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Air Masses and Fronts. Ms. Luginbuhl. What is an air mass?. An air mass is a huge body of air that has similar temperature, humidity, and air pressure throughout it. Types of Air Masses. Scientists classify air masses according to temperature and humidity. Types of Air Masses.

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what is an air mass
What is an air mass?
  • An air mass is a huge body of air that has similar temperature, humidity, and air pressure throughout it.
types of air masses
Types of Air Masses
  • Scientists classify air masses according to temperature and humidity.
types of air masses1
Types of Air Masses
  • Tropical – warm air masses, form in the tropics and have low air pressure
  • Polar – cold air masses, form north of 50◦ north latitude and south of 50◦ south latitude (the poles!) and have high air pressure
  • Maritime – air masses that form over oceans, air can be very humid
  • Continental – air masses that form over land, air is very dry
air masses
Air Masses
  • Four major types of air masses influence the weather in North America
    • Maritime tropical
    • Continental tropical
    • Maritime polar
    • Continental polar
how air masses move
How Air Masses Move
  • Recall that the prevailing westerlies are the major wind belts in the continental United States.
  • The prevailing westerlies generally push air masses from west to east.
how air masses move1
How Air Masses Move
  • Within the prevailing westerlies, there are jet streams.
  • Recall that jet streams are bands of high-speed winds about 10 kilometers above Earth’s surface.
  • As jet streams blow from west to east, air masses are carried along their tracks.
  • Fronts are the area where the air masses meet and don’t not mix.
  • There are four types of fronts:
    • Cold fronts
    • Warm fronts
    • Stationary fronts
    • Occluded fronts
  • A cold front forms when cold air moves underneath warm air, forcing the warm air to rise.
    • Abrupt weather changes (thunderstorms) but lead to clear skies and cool temperatures
  • A warm front forms when warm air moves over cold air.
    • Lead to rain or snow
  • When a cold air mass and a cool air mass come together warm air can be caught between them and forced upward. This is a occluded front.
    • Clouds and precipitation
  • A stationary front forms when a cold air mass and a warm air mass meet but neither has enough force to move the other.
    • Cool, cloudy and wet

How a Front Forms The boundary where unlike air masses meet is called a front. A front may be 15 to 600 kilometers wide and extend high into the troposphere

  • A swirling center of low air pressure is called a cyclone.
  • Winds spiral inward toward the center of the cyclone.
  • Cyclones are associated with clouds, wind, and precipitation.
  • “L” on a weather map
  • Winds spin counterclockwise in the Northern Hemisphere
  • Anticyclones are high pressure centers of dry air.
  • Winds in an anticyclone from the spiral outward from the center, moving towards areas of low pressure
  • The descending air in an anticyclone generally causes dry, clear weather.
  • Because of the Coriolis effect, winds spin clockwise in the Northern Hemisphere
  • “H” on a weather map