4.5: Global wind patterns

Properties of air that affect circulation

• More of the sun’s rays strike the Earth at the equator 

• The tilt of Earth’s axis points regions toward or away from the sun.

  • Regions pointed towards the sun receive more direct/intense light.

  • THIS CAUSES THE SEASONS!

Effects of air properties globally

Atmospheric convection current: 

• Warm gases expand, become less sense, and rise, creating vertical air flow called convection currents.

• Warm air currents may also contain a lot of moisture compared to the surrounding air.

Hadley cell

A convection current in the atmosphere that cycles between the equator and 30° N and 30° S.

• Precipitation in from Hadley Cells is one reason for the abundant rainforests found at/near the equator. 

Polar cells

follow the same process, but start at the 60 degree latitude

• smallest cells (cold dense air descending)

Ferrell cells

between Hadley and Polar and are driven by them

• not by temp, just go against the hadley and polars

Density

Air that is less dense rises

Saturation point

• The maximum amount of water vapor in the air at a given temperature.

• Warmer air has a higher capacity for water vapor.

Latent heat release

The release of energy when water vapor in the atmosphere condenses into liquid water; causes air to rise

Adiabatic cooling

The cooling effect of reduced pressure on air as it rises higher in the atmosphere and expands.

Adiabatic heating

The heating effect of increased pressure on air as it sinks toward the surface of Earth and decreases in volume.

• Gas laws: Pressure and Temperature rise and fall together

Intertropical convergence zone (ITCZ)

The latitude that receives the most intense sunlight, which causes the ascending branches of the two Hadley cells to converge.

• Zone is not fixed because Earth’s axis is tilted

Coriolis effect

The deflection of an object’s path due to the rotation of Earth.

• The prevailing winds of the world are produced by a combination of atmospheric convection currents and the Coriolis effect.