An air mass can change as it moves into different environments. For example, if a continental polar air mass moves into warmer areas and over the ocean the air will warm and moisture may evaporate from the ocean surface into the air, adding humidity.
Cold and warm air masses usually come together in middle latitudes areas such as the United States, where they form weather fronts and can produce massive storms. Skip to main content. Weather Basics. Hence, mP air becomes cP air after it is forced over the Rockies. Figure 1 - Air Mass Source Regions.
Five air masses affect the United States during the course of a typical year: continental polar, continental arctic, continental tropical, maritime polar, and maritime tropical. Continental air masses are characterized by dry air near the surface while maritime air masses are moist.
Polar air masses are characterized by cold air near the surface while tropical air masses are warm or hot. Arctic air masses are extremely cold. Continental polar cP or continental arctic cA air masses are cold, dry, and stable. Maritime polar mP air masses are cool, moist, and unstable. Maritime tropical mT air masses are warm, moist, and usually unstable.
Continental tropical cT air masses are hot, dry, unstable at low levels and generally stable aloft upper-level ridge Continental tropical air masses originate in northern Mexico. Air masses are also identified based on whether they form over land or over water. Maritime air mass es form over water and are humid. Continental air mass es form over land and are dry. Therefore, an air mass that develops over northern Canada is called a continental polar air mass and is cold and dry.
One that forms over the Indian Ocean is called a maritime tropical air mass and is warm and humid. Air masses are classified on weather maps using two or three letters. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.
Caryl-Sue, National Geographic Society. Dunn, Margery G. For information on user permissions, please read our Terms of Service. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. They will best know the preferred format. When you reach out to them, you will need the page title, URL, and the date you accessed the resource.
If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media. Text on this page is printable and can be used according to our Terms of Service. Northern Canada and Siberia are common sources of these cold, dry masses, although they can also form over water. Because they are extremely dry, polar masses have few clouds. Meteorologists use a capital P to refer to these masses. Some resources differentiate between polar air masses and extremely cold ones that form very close to the poles.
Tropical air masses form within 25 degrees latitude of the equator. This means that the temperature will be warm or even hot. As the air from these air masses moves over the land of the US, they will rapidly cool and usually result in precipitation and storms. Continental air masses develop between 25 and 60 degrees latitude, either north or south of the equator.
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