Transcript Unit 3 The Water Cycle

Unit 4
Weather
Lesson 1
How Does Uneven Heating
of Earth Affect Weather?
The Atmosphere
-The atmosphere is a
thin blanket of air that
surrounds Earth.
-It is very thin compared
to the size of Earth.
-The atmosphere is
made up of many layers:
troposphere,
stratosphere, and ozone.
Troposphere
 The troposphere is the
layer that is closest to
Earth’s surface.
 It contains 90% of the
atmosphere’s gases.
 Most of the Earth’s
weather happens in
the troposphere.
How Do You Know Air is There?
 You know the air is there
because you can feel it
every time the wind blows.
 You can feel air blow
against you because it has
mass.
 Everything on Earth that
has mass is pulled toward
Earth’s center by gravity.
 This pull causes air to
have weight.
Air Pressure
 Air particles closer to
Earth’s surface have
more weight than the
air higher in the
atmosphere.
 This means that air
pressure, or the weight
of air in the
atmosphere in one unit
area, is greatest at sea
level.
Air Pressure (cont.)
 The higher you go into the
atmosphere, the less air there is
above you.
 Air pushes downward as well as
in all directions. This is because
gas molecules are constantly
moving in all directions.
 Temperature also affects air
pressure. Cold air is denser
than warm air. Because of this,
it sinks toward Earth’s surface.
This forces warmer, less dense
air to rise. As warm air rises, it
cools. The cooler air is now
denser, so it sinks back to the
surface.
Air Density
 Another factor that causes air pressure
to be greater at sea level is air density.
 Gravity pulls most of the air in the
atmosphere down to the surface.
 Because of this, the air closer to
Earth’s surface is much denser than
the air father away from the surface.
Convection Currents
 Air that is warm is less
dense, so it is pushed
upward by the cooler,
denser air.
 This upward and
downward movement
of air is called
convection currents in
the atmosphere
Sea & Land Breezes
 During the day, the land
heats up faster than the
sea. Cooler sea air moves
toward the land. This is
called a sea breeze.
 At night, the land loses
heat faster than the sea
does. Cooler air over the
land moves toward the
sea. This is called a land
breeze.
Local Wind
 Winds can be local, affecting small areas, or
global, affecting larger parts of the Earth.
 Sometimes, places in the same general
area have slightly different temperatures.
This produces local wind, or wind that
results from a local difference in
temperature.
 Local winds often occur along lakeshores or
seashores.
Global Winds
 A prevailing wind is a global wind that almost always blows from the
same direction.
 Prevailing winds result from uneven heating of large parts of Earth’s
surface.
 An area’s latitude (distance from the equator), Earth’s rotation, and
uneven heating of Earth’s surface all affect prevailing winds.
Trade Winds &
Prevailing Westerlies
 Winds moving north curve
to the east. Winds moving
south curve to the west.
 Around the equator, this
curving causes the
prevailing winds – called
trade winds – to blow from
the east.
 In the United States, this
curving causes the
prevailing winds – the
prevailing westerlies – to
blow from the west.
Bill Nye Videos
Atmosphere Part 1
http://www.gamequar
ium.org/cgi-bin/search/linfo.cgi?id=8436
Atmosphere Part 2
http://www.gamequarium.org/cgibin/search/linfo.cgi?id=8437
Atmosphere Part 3
http://www.gamequarium.org/cgibin/search/linfo.cgi?id=8438