In the center latitudes, many weather patterns space the result of the movements of large bodies of air, called air masses. An wait mass is a big body that air, normally 1600 kilometers or more across and also perhaps number of kilometers thick, which is identified by homogeneous physics properties (in particular, temperature and moisture content) at any type of given altitude. A region under the affect of an air mass will probably experience generally constant weather conditions, a case referred to together air-mass weather.

Areas in which air masses originate space called source regions. Suitable source region must meet two criteria. First, it should be substantial and physical uniform area. The second criterion is the the area is characterized by a basic stagnation of atmospheric circulation so the air will remain over the an ar long enough to involved some measure up of equilibrium v the surface.

The classification of an waiting mass depends on (1) the latitude of the source region, and also (2) the nature the the surface in the area the origin—ocean or continent. Air masses are identified by two-letter codes. With recommendation to latitude (temperature), wait masses are inserted into among three categories: polar (P), arctic (A), and also tropical (T). A small letter letter (m, because that maritime, or c for continental) is placed in front of the uppercase letter come designate the nature that the surfaces in the source region and as such the humidity characteristics of the waiting mass. Using this classification scheme, the complying with air masses room identified: cA, cP, cT, mT, and also mP. Wait Mass Classification based on source an ar temperature and also moisture properties.

BELOW video clip CHAPTER 7 and CHAPTER 8.

chapter 8 video clip

IMPORTANT PAGES come LOOK at pages 206-212. Wait masses on web page 207

Table 8.1 page 208

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c - continental (land) m - marine (water) p - polar (cold) A - arctic (extremely cold) T - dry (warm)

cP - cold, dry, stable cT - hot, dry, secure air aloft, turbulent at surface ar mP - cool, moist, rough mT - warm, moist, unstable

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Once an air mass move from its resource region, the not just modifies the weather of the area it is traversing, yet it is likewise gradually modified by the surface ar over which the is moving. Modifications can an outcome from temperature differences between an wait mass and the surface, vertical motions induced through cyclones and also anticyclones, or topography.

The day-to-day weather us experience relies on the temperature, stability, and also moisture content of the wait mass we room experiencing. Continental polar (cP) and also continental arctic (cA) wait masses are, as their category implies, cold and dry. Back cP waiting masses space not, as a rule, linked with heavy precipitation, those that cross the great Lakes during late autumn and winter sometimes carry lake-effect snows come the leeward shores. Maritime polar wait masses (mP) form over seas at high latitudes and are cool to cold and also humid. The weather associated with an intrusion of mP waiting from the Atlantic right into an area east of the Appalachians and also north of Cape Hatteras is well-known as a nor"easter. Naval tropical (mT) air masses affecting north America most regularly originate over the warm waters that the Gulf the Mexico, the Caribbean Sea, or the nearby western Atlantic Ocean. Together expected, mT waiting masses are warm to hot and they space humid. Throughout winter, when cP air dominates the central and eastern unified States, mT wait only occasionally enters this part of the country. However, during the summer, mT air masses indigenous the Gulf, Caribbean, and surrounding Atlantic sheathe a much more comprehensive area the the continent and also are current for a greater period. The mT waiting masses from the Gulf-Caribbean-Atlantic source region are additionally the resource of much, if no most, that the precipitation obtained in the eastern two-thirds the the joined States. Isohyets, lines attracted on a map that connect places having equal rainfall, illustrate the greatest rainfall in the Gulf an ar and a to decrease in precipitation with raising distance native the mT resource region.


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Hot and also dry continental tropical (cT) wait is developed only in the summer in northern interior Mexico and surrounding parts of the arid southwestern united States.