Atmospheric Circulation

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Atmospheric Circulation Weather

• Chap 8

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Composition of the Atmosphere

• Nitrogen 78.084
• Oxygen 20.946
• Argon 0.934
• Carbon Dioxide 0.033
• Other gases 0.003

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GLOBAL HEATING DRIVES ATMOSPHERIC CIRCULATION

• 1. THE EARTH IS HEATED UNEVENLYLower
  latitudes are heated more intensely than higher
  latitudes, so there is a surplus of heat at low
  latitudes2. THE ATMOSPHERE IS HEATED FROM
  BELOWThe atmosphere is warmed by heat radiating
  from the earth's surface. The atmosphere is
  transparent to most solar radiation, so little of
  the sun's energy heats it directly.

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• 3. THE RESULT THE ATMOSPHERE CIRCULATES IN
  CONVECTION CELLS.Convection transfers heat from
  low latitudes (where there is a surplus) to
  higher latitudes BUT this process is complicated
  by the fact that the earth rotates.

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Global Circulation

• Heat Expand, Cooling Contracts Atmosphere ( 8.1)
• 1. Sun Radiation Greater In The Equator Air Heat
  And Rise
• 2. Poles - Air Is Contracting And Descending
• 3. Convectional Circulation - Low Pressure
  Equator, High Poles

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Coriolis Effect

• Deflection Of Object Due To The Earth Rotation
  (8.11)
• 1. Right In The N. Hemisphere (clockwise)
• 2. Left In The S. Hemisphere (counterclockwise)
• 3. No Deflection In The Equator

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Review the Concepts

• List the most common gases of the atmosphere in
  order of abundance.
• Describe what causes uneven heating of the earth.
• What is the Coriolis effect?

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Atmospheric Circulation

• 1. Six circulation cells ( 8.12)
• 2. Equatorial - Doldrums, Low, Cools, Condense,
  Precipitation
• 3. Westerlies - N S - from West
• 4. Trade Winds - N S
• 5. Easterlies - Polar Areas - N S - from East

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• In between the pressure belts, where atmospheric
  circulation is parallel to the surface, are THREE
  wind belts
• Note The wind direction is given as the
  direction from which the wind is coming.WEST or
  WESTERLY winds is FROM the west, blowing from
  west to east.
• EAST or EASTERLY wind is FROM the east, blowing
  from east to west.

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• The Landmasses - Surface Winds Form Elliptical
  Cells
• Seasonal Temperature Variation (8.16)
• Warm In The Summer - Low Pressure In Land
• Cold In Winter - High Pressure In Land
• The uneven distribution of heat and moisture
  creates the earth biomes

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Trade Winds

• 5 - 30 N and S
• moist atmosphere
• at least 500 km away from equator
• Not affected by Coriolis effect
• Northeasterly in the Northern Hemisphere

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The Westerlies

• 35 - 60 N and S
• Related to the divergent flow off of the poleward
  side of Subtropical High
• Can also be predicted by Coriolis Effect on
  circulation cells

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Polar Easterlies

• 65 - 85 N and S
• Not as persistent as other two wind belts
• Direction and speed more variable
• Strongly influenced by storms at Polar Front

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Review the Concepts

• Describe what causes the seasons.
• Name the surface winds of the Earth.

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ATMOSPHERE - OCEAN INTERACTIONS

• 1. Hydrologic cycleEvaporation-Condensation-Preci
  pitation involves moisture that originates in the
  oceans.2. Surface ocean currents follow the
  wind pattern above

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• 3. Monsoons(8.15)
• seasonal reversal of wind direction caused by
  difference in thermal properties of land and
  water
• Areas have wet summers and dry winters
• Linked to the intertropical convergence zone
  (ITCZ)
• Affects Africa, Asia, India

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Land - Sea Breeze

• Atmospheric Circulation - Spatial Variations In
  Air Temperature (8.16)
• 1. Sea Breeze - Land Heat Up, Air Heat Up And
  Expand - Low pressure
• a. High Pressure Over The Water Causes
  Circulation

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• 2. Land Breeze - Air Over Land Cools Rapidly - Hi
  Atmospheric Pressure
• a. Circulation Moves Air From The Land Toward
  The Sea

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Hurricanes (Typhoons)

• Large low pressure system with cyclonic
  circulation (clockwise in the northern
  hemisphere)
• Wind speeds greater than 74 mph (at lower speeds,
  the low pressure systems are called tropical
  storms or tropical depressions)
• Called Willy-Willys, Typhoons, Cyclones, or
  Hurricanes

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• Necessary conditions for formation
• moist atmosphere--high relative humidity
• at least 500 km away from equator so that the
  Coriolis force is strong enough to produce
  rotation
• warm ocean (80 F 27 C or above)

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• Hurricanes are seasonal (late summer and early
  fall) because they need heat from ocean to
  sustain the energy of the storm.
• Hurricanes lose energy over land and cold water.

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HURRICANES

• Necessary conditions    
• Formed from thunderstorms     
• Ocean temperature greater than 80 F 27 C     
• More than 500 km from the Equator

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• Related factors    
• High relative humidity in lower and middle
  troposphere     
• Low wind shear
• Convection Growth Process

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CISK

• Convective Instability of the Second Kind.
• A positive feedback mechanism    1.   Surface
  convergence causes air to rise.    2.   Air
  rises and cools, and condensation occurs.

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•  3.   Condensation releases latent heat into
  atmosphere, thus warming the
  atmosphere.    4.   Warmed air expands.    5.
    Surface pressure decreases, and a low
  pressure center develops.     6.   Decreased
  surface pressure increases the winds.

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• 7.   Increased winds reinforces surface
  convergence and the cycle repeats again.
• The storm builds strength with every cycle.What
  stops the process?
• Cool water or Strong wind shear or Land

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Hurricane Stages

• 1.  Tropical Depression     Sustained winds of
  23-39 mph     One closed isobar     Slight
  organization2.  Tropical Storm     Winds 39-73
  mph     Organized, circular in shape  
    Rotation apparent     Assigned a name at this
  stage     Damage Heavy rainfall (5-10 inches)

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• 3.   Hurricane     Winds 74 mph or higher
  classified by Safir-Simpson scale (1-5)  
    Distinct eye and spiral bands     Pronounced
  rotation

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Important features

• 1.   Eye 12-30 miles in diameter center of storm
  lowest pressurenot destructive
• clear sky, light winds
• winds deflected away from the eye by the
  Coriolis force 

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•  2.   Eye Wallmost devastating portion with high
  winds and heavy rain
• latent heat production maximized

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• 3.   Spiral Bands 60-120 miles in length radiate
  outward from eye wall
• rain free areas can occur between bands

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Review the Concepts

• Contrast Land Breeze and Sea Breeze
• Contrast the following phenomena
• Hurricanes
• Typhoons
• Cyclones
• Willy-Willys

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Damage

• 1.   Storm surge causes flooding in
  coastal areas2.   Strong winds3.   Heavy rains
  cause flooding in inland and coastal areas4.
    Tornadoes (occasional)

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Movement

• Path depends mainly on the wind belt in which
  hurricane is located.
• 5 to about 30 moves westward, pushed by
  easterly
• Trade Winds Weakens slightly as it crosses the
  Subtropical High pressure belt
• 30 to 60 moves eastward, pushed by west winds
  of Prevailing Westerlies

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