Radiation 3

Question 1

What is the difference between heat received by a flat non-rotating disk and a rotating sphere (Earth)?

Answer 1

The surface of a flat non-rotating disk receives 4 times as much radiation per unit area.

Flat non-rotating disk - 1360 Wm
Sphere - 340 Wm

Question 2

How is radiation from the sun distributed across the different latitudes on Earth?

Answer 2

As latitude increases, each square metre of land receives proportionately less radiation (radiation shines at an angle).

Radiation absorbed on Earth decreases strongly when latitude increases, while radiation emitted remains constant.

Low latitudes - net absorption of energy (surplus)
High latitudes - net emission of energy (deficient)

Question 3

As the Earth’s energy is in equilibrium, how does the excess energy in the tropics get transferred to the extratropics?

Answer 3

Poleward heat transport:

• atmosphere (2/3 of energy transfer)
  i) atmospheric winds (sensible heat) - warm air moves poleward while cold air moves equatorward
  ii) water vapour flux (latent heat) - winds carry water vapour and precipitation releases heat

** latent heat is transferred back to the equator from 30°N and 30°S

• oceans (1/3 of energy transfer)
  i) ocean currents - warm water moves poleward while cool water moves equatorward

Question 4

What causes the difference in water vapour flux (latent heat) on Earth?

Answer 4

Water vapour flux is relative to the wind circulation. Wind flows away from the subtropics to the equator and the mid latitudes.

• Converges at tropics (tropical rainforests)
• Diverges at the subtropics (deserts)
• Converges at the mid-latitudes (temperate forests)