GARP 0102 Earth Radiation Balance (Part 1)
Class 8: Earth’s Radiation Balance I (Chapter 4)
Hand-outs
1. Earth’s Radiation Balance:
Sun, Atmosphere, and Earth’s Surface as a System
Fig. 4-17
Extras from Friday
Graded Stuff
2. Electromagnetic Radiation:
Shortwave vs. longwave radiation (Page 69-71)
3. Earth’s Radiation Balance:
Shortwave vs. longwave radiation balance (Page 77-81)
4. A “typical” Radiation Day
GARP 0102 Earth Radiation Balance (Part 1)
GARP 0102 Earth Radiation Balance (Part 1)
Class 8: Earth’s Radiation Balance I (Chapter 4)
1. Earth’s Radiation Balance:
Sun, Atmosphere, and Earth’s Surface as a System
2. Electromagnetic Radiation:
Shortwave vs. longwave radiation (Page 69-71)
3. Earth’s Radiation Balance:
Shortwave vs. longwave radiation balance (Page 77-81)
4. A “typical” Radiation Day
Big Picture!
Input (of energy) to the
Earth
=
Output (of energy) from the
Earth
 Balance!
GARP 0102 Earth Radiation Balance (Part 1)
What’s the Role of the Atmosphere in all this?
In the Atmosphere:
Solar Radiation hitting
the Top of the Atmosphere
1. Reflection
2. Absorption
3. Transmission
of solar radiation.
Solar Radiation received
at the Earth’s surface
GARP 0102 Earth Radiation Balance (Part 1)
Big Picture: The Role of the Atmosphere
Solar energy arriving at the
top of the atmosphere.
Solar energy transmitted
through the atmosphere:
transmission
absorption
reflection
The Radiation Balance of the Earth (Fig. 4-17)
Solar energy arriving at the
Earth’s surface. (reflection
and absorption)
 Heating!
GARP 0102 Earth Radiation Balance (Part 1)
The Atmosphere is heated by the Earth’s
Surface!
The solar energy does NOT heat the
atmosphere directly.
Think: Cold Water on a Hot Stove!
Instead, the sun heats the surface of the Earth.
The electricity does NOT heat the water
directly…it heats the burner plate.
The (warm) surface of the Earth heats the
overlying (cold) atmosphere from below.
And the hot burner plate heats the cold
water from the bottom!
 Unstable Situation!
GARP 0102 Earth Radiation Balance (Part 1)
“Colder” Atmosphere
“Colder” Water
“Hot” Earth Surface
“Hot” Stovetop
Not a Stable Situation!
Imbalance!
 Nature/Physics tries to
create a Balance!
1) Atmosphere/Water heat up!
2) Convection (bubbles rise!)
3) Vertical Mixing
Weather!
GARP 0102
0102 “Introduction
to Physical
Geography”
GARP
Earth Radiation
Balance
(Part 1) Lecture 7 (Wednesday, 02/03/10)
Fig. 4-16
Overall – there has to be a balance between:
1) The energy we receive from the sun!
2) The energy we send back into space!
Otherwise…we would melt!
GARP 0102 Earth Radiation Balance (Part 1)
Class 8: Earth’s Radiation Balance I (Chapter 4)
1. Earth’s Radiation Balance:
Sun, Atmosphere, and Earth’s Surface as a System
2. Electromagnetic Radiation:
Shortwave vs. longwave radiation (Page 69-71)
3. Earth’s Radiation Balance:
Shortwave vs. longwave radiation balance (Page 77-81)
4. A “typical” Radiation Day
Big Picture!
Electromagnetic radiation
is your cell phone!
GARP 0102 Earth Radiation Balance (Part 1)
Electromagnetic Radiation/Waves
= Radiation/waves that are able to transport energy without going through a solid medium
(think radio waves, cell phone waves, etc.)
 We characterize electromagnetic radiation based on its wavelength (= the distance from
one wave crest to the next).
The Electromagnetic
Spectrum
Fig. 4-5
Visible Light = Sun
Wavelength between 0.4 and 0.7 micrometers. “Visible” to Us! = Humans have build-in
“sensors” that can “measure” or “receive” these particular wavelengths – our eyes!
The Electromagnetic
Spectrum
Fig. 4-5
Fig. 4-5
413-575-2030
Visible Light = Sun
Wavelength between 0.4 and 0.7 micrometers. “Visible” to Us! = Humans have build-in
“sensors” that can “measure” or “receive” these particular wavelengths – our eyes!
Longer Wavelengths
= Microwaves/radar/cell phone/radio/TV waves. “Invisible” to Us! = Humans have no “sensors”
to “receive” them – but…your TV or radio or cell phone can “see” them!
The Electromagnetic
Spectrum
Fig. 4-5
Fig. 4-5
Visible Light = Sun
Wavelength between 0.4 and 0.7 micrometers. “Visible” to Us! = Humans have build-in
“sensors” that can “measure” or “receive” these particular wavelengths – our eyes!
Longer Wavelengths
= Microwaves/radar/cell phone/radio/TV waves. “Invisible” to Us! = Humans have no “sensors”
to “receive” them – but…your TV or radio or cell phone can “see” them!
Shorter Wavelengths
= X-rays/UV rays. “Invisible” to Us”! = Visible on X-ray films, which can “receive” them.
GARP 0102 Earth Radiation Balance (Part 1)
Facts of Physics:
 Page 69-71
1. All bodies/objects emit electromagnetic radiation all the time.
2. The amount/intensity of the emitted electromagnetic radiation, and its wavelength, are
determined by the temperature of the body/object.
(Now, we could derive these 2 facts using a whole bunch of scary
differential equations…let’s not do that…)
GARP 0102 Earth Radiation Balance (Part 1)
Facts of Physics:
 Page 69-71
1. All bodies/objects emit electromagnetic radiation all the time.
2. The amount/intensity of the emitted electromagnetic radiation, and its wavelength, are
determined by the temperature of the body/object.
(Now, we could derive these 2 facts using a whole bunch of scary
differential equations…let’s not do that…)
All bodies…
You, me, your pencil, the cat, the
table, the wall, the tree outside, the
pond, the car, the ice cube, the
freezer, the heater, the fan, the
mountain, the shoe, the ground, the
ice on the lake, etc.
Including…
the clouds, the water vapor
molecules, the dust in the air, the
rain drop, the snow flake, the CO2
molecule, the fog in the morning,
the haze, the smog, etc.
(doesn’t matter if liquid or solid)
GARP 0102 Earth Radiation Balance (Part 1)
Facts of Physics:
 Page 69-71
1. All bodies/objects emit electromagnetic radiation all the time.
2. The amount/intensity of the emitted electromagnetic radiation, and its wavelength, are
determined by the temperature of the body/object.
(Now, we could derive these 2 facts using a whole bunch of scary
differential equations…let’s not do that…)
All bodies…
You, me, your pencil, the cat, the
table, the wall, the tree outside, the
pond, the car, the ice cube, the
freezer, the heater, the fan, the
mountain, the shoe, the ground, the
ice on the lake, etc.
Including…
the clouds, the water vapor
molecules, the dust in the air, the
rain drop, the snow flake, the CO2
molecule, the fog in the morning,
the haze, the smog, etc.
(doesn’t matter if liquid or solid)
The hotter the object… (=Sun)
• The more energy it emits.
• The shorter the wavelength at which
it emits this energy.
GARP 0102 Earth Radiation Balance (Part 1)
Facts of Physics:
 Page 69-71
1. All bodies/objects emit electromagnetic radiation all the time.
2. The amount/intensity of the emitted electromagnetic radiation, and its wavelength, are
determined by the temperature of the body/object.
(Now, we could derive these 2 facts using a whole bunch of scary
differential equations…let’s not do that…)
All bodies…
You, me, your pencil, the cat, the
table, the wall, the tree outside, the
pond, the car, the ice cube, the
freezer, the heater, the fan, the
mountain, the shoe, the ground, the
ice on the lake, etc.
Including…
the clouds, the water vapor
molecules, the dust in the air, the
rain drop, the snow flake, the CO2
molecule, the fog in the morning,
the haze, the smog, etc.
(doesn’t matter if liquid or solid)
The hotter the object… (=Sun)
• The more energy it emits.
• The shorter the wavelength at which
it emits this energy.
The colder the object… (=Earth)
• The less energy it emits.
• The longer the wavelength at which it
emits this energy.
GARP 0102 Earth Radiation Balance (Part 1)
Facts of Physics:
 Page 69-71
1. All bodies/objects emit electromagnetic radiation all the time.
2. The amount/intensity of the emitted electromagnetic radiation, and its wavelength, are
determined by the temperature of the body/object.
(Now, we could derive these 2 facts using a whole bunch of scary
differential equations…let’s not do that…)
All bodies…
You, me, your pencil, the cat, the
table, the wall, the tree outside, the
pond, the car, the ice cube, the
freezer, the heater, the fan, the
mountain, the shoe, the ground, the
ice on the lake, etc.
Including…
the clouds, the water vapor
molecules, the dust in the air, the
rain drop, the snow flake, the CO2
molecule, the fog in the morning,
the haze, the smog, etc.
(doesn’t matter if liquid or solid)
The hotter the object… (=Sun)
• The more energy it emits.
• The shorter the wavelength at which
it emits this energy.
The colder the object… (=Earth)
• The less energy it emits.
• The longer the wavelength at which it
emits this energy.
Intensity = constants * T4 (Stefan-Boltzman Law)
Wavelength = constant / T (Wien’s Law)
GARP 0102 Earth Radiation Balance (Part 1)
All objects radiate electromagnetic energy all the time (day and night).
Hotter objects (i.e. the coffee cup) radiate with greater intensity than cooler objects (i.e. the
soft drink).
GARP 0102 Earth Radiation Balance (Part 1)
The Sun and the Earth emit electromagnetic radiation all the time!
But the Sun is much hotter  It emits more energy and at a shorter wavelength.
The Earth is much colder  It emits less energy and at a longer wavelength.
Sun (temperature ~11,000°F)
Emits most of its electromagnetic waves
(= energy) between 0.4 and 0.7
micrometer wavelength.
That…happens to be the wavelength
that our eyes can “measure” (= see!).
Sun (temperature ~11,000°F)
Earth/Atmosphere (temperature ~55°F)
Emits most of its electromagnetic waves
(= energy) between 0.4 and 0.7
micrometer wavelength.
Emits most of their electromagnetic
waves (= energy) between 5 and 30
micrometer wavelength.
That…happens to be the wavelength
that our eyes can “measure” (= see!).
And that…we can’t see with our eyes,
but we can see it with special films!
GARP 0102 Earth Radiation Balance (Part 1)
Orange = Lot’s of Heat Loss
Purple = Much less Heat Loss
Earth/Atmosphere (temperature ~55°F)
Emits most of their electromagnetic waves (=
energy) between 5 and 30 micrometer
wavelength.
And that…we can’t see with our eyes, but
we can see it with special films!
GARP 0102 Earth Radiation Balance (Part 1)
Class 8: Earth’s Radiation Balance I (Chapter 4)
1. Earth’s Radiation Balance:
Sun, Atmosphere, and Earth’s Surface as a System
2. Electromagnetic Radiation:
Shortwave vs. longwave radiation (Page 69-71)
3. Earth’s Radiation Balance:
Shortwave vs. longwave radiation balance (Page 77-81)
4. A “typical” Radiation Day
Fig. 4-16
Big Picture!
Now it gets complicated!
But, overall, input has to
equal output!
GARP 0102 Earth Radiation Balance (Part 1)
The Basics…
The Earth is constantly gaining energy from the Sun
via shortwave solar radiation.
At the same time, the Earth is constantly loosing
energy via its own longwave radiation.
 In the long-term, there has to be a balance
between our energy gains and losses, otherwise
the Earth would be an Unstable System!
Fig. 4-16
Analogy: Heating a House…
GARP 0102 Earth Radiation Balance (Part 1)
The Simplified Radiation Balance
Following the main pathways of
solar radiation and earth
radiation.
Greenhouse
Effect
Earth’s Radiation Balance includes two types of electromagnetic radiation.
1. Solar Radiation (also called “shortwave” radiation).
2. Earth Radiation (also called “terrestrial” or “longwave” or “infrared” radiation).
2a) Longwave radiation emitted by the earth’s surface upwards.
2b) Longwave radiation emitted by the atmosphere (e.g. clouds, water vapor, greenhouse
gases, dust, etc.) upwards and downwards.
 Solar Radiation and Earth Radiation are linked by the Greenhouse Effect.
GARP 0102 Earth Radiation Balance (Part 1)
Mean – Global – Still Simplified! (Fig. 4-17)
GARP 0102 Earth Radiation Balance (Part 1)
We will look at the details…
But – overall – the amount of energy we receive from the sun has to be balanced
by the amount of energy we emit back into space from the atmosphere.
Otherwise…it would get very hot down here very fast…
Incoming from Sun: 100 units (= 100 percent)
Outgoing from Earth: 31 + 61 + 8 = 100 units (= 100 percent)
 Overall Balance!
Confused? Page 77 - 79 (Fig. 4-17)
Mean – Global – Still Simplified! (Fig. 4-17)
GARP 0102 Earth Radiation Balance (Part 1)
Shortwave Balance
Longwave Balance
GARP 0102 Earth Radiation Balance (Part 1)
The Shortwave (Solar) Radiation Balance
100%/100 units of energy arrive from the Sun…
31% get reflected by the Earth’s surface or the atmosphere
(without heating anything) back into space.
24% get absorbed in the atmosphere (by dust, ozone,
clouds, water vapor, etc.) and heat up the atmosphere a bit.
45% finally arrive at the Earth’s surface…
Shortwave Balance
GARP 0102 Earth Radiation Balance (Part 1)
The Shortwave (Solar) Radiation Balance
100%/100 units of energy arrive from the Sun…
31% get reflected by the Earth’s surface or the atmosphere
(without heating anything) back into space.
24% get absorbed in the atmosphere (by dust, ozone,
clouds, water vapor, etc.) and heat up the atmosphere a bit.
45% finally arrive at the Earth’s surface…
At the Earth’s Surface
1. The surface of the Earth absorbs this solar radiation!
2. The energy transported by the electromagnetic waves
from the sun is exchanged…
3. …and the surface of the Earth is heated up.
The Earth’s surface, in turn, heats the overlying cool
atmosphere from the bottom!
Shortwave Balance
GARP 0102 Earth Radiation Balance (Part 1)
Solar Radiation enters the Atmosphere…
 Some solar energy is reflected by the atmosphere or by
clouds (i.e. it does not heat the atmosphere).
 Some solar energy reaching the Earth’s surface is
reflected back into space without any surface heating (think
snow!).
 A small amount of solar energy is absorbed and heats
the atmosphere directly.
 45% of solar energy reaches the Earth’s surface, warms
the surface, and the surface in turn heats up the (cold)
atmosphere from below! (Think stove top!)
Shortwave Balance
GARP 0102 Earth Radiation Balance (Part 1)
GARP 0102 Earth Radiation Balance (Part 1)
Shortwave Balance
Longwave Balance
GARP 0102 Earth Radiation Balance (Part 1)
61 = 21 + 3 + 4 + 19 + 14
Shortwave Balance
Longwave Balance
GARP 0102 Earth Radiation Balance (Part 1)
We will look at the details…
But – overall – the amount of energy we receive from the Sun has to be balanced
by the amount of energy we emit back into Space from the Atmosphere.
Otherwise…it would get very hot down here very fast…
Incoming from Sun: 100 units (= 100 percent)
Outgoing from Earth: 31 + 61 + 8 = 100 units (= 100 percent)
 Overall Balance!
Confused? Page 77 - 79 (Fig. 4-17)
GARP 0102 Earth Radiation Balance (Part 1)
Radiation Balance – Cliff Notes…
•
Sun heats up the Earth’s Surface
(mostly) and the overlying
Atmosphere (a bit).
•
The Earth’s Surface heats the
Atmosphere by emitting
longwave radiation.
GARP 0102 Earth Radiation Balance (Part 1)
Radiation Balance – Cliff Notes…
•
Sun heats up the Earth’s Surface
(mostly) and the overlying
Atmosphere (a bit).
•
The Earth’s Surface heats the
Atmosphere by emitting
longwave radiation.
•
The Atmosphere emits most of
the energy back to us (=
Greenhouse Effect) and into
Space to balance the Radiation
Balance = Recycling Loop.
The Atmosphere performs two critical functions
1. It traps much of the energy emitted by the Earth
and sends it back down = Greenhouse Effect,
which makes the Planet inhabitable.
2. It also sends this energy upwards into Space to
balance the energy balance.
GARP 0102 Earth Radiation Balance (Part 1)
Radiation Balance – Cliff Notes…
•
Sun heats up the Earth’s Surface
(mostly) and the overlying
Atmosphere (a bit).
•
The Earth’s Surface heats the
Atmosphere by emitting
longwave radiation.
•
The Atmosphere emits most of
the energy back to us (=
Greenhouse Effect) and into
Space to balance the Radiation
Balance = Recycling Loop.
The atmosphere is heated from the
bottom – by the Earth’s surface.
The Atmosphere performs two critical functions
1. It traps much of the energy emitted by the Earth
and sends it back down = Greenhouse Effect,
which makes the Planet inhabitable.
2. It also sends this energy upwards into Space to
balance the energy balance.
GARP 0102 Earth Radiation Balance (Part 1)
Class 8: Earth’s Radiation Balance I (Chapter 4)
1. Earth’s Radiation Balance:
Sun, Atmosphere, and Earth’s Surface as a System
2. Electromagnetic Radiation:
Shortwave vs. longwave radiation (Page 69-71)
3. Earth’s Radiation Balance:
Shortwave vs. longwave radiation balance (Page 77-81)
4. A “typical” Radiation Day
GARP 0102 Earth Radiation Balance (Part 1)
Surface Radiation Balance 1 Day
NET R =
+SW (incoming solar radiation)
–SW (reflected solar radiation)
+LW (incoming longwave radiation
from atmosphere, clouds, dust, etc.)
–LW (emitted longwave radiation
from Earth’s Surface)
Night: Negative Balance (Earth is
loosing Energy)  Cooling!
Day: Positive Balance (Earth is
gaining Energy)  Warming!
Typical summer/fall day in the mid-latitudes
GARP 0102 Earth Radiation Balance (Part 1)
The Warmest Time of the Day…
Does NOT occur at noon (= time of
maximum solar radiation)
But (usually) in the late afternoon!
Why??
When a maximum amount of solar
energy is absorbed by the earth’s
surface and emitted back into the
atmosphere as longwave radiation.
 Maximum heating of the
atmosphere!
GARP 0102 Earth Radiation Balance (Part 1)
Imagine…
A clear night (no clouds)
An overcast night (with clouds)
 There’s no sun, so we’re not receiving any
electromagnetic energy from the sun.
GARP 0102 Earth Radiation Balance (Part 1)
Imagine…
A clear night (no clouds)
An overcast night (with clouds)
 There’s no sun, so we’re not receiving any
electromagnetic energy from the sun.
Clear Skies
The Earth still emits its electromagnetic
radiation into space  Most cooling!
Overcast Skies
Now, the radiation from the earth is trapped by
the clouds. And the clouds also emit
electromagnetic radiation – both into space and
back to Earth  Much warmer!
( = Greenhouse Effect)
GARP 0102 Earth Radiation Balance (Part 1)
Class 8: Earth’s Radiation Balance I (Chapter 4)
Hand-outs
1. Earth’s Radiation Balance:
Sun, Atmosphere, and Earth’s Surface as a System
Fig. 4-17
Extras from Friday
Graded Stuff
2. Electromagnetic Radiation:
Shortwave vs. longwave radiation (Page 69-71)
3. Earth’s Radiation Balance:
Shortwave vs. longwave radiation balance (Page 77-81)
4. A “typical” Radiation Day
GARP 0102 Earth Radiation Balance (Part 1)
3-2-1 Response
That was a lot of material!
• The 3 most interesting things you just learned.
• The 2 most confusing things you just learned.
• The 1 burning question you need to answer.
 Share with your neighbor.
That’s what happens when you attend a talk,
lecture, or meeting. Some things will be
interesting, others boring. Some things will be
clear and well-explained, other not so much.
Hopefully there will be at least 1 question you
really need to find an answer to.
 Google, Wikipedia, Textbook, etc.