Chapter 3 Atmospheric Radiative Transfer and ClimateChapter 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 here1)How greenhouse gases affect radiation,2)How clouds influence radiation, 3)How they together impact temperature profiles, and4)What is cloud radiative forcing?

Recap of the greenhouse effect

Long-waveradiation

236 Wm-2

Equivalent T = 255 K (-18ºC)

390 Wm-2

T = 288 K (+15ºC)

236 Wm-2

Solar radiation

Do you know where is this 236 coming from?Do you know where is this 236 coming from?

How greenhouse gases affect radiation?How greenhouse gases affect radiation?

How does How does the atmosphere the atmosphere affect radiation?affect radiation?

Atmospheric AbsorptionAtmospheric Absorption

Solar radiation Solar radiation passes rather freely passes rather freely through earth's through earth's atmosphere.atmosphere.

Earth's re-emitted Earth's re-emitted longwave energy longwave energy either fits through a either fits through a narrow window narrow window or is or is absorbed by absorbed by greenhouse gases greenhouse gases and re-radiated and re-radiated toward earth.toward earth.

Wavelength

Abs

orpt

ion

(100

%)

Nitrous Oxide

Methane

Ozone

Water Vapor

Carbon Dioxide

Total Atmo

IR

UV

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 What are the dominant gases in the atmosphere?atmosphere?

Diatomic molecules like N2 and O2 have no permanent Diatomic molecules like N2 and O2 have no permanent dipole moment and no bending moment and so have no dipole moment and no bending moment and so have no capacity to absorb or emit low energy thermal radiation. capacity to absorb or emit low energy thermal radiation.

N2 and O2N2 and O2

Are they Are they greenhouse gases?greenhouse gases?

Why not?Why not?

What are What are greenhouse gases?greenhouse gases?

CO2, N2O,H2O, O3CO2, N2O,H2O, O3

Nuclear Configuration and Permanent Dipole Nuclear Configuration and Permanent Dipole MovementMovement

Symmetric, Symmetric, linear molecules linear molecules (Both ends look (Both ends look the same)the same)

Nonlinear or Nonlinear or bentbent

Have pure Have pure rotation bandsrotation bands

Vibrational Modes of Diatomic and Vibrational Modes of Diatomic and Triatomic MoleculesTriatomic Molecules

How do greenhouse gases affect the How do greenhouse gases affect the temperature profile? (1/2)temperature profile? (1/2)

How do greenhouse gases affect the How do greenhouse gases affect the temperature profile? (2/2)temperature profile? (2/2)

Thermal equilibrium profiles

How do clouds affect radiation?How do clouds affect radiation?1. Liquid water path and solar zenith angle1. Liquid water path and solar zenith angle

How do clouds affect radiation?How do clouds affect radiation?2. Cloud particle size2. Cloud particle size

How do clouds affect radiation?How do clouds affect radiation?3. Cloud phase (water versus ice)3. Cloud phase (water versus ice)

How do clouds affect the temperature How do clouds affect the temperature profile? profile?

How do clouds affect net radiation at TOA?How do clouds affect net radiation at TOA?

How do clouds affect shortwave radiation?How do clouds affect shortwave radiation?

Cloud forcing = average ( or cloudy) – cloud-freeCloud forcing = average ( or cloudy) – cloud-free

How do clouds affect longwave radiation?How do clouds affect longwave radiation?

Cloud forcing = Cloud forcing = cloudy – cloud-freecloudy – cloud-free

How do clouds affect net radiation?How do clouds affect net radiation?Cloud forcing = Cloud forcing =

cloudy – cloud-freecloudy – cloud-freeNET = SW + LWNET = SW + LW

How do clouds distribute globally?How do clouds distribute globally?

How are clouds measured from space?How are clouds measured from space?

High clouds measured from space?High clouds measured from space?

Low clouds measured from space?Low clouds measured from space?

SummarySummary

Now, we have learned:1)How greenhouse gases affect radiation,2)How clouds influence radiation, 3)How they together impact temperature profiles, and4)What cloud radiative forcing is.

Seasonal patterns of shortwave cloud radiationSeasonal patterns of shortwave cloud radiation

Seasonal patterns of longwave cloud radiationSeasonal patterns of longwave cloud radiation

Seasonal patterns of net radiation cloud forcingSeasonal patterns of net radiation cloud forcing