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Atmosphere in Motion
Air Around You
Chapter 16
Atmosphere
• What is the atmosphere?
– A layer of gases surrounding Earth
– Composed of matter and has mass
– Subject to the pull of gravity
Gas Composition of Earth's
Atmosphere
• Nitrogen - 78% of
atmosphere
• Oxygen - 21% of
atmosphere
• Trace gases - 1% Neon, Helium,
Hydrogen, Methane,
Atmosphere
Carbon Dioxide Formation of the
Atmosphere:
• The Earth's atmosphere was formed by a
process in which gases like carbon
dioxide, water vapor, sulphur dioxide and
nitrogen were released from the interior of
the Earth from volcanoes and other
processes.
Atmosphere
• Levels
–Troposphere–Stratosphere
–Mesosphere
–Thermosphere
–Exosphere
Levels of Atmosphere
• Troposphere- approx. ground to 10
kilometers ( approx 7 miles up)
– The closest layer to the Earth.
– Contains 75% of our atmospheres gases
– Weather clouds and smog occur in the
troposphere
• The troposphere is the layer where most of
the world's weather takes place.
• Since temperature decreases with altitude in
the troposphere, warm air near the surface of
the Earth can readily rise, being less dense
than the colder air above it.
• air molecules can travel to the top of the
troposphere and back down again in a just a
few days.
• vertical movement or convection of air
generates clouds and ultimately rain from the
moisture within the air, and gives rise to
much of the weather which we experience.
Stratosphere
• approximately 10 km - 45 km up (approx
7miles-30miles)
• The ozone layer is located here
• the jet stream is located here
• Little or no water vapor here
• a layer in which temperatures rises with
increasing altitude.
• At the top of the stratosphere the thin air may
attain temperatures close to 0°C. This rise in
temperature is caused by the absorption of
ultraviolet (UV) radiation from the Sun by the
ozone layer.
• Such a temperature profile creates very stable
atmospheric conditions, and the stratosphere
lacks the air turbulence that is so prevalent in
the troposphere.
• almost completely free of clouds or other forms
of weather.
• Mesosphere - approximately 45 km -95
km up (30 - 50 miles up)
– the coldest part of the atmosphere
Thermosphere • approximately 95 km -to 500 km (50 miles
and up)
– Warmest layer of the atmosphere.
• lower layer of thermosphere is called the
ionosphere
IONOSPHERE
Exosphere
• approximately 500 kilometers and
beyond
– Outer most layer of our atmosphere
– Very few air molecules in this layer
– No clear boundary between this layer and
space
Test study Question
• Discuss the layers of the atmosphere and
the importance of each layer.
Video
http://aimedu.vo.llnwd.net/o35/s/wm/384k/1_1000/1_1101
_384k.wmv?e=1289359409&h=c82fe644878cd1ddbae97
3656b08df52&title=Video%20Quiz%20The%20Air%20Up
%20There
Water Cycle
• http://www.teachertube.com/view_video.p
hp?viewkey=53bdf2518c53ddf3bce6
Water Cycle
What is weather?
• Temperature
• Energy Transfer
• Atmospheric Pressure • Humidity
• Relative Humidity
What is weather? Describes the current condition of the
atmosphere.
Factors include- temperature, cloud
cover, wind speed & direction,
humidity, and air pressure
What is weather?
• Temperature– Measures how fast air
molecules are moving
– Rapid-warm/slow-cold
• Atmospheric Pressure
– Air has weight, and the
weight exerts pressure
– When air is heated
molecules move faster and
air expands, making air
less dense. This is why it is
moved upward
– Warm rises/cool sinks
• Energy Transfer
– Fast moving
molecules transfers
to slow moving,
transfer of energy
when molecules
collide is
conduction
– Warm air rising
cool air sinking is
convection (main
way heat is
transferred in
atmosphere)
• Humidity– amount of water
vapor in the
atmosphere
– Warmer more
evaporation occurs
thus more water
vapor
– Dew pointtemperature at which
condensation can
occur. when the air is
saturated (holds all
the vapor it can)
condensation can
occur
Clouds
Clouds are classified into a system that uses
Latin words to describe the appearance of
clouds as seen by an observer on the
ground.
Clouds
• Low clouds
• Middle Clouds
• High and vertical
clouds
Low Clouds
• Low clouds are of mostly composed of
water droplets since their bases generally
lie below 6,500 feet (2,000 meters).
However, when temperatures are cold
enough, these clouds may also contain ice
particles and snow.
Low Clouds
–Stratus- dull, gray sheets cover sky
–Nimbostratus- low, dark thick layers
block out sun (rain sheets)
–Cumulonimbus- thunder heads
(vertical development produce
thunder and lighting) all levels of
troposphere
–Stratocumulus–Cumulus- puffy clouds
Cumulus
Mid-Level Clouds
• The bases of mid-level clouds typically
appear between 6,500 to 20,000 feet
(2,000 to 6,000 meters). Because of
their lower altitudes, they are
composed primarily of water droplets,
however, they can also be composed
of ice crystals when temperatures are
cold enough.
Middle Clouds
• Layered variety of
clouds
• Contain enough
moisture to produce
light precipitation
• Altocumulus
• Altostratus
High Level Clouds
• High-level clouds form above 20,000 feet
(6,000 meters) and since the
temperatures are so cold at such high
elevations, these clouds are primarily
composed of ice crystals.
• typically thin and white in appearance, but
can appear in a magnificent array of colors
when the sun is low on the horizon.
High and vertical clouds
• Made up entirely of ice crystals, high
in atmosphere
–Cirrus- wispy, high-level clouds
–Cirrocumulus
–Cirrostratus- high, layered cover entire
sky
–Cumulonimbus- create heaviest
precipitation thunderstorm cloudsvertical development
Cloud types
• Cirrostratus
Clouds
Clouds
• Low clouds
– Stratus
– Nimbostratus
– Stratocumulus
– Cumulonimbus
• Middle Clouds
– Altostratus
– Altocumulus
• High and vertical
clouds
– Cirrus– Cirrocumulus
– CirrostratusCumulonimbus-
Precipitation
• When drops of water become too
heavy to remain suspended in the
clouds
– Rain
– Snow
– Sleet
– Hail- balls of ice that form in
cumulonimbus clouds
Winds
• When molecules are heated in
atmosphere and they move quickly
and spread apart. Causes regions of
low pressure
• When cooled molecules move more
slowly and closer together air
becomes less dense and sinks
forming regions of high pressure
Wind
• Air moving from one pressure to
another
• Greater pressure differences greater
the winds
• Measure by anemometer- indicates
wind speed
Anemometer
Surface Winds
• Winds blowing near the Earth's surface.
• It is measured, by convention, at a height
of 10 m above ground in an area where
the distance between the anemometer
and any obstruction is at least 10 times
the height of the obstruction.
Coriolis Effect
• Once air has been set in motion by the
pressure gradient force, it undergoes an
apparent deflection from its path, as seen
by an observer on the earth. This
apparent deflection is called the "Coriolis
force" and is a result of the earth's
rotation.
• As air moves from high to low
pressure in the northern hemisphere,
it is deflected to the right by the
Coriolis force.
• In the southern hemisphere, air
moving from high to low pressure is
deflected to the left by the Coriolis
force.
Easterlies and Westerlies
Coriolis Effect
Clouds
•
http://ww2010.atmos.uiuc.edu/(Gh)/guides/
mtr/cld/cldtyp/home.rxml
•
http://vortex.plymouth.edu/clouds.html/
Air Masses and Fronts

Fronts
Cold

Warm

Occluded

Stationary
Air masses
•
•
•
•
Air masses move due to wind
Dry or moist and warm or cool, depending
on where it begins (pg 458)
Mass of air that remains over a region for a
few days and takes on the characteristics of
the area it occurs
When air masses of different temperature
meet, a boundary is formed called a front
Cold Fronts




pushes under warm air
pushing it up,
Cumulus &
cumulonimbus brings
narrow band of
precipitation can occur
(short period of heavy
precip.)
cold air in (temp
drops)
Cumulonimbus
Warm Fronts

Warm less dense (warm) slides up and over
cold air;
 high cirrus clouds first and then
stratus
 Long periods of slow precip.
 Temperature rises
Occluded Fronts
Fast moving cold
front takes over a
slow moving
warm
 Both may
produce clouds
with
precipitation.

Occluded Front


weather conditions will likely turn from cool
to cold.
Winds will swing around from easterly to
westerly or southwesterly with rain or snow
showers possible, (depending upon how
cold the temperatures are).
Stationary Front
•
Warm air & cold air
meet and neither
advances
•
Remains in same
location for days
•
Cloudiness and
precip. may occur
High and low pressure centers

Moves from high to low areas

High pressure areas air sinks
 Moves from high to low
 Air moves clockwise due to Coriolis
 Usually dry with few clouds

Low pressure area- air rises and cools
 Air circulates in counterclockwise
 Air reaches dew point water vapor
condenses forming clouds and
precipitation
Severe Weather



Thunderstorms

Lightning

Thunder- what causes?
Tornadoes
Hurricanes
Severe Weather

Thunderstorms- cumulonimbus clouds
(along cold fronts)
 Lightning- energy flow that occurs
between areas of opposite electrical
charge

Lightning happens
when the negative
charges (electrons) in
the bottom of the
cloud (and your
finger) are attracted to
the positive charges
(protons) in the
ground.

The accumulation of
electric charges has to
be great enough to
overcome the
insulating properties
of air. When this
happens, a stream of
negative charges
pours down towards a
high point where
positive charges have
clustered due to the
pull of the
thunderhead.

The connection is made
and the protons rush up
to meet the electrons. It
is at that point that we
see lightning. A bolt of
lightning heats the air
along its path causing it
to expand rapidly.
Thunder is the sound
caused by rapidly
expanding air.

Outdoor Lightning Safety:
 Seek shelter indoors or in a car.
 Stay away from single tall objects (such as a tree) and
metal objects (fences, pipes, rails).
 Don't hold golf clubs, fishing poles.
 Remove backpacks with metal frames.
 It is not safe to be riding bicycles, motor scooters,
motorcycles, or golf carts.
 If you are out in the open and cannot get to shelter,
stand in a low spot under a group of trees (not under
a lone tree)
 or crouch down on the balls of your feet—do not
lie flat on the ground. If you are swimming or
boating, get out of the water.
Thunder
 Thunder-
what causes?
 5 times hotter than sun’s surface-causes air
to expand quickly, then cools quickly and
contracts producing rapid movement of
molecules
 Sound due to expansion and contraction
of the heated air
Can you tell how far away?

If You Can Hear It, Clear It; If You Can See It,
Flee It: This saying means that you should take
shelter if the time between a lightning flash
and the thunder is 30 seconds or less, which
means that the lightning is about 5 miles away.

(To determine the distance, count the seconds
between the flash and the thunder and divide
by 5.) Lightning can strike 5-10 miles ahead of
the storm, so don't wait until the lightning is
upon you to go inside. Don't resume activities
until 30 minutes after you hear the last
thunder.
Tornados
A
tornado is a powerful column of
winds spiraling around a center of
low atmospheric pressure. It looks
like a large black funnel hanging
down from a storm cloud. The narrow
end will move over the earth,
whipping back and forth like a tail.
cold air on top begins to sink, sending the
rising warm wind spinning upward.
 The warm winds rotates faster and faster
in a high column. When the updraft is
strong, the column can rise to heights of
10 miles or more, twisting at speeds of up
to 100 miles an hour. The rotating winds
produce strong storm clouds about 70,000
feet high, sometimes spreading 10 miles
wide.

Hurricanes
• Hurricanes are the most destructive
natural disaster;
• they are very powerful and violent
storms, often associated with strong
winds and heavy rains.
• A storm is classified as a hurricane
when the speed of wind reaches 74
miles (119 kilometers) per hour.
• Hurricane storms usually start over
warm sea (near the equator) and are
accompanied by fierce winds, flash
floods, mudslides and huge waves.
• Hurricanes are intense low pressure
areas that form over warm ocean
waters in the summer and early fall.
• Their source of energy is water vapor
which is evaporated from the ocean
surface. This is the "fuel" for the
hurricanes.
Sources
 ww2010.atmos.uiuc.edu/(Gh)/guides/
mtr/cld/.../home.rxml –
 http://www.buzzle.com/articles/cause
s-and-effects-of-hurricanes.html
 www.weatherquestions.com/What_ca
uses_hurricanes.html
 http://www.buzzle.com/articles/typho
on-vs-hurricane-vs-cyclone.html