Download 8_Ch17 - Clinton Public Schools

Energy in Earth’s
Atmosphere
 Where does heat in the Atmosphere come from?
 The sun.
 In what form does this energy travel to Earth?
 Electromagnetic Waves
 Radiation – the direct transfer of energy by electromagnetic
waves
 Most energy from the sun travels in the form of:
 Visible light & Infrared Radiation
 Small amount as Ultraviolet Radiation
Energy in the Atmosphere
 What happens to the sun’s energy before reaching Earth?
 Some is Absorbed
 Most by ozone layer in stratosphere
 By water vapor, carbon dioxide, clouds, dust
 Some is Reflected
 By Clouds (reflect it back into space)
 By Dust particles and gas (called scattering)
 Gas mostly scatters short wavelength  why daytime sky looks blue
 Some Reaches Earth’s Surface
 50 % absorbed by land and water and changed to heat  most of
energy then radiates back to the atmosphere as infrared radiation
 Greenhouse effect – process by which gases hold heat in the air
Thermal Energy and
Temperature
 Review:
 All substances contain tiny, constantly moving particles.
 The faster they move  the more energy they have
 Temperature –AVERAGE amount of energy of motion of each
particle of a substance (measure of hot/cold of object)
 Thermal Energy – the TOTAL energy of motion in particles of
a substance
Temperature
 One of the most important factors affecting weather
 Thermometer – measures Temperature
 Thin glass tube, bulb on one end, usually filled with mercury
 Mercury expands when heated & contract when cooled
 Celcius Scale - 0 is freezing/ 100 is boiling
 Fahrenheit - 32 is freezing/ 212 is boiling
How is Heat Transferred
 Heat –

transfer of thermal energy from hotter object
to co0ler object
 Transferred in Three Ways:
 1.

 2.

Radiation
Directly from the sun
Conduction
Direct transfer of heat from one substance
to another by touch
 Touching warm substances: ground,
buildings, cars
 Convection
 Transfer of heat by the movement of a
fluid(liquids & gases)
 Movement  hot rises/ cool sinks  cycle
is created
Heating the Troposphere
 Radiation, conduction, &
convection work together
to heat the troposphere.
 How?
 During the day, the sun
heats Earth’s surface
(radiation)
 Land is warmer than air
 Air is warmed by
radiation and conduction
 Most heat is transferred by
convection
 CONVECTION CURRENTS
What is Wind?
 The horizontal movement of air from an area of high
pressure to an area of lower pressure
 Caused by differences in air pressure:
 Most differences in air pressure caused by unequal heating
(convection currents)
 Sun heats Earth’s surface air above the heated Earth
expands & is less dense  air pressure decreases(due to
density)  Cooler, more dense air with higher pressure flows
underneath the warm, less dense air  cooler air forces
warmer air to rise
Wind
 Winds are described by their direction &
speed.
 Direction of Winds:
 Determined with a wind vane
 Wind swings the wind vane in the
direction it is blowing
 Name of the wind identifies where it is
coming from
 South wind from the south; North
winds from the North
 Speed of Winds:
 Measured with an anemometer
 3 or 4 cups on the ends of a spoke that
spin on an axle
 A meter on the axle shows the speed
 Wind-Chill Factor
 The increased cooling a wind can cause
 How?
 As wind blows over your skin it removes your body heat
Types of Winds:
Local Winds
 Local Winds
 Winds that blow over short distances
 Caused by unequal heating of Earth’s surface within a small area
 Form ONLY when large-scale winds are weak
 2 Types:
 1. Sea Breeze
 2. Land Breeze
Sea Breeze
 Daytime:
Land Breeze
 Nighttime:
 sun heats the land faster than water
 Land cools more quickly than water
 Air over land is warmer than air over
water
 Air over the land becomes cooler
than air over the water
 Warm “land air” expands & rises 
Low-pressure area
 Warm “water air” expands and
rises
 Cool “water air” blows inland from
over the water and moves under
the warm air creating a breeze
 Cool “land air” moves beneath the
warm “water air”  creating a
breeze
Global Winds
 Winds that blow steadily from specific directions over long
distances
 Created by the unequal heating of Earth’s surface
 Occur over LARGE areas
 Temperature near poles are much lower than near equator
 Equator + middle of the day + sun almost directly over =
intense heating to the middle of the Earth
 Near the Poles + sun’s rays strike Earth at lower angle + sun’s
energy spread over larger area = less heat to poles
How do Global Winds Develop?
 Global Convection
Currents:
 Temperature difference between
equator and poles create GIANT
convection currents
 Warm air at the equator rises
lower air pressure at equator
 Cold air at the poles sinks  higher
air pressure at poles
 Difference in pressure  winds at
Earth’s surface blow from the poles
toward the equator
 Higher in Atmosphere  air flows
away from equator toward poles
How do Global Winds Develop?
 Coriolis Effect
 The Way Earth’s rotation
makes winds curve
 As the winds blow, Earth
rotates from West to East
underneath  makes it seem
as if the winds curve
 Global winds in Northern
Hemisphere turn RIGHT.
 Global winds in Southern
Hemisphere turn LEFT.
Global Wind Belts
 Coriolis Effect + other factors = a pattern of calm areas &
wind belts around Earth
 Calm Areas:
 Doldrums
 Horse Latitudes
 Major Global Wind Belts:
 Trade Winds
 Prevailing Westerlies
 Polar Easterlies
Calm Areas
 Doldrums
 Regions near the equator with little or no wind
 Weak Winds due to Little Horizontal motion
 Heated by the sun  warm air rises = area of
low pressure
 Cool air moves into the area but is warmed
rapidly & rises also
 Horse Latitudes (Latitude – distance from the
equator)
 Warm, rising air from equator flows North &
South
 Around 30 degrees North & South from Equator
the air cools and sinks = belt of calm air
 Sailors caught in these calm waters too long
threw their horses over board when they no
long had food/water for them.
Major Global Wind Belts
 1. Trade Winds
 Regions of High pressure created when
the cold air over the horse latitudes sink.
 High pressure causes surface winds to
blow toward equator and poles
 Coriolis Effect causes:
 Winds blowing to Equator to turn
West
 Northern Hemisphere winds
between 30 degrees N and the
equator blow from Northeast
 Southern Hemisphere winds
between 30 degrees S and the
equator blow from Southeast
Major Global Wind Belts
 2. Prevailing Westerlies
 Location: mid-latitudes, between 30
degrees and 60 degrees N and S
 Winds that blow toward the poles
from the Horse Latitudes
 Turned East by the Coriolis Effect
 In Northern Latitude 
blow FROM the southwest
 In Southern Latitude 
blow FROM the northwest
 Play an important role weather of
the United States
Major Global Wind Belts
 3. Polar Easterlies
 Cold air near the poles sinks
and flows back toward lower
latitudes
 Shift to the west due to
Coriolis Effect
 Meet the Prevailing Westerlies
at about 60 degrees N and S
 Polar Front
 Mixing of warm air
(Prevailing Westerlies) and
cold air (Polar Easterlies)
 major effect on United
States Weather
 Jet Streams
 About 10 km above Earth’s surface
 Bands of high-speed winds
 Hundreds of km wide; only few km deep
 Usually blow from west to east at 200 to 400 km per hour
Water in the Atmosphere
 Water cycle – movement of water between the
atmosphere and Earths surface
Humidity
 Humidity – measure of amount of water vapor in the air
 Relative Humidity
 Percentage of water vapor ACTUALLY in the air compared to the
maximum amount of water vapor the air can hold at that
temperature
 Example:
 at 10 degree C, 1 cubic meter of air CAN hold up to 8 grams of water vapor
 If 8 grams of water vapor in air  relative humidity is 100 % or SATURATED
 If 4 grams of water vapor in air  humidity humidity is 50 %
 Psychrometer
 Instrument used to measure relative humidity
 Consists of two thermometers: a wet-bulb & a dry-bulb
Clouds
 How do they form?
 When water vapor in the air condenses to
form liquid water of ice crystals

2 conditions required for Condensation:
 1. Dew Point - temperature where
condensation begins
 Cooler air holds less water vapor than
warm air.
 Above freezing water droplets form
 Below freezing ice crystals form
 2. Particles – have to be present for water to
condense on
 In Clouds Salt crystals, dust from soil,
smoke
 Solid Surface  grass, window panes
 Dew vs frost
Types of Clouds
 3 Main Types:



1. Cirrus
 Wispy, feathery
 Only at high levels with low temps
 Made of Ice Crystals
2. Cumulus
 Fluffy, rounded piles of cotton
 Found at middle levels
 If not very tall = fair weather
 If towering with flat tops = thunderstorms
(cumulonimbus clouds)
3. Stratus
 Flat layers
 Usually cover all or most of the sky
 Uniform, dull, gray color
 If thicken to produce drizzle, rain, or snow 
called nimbostratus clouds
 Cloud Names based on height:


Altocumulus – “higher” than regular cumulus
Altostratus – “higher” than regular stratus
Types of Precipitation
 Rain
 Sleet
 Freezing Rain
 Snow
 Hail