Class 22 -- The Oceans

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Class 22 -- The Oceans

• ATMOSPHERE CIRCULATION AND WINDS
• Coriolis effect
• Prevailing winds and vertical circulation
• Factors modifying these winds
• -- Differential heating of land and sea

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What drives the global wind patterns? Warm,
moist air rising at low latitudes Cold, dry air
sinking at higher latitudes
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Fig. 6-7 If the earth were NOT rotating,
convection cells in the atmosphere would look
like this.
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http//ww2010.atmos.uiuc.edu/
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Coriolis effect Winds traveling long distances
are deflected turn to the right in Northern
Hemis. turn to the left in Southern Hemis. Why?
--Speed due to earths rotation 90 0
km/hr 60 800 km/hr 30 1400 km/hr 0 1600
km/hr
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Missile fired exactly southward from the north
pole. Viewed from space, the missile follows a
straight path....
But a person in Chicago is moving toward the east
at 1000 km/hr.
What does that person see?
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Student animations CD-ROM Coriolis effect
animations
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• Coriolis Effect Practical result
• Things moving long distances on earth tends to be
  deflected by Coriolis force
• Deflection in N hemis. TO THE RIGHT(i.e.,
  right hand turn relative to initial direction)
• in S hemis. TO THE LEFT

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Amount of deflection depends on ... ... time of
travel (how long it moves) ... distance of travel
(how far it moves) Winds are deflected a large
amount- they move for long time periods over long
distances.
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Fig. 6-7 If the earth were NOT rotating,
convection cells in the atmosphere would look
like this.
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GLOBAL WIND SYSTEM Major zones Trade
Winds Westerlies Polar Easterlies
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1. Convection Cells Occur at the Global scale,
the continental scale, and the local scale
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• Convergent divergent zones between cells
• Convergent -- air masses come together rise
• Divergent -- sinking air comes down and spreads
  out

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• Descending air
• high atm. Pressure, dry air
• Ascending air
• low atm. Pressure, rising moist air, high
  rainfall

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1. Convection Cells Occur at the Global scale,
the continental scale, and the local scale
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Wind patterns, contd -- Air vs. land
Temperature Contrasts

• Seasonal heating/cooling cycles
• Daily /
• Oceans and lakes -- little T change
• Land areas -- greater T change

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Example 1. Convection in coastal areas
Daily cycle of winds in many places (think
Miami Beach) Day onshore winds Night
offshore winds
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Day
Night
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San Francisco in the summer Leave your shorts
at home!
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• Land heats up- air rises
• Onshore winds bring warm, moist air over cool
  water (upwelling)
• This creates Fog- moves inland

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2. Seasonal monsoon winds (India, Southeast
Asia)
Same idea, larger scale Summer Hot continent
- rising air above it Creates onshore winds (and
rain) Winter Cold continent, offshore winds
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Summer (Wet)
Winter (Dry)
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Summer
Winter
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3. Seasonal changes in H and L pressure zones
over continents and oceans
Summer- Wheres the Low Pressure Area?
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Winter
Wheres the High Pressure Area?
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Winter Low Pressure areas over oceans High ..
continents
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Winter Low Pressure areas over oceans High ..
continents
January
Fig. 6-11
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January
Summer High Pressure areas over oceans Low .
continents
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4. Winds circle around low/high pressure zones
Coriolis effect

• Northern Hemisphere
• Clockwise around Hs
• Counterclockwise around Ls
• These motions are superimposed on the Trades,
  Westerlies, etc.

4 Jan., 2008
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Hurricanes

• Hot, humid air rising-- Intense LOW PRESSURE
• High Storm tides- sea surface dome in low-P
  center
• Plus wind-driven surface currents
• Flooding of coastal areas

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Summer
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Winter