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Wind
Coriolis Effect (p. 516)
Prevailing Winds (p. 516-519)
Coriolis Effect
• The spinning of the Earth creates an effect
on any item that is in the air for a long
period of time
– Winds are therefore affected
• Was discovered by Gustave Coriolis when
working with the army
– They couldn’t figure out why their carefully
aimed canons weren’t hitting their target
Coriolis Effect
• In the Northern hemisphere, the rotation
is to the East (counterclockwise)
– Objects will ‘drift’ to the right
• In the Southern hemisphere, the rotation
is to the West (clockwise)
– Objects will ‘drift’ to the left
• The Coriolis effect is noticed the least at
the equator and the most at the poles
Winds
• Some winds are small and regional
• Many are major wind patterns that cover
large areas
– These winds are called Prevailing Winds
Wind Patterns (Surface)
• Between 60° latitude and the poles
– Winds move from East to West
– They are called the Polar Easterlies
W
E
Wind Patterns (Surface)
• Between 30° and 60° latitude
– Winds flow from West to East
– They are called the Westerlies
W
E
Wind Patterns (Surface)
• Between the equator and 30° latitude
– Wind flows from East to West
– North of the equator they are called the
Northeast Trade Winds
– South of the equator they are called the
Southeast Trade Winds
Jet Streams
• Jet streams are high speed winds in the
upper troposphere
• They flow from West to East and steer the
weather like highs and lows
Causes of Prevailing Wind
• Solar energies (the ones that make it
through the atmosphere) strike close to
the equator
• Here, hot air rises and expands leaving a
LOW pressure area behind
• When the rising air reaches the
tropopause it moves North
Causes of Prevailing Winds #2
• Once the air reaches 30° latitude it has
become colder and more dense so it sinks
– A HIGH pressure area is created
• Air at the surface then moves away from
the HIGH pressure towards the LOW at
the equator that was created previously
– As it moves it twists to the right
• THE NORTHEAST TRADE WINDS!!!
Causes of Prevailing Winds #3
• Not all of the air goes back to the equator
once it has reached the surface
• Some of it is deflected North towards the
LOW pressure area at 60° latitude
– Twists to the right and creates the midlatitude Westerlies
• At 60° latitude polar air creates a LOW
when it pushes warmer air up to the jet
stream
Causes of Prevailing Winds #4
• At the North pole the air is cold and dense
so it sinks creating a HIGH pressure area
at the surface
• Surface air moves South, away from this
high pressure area
– It twists to the right creating polar easterlies
• Air rising at the 60° latitude can go North
or South once it reaches the tropopause
Effects of Prevailing Winds
• The high and low pressure areas that are
created by the prevailing winds allow heat
to be transferred throughout the world
• They also cause precipitation and affect
the climate of different regions
– Rising air is warm and moist
– Falling air is cold and dry
• Can you point out some of the climates?
• Prevailing winds and jet streams change
with the seasons
– They follow the sun!!
• The Northeast trade winds move south,
closer to the equator during the winter