Download Air Pressure and Winds

Air Pressure and Winds
What makes the wind blow?
What is Air Pressure?


It is the pressure exerted by the
weight of the air in the atmosphere
(the column of air above the land
surface has weight. That weight
pushes down)
Air pressure is exerted in all
directions – up, down, sideways.
• Because air pressure “happens” in all
directions, it’s always in balance around
an object.
What is Wind?

Wind is the result of horizontal
differences in air pressure.
• Air flows from areas of high pressure to
areas of lower pressure


High pressure – areas with barometric
pressure greater than standard pressure.
Low pressure – areas with barometric
pressure less than standard pressure.
How is Wind Generated?

It is the result of the unequal heating
of Earths surface by the sun
• How does that produce wind?

Winds are controlled by:
• Pressure differences (pressure gradient)
• The Coriolis effect
• Friction
High and Low Pressure Centers

Low Pressure
• Referred to as cyclones. Lowest
pressures are toward the center.

High Pressure
• Referred to as anticyclones. Highest
pressures are toward the center.
Weather and Air Pressure
Clear
Cloudy
Sinking
Rising
Air
Air
Low Pressure
High Pressure
Isobars
Isobars are lines on a map that show areas of equal pressure
If there are several isobars close together on a map it is showing an
area where there is a greater difference in pressure.
Greater difference in pressure = stronger winds
H
L
What might be
causing the high
pressure over
Utah and Nevda?
Can
Where
Where
you tell
are
arewind
the
the
direction
high
highest
pressure
on
wind
this
map?
areas?
speeds?
Measuring Air Pressure


Standard air
pressure is 1013.2
millibars (the
metric unit of
atmospheric
pressure) at sea
level.
A barometer is
used to measure
air pressure.
Coriolis Effect

Deflects moving objects (wind) due
to Earths Rotation
• Affects direction, not speed
• Is strongest at the poles, weakest at
equator.
• Deflects to right in Northern Hemisphere
• Deflects to left in Southern Hemisphere
NC Weather Today
National Geographic Coriollis Effect
http://channel.nationalgeographic.co
m/street-genius/videos/corioliseffect/
Global Wind Patterns


Earths Atmosphere try's to balance
the different temperatures at
different locations on Earth by
continuously transferring heat from
lower latitudes (near the equator)
towards the poles and moving colder
polar air toward the equator.
This creates global wind patterns
Global Wind Patterns
Air Flow
Cold
Warm
Cold
Complete the Process Flow
L
____  ____  ____  ____  _____  Low Pressure
Sun heats Earth  Earth radiates heat to
atmosphere  Atmosphere warms  Density
of air is reduced  lower density air rises 
low pressure system forms
Section 19.1 Reading
Quiz
Use your own paper to write
answers.
Reading Quiz – No Books
1.
2.
3.
4.
5.
What is air pressure?
What is required to create wind?
What factors work together to
control wind direction and speed?
What is an isobar?
How does the Coriollis Effect
change wind direction in the N.
hemisphere?
Reading Quiz
6.
Look at the map. What direction
would you expect the wind to be
blowing in the Eastern U.S.?
Reading quiz
7.
This is a
map of the
relative
humidity in
NC. What
factor(s)
could make
relative
humidity
higher in
the western
part of the
state?
Quiz Answers
1.
2.
Air pressure is the weight of the
column of air pressing down on
Earth in all directions.
Wind requires horizontal differences
in air pressure and the uneven
heating of Earths Surface.
3.
4.
5.
Wind speed and direction are
controlled by differences in air
pressure, friction, coriollis effect
An isobar is a line of equal air
pressure (a contour line)
Coriollis Effect deflects wind to the
right (if you were looking South
from the North Pole)
Reading Quiz
6.
What direction would you expect
the wind to be blowing in the
Eastern U.S.?
Reading quiz
7.
This is the
relative
humidity in
NC today.
What
factor(s)
could make
it higher in
the western
part of the
state?
Lower temperatures in the mountains
could cause higher humidity.
Global Winds – Another View
Polar Easterlies
Polar Front
Westerlies
NE Trades
SE Trades
Westerlies
Polar Front
Polar Easterlies
Quiz Review

What is the ultimate source of energy for
most winds?
• Sun/solar radiation (not just “radiation”)

What causes air pressure?
• The mass (weight) of the air above earth
pressing down on the surface of the earth.
• Differences in air pressure are due to
differences in density of the air or temperature
differences (which affect density)
Quiz review

What causes winds
• Differences in air pressure between two
locations (horizontal difference)
LH
winds go from areas of high
pressure to areas of low pressure

Which type of pressure system often
results in clouds and precipitation?
• Low or cyclone
Quiz Review

What is an isobar?
• A line that represents a constant value
of air pressure. (not wind speed, not an
instrument)

At what location are the greatest
wind speeds likely to be?
• To find the location, look for the spot
where the isobars are closest together –
this is the area of greatest wind speed.
End of chapter 19