Air Masses and Fronts

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Air Masses and Fronts

• By Lauren Malloy
• T-5 Clancys
• 11-14-05

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What are the four types of air masses?

• Maritime Tropical
• Maritime Polar
• Continental Tropical
• Continental Polar

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Maritime Tropical

• Warm humid air masses from oceans near the
  tropics.
• They form over the Gulf of Mexico and the
  Atlantic Ocean.
• In the summer time maritime tropical usually
  bring hot humid weather.
• In winter, a humid air mass can bring heavy rain
  or snow.

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Maritime Polar

• Cool humid air masses form over the icy cold
  North Pacific and North Atlantic oceans.
• The air masses affect the west coast more than
  the east coast.
• In the summer they often bring rain, fog, and
  cool temperatures to the west coast.

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Continental Tropical

• Hot dry air masses form only in the summer over
  dry areas of southwestern and northern Mexico.
• Cover a smaller area than other air masses.
• Bring hot, dry weather to the south.

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Continental Polar

• Form over central and northern Canada and Alaska.
• Bring cool and cold air.
• In winter they bring clear, cool, and dry air to
  most of northern America.
• In the summer, storms may occur when continental
  air masses move south and meet maritime tropical
  that move north.

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How do air masses move?

• The prevailing westerlies are the major wind
  belts in the United States.
• Prevailing westerlies push air masses from west
  to east.

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Fronts

• When air masses meet is a front, the collision
  often causes storms and weather changes.
• A front may be 15 to 200 kilometers wide and
  extend as much as 10 kilometers up to the
  troposphere.
• The kind of front that develops depends on the
  characteristics of the air masses and how they
  move.

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There are four types of fronts.

• Cold Fronts.
• Warm Fronts.
• Stationary Fronts.
• Occluded Fronts.

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Cold Fronts

• Cold air is dense and tends to sink.
• Warm air is less dense and tends to rise.
• When a moving cold air mass runs into a slowly
  moving warm air mass, the denser cold air slides
  under the warmer air.
• Warm air can hold more water vapor than cool air.
• If there is a lot of water vapor in the warm air
  heavy rain or snow may fall.
• Cold fronts move quickly so they can cause
  weather changes.
• After a cold front passes, cool, dry air moves in.

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Warm Fronts

• A moving warm air mass collides with a slowly
  moving cold air mass.
• If the warm air is humid showers and light rain
  might. fall along the front where the warm and
  cold air meet.
• If the warm air is dry scattered clouds may form.
• After a warm front passes through an area the
  weather is likely to be warm and humid.
• Winter warm fronts bring snow.

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Stationary Fronts

• Sometimes cold and warm air masses meet but
  neither one has enough force to move.
• Where the warm and cold air meet, water vapor in
  the warm air turns into rain, snow, fog, or
  clouds.

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Occluded Fronts

• A warm air mass is caught between two cooler air
  masses.
• As warm air cools and its water vapor condenses,
  the weather may turn cloudy, rainy, or snowy.

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Cyclones and Anticyclones

• As warm air at the center of a cyclone rises ,
  the air pressure decreases.
• Winds in s cyclone spin counterclockwise in the
  Northern Hemisphere.
• As air rises in a cyclone the air cools forming
  clouds and precipitation.
• Winds spiral outward from the center of an
  anticyclone, moving towards areas of low
  pressure.
• Winds in an anticyclone spin clockwise in the
  Northern Hemisphere.

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Cyclones

• Hurricanes are very large cyclones that can cause
  widespread damage.

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Anticyclones

• Air flows clockwise around a high-pressure system
  in the northern hemisphere.
• Air tends to sink near high-pressure centers,
  which inhibits precipitation and cloud formation.
  

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Vocabulary

• Air mass- a huge body of air that has similar
  temperature, humidity, and pressure.
• Tropical- or warm air masses form in the tropics
  and have low air pressure
• Polar- or cold air masses from North of 50o N
  latitude and South of 50o S latitude.
• Maritime- air masses that form over oceans
• Continental- air masses form over land in the
  middle of continents and are dry.
• Front- the area where the masses meet and do not
  mix.
• Occluded- the warm air masses is cut off.
• Cyclone- a swirling center of low air pressure.
• Anticyclone- area of high pressure centers of dry
  air.

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Section 1 Review

• 1.) What two main characteristics are used to
  classify air masses?
• Temperature
• Humidity

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Section 1 Review

• 2.) What's a front? Name and describe the four
  fronts.
• Front- the area where the masses meet but do not
  mix.
• Cold Fronts- when a rapidly moving cold air mass
  runs into a slowly moving air mass, the denser
  cold air slides under the lighter warm air.
• Warm Fronts- a moving warm air mass collides with
  a slowly moving cold air mass.
• Stationary Fronts- sometimes cold and warm air
  masses meet but neither one has enough force to
  move.
• Occluded Fronts- a warm air mass is caught
  between two cooler air masses.

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Section 1 Review

• 3.) What is a cyclone? What kind of weather does
  it bring?
• Cyclone- a swirling center of low air pressure.
• A cyclone usually brings precipitation and
  usually forms clouds.

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Section 1 Review

• 4.) Why do maritime polar air masses have more
  affect on the west coast than the east coast?
• Maritime polar air masses has more affect on the
  west coast than the east coast because,
• of the cool humid air.