Earth Systems ScienceChapter 3

I. Global Energy Balance and the Greenhouse Effect:The Physics of the Radiation Balance of the Earth

1. Electromagnetic Radiation: waves, photons

2. Electromagnetic Spectrum

3. Flux

4. Blackbody Radiation

5. Planetary Energy Balance

ELECTROMAGNETIC RADIATION: WAVES

c = speed of light in a vacuum = 3.0 x 108 m/s = wavelength (m)v = frequency (1/s or s-1)

v = c

= c/v

V/c = 1

ELECTROMAGNETIC RADIATION: WAVES

Relationship between v, c, and

ELECTROMAGNETIC RADIATION: PHOTONS

E = hv = hc/

E = Energy (joules, or j)

h = Planck’s constant = 6.63 x 10-34 j-s

v = frequency (1/s or s-1)

c = speed of light in a vacuum (m/s)

= wavelength (m)

ELECTROMAGNETIC SPECTRUM

http://www.lbl.gov/MicroWorlds/ALSTool/EMSpec/EMSpec2.html

FLUX

FLUX: INVERSE SQUARE LAW

BLACKBODY RADIATION

Planck function Wien’s Law Stefan-Boltzman law

BLACKBODY RADIATION

T = temperature (K)

= Stefan – Boltzman constant

BLACKBODY EMISSION RATES:PLANCK FUNCTIONS FOR SUN,EARTH

At the Sun’s surface

RADIATION BALANCE OF THE EARTH:

SOLAR (SHORTWAVE) RADIATION

Note: area of circle is used here: r2

SWin = area * fluxSWin = r2S - r2SASWin = r2S(1-A)

RADIATION BALANCE OF THE EARTH:

SOLAR (SHORTWAVE) RADIATION:

Why we use the area of a circle

Earth

RADIATION BALANCE OF THE EARTH:

SOLAR (SHORTWAVE) RADIATION:

Why we use the area of a circle

Earth

RADIATION BALANCE OF THE EARTH:

SOLAR (SHORTWAVE) RADIATION

Net SW = Incoming – Outgoing

Net SW = r2S – r2SA

Net SW = r2S (1-A)

Earth’sEnergy

SWin SWout

RADIATION BALANCE OF THE EARTH:

TERRESTRIAL (LONGWAVE) RADIATION

Earth

Note: area of sphere is used here: 4r2

LWout = area * fluxLWout = 4r2Te

4

RADIATION BALANCE OF THE EARTH:

TERRESTRIAL (LONGWAVE) RADIATION

Net LW = Incoming – Outgoing

Net LW = 0 – 4r2Te4

Net LW = -4r2Te4

Earth’sEnergy

LWout

Net LW = -4r2Te4

Te = effective radiating temperature

Earth’sEnergy

LWout

RADIATION BALANCE OF THE EARTH:

TERRESTRIAL (LONGWAVE) RADIATION

RADIATION BALANCE OF THE EARTH: TOTAL RADIATION

Assume dynamic equilibrium: IN = OUTNet SW + Net LW = 0Net SW = r2S(1-A)Net LW = -4r2Te

4

r2S(1-A) – 4r2Te4 = 0

Te4 = (S/4) (1-A)

Te = [ (S/4) (1-A) ]0.25

Earth’sEnergy

SWinSWout

LWout

RADIATION BALANCE OF THE EARTH: TOTAL RADIATION

Te = [ (S/4) (1-A) ]0.25

S = 1370 W/m2

A = 0.3 = 5.67 x 10-8 W/(m2-K4)

Te = 255K = -18°C = 0°F

RADIATION BALANCE OF THE EARTH:GREENHOUSE EFFECT

Te = 255K

Ts = 288K

Tg = Ts-Te

Tg = 33K = 33°C = 59°F

RADIATION BALANCE OF THE EARTH:GREENHOUSE EFFECT

Earth’s Surface

Earth’s Atmosphere

SW LW You can do the same calculation including an atmosphere

Atmospheric Energy Balance

II. Atmospheric Composition and Structure

Vertical Pressure and Temperature Structure

Note: logarithmic scale !

Vertical Ozone Structure

Modes of Energy Transfer in the Atmosphere

Physical Causes of the Greenhouse Effect

Physical Causes of the Greenhouse Effect

Physical Causes of the Greenhouse Effect

Effects of Clouds on the Atmospheric Radiation Budget: SW radiation

SW A*SW SW A*SW

Effects of Clouds on the Atmospheric Radiation Budget: LW radiation

Globally Average Energy Budget

Introduction to Climate Modeling

Many types of climate models exist. We discuss some of the more common types, which have different levels of complexity:

• Zero-dimensional radiation balance models

• 1-dimensional radiative-convective models

• 2-dimensional diffusive models

• 3-dimensional Atmospheric General Circulation Models (AGCM)

• 3-D coupled atmosphere – ocean models (AOGCM)

Te = [ (S/4) (1-A) ]0.25

Earth’sEnergy

SWinSWout

LWout

Introduction to Climate Modeling:zero-dimensional radiation balance model

Introduction to Climate Modeling:1-dimensional radiative-convective model

One-Layer Radiation Model

Introduction to Climate Modeling:1-dimensional radiative-convective model

1-D Rad-Conv Model

surface

S/4 (S/4)*A

Radiation in each wavelength band

Convection, latent fluxes

Surface: latent, sensible

Introduction to Climate Modeling:2-dimensional climate model

Surface

North Pole

South Pole

http://www.arm.gov/docs/documents/project/er_0441/bkground_5/figure2.html

Introduction to Climate Modeling:3-dimensional General Circulation Model (GCM)

surface

Introduction to Climate Modeling:3-D coupled atmosphere – ocean models

Atmosphere

Ocean

Climate Feedbacks

Water vapor feedback

snow/ice albedo feedback

IR flux/temp feedback

Cloud feedback ???