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 (30 o N and S), creating high pressure  This circulation is called the Hadley Cell

Air always move from an area of High 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 Effect When 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