockwood] 28 May 2003 Imperial College London](https://slidetodoc.com/presentation_image/58c27d08cd6eeb130e660d6ae5fd7715/image-20.jpg "Solar spectr um Lean (1991) [adapted by Lockwood] 28 May 2003 Imperial College London")
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Environmental Physics: Climate Dynamics aspects Arnaud Czaja Space & Atmospheric Physics
Overview (Lectures #7 -14) • • Greenhouse effect (#7, i. e. today) Water Vapour feedback (#8) Cooling mechanisms for the planet (#9) Climate models (#10) + MATLAB session Climate timescales (#11) Climate sensitivity (#12) Modes of climate variability (#13) Discussion of a hot Topic (#14)
Our own EP Climate Model! Atmosphere Tropics Ocean Extra Tropics
Our own EP Climate Model! Atmosphere (i) Use of model is not mandatory and thus the model is not examinable (ii) MATLAB session on Thursday Feb 7 (5 -6 pm) (come if you wish, this is not mandatory) Tropics Ocean Extra Tropics
Lecture 7 The Greenhouse effect
Lecture 7 The Greenhouse effect Student: Oh yeah! It’s the trapping of radiation by the atmosphere
Lecture 7 The Greenhouse effect Lecturer: Let’s be a bit more precise!!
7. 1 Motivation: Observations of Earth from Space
Total radiation seen by a satellite NB: Photon energy is the main form of energy exchanged between the earth and space (GERB project in Space & Atmospheric Physics)
LW Long wavelength photons (emitted by the Earth) SW + Short wavelength photons (reflected from the Sun)
Terrestrial radiation λ≈10 -20μm 1 erg s-1 cm-2 = 10 -3 W m-2
Sun radiation Solar radiation λ≈0. 2 -1μm
To zero order… • Solar photons are absorbed by the atmosphere (clouds, water vapour, ozone) • …but much less so than are the terrestrial photons. • This is because of the atmospheric composition, with tri-atomic molecules efficient at interacting with λ≈10 -20μm photons (“greenhouse absorbers”).
Atmospheric composition (fraction of total molecules) N 2 O 2 CO 2 Main Greenhouse gas (GHG) is Water vapour (variable ≈1%) Man influenced GHG Pre-industrial IPCC (2007) CO 2 CH 4 280 ppmv 700 ppbv 380 ppmv 1800 ppbv N 2 O 270 ppbv 320 ppbv NB: 1 ppmv = 1 molecule out of a million 1 ppbv = 1 molecule out of a billion
What is meant by variable H 2 O… Low level enthalpy Upper tropospheric RH on April 27, 1999 3. 5 2. 5 0 100
7. 3 Observations of the greenhouse effect (G)
Observed Greenhouse effect 180 50 Water vapour content 50 10 303 Sea surface temperature 273 NB: All are annual mean data (from Held & Soden, 2000)
Solar spectr um Lean (1991) [adapted by Lockwood] 28 May 2003 Imperial College London 20