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Chapter 22
The Atmosphere
Characteristics of the Atmosphere
• Layers of the Atmosphere
– Several layers: differ in temperature, in density,
and in the relative amounts of the different
gases
– Gases in the atmosphere:
• Nitrogen: 78%
• Oxygen: 21%
• Trace gases: 1%
Characteristics of the Atmosphere
Characteristics of the Atmosphere
• We live in the Troposphere:
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Layer closest to the Earth surface
Densest layer (gases above pushing down)
Most weather occurs here
Gets cooler with higher altitude
Lower region warmer because of the radiation and conduction of
solar energy warming the Earth’s surface
– Top of the troposphere is the tropopause:
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Poles: 8km (5mi)
Equator: 18km (11mi)
Temperature: -550C
This low temperature keeps water vapor in the troposphere
Acts like a lid keeping water vapor in
– Clouds, rain, snow
Characteristics of the Atmosphere
• Troposphere:
– Upper region: cool air
– Lower region: warm air
– Temperature inversion: cool air gets trapped
beneath warm air
• Can trap pollutants
– Not healthy
Characteristics of the Atmosphere
• Stratosphere gets warmer with increasing altitude
– Cold, low pressure
– From near the top of the tropopause of about 25km (16
mi), the temperature is about -550C (-670F) to about
25km the temperature increases to approximately 00C
(320F) in the stratosphere
– Top is about 50km (31mi)
– Gets warmer
– Little water vapor (few clouds: no storms)
Characteristics of the Atmosphere
• Stratosphere:
– The increase in temperature in the upper region
occurs in the atmospheric layer known as the
ozone layer
• Warmer because it contains a layer of oxygen
known as ozone that absorbs solar radiation
– Ozone absorbs much of the Sun’s UV radiation
– Shields living organisms on Earth from ultravioletradiation damage
Characteristics of the Atmosphere
• In the stratosphere (at altitudes of 15 to 35 km) the
ozone layer acts as a natural filter absorbing most
of the sun's damaging ultraviolet rays - those that
burn skin and cause some forms of skin cancer.
Hence the concern about the depleting ozone layer
in the earth's upper atmosphere.
• CFCs (chlorofluorocarbons) refrigerant and in
spray cans has been shown to damage the ozone
layer
Characteristics of the Atmosphere
• At ground level, ozone is a major component of
photochemical smog which has a noticeable light
brown color and results in reduced visibility and
health concerns. The term smog has been in use
since 1905 when it was used to describe the smoke
and fog in many Scottish cities. In the 1940s
increased concentrations of ground-level ozone
were observed in Los Angeles. The concern with
tropospheric or ground-level ozone is its very
presence, because as a component of smog it is a
serious pollutant.
Characteristics of the Atmosphere
• Mesosphere:
– 50 to 80km (31 to 50mi)
– Temperature begins to fall as you go up
– Top: -800C (-1120F): the coldest temperatures
in Earth’s atmosphere
Characteristics of the Atmosphere
• Thermosphere:
– 80 to 480km (50 to 298mi)
– Temperatures began to rise
– Main gases still nitrogen and oxygen, but the
particles are very far apart
• Because of the small amount of molecular oxygen
the thermosphere heats up as it absorbs intense solar
radiation
Characteristics of the Atmosphere
• Exosphere:
– 480 km (298mi)
– Some gases escape from the gravitational pull
of Earth and exit into space
– Also, some gases are captured by Earth’s
gravitational field and added to Earth’s
atmosphere
Characteristics of the Atmosphere
• Ionosphere:
– When solar energy is absorbed in the lower
thermosphere and upper mesosphere,
electrically charged ions are formed
• This is the area of the atmosphere where these ions
collect
• Electrons here reflect radio waves
• Without this layer radio waves would travel out into
space
Characteristics of the Atmosphere
• Ionosphere:
– Because the ions form as a result of solar
radiation, there are fewer of them at night in the
lower layers of the ionosphere
– So, the radio waves can travel higher into the
atmosphere before being reflected.
– As, a result the radio waves return to Earth’s
surface farther from their source than they do in
the daytime
Characteristics of the Atmosphere
• Auroras take place in the ionosphere
– Colorful light displays
• Encircling Earth’s magnetic poles
• Form when ions from the sun hit atoms and
molecules causing photons to be emitted
Characteristics of the Atmosphere
• Changes in Earth’s atmosphere:
– When Earth began to solidify about 4.4 billion years
ago, volcanic eruptions released a variety of gases
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Hydrogen: H2
Water vapor: H2O
Ammonia: NH3
Methane: CH4
Carbon monoxide: CO
Carbon dioxide: CO2
Nitrogen: N2
BUT NO OXYGEN: O2
Characteristics of the Atmosphere
• The evolution of plants contributed oxygen
to the atmosphere
– Needed carbon dioxide and water, and sunlight
• All of which was plentiful
– Photosynthetic organisms first evolved in the
oceans since the land masses had high levels of
UV light
– Oxygen levels gradually increased and the
ozone layer formed
Characteristics of the Atmosphere
• Once ozone layer formed life could evolve
on the land:
– Land plants evolved: oxygen production
– Animals evolved: carbon dioxide production
– These gases are recycled
Characteristics of the Atmosphere
• Greenhouse Effect:
– Energy released by the Sun as radiation is
absorbed by Earth’s surface
– Some of this energy is released back toward
space as radiation
– Carbon dioxide, water vapor, nitrous oxide, and
methane gases absorb some of this energy, so
the atmosphere become warmer
Characteristics of the Atmosphere
• Too much carbon dioxide may cause global
warming
– Higher temperatures
– Greater storms
– Rising seas
• Must reduce carbon dioxide emissions
Water and Wind
• Water is continuously being moved through
the troposhpere by the water cycle
Water and Wind
• Clouds form as warm, moist air rises
– Water condenses into tiny droplets of liquid
– Happens only in the troposphere
Water and Wind
• Cloud names describe their shape and the altitude at which
they form
– Clouds are named using combinations of the root words cirrus,
stratus, and cumulus
– Cirrus: thin and wispy
• Occur at high altitudes (between 3.7 and 6.8 mi)
– Stratus: layered and look like sheets
• Form at lower altitudes (less than 3.8 mi)
– Cumulus: white and fluffy with somewhat flat bottoms
• Form anywhere from about 500m to about 12km (7.5)
• Flat base is the place where rising air reaches the dew point (the
temperature at which the rate of condensation equals the rate of
evaporation for water vapor in the atmosphere
Water and Wind
• Dew point:
1. the atmospheric temperature (varying
according to pressure and humidity) below
which water droplets begin to condense
and dew can form.
Water and Wind
• Cloud names reflect combined
combinations characteristics:
– Cirrostratus: high, layered clouds that form a
thin, white veil over the sky
– Altostratus and altocumulus: are simply stratus
and cumulus clouds that occur at middle
altitude
Water and Wind
• When a cloud name includes the root nimbo
or nimbus, the cloud is a type that produces
precipitation
– Cumulonimbus: clouds are towering rain clouds
that often produce thunderstorms
– Nimbostratus: clouds are large, gray clouds that
often produce steady precipitation
Water and Wind
• It's pretty well-known that most clouds are white, while
rain clouds are usually a darker shade of gray. But why are
rain clouds so dark?
• Let's start by discussing how clouds form. The air around
you is full of water in its gaseous form, called water vapor.
When the air near the ground warms, it starts to rise,
taking the water vapor along with it.
• The air starts to cool as it rises higher into the sky, causing
the water vapor to condense onto atmospheric dust from
volcanoes, car exhaust and other sources. The resulting
water droplets and ice crystals coalesce, or join together, to
form clouds.
Water and Wind
• Unlike atmospheric particles that scatter more blue light than other
colors (making the sky blue), the tiny cloud particles equally scatter
all colors of light, which together make up white light.
• However, rain clouds are gray instead of white because of their
thickness, or height.
• That is, a cloud gets thicker and denser as it gathers more water
droplets and ice crystals — the thicker it gets, the more light it scatters,
resulting in less light penetrating all the way through it.
• The particles on the underside of the rain cloud don't have a lot of light
to scatter to your eyes, so the base appears gray as you look on from
the ground below.
• This effect becomes more pronounced the larger the water droplets get
— such as right before they're large enough to fall from the sky as rain
or snow — because they become more efficient at absorbing light,
rather than scattering it.
Water and Wind
• Air Pressure:
– Barometers are instruments used to measure air
pressure
– Changes in barometric pressure often accompany
changes in weather
– Barometric pressure, also called atmospheric pressure
or air pressure, is the pressure that results from the
weight of a column of air extending from the top of the
thermosphere to the point of measurement
Water and Wind
• An air mass is a large (usually thousands
of miles across) volume of air that has
horizontally uniform properties in terms
of temperature, and to a lesser extent
humidity.
• Falling pressure may mean that a large air mass is
leaving the area
• Rising pressure can mean that an air mass is moving
in
Water and Wind
• Mercury barometers indicate air pressure by a column of
mercury
– At sea level: barometric pressure of air at 00C is about
760mm of Hg
• This amount of pressure is defined as1atmosphere
• (1 atm) of pressure
– SI unit: is the Pascal (Pa)
» One Pa is equal to 1 Newton per square
meter
Water and Wind
• Aneroid barometers indicate the pressure
based on the volume of a sealed chamber of
air more portable but not as accurate as
mercury thermometer
Water and Wind
• Wind: difference in pressure creates winds
– If an airplane window were to break, the dense air in
the plane’s cabin would spread out into the less dense
air outside the cabin. The flow of air produced in this
situation would push loose objects out the window
– Differences in pressure in the atmosphere from one
place to another is called a pressure gradient
• The air in a pressure gradient moves from areas of high
pressure to areas of low pressure
• The movement of air from a high-pressure area to a lowpressure area is called wind
Water and Wind
• Coriolis Effect: Earth’s rotation affects the
direction of the wind
– Different latitudes on Earth move at different
speeds as Earth rotates
• Equator rotates faster (larger circle) than higher
latitudes (smaller circle)
– Each goes through one full rotation in 24 hours
– Equator rotation speed is 1,610 km/h (1,000 mi/h) to the
east
Water and Wind
• Coriolis Effect:
– The Coriolis effect is caused by the rotation of the Earth and the inertia of
the mass experiencing the effect. Because the Earth completes only one
rotation per day, the Coriolis force is quite small, and its effects generally
become noticeable only for motions occurring over large distances and
long periods of time, such as large-scale movement of air in the
atmosphere or water in the ocean. Such motions are constrained by the
surface of the earth, so only the horizontal component of the Coriolis force
is generally important. This force causes moving objects on the surface of
the Earth to be deflected in a clockwise sense (with respect to the direction
of travel) in the Northern Hemisphere and in a counter-clockwise sense in
the Southern Hemisphere. Rather than flowing directly from areas of high
pressure to low pressure, as they would in a non-rotating system, winds
and currents tend to flow to the right of this direction north of the equator
and to the left of this direction south of it. This effect is responsible for the
rotation of large cyclones.
Water and Wind
• When winds move North in the Northern
Hemisphere, they curve to the right
• When winds move South in the Southern
Hemisphere, they curve to the left
Water and Wind
• Wind moving South from the North Pole lags
behind the rotation of Earth and travels West (to
the left)
– Wind has a slower speed than the spinning
Earth
• Wind moving North from the South Pole travels
West (to the left) because of its slower speed
– Wind has a slower speed than the spinning
Earth
Water and Wind
• Coriolis Effect is greatest near the equator,
and decreases towards the poles.
Weather and Climate
• Front: is the place where a cold air mass and a
warm air mass meet
– A cold front is shown as a blue line with blue triangles
– A warm front is shown as a red line with red
semicircles
• Clouds, rain, and sometimes snow can occur at
fronts
• When fronts move through an area, the result is
usually precipitation and a change in wind
direction and temperature
Weather and Climate
• Lightning is a discharge of electrical energy
– Lightning is a massive electrostatic
discharge between the electrically
charged regions within clouds or between a
cloud and the surface of a planet.
Weather and Climate
• Lightning instantly heats the air around it so
much that the air expands faster than the
speed of sound.
– The shock wave created is thunder
Weather and Climate
• Tornadoes:
– Air inside the funnel has very low pressure
– As the funnel reaches the ground, higherpressured air rushes into the low-pressured area
• The result is high-speed winds
Weather and Climate
• Hurricanes: large, rotating tropical storm
systems
– Occur over warm oceans
– Named:
• Hurricanes in North America and the Caribbean
• Cyclones in the Indian Ocean
• Typhoons in the western Pacific
– Intense low pressure
– The rising air currents create fierce winds
Weather and Climate
• Temperatures tend to
be higher at the
equator
Weather and Climate
• Earth’s tilt and rotation account for our
seasons
Weather and Climate
• Earth’s surface features affect climate