Download Wind Lecture

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 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