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Meteorology
U.E.Q.: How do atmospheric changes
create different weather patterns and
how can they be predicted?
Air Composition
• Composition - the combining of distinct
parts or elements to form a whole.
• 78% Nitrogen
• 21% Oxygen
• 1% Other
Air Composition
The atmosphere is
important because it
makes conditions suitable
for living things.
Air Pressure
• Properties of Air
– Density - the amount of
mass in a given volume
– Pressure – force pushing
on an area or surface
– Observe: Pressure
– Air pressure is the result of
the weight of an air column
pushing down on an area
Air Pressure
• Measuring Air Pressure
– Barometer is instrument
used
– Mercury barometers
• A glass tube open at the
bottom and partially filled
with mercury
– Aneroid barometers
• Without liquid; airtight metal
chamber with thin flexible
walls
Air Pressure
– National Weather Service uses millibars as
unit for air pressure
– One inch of mercury is equal to 33.87 mb
• Altitude and Air Properties
– Altitude is the distance above sea level, or
elevation
– As altitude increases, air pressure decreases,
air density decreases
Air Pressure
• Which layer has the highest pressure?
• Which layer has the lowest pressure?
Layers of the Atmosphere
• Observe: Atmosphere Intro
• Atmosphere divided into four layers:
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Troposphere
Stratosphere
Mesosphere
Thermosphere
• Troposphere
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Where Earth’s weather occurs
Contains almost all of the mass of the atmosphere
Temperature decreases about 6.5 C each km.
0-12 km from Earth’s surface
Layers of the Atmosphere
• Stratosphere
– Contains the ozone layer
– Ozone is the three atom form of oxygen
– Upper stratosphere is warmer than lower
stratosphere due to ozone reflecting Sun’s
radiation
– 12-50 km from Earth’s surface
Layers of the Atmosphere
• Mesosphere
– Protects earth from being hit with meteoroids
– Temperatures near -90 C
– 50-80 km from Earth’s surface
Layers of the Atmosphere
• Thermosphere
– The outermost layer of atmosphere
– The air is thin, and hot 1800 C
– First layer the Sun’s radiation hits
– 80 km-?? above Earth’s surface; No outer
limit
Layers of the Atmosphere
• Thermosphere divided into two layers:
– Ionosphere (80km-400km)
• Sun’s energy causes particles to be electrically
charged, ions
• Observe Aurora Borealis – the northern lights
• Exosphere (400km-Beyond)
• Observe: Atmosphere Diagram
Layers of the Atmosphere
Air Pollution
• An air pollutant is any unwanted
substance or chemical that contaminate
the air that we breathe resulting in a
decline in air quality. Air pollutants occur
both outdoors and indoors.
Effects of Air Pollution
Pollutant
Source
Health Effect
Carbon
monoxide
Nitrogen Dioxide
Burning fossil fuels
Reduced ability of blood to
deliver oxygen to the cells
Burning fossil fuels
Breathing problems, lung
damage
Ozone
Chemical reaction of
certain carbon
compounds
Breathing problems, asthma,
eye irritation
Particles of dust,
smoke, or soot
Burning of wood and
fossil fuels, volcanic
Respiratory illnesses, nose
and throat irritation
Sulfur dioxide
Burning of fossil fuels,
volcanic eruptions
eruptions
Breathing problems, lung
damage
Energy in Earth’s Atmosphere
• The energy in Earth’s
atmosphere comes
from the Sun.
• Energy travels as
electromagnetic (EM)
waves
• Energy from EM waves
is called radiation.
Energy in Earth’s Atmosphere
Greenhouse Effect
Greenhouse Effect
• Sunlight travels through Earth’s
atmosphere
• Earth’s surface gives off infrared radiation
• The energy is held in by the atmosphere
thus warming it
• Observe: Greenhouse Effect
Heat Transfer
• Temperature is the average amount of
energy of motion of each particle of a
substance
• Thermal Energy is the total energy of
motion in the particles of a substance
• Temperature is measured with a
thermometer
• Observe: Global Temperature
Heat Transfer
Types of Heat Transfer
Type
Means
Example
Radiation
EM waves microwave
Conduction
Direct
contact
Fluid
(liquids or
gases)
Convection
stove top
boiling
Winds
• Local Winds
– Sea Breezes –
blows from water to
land
– Land Breezes –
blows from land to
water
Winds
• Global Winds
– Doldrums – calm area near equator of rising air
– Trade Winds – blow from the horse latitudes toward the equator
in both hemispheres from east to west
– Horse Latitudes – 30 degrees north or south of the equator; calm
area of falling air
– Prevailing Westerlies – blow from horse latitudes toward the
poles in both hemispheres from west to east
– Polar Easterlies – blow cold air away from the poles in both
hemispheres from east to west
• Observe: Global Winds
Water in the Atmosphere
• Is there water in the air?
• Observe: Water Cycle
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Evaporation – transformation of water from liquid to gas
Condensation – transformation of water from gas to liquid
Infiltration – flow of water into the ground
Precipitation – condensed water vapor that falls to Earth
Evapotranspiration – evaporation of water from living plants
Run-off – movement of water across land
Water in the Atmosphere
• Water is introduced into the atmosphere through
evaporation
• Humidity
– The amount of water vapor in the air varies
depending on air temperature and moisture
– SPECIFIC HUMIDITY: The actual amount of water
vapor in the air.
• Depends on air temp.
• Warm air holds more vapor than cool air
– When the air has a maximum amount of water vapor
it can hold, it is said to be saturated.
• Saturation is when actual vapor density=saturation vapor
density
Water in the Atmosphere
• Air with higher temperatures can hold more water
vapor than air at lower temperatures.
– Relative Humidity: How near the air is to
saturation.
• Looks at actual vapor density in relation to
saturation vapor density for air at a given
temperature.
• @ 10 C a cubic meter of air holds at most 8 grams
of water vapor
– If there were 8 grams in the air R.H. = 100%
– If there were 4 grams in the air R.H. = 50%
Water in the Atmosphere
– Measuring Humidity
• Air temperature is measured with a dry-bulb
thermometer
• Wet bulb thermometer uses evaporation as a
cooling process.
– Drier air has higher rates of evaporation, which causes a
lower wet-bulb temperature.
– More moist air has lower rates of evaporation, which
causes a higher wet-bulb temperature.
• Difference between dry-bulb temperature and wetbulb temperature can give relative humidity.
Water in the Atmosphere
• Humidity and Condensation
– Condensation occurs when air becomes
cooler.
– Temperature at which condensation occurs for
a given humidity is known as dew point.
• Ex.: Wet grass in the morning
Water in the Atmosphere
• Measuring Relative Humidity
– Psychrometer
• Has a wet-bulb and dry-bulb thermometer
• The bulb of the wet-bulb thermometer has a cloth covering
moistened in water
• When slung air blows over both thermometers
• The wet-bulb thermometer is cooled by evaporation and the
reading drops below the dry-bulb thermometer reading
• The relative humidity can be found by comparing the
temperatures of the wet-bulb and dry-bulb thermometers
Water in the Atmosphere
Clouds
• Clouds form from water vapor condensing to
form liquid water or ice crystals
Clouds
• Observe: Dew Point - the
temp. at which
condensation begins
• For water vapor to
condense into clouds,
tiny particles must be
present so the water has
a surface on which to
condense
– Salt crystals, dust, and
smoke
Clouds
• Observe: Cloud Types
Clouds
• Clouds are classified in three types by their
shape:
– Cirrus – means curl of hair; wispy, feathery
• Cirrocumulus – rows of cotton balls, mean storms on its way
– Cumulus – means heap or mass; fluffy, rounded piles
of cotton
• Altocumulus – high altitude faint cumulus clouds
• Cumulonimbus – towering clouds that indicate thunderstorms
– Stratus – means spread out; form in flat layers
• Altostratus – high altitude faint stratus clouds
• Nimbostratus – thick stratus; produce drizzle, rain or snow
Precipitation
• Precipitation - any form of water that:
• falls from clouds
• reaches Earth's surface
• Types of Precipitation
– Rain
• Most common
• Drops at least 0.5 mm in Diameter
• Smaller drops are drizzle, even smaller are mist
– Sleet
• When raindrops fall through a layer of air below 0 C
• Ice particles smaller than 5 mm
Precipitation
– Freezing Rain
• When raindrops fall through cold air near the
ground
• Freeze when they touch the cold surface
– Snow
• When water vapor is converted directly into
crystals
• Snow flakes have six branches
– Hail
• Ice larger than 5 mm in diameter
• Only form in cumulonimbus clouds
Precipitation
• Drought - long periods of unusually low
precipitation
• Cloud seeding - sprinkling crystals of silver
iodide and dry ice from an airplane.
• Rain measurements are done with an
open ended tube called a rain gauge.
Air Masses
• Air Mass – huge body of air at any given
height that has similar:
– Temperature
– Humidity
– Air pressure
• An Air Mass Could be:
– Millions of square kilometers in spread
– Up to 10 kilometers deep
Air Masses
• Four major types of air masses for North America:
– Maritime Tropical - bring warm, humid air
• From the Pacific Ocean to California and West Coast
• From the Gulf of Mexico to the Eastern U.S.
– Continental Tropical - bring hot, dry air
• Move in from the Mexico to the Southern Plains
– Maritime Polar - bring cool, humid air
• From the Pacific to West Coast
• From the Atlantic and Eastern Canada often pushed out to sea by
westerly winds
– Continental Polar – bring cold air
• From Central and Northern Canada to Central and Eastern U.S.
Air Masses
Air Masses
• Air masses move by
prevailing westerlies
and jet streams
– Prevailing Westerlies
– wind belts over the
continental U.S., blow
from west to east
– Bands of high speed
winds about 10 km
altitude, west to east
El Nino v. La Nina
 What
are the major differences
between El Nino and La Nina events?
 What kind of weather do you think
each event brings to our area?
• El Nino
• La Nina
Fronts and Systems
• Fronts – boundary where air masses meet
• Four Types of Fronts:
– Cold Fronts
• Cold air mass runs into warm air mass
• denser cold air mass slides under the lighter warm air mass
• Bring colder, drier air; clear skies, shift in wind and lower
temperatures
– Warm Fronts
• Warm air mass runs into cold air mass
• lighter warm air mass moves over the denser cold air mass
• Brings warm humid weather
Fronts and Systems
– Stationary Fronts
• Cold and warm air mass meet but neither moves the other
• Water vapor in the warm air condenses into precipitation
– Occluded Fronts
• Warm air mass gets caught between two cooler air masses
• Cool air moves under warm air; Warm air mass is cut off
from the ground
• Brings weather that may turn cloudy and precipitate.
Fronts and Systems
• Cyclones
– Low pressure centers often moist air
– Winds spiral inward from the center
– Brings clouds, wind and precipitation
• Anticyclones
– High pressure centers of dry air
– Winds spiral out from the center
– Brings dry, clear weather
Hurricanes
• A hurricane is a rotating tropical storm with winds of at least 74 miles
(119 kilometers) an hour.
– These storms are called:
• hurricanes - Atlantic or eastern Pacific Oceans.
• cyclones - Bay of Bengal and the northern Indian Ocean.
• typhoons - western Pacific.
• http://www.nationalgeographic.com/forcesofnature/interactive/index.
html
• The eye is the low-pressure center of the hurricane.
– Air sinks inside the eye, clearing the skies and making it relatively calm.
– A ring-shaped eye wall surrounds the eye and carries the storm's most
violent winds and its most intense rains.
Hurricanes
• Hurricane season in the Atlantic, Caribbean, Gulf of Mexico, and
central Pacific is from June 1 to November 30. In the eastern Pacific,
it is from May 15 to November 30.
– Hurricanes can cause floods, flash floods, tornadoes, and landslides.
• Storm surge - an abnormal rise in sea level
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usually the most dangerous part of a hurricane
cause beach erosion
wash out roads
decimate homes
• Forecasters at the U.S. National Hurricane Center in Florida track
storms with:
– satellite imagery
– airborne reconnaissance
– computer-model projections
Thunderstorms
• Storm – violent disturbance in the
atmosphere
• Thunderstorms
– form in cumulonimbus clouds; thunderheads
• On hot, humid afternoons
• When warm air is forced up a cold front
– Heavy rainfall possibly hail; strong updrafts
and downdrafts
– Most common in spring and summer
Thunderstorms
– Lightning
• Areas of positive and negative electrical charges build up in
clouds
• As charges jump:
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Between parts of a cloud
Between clouds
Between the cloud and the ground
Heats the air to ~30,000 C
– Thunder
• The expansion causes an explosion in the air
• See the lightning before you hear the thunder
– Floods due to high precipitation
Tornadoes
• Tornadoes
– Rapidly whirling, funnel-shaped cloud that touches
earth’s surface
– Winds speeds approach 500 km/h
– Formation
• From cumulonimbus clouds
• Warm moist air flows in at the bottom of a cumulonimbus
cloud and moves upward.
• A low pressure system form inside the cloud
• The warm air begins to rotate as it meets winds blowing in
different directions at different altitudes
• A tornado forms as part of the cloud descends to earth in a
funnel
Tornadoes
• Most tornadoes occur in the United States.
• Supercells - large thunderstorms that have
winds already in rotation.
• Most tornadoes in the United States occur
in Tornado Alley
– from Texas to Nebraska
Tornadoes
• The average twister
– about 660 feet (200 meters) wide
– moves about 30 mph (50 kmh)
• Meteorologists at the U.S. National Weather
Service watch the skies for severe storms and
tornadic activity with:
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Doppler radar
Satellites
weather balloons
computer modeling
• http://www.nationalgeographic.com/forcesofnatur
e/interactive/index.html
Winter Storms
• If the air is colder than 0 C all the way to the
ground, precipitation falls as snow
• Blizzard - a severe winter storm condition
characterized by:
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winds of 40 km/h (25 mph) or more
have snow or blowing snow
visibility less than 1 km (about 5⁄8 mile)
a wind chill of less than −25 °C (−13 °F),
All of these conditions must last for 4 hours or more
Winter Storms
• Lake-effect snow
1. Frigid air flows over warm water and is heated from below.
Moisture evaporates into the air.
2. Warmer more moist air rises downwind of lakes and often forms
heavy snow squalls.
Reading Weather Maps
• Meteorologists – scientists who study the causes
of weather and try to predict it using:
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Maps
Charts
Computer models
Radar
Balloons
Satellites
Surface instruments
Reading Weather Maps
• A weather map is a “snapshot” of the conditions at a
particular time over a large area
– Isobars – lines joining places with similar pressure
– Isotherms – lines joining places with similar temperature
• Symbols on weather maps show:
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Fronts
Areas of high and low pressure
Types of precipitation
Temperatures
• Limits to forecasting due to “Butterfly Effect”