Notes
Outline
Lecture 2: Global Energy Balance
Slide 2
Planetary Energy Balance
Solar Energy Incident On the Earth
 Solar energy incident on the Earth
      =  total amount of solar energy can be absorbed by Earth
      =  (Solar constant) x (Shadow Area)
      =  S x p R2Earth
Albedo = [Reflected] / [Incoming] Sunlight
Greenhouse Effect
Three Factors To Determine
 Planet Temperature
 Distance from the Sun
 Albedo
 Greenhouse effect
Earth, Mars, and Venus
Global Temperature
Greenhouse Effects
 On Venus è 510°K (very large!!)
 On Earth   è 33°K
 On Mars   è 6°K (very small)
Why Large Greenhouse Effect On Venus?
 Venus is too close to the Sun
 Venus temperature is very high
 Very difficult for Venus’s atmosphere to get saturated in water vapor
 Evaporation keep on bringing water vapor into Venus’s atmosphere
 Greenhouse effect is very large
 A “run away” greenhouse happened on Venus
 Water vapor is dissociated into hydrogen and oxygen
 Hydrogen then escaped to space and oxygen reacted with carbon to form carbon dioxide
 No water left on Venus (and no more chemical weathering)
Why Small Greenhouse Effect on Mars?
 Mars is too small in size
Mars had no large internal heat
Mars lost all the internal heat quickly
No tectonic activity on Mars
Carbon can not be injected back to the atmosphere
Little greenhouse effect
A very cold Mars!!
Vertical View of the Energy Balance
Vertical Distribution of Energy
Where Does the Solar Energy Go?
Where Is Earth’s Radiation Emitted From?
Cloud Types Based On Height
Important Roles of Clouds In Global Climate
Slide 19
Zenith Angle and Insolation
The larger the solar zenith angle, the weaker the insolation, because the same amount of sunlight has to be spread over a larger area.
Latitudinal Variations of Net Energy
Polarward heat flux is needed to transport radiation energy from the tropics to higher latitudes.
Polarward Energy Transport
How Do Atmosphere and Ocean Transport Heat?
Slide 24