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Transcript

  • 1. Chapter 5: Atmospheric Pressure, Winds, and Circulation Patterns Physical Geography Ninth Edition Robert E. Gabler James. F. Petersen L. Michael Trapasso Dorothy Sack
  • 2. Pressure
    • Atmospheric Pressure
      • Variations in pressure create atmospheric circulation (including wind).
  • 3. Pressure
    • Mercury Barometer
      • Standard Sea level pressure is 1013.2 mb. (29.92 inches of mercury)
      • When air pressure increases, what happens to the mercury in the tube?
  • 4. 5.1 Variations in Atmospheric Pressure
    • Vertical Variation
      • Air Pressure and air density decrease rapidly with altitude (height).
      • By approximately how much does density drop between 0 and 100 km?
  • 5. 5.1 Variations in Atmospheric Pressure
    • Horizontal Variations
      • Determined by thermal (temp) or dynamic (motion of atmosphere) conditions.
      • Thermal
        • Warm/hot air is less dense and wants to rise. This creates low pressure near the equator.
        • Cold air is more dense and wants to sink, creating high pressure, near the poles.
      • Dynamic:
        • High pressure in the subtropics.
        • Low pressure in the subpolar regions (e.g. 40-60 o N and S)
  • 6. 5.2 Basic Pressure Systems
    • Low (Cyclone) = L
      • Air is ascending (rising)
      • Low pressure
    • High (anticyclone) = H
      • Air is descending (subsidence)
      • High Pressure
  • 7. 5.3 How is Temp related to the Density of Air
    • Convergence: wind going toward center (L)
    • Divergence: wind going away from center (H)
  • 8.
    • Mapping Pressure Distribution
      • Adjust to sea level pressure
      • Isobars: lines of equal pressure
      • strong pressure gradient (isobars close together causes stronger winds
      • Weak pressure gradient (isobars farther apart) causes weaker winds
    5.3 How is Temp related to the Density of Air
  • 9.
    • Wind is the horizontal movement of air due to pressure differences.
    • Pressure Gradient
      • Where on this figure would winds be the strongest?
    5.4 Wind
  • 10.
    • Coriolis Effect
      • Apparent deflection of the wind
      • N. hem: wind is deflected to the right
      • S. hem: wind is deflected to the left.
    5.4 Wind
  • 11.
    • Friction and Wind
      • Upper Levels (no friction): Ground has little effect. Wind is parallel to isobars. This is a geostrophic wind.
      • At or near surface, friction slows the wind and reduces the Coriolis force. Surface wind blows across isobars.
    5.4 Wind
  • 12.
    • Wind Terminology
      • Winds are named for where they come from
        • Wind from northeast is called NE wind
      • Windward
      • Leeward
    5.4 Wind
  • 13.
    • Anticyclone (H) – wind moves away from center in a clockwise spiral in N. hem.
    • Wind goes form high to low pressure
    • Cyclone (L) – wind moves towards center in a counterclockwise spiral in N. hem
    5.4 Wind
  • 14.
      • What do you think might happen to the diverging
      • air of an anticyclone if there is a cyclone nearby?
    5.4 Wind
  • 15.
    • Global Pressure Belts
      • Equator (trough or L)
      • 30 o N and S – subtropical High
      • Subpolar low (L)
      • Polar high (H)
      • This idealized pressure pattern is affected by landmasses and topography.
    5.5 Global Pressure Belts
  • 16.
    • Seasonal Variations in the Pressure pattern
      • Shift northward in July and southward in January due to location of sun’s direct rays.
      • January :
        • Icelandic Low
        • Aleutian low
      • July
        • Bermuda/Azores High
        • Pacific High
    5.5 Global Pressure Belts
  • 17.
      • What is the difference between the January and July average sea-level pressure at your location? Why do they vary?
    5.5 Global Pressure Belts
  • 18. 5.6 Global Surface Wind Systems
  • 19.
    • Latitudinal Zones
      • Trade Winds (5 o -25 o )
      • Doldrums
        • A zone of calm and weak winds
        • Trade winds converge
        • ITCZ (Intertropical Convergence Zone)
        • ITCZ = region with high precip. and cloud cover.
    5.6 Global Surface Wind Systems
  • 20.
    • Subtropical Highs
    • Westerlies
    • Polar Winds
    • Polar Front
    5.6 Global Surface Wind Systems
  • 21.
    • Effects of Seasonal Migration greatest at transition zone
      • 5 o -15 o (ITCZ and subtropical high)
      • 30 o -40 o (subtropical high and polar front)
    5.6 Global Surface Wind Systems
  • 22.
    • Longitudinal Differences in Winds
    5.6 Global Surface Wind Systems
  • 23.
    • Jet Stream – very strong, narrow band of winds embedded within the upper air westerlies
    5.7 Upper Air Winds and Jet Streams
  • 24.
    • Polar front Jet Stream
    • Subtropical Jet Stream
    • Which jet stream is most likely to affect you in January?
    5.7 Upper Air Winds and Jet Streams
  • 25. 5.7 Upper Air Winds and Jet Streams
  • 26.
    • Rossby waves
    5.7 Upper Air Winds and Jet Streams
  • 27.
    • Monsoons: seasonal shift of the winds
      • Low pressure (summer) - wet
      • High pressure (winter) - dry
    5.8 Subglobal Surface Wind Systems
  • 28.
    • Local Warming Winds
      • Air is compressed and heated as it moves downslope
      • Chinooks
      • Santa Ana
    • Local Drainage Winds
      • Katabatic
    5.8 Subglobal Surface Wind Systems
  • 29.
    • Land-Sea Breeze
      • Diurnal (daily reversal of wind)
      • Differential heating between land and water
    5.8 Subglobal Surface Wind Systems
  • 30.
    • Mountain Breeze-valley breeze
      • Diurnal
    5.8 Subglobal Surface Wind Systems
  • 31.
    • Ocean Currents
    • Gyres: major surface currents
    • Warm currents
      • Gulf Stream
      • Kuroshio Current
    5.9 Ocean-Atmosphere Relationships
  • 32.
    • How does this map of ocean currents help explain the mild winters in London, England?
    5.9 Ocean-Atmosphere Relationships
  • 33.
    • El Niño: weak warm countercurrent that replaces cold coastal waters off the coast of Peru (equatorial Pacific) .
    5.9 Ocean-Atmosphere Relationships
  • 34.
    • El Niño Southern Oscillation (ENSO): Easterly surface winds weaken and retreat to the eastern Pacific, allowing central Pacific to warm and the rain area migrates eastward.
    • La Niña – opposite of ENSO
    5.9 Ocean-Atmosphere Relationships
  • 35.
    • El Niño and Global Weather
    5.9 Ocean-Atmosphere Relationships
  • 36.
    • North Atlantic Oscillation (NAO): relationship between Azores High and Icelandic Low.
    • + NAO = larger pressure difference between Azores and Icelandic. Eastern US may be mild and wet during winter.
    5.9 Ocean-Atmosphere Relationships
  • 37. Physical Geography End of Chapter 5: Atmospheric Pressure, Winds, and Circulation Patterns