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Air Masses, Fronts and Global Wind Patterns

Air Masses, Fronts and Global Wind Patterns. Meteorology CGS – Earth Science. Air Masses. Definition:. Air mass - a large dome of air which has similar horizontal temperature and moisture characteristics throughout. Very similar to a balloon. Continental Arctic (cA): .

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Air Masses, Fronts and Global Wind Patterns

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  1. Air Masses, Fronts and Global Wind Patterns Meteorology CGS – Earth Science

  2. Air Masses

  3. Definition: • Air mass - a large dome of air which has similar horizontal temperature and moisture characteristics throughout. • Very similar to a balloon.

  4. Continental Arctic (cA): • Frigid – record low temperatures • Dry - very low dew points • Dense - very high barometric pressure • Usually originate north of the Arctic Circle • Siberian Express • Usually once or twice a winter • very rarely form during the summer • because the sun warms the Arctic.

  5. Continental polar (cP): • Cold and dry - stable • Usually originates in NW Territory of Canada • Influences mainly the northern USA • Responsible for clear and pleasant weather during the summer • Usually in winter • Creates troughs in the polar jet stream • Lake effect snow in Great Lakes areas

  6. Maritime polar (mP): • Cool and moist - unstable • Originate over N. Atlantic and N. Pacific • Main Influence - the Pacific Northwest and the Northeast. • can form any time of the year • Generally not as cold as cP air masses

  7. Maritime tropical (mT): • Warm and very moist – unstable • Originate in the Gulf of Mexico and the Southern Atlantic Ocean • Influences the eastern USA • Most prevalent during summer • Responsible for hot, humid summer days across the South and the East.

  8. Continental Tropical (cT): • Very Hot and very dry – stable aloft • Originates in Desert Southwest and northern Mexico • Occurs in the summer, rarely in winter • Usually keeps the Desert Southwest scorching above 100oF during summer • Generally clear skies, hot, low humidity

  9. Source Regions

  10. Reasoning for Tornadoes • Orographic Perfection • Meeting of • Moist - mT • Hot - cT • Cool – cP Rocky Mtn.

  11. Tornado Alley • http://www.britannica.com/thunderstorms_tornadoes/video/ocliwea124v4.mov

  12. Fujita Scale (NationalAtlas.com)

  13. Fronts and their symbols

  14. Fronts: • Boundary between two air masses • Characterized by shift in weather • Cold • Warm • Stationary • Occluded

  15. 5 Characteristics of a Front • Sharp temperature changes over a relatively short distance. • Changes in air moisture content • Shifts in wind direction • Pressure changes • Clouds and precipitation

  16. Cold Fronts • Temperature – drops rapidly • Pressure – rises steadily • Clouds – Vertical building • Precipitation – Heavy along front • Winds – Strong and shifting • Typically move faster than warm front

  17. Cold Front

  18. Cold Front (Fozzy)

  19. Cold Front

  20. In the summer, cold fronts can trigger: • thunderstorms • large hail • dangerous winds • tornadoes

  21. Graphic Depiction!

  22. Warm Fronts • Temperature – rises slowly • Pressure – slight rise, then fall • Clouds – strato- and cirro- • Precipitation – long, steady • Winds – variable and light • Typically will have affect for days

  23. Warm Front

  24. Warm Front

  25. Warm Front

  26. Effects of warm fronts • Slow-moving warm front can mean days of wet weather before warm air • Sometimes water vapor in warm fronts condense to produce • rain • snow • sleet • freezing rain

  27. Stationary Front

  28. Stationary Fronts • Temperature – stagnent • Pressure – slightly fluctuates • Clouds – altocumulus • Precipitation – none • Winds – variable and light • Can last for days weeks

  29. Occluded Front

  30. Occluded Fronts • Temperature – • Warm – gets milder • Cold – gets colder • Pressure – • Warm - slight drop • Cold – slight rise • Clouds – cumulus • Precipitation – steady and light • Winds – variable and light

  31. Occluded Front

  32. Different Temperatures - Different Pressures Less Dense Less Pressure Cool Air Denser More Pressure Warm Air

  33. Pressure and Air Movement

  34. Pressure Gradient Force • Difference in pressure over a given distance---between isobars • Close together = step pressure gradient • STRONGwinds • Far apart = gentle pressure gradient • Light winds • Just like contour lines

  35. Pressure Gradient Force

  36. Isobaric Maps

  37. Coriolis Effect • Apparent force due to the rotation of the Earth(Think Merry-go-round) • N. Hemisphere  wind turns right • S. Hemisphere  wind turns left • Strength depends on latitude and wind speed

  38. Coriolis Effect

  39. Coriolis Effect

  40. Centripetal Force • In-ward directed force • Allows an object to remain in circular motion • Winds moving around high and low pressure areas • Clockwise around Highs. • Counter-clockwise around Lows.

  41. Friction (What a Drag) • The resistance to movement • Surface winds are affected by friction • Why? Ground resistance: • trees, mountains, houses, buildings, etc. • This drag causes winds to blow across pressure gradient at the surface.

  42. Pressures All Together

  43. General Planetary Circulation

  44. Winds • Horizontal movements at surface • Names from WHERE it came from…not where it is going!!!

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