SDUSD Teacher Professional Development - 6th Grade - Earth Science

March 18th, 2009, Mission Bay High School
Presenter - Memorie Yasuda


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The atmosphere and its circulation

Atmosphere basics



Where air gets the energy to move

  • Energy from the Sun fuels practically all the motion of air, water and life on the Earth, with the major exception being the motion of plates fueled by energy within the Earth.
  • Energy is emitted by the Sun in the form of electromagnetic radiation that can travel through the near-vacuum of outer space. Sunlight is radiation.
  • When sunlight encounters the Earth and its atmosphere, some of it collides with substances in the air returns to space by reflection, or it is temporarily absorbed and then emitted to space.
  • Radiation absorbed by matter can raise the temperature of substances. That absorbing substance increases its energy.
  • When that same energy is released by matter when it is emitted, energy is lost.
  • There is a general balance between incoming and outgoing radiation to space so that the Earth's surface temperature stays relatively constant over time.
  • The average temperature of the Earth's surface has varied over a small range over time depending on changes in the reflectivity of the Earth, solar output, and concentration of greenhouse gases in the atmosphere.



How air moves and why

  • Air is mostly heated by the ground.
  • When air is heated, it expands, separates from the ground and rises.
  • As air rises, it encounters lower pressure and it expands and cools.
  • The temperatues at elevation can become cool enough so that water vapor condenses into liquid water. That's how clouds form when moist air rises.
  • As air moves upward, its temperature drops by about 6-10° C per 1,000 m.
  • The average temperature of the Earth's surface has varied over a small range over time depending on changes in the reflectivity of the Earth, solar output, and concentration of greenhouse gases in the atmosphere.



Clouds and precipitation - where and how they form

  • Clouds are made up of droplets of liquid or frozen water
  • Clouds form when temperature and pressure conditions are just right for water vapor to change into the liquid of solid phase.
  • Clouds form in the sky when air that contains water vapor moves to higher altitude where it is colder.
  • Clouds form in places where air rises. The places where air rises are associated with low atmospheric pressure.
  • Common places where air rises are over the ITCZ just north of the equator, at the polar front, over mountains, in the center of cyclones that are centers of low atmospheric pressure, and over land during the summer when sea breezes and monsoons occur.



Few clouds and little precipitation - where and how this happens

  • Liquid water vaporizes as temperature rises.
  • When air that contains water vapor moves to lower altitude where it is hotter, clouds tend to vaporize.
  • Clouds tend to disappear in high pressure areas where air falls. This happens near 30 degrees north and south of the ITCZ. San Diego and the Earth's major deserts are at these latitudes.
  • The dry part of monsoons and the dryness of Santa Ana winds depend on this phenomena.



Relevance

San Diego water supply and floods








Supporting science



Questions in science

Image credits

Left-to-right and top-to-bottom:
  • Bar-headed goose: Image by World of Oddy.
  • Halo jumping Public domain. U.S. Air force photograph of U.S. Army paratroopers jumping from a C-130, flying 25,000 feet over the Arizona desert. Photo by Master Sergeant Val Gempis. From article by Tech. Sgt. Pat McKenna, 1997, A Bad Altitude. United States Air Force.