ATMOSPHERE Air Circulation

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ATMOSPHERE Air Circulation

• UNIT 7
• Meteorology and Climate

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Atmosphere-Ocean Coupling

• Why study atmospheric circulation?
• Atmosphere and ocean processes are intertwined
• Atmosphere-ocean interaction moderates surface
  temperatures, weather and climate
• Weather local atmospheric conditions
• Climate regional long-term weather
• Atmosphere drives most ocean surface waves and
  currents

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Composition of the Atmosphere

• Dry Air 78 Nitrogen, 21 Oxygen
• BUT it is never completely dry
• Typically contains about 1 water vapor
• Chemical residence time of water vapor in the air
  is about 10 days
• Warm air holds much more water vapor than cold
  air

http//www.nature.com/scitable/knowledge/library/t
he-global-climate-system-74649049
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Density of Air

• Typical air density 1 mg/cm3
• Temperature and pressure affect the density of
  air
• Temperature Hot air is less dense than cold air
• Pressure Air expands with elevation above sea
  level

http//www.physicalgeography.net/fundamentals/7d.h
tml
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Density and Temperature

• Rising air expands and cools
• Vapor condenses into clouds and precipitation
• Sinking air is compressed and warms
• Clear air

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Expanding Air Cools and Condenses

• Like opening a pressurized bottle of soda
• Air expands and cools
• Water vapor condenses cloud formation

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Solar Heating of the Earth

• Solar energy absorbed unevenly over Earths
  surface why is air rising?
• Energy absorbed / unit surface area varies with
• Angle of the Sun
• Reflectivity of the surface (i.e., ice versus
  ocean)
• Transparency of the atmosphere (i.e. clouds)

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Solar Insolation Variations with Latitude
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Solar Heating of the Earth

• Sunlight heats the ground more intensely in the
  tropics than near poles

July
January
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Solar Heating and Seasons

• Seasons are caused by Earths 23.5 tilt

http//astro.unl.edu/naap/motion1/animations/seaso
ns_ecliptic.html
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Solar Heat Energy

• Equator absorbs more heat from the sun than it
  radiates away
• Polar regions radiates much more heat than they
  absorb from the sun
• Energy in at equator and heat out at poles
• Heat transfer from
• E.g. Equator isnt that hot Poles arent that
  cold
• Evidence that the atmosphere (2/3) and oceans
  (1/3) redistribute heat (wind and ocean currents)
• Convective heat transfer moderates Earth climate

http//oceanmotion.org/html/resources/solar.htmvi
shead
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Convective Heat

• Convective heat transfer models Earth climate
• Heated air expands and rises, then cools and sinks

Equator
Poles
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Atmospheric Circulation
Cold, more dense air sinks near the Poles
Warm, less dense air rises near the Equator
Cold, more dense air sinks near the Poles
Wind from the north
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Actual Atmospheric Circulation

• Air rises and sinks
• More than one convection cell
• Earth spins once per day that amounts to a speed
  for us at the surface of Earth of 100s of miles/
  hour
• Coriolis Effect

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Coriolis Effect Movies
http//earthsciweb.org/GeoMod/index.php?titleCori
olis
http//science.nasa.gov/science-news/science-at-na
sa/2004/23jul_spin/
http//ww2010.atmos.uiuc.edu/28Gh29/guides/mtr/f
w/gifs/coriolis.mov
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The Coriolis Effect on Earth

• Surface velocity increases from poles to equator
• Points on the equator must move faster than
  points near the poles to go around once a day
• Latitude velocity differences land to curving
  paths
• Northern hemisphere deflected to right

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The Coriolis Effect

• Strength of Deflection varies with latitude
• Maximum at the poles
• Zero(!) at equator
• Faster a planet rotates, the stronger the
  Coriolis effects
• The larger the planet, the stronger the Coriolis
  effects (Jupiter spins once every 10 hours)

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Hurricanes

• A storm with lots of clouds has rising air thus
  low-pressure at the surface!
• Converging air sets up counter-rotation
  (cyclonic)

Spinning clockwise Bending to the right
Spinning counter clockwise Bending to the left
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Hurricanes Low Pressure

• Hurricane is rising and already has moisture in
  it
• Low pressure system at the surface air rising
  so that means air is being sucked in at the base
• Arrows get defected by Coriolis to the right
• Set up a counter clockwise circulation in the
  northern hemisphere

L
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High Pressure

• Air sinks and compresses and it gets warmer and
  dry
• See clear air not clouds
• Pushes air away
• Rotate clockwise in northern hemisphere

H
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Atmospheric Circulation

• Sinking air at 30 deserts
• Easterly winds trade winds
• Westerly winds at 30 and 60

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Atmospheric Circulation

• 3 convection cells in each hemisphere
• Each cell 30 latitudinal width
• Veritcal Motions
• Rising Air 0 and 60 Latitude
• Sinking Air 30 and 90 Latitude
• Horizontal Motions
• Zonal winds flow nearly along latitude lines
• Zonal winds within each cell band
• DUE to DEFLECTIONS BY CORIOLIS!

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Sea Breeze

• Land warms fastest during the day. Air during the
  day expands and rises
• Ocean surface temperature changes slowly. Air
  cools and becomes more dense, sinks then begins
  to rise over the land.
• Result wind from sea towards land

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Land Breeze

• Land cools fastest at night. Low heat capacity.
  Air contracts and sinks
• Ocean surface temperature changes slowly. Air is
  pushed away and up by cooler denser land air.
• Result wind from land towards sea

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Marine Layer

• Cold waters, warm air think cloud layer on ocean
  surface
• Subtropics H pressure, regional subsidence
• Cloud layer flows onto land at night
• Evaporates over land by day

LAND
OCEAN
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Marine Layer

• Cold waters, warm air think cloud layer on ocean
  surface
• Subtropics H pressure, regional subsidence
• Cloud layer flows onto land at night
• Evaporates over land by day

LAND
OCEAN
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Marine Layer

• Cold waters, warm air think cloud layer on ocean
  surface
• Subtropics H pressure, regional subsidence
• Cloud layer flows onto land at night
• Evaporates over land by day

LAND
OCEAN
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Marine Layer

• Cold waters, warm air think cloud layer on ocean
  surface
• Subtropics H pressure, regional subsidence
• Cloud layer flows onto land at night
• Evaporates over land by day

LAND
OCEAN
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Marine Layer

• Cold waters, warm air think cloud layer on ocean
  surface
• Subtropics H pressure, regional subsidence
• Cloud layer flows onto land at night
• Evaporates over land by day

LAND
OCEAN