1. Natural Environments: The Atmosphere
GG 101 – Spring 2005
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-07-05
(1 of 10)
Further Reading: Chapter 04 of the text book
Outline
- geographic patterns of energy balance
- net radiation
- meridional transport

2. Natural Environments: The Atmosphere
GG 101 – Spring 2005
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-07-05
(2 of 10)
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
Although the system strives for thermal equilibrium, changes in the system allow for different climates -> “climate change”

3. Natural Environments: The Atmosphere
GG 101 – Spring 2005
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-07-05
(3 of 10)
Insolation
Today, we will look at the geographic patterns in the radiation balance
Insolation
Albedo
Longwave Radiation
Net Radiation
Insolation:
depends on latitude & time of the year

4. Natural Environments: The Atmosphere
GG 101 – Spring 2005
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-07-05
(4 of 10)
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 over equatorial lands can be high due to persistent cloud cover

5. Natural Environments: The Atmosphere
GG 101 – Spring 2005
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-07-05
(5 of 10)
Absorbed Shortwave Radiation
More solar radiation is absorbed by the oceans than adjacent lands
about the equator due to clouds on land
Less solar radiation is absorbed at the poles than at the equator (in general)

6. Natural Environments: The Atmosphere
GG 101 – Spring 2005
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-07-05
(6 of 10)
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 incoming solar radiation
High in tropics
Decreases towards poles

7. Natural Environments: The Atmosphere
GG 101 – Spring 2005
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-07-05
(7 of 10)
Net Radiation
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

8. Natural Environments: The Atmosphere
GG 101 – Spring 2005
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-07-05
(8 of 10)
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)

9. Natural Environments: The Atmosphere
GG 101 – Spring 2005
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-07-05
(9 of 10)
Meridional Transport via The Atmosphere
Transports warm tropical air to high latitudes; e.g., tropical air masses

10. Natural Environments: The Atmosphere
GG 101 – Spring 2005
Boston University
Myneni
Lecture 08:Patterns of Radiation
Feb-07-05
(10 of 10)
Meridional Transport via The Oceans
Transports warm tropical water to high latitudes; e.g. Gulf Stream