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Chapter 11: Atmosphere
11.1 Atmospheric Basics
Main Idea: Energy is transferred throughout Earth’s atmosphere.
Atmospheric Composition
Atmosphere: the layer of gases that surrounds Earth; air that surrounds the geosphere
Air: combination of gases, such as nitrogen and oxygen, and particles, such as
dust, water droplets, and ice crystals.
o

Earth’s atmosphere consists mainly of nitrogen (78%) and oxygen (21%)
The amounts of nitrogen and oxygen have remained fairly consistent over time, whereas other
atmospheric gases have fluctuated more.
Water vapor - varies the season, altitude of a particular mass
air, and the properties of the surface beneath the air.
Carbon Dioxide - the concentration of CO2 has increased over
the past 150 years, due to primarily the burning of fossil fuels.
Ozone - molecules of ozone are formed
by the addition of an oxygen atom to an
oxygen molecule.
o
The ozone layer blocks harmful
ultraviolet rays from reaching
Earth’s surface.
Layers of the Atmosphere
 Classified into five different layers: troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
Troposphere (0-12km) - all weather occurs in this layer;
temperature decreases as altitude increase
 Tropopause: where the temperature stops decreasing
Stratosphere (12-48km) - contains the ozone layer; temperature
increases as altitude increases
 Stratopause (48 km): where the temperature stops increasing
Mesosphere (50km-100km) - very little solar radiation is absorbed
in this layer; temperature decreases as altitude increases
 Mesopause: where the temperature stops decreasing
Thermosphere (100km-500km) - absorbs a lot of solar radiation;
extremely low density of the air causes the temperature to rise as
the altitude increases (temperatures can be more than 1000oC)
 Contains the ionosphere (made of ions) which allows for
radio broadcasting and auroras
Exosphere (500km-700km) - outermost layer of Earth’s
atmosphere; thought of as the transitional region between Earth’s
atmosphere and outer space; satellites orbit the earth here
 Gas molecules can be exchanged between the atmosphere
and space
Energy Transfer in the Atmosphere
Thermal Energy: total energy of the particles in an object due to their random motion.

Thermal energy is transferred from the Sun to Earth by radiation.

Three ways thermal energy can be transferred:
Radiation: transfer of thermal energy by electromagnetic waves.
o
Incoming solar radiation is either reflected back into space
or absorbed by Earth’s atmosphere or its surface.
Conduction: transfer of thermal energy between objects when
their atoms or molecules collide.
Convection: transfer of thermal energy by the movement of
heated material from one place to another.
Name: ___________________________________________________________________ Date: ____________________________ Period: __________
11.2 Properties of the Atmosphere
Main Idea: Atmospheric properties, such as temperature, air pressure, and humidity describe weather conditions.
Review - Density: the mass per unit of volume of a material
Temperature
Temperature: measure of average kinetic energy of the particles in a material
o
Fahrenheit (°F), Celsius (°C), and Kelvin (SI Unit)

Fahrenheit and Celsius are based on the freezing/boiling point of water and Kelvin is based on
absolute zero being the zero point
1) Convert 37°C to °F

98.6°F
2) Convert 70°F to °C

21.1°C
 Conversion Formulas

°C x 9/5 + 32 = °F

(°F - 32) x 5/9 = °C
Air Pressure
Air pressure: the pressure exerted on a surface by the
weight of the atmosphere above the surface
o
The units for pressure are N/m2.

Air pressure is often measured in units of
millibars (mb), where 1 mb equals 100 N/m2.
 The density and pressure of the layers of the
atmosphere decrease as altitude increases (see right)
Pressure-temperature-density Relationship - Video
 Temperature, pressure, and density are all related to
one another.
o
If temperature increases, but density is constant,
the pressure increases.
o
If the temperature increases and the pressure is
constant, the density decreases.
Temperature inversion: an increase in temperature with height in an
atmospheric layer (see left).

If the land does not radiate thermal energy to the lower layers of the
atmosphere, such as on a cold, clear, winter night when the air is calm, the
lower layers of air become cooler than the air above them.

Wind
A temperature inversion can lead to fog or low-level clouds. In some cities,
a temperature inversion can worsen air-pollution problems.
Wind: The movement of air is commonly known as wind; caused by the differences in air temperature (but
could also say density and/or pressure).

In the lower atmosphere, air generally moves from regions of higher density and pressure to regions of
lower density and pressure.

Near Earth’s surface, wind is constantly slowed by the friction that results from contact with surfaces
including trees, buildings and hills.

Higher up from Earth’s surface, air encounters less friction and wind speeds increase.
Humidity
Humidity: the amount of water vapor in the atmosphere at a given location on Earth’s surface.
Saturation: occurs when the amount of water vapor in a volume of air has reached the maximum amount
possible for that temperature.
Relative Humidity (Video): the amount of water vapor
in a volume of air relative to the amount of water vapor
needed for that volume of air to reach saturation is called
relative humidity (see right).
Dew point: temperature to which air must be cooled at
constant pressure to reach saturation.
Latent heat: the extra thermal energy contained in
water vapor compared to liquid water.

A process in which temperature changes without
the addition or removal of thermal energy from a
system is called an adiabatic process.
o
Adiabatic heating occurs when air is compressed, and adiabatic cooling occurs when air
expands.
Name: ___________________________________________________________________ Date: ____________________________ Period: __________
11.3 Clouds and Precipitation
Main Idea: Clouds vary in shape, size, height of formation, and type of precipitation.
Cloud Formation

As a warm air mass rises, it expands and cools adiabatically. The cooling of an air
mass as it rises can cause water vapor in the air mass to condense.
Condensation nucleus: a small particle in the atmosphere around which
water droplets can form.
o
When the number of these droplets is large enough, a cloud is visible.
Atmospheric stability

As an air mass rises, it cools. However, it will continue to rise if it is warmer than the surrounding air.

When an air mass sinks back to its original position and resists rising, it is considered stable.

The stability of air masses determines the type of cloud that form and the associated weather patterns.

o
Stable air – tendency to resist movement.
o
Unstable air – does not resist vertical displacement.
When the temperature of a mass of air is greater than
the temperature of the surrounding air, the air mass
rises. When the temperature of the surrounding air is
greater than that of the air mass, it sinks.
Atmospheric lifting

Clouds can form when moist air rises, expands, and cools
enough for water vapor to condense.

Clouds can also form when air is forced upward or lifted by
mechanical processes.
Orographic lifting: occurs when an air mass is forced to rise
over a topographic barrier.
o
Air can be lifted by convergence, which occurs when air
flows into the same area from different directions and
some of the air is forced upward.
o
This process is even more pronounced when air masses at
different temperatures collide.
Types of Clouds - Video

Clouds are generally classified by the altitude at which they form and their shape or appearance.
Low Clouds - Cumulus clouds are puffy, lumpylooking clouds that usually occur below 2000 m.
Cirrostratus
Another type of cloud that forms at heights
below 2000 m is a stratus, a layered sheet-like
cloud that covers much or all of the sky in a
given area.
Middle clouds - Altocumulus and altostratus
clouds form at altitudes between 2000m and
6000m and are made up of ice crystals and
Cumulonimbus
water droplets.
High clouds - High clouds, made up of ice
crystals, form at heights of 6000m where
temperatures are below freezing. Some, such as
Altostratus
cirrus clouds, often have a wispy, indistinct
appearance.
Vertical development clouds - If the air that
makes up a cumulus cloud is unstable, the cloud
Cumulus
will continue to grow upward through middle
Stratus
Nimbostratus
altitudes as a towering cumulonimbus. If
conditions are right, it can reach nearly 18km.
Precipitation: all forms of water that fall from clouds to the ground.

Rain, snow, sleet, and hail are the four main types of precipitation.
Coalescence: occurs when cloud droplets collide and join together to form a larger droplet.
 When the droplets become too heavy to remain suspended in the cloud, they fall to Earth as precipitation.
Snow, sleet, and hail
 The type of precipitation that reaches Earth depends on the vertical variation of atmospheric temperature.
Water Cycle
 Water moves from Earth to the
atmosphere and back to Earth in the water
cycle.
 H2O is moved through each of Earth’s four
systems: Atmosphere, Hydrosphere,
Biosphere, and Geosphere.
Cloud Descriptors
Directions: Create a three-dimensional viewing of the different types of clouds based on their
altitude. Each cloud should include a detailed description that is viewable when the cloud is lifted.
Some sample descriptors of clouds that may not be described in the textbook. Your
descriptors do NOT have to include all of the following AND should be in your own words.
Cirrus: The most common form of high-level clouds are thin and often wispy cirrus clouds.
Typically found at heights greater than 20,000 feet (6,000 meters), cirrus clouds are composed of
ice crystals that originate from the freezing of supercooled water droplets. Cirrus generally occur in
fair weather and point in the direction of air movement at their elevation.
Cirrostratus clouds are sheet-like, high-level clouds composed of ice crystals. Though cirrostratus
can cover the entire sky and be up to several thousand feet thick, they are relatively transparent, as
the sun or the moon can easily be seen through them. These high-level clouds typically form when
a broad layer of air is lifted by large-scale convergence.
Altocumulus may appear as parallel bands (top photograph) or rounded masses (bottom
photograph). Typically a portion of an altocumulus cloud is shaded, a characteristic which makes
them distinguishable from the high-level cirrocumulus. Altocumulus clouds usually form by
convection in an unstable layer aloft, which may result from the gradual lifting of air in advance of
a cold front. The presence of altocumulus clouds on a warm and humid summer morning is
commonly followed by thunderstorms later in the day.
Cumulonimbus clouds are much larger and more vertically developed than fair weather cumulus.
They can exist as individual towers or form a line of towers called a squall line. Fueled by vigorous
convective updrafts (sometimes in excess 50 knots), the tops of cumulonimbus clouds can easily
reach 39,000 feet (12,000 meters) or higher.
Nimbostratus clouds are dark, low-level clouds accompanied by light to moderately falling
precipitation. Low clouds are primarily 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.
Stratocumulus clouds generally appear as a low, lumpy layer of clouds that is sometimes
accompanied by weak intensity precipitation. Stratocumulus vary in color from dark gray to light
gray and may appear as rounded masses, rolls, etc., with breaks of clear sky in between.