Topic 11 Global Atmospheric Circulation

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Topic 11Global Atmospheric Circulation

• GEOL 2503
• Introduction to Oceanography

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Earths Sources of Heat

• Internal Heat from Radioactivity
• Drives mantle convection and plate tectonics
• External Heat from Solar Radiation
• Drives the hydrologic cycle and convection
  currents in the atmosphere and oceans

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Same incoming solar energy, but more concentrated
in tropics
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CONVECTION CURRENTS
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On a hypothetical non-rotating Earth, atmospheric
circulation would be a single convection cell in
each hemisphere.
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But because of rotation, the picture is more
complex
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Coriolis Effect

• Because of Earths rotation
• Deflects moving objects to the right in northern
  hemisphere
• Deflects moving objects to the left in southern
  hemisphere
• Caused because of the variation of rotation speed
  with latitude

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• Motions must be large enough for Earths rotation
  to have an effect
• Large scale movements only
• Will not be the case for cats, nor for water
  going down a drain

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What is wind?

• Horizontal movement of air
• Rising or sinking air is technically not wind
• Winds are named for the direction from which they
  blow
• Trade winds are belts of fairly steady wind, so
  named because of their importance to commerce, or
  trade

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Can you point out the Intertropical Convergence
Zone?
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US weather moves west to east
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Modifying the Wind Bands

• Seasonalmonsoons
• Day/nightseabreeze/ landbreeze
• Topographyorographic effect

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Seasonal Changes

• Summer
• Land warmer than ocean
• Air rises over landlow pressure
• Air sinks over oceanhigh pressure
• Winter
• Land colder than ocean
• Air sinks over landhigh pressure
• Air rises over oceanlow pressure

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Meteorological equator
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Note latitudinal migration of high and low
pressure centers with the seasons (equator in red)
Is the ITCZ high or low pressure?
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The Monsoon Effect

• Changing wind direction caused by seasonal
  changes in heating
• Most pronounced in Southeast Asia
• We also have monsoons in U.S.

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Summer Monsoon

• Land warmer
• Air rises over land
• Moist air flows in from ocean
• Rising air cools, moisture condenses
• Rainfall on land
• Also call wet monsoon

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Winter Monsoon

• Ocean warmer
• Air rises over ocean
• Dry air flows off land to ocean
• Little chance of rain on land
• Also called dry monsoon

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Air flows from high pressure to low pressure
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Day/Night Effect

• Daytime
• Land warmer
• Air rises over land
• Air flows in from ocean
• Get an onshore-blowing breeze
• Called a seabreeze

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Day/Night Effect

• Night time
• Water warmer than land
• Air rises over water
• Air flows from land to water
• Get an offshore-blowing breeze
• Called a landbreeze

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Seabreeze
Landbreeze
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The Topographic Effect

• Also called the orographic effect
• Mountains force winds to rise
• Moisture condenses
• Rainfall on oceanside of mountainscalled
  orographic rainfall
• Dry on opposite side of mountainscalled rain
  shadow

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