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Weather Factors
Energy in the Earth’s Atmosphere
Key Concepts:
• In what forms does
energy from the sun travel
to Earth?
•What happens to the
sun’s energy when it
reaches Earth?
Key Terms:
•Electromagnetic waves
•Radiation
•Infrared radiation
•Ultraviolet radiation
•Scattering
•Greenhouse effect
Energy From the Sun
• You will learn that heat is a major factor in the
weather- the movement of heat in the
atmosphere causes temperatures to change,
winds to blow, and rain to fall.
• Where does the heat come from? Nearly all
energy in the Earth’s atmosphere come from the
sun.
• This energy travels to Earth as electromagnetic
waves, a form of energy that can move through
space
Energy From the Sun
• Radiation is the direct transfer of energy by
electromagnetic waves.
• Most of the energy from the sun travels to
Earth in the form of visible light and infrared
radiation. A small amount arrives as ultraviolet
radiation.
Energy From the Sun
• Visible light- includes all colors that you see in
a rainbow
• Non-visible radiation- not visible, but can be
felt as heat.
– Sun also gives off ultraviolet radiation. This causes
sunburns, can cause skin cancer and eye damage.
Energy in the Atmosphere
• Before reaching the Earth’s surface, sunlight
must pass through the atmosphere.
• Some sunlight is absorbed or reflected by the
atmosphere before it can reach the surface.
The rest passes through the atmosphere to
the surface.
Energy in the Atmosphere
Energy in the Atmosphere
– Sunlight is absorbed in the atmosphere. The ozone
absorbs most of the ultraviolet radiation. Water
and carbon dioxide absorb some infrared
radiation. Clouds, dust, and other gases absorb
energy too.
– Some sunlight is reflected. Clouds act like mirrors,
reflecting sunlight back into space. Dust particles
and gases reflect light in all directions, a process
called scattering.
Energy in the Atmosphere
Scattering:
• When you look at the sky, the light you see has been
scattered by gas molecules in the atmosphere. Gas
molecules scatter more short wavelengths of visible light
(blue and violet) more than long wavelengths (red and
orange). Scattered light therefore looks bluer than sunlight
and the daytime sky looks blue
• When the sun is rising or setting, its light passes through a
greater thickness of the atmosphere than when the sun is
higher in the sky. More light from blue end of the spectrum
is removed by scattering before it reaches your eyes. The
remaining light is mostly red and orange light. The sun
looks red, and clouds around it become colorful
Energy in the Atmosphere
Scattering:
sunset
sunrise
daytime
Energy at Earth’s Surface
• Some of the sun’s energy reaches Earth’s
surface and is reflected back into the
atmosphere.
• About half of the sun’s energy, however, is
absorbed by the land and water and changed
into heat.
• When Earth’s surface is heated, it radiates
most of the energy back into the atmosphere
as infrared radiation.
Energy at Earth’s Surface
• Much of the infrared radiation cannot travel all
the way through the atmosphere back into space.
Instead it is absorbed by water vapor, carbon
dioxide, methane, and other gases in the air.
• The energy from the absorbed radiation heats
the gases in the air. These gases form a “blanket”
around Earth that holds heat in the atmosphere.
• The process by which gases hold heat in the air is
called the greenhouse effect.
Energy at Earth’s Surface
• Greenhouse effect:
– This is a natural process that keeps Earth’s
atmosphere at a temperature that is comfortable for
most living things.
– Over time, the amount of energy absorbed in the
atmosphere and Earth’s surface is in balance with the
amount that is radiated into space. In this way, Earth’s
average temperature remain fairly constant.
– However, emissions from human activities may be
altering this process.
Energy at Earth’s Surface
Weather Factors
Heat Transfer
Key Concepts:
• How is temperature
measured?
•In what three ways is
heat transferred?
•How is heat transferred in
the troposphere?
Key Terms:
•Kinetic energy
•Temperature
•Thermal energy
•Thermometer
•Heat
•Radiation
•Conduction
•Convection
•Convection currents
• You pour a cup of steaming tea into a cup. The
cup feels warms to the touch. Somehow, heat
was transferred from one object (the cup) to
another (your hand) that it was touching.
How?
• We will find out that heat transfer in the
troposphere plays an important role in
influencing Earth’s weather.
Thermal Energy and Temperature
• The tea in the cup and in the teapot are at the same temperature,
but have a different amount of total energy.
• All substances are made up of tiny particles that are constantly
moving. The faster the particles are moving, the more energy they
have. This energy is called kinetic energy
• Temperature is the average amount of energy of motion of each
particle of a substance. That is it is a measure of how hot or cold
something is.
• Thermal energy is the total energy of motion of in the particles of a
substance
• The hot tea in tea pot has more thermal energy than the hot tea in
the cup because it has more particles.
• http://www.fossweb.com/modulesMS/kit_multimedia/Weatherand
Water/matterandenergy/molecules.html
Thermal Energy and Temperature
Measuring Temperature:
– Temperature is one of the most important factors
affecting weather.
– Air temperature is usually measured with a
thermometer.
– A thermometer is a thin glass tube with a bulb on
one end that contains a liquid, usually mercury or
colored alcohol
– Thermometers work because liquids expand when
they are heated and contract when cooled. As air
temperature rises, the temperature of the liquid in
the bulb also increase. This causes the liquid to
expand and rise up the column.
Thermal Energy and Temperature
Temperature Scales:
– Temperature is measured in
units called degrees.
– The two common temperature
scales are the Celsius and
Fahrenheit scales.
– Scientists use the Celsius scale.
• Freezing point of water is 0*C/
32*F
• Boiling point of water is
100*C/212*F
How Heat is
Transferred
• Heat is the transfer of thermal energy from
a hotter object to a cooler one.
• Heat is transferred in three ways: radiation,
conduction, and convection.
Radiation:
– If you have ever felt heat from the sun on your
face, you are feeling energy coming directly
from the sun as radiation. Radiation is the
direct transfer of energy by electromagnetic
waves. Most of the heat you feel from the sun
travels as infrared radiation and cannot be
seen, but felt as heat.
How Heat is
Transferred
Conduction:
– When you walked barefoot on the hot sand, your felt hot
because heat moved directly form the sand into your feet.
– The direct transfer of heat from one substance to another
that it is touching is conduction.
– When a faster moving sand molecule bumps into a slowermoving molecule, the faster molecule transfers some of its
energy
– The closer together atoms or molecules in a substance are,
the more effectively they can conduct heat.
– Conduction works well in some solid, such as metals, but
not as well in liquids and gases. Air and water do not
conduct heat very well.
How Heat is
Transferred
Convection:
– In fluids (liquids and gases), particles can move
easily from one place to another.
– As the particles move, their energy goes along
with them.
– The transfer of heat by the movement of a fluid is
called convection
How Heat is Transferred
3 types of heat transfer:
Heating the Troposphere
• Radiation, conduction, and convection work
together to heat the troposphere.
– During the day, the sun’s radiation heats Earth’s
surface. The land becomes warmer than the air. Air
near the surface is warmed by both radiation and
conduction. (However, heat is not easily transferred
from one particle to another by conduction. So only a
few meters of the troposphere are heated by
conduction.)
– Thus the air close to the ground is usually warmer
than the air a few meters up.
Heating the Troposphere
Heating the Troposphere
• Radiation, conduction, and convection work together
to heat the troposphere.
– Heat is transferred mostly by convection in the
troposphere.
– When the air near the ground is heated, its particles move
more rapidly. As a result they bump into one another and
move farther apart.
– The air becomes less dense. Cooler, denser air sinks
toward the surface, forcing the warmer air to rise. The
upward movement of warm air and the downward
movement of cool air form convection currents.
– Convection currents move heat throughout the
troposphere.
Heating the Troposphere
Weather Factors
Winds
Key Concepts:
• What causes winds?
•How do local winds and
global winds differ?
•Where are the major
global wind belts located?
Key Terms:
•Wind
•Anemometer
•Wind-chill factor
•Local winds
•Sea breeze
•Land breeze
•Global winds
•Coriolis effect
•Latitude
•Jet stream
What is Wind?
• Air is a fluid, and because of that, it can move
easily from place to place.
• Differences in air pressure cause the air to move.
• A wind is the horizontal movement of air from an
area of higher pressure to an area of lower
pressure.
• Winds are caused by differences in air pressure.
What is Wind?
• Most differences in air pressure are caused by the
unequal heating of the atmosphere.
• Convection currents form when an area of the
Earth’s surface is heated by the sun’s rays. Air
over the heated surface expands and becomes
less dense. As the air becomes less dense, its air
pressure decreases.
• If a nearby area is not heated as much, the air
above the less-heated area will be cooler and
more dense. The cool, dense air with a higher
pressures flows underneath the warm, less dense
air. This forces the warm air to rise.
What is Wind?
Measuring Wind:
– Winds are described by their direction and speed.
– Wind direction is determined by a wind vane. The
name of a wind tells you where the wind is coming
from. Ex. A south wind blows from the south to the
north
– Wind speed can be measured by an anemometer
Wind-Chill Factor:
– When wind blows over your skin and removes body
heat. The stronger the wind, the colder you feel. The
increased cooling a wind can cause is called wind-chill
factor
Local Winds
• Have you noticed the breeze at the beach on a
summer day, if so, you have felt a local wind.
• Local winds are winds that blow over short
distances.
• Local winds are caused by the unequal heating
of Earth’s surface within a small area.
• They only form when large-scale winds are
weak.
Local Winds
Sea Breeze:
– Unequal heating that occurs along the shore of a large
body of water.
– It takes more energy to heat water than it does an equal
part of land. As the Earth’s surface heats during the day,
the land warms up faster. As a result, the air over the land
becomes warmer than the air over the water. The warm air
expands and rises, creating a low-pressure area.
– Cool air blows inland from over the water and moves
underneath the warm air, causing a sea breeze
– A sea breeze is a local wind that blows from an ocean or
lake.
Local Winds
Land Breeze:
– At night the process is reversed.
– Land cools more quickly than water, so the air
over the land becomes cooler than the air over
the water. As the warmer air over the water
expands and rises, cooler air from the land moves
beneath it.
– The flow of air from land to a body of water is
called a land breeze.
Local Winds
Global Winds
• Global winds are winds
that blow steadily from
specific directions over
long distances.
• Like local winds, global
winds are caused by the
unequal heating of
Earth’s surface. But
unlike local winds,
global winds occur over
a large area.
Global Winds
• The sun’s radiation directly
hits the equator year
round. This causes that
area to be intensely warmtropics
• The sun’s rays don’t hit as
directly at the poles and
therefore the surface gets
heated less.
• As a result, temperatures
near the poles are much
lower than they are near
the equator.
Global Convection Currents
• Global winds develop because of the temperature
differences between the equator and the poles. This
develops giant convection currents.
• Warm air rises at the equator and cold air sinks at the
poles.
• Air pressure tends to be lower at the equator and
higher at the poles.
• This difference in pressure causes winds at the surface
to blow from the poles to the equator.
• Higher in the atmosphere, air flows away from the
equator towards the poles
Global Convection Currents
The Coriolis Effect
• If Earth did not rotate, global winds would
blow in a straight line from the poles toward
the equator.
• Because Earth is rotating, however, global
winds do not follow a straight path.
• As winds blow, Earth rotates from west to east
underneath them, making it seem as if the
winds have curved. This is the Coriolis effect.
The Coriolis Effect
Global Wind Belts
• The Coriolis effect and other factors combine
to produce a pattern of calm areas and wind
belts around Earth.
• The major global wind belts are: the trade
winds, the polar easterlies, the prevailing
westerlies
• The calm areas are called Doldrums and Horse
Latitudes.
Global Wind Belts
• Doldrums- located near the equator. Here the warm air
rises and “cooler” air moves in and is heated really
quickly. There is little horizontal movement, so winds
are very weak
• Horse Latitudes- warm air rising at the equator splits
and goes north and south. About 30* north and south
latitudes, the air stops moving toward the poles and
sinks. This is another area of calm.
– Historically, sailors would be caught in these areas and ran
out of food and water for their horses, so they would
throw them overboard. This is how they got their name.
• A latitude is the distance from the equator measured in
degrees.
Global Wind Belts
• Trade Winds- when the cold air over the horse latitudes
sinks, it produces a region of high pressure. This high
pressure area causes surface winds to blow both
toward and away from the equator. Because of the
Coriolis effect, these winds would blow in a specific
direction.
• In the Northern Hemisphere, they generally blow from
the northeast and in the Southern Hemisphere, they
blow from the southeast.
• Sailors relied on those winds to move ships carrying
goods from Europe to the West Indies and South
America- thus they became known as the trade winds.
Global Wind Belts
• Prevailing Westerlies: between 30* and 60*
north and south latitudes, these winds blow
toward the poles and turn east due to the
Coriolis effect. Because they blow from west
to east, they are called prevailing westerlies.
• These winds play an important role in the
weather that we get in the United States.
Global Wind Belts
• Polar Easterlies: Winds that blow cold air from
east to west due to the Coriolis effect near the
poles.
• These winds meet the prevailing westerlies
along a region called the polar front.
• This mixing of warm and cold air along the polar
front has a major effect on weather in the United
States.
Global Wind Belts
Global Wind Belts
• Jet Streams:
• Located about 10 kilometers above the Earth’s
surface, these are bands of high speed winds
• Generally blow from west to east at speeds of 200 to
400 km/hr
• 2 major ones that affect the U.S.- the polar jet stream
along northern U.S and the subtropical jet stream that
runs along southern U.S.
• Can fluctuate more north and more south which can
affect weather in the U.S.
• Pilots of airplanes use the jet streams to save time and
money on fuel
Global Wind Belts
Wind Map Symbols
Weather Factors
Water in the Atmosphere
Key Concepts:
• What is humidity and
how is it measured?
•How do clouds form?
•What are the three main
types of clouds?
Key Terms:
•Water cycle
•Evaporation
•condensation
•Humidity
•Relative humidity
•Psychrometer
•Condensation
•Dew point
•Cirrus
•Cumulus
•stratus
Let’s Talk about Water!
•Vital for all forms of life
•Covers 70% of Earth’s surface
•Of that 96% in oceans- saltwater
•1.7 % in groundwater- freshwater
•1.7% in glaciers of Antarctica and
Greenland-freshwater
•Small % in other bodies of water
on Earth
•0.001% in air as water vapor,
clouds, and precipitation
Let’s Talk about Water!
•Can exist on Earth in
three states: solid, liquid,
and gas
•In order for water to
change states, heat must
be added or taken away.
•When heat transfers from liquid water, the
kinetic energy of the molecules decreases to a
very slow movement, they can no longer move
past one another. This is a solid state or ice.
•When energy transfers to ice, kinetic energy
increases until the molecules begin to move
past one another again, the rigid ice structure
is destroyed as the ice melts and water
become its liquid state.
•If more energy is transferred to the liquid
water, the kinetic energy increases so much
that the molecules escape into the
atmosphere as individual molecules as they
become a gas.
Let’s Talk about Water!
Let’s Talk about Water!
•Can be in the atmosphere or a part of
it:
•It’s in the atmosphere when it is a
liquid or solid
•Water is a part of the atmosphere
only when it is in the form or water
vapor, an invisible gas.
Do you recognize this picture? What do you observe?
• As the sun heats the land and oceans, the
amount of water in the atmosphere changes.
Water is always moving between the
atmosphere and Earth’s surface.
• The movement of water between the
atmosphere and Earth’s surface is called the
Water Cycle.
• In the water cycle, water moves from oceans,
lakes, rivers, and plants into the atmosphere
and then falls back to Earth.
Water Cycle
1. Water vapor enters the air
by evaporation from the
oceans and other bodies of
water. Water vapor is also
added to the air by living
things. Water enters the
roots of plants, rises to
leaves, and is released as
water vapor.
Evaporation: the
process by which
water molecules in
liquid water escape
into the air as water
vapor.
Water Cycle
2. As part of the water cycle,
some of the water vapor in
the atmosphere condenses
to form clouds.
3. Rain and snow fall from the
clouds towards the surface.
4. Then water runs off the
surface or moves through
the ground, back into the
lakes, streams, and oceans.
Condensation: the
process by which
molecules of water
vapor in the air
become liquid water.
Humidity
• Humidity is a measure of the amount of water
vapor in the air.
• Air’s ability to hold water vapor depends on its
temperature. Warm air can hold more water
vapor than cool air. Why?
A psychrometer, a tool to
measure humidity.
Humidity
• In weather reports, we typically hear the term
relative humidity when it comes to water vapor.
• Relative humidity is the percentage of water
vapor that is actually in the air compared to the
maximum amount of water vapor the air can hold
at a particular temperature.
– For example, at 10*C, 1 cubic meter of air can hold 8
grams of water vapor. If there were actually 8 grams
of water vapor in the air, then the relative humidity
would be 100%, which is saturated, or full.
• What about if there were only 4 grams of water vapor in the
same area that could hold 8? What is the relative humidity?
Humidity
Measuring Relative Humidity:
– Measured with an instrument called a psychrometer.
– A psychrometer has 2 thermometers inside, one that
is wet and the other that is dry. The wet one has a
cloth covering that is moistened with water.
– A psychrometer is “slung” or spun and as air blows
over the thermometers, the wet one is cooled by
evaporation .
– If humidity is high, the wet bulb water is slow to
evaporate. If its low, the water evaporates quickly.
– Humidity is found by comparing the temperatures
between the two bulbs.
Humidity
Measuring Relative
Humidity:
How Clouds Form
• When you look at a cloud, you are seeing
millions of tiny water droplets or ice crystals.
• Clouds form when water vapor in the air
condenses to form liquid water or ice crystals.
• Two conditions are required for condensation
of the water vapor:
– The air has to cool
– There has to be particles in air
How Clouds Form
• Role of Cooling:
– We know that cold air holds less water vapor than
warm air.
– As the air cools, the amount of water vapor it can hold
decreases. The water vapor condenses into tiny
droplets of water or ice crystals.
– The temperature at which condensation begins is
called the dew point. If the dew point is above
freezing, the water vapor will form water droplets. If
its below freezing, the water vapor turns into ice
crystals.
How Clouds Form
• Role of Particles:
– For water vapor to condense, tiny particles must be
present so the water has something to condense on.
– In cloud formation, most of these particles are salt
crystals, dust from soil, and smoke.
– Water vapor also condenses onto solid surfaces, such
as blades of grass or window panes.
– Liquid water that condenses from the air is called dew.
Ice that has been deposited on a surface is called
frost.
How Clouds Form
Types of Clouds
• Clouds come in many different shapes.
• Scientists classify clouds into three main types
based on their shape:
– Cirrus
– Cumulus
– Stratus
• Each type of cloud is associated with a
different type of weather.
Types of Clouds
Cirrus Clouds
• Wispy, feathery clouds
• Cirrus comes from the
word meaning curl of hair
• Form only at high levels
above 6 km, where
temperatures are very
low; typically made of ice
crystals
Types of Clouds
Cumulus Clouds
• Look like fluffy, rounded piles of
cotton
• Cumulus means “heap” or
“mass”
• Form less than 2 km above the
ground, but can grow in size and
height up to 18 km
• Low cumulus clouds indicate fair
weather
• Tall ones called cumulonimbus
produce thunderstorms
• Nimbus means “rain”
Types of Clouds
Stratus Clouds:
– Form in flat layers
– Strato means “spread out”
– Usually cover all or most of
the sky and are uniform in
dull, gray color
– May produce drizzle, rain,
or snow- called
nimbostratus
Types of Clouds
Altocumulus and Altostratus:
– Names of clouds between 2
and 6 km above the ground
– Alto- means “high”
– Middle level clouds
Fog:
– Clouds that form at or near
the ground
– Forms after ground has
cooled after a hot, humid
day
The cold ocean water
of San Francisco Bay
is often covered by fog
in the early morning.
What will happen as
the sun rises and
warms the air?
Types of Clouds
Weather Factors
Precipitation
Key Concepts:
• what are the common
types of precipitation?
•How is precipitation
measured?
Key Terms:
•Precipitation
• In Arica, Chile, the average
rainfall is less than 1
millimeter per year.
• In Hawaii, the average
rainfall on Mount Waialeale
is 12 meters per year.
• In Boston, MA, the average
rainfall is approximately 1
millimeter.
• As you can see, rainfall varies
greatly around the world.
Global Rainfall
• Water evaporates from every water surface on
Earth and from living things. But that water
eventually returns to Earth’s surface.
• Precipitation is any form of water that falls
from clouds and reaches Earth’s surface.
• Not all clouds produce precipitation. In order
for precipitation to occur, cloud droplets or ice
crystals must grow heavy enough to fall
through the air.
– In order to do this, some droplets collide and
combine to form large droplets. Finally they
become heavy enough to drop as raindrops.
Types of Precipitation
• In warm parts of the world, precipitation is
almost always in the form of rain. In colder
regions, precipitation may fall as snow or ice.
• Common types of precipitation include rain,
sleet, freezing rain, snow, and hail.
• Rain- most common type. In order to be called
rain, droplets must be a certain size. If they
are too small they are called drizzle or mist.
Types of Precipitation
• Sleet: forms when raindrops fall through a
layer of air below 0*C. As they fall, they
freeze.
• Freezing rain: when raindrops fall through cold
air near the ground and do not freeze in the
air. During ice storms, this can cause smooth
thick layers of ice to form on every surface.
This can be dangerous.
Types of Precipitation
• Snow: when water vapor is converted directly
into ice crystals called snowflakes. Snowflakes
have an endless number of different shapes and
patterns.
• Hail: round pellets of ice larger than 5 mm in
diameter are called hailstones. Hail forms only
inside cumulonimbus clouds during
thunderstorms. Formed by tiny ice pellets being
tossed up and down in clouds, growing larger
until they are heavy enough to fall.
Types of Precipitation