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  • Insert cover image for Chapter 7 (p. 170).
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  • 7

    1. 1. Chapter 7: Air Masses and Weather Systems Physical Geography Ninth Edition Robert E. Gabler James. F. Petersen L. Michael Trapasso Dorothy Sack
    2. 2. Ch. 7: Air Masses and Weather Systems
    3. 3. 7.1 Air Masses <ul><li>Air Mass: large body of air whose temperature and moisture characteristics are similar. </li></ul><ul><li>Due to General Atmospheric Circulation, air masses move and cause changing weather. </li></ul><ul><li>Source Region: </li></ul><ul><ul><li>m = maritime (sea) </li></ul></ul><ul><ul><li>c = continental (land) </li></ul></ul><ul><ul><li>E = Equatorial (very warm) </li></ul></ul><ul><ul><li>T = Tropical (warm) </li></ul></ul><ul><ul><li>P = Polar (cold) </li></ul></ul><ul><ul><li>A = Arctic (very cold) </li></ul></ul>
    4. 4. 7.1 Air Masses
    5. 5. 7.1 Air Masses Q: Which air mass affect your location? Are there seasonal variations?
    6. 6. 7.1 Air Masses <ul><li>Air Mass Modification </li></ul><ul><ul><li>cP or CA moves over Great Lakes and picks up moisture, and may cause Lake effect snow. </li></ul></ul>
    7. 7. 7.1 Air Masses <ul><li>Continental Arctic (cA): Dry and very cold </li></ul><ul><ul><li>occasionally impacts U.S. in the winter </li></ul></ul><ul><ul><li>it often produces record breaking cold. </li></ul></ul><ul><li>Continental Polar (cP): Dry and cold. </li></ul><ul><ul><li>May reach Gulf of Mexico in winter. </li></ul></ul><ul><ul><li>Rarely affects west coast. </li></ul></ul><ul><li>Maritime Polar (mP): moist and cool </li></ul><ul><ul><li>Westerlies bring air mass to west coast, especially in winter. Occasionally affects east U.S. </li></ul></ul>
    8. 8. 7.1 Air Masses <ul><li>Maritime Tropical (mT): moist and warm </li></ul><ul><ul><li>May originates in Gulf of Mexico </li></ul></ul><ul><ul><li>Major impact on central and eastern U.S </li></ul></ul><ul><ul><ul><li>T-storms in the summer </li></ul></ul></ul><ul><ul><ul><li>Clashes with cP </li></ul></ul></ul><ul><li>Continental Tropical (cT): dry and hot </li></ul><ul><ul><li>Small source region (SW deserts and N. Mexico </li></ul></ul><ul><ul><li>Dry line </li></ul></ul><ul><ul><li>Smallest player in U.S. weather </li></ul></ul>
    9. 9. 7.2 Fronts <ul><li>Fronts </li></ul><ul><ul><li>clash between air masses </li></ul></ul><ul><ul><li>Generally move with westerlies </li></ul></ul><ul><ul><li>3-dimensional </li></ul></ul><ul><ul><li>Frontal uplift </li></ul></ul>
    10. 10. 7.2 Fronts <ul><li>Cold Front: </li></ul><ul><ul><li>Cold air moves in on warm air </li></ul></ul><ul><ul><li>Warm air (less dense) rises above cold air </li></ul></ul><ul><ul><li>Steep slope </li></ul></ul><ul><ul><li>Cumulonimbus </li></ul></ul><ul><ul><li>may form a Squall line </li></ul></ul><ul><ul><li>Sharp changes in temperature, pressure, and wind </li></ul></ul>
    11. 11. 7.2 Fronts <ul><li>Warm Front: </li></ul><ul><ul><li>Warm air moves in on cooler air </li></ul></ul><ul><ul><li>Warm air (less dense) rises above cold air </li></ul></ul><ul><ul><li>Slope is not as steep </li></ul></ul><ul><ul><li>Light precipitation which may last longer </li></ul></ul><ul><ul><li>Usher in warmer conditions </li></ul></ul>
    12. 12. 7.2 Fronts <ul><li>Stationary Front </li></ul><ul><ul><li>Boundary between air masses that is not moving </li></ul></ul><ul><ul><li>Extended period of light precipitation and occasionally strong T-storms </li></ul></ul><ul><li>Occluded Front </li></ul><ul><ul><li>Cold air is overtaking warm air </li></ul></ul><ul><ul><li>Dying storm </li></ul></ul>
    13. 13. 7.2 Fronts <ul><li>Four Major Frontal Symbols used on weather maps. </li></ul>
    14. 14. 7.3 Atmospheric Disturbances <ul><li>Middle Latitude Cyclones </li></ul><ul><ul><li>Common location for a clash between cold, polar air and warm, subtropical air </li></ul></ul><ul><ul><li>Convergence </li></ul></ul><ul><ul><li>Guided by polar jet stream </li></ul></ul><ul><ul><li>Variable weather </li></ul></ul>
    15. 15. 7.3 Atmospheric Disturbances <ul><li>Cyclones (L) </li></ul><ul><ul><li>Move with jet stream/westerlies </li></ul></ul><ul><ul><li>Converging, rising air </li></ul></ul><ul><ul><li>Fronts </li></ul></ul><ul><ul><li>Precipitation </li></ul></ul><ul><li>Anticyclone (H) </li></ul><ul><ul><li>Move with path of westerlies </li></ul></ul><ul><ul><li>Divergence, sinking air </li></ul></ul><ul><ul><li>Dry weather </li></ul></ul>
    16. 16. 7.3 Atmospheric Disturbances <ul><li>Horizontal and Vertical Structure of pressure systems </li></ul><ul><li>Where would the strongest and weakest winds be? </li></ul>
    17. 17. 7.3 Atmospheric Disturbances <ul><li>Common track of storms (mid-latitude cyclones) </li></ul><ul><li>What storm track (jet stream) influences your location? </li></ul>
    18. 18. 7.3 Atmospheric Disturbances <ul><li>Stages in the development of a mid-latitude cyclone </li></ul><ul><li>Q: Where would you expect precipitation. Why? </li></ul>
    19. 19. 7.3 Atmospheric Disturbances <ul><li>Cyclones and Local Weather </li></ul><ul><li>Q: Describe the front(s), temp, air mass type, wind direction, and precip. at Des Moines, St Louis, and Pittsburg. </li></ul>
    20. 20. 7.3 Atmospheric Disturbances <ul><li>Cyclones and Upper Air Flow </li></ul><ul><li>Polar jet stream </li></ul><ul><li>Major impact on temperature and precip. </li></ul><ul><li>Q: Where would you expect storms to develop? </li></ul>
    21. 21. 7.3 Atmospheric Disturbances <ul><li>Polar Jet Stream Analysis </li></ul><ul><li>Anticyclones </li></ul><ul><li>Q: Which country does most of this pattern occupy? Where is an anticyclone? </li></ul>
    22. 22. 7.3 Atmospheric Disturbances <ul><li>Hurricanes </li></ul><ul><ul><li>Circular, cyclonic storm with wind speeds greater than 74 mph (118 km/hr) </li></ul></ul><ul><ul><li>Smaller than mid-latitude cyclone </li></ul></ul><ul><ul><li>Same air mass type </li></ul></ul><ul><ul><li>More destructive </li></ul></ul><ul><ul><li>Also called tropical cyclones </li></ul></ul>
    23. 23. 7.3 Atmospheric Disturbances <ul><li>Cross section of a hurricane </li></ul>
    24. 24. 7.3 Atmospheric Disturbances <ul><li>Storm Surge </li></ul><ul><li>Q: Why is the timing of landfall so critical to coastal areas? </li></ul>
    25. 25. 7.3 Atmospheric Disturbances <ul><li>Major “Hurricane Alleys” </li></ul><ul><li>Which coastlines seem unaffected by these tracks? </li></ul>
    26. 26. 7.3 Atmospheric Disturbances <ul><li>Hurricane development </li></ul><ul><ul><li>Warm water (>25 o C or 77 o F) </li></ul></ul><ul><ul><li>Most air </li></ul></ul><ul><ul><li>Coriolis force (do not form or survive near equator) </li></ul></ul><ul><li>Stages of Development </li></ul><ul><ul><li>Tropical disturbance </li></ul></ul><ul><ul><li>Tropical depression </li></ul></ul><ul><ul><li>Tropical Storm (become named) </li></ul></ul><ul><ul><li>Hurricane (categorized by Saffir-Simpson Scale) </li></ul></ul>
    27. 27. 7.3 Atmospheric Disturbances <ul><li>Saffir-Simpson Scale </li></ul>
    28. 28. 7.3 Atmospheric Disturbances <ul><li>Three hurricane tracks </li></ul><ul><li>Subtropical High (Bermuda High) </li></ul>
    29. 29. 7.3 Atmospheric Disturbances <ul><li>Hurricane Strikes </li></ul><ul><li>Q: What areas of our coasts seem to have escaped landfall? </li></ul>
    30. 30. 7.3 Atmospheric Disturbances <ul><li>Snow Storms and blizzards </li></ul><ul><ul><li>Mid and high latitudes </li></ul></ul><ul><li>Blizzard </li></ul><ul><ul><li>Severe weather event </li></ul></ul><ul><ul><li>Heavy snow and strong winds (55 km/hr or 35 mph) </li></ul></ul><ul><ul><li>Visibility reduced </li></ul></ul>
    31. 31. 7.3 Atmospheric Disturbances <ul><li>Thunderstorms </li></ul><ul><ul><li>Low and mid latitudes </li></ul></ul><ul><ul><li>Lightning: intense discharge of electricity </li></ul></ul><ul><ul><li>Thunder: sonic boom created by the expansion of air around the lightning bolt </li></ul></ul><ul><ul><li>Usually cover a small area </li></ul></ul>
    32. 32. 7.3 Atmospheric Disturbances <ul><li>Types of Thunderstorms </li></ul><ul><ul><li>Convective (thermal) </li></ul></ul><ul><ul><li>Orographic </li></ul></ul><ul><ul><li>Frontal </li></ul></ul>
    33. 33. 7.3 Atmospheric Disturbances <ul><li>Tornadoes </li></ul><ul><ul><li>Occur almost anywhere but are most common in North America (Tornado Alley) </li></ul></ul><ul><ul><li>Small intense, cyclonic storm of low pressure, violent winds, and converging air </li></ul></ul>
    34. 34. 7.3 Atmospheric Disturbances <ul><li>Destruction caused by an F5 tornado in Greensburg, Kansas on May 16, 2007 </li></ul>
    35. 35. 7.3 Atmospheric Disturbances <ul><li>Average annual # of tornadoes </li></ul><ul><li>and seasonal variation </li></ul>
    36. 36. 7.3 Atmospheric Disturbances <ul><li>Doppler radar: </li></ul><ul><ul><li>improves tornado detection and forecasting </li></ul></ul><ul><ul><li>Able to determine wind speed and direction </li></ul></ul><ul><li>Q: How many squall lines can you see on this image? </li></ul>
    37. 37. 7.3 Atmospheric Disturbances <ul><li>Fujita Scale (F-0 to F-5) </li></ul><ul><li>Enhanced Fujita Scale (EF-0 to EF-5) </li></ul>
    38. 38. 7.3 Atmospheric Disturbances <ul><li>Weak tropical Disturbances </li></ul><ul><ul><li>Easterly Wave </li></ul></ul><ul><ul><li>Polar Outbreak </li></ul></ul>
    39. 39. 7.3 Atmospheric Disturbances <ul><li>Weather Forecasting </li></ul><ul><ul><li>Doppler radar </li></ul></ul><ul><ul><li>Weather satellites (e.g. GOES East) </li></ul></ul><ul><ul><li>High speed computers </li></ul></ul><ul><ul><li>Improving! </li></ul></ul>
    40. 40. Physical Geography End of Chapter 7: Air Masses and Weather Systems