WHAT MAKES THE WIND BLOW?

Recall the effect of solar radiation

At the Equator

Atmosphere is heated

Air becomes less dense and rises

Rising air creates low pressure at the equator

Air cools as it rises

Water vapor condenses (rains) as the air cools with increasing altitude

As air mass cools it increases in density and decends bac to the surface in the subtropics (30o N and S), creating high pressure

This circulation is called the Hadley Cell

Air always move from an area ofHigh pressure to an area of Low

pressure

Hadley Cell

Global Wind Pattern

Global Winds• Greater heating of the atmosphere over equator causes air to

expand, become less dense and rise- this is a permanent low

pressure belt - Very humid

• Warm equatorial air then travels some distance north and south of equator and descends in subtropical regions around 30° latitude; when it descends, it becomes compressed and

denser and creates a high pressure belt in subtropics - Very Dry

• This descending subtropical air spreads along earth's surface both back towards the equator (these are the trade winds, between 0-30° N or S) and also to higher latitudes (westerly

wind belts, 30-60° N or S)

Coriolus EffectWhen decending air comes into contact with the earth in motion.

If the Earth didn't rotate we would only have a a single circulation cell in each hemisphere.

Because of fluid motion on a rotating sphere, Earth has three circulation cells in each

hemisphere:

Sea Breezes