Winds & Climate
World Climate Patterns
World Geo 3200/3202
Unit 2
November 2010
Lesson Outcomes
• 2.3.1 Define the term prevailing winds. (k)
• 2.3.2 Describe conditions that result in land
breezes and sea breezes. (k)
• 2.3.3 State the impact of the Coriolis effect on
wind direction. (k)
• 2.3.4 Infer how wind systems relate to major
pressure belts. (a)
High Pressure & Low Pressure
• Winds blow from regions of high atmospheric pressure
to areas of low atmospheric pressure.
• High and low pressures in the earth’s atmosphere are
responsible for wind.
• Air under high pressure has a tendency to want to
“escape” towards low pressure areas
High Pressure & Low Pressure
• Think—Air inside a balloon. If left untied the air will
escape the high pressure of the balloon and create a wind
blowing from high pressure inside the balloon to
relatively low pressure outside the balloon.
• Think—Exhaling: when you exhale the air leaves your
lungs because you create a high pressure inside your
chest cavity and breath (wind is created from high
pressure inside your chest to a lower pressure outside
your chest.
Prevailing Winds
• Regular, predictable, normal
wind direction are known as
prevailing winds
• They are caused by global
convection cells in the earth's
atmosphere. (fig 4.10 on pg.
63)
Prevailing Winds
• The global convection cells are created because of the
differential heating of the earth's surface.
• As the equatorial regions heats the air it rises creating a
low pressure at the equator.
• The air falls to earth 30º North and south creating high
pressure belts.
• The other lows and highs can be predicted every 30º of
latitude.
• Remember that wind directions move from highs to lows
• Low pressure belts are
created at the equator
& at 60° N & S
• High pressure belts
are created at 30° N &
S and at the poles
• Remember that wind
directions move from
highs to lows
Local Winds….Sea Breezes (4.8 p 61)
• In the day time the land heats much faster than the
water (land has greater thermal conductive & water has
the ability to dissipate heat at a faster rate)
• As a result, the air over the land heats & rises creating a
relatively low pressure over the land
• The air pressure over the water/sea would be cooler and
relatively high
• Winds therefore would blow from the sea towards the
land as the cool ocean air moves in to replace the warm
rising air above the land
Local Winds….Sea Breezes (4.8 p 61)
• The wind is blowing off the sea
hence the name sea breeze
• We experience this in a lot of
summer time situations.
• The opposite is true for ‘land
breeze’.
Sea Breezes
• Remember—winds are named for where they come from;
▫ Easterly winds come out of the east;
▫ Southerly winds come out of the south;
▫ Sea breezes come from the sea.
▫ Land breezes comes from the land.
Global Convection Cells
• Alternating high and low pressures result from the convection cells.
A low pressure belt is created at the equator and at 60º N and 60º S
while high pressure belts are created at 30º N and 30ºS and at the
poles.
• Prevailing Winds form global patterns because of these global
pressure belts. They follow the laws of physics and blow from the
high pressure belts to the low pressure belts.
Prevailing Wind Names
• 0-30º N = Northeast trade
winds
• 0-30º S = Southeast trade
winds
• 30-60º N and 30-60º S =
Prevailing Westerly winds
• 60-90º N = North Polar
easterlies
• 60-90º N = South Polar
easterlies
Coriolis Effect
• The Coriolis effect explains why the winds are
deflected in the directions indicated on the in figure
4.11.
Coriolis Effect
• The coroilis effect is a law of
physics that sates: objects in
motion in the northern
hemisphere are deflected to
the right while in the southern
hemisphere they are deflected
to the left.
• Therefore winds in the north
are deflected right and the
winds in the south are
deflected left.
Local Weather Patterns
• In our area, Eastern North America, prevailing
winds are generally from west to east
• Generally, air masses move along a path from
southwest to northeast
• We see this regularly in our weather patterns as
low pressure systems (hurricanes, blizzards)
move from the Eastern seaboard of the USA up
to Atlantic Canada & over NL
Local Weather Patterns
Review
• What causes wind to blow? DIFFERENCES IN
AIR PRESSURE
• What causes winds to be deflected from a
straight path? CORIOLIS FORCE
• What causes the development of global
convection cells and pressure belts.
DIFFERENTIAL HEATING OF THE EARTH
• Winds that normally blow in a region are
referred to as _?_. PREVAILING
Review
• When do sea breezes occur? DAY WHEN LAND
IS HOTTER THAN SEA
• What name is given to the prevailing winds
between 60 and 90 degrees N. NORTH POLAR
EASTERLIES
• What name is given to the prevailing winds
between 60 and 90 degrees S. SOUTH POLAR
EASTERLIES
• What name is given to the prevailing winds
between 30 and 60 degrees N. WESTERLY
Review
• What name is given to the prevailing winds
between 60 and 90 degrees S? WESTERLY
• What name is given to the prevailing winds
between 0 and 30 degrees N? Northeast trade
winds
• What name is given to the prevailing winds
between 0 and 30 degrees S. SOUTHEAST
TRADE WINDS
• When hot air rises what type of pressure is
created?