351:
342:. Continental tropical air masses are extremely hot and dry. Arctic, Antarctic, and polar air masses are cold. The qualities of arctic air are developed over ice and snow-covered ground. Arctic air is deeply cold, colder than polar air masses. Arctic air can be shallow in the summer, and rapidly modify as it moves equatorward. Polar air masses develop over higher latitudes over the land or ocean, are very stable, and generally shallower than arctic air. Polar air over the ocean (maritime) loses its stability as it gains moisture over warmer ocean waters.
462:
492:
and moisture are transported upward, condensing into vertically oriented clouds (see satellite picture) which produce snow showers. The temperature decrease with height and cloud depth are directly affected by both the water temperature and the large-scale environment. The stronger the temperature decrease with height, the deeper the clouds get, and the greater the precipitation rate becomes.
52:
214:
325:
Continental Polar air masses (cP) are air masses that are cold and dry due to their continental source region. Continental polar air masses that affect North
America form over interior Canada. Continental Tropical air masses (cT) are a type of tropical air produced by the subtropical ridge over large
491:
bands. Those bands bring strong localized precipitation since large water bodies such as lakes efficiently store heat that results in significant temperature differences (larger than 13 °C or 23 °F) between the water surface and the air above. Because of this temperature difference, warmth
301:
Tropical and equatorial air masses are hot as they develop over lower latitudes. Tropical air masses have lower pressure because hot air rises and cold air sinks. Those that develop over land (continental) are drier and hotter than those that develop over oceans, and travel poleward on the southern
225:
classification is the most widely accepted form of air mass classification, though others have produced more refined versions of this scheme over different regions of the globe. Air mass classification involves three letters. The first letter describes its moisture properties – "c" represents
274:, denoted as "cPk". Occasionally, one may also encounter the use of an apostrophe or "degree tick" denoting that a given air mass having the same notation as another it is replacing is colder than the replaced air mass (usually for polar air masses). For example, a series of fronts over the
482:
Air masses can be modified in a variety of ways. Surface flux from underlying vegetation, such as forest, acts to moisten the overlying air mass. Heat from underlying warmer waters can significantly modify an air mass over distances as short as 35 kilometres (22 mi) to 40 kilometres
318:. Monsoon air masses are moist and unstable. Superior air masses are dry, and rarely reach the ground. They normally reside over maritime tropical air masses, forming a warmer and drier layer over the more moderate moist air mass below, forming what is known as a
149:
269:
The stability of an air mass may be shown using a third letter, either "k" (air mass colder than the surface below it) or "w" (air mass warmer than the surface below it). An example of this might be a polar air mass blowing over the
188:
and their continental or maritime source regions. Colder air masses are termed polar or arctic, while warmer air masses are deemed tropical. Continental and superior air masses are dry, while maritime and
285:
may be shown as "cA-mPk". Yet another convention indicates the layering of air masses in certain situations. For instance, the overrunning of a polar air mass by an air mass from the
937:
Jun Inoue; Masayuki
Kawashima; Yasushi Fujiyoshi; Masaaki Wakatsuchi (October 2005). "Aircraft Observations of Air-mass Modification Over the Sea of Okhotsk during Sea-ice Growth".
281:
Another convention utilizing these symbols is the indication of modification or transformation of one type to another. For instance, an Arctic air mass blowing out over the
692:
632:
449:, and the density contrast across the frontal boundary vanishes, the front can degenerate into a line which separates regions of differing wind velocity, known as a
426:. The weather usually clears quickly after a front's passage. Some fronts produce no precipitation and little cloudiness, although there is invariably a wind shift.
1010:
585:
306:. Maritime tropical air masses are sometimes referred to as trade air masses. Maritime tropical air masses that affect the United States originate in the
848:
383:, fronts are depicted using various colored lines and symbols, depending on the type of front. The air masses separated by a front usually differ in
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819:
752:
662:
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611:
350:
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823:
1041:
135:
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700:
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536:
525:
Please note that the latitudes in the picture are incorrect on the northern hemisphere. 60 should read 70 and 30 should read 40.
330:
in northern Africa, which is the major source of these air masses. Other less important sources producing cT air masses are the
258:
drying and warming air formed by significant downward motion in the atmosphere. For instance, an air mass originating over the
893:
852:
756:
726:
696:
666:
636:
581:
73:
205:
can quickly modify its character. Classification schemes tackle an air mass's characteristics, as well as modification.
152:
Different air masses which affect North
America as well as other continents, tend to be separated by frontal boundaries
116:
786:
419:
88:
339:
38:
62:
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69:
31:
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577:
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909:
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might be shown with the notation "mT/cP" (sometimes using a horizontal line as in fraction notation).
946:
897:
790:
227:
84:
487:, curved cyclonic flow bringing cold air across the relatively warm water bodies can lead to narrow
730:
760:
670:
962:
193:
air masses are moist. Weather fronts separate air masses with different density (temperature or
184:, and adapt to the characteristics of the surface below them. They are classified according to
434:
331:
303:
262:
of the United States in summer may be designated "cT". An air mass originating over northern
230:, and "m" represents maritime air masses (moist). Its source region follows: "T" stands for
1014:
954:
905:
501:
488:
477:
466:
446:
259:
812:
30:
This article is about air volumes defined by temperature and humidity. For other uses, see
607:
950:
901:
438:
430:
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355:
286:
282:
109:
1035:
966:
473:
416:
362:
327:
307:
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202:
461:
441:, cold fronts and cold occlusions move faster than warm fronts and warm occlusions.
396:
235:
222:
197:) characteristics. Once an air mass moves away from its source region, underlying
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and warm bodies of water can slow the movement of fronts. When a front becomes
404:
384:
271:
181:
173:
157:
51:
958:
412:
392:
319:
198:
148:
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areas of land and typically originate from low-latitude deserts such as the
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243:
17:
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408:
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194:
185:
177:
372:
315:
311:
263:
251:
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might show an air mass denoted mPk followed by another denoted mPk'.
239:
165:
460:
349:
212:
147:
27:
Volume of air defined by its temperature and water vapor content
354:
Picture of cold front (left part of the image) moving over the
423:
169:
45:
877:
Jeffrey M. Freedman; David R. Fitzjarrald (August 2001).
433:
generally move from west to east, while warm fronts move
310:, southern Gulf of Mexico, and tropical Atlantic east of
910:
10.1175/1525-7541(2001)002<0419:PAM>2.0.CO;2
371:
is a boundary separating two masses of air of different
76:. Unsourced material may be challenged and removed.
437:. Because of the greater density of air in their
180:. Air masses cover many hundreds or thousands of
37:"Air stream" redirects here. For other uses, see
1011:University Corporation for Atmospheric Research
544:Papers in Physical Oceanography and Meteorology
322:inversion over the maritime tropical air mass.
571:
569:
567:
781:Climate Change Research Center (2000-11-10).
8:
453:. This is most common over the open ocean.
606:United States Weather Bureau (1950-02-01).
483:(25 mi). For example, southwest of
136:Learn how and when to remove this message
518:
829:from the original on 29 September 2006
608:"Daily Weather Maps: February 1, 1950"
507:Spatial Synoptic Classification system
847:Glossary of Meteorology (June 2000).
820:Hydrometeorological Prediction Center
751:Glossary of Meteorology (June 2000).
721:Glossary of Meteorology (June 2000).
691:Glossary of Meteorology (June 2000).
661:Glossary of Meteorology (June 2000).
631:Glossary of Meteorology (June 2000).
576:Glossary of Meteorology (June 2000).
552:Massachusetts Institute of Technology
403:, and may on occasion be preceded by
334:, the central arid/semi-arid part of
7:
783:"Lesson 7: Clouds and Precipitation"
612:United States Department of Commerce
266:in winter may be indicated as "cA".
74:adding citations to reliable sources
217:Source regions of global air masses
879:"Postfrontal Airmass Modification"
25:
813:"Unified Surface Analysis Manual"
588:from the original on 11 June 2008
465:Lake-effect snow bands near the
375:, and is the principal cause of
50:
894:American Meteorological Society
853:American Meteorological Society
757:American Meteorological Society
727:American Meteorological Society
697:American Meteorological Society
667:American Meteorological Society
637:American Meteorological Society
582:American Meteorological Society
61:needs additional citations for
537:"American Air Mass Properties"
1:
395:may feature narrow bands of
228:continental air masses (dry)
886:Journal of Hydrometeorology
787:University of New Hampshire
535:H. C. Willett (June 1933).
209:Classification and notation
1063:
939:Boundary-Layer Meteorology
471:
360:
340:Southwestern United States
39:Airstream (disambiguation)
36:
29:
959:10.1007/s10546-004-3407-y
811:David Roth (2006-12-14).
338:and deserts lying in the
32:Air mass (disambiguation)
1042:Meteorological phenomena
1005:Greg Byrd (1998-06-03).
578:"Airmass Classification"
415:are usually preceded by
381:surface weather analyses
377:meteorological phenomena
1047:Atmospheric circulation
485:extratropical cyclones
469:
358:
218:
153:
986:University of Wyoming
464:
353:
291:Central United States
254:, and "S" stands for
216:
151:
70:improve this article
1007:"Lake Effect Snows"
951:2005BoLMe.117..111I
902:2001JHyMe...2..419F
793:on January 11, 2005
346:Movement and fronts
982:"Lake Effect Snow"
980:B. Geerts (1998).
470:
359:
219:
154:
332:Arabian Peninsula
304:subtropical ridge
302:periphery of the
250:, "E" stands for
246:, "M" stands for
238:, "A" stands for
234:, "P" stands for
146:
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138:
120:
16:(Redirected from
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1013:. Archived from
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759:. Archived from
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729:. Archived from
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502:Solar irradiance
489:lake-effect snow
478:Lake-effect snow
467:Korean Peninsula
429:Cold fronts and
260:desert southwest
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54:
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1017:on 17 June 2009
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297:Characteristics
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172:defined by its
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945:(1): 111–129.
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693:"Superior air"
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633:"Tropical air"
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401:severe weather
361:Main article:
356:Czech Republic
347:
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287:Gulf of Mexico
283:Gulf of Alaska
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919:on 2005-11-13
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859:on 2007-03-14
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733:on 2012-03-15
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703:on 2011-06-06
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673:on 2011-06-06
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474:Precipitation
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420:precipitation
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397:thunderstorms
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369:weather front
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363:Weather front
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328:Sahara Desert
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308:Caribbean Sea
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59:This article
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33:
19:
1019:. Retrieved
1015:the original
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989:. Retrieved
975:
942:
938:
932:
921:. Retrieved
914:the original
889:
885:
872:
861:. Retrieved
857:the original
849:"Shear Line"
842:
831:. Retrieved
806:
795:. Retrieved
791:the original
776:
765:. Retrieved
761:the original
746:
735:. Retrieved
731:the original
723:"Arctic air"
716:
705:. Retrieved
701:the original
686:
675:. Retrieved
671:the original
656:
645:. Retrieved
641:the original
626:
615:. Retrieved
601:
590:. Retrieved
555:. Retrieved
547:
543:
530:
521:
481:
457:Modification
428:
405:squall lines
368:
366:
324:
314:through the
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220:
203:water bodies
182:square miles
161:
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132:
123:
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68:Please help
63:verification
60:
43:
896:: 419–437.
753:"Polar air"
663:"Trade air"
413:Warm fronts
393:Cold fronts
385:temperature
272:Gulf Stream
174:temperature
158:meteorology
1036:Categories
1021:2009-07-12
991:2008-12-24
923:2009-08-22
863:2006-10-22
833:2006-10-22
797:2007-04-29
767:2009-10-28
737:2009-10-28
707:2009-10-28
677:2009-10-28
647:2009-10-28
617:2009-10-28
592:2008-05-22
557:2009-10-28
513:References
472:See also:
447:stationary
417:stratiform
320:trade wind
252:Equatorial
199:vegetation
96:newspapers
85:"Air mass"
18:Air stream
967:121768400
451:shearline
443:Mountains
409:dry lines
373:densities
336:Australia
289:over the
244:Antarctic
824:Archived
586:Archived
496:See also
435:poleward
389:humidity
232:Tropical
223:Bergeron
195:moisture
186:latitude
178:humidity
162:air mass
126:May 2023
947:Bibcode
898:Bibcode
316:Bahamas
312:Florida
276:Pacific
264:Siberia
248:monsoon
191:monsoon
110:scholar
965:
240:Arctic
166:volume
112:
105:
98:
91:
83:
963:S2CID
917:(PDF)
892:(4).
882:(PDF)
827:(PDF)
816:(PDF)
550:(2).
540:(PDF)
379:. In
236:Polar
164:is a
160:, an
117:JSTOR
103:books
476:and
439:wake
422:and
399:and
387:and
221:The
201:and
176:and
89:news
955:doi
943:117
906:doi
424:fog
407:or
242:or
170:air
168:of
156:In
72:by
1038::
1009:.
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566:^
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367:A
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548:2
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124:(
114:·
107:·
100:·
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41:.
34:.
20:)
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