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6. Secondary Circulation
An air mass is an extremely large body of air
An air mass may cover many thousands of kilometres. Its temperature and moisture properties will be fairly similar in any horizontal direction at any given altitude. Air masses originate in source regions and in order for their uniform characteristics to be developed, such regions should be generally flat and of uniform composition, with light surface winds. Consequently, ideal source regions are usually those areas dominated by high pressure. They include the ice and snow covered arctic plains in winter and subtropical oceans and desert regions in summer. Air masses are grouped into four general categories according to their source region - polar, tropical, continental and maritime.
What are the ideal source regions for air masses? what are the four categories of air masses?