Transcript No Slide Title

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
What drives the global wind patterns?
Warm, moist air rising at low latitudes
Cold, dry air sinking at higher latitudes
Fig. 6-7
If the earth
were NOT
rotating,
convection
cells in the
atmosphere
would look
like this.
http://ww2010.atmos.uiuc.edu/
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 earth’s rotation…
90˚
0 km/hr
60˚
800 km/hr
30˚ 1400 km/hr
0˚ 1600 km/hr
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?
Student animations CD-ROM
Coriolis effect animations
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
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.
Fig. 6-7
If the earth
were NOT
rotating,
convection
cells in the
atmosphere
would look
like this.
GLOBAL WIND SYSTEM
Major zones
Trade Winds
Westerlies
Polar Easterlies
1. Convection Cells
Occur at the Global scale, the continental
scale, and the local scale
Land/Ocean surface
Convergent & divergent zones between cells :
•Convergent -- air masses come together + rise
•Divergent -- sinking air comes down and
spreads out
Descending air:
–high atm. Pressure, dry air
•Ascending air:
–low atm. Pressure, rising moist air, high rainfall
1. Convection Cells
Occur at the Global scale, the continental
scale, and the local scale
Earth surface
Wind patterns, cont’d
-- Air vs. land Temperature Contrasts:
Seasonal heating/cooling cycles
Daily
“
/ “
“
•Oceans and lakes -- little T change
•Land areas -- greater T change
Example 1. Convection in coastal areas
Daily cycle of winds in many places:
(think Miami Beach)
Day: onshore winds
Night: offshore winds
Day
Night
San Francisco in the summer:
Leave your shorts at home!
•Land heats upair rises
•Onshore winds
bring warm, moist air
over cool water
(upwelling)
•This creates Fogmoves inland
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
Summer (Wet)
Winter (Dry)
Summer
Winter
3. Seasonal changes in H and L pressure
zones over continents and oceans
Ocean
Land
Ocean
Summer- Where’s the Low Pressure Area?
Winter
Ocean
Land
Ocean
Where’s the High Pressure Area?
Winter:
Low Pressure areas over oceans
High …..
continents
Winter:
Low Pressure areas over oceans
High …..
continents
Fig. 6-11
January
January
Summer:
High Pressure areas over oceans
Low ….
continents
4. Winds circle around low/high pressure zones:
Coriolis effect:
Northern Hemisphere:
•Clockwise around H’s
•Counterclockwise
around L’s
•These motions are
superimposed on the
Trades, Westerlies, etc.
4 Jan., 2008
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
Summer
Winter