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There are four basic bodies of air. These large bodies of air drift across the globe. When they are pushed together, the weather can change. |
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Kinds of Air Masses |
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Suppose your cousins just returned from a trip. You want to figure out where they went. When they show you the seashells they collected, you know that your cousins were at a beach. You can figure out where air has been too. The air’s temperature and water vapor content can give you clues. |
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If air stays over an area for some time, it takes on properties of that area and becomes an air mass. An air mass is a large body of air with similar properties all through it. The most important properties are temperature and amount of water vapor. An air mass keeps its original properties for a while as it moves to a new area. |
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Four kinds of air masses are seen in the picture to the right. Generally, the kind of weather you have at any time is because of the air mass in your area. If you are having several warm, clear days, the weather will remain that way until a new air mass comes into your area. Some kinds of weather usually happen only at the edges of air masses. |
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Air masses move because of winds. These winds may be near the ground. Some air masses are guided by the jet stream high above the ground. If the jet stream guides an air mass from Canada to the middle of the United States, northerly winds will probably bring cold, dry air. At the edge of this air mass, storms may occur. |
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How do air masses form and move? |
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Descriptive In a letter, a friend wonders why the weather has been so hot and humid. In your science journal, write a reply to your friend explaining the role of air masses in making the weather hot and humid. |
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