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The Atmosphere
Know basic facts and general principles of the
atmosphere.
1. Define a list of terms related to the atmosphere.
2. Describe the roles of water in the atmosphere.
Overview
1. Describing the Atmosphere.
2. Roles of Water and the Atmosphere.
Atmospheric Elements
 The whole mass of air surrounding the Earth.
 Made up of a mixture of gases:
• 78% Nitrogen (N2)
• 21% Oxygen (O2)
• 1% Mixture of other gases
Atmospheric Elements
 Absorbs energy from the Sun, recycles water and other
chemicals, and works with the electrical and magnetic
forces to provide a moderate temperature.
 Protects us from high-energy radiation and the frigid
vacuum of space.
 Four distinct layers have been identified.
Atmospheric
Layers
Troposphere
 Starts at Earth’s surface and
extends 10 to 13 kilometers.
 Lowest, densest part of Earth’s
atmosphere in which most
weather changes occur.
Stratosphere
 Starts just above the
troposphere and extends to 50
kilometers.
 Very dry and less dense
compared to troposphere.
 The ozone layer is located
within the stratosphere.
Mesosphere
 Starts above the stratosphere
and extends to 85 kilometers
above the Earth’s surface.
 Temperatures as low as -90o C.
Thermosphere
 Starts just above the mesosphere
and extends to 600 kilometers
high.
 Temperatures reach up to 1,727o C.
 Known as the upper atmosphere.
Atmospheric Pressure
 The downward pressure
exerted by the weight of the
overlying atmosphere.
 Greatest at sea level and
decreases outward from the
Earth.
 Plays a significant role in the
type of weather that occurs.
THE BOOK TEST
Atmospheric Pressure
 By watching atmospheric
pressure changes at a
location, forecasters can
obtain clues to the expected
changes in other weather
elements.
Atmospheric Pressure
 Low pressure regions usually experience more stormy
weather with more cloudiness, higher humidity, and
unstable conditions. (LOW = Lousy Weather)
 High pressure regions are more likely to be associated
with fewer clouds, lower humidity, and more stable
conditions. (HIGH = Good Weather)
 Winds blow because of the differences in air pressure on
and above the Earth’s surface.
Atmospheric Pressure and Wind
• Air flows from areas of high pressure
into those of low pressure producing a
clockwise circulation around an area
of high pressure. The opposite is true
of low-pressure areas; the air flows
toward an area of low pressure and is
deflected to create a counterclockwise or cyclonic circulation.
Atmospheric Pressure and Wind
Roles of Water & Particulate Matter
Water in the Atmosphere
 In the troposphere, water goes through a cycle from
vapor to condensation to precipitation. As it goes
through this cycle, it takes on several forms.
• Liquid
• Solid
• Condensation
Evaporation
 The process by which liquid
water molecules change to a gas
or vapor state and enter the
Earth’s atmosphere.
 Temperature and pressure are
the primary cause of water
vapor in the air changing into
clouds or falling to Earth.
Humidity
Humidity
 Absolute Humidity
• The actual amount of water vapor in the air at a given time.
• The amount of water vapor the air is able to hold depends on
the temperature.
Humidity
 Relative Humidity
• The amount of water vapor that can still enter the air
mass before it becomes saturated.
• Expressed by a percentage figure which is the ratio
of the amount of water vapor in the air to the
maximum amount that the same volume of air could
contain at a given temperature and pressure.
• Saturation Point = DEW POINT
Condensation and Precipitation
 When part of the water vapor in the air returns to a
liquid or solid form, it is seen as either condensation
and/or precipitation.
Dew Point Temperature
 The temperature at or below which water vapor will
condense is the key factor in condensation and
precipitation.
Summary
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Levels of the Atmosphere
Atmospheric Pressure
Water in the Atmosphere
Humidity
Condensation and Precipitation