weather patterns earth science chapter 17. air mass huge body of air with similar temperature,...
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![Page 1: Weather Patterns Earth Science Chapter 17. Air mass Huge body of air with similar temperature, humidity, and air pressure at any height Can be huge Classified](https://reader035.vdocument.in/reader035/viewer/2022062315/56649d2e5503460f94a0607f/html5/thumbnails/1.jpg)
Weather Patterns
Earth Science Chapter 17
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Earth Science chapter 17 2
Air mass
• Huge body of air with similar temperature, humidity, and air pressure at any height
• Can be huge• Classified by temperature and humidity
• Tropical or polar• Temperature
• Maritime or continental• humidity
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Earth Science chapter 17 3
Maritime Tropical
• Warm and humid• Form over tropical oceans• Then move across land• Hot and humid in summer• Bring heavy rain or snow in winter
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Earth Science chapter 17 4
Maritime Polar
• Cool and humid• Form over polar oceans• Affect west coast more than east coast• Bring fog, rain, and cool temperatures
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Earth Science chapter 17 5
Continental Tropical
• Hot and dry• Form over dry land areas – southwest and
Mexico• Smaller than other air masses• Bring hot, dry weather
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Earth Science chapter 17 6
Continental Polar
• Cool and dry• Form over Canada and Alaska• Can bring bitterly cold and dry weather in
winter• Milder in summer• Cause storms when colliding with maritime
tropical masses
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Earth Science chapter 17 7
Air mass movement
• Caused by prevailing westerlies and jet streams (in US)
• Prevailing westerlies push from west to east• Jet streams push from west to east faster
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Earth Science chapter 17 8
Fronts
• Air masses don’t easily mix• Front – boundary where air masses meet
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Earth Science chapter 17 9
Discuss
• What two characteristics are used to classify air masses?
• What are the four types of air masses?• What is a front?
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Earth Science chapter 17 10
Cold fronts
• Rapidly moving cold air mass runs into a slowly moving warm air mass – from opposite directions
• Denser cold air slides under• Warm air pushed up and cooled
• Causes water vapor to condense• Clouds form• Can cause heavy rain or snow
• Cause abrupt weather changes• After front moves through, usually clear skies,
cooler, and wind shifts
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Earth Science chapter 17 11
Warm fronts
• Fast-moving warm air mass overtakes a slowly moving cold air mass
• Moving same direction• Warm air moves over
• Light rain or snow• Cloudy skies
• After front usually warm and humid
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Earth Science chapter 17 12
Stationary fronts
• Warm and cold meet, but don’t move each other
• From opposite directions• Rain, snow, fog, or clouds• Can last many days
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Earth Science chapter 17 13
Occluded fronts
• Most complex• Warm air mass caught between two cold air
masses• Warm air moves up• Cold air masses may mix• Surface temperature becomes cool• Cloudy, rain, or snow
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Earth Science chapter 17 14
Cyclones
• Air at a frontal boundary gets distorted, bends and swirls• Caused by mountains or jet stream
• Swirling area of low pressure• Winds spiral in• Spin counterclockwise in northern
hemisphere• Clouds, wind, and precipitation
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Earth Science chapter 17 15
Anticyclones
• High pressure and dry air• Winds spiral out• Spin clockwise in northern hemisphere• Dry, clear weather
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Earth Science chapter 17 16
Discuss
• Name the four types of fronts and they types of weather each one brings.
• Compare and contrast cyclones and anticyclones.
• What type of front would most likely be responsible for several days of rain and clouds?
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Earth Science chapter 17 17
Storm
• Violent disturbance in atmosphere• Sudden changes in air pressure
• Rapid air movements
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Earth Science chapter 17 18
Thunderstorms
• Small storm with heavy precipitation and frequent lightning and thunder
• Form in cumulonimbus clouds (thunderheads)
• Heavy rain, maybe hail
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Earth Science chapter 17 19
Lightning and thunder
• Lightning• Sudden spark between areas of different
electrical charge• Within a cloud• Cloud to cloud• Cloud to ground
• Thunder• Lightning heats air rapidly and makes it expand
and explode
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Earth Science chapter 17 20
Thunderstorm damage
• Flooding• Overloaded rivers/streams• Saturated ground• Urban areas with little access to ground
• Lightning damage• Hail damage
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Earth Science chapter 17 21
Thunderstorm safety
• Safer inside• Avoid touching electrical appliances or
plumbing• Avoid metal or bodies of water• If outside, find a low area away from
anything tall
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Earth Science chapter 17 22
Tornadoes
• Rapidly whirling, funnel-shaped cloud• Usually brief, but can be deadly• Wind speeds up to 500 km/hr• Most often form in thunderheads when cold
air and warm air meet
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Earth Science chapter 17 23
Tornado damage
• Strong winds and flying debris• Low pressure sucks object up into cloud
• May deposit many miles away
• Unpredictable path• Tornadoes ranked from F0 to F5 by damage
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Earth Science chapter 17 24
Tornado safety• Tornado watch – conditions are favorable
for tornado formation• Watch for thunderstorms and stay near radio,
TV or internet for weather info
• Tornado warning – a tornado has been seen• Get to a safe place ASAP• Basement of a well-built building• Middle of ground floor, away from windows
and doors• Lie flat in a ditch
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Earth Science chapter 17 25
Discuss
• What weather conditions are most likely to produce tornadoes?
• Why do tornadoes occur most often in “tornado alley”?
• What safety precautions should be taken in a thunderstorm?
• What safety precautions should be taken in a tornado?
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Earth Science chapter 17 26
Hurricane
• Tropical cyclone with winds of 119 km/hr or higher
• About 600 km across
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Earth Science chapter 17 27
Hurricane formation
• Forms as a low-pressure area over warm ocean water
• Warm air from water rises and forms clouds, draws more air up
• Has bands of very high winds and heavy rains
• Strongest winds around calm “eye”
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Earth Science chapter 17 28
Hurricane motion
• Last longer than most storms – a week or more
• Form in Atlantic and move towards Caribbean and southeastern US – carried by trade winds
• Lose energy when hit land – no more warm, moist air to draw up• Can cause several days of heavy rain over land
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Earth Science chapter 17 29
Hurricane damage
• High waves, severe flooding, and wind damage
• Low pressure and high winds raise ocean level up to six meters• Storm surge – dome of water that hits coast
where hurricane lands• Major flooding and erosion
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Earth Science chapter 17 30
Hurricane safety
• Hurricane watch – possible within 36 hours• Prepare to evacuate
• Hurricane warning – expected within 24 hours• Leave area immediately if told to evacuate• If you stay in a house, move away from
windows
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Earth Science chapter 17 31
Winter storms
• Precipitation falls as snow if the air is below freezing all the way down to the ground• Heavy snow – can block roads• Extreme cold – can damage crops and freeze
pipes• High winds – reduce visibility and break trees
and power lines
• For safety – find shelter from wind and try to stay dry
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Earth Science chapter 17 32
Lake – effect snow
• Falls south and east of Great Lakes• Cold dry air moves across warmer water
and gets humid• Moves across land, cools, and can’t hold all
the humidity
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Earth Science chapter 17 33
Discuss
• How do hurricanes form?• What is lake-effect snow?• What should you do if you are caught in a
snowstorm?
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Earth Science chapter 17 34
Weather Forecasting
• First, make observations and collect data• Simple observations
• Watch the clouds• Cumulus clouds growing taller may mean a
thunderstorm• High thin cirrus clouds may mean an approaching
warm front
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Earth Science chapter 17 35
More complex data
• Meteorologists use• Local observers• Radar• Instruments in balloons, satellites, and global
weather stations• Mostly from national weather service
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Earth Science chapter 17 36
Weather Technology
• Weather balloons• Carry instruments into lowest layers of
atmosphere• Measure temperature, air pressure, and
humidity• Weather satellites
• Orbit in uppermost atmosphere• Send images back to Earth• Can show temperature, humidity, solar
radiation, wind speed, and wind direction
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Earth Science chapter 17 37
More Weather Technology
• Automated weather stations• Surface locations• Temperature, air pressure, relative humidity,
rainfall, wind speed, and wind direction
• Computer forecasts• Process large amounts of data quickly• Make predictions using mathematical models
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Earth Science chapter 17 38
Discuss
• What tools do meteorologists rely on to forecast the weather?
• How does the large amount of weather data gathered by various modern technologies affect the accuracy of weather forecasts?
• What types of weather information is gathered by satellites?
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Earth Science chapter 17 39
Weather Service maps
• Assemble data from all over the country• Show temperature, wind speed and
direction, fronts, air pressure• Isobars – lines connecting areas with the
same air pressure• Isotherms – lines connecting areas with the
same temperature
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Earth Science chapter 17 40
Newspaper Weather Maps
• Simpler than weather service maps• Use standard symbols
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Earth Science chapter 17 41
Limits of weather forecasts
• A small change in one part of the atmosphere can cause a large change in the forecast a few days later• The butterfly effect
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Earth Science chapter 17 42
Doppler Radar
• Uses the Doppler effect• Uses changes in radio waves as they reflect off
moving objects
• Radio waves bounce off particles in the air, like raindrops, snowflakes, hail, and dust
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Earth Science chapter 17 43
Doppler radar effectiveness
• Can give people more advance warning for storms like tornadoes
• Can be blocked by mountains or buildings• Doesn’t always pick up drizzle• Dust can interfere with it
• Meteorologists must use more than just Doppler to forecast the weather
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Earth Science chapter 17 44
Discuss
• According to the weather map on page 604, what is the weather like in Chicago? How might it change in a few hours?