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Chapter 20. Weather. Section 20.1. Meteorology- study of weather. Air mass: - large body of air, in the lower troposphere. -May be several kilometers in diameter and height -has similar temperature and humidity through out the air mass.

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Chapter 20

Chapter 20

Weather


Section 20 1
Section 20.1

  • Meteorology- study of weather


  • Air mass:

    - large body of air, in the lower troposphere.

    -May be several kilometers in diameter and height

    -has similar temperature and humidity through out the air mass


-the temperature and humidity of the air mass depends on where the air mass originates

-air masses from the poles are cold and air masses from the tropics are warm.

-Air masses formed over land will be dry

- Air masses formed over water will be humid



5 types of air masses
5 types of air masses where the air mass originates

  • Classified by where they originate

    -Temperature is determined by where it began:

    -Arctic, Polar, or Tropical

    -Humidity is determined if air mass began over sea (maritime) or over land (continental)


  • Continental Arctic where the air mass originatescA

    • Originates over arctic land

    • Extremely cold, it may warm up slightly

    • Very dry air


  • Continental Polar where the air mass originatescP

    • Originates over Alaska and Canada

      • A bit warmer than cA

      • Air is dry, but it will pick up moisture as it passes over the great lakes, bringing snow on the other side. This is called lake effects snow


  • Maritime Polar where the air mass originatesmP

    • Originates over ocean in high latitudes so it is cold and damp

    • b/c the ocean is warmer than the continents the mP air masses are slightly warmed than the cP air masses



  • Maritime tropical coast.mT

    • Air masses over warm topical oceans

    • Air is warm and humid

    • Can cause summer time thunder storms


  • Continental Tropical coast.cT

    • Originates over hot and dry deserts

    • May begin as a maritime air mass, but becomes dry as it passes over a mountain range

    • In the summer it creates heat waves w/o thunderstorms

    • Can cause drought conditions


Section 20 2
Section 20.2 coast.

  • Fronts and lows





  • Four kinds of fronts forced up over the denser air mass (colder)

    1. cold

    2. warm

    3. occluded

    4. Stationary



  • When a masscP meets with a mT in the summer- thunderstorms are created in winter a cold front may bring a quick rain/snow storm



  • Warm front: be much change in the weather- maybe change wind direction

  • a warm front pushes out a cold front


  • Warm air rises over the slower cold front be much change in the weather- maybe change wind direction

  • Weather changes are not dramatic

  • Produces high cirrus clouds changing to thicker nimbus clouds

  • Clouds thick enough to block the sun/moon



  • Occluded front be much change in the weather- maybe change wind direction

  • 2 Cold fronts squeeze a warm front

  • The warm front has to rise over the cold air


  • Stationary front- not moving be much change in the weather- maybe change wind direction

  • If it carries rain- it could lead to local flooding


20.3 be much change in the weather- maybe change wind direction

  • Thunderstorms

  • Contain thunder lightning and sometimes hail

  • Usually only a few kilometers across

  • Started in a cumulonimbus clouds

  • Form in warm moist air


  • Clouds may be 20 kilometers high be much change in the weather- maybe change wind direction

  • May occur at any hour- but mote often in the afternoon (because the air is warmer then)


  • Thunderstorms are formed as convection cells (page 445) be much change in the weather- maybe change wind direction

  • The convection cell has a life span of about 1 hour. There are many convection cells in a thunderstorm

  • A frontal thunderstorm is one that occurs ahead of a weather front. Often called a squall line. Contains strong winds and may lead to flooding



  • Lightning- found in all thunderstorms rotating updrafts.

  • -discharge of electricity that may follow a path of :

    Cloud to cloud

    Cloud to ground

    One point in a cloud to a second point in the same cloud



  • Lightning heats the air to 25,000 C eruptions

  • This causes an expansion in the air which we hear as thunder

  • Light travels faster than sound. So even though thunder and lightning start at the same place, we see the lightning before we hear the thunder




  • Tornado thunder.

  • A byproduct of a thunderstorm

  • It is a rotating column of air

  • Formation is unpredictable



  • Tornadoes appear funnel shape thunder.

    may be a meter wide to 1 km wide

    May occur anywhere and anytime of year.

    US has the highest number of tornadoes than anywhere else in the world



Hurricane
Hurricane early summer (March to May)

  • Area of low pressure – wind and rain spiral around. May include tornadoes

  • Can be 300- 600 km across



Naming hurricanes
Naming hurricanes surge

  • Before 1953, hurricanes were named for where they came ashore

  • 1953- hurricanes were given women's names in alphabetical order

  • 1970’s- hurricanes are now given men and women's names, alternating and alphabetically.





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