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Do You Remember?
1.
2.
3.
Which heats faster: land or water?
What causes the transfer of energy
(heat) from one object to another?
Which has greater temperature variation:
land or water?
Moisture, Clouds and
Precipitation
2.5.4c Explain the importance of water vapor and its
influence on weather (clouds, relative humidity, dew
point, precipitation).
Objectives

Today I will be able to:
◦ Evaluate the most important gas in the
atmosphere.
◦ Compare and contrast saturation and relative
humidity.
Key Points - Moisture
Water vapor is the most important gas for
understanding atmospheric processes.
 Water vapor makes up 0-4 % of atmospheric
gases.
 Air that has reached its water vapor capacity is
said to be saturated.
 Warm, saturated air contains more water vapor
than cold air.
 Relative humidity is the ratio of air’s water-vapor
content to its capacity to hold water vapor at that
same temperature.

Water in the Atmosphere
Water exists in three different forms.
 What are they?

1. SOLID Examples: Snow, ice
2. LIQUID Examples: Rain, water
3. GAS Examples: Clouds, water vapor

How do each of these forms of water
influence weather?
Water in the Atmosphere

When it comes to understanding
atmospheric processes, water vapor
is the most important gas in the
atmosphere.

Why do you think water vapor is so
important?
Water in the Atmosphere

Even though water vapor is important, it only
makes up from 0 – 4% of the atmospheric
gases.
When have you felt water vapor at close to
4%?
 What about 0%?
 How do you know?

◦ Water vapor is the HUMIDITY that you feel in the
air!
Water in the Atmosphere

What do you think the word
“SATURATED” means?

What do you think it would mean if air is
Saturated?

Air that has reached its water vapor
capacity is said to be saturated.
Water in the Atmosphere
Warm, saturated air contains more water
vapor than cold air.
 Dew point is the temperature to which
air is cooled to reach saturation.

◦ The point at which condensation can occur
When have you noticed the humidity
more, in the summer or in the winter?
 That’s because warm air can hold more
water vapor!

Water in the Atmosphere
Relative humidity is the ratio of air’s watervapor content to its capacity to hold water
vapor at that same temperature.
 Relative humidity indicates how near the air is
to saturation, not the actual quantity of water
vapor in the air.
 Relative Humidity varies with temperature.
 Cooling air increases its relative humidity.
 Warming air decreases its relative humidity.

Water in the Atmosphere

Relative Humidity –

Why does lowering the air temperature cause
Relative humidity to increase?
◦ Because colder air cannot hold as much water vapor!

Why does increasing air temperature cause
relative humidity to decrease?
◦ Because warm air can hold more water vapor and it will
take more water vapor for it to become saturated.
◦ Why is it important to know humidity?
Vocabulary and Questions
Define the following terms:
 Water vapor
 Saturation
 Relative humidity
Answer the following questions:
1. What gas is most important for understanding
atmospheric processes?
2. Water vapor makes up what fraction of
atmospheric gases?
3. Which holds more water vapor: warm air or cool
air?
4. How is the humidity different from the
summertime to the wintertime?
Matching- answer a, b or c for each
of the situations.
Situation
1. Water vapor is
added
2. Air temperature
decreases
3. Water vapor is
removed
4. Air temperature
increases
Change in Relative Humidity:
A. Increases
B. No
change
C. decreases
Follow up
Air that has reached its water-vapor
capacity is said to be:
a. Dry b. unstable c. stable d. saturated
2. The ratio of air’s water content to its
capacity to hold water at the same
temperature is:
a. Vapor pressure b. relative humidity
c. specific humidity d. wet adiabatic rate
3. Water vapor makes up what fraction
(%) of atmospheric gases?
1.
Objectives

I will be able to:
◦ Describe how air is lifted to form clouds.
◦ Differentiate between the different types of
clouds by making a poster.
◦ Describe the weather associated with the
different types of clouds.
Key Points - Clouds
When air is compressed the air
temperature rises and the air molecules
move faster.
 Processes that lift air include orographic
lifting, frontal wedging and convergence.
 Examples of condensation nuclei include
dust, smoke and salt particles.
 Nimbus means “rainy cloud”.
 Cumulonimbus clouds are often
associated with thunder and lightning.

Cloud Formation
 When air is compressed the air
temperature rises and the air molecules
move faster.
 Air compression causes temperature
changes even though heat isn’t added or
subtracted.
• When air is allowed to expand, it cools,
and when it is compressed, it warms.
Cloud Formation
Cool, expanded air
Clouds form
because as you
go up in
elevation, it gets
colder.
Warm, compressed air
Cold air cannot
hold as much
water vapor so
it transforms
into clouds.
Cloud Formation
 Four mechanisms that can cause air to rise
are orographic lifting, frontal wedging,
convergence, and localized convective
lifting.
 Fill out each box with the underlined
words and a picture as we discuss them.
1. Orographic Lifting
• Orographic lifting occurs when mountains act
as barriers to the flow of air, forcing the air to
ascend.
Cloud Formation
Processes that lift the air
How does the relatively flat central region of
the US receive precipitation?
2. Frontal Wedging
• A front is the boundary between two adjoining of
air masses having contrasting characteristics.
Orographic Lifting and Frontal Wedging
1. Orographic Lifting
2. Frontal Wedging
Cloud Formation
Processes That Lift Air
3. Convergence
• Convergence is when air flows together and
rises.
4. Localized Convective Lifting
• Localized convective lifting occurs where
unequal surface heating causes pockets of air to
rise because of their buoyancy.
Convergence and Localized
Convective Lifting
3. Convergence
4. Localized Convective Lifting
Cloud Formation
Condensation – How clouds form
 For any form of condensation to occur, the
air must be saturated.
 Types of Surfaces
• Generally, there must be a surface for water
vapor to condense on.
• Condensation nuclei are tiny bits of particulate
matter that serve as surfaces on which water
vapor condenses when condensation occurs in
the air.
• Examples of condensation nuclei include dust,
smoke and salt particles.
Cloud Types and Precipitation
Types of Clouds
 Clouds are classified on the basis of their
form and height.
Cloud Types and Precipitation
Types of Clouds by Form
 There are three basic forms of clouds. All other
clouds one of these three or are combinations or
modifications of them.
1. Cirrus (cirrus = “curl of hair”) are clouds that
are high, white, and thin.
2. Cumulus (cumulus = “a pile”) are clouds that
consist of rounded individual cloud masses.
3. Stratus (stratus = “a layer”) are clouds best
described as sheets or layers that cover much
or all of the sky.
Cloud Types and Precipitation
What type of cloud is this?
Cirrus
Cloud Types and Precipitation
What type of cloud is this?
Cumulus
Cloud Types and Precipitation
What type of cloud is this?
Stratus
Cloud Types and Precipitation
Types of Clouds by Height
1. High Clouds
• Cirrus clouds are high, white, and thin.
• Cirrostratus clouds are flat layers of clouds.
• Cirrocumulus clouds consist of fluffy masses.
2. Middle Clouds – “Alto”
• Altocumulus clouds are composed of rounded
masses that differ from cirrocumulus clouds in
that altocumulus clouds are larger and denser.
• Altostratus clouds create a uniform white to
gray sheet covering the sky with the sun or moon
visible as a bright spot.
Cloud Types and Precipitation
Types of Clouds by Height
3. Low Clouds
• Stratus clouds are best described as sheets or
layers that cover most of the sky.
• Stratocumulus clouds have a scalloped bottom
that appears as long parallel rolls or broken
rounded patches.
• Nimbostratus clouds are the main precipitation
makers.
Cloud Classification
Answer the following
1.
What happens when air is compressed?
Air temperature rises.
b. Air temperature cools.
c. Air molecules move faster.
d. both a and c
a.
2.
What term means “rainy cloud”?
a. stratus b. nimbus c. cumulus d. cirrus
3.
Name one example of condensation
nuclei: