1. Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-02-07
(1 of 11)
Further Reading: Chapter 04 of the text book
Outline
- geographic patterns of energy balance
- net radiation
- meridional (latitudinal) transport

2. Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-02-07
(2 of 11)
Introduction
Previously, we discussed the energy balance on a global scale and found that there are complex interactions between subsystems but that overall there is no net gain or loss of energy within any subsystem
Has important implications:
Global energy balance is the primary control on global climate
The natural Greenhouse effect (i.e. absorption and re-emission of longwave radiation by the atmosphere) is the key to temperature control of the entire system
The concept of thermal equilibrium suggest that the system establishes an energy balance by adjusting the temperature of the system
If incoming energy is greater than outgoing energy, then the temperature increases, increasing the outgoing radiation
This is the key to understanding the global warming debate: if humans add CO2, the Greenhouse effect increases, more re-radiated energy reaches the surface, hence incoming radiation increases, thus the temperature increases, increasing outgoing radiation until the system is balanced again

3. Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-02-07
(3 of 11)
Insolation
Today, we shall look at the geographic patterns in the radiation balance
Insolation
Albedo and Reflected (Absorbed) Shortwave Radiation
Longwave Radiation
Net Radiation
Insolation:
depends on latitude & time of the year
TOA Insolation for January
note the darkness in Northern Hemisp.

4. Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-02-07
(4 of 11)
Albedo
Albedo is the fraction of incident shortwave radiation that is reflected by a surface
It determines the amount of solar radiation absorbed by a surface
Albedo is high near the poles (snow & ice), low over water bodies, medium over land
Albedo of barren lands is higher than vegetated lands

5. Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-02-07
(5 of 11)
Reflected Shortwave Radiation
On Winter Solstice, the polar North receives no
energy from the Sun. In contrast, the amount of
incoming solar energy the Earth receives on
June 21, Summer Solstice, is 30 percent higher
at the North Pole than at the Equator.
In the top image, taken on Winter Solstice 2004,
the far North is dark blue, indicating that no
sunlight is being reflected back into space. The
most sunlight is being reflected out of the
Southern Hemisphere, where December 22
marked the longest day of the year.
The lower image shows Summer Solstice 2005.
Darkness dominates the South, while the North
is now the location receiving and reflecting the
most light.
In both images, bright white clouds stand out
because they are reflecting so much light back
into space.

6. Less solar radiation is absorbed at the poles than at the equator
Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-02-07
(6 of 11)
Absorbed Shortwave Radiation
More solar radiation is absorbed by the oceans than adjacent lands
Less solar radiation is absorbed at the poles than at the equator

7. Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-02-07
(7 of 11)
Outgoing Longwave Radiation
Outgoing longwave radiation is very similar to absorbed shortwave radiation
This is because longwave radiation is determined by the underlying temperature which
is determined by the amount of absorbed solar radiation
High in tropics
Decreases towards poles

8. Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-02-07
(8 of 11)
Outgoing Longwave Radiation
Note the North-South shift in max OLR emission
Note the change in OLR emission in Antarctica

9. Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-02-07
(9 of 11)
Net Radiation = (ABS_SW - OLR)
Remember, globally net radiation was zero, i.e. incoming balanced outgoing radiation
This is not true for given latitudes
At the tropics, the incoming is greater than the outgoing due to high insolation and low albedo
At the poles, outgoing is greater than incoming due to low insolation and high albedo
Why does the temperature at the equator not rise and the temperature at the poles not decrease?
Because energy is physically transported from the equator to the poles by the atmosphere and the ocean -> it is this difference in energy between the poles and equator which drives almost all dynamics in the system

10. Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-02-07
(10 of 11)
Meridional Transport
Driven by gradient in TOA net radiation
Net Radiation at TOA
Low latitudes: Positive
High latitudes: Negative
Outgoing energy partly derived from tropics
Transport accomplished via two mechanisms (Atmosphere & Oceans)

11. Natural Environments: The Atmosphere
GE 101 – Spring 2007
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-02-07
(11 of 11)
Meridional Transport via The Oceans
Transports warm tropical water to high latitudes; e.g. Gulf Stream