The Ocean-Atmosphere Connection, Winds & Surface Currents
Geosc040, Lecture 9 Feb 11, 2014 Gimme some Water See web for Extra
Credit Opportunities See web for Extra Credit Opportunities Thanks
to Adam C. Somewhere Beyond The Sea Frank Sinatra Thanks to Steve
P. Ocean Avenue Yellowcard Thanks to Adam R.
Slide 2
Thanks to Kim S. and Bronte A. On-line Assignment (OLA) 4 due
today, OLA 5 due Thursday OLA 4 = OLA 5, Make sure to get 100% on
5. You have two attempts. Highest score counts OLA 6 due on Feb 18
th Homework 2 will be posted tomorrow Read Chapter 7
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Quiz 1 Mean was 79.4. It is now 83.4. I added 4 points to
everyones score. Your score on Angel includes the bonus points. I
add extra credit points, for cell phone recycling, to quiz 1 at the
end. Ill add in the extra credit any time I use quiz 1, when I
calculate your final exam grade, if you decide not to take the
final when I calculate the final grade
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The Ocean-Atmosphere Connection, Winds & Surface Currents
EARTHs ORBIT (elliptical) In 4 easy pieces: Heating, Wind,
Currents, Coriolis,
Slide 5
EARTHs ORBIT (elliptical) SEASONALITY Effects of Earths Axial
Tilt Northern Hemisphere summer (solstice) occurs when tilt is
toward the sun. Systematic variation in solar energy receipt on a
yearly basis is produced by Earth s axial tilt and orbit around the
sun. The Earth is closest to the sun in January
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Seasonal variations, but the equatorial regions receive more
heat YEAR IN and YEAR OUT!
Slide 7
GLOBAL ATMOSPHERIC CIRCULATION (WINDS) Temperature gradients
create pressure differences which drive winds
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GLOBAL ATMOSPHERIC WINDS, PLUS THERMOHALINE CIRCULATION, DRIVE
OCEAN SURFACE CURRENTS
Slide 9
Gulf Stream as an example of a Western Boundary Current
Slide 10
In 4 easy pieces: Heating, Wind, Currents, Coriolis, The
Ocean-Atmosphere Connection, Winds & Surface Currents
Slide 11
Some Strange Doings In order to comprehend the pattern of
surface circulation produced by the global wind systems (responding
to pressure differences), we need to introduce: The Coriolis Effect
(Coriolis Force)
Slide 12
Gustav Why do winds circulate in an organized pattern around
High and Low pressure systems? In the N. Hemisphere winds
circulate: Counterclockwise around low pressure Clockwise around
high pressure
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Coriolis Considerations angular rotation rate is same but
velocity changes with circumference as a function of latitude
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Coriolis Considerations Quito travels a greater distance during
a day than does Buffalo What happens if you move something (wind!)
from Quito to Buffalo? Think about inertia!
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Coriolis Considerations Think about inertia!
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Coriolis Considerations Coriolis Effect ( Force ) moves things
to the right in the Northern hemisphere and to the left in the
Southern hemisphere Angular Momentum and Inertia of wind and water
currents mean that they do not travel in a straight line on
Earth
Slide 17
North Atlantic Gyre Effect of winds and coriolis Download this
file to see the video: http://www.youtube.com/
watch?v=_36MiCUS1ro
Slide 18
North Atlantic Gyre Effect of winds and coriolis Download this
file to see the video: http://www. youtube.co m/watch?v =_36MiCU
S1ro
Slide 19
Coriolis Considerations angular rotation rate is same but
velocity changes with circumference, which varies with latitude
Coriolis effect arises from conservation of momentum (angular
momentum)
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Coriolis Considerations In the northern hemisphere: Coriolis
Effect ( Force ) moves things to the right of their initial
trajectory
Slide 21
Coriolis Considerations In the northern hemisphere: Coriolis
Effect ( Force ) moves things to the RIGHT of their initial
trajectory
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Coriolis Considerations In the Southern hemisphere Coriolis
Effect moves things to the LEFT OF THEIR INITIAL TRAJECTORY
Slide 23
North Atlantic Gyre Effect of winds and coriolis
Slide 24
Credit: NASA In the northern hemisphere: Coriolis Effect (
Force ) moves things to the right of their initial trajectory In
the Southern hemisphere Coriolis Effect moves things to the LEFT OF
THEIR INITIAL TRAJECTORY
Slide 25
The Coriolis effect causes objects in motion to veer off their
initial trajectories. Which of the following is/are true: A.Objects
are deflected to the right in the northern hemisphere B.Objects are
deflected to the left in the northern hemisphere C.Winds blowing
from south to north in the northern hemisphere are deflected to the
east. D.Winds blowing from south to north in the northern
hemisphere are deflected to the west. E.A and C
Slide 26
The Coriolis effect. Which of the following are true: A.Winds
blowing to the south in the Southern hemisphere are deflected to
the east. B.Winds blowing to the north in the Southern hemisphere
are deflected to the west. C.Winds blowing to the north in the
Southern hemisphere just go straight D.A and B E.None of the
above
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Which statement(s) is/are true about global wind patterns? A)
Low pressure develops at 30 N and 30 S B) Easterly winds between
the Equator and 30 N are caused by surface winds that blow south
and are deflected by the Coriolis effect C) High pressure develops
over the equator because of rising air D) Winds blow directly from
the equator to the poles along the surface in one large convection
cell E) All of the above
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Strange Doings Coriolis acceleration a c where is the angular
velocity (magnitude equal to the rotation rate ) and v is the
velocity of the object in the rotating systemangular velocity The
Coriolis acceleration may be multiplied by the mass of the relevant
object to produce the Coriolis force: F c = m a c See:
http://en.wikipedia.org/wiki/Coriolis_effect
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North Atlantic Gyre Effect of winds and coriolis Variation of
Coriolis with latitude causes differences between Eastern and
Western Boundary Currents
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Lets look at the Gulf Stream as an example of a Western
Boundary Current formed in this way WBC EBC
Slide 31
Gyres and Sea-surface Topography The Hill is a balance between
Coriolis and Pressure
Slide 32
Sea-Surface Height Differences Differences of up to 1 meter
maintained by wind Notice the pileup of water in Western Pacific
warm pool Also note the pileup around Bermuda in the N. Atlantic
gyre
Slide 33
More Strange Doings In order to comprehend the pattern of
surface circulation produced by the global wind systems (responding
to pressure differences), we need to introduce another issue: The
Ekman Spiral
Slide 34
Wind Wind moves surface water (friction) Velocity of water
decreases with depth because of friction between water molecules
Let s now examine how winds drive surface ocean circulation
Surface
Slide 35
Effects of friction on Surface Currents In the northern
hemisphere water at the sea surface moves to the right of the wind
direction
Slide 36
Wind currents drive ocean surface currents Energy from wind
transferred to water by friction Then, due to the Coriolis Effect:
Overall, the Oceans surface waters (recall pycnocline and deep
water) move, on average, 90 o to the wind direction
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0 30 60 Consider a hypothetical ocean with straight coastlines
In the southern hemisphere water at the sea surface moves to the
left of the wind direction How do global wind patterns influence
ocean surface currents?
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0 30 60 Consider a hypothetical ocean with straight coastlines
Blue arrows show local wind direction at the sea surface Now, think
about local current direction of ocean surface water (yellow
arrows)
Slide 39
Ocean currents form large GYRES 0 30 60 These are a product of
wind direction, the Coriolis effect, and Ekman spiral effects.
Slide 40
Wind-driven circulation Western Boundary Currents Gulf Stream,
Kuroshio, Labrador, Kamchatka (Oyashio) Eastern Boundary Currents
Canary, California Ocean Surface Currents How does this work?
Slide 41
Slide 42
In Earth s southern hemisphere: a) western boundary currents in
the ocean bring warm water southward. b) winds rotate clockwise
around low pressure systems c) winds only blow from north to south.
d) circulation in large scale oceanic gyres is clockwise e) (a) and
(b)
Slide 43
The Coriolis effect causes objects in motion to veer off their
initial trajectories. Which of the following are true: A. Objects
are deflected to the left in the southern hemisphere B. Objects are
deflected to the right in the northern hemisphere C. Winds blowing
from south to north in the northern hemisphere are deflected to the
east. D. Winds blowing from south to north in the southern
hemisphere are deflected to the west. E. All of the above
Slide 44
Which of the following are true: A. Winds blowing to the south
in the Southern hemisphere are deflected to the east. B. Large
scale Gyres in the ocean are surface currents that are not affected
by the Coriolis effect C. Western boundary currents are fast and
narrow because of variations in the Coriolis effect with latitude
D. The Coriolis effect causes water to pile up in the center of
gyres E. All but B.
Slide 45
Example: The Gulf Stream Note these features: Sharp boundaries
of currents (1 & 2) Eddies Warm-core rings (3) Cold-core rings
(4) Labrador Current Gulf Stream This is a map of surface water
temperature Surface currents transport heat toward poles
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Gulf Stream Heat Transfer: Is that all there is to it? OK, warm
water flows toward the poles, but How does heat actually get
transferred?? Two mechanisms: 1) Sensible heat transfer to
atmosphere 2) Latent heat transfer (remember: evaporation-
precipitation?)