Global and Local Winds
Why Air Moves
• Winds blow from areas of high pressure to
areas of low pressure.
• The greater the pressure difference, the faster
the wind moves.
• Unequal heating of the Earth causes
differences in air pressure. Warm less dense
air rises at the Equator and the cold dense air
sinks at the Poles.
Pressure Belts
• Air travels in circular convection cells rising
and falling about every 30 of latitude.
• Bands of high and low pressure, called
pressure belts, separate the convection cells.
• Cool, sinking air causes high pressure belts
near 30 north and 30 south latitude.
• Warm, rising air causes low pressure belts
near 60 north and 60 south latitude..
The Coriolis Effect
• As air travels north and south across the Earth,
the rotation of the Earth beneath the moving
air causes an apparent curving of the winds.
• This apparent curving is called the Coriolis
effect.
• Diagram of the Coriolis effect.
Global Winds
• The combination of convection cells and the
Coriolis effect produce patterns of air
circulation called global winds.
• These are polar easterlies, westerlies, and
trade winds.
Global Winds
Don’t travel North and South
because of the
Earth rotating on its axis.
• 4 Types of Global Winds
– Doldrums
– Trade Winds
– Prevailing Winds
– Polar Easterlies
Polar Easterlies
• Cold, but weak winds
• Near the north and south
poles
• US weather is influenced by
these
• Cooling takes place between
the 50-60 degree latitude as it
approaches the poles
Prevailing Westerlies
• Strong winds
• Located in the belt from 30-60
degrees latitude in both
hemispheres.
• Has an impact on the US weather
Trade Winds
• 30 degrees N & S of Equator
• Calm winds, few clouds,
little rain fall
• Warm air rising from
Equator cools and sinks
• Also known as Horse
Latitudes
Doldrums
•At the equator, surface winds
are calm and weak.
•Why would these winds be
calm and weak?
•When would this cause a
problem?
Jet Streams
• Discovered in 1940’s
• Can be found in the upper
troposphere
• Strong high speed and high
pressure
• Moves west to east across the US,
moving storms