Air Masses
Introduction:
An air mass is a large body of air with similar temperature and moisture
properties throughout. The best source regions for air masses are large flat
areas where air can be stagnant long enough to take on the characteristics of the
surface below. As an air mass moves away from its source region, it is modified
as it encounters conditions different than those found in the source region.
Air masses typically clash in the middle latitudes, producing some very
interesting weather.
The purpose of this
activity is to introduce air masses that commonly influence the weather in the
United States, characteristics of these air masses, and how to identify air
masses on weather maps. Key words throughout this activity link directly to
helper resources that provide useful information for answering the questions.
Characteristics of Air Masses:
1) The diagram below depicts two types of air masses that commonly influence
weather in the United States. For each air mass, identify the following characteristics.
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Type of Air Mass Source Region: Relative Temperature: Wind Direction Moisture Content: |
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Find the Air Masses:
2) One way of identifying a tropical air mass on the weather map below is to
look for a region of higher temperatures. To find a polar air mass,
look for a region of colder temperatures. The image below is a map of surface observations and for this part of
the activity, use the temperature field to draw two lines; a red line to
outline the edge of a tropical air mass and a blue line to identify a polar air
mass. Here is an example. You may label the diagram in one
of two ways; 1) by printing out a copy of this activity and marking your
answers directly onto the printout or 2) by saving the image into your favorite
graphics software and modifying the image using that graphics package.
3) Now examine the regions you have outlined. Look particularly close at the wind barbs for wind direction and also examine the reports of dew point temperature. In question #1, you determined typical wind direction and dew point temperatures associated with a tropical air mass and a polar air mass. Use this additional information to again identify the tropical and the polar air masses in the diagram below. Label the edge of a tropical air mass with a red line and use a blue line to indicate the outer edge of a polar air mass.
4) Are there any differences between your first analysis and the second analysis? Explain why they are different (if they indeed are).