Module Six

• Air Mass - a body of air that covers a relatively wide area and exhibits horizontally uniform properties
• Atmosphere - the air surrounding and which is bound to the Earth
• Conduction - flow of heat in response to a temperature gradient within an object or between objects that are in physical contact
• Convection - the transfer of heat within the air by its movement

  • Used specifically to describe the vertical transport of heat and moisture, especially by updrafts and downdrafts in an unstable atmosphere
• Clouds - a visible aggregate of minute water droplets or ice particles in the atmosphere above the Earth's surface
• Mesosphere - the atmospheric shell between about 20 km and about 70 to 80 km, extending from the top of the stratosphere (the stratopause) to the upper temperature minimum that defines the mesopause (the base of the thermosphere)
• Ozone - a form of oxygen in which the molecule is made of three atoms instead of the usual two

  • Usually found in the stratosphere
  • Responsible for filtering out much of the sun's ultraviolet radiation
  • Primary component of smog
• Stratosphere - the region of the atmosphere extending from the top of the troposphere to the base of the mesosphere

  • Important area for monitoring stratospheric ozone
• Thermosphere - the atmospheric shell extending from the top of the mesosphere to outer space

  • Temperature increases steadily with height
• Tropical - areas of the Earth within 20 degrees North and South of the equator
• Troposphere - the layer of the atmosphere from the earth's surface up to the tropopause

  • Decreasing temperature with height, vertical wind motion, appreciable water vapor content, sensible weather
• Water Vapor - a dispersion, in the air, of molecules of water, especially as produced by evaporation at ambient temperatures rather than by boiling
• Atmosphere:

  • Nitrogen (78.1%) - dilutes the oxygen and is used by living things to make proteins
  • Oxygen (21%) - used by nearly all living things for respiration
  • Argon (0.9%) - used in light bulbs and double pane windows
  • Carbon Dioxide (0.035%) - used by plants to make oxygen, serves as a blanket for the earth to hold in heat
• As you travel up through the atmosphere, moving toward space, the temperature changes and the air pressure decreases and become thinner.
• Layers of the atmosphere:

  A) Thermosphere

  B) Mesosphere

  C) Stratosphere

  D) Troposphere

  E) Mesopause

  F) Stratopause

  G) Tropopause

  
• Exosphere

  • outermost layer
  • 375-6200 miles above the earth
  • low air density, molecules escape into space
• Thermosphere

  • 53-375 miles above the earth
  • air is still thin but becomes denser moving closer to earth
  • temperature increases as height increases due to UV light and radiation
• Mesosphere

  • 31-53 miles above the earth
  • temperature decreases (moving toward space)
  • gasses are dense enought to slow meteors
• Stratosphere

  • Troposphere-31 miles above the earth
  • temperature increases (moving away from earth)
• Troposphere

  • 4-12 miles from earth
  • where weather occurs
  • temperature decreases
• As elevation increases, air pressure decreases
• Air pressure is usually measured using a barometer and recorded in “inches of Mercury” or “millibars”
• Movement of Heat:

  A) Radiation

  B) Convection

  C) Conduction

  
• Frontal Boundary - a boundary or transition zone between two air masses of different density, and thus (usually) of different temperature

  • A moving front is named according to the advancing air mass
• Jet Stream - relatively strong winds concentrated in a narrow stream in the atmosphere, normally referring to horizontal, high altitude winds

  • Position and orientation of jet stream vary day to day
  • General weather patterns are related closely to the position, strength , and orientation of the jet stream(s)
• Air Mass

  First Part of Name - Location:

  • Maritime - air mass over ocean
  • Continental -air mass over land


  Second Part of Name - Temperature

  • Arctic - closest to the poles, considered frigid
  • Polar - cold areas
  • Tropical - warms areas, close to the equator
• • continental-Tropical (cT) - form over deserts, hot and dry
  • continental-Polar (cP) - form over cold, dry land
  • continental-Arctic (cA) - form over frozen land, coldest and driest
  • maritime-Tropical (mT) - form over water, warm and humid
  • maritime-Polar (mP) - forms over cold water, cold but humid
• Front - boundary between two air masses with different temperatures and moisture contents

  • Often cause active weather events
• Stationary Front:

  • when a front stops moving
  • noticeable differences in temperature and winds on either side of the front
  • begins moving again, it resumes its cold/warm front status
  • Cyclones moving along a stationary front often produce a lot of precipitation


  Occluded Front:

  • A cyclone forms when a cold front overtakes a warm front, the warm air is occluded from the center of the cyclone
• Cold Front:

  • area where a cold (and dry) air mass is replacing a warm air mass
  • generally move from NW to SE

  Warm Front:

  • area where a warm (and humid) air mass is replacing a cold air mass
  • generally move from SE to NW
• Dry Line:

  • Separation of a dry air mass from a moist air mass
  • Big difference in humidity
  • Dry air behind the dry line lifts the moist air ahead of it which creates thunderstorms
• Types of Clouds:

  • Cirrus - wispy, composed of ice crystals. Found at higher altitudes and can be seen ahead of a low pressure system (ex. Hurricane)
  • Cumulus - fluffy, dense with flat bottoms which designate the altitude where moisture begins to condense
  • Stratus - flat and broad
  • Nimbus - rain clouds
• Types of Precipitation:

  • Snow - water vapor that freezes and falls to the ground
  • Sleet - snow that melts and then refreezes when it hits the ground
  • Freezing Rain - snow that melts and then refreezes when it hits the ground
  • Hail - begins as frozen water and falls through the atmosphere, an updraft catches the ice and pushes it back up where it collects more water that freezes
• Cyclonic Storm - a thunderstorm that undergoes cycles of intensification and weakening (pulses) while maintaining its individuality

  • Capable of producing multiple tornadoes or bursts of severe weather
• Relative Humidity - a dimensionless ratio, expressed in percent, of the amount of atmospheric moisture present relative to the amount that would be present if the air was saturated

  • Function of moisture content and temperature
  • Does not indicate actual amount of atmospheric moisture present (dew point)
• Increase air pressure by adding more molecules and warming the temperature
• More movement, lower pressure
• When air pressure decreases, it indicates:

  • hot weather - thunder
  • fair weather - high winds
  • cold weather - thaw


  When air pressure increases, it indicates:

  • winter - frost
  • frosty - snow
  • wet weather - fair weather
• High-Pressure

  • high pressure in the middle
  • blows clockwise
  • calm day with no rain

  Low-Pressure

  • low pressure in the middle
  • blows counterclockwise
  • cloud, hurricanes, typhoons
• With the unstable air moving, positive and negative charges build and quick discharge of electricity is released - lightning. 


  The temperature rises so quickly that it causes the air to expand creating a sound wave - thunder.