Chapter 20 – Weather Page 435 How do you think the waves caused damage to this house? If this was...
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Transcript of Chapter 20 – Weather Page 435 How do you think the waves caused damage to this house? If this was...
Chapter 20 – WeatherChapter 20 – Weather
• Page 435
• How do you think the waves caused damage to this house?
• If this was your house, would your rebuild in the same place?
• What can people do to avoid such damage?
• How are you able to predict the weather?
Chapter 20.1Chapter 20.1
Air Masses and WeatherAir Masses and Weather
• Meteorology – the study of processes that govern Earth’s Atmosphere
Origin of an Air MassOrigin of an Air Mass
• An Air Mass is a large body of air with the same humidity and temperature– The humidity and temperature of the air mass
is determined by where they form• Over a southern ocean – moist and warm
– When the air mass travels, it takes with it the temperature and humidity of its place of origin.
Origins of air massesOrigins of air masses
• Classification due to where they form– Continental Arctic (cA) – extremely cold and dry
• Forms over land (continental) and cold temperature causes it to be dry.
– Continental Polar (cP) – cold and dry– Maritime Polar (mP) maritime – moist; plus wet
and cold– Maritime Tropical (mT) – warm and wet– Continental Tropical (cT) – hot and dry
Chapter 20.2Chapter 20.2
Fronts and LowsFronts and Lows
• What is a front?– Front – Boundary that separates opposing
air masses• Can range from 200 meters, to 200 kilometers
• Can be as high as 5 kilometers
• Can be as long as 2000 kilometers
– Air masses on either side differ in humidity, temperature and wind direction.
Kinds of frontsKinds of fronts
• Cold front – boundary between an advancing cold air mass and warmer air mass it is displacing.– Cold air denser therefore it slides under the
warm air in front of it, forming a steep slope– The precipitation along the cold front is
usually heavy and fast (thunderstorms)– However, the passing front may cause no
greater change than a shift in wind direction.
• Warm front – boundary between an advancing warm air mass displacing a cold air mass– Warm air is less dense therefore, it rises up over
the cold air forming a gentle slope.– The first signs of an approaching warm front
are high cirrus clouds, which are followed by cirrostratus then lower stratiform clouds.
– Eventually nimbostratus clouds which give steady rain or snow.
– Occluded front – occurs when the faster moving cold front catches up to a warm front.
• The warm air gets pushed up between the two cold air masses causing cloudiness and precipitation.
– Stationary front – front is not moving forward
• May give many days of steady rain causing flooding.
Life Cycle of a Mid-Latitude LowLife Cycle of a Mid-Latitude Low
• Warm air mass meets a cold air mass in the mid latitudes
• Circulation begins due to the warm air moving northward and the cold southward (p. 442)
• The circulation around the Low is counterclockwise in the Northern Hemisphere
• This counterclockwise motion of a Low sucks air off the earth’s surface. Air is constantly spiraling into a low-pressure system.
• Troughs and Highs (p. 443)• Low pressure is associated with unfavorable
weather.• High pressure is associated with clear
conditions.
Chapter 20.3Chapter 20.3
Thunderstorms and TornadoesThunderstorms and Tornadoes
Thunderstorms – storms with Thunderstorms – storms with lightning and thunder formed in lightning and thunder formed in
cumulonimbus clouds.cumulonimbus clouds.• The cloud can be as tall as 20km
• Formed in convection cells – warm air being lifted up while cool air descends (p. 445)
• Often form along fronts there may be many cells
• Squall line – many thunderstorms along a front
• Supercells – very large singlecell thunderstorm that can produce tornadoes
• Lightning – a discharge of electricity – cloud to cloud, cloud to ground. Can occur in thunderstorms, snowstorms, dust storms or volcanic eruptions.
Tornadoes – byproducts of Tornadoes – byproducts of supercell thunderstormssupercell thunderstorms
• Violently rotating column of air• Tornado formation• Form from between the wall clouds of a
mesocyclone (p. 447)• A tornado’s funnel cloud results when
the air pressure at its center is very low and air sucked into the funnel expands and cools; water vapor in the air condenses.
Storm and Tornado watches Storm and Tornado watches and warningsand warnings
• Watch – conditions are right
• Warning – one has been spotted
Chapter 20.4Chapter 20.4
Hurricanes and WinterstormsHurricanes and Winterstorms
Hurricanes – huge rotating storm of Hurricanes – huge rotating storm of tropical origin that has sustained tropical origin that has sustained
winds of at least 119 km/hwinds of at least 119 km/h
• Winds and rain are strongest at the eye wall
• Hurricanes rely on the transfer of heat from the ocean, they form only when surface ocean waters are sufficiently warm, and they weaken as soon as they make landfall.
• Steered by global wind patterns
• Storm surge results, in part, from strong winds of the eye wall which blows water into a broad dome.
• If storm surge strikes land the same time as high tide, hurricane disaster worsens.
• Hurricanes are ranked according to the Saffir-Simpson Hurricane Scale on p. 452
Winter StormsWinter Storms
• Blizzard – must have winds higher than 56 km/hr, temperature –7°C or lower, and reduced visibility due to falling or blowing snow
Chapter 20.5Chapter 20.5
Forecasting WeatherForecasting Weather
Gathering dataGathering data
• Satellites – visible images and infrared– Visible – the whiter the clouds the thicker –
meteorologists can track the clouds to get speed and direction.
– Are not available at night– Infrared satellite – use temperature to plot
colors– The cooler the cloud tops the higher it is in the
atmosphere– Can be used at night
• Rawinsondes – measure temperature, pressure and humidity of air at different altitude.– Attached to a large balloon and tracked by
radar– Identifies the shape of the jet stream
• Surface Observations– Most are at airports– Information can help to locate fronts, highs
and lows– Provide – temperature, dew point, barometric
pressure, wind speed and direction, visibility, precipitation, height of clouds and the amount.