Geo 105, Role of atmosphere >> blanket & circulation

What do we expect the temp of Earth to be?

Recall that:

• Due to spherical shape, the equatorial region receives its full share of solar energy, while the polar regions have much less incoming energy. Thus, a solid Earth would be cool at the equator, and incredibly cold in the polar regions!

Atmosphere

• Atmosphere is hot at bottom, colder higher up
• Thus, the temp. that the Earth must be to remain in radiative equlibrium occurs near the top of the atmosphere, while we live at the bottom where it is warmer
• In detail, this picture is true for the bottom 10 km of the atmosphere (troposphere), temp. decreases from a comfortable value at bottom to about 200 deg K at 10 km.
• above this temp. minimum is the stratosphere, where temp increases as we go up
• The fact that temp is hotter at bottom of troposphere makes it "unstable" to thermal convection
• thermal convection: hotter air is less dense, therefore wants to rise, & colder air is denser, wants to sink. Forms a "convection cell", hot air rising and spreading out horizontally at top of troposphere, colder air moving horizontally along surface to replace the rising hot air.
• apply this idea to global scale, expect hot air rising at equator, flowing toward the poles, then sinking as it cools due to radiative heat loss.
  expect cold air at poles to flow toward the equator, heating up as it absorbs radiation from the hotter land surface.