Chapter 3 Atmospheric Radiative Transfer and Climate
To date, we have learned
1) The greenhouse effects, through understanding the simplest
greenhouse model,
2) The aerosols effects on radiation, clouds, and temperature,
3) The global energy balance, that shows how global energy
components are budgeted at the TOA, in the atmosphere, and
at the surface.
Now, we will further learn here
1) How greenhouse gases affect radiation,
2) How clouds influence radiation,
3) How they together impact temperature profiles, and
4) What is cloud radiative forcing?
Recap of the greenhouse effect
Solar radiation
Long-wave
radiation
236 Wm-2
236 Wm-2
Equivalent T = 255 K (-18ºC)
390 Wm-2
T = 288 K (+15ºC)
Do you know where is this 236 coming from?
How greenhouse gases affect radiation?
How does the atmosphere affect radiation?
Nitrous Oxide
Atmospheric Absorption
Earth's re-emitted
longwave energy
either fits through a
narrow window or is
absorbed by
greenhouse gases
and re-radiated
toward earth.
Methane
Absorption (100%)
Solar radiation
passes rather freely
through earth's
atmosphere.
Ozone
Water Vapor
Carbon Dioxide
UV
IR
Total Atmo
Wavelength
Through this
atmospheric “window”,
satellite sensors are
designed to “see”,
observe, measure or
monitor the Earth’s
surface.
Spectra of outgoing
radiation from Earth
observed by IRIS on
Nimbus 3
What are the dominant gases in the atmosphere?
N2 and O2
Are they greenhouse gases?
Why not?
Diatomic molecules like N2 and O2 have no permanent
dipole moment and no bending moment and so have no
capacity to absorb or emit low energy thermal radiation.
What are greenhouse gases?
CO2, N2O,H2O, O3
Nuclear Configuration and Permanent Dipole Movement
Symmetric,
linear molecules
(Both ends look
the same)
Nonlinear or
bent
Have pure
rotation bands
Vibrational Modes of Diatomic and Triatomic
Molecules
How do greenhouse gases affect the temperature
profile? (1/2)
How do greenhouse gases affect the temperature
profile? (2/2)
Thermal equilibrium profiles
How do clouds affect radiation?
1. Liquid water path and solar zenith angle
How do clouds affect radiation?
2. Cloud particle size
How do clouds affect radiation?
3. Cloud phase (water versus ice)
How do clouds affect the temperature profile?
How do clouds affect net radiation at TOA?
How do clouds affect shortwave radiation?
Cloud forcing = average ( or cloudy) – cloud-free
How do clouds affect longwave radiation?
Cloud forcing =
cloudy – cloud-free
How do clouds affect net radiation?
Cloud forcing =
cloudy – cloud-free
NET = SW + LW
How do clouds distribute globally?
How are clouds measured from space?
High clouds measured from space?
Low clouds measured from space?
Summary
Now, we have learned:
1) How greenhouse gases affect radiation,
2) How clouds influence radiation,
3) How they together impact temperature profiles, and
4) What cloud radiative forcing is.
Seasonal patterns of shortwave cloud radiation
Seasonal patterns of longwave cloud radiation
Seasonal patterns of net radiation cloud forcing