Fronts: Moving Air Masses (page 2)

Design Your Own Experiment

1. The region where air masses form is called a source region. The four source regions are ocean, land, tropics, and Poles. An air mass that forms over an ocean is called a maritime air mass. This type of air mass is generally humid. An air mass that forms over land is called a continental air mass and tends to be dry. An air mass that forms near the Poles is called a polar air mass and tends to be cold. An air mass that forms over the tropics, or horse latitudes (region between latitudes 23¹/₂° N and 23¹/₂° S) is called a tropical air mass and tends to be warm. These names of air masses can be combined to describe two characteristics—the humidity and the temperature of the source region. For example, a continental polar air mass forms over land near the Poles and tends to be dry and cold. Prepare a display representing the different source regions of air masses and their characteristics.



2. Clouds are visible atmospheric masses, consisting of a high concentration (amount of substance dissolved or mixed in a specified quantity of a solution or mixture) of minute water droplets or ice crystals in air. Clouds can be used to identify the type of an approaching front. Use an earth science text to identify the types of clouds present at each front. Prepare drawings similar to Figure 27.2, and use them to compare the clouds associated with each type of front, and the shape and movement of air masses of each type of front. For descriptions of cloud types, see National Audubon Society Field Guide to North American Weather (New York: Knopf, 1995), pp. 79-92.
3.  
   1. At the frontal area, air rises or is lifted. Air cools as it rises, eventually reaching dew point, which is the temperature at which water vapor condenses. At the dew point, the invisible water vapor in air condenses on cool surfaces in a collection of tiny water drops that form clouds. Show how cloud water droplets form by condensation by filling a glass with ice, then adding enough water to cover the ice. Observe the outside of the glass for the condensate (liquid formed by condensation).
   2. Measure the dew point by repeating the previous experiment, placing a thermometer in the glass. Determine the temperature at which the water vapor in the air condenses on the glass.

Get the Facts

1. The jet stream is a narrow band of high-speed wind in the upper atmosphere. Its general direction is from west to east. How does the position of the jet stream affect the movement of air masses? For information about jet streams, see National Audubon Society Field Guide to North American Weather (New York: Knopf, 1995), p.47.
2. Meterologists are scientists who study the atmosphere and how it behaves. They gather information and prepare detailed weather maps. Symbols are used to show each bit of information. Weather maps appear daily in the newspaper. What symbols on the maps are used to represent the different fronts? How is the direction of a front represented? For information about weather map symbols for fronts, see Jack Williams, The Weather Book (New York: Vintage Books, 1992), p. 45.

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