Earth Science- Atmosphere Study Guide
Composition of the Atmosphere
Atmosphere- a mixture of gases that surrounds a planet, such as Earth
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Elements in the air are nitrogen, oxygen and argon
o 78% of the atmosphere is made up of nitrogen
o 21% of the atmosphere is made up of oxygen
o Photosynthesis-large quantities of oxygen produced by land and ocean plants
Compounds in the air are carbon dioxide (CO2) and water vapor (H2O)
o Water Vapor- as water evaporates from oceans, lakes, streams and soil it enters
air as invisible gas
 Water vapor varies depending on time of day, location and season
o Ozone- gas molecule that is made up of three oxygen atoms
 Ozone Layer- absorbs harmful ultraviolet radiation from the sun
 A number of human activities damage the ozone layer
Particulates- volcanic dust, ash from fires, microscopic organisms or mineral particles
lifted from soils by wind. Pollen from plants and particles from meteors are also
particulates
Atmospheric Pressure
Atmospheric Pressure- the force per unit area that is exerted on a surface by the weight of the
atmosphere.
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Atmospheric Pressure decreases as altitude increases
As temperature increases, atmospheric pressure at sea level decreases
Atmospheric pressure is measured in three units:
1 atmosphere (atm) = 760 mm of mercury = 1000milibars.
The average atmospheric pressure at sea level is 1 atm
o Barometer-instrument used to measure atmospheric pressure
 The greater the atmospheric pressure the higher the mercury rises
Layers of the Atmosphere
1. Troposphere- lowest layer of the atmosphere. Temperature drops as altitude increases
1a. Tropopause- When the average altitude is 12 km the temperature stops decreasing, the
upper boundary of the troposphere
2. Stratosphere- the layer of the atmosphere that lies between the troposphere and the
mesosphere. Temperature increase as altitude increases; contains the ozone layer. Air in the
stratosphere is heated from above by absorption of solar radiation by ozone
3. Mesosphere- the coldest layer of the atmosphere between the stratosphere and the
thermosphere in which the temperature decreases as the altitude increases
3a. Mesopause- the upper boundary of the mesosphere which has an average temperature
on -90C which is the coldest temperature in the atmosphere
4a. Ionosphere- The lower region of the thermosphere at an altitude of 80 to 400 km
4. Thermosphere- the uppermost layer of the atmosphere in which temperature increases as
altitude increases.
Temperature Inversions
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Air Pollutant- any substance in the air that is harmful to people, plants or property
Temperature Inversion- a condition that makes air pollution worse by the layer of warm
air on top of cool air
Under conditions in which air cannot circulate up and away from an area, trapped
automobile exhaust can produce smog
Smog- a general term of air pollution that indicates a combination of smoke and fog
Radiation
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Radiation- is all forms of energy that travel through space as waves.
The Atmosphere and Solar Radiation
Scattering - occurs when particles (clouds, dust, and water droplets) and gas molecules in the
atmosphere reflect and bend solar rays in all directions without changing their wavelength
Albedo- the fraction of solar radiation that is reflected off the surface of an object.
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The amount of energy that is absorbed or reflected depends on characteristics such as
color, texture, composition, volume, mass, transparency, state of matter and specific heat
of the material on which the solar radiation falls. (choose 3 of these to remember)
Absorption and Infrared Energy
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Solar radiation that is not reflected is absorbed by rocks, soil, water and other surface
materials
The absorption of thermal energy from the ground heats the lower atmosphere and keeps
Earth’s surface much warmer than it would be if there were no atmosphere.
Greenhouse Effect- the warming of the surface and lower atmosphere of the Earth that occurs
when carbon dioxide, water vapor and other gases in the air absorb and reradiate radiation
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Increases in the amount of carbon dioxide may intensify the greenhouse effect and may
cause Earth to become warmer in some areas and cooler in others
Variations in Temperature
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The temperatures of the atmosphere in any region on Earth’s surface depends on several
factors: latitude, surface features and the time of year and day
Because Earth is a sphere the sun’s rays do not strike all areas at the same angle
The energy that reaches the equator is more intense than the energy that strikes poles,
so average temperatures are higher near the equator than near the poles
Because water vapor stores heat, the amount of water in the air affects the temperature
of a region.
Land areas close to large bodies of water generally have more moderate temperatures
The wind patterns in an area also affect temperature.
Conduction and Convection
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Conduction heats only the lowest few centimeters of the atmosphere where air comes
into direct contact with the warmed surface of the Earth
The continuous cycle in which cold air sinks and warm air rises warms Earth’s atmosphere
evenly
The atmospheric pressure is lower beneath a mass of warm air. A dense, cool air moves
into a low-pressure region, the less dense, warmer air is pushed upwards.
The pressure differences which are the result of the unequal heating that causes
convection, create winds
Global Winds
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Convection Cells- each hemisphere contains three looping patterns
Wind Belt- Each convection cell correlates to an area of Earth’s surface, that are
characterized by winds that flow in one direction
Prevailing Winds- winds that flow in one direction
Coriolis Effect- the curving of the path of a moving object from an otherwise straight path
due to Earth’s rotation
Trade Winds- prevailing winds that blow from east to west from 30 latitude to the equator
in both hemispheres.
o Northeast Trade winds- the trade winds that flow northeast
o Southeast Trade Winds- trade winds that flow southeast
Westerlies- prevailing winds that blow from west to east between 30 and 60 latitude in
both hemispheres
o In the Northern Hemisphere the westerlies are the southwest winds.
o In the southern Hemisphere they are the northwest winds
Polar Easterlies- prevailing winds that blow from east to west between 60 and 90 latitude
in both hemispheres
Where the Polar Easterlies meet warm air from the westerlies, a stormy region known as
a front forms
Jet Streams- a narrow bans of strong winds that blow in the upper troposphere. They
exist in the Northern and Southern Hemisphere
o Types: Polar Jet Streams and Subtropical Jet Stream
Doldrums- the trade wind systems of the Northern Hemisphere and Southern
Hemisphere meet at the equator in a narrow zone
Horse Latitudes- a sub-tropic high-pressure zone
Local Winds- movement of air that are influenced by local condition and temperature
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Breeze- gentle winds that extend over distances of less than 100k
Sea Breeze- cool wind moving from water to land
Land Breeze- when the land cools more rapidly than water does and the sea breeze is
replaced
Valley Breeze- when warm air from the valleys moves upslope
Mountain Breeze- At night, the mountains cool more quickly than the valleys do. At that
time cool air descends from the mountain peaks