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The Atmosphere
The Atmosphere
• The atmosphere is a mixture of gases that
surrounds a planet, such as Earth.
• Nitrogen, oxygen, carbon dioxide, and
other gases are all parts of this mixture.
• Gases can be added to and removed from
the atmosphere through living organisms.
For example, animals remove oxygen when
they breathe in and add carbon dioxide
when they breathe out.
The Atmosphere
• The atmosphere insulates Earth’s surface.
• This insulation slows the rate at which the
Earth’s surface loses heat and keeps Earth
temperature at which living things can survive.
Composition of the Atmosphere
• Nitrogen makes up 78 percent
of the Earth’s atmosphere, and
enters the atmosphere when
volcanoes erupt and when dead
plants and animals decay.
• Oxygen is the second most
abundant gas in the atmosphere
and is primarily produced by
plants.
• In addition to gases, the
atmosphere contains many types
of tiny, solid particles, or
atmospheric dust.
Layers of The Atmosphere
• The atmosphere is divided into four
layers based on temperature changes
that occur at different distances above
the Earth’s surface.
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•
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The Troposphere
The Stratosphere
The Mesosphere
The Thermosphere
The Troposphere
• The troposphere is the lowest layer of the
atmosphere in which temperature drops at
a constant rate as altitude increases.
• This is the part of the atmosphere where
weather conditions exist.
• The troposphere is Earth’s densest
atmospheric layer and extends to 18 km
above Earth’s surface.
The Stratosphere
• The stratosphere is the layer of the
atmosphere that lies immediately above
the troposphere and extends from
about 10 to 50 km above the Earth’s
surface increases.
• Temperature rises as altitude increases
because ozone in the stratosphere
absorbs the sun’s ultraviolet (UV)
energy and warms the air.
Ozone
• Ozone is a gas molecule that is made up
of three oxygen atoms.
• Almost all of the ozone in the
atmosphere is concentrated in the
stratosphere.
• Because ozone absorbs UV radiation, it
reduces amount of UV radiation that
reaches the Earth. UV radiation that
does reach Earth can damage living
cells.
The Mesosphere
• The layer above the stratosphere is the
mesosphere.
• This layer extends to an altitude of
about 80 km.
• This is the coldest layer of the
atmosphere where temperatures have
been measured as low as
–93ºC.
The Thermosphere
• The atmospheric layer located farthest from
Earth’s surface is the thermosphere.
• Here, nitrogen and oxygen absorb solar
radiation resulting in temperatures measuring
above 2,000 ºC.
• The air in the thermosphere is so thin that
air particles rarely collide, so little heat is
transferred, and would therefore not feel hot
to us.
Heating of the Atmosphere
• About half of the solar energy that enters the
atmosphere passes through it and reaches the Earth’s
surface, while the rest of the energy is absorbed or
reflected in the atmosphere by clouds, gases, and
dust or it is reflected by Earth’s surface.
• The Earth does not continue to get warmer because
the oceans and the land radiate the absorbed energy
back into the atmosphere.
• Because the ocean both absorbs and releases heat
slower than land, the temperature of the atmosphere
changes more slowly.
Movement of Air in the Atmosphere
• As a current of air, warmed by Earth’s
surface, rises into the atmosphere, it
begins to cool, and eventually becomes
more dense the air around it and sinks.
This current then moves back toward
the Earth until heated and less dense
and then begins to rise again.
• The continual process of warm air rising
and cool air sinking moves air in a
circular motion is called a convection
current.
Weather
 Temporary behavior of atmosphere
(what’s going on at any certain time)
 Small geographic area
 Can change rapidly
Climate
 Long-term behavior of atmosphere
(100+ years)
 Large geographic area
 Very slow to change
Air Masses
• Body of air with a certain temperature and
moisture level
• As it moves, the characteristics of an air
mass change and so does the weather.
• Can be warm(T) or cold(P)
• Can contain a lot of moisture(m) or not a
lot of moisture(c)
• Named according to their source region.
Ex: cP, mT
Fronts
• places where air masses meet
• 4 Types: Warm, Cold, Occluded,
Stationary
• Each kind can bring different
kinds of weather
Fronts
• Cold Front – cold,
dense air moves
into a region
occupied by warmer
air, leads to heavy
downpours and
gusty winds
• Warm Front –
warm air moves
into an area
occupied by cooler
air, Brings warmer
temperatures and
precipitation,
Fronts
• Occluded Front –
an active cold front
takes overtakes a
warm front;
complex weather
pattern
Occluded Front
• Stationary Front –
flow of air is neither
toward cold or warm
air mass
Stationary
Front
How does Air Pressure affect
weather?
• Pressure exerted by weight of air
above it. Exerted in ALL directions
• Measured with a BAROMETER
• If it CHANGES, then new weather is
on the way:
– Falling Air Pressure = stormy weather
coming
– Rising Air Pressure = fair weather
coming
– Steady Air Pressure = no change is
coming
Winds = horizontal movement
of air created from
differences in air pressure
• Moves from areas of HIGH to LOW pressure
• Greater the difference in pressure, the
FASTER the wind blows
• Labeled from which direction they blow
Pressure Centers and Winds
• Cyclones – centers of low pressure;
pressure decreases from outer
isobars toward the center.
• Anticyclones – centers of high
pressure; pressure increases from
outside toward center
Severe Storms
• Thunderstorms – form when warm, humid air rises
in an unstable environment; produce gusty winds
and heavy precipitation
• Tornadoes – violent windstorms that take the
form of a rotating column of air called a vortex.
Vortex extends downward from a cumulonimbus
cloud.
– U.S. -770 per year; most form in association
with severe thunderstorms
• Hurricane – a whirling tropical cyclone that
produces wind of at least 119 km/h; most powerful
severe storm; develops when water temps. are
warm enough to provide the necessary heat and
moisture in the air
Humidity
Humidity – amount of water vapor in
the air
Controlled by temperature
1. Warm air holds more moisture than
cool air (more space for water vapor
between air molecules)
2. As air warms, relative humidity
decreases
3. As air cools, relative humidity
increases
Relative Humidity
 Measure of the amount of
moisture in the air compared to
what the air could hold
 How “full” of water the air is
 Expressed as %
 100% relative humidity =
saturated air
Dew Point
•
•
Dew point is the
temperature the
moisture in the air
will condense to
liquid water.
Higher dew point=
more humid.
Dew point and human comfort
Dew point F°
Over 80
75-79
70-74
65-69
60-64
55-59
50-54
Less than 49
Human Comfort
Severely high. Even deadly
for asthma related illnesses
Extremely
uncomfortable
Quite uncomfortable
Somewhat
uncomfortable
Ok, but feels humid
Comfortable
Very comfortable
Dry
Human Impact on the
Atmosphere
Air pollution
Acid rain
Smog
Global warming
Ozone Damage
Air pollution
Human activity produces two main types of air
pollutant:
 noxious gases – Include carbon dioxide (CO2), sulfur
dioxide (SO2) and nitrogen oxides (NOx).
 particulates – Tiny particles suspended in air (e.g.
smoke) and are usually produced by the combustion of
fossil fuels.
Air pollution has been a major problem since the
Industrial Revolution of the late 18th Century, and has
been made worse by humans’ reliance on burning fossil
fuels for energy.
Air pollution, global warming, acid rain, damage to the
ozone layer and smog. Each of these has serious
implications for the environment and human health.
Greenhouse Effect
• The greenhouse effect is the warming
of the surface and lower atmosphere of
Earth that occurs when carbon dioxide,
water vapor, and other gases in the air
absorb and reradiate infrared radiation.
• Without the greenhouse effect, the
Earth would be too cold for life to
exist.
Greenhouse Effect
• The gases in the atmosphere that trap and
radiate heat are called greenhouse gases.
• The most abundant greenhouse gases are
water vapor, carbon dioxide, methane, and
nitrous oxide, although none exist in high
concentrations.
• The quantities of carbon dioxide and methane
in the atmosphere vary considerable as a
result of natural and industrial processes.
Global warming and
greenhouse gases
One of the greatest threats caused by air pollution is
global warming. Global warming is caused by a build-up of
greenhouses gases, which leads to an increase in the
Earth’s temperature. Other effects include bizarre
weather patterns, and melting of polar ice caps
Key greenhouses gases include:
 carbon dioxide
 methane
 water vapour
 nitrous oxide
Acid Precipitation
• Caused by the
release of sulfur
dioxide and nitrogen
oxide from factories
• Effects include soil
erosion, death of
animals and
vegetation, erosion
of buildings
Ozone Depletion
• Caused by the use of
coolants and aerosol
cans
• Effects include
increased UV
radiation, skin
cancer and eye
disorders
Smog
Smog is a mixture of air pollutants and particulates that
is sometimes found in the lower levels of the
atmosphere. It has a distinctive brownish haze.
Smog can reach
dangerous levels in builtup areas, causing
irritation to the eyes and
lungs.