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Chapter 2 – Weather factors
2.1 Energy in the Atmosphere
Think about it…
• Where does the energy of our Earth
come from?
Electromagnetic Radiation
• Nearly all of the energy in Earth’s
atmosphere comes from the sun
• Energy travels as electromagnetic waves.
• Electromagnetic waves are a form of
energy that can move through the vacuum
of space.
• Electromagnetic waves are classified
by their wavelengths
Electromagnetic Radiation
• The direct transfer of energy by
electromagnetic waves is called
radiation.
• Most energy from the sun reaches
the Earth in the form of infrared
radiation, visible light, and ultraviolet
radiation.
Wavelengths
https://www.youtube.com/watch?v=l4yg4HTm3uk
Analyze the picture …take 1 minute and
discuss with a partner…
• Why do we see different colors?
• How do color and wavelength compare?
• Which colors have the shortest wavelengths?
• Which colors have the longest wavelengths?
• What type of radiation has wavelengths that are
shorter than visible light? Longer?
Were you right?
• Why do we see different colors? Because of
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different wavelengths
How do color and wavelength compare? Short
and long wavelengths result in different colors
Which colors have the shortest wavelengths?
Violet
Which colors have the longest wavelengths? Red
What type of radiation has wavelengths that are
shorter than visible light? Longer? Ultraviolet
radiation, x-rays and gamma rays / infrared
radiation and radio waves
Visible Light: ROY G BIV-
a form of
electromagnetic radiation that is perceivable to human beings and is
seen in the colors of the rainbow
• Infrared Radiation – wavelengths are longer
than red light.
• The color of visible light with the longest
wavelength is Red.
• The color of visible light with the shortest
wavelength is violet.
• Ultra-violet Radiation – wavelengths are shorter
than violet light
Wave diagram
• Crest – the top of a wave
• Trough – the bottom of a wave
• Wavelength – the distance from crest to crest or trough to trough in
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a wave
Frequency – the number of wavelengths that pass a given point in a
set amount of time
Origin – the center/start or midpoint of a wave
Amplitude – the distance from the origin to the crest or the trough of
a wave
Speed of light – c- the rate at which all forms of electromagnetic
radiation travel through a vacuum = 3.0x108 m/s
Wavelength and frequency are inversely
proportional so……
High frequency = Short Wavelength
Low frequency = Long Wavelength
Energy
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Water Vapor and Carbon Dioxide absorb some infrared
radiation
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Some of the sun’s rays are reflected by clouds, dust,
and molecules of gases called scattering.
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Gas molecules scatter short wavelengths of blue and
violet more than red and orange making the daytime
sky look blue.
Energy
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The ozone layer absorbs most of the ultraviolet
radiation
•
Green house effect- natural process by which gas
holds heat in the air.
•
Gases include water vapor, carbon dioxide, methane,
and other gases that form a blanket around earth.
•
Some energy reaches the surface and warms the land
and water
Energy in the atmosphere
What are your thoughts?
• What might conditions on Earth
be like without the Greenhouse
effect?
Chapter 2 – Weather factors
2.2 Heat Transfer
Energy and Temperature
• Thermal energy is the total energy of
MOTION of the molecules in a
substance.
• Temperature is an average amount of
energy of motion of the molecules in a
substance.
Hot = fast moving molecules
Cold = slow moving molecules
Measuring Temperature
• Thermometers are used to measure
temperature
• Liquids expand when they are heated
and contract when they are cooled
• Temperature is measured in units called
degrees. (Celsius or Fahrenheit)
• Water freezes at 0ºC and boils at 100ºC
How Heat is Transferred
• Heat is the energy transferred from a
hotter object to a cooler one.
Heat is transferred 3 ways
• Radiation is the direct transfer of energy
by electromagnetic waves.
ex) feeling the warmth of the fire on
your skin
Heat is transferred 3 ways
• Conduction is the direct transfer of heat
from one substance to another substance
( must be touching)
Heat is transferred 3 ways
• Convection is the transfer of heat by the
movement of a fluid.
ex) heating up soup in a pan.
Heat Transfer in the Troposphere
A comparison…
Chapter 2 - Weather factors
2.3 Winds
What Causes Winds?
• Wind is the horizontal movement of air
from an area of high pressure to an area
of lower pressure.
• All winds are caused by differences in air
pressure.
• Differences in air pressure are caused by
unequal heating of the atmosphere.
Measuring Wind
• Wind vanes are used to determine wind
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direction.
The name of a wind tells you where the wind is
coming from.
Anemometers are used to measure wind speed.
Wind over your skin removes body heat.
The increased cooling that a wind can cause is
called

the wind- chill factor.
Local Winds
• Winds that blow over short distances.
• Caused by unequal heating of Earth’s
surface within a small area.
• Usually occurs near a body of water.
Local Winds
• Land heats up faster during the day, warming the air
above it. Warm air expands and rises, creating a lowpressure area. Cool air blows inland from the water to
replace the warm air.
Local Winds
• sea breeze – a wind that blows FROM an
ocean or a lake onto land
• land breeze – the flow of air FROM land to
a body of water
Monsoons
• Sea and land breezes over a large region
that change direction with the seasons
Global Winds
• Winds that blow steadily from specific
directions over large distances.
• Caused by unequal heating of Earth’s
surface. (equator vs. poles)
• Global Convection Currents cause wind at
Earth’s surface to blow from the poles to
the equator.
• Higher in the atmosphere, air flows away
from the equator and toward the poles.
Global Winds
• The movement of air between the equator and
the poles produces global winds.
• Coriolis Effect – winds do not blow in straight
lines because the Earth is spinning underneath
them. This causes the winds to curve.
• In the NORTHERN HEMISPHERE – the Coriolis
Effect causes our wind to turn towards the right.
It is the opposite in the southern hemisphere.
Jet Stream
• Bands of high-speed wind about 10km
above Earth’s surface.
• They blow from west to east at about 200400 km per hour
Global Wind Belts
• DOLDRUMS:
•Caused by rapid warming of air
•near the equator
•air is almost always warm so there
are little to no winds
Global Wind Belts
• HORSE LATITUDES:
•Caused when air from equator stops
moving towards poles and sinks
•Latitude is the distance from the
equator, measured in degrees
•30º north and south latitudes, Calm
air
Global Wind Belts
• TRADE WINDS:
•Caused when cold air over the
horse latitudes sinks and
produces a high pressure region
•Blow towards the equator from
about 30º north and south
Global Wind Belts
• PREVAILING WESTERLIES: Caused when
winds that blow toward the poles are
turned toward the east by the Coriolis
effect.
• Between 30º and 60º north and south
latitudes.
• Blow FROM West to East
• They play an important role in the United
State’s weather
Global Wind Belts
• POLAR EASTERLIES:
•Caused when cold air near the poles
sinks and flows back toward lower
latitudes
•They meet the prevailing westerlies at
about 60º north and south latitudes
at the Polar Front.
•The polar front has a major effect on
weather changes in the US.
Chapter 2
• 2.4 Water in the Atmosphere
Water cycle- movement of water between the atmosphere
and earth’s surface
2-4 Water in the Atmosphere
 Evaporation – the process by which water
molecules in liquid water escape into the
air as water vapor.
Humidity
• Humidity – a measure of the amount of
water vapor in the air.
• Relative Humidity – the percentage of
water vapor in the air compared to the
maximum amount the air could hold.
– Used on weather reports!
Measuring Relative Humidity
• Relative humidity can be measured using a
psychrometer.
• A psychrometer has two thermometers, a wet
bulb and a dry bulb.
• The wet bulb is covered with a damp fabric.
• Evaporation cools the wet bulb.
• Relative humidity can be found by comparing
the temperature of the wet and dry bulb
thermometers.
A problem…
• What would the relative humidity be if
your dry bulb showed a temperature of
60ºF and the wet bulb showed a
temperature of 54ºF? ( a difference of 6º)
Answer
• 60 – 54 = 6
• Dry bulb temp is 60
• Relative Humidity = 68%
How Clouds Form
• Clouds of all kinds form when water vapor in the air
becomes liquid water or ice crystals.
• Condensation – the process by which molecules of water
in the air become liquid water
• Cold air can hold less water vapor than warm air
• As air cools, the amount of water vapor it can hold
decreases
• Some of the water vapor in the air condenses to form
droplets of liquid water
How Clouds Form
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Dew Point – the temperature at which condensation begins
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For water to condense, tiny particles must be present so the
water has a surface on which to condense
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Particles are usually salt crystals, dust from soil, and smoke.
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Dew is water than condenses above the freezing point and land
on a solid surface such as a blade of grass.
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Frost is ice that has been deposited directly onto a surface that is
below the freezing point.
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Clouds form whenever air is cooled to its dew point
Types of Clouds
• Meteorologists classify clouds into three
main types:
• cumulus
• stratus
• cirrus.
Types of Clouds
• Cumulus clouds look like fluffy, rounded
piles of cotton that indicate nice weather
when not tall
Cirrocumulus-rows of cotton balls
indicating a storm is on the way.
Cumulonimbus clouds often produce
thunderstorms
Stratus clouds form in flat layers that can thicken and can
produce drizzle, rain, or snow (nimbostratus)
Cirrus clouds are wispy and feathery and only form
at high altitudes. (made of ice crystals)
• Altostratus and Altocumulus are clouds
that form 2-6km above earth’s surface.
• Middle level clouds
Clouds that form at or near the ground are called fog. Form
when the ground cools at night after a warm humid
day.
Chapter 2 Weather
• 2.5 Precipitation
Precipitation
Precipitation is any form of water that falls
from clouds and reaches Earth’s surface
Types of Precipitation
• Common types of precipitation
include rain, sleet, freezing rain,
hail and snow.
• Rain – most common type of
precipitation, drops of water are
at least 0.5mm in diameter,
smaller drops are mist and
drizzle which usually fall from
nimbostratus clouds
• Sleet – raindrops freeze as they
fall, ice particles are smaller
than 5mm in diameter
• Freezing Rain – raindrops freeze when
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they touch a cold surface
Hail – round pellets of ice larger than
5mm in diameter, only forms inside
cumulonimbus clouds during
thunderstorms
Snow – water vapor in cloud is
converted directly into ice crystals called
snowflakes, all have six sides or
branches
Measuring Precipitation
• Meteorologist measure rainfall with a rain gauge.
• Rain gauge – an open-ended can or tube that collects
rainfall.
Controlling Precipitation
• Droughts – long periods of unusually low
precipitation
• In cloud seeding, tiny crystals of dry ice (solid
carbon dioxide) and silver iodide are sprinkled
into clouds from airplanes.
• The super cooled water droplets in the cloud can
then condense around the silver iodide particles.
• Dry Ice cools the water even more so it freezes
without a surface to condense on.