Download
air masses and fronts n.
Skip this Video
Loading SlideShow in 5 Seconds..
Air Masses and Fronts PowerPoint Presentation
Download Presentation
Air Masses and Fronts

Air Masses and Fronts

317 Vues Download Presentation
Télécharger la présentation

Air Masses and Fronts

- - - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

  1. Air Masses and Fronts

  2. Air Mass • A large body of air in which there are similar horizontal temperature and moisture properties. • Properties are largely acquired from the underlying surface

  3. Air Mass • Air mass over cold ground Cold and dry • Air mass over water More moist How does water temp affect moisture?

  4. Air Mass Classification • Air masses are classified according to their temperature and moisture characteristics • “continental” = dry (c) • “maritime” = wet (m) • “polar” = cold (p) • “tropical” = warm (t) • “arctic” = frigid (a) • These are combined to create categories

  5. Air mass classification • mT = maritime tropical • warm/moist; originate over tropical oceans • cT = continental tropical • warm/dry; originate over areas like SW U.S. • mP = maritime polar • cold/moist; originate over polar oceans • cP = continental polar • cold/dry; originate over interior continents in winter • cA = continental arctic • frigid/dry; form at very high latitudes

  6. Source RegionsFigure from apollo.lsc.vsc.edu/classes/met130

  7. Fronts • “Boundary between different air masses” • Types of fronts • Cold • Warm • Stationary • Occluded

  8. Maritime Polar (mP) • Forms over the oceans at high latitudes • Moist • Cold • Can contribute to significant snowfall events in mid-Atlantic • Figure from apollo.lsc.vsc.edu/classes/met130

  9. Continental Polar (cP) • Forms over the northern continental interior (e.g., Canada, Alaska) • Long, clear nights allows for substantial radiational cooling (stability?) • Assisted by snowpack • Dry • Cold • Figure from apollo.lsc.vsc.edu/classes/met130

  10. Arctic (A,cA) • Similar to cP, but forms over very high latitudes (arctic circle) • Dry • Extremely cold • Figure from apollo.lsc.vsc.edu/classes/met130

  11. Continental Tropical (cT) • Forms over southwest U.S. & Northern Mexico • Source region includes west Texas • Dry • Warm • Limited water bodies and vegetation limits effect of evaporation and transpiration • Figure from apollo.lsc.vsc.edu/classes/met130

  12. Maritime Tropical (mT) • Forms over Gulf of Mexico as well as subtropical Atlantic and Pacific Oceans • Moist • Warm • Figure from apollo.lsc.vsc.edu/classes/met130

  13. Air Mass Modification • Air masses can be modified once they leave their source region. • Temperature & moisture content can increase or decrease • So how are air masses modified?

  14. Air Mass ModificationFigure from ww2010.atmos.uiuc.edu • 1. Move over warmer or colder ground

  15. Air Mass ModificationFigure from ww2010.atmos.uiuc.edu • 2. Move over a large body of water Fig. 9-12, p. 264

  16. Example: Lake Effect Snow Box 9-2, p. 263

  17. Air Mass ModificationFigure from www.usatoday.com/weather/wdnslope.htm • 3. Move over a mountain range

  18. Air Mass Modification • Stability of the air mass can also modified

  19. Fronts • Air masses move from source region through advection • Air masses do not readily mix together • Front – A boundary between two different air masses • Can be hundreds of miles long

  20. Types of Fronts • Cold Front • Warm Front • Stationary Front • Occluded Front

  21. Cold Front • Cold air advances, replaces warm air at the surface • Change in wind direction/speed • Minimum in atmospheric pressure Fig. 9-14, p. 266

  22. Cold Front Cross Section • A front is a 3-D boundary • Front slopes back over the cold air mass • Warm, less dense air is lifted • Clouds/precipitation associated with a front depend on stability and moisture • Sharp vertical motion at cold front can force thunderstorm activity Fig. 9-15, p. 266

  23. Fig. 9-16, p. 267

  24. Slope of a Front • Depends on temperature and wind differences between the two air masses • Shallow vs. steep slope

  25. Warm Front • Warm air advances • Replaces the cold air at the surface • Change in wind direction/speed Fig. 9-17, p. 268

  26. Warm Front Cross Section • Front slopes back over the cold air mass • Slope is more gentle than with a cold front (less thunderstorm activity) • Warm, less dense air lifted over the cold air (called overrunning) • Clouds/precipitation depend on moisture and stability, usually follow a set progression with an increase in altitude • Responsible for a lot of hazardous winter weather Fig. 9-18, p. 269

  27. Fig. 9-19, p. 270

  28. Stationary Front • Air masses at surface do not move, so the front is stationary • Overrunning still occurring, so we often still see cloudiness • Figure from ww2010.atmos.uiuc.edu

  29. Occluded Front • Separates cool air from relatively colder air at the surface • Sometimes thought of as the “cold front catching up to warm front” • The warm air mass is found above the ground • Two types: • Cold-type occluded front • Warm-type occluded front • Figure from ww2010.atmos.uiuc.edu

  30. Development of Occluded FrontFigures from ww2010.atmos.uiuc.edu

  31. Cross Section of Occluded Front Fig. 9-20, p. 271

  32. Occluded Front

  33. Dryline • Dry air (lower dewpoint temperatures) found to west, moist air (higher dewpoint temperatures) found to east • Temperature change is rather limited across the boundary • Common in the southern plains during the spring • It is a convergence line for wind at the surface, and is therefore responsible for initiating many of our tornadic thunderstorms in the south Plains • Motion is tied strongly to insolation, and typically exhibits a diurnal “sloshing” motion (moving eastward during the day, westward at night)

  34. Fig. 9-21, p. 272

  35. Air Masses with the Drylinewww.geog.umn.edu/faculty/klink/geog1425/images/front/dryline_airmass.jpg

  36. Surface Dew Points

  37. Animation • Satellite • WTM

  38. Fronts • “Boundary between different air masses” • Types of fronts • Cold • Warm • Stationary • Occluded

  39. Identification of Fronts on a Weather Map Look for sharp changes in: a) temperature b) dew point c) wind direction d) pressure and e) cloud/precipitation patterns.

  40. Cold Fronts • Divides cold/dry air (usually a cP air mass) from a warm/moist air mass (mT) • Cold air is advancing on the warm air • Cold air is denser, pushes warm air up and over • May result in heavy localized precipitation ahead of the front • Usually trails down and to the south of a mid-latitude cyclone

  41. Cold Front Transition Most precipitation and deep clouds form ahead of front Cirriform clouds spread ahead of front Warm air rises in a steep fashion over intruding cold air

  42. cP Air mass mT airmass