Download Slides 2.3 Winds and Climate

World Geo 3202
2.3 WINDS
 Understand the cause of winds
and how they affect climate
 Chapter 4
 Pages 59-67
2.3.1
Air moves from areas of high
pressure to areas of low pressure.
 Think of:
1. Air inside a balloon
2. Air exhaled from a person’s lungs
3. Air powered pellet gun
 The movement of air from high and low
pressures in the earth’s atmosphere are
responsible for wind!
 P. 59-61
2.3.1
What is Wind?
Wind: * It is the flow or movement of air.
* It results from air masses of different
temperatures lying next to each other
* The resulting pressure variation causes “wind” to
blow from high pressure area to low pressure area.
2.3.1 Define the term Prevailing
Wind. p.61-63
Prevailing Winds:
• They are regular,
predictable, normal
winds in the same
direction
• They are caused by
global convection
cells
More on these later!
2.3.2 Describe conditions that
result in Land and Sea Breezes
Sea Breezes:
1. During the day the land heats much faster than
the water, consequently the air over the land
heats and rises.
2. The rising air over the land leaves a relatively
low pressure. The air pressure over the water is
relatively high, therefore wind blows from high
pressure (water) to low pressure (land)
3. Hence the name 'sea breeze'—the wind is
blowing off the sea.
 Land Breezes:
1. The sea air is warmer than land air.
Because this air is warmer, it rises and leaves
a relatively low pressure over the sea.
2. The land air then blows to the low
pressure over the sea.
 Remember—winds are named for where
they come from.
 For example, easterly winds come out of the
east; southerly winds come out of the south;
sea breezes come from the sea.
2.3.2 Describe Conditions that result in
Land and Sea Breezes
Sea Breeze
•Land air is warmer than sea air
•Air rises over land, leaving a
relative low pressure
•Sea air moves to lower pressure
Land Breeze
•Sea air warmer than land air
•Air rises over sea, leaving a
relative low pressure
•Land air moves to lower pressure
2.3.3
Describe how the Coriolis
Effect affects Wind Direction.
Coriolis Effect:
 In northern hemisphere, objects in motion tend to
deflect to the right
 In southern hemisphere, objects in motion tend to
deflect to the south
Impact on winds:
 In the northern hemisphere, winds tend to
curve to the right
 In the southern hemisphere , winds deflect
to the left.
Coriolis Effect
2.3.4 Wind Systems relate to
Pressure Belts
 Global
convection cells are cycles of air
movement over the earth
 They are created because of the differential
heating of the earth's surface
 As the equatorial regions heat the air, it rises
creating a low pressure at the equator. The rising
air cools, falls to earth at 30º North/South, leaving
high pressures.
 The other lows and highs can be predicted every
30º of latitude north and south!
 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.
2.3.4 Make inferences about how winds are
related to major pressure belts. p.63
 Air rises from the equator
 Low pressures result
where hot air rises.
 High pressures
 Result is 6 convection cells
result where air
 3 above and 3 below the equator.
cools and settles
 Settles at the poles
2.3.5 Explain how wind systems
and temperature are related.
 Prevailing winds from the south bring warm
air toward the north, such as the Westerly
Winds. Whereas the North Polar Easterlies
bring cold air from the north toward the
south.
Prevailing Winds
2.3.5 Explain how wind systems and
temperature are related.
 How do the
1.
2.
3.
4.
prevailing winds
affect temperature in:
Argentina
Columbia
Baffin Island
Newfoundland
Remember!
 The affect on temperature varies with
seasons as well! Wind off the land in
summer results in heat, whereas, wind off
the land in the winter results in cold
temperatures.
 Land heats up faster than water and
therefore the wind blowing over it will pick
up the heat. Conversely, land also cools
down faster than water and winds blowing
over the frozen cold interior will lose its
heat.
2.3.6 Define windward, leeward
and rain shadow
 Windward is on the side facing the wind.
Wind carries precipitation
 Leeward is on the side sheltered away from
the wind. Wind is usually drier
 Rain shadow is a dry area on the leeward
side of a mountain
2.3.7 Type of rainfall is located
to nature of location
 Types of rainfall:
1.
Relief/Orographic Rainfall
– moist air blows off the sea;
– it is forced up by mountains (high relief);
– air cools at higher altitudes;
– cool air holds less moisture;
– clouds condense and rain falls;
– most rain falls on the windward side of the relief;
– the leeward side is often in a dry rain shadow because
the moisture has all been lost.
 Types of rainfall:
2. Frontal Rainfall
– Warm Moisture laden air meets cold air;
– warm air is less dense & is forced up over the
cooler, more dense air;
– warm moisture laden air cools at higher
altitude;
– cool air holds less moisture;
– clouds condense and rain falls.
 Types of rainfall:
3.
Convectional Rainfall
– usually occurs in hot areas like tropics or continental
summer;
– sun heats the earth causing large amounts of water to
evaporate;
– hot air rises forming convection currents;
– warm moisture-laden air cools at higher altitude;
– cool air holds less moisture;
– consequently clouds condense and rain falls.
2.3.8 Explain the relationship between wind
systems and precipitation
 Prevailing winds blowing off the ocean and onto
the land results in high precipitation. Especially if
the wind is blowing off a warm ocean, like the
Indian Ocean or the south Pacific.
 If wind is blowing off the land, then there is very
little moisture in it, resulting in low precipitation.
 Knowing the direction of winds over
mountains is also important in predicting
precipitation.
 The windward side of a mountain is going
to receive the greatest rainfall, while the
leeward side will find itself in a rain
shadow.
2.3.8 Explain the relationship between
wind systems and precipitation
 How do the prevailing
1.
2.
3.
4.
5.

winds affect
precipitation in:
England
Midwestern U.S.
British Columbia
Northern Africa
Central Australia
Question #26 p. 67: