Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling

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Ocean circulationArnaud Czaja1. Ocean and
Climate2. Key observations3. Mechanisms of
ocean-atmosphere coupling
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Part IOcean and Climate(heat transport and
storage)
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Net energy loss at top-of-the atmosphere


Poleward energy transport
Ha
Ho
Imbalance between and energy (heat)
storage
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Poleward heat transport and storage are small
Energy exchanged at top-of-atmosphere
Planetary albedo
Solar constant
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SeasonalHeat storage
Q5
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Bjerknes (1964) monograph. Data from Sverdrup
(1957) Houghton (1954)
Heat transport a long history of measurements
HaHo
Ha
Northward heat transport
Ho
Equator
Pole
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HaHo
Ha
Northward heat transport
Ho
70N
50N
30N
10N
Vonder Haar Oort, JPO 1973.
GERBE approved!
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NB 1PW 1015 W
Poleward heat transport at 24ºN
Pacific 0.76 /- 0.3 PW
Atlantic 1.2 /- 0.3 PW
AtlanticPacific 2 /- 0.4 PW
Across the same latitude, Ha is 1.7PW. The
ocean therefore can be considered to be more
important than the atmosphere at this latitude
in maintaining the Earths budget.
Hall Bryden, 1982 Bryden et al., 1991.
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GERBE approved!
(ask more to Chris D.!)
Trenberth Caron, 2001
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GERBE approved!
HaHo
Ho
Ha
Wunsch, JCl. 2005.
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Ganachaud Wunsch, 2003
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Sometimes effects of heat storage and transport
are hard to disentangle

• Is the Gulf Stream responsible for mild
  European winters?

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WARM!
COLD!
Eddy surface air temperature from NCAR
reanalysis (January, CI3K)
Every West wind that blows crosses the Gulf
Stream on its way to Europe, and carries with it
a portion of this heat to temper there the
Northern winds of winter. It is the influence of
this stream upon climate that makes Erin
the Emerald Isle of the Sea, and that clothes
the shores of Albion in evergreen robes while in
the same latitude, on this side, the coasts of
Labrador are fast bound in fetters of
ice. Maury, 1855.
Lieutenant Maury The Pathfinder of the
Seas
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Model set-up (Seager et al., 2002)

• Full Atmospheric model
• Ocean only represented as a motionless slab of
  50m thickness, with a specified q-flux to
  represent the transport of energy by ocean
  currents

Atmosphere
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Q3
Seager et al. (2002)
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Heat storage and Climate change
The surface warming due to 4Wm-2
(anthropogenic forcing) is not limited to the
mixed layer How thick is the layer is a key
question to answer to predict accurately the
timescale of the warming.
Ho 50m
Ho 150m
Ho 500m
NB You are welcome to download and run the model
http//sp.ph.ic.ac.uk/arnaud
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Ensemble mean model resultsfrom the IPCC-AR4
report
Q1
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Strength of ocean overturning at 30N (A1B
Scenario constant after yr2100)
Q4
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Part IISome key oceanic observations
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World Ocean Atlas surface temperature
ºC
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Thermocline
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World Ocean Atlas Salinity (0-500m)
psu
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The great oceanic conveyor belt
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The ocean is conservative below the surface
(100m) layer

• Temperature No heat exchange, only pressure
  effects.
• Salinity. No phase change in the range of
  observed concentration.

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Conservative nature of the ocean
Salinity on 1027.6 kg/m3 surface
Spatial variations of temperature and
salinity are similar on scales from several
hundreds of kms to a few kms.
10km
2km
50km
Ferrari Polzin (2005)
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Matsumoto, JGR 2007
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Circulation scheme
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Q6
Broecker, 2005
NB 1 Amazon River 0.2 Million m3/s
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Circulation scheme
Two sources of deep water NADW North
Atlantic Deep Water AABW
Antarctic Bottom Water
Williams Follows (2009)
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In situ velocity measurements
Amplitude of time variability
Location of long (2yr) currentmeters
Depth
NB Energy at period lt 1 day was removed
From Wunsch (1997, 1999)
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Moorings in the North Atlantic interior (28N,
70W MODE)
(ask more to Ute and Chris. O.!)
1 yr
NB Same velocity vectors but rotated
Schmitz (1989)
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Direct ship observations
NB 1m/s 3.6kmh 2.2mph 1.9 knot
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Surface currents measured from Space
Geostrophic balance
Standard deviation of sea surface height
Time mean sea surface height
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Momentum balance
Rotation rate f/2
East to west acceleration
f V
East to west deceleration
up
North
NB f 2 O sin?
East
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Geostrophic balance!
Rotation rate f/2
High Pressure
Low Pressure
East to west acceleration
f V
East to west deceleration
up
North
East
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10-yr average sea surface height deviation from
geoid
Subtropical gyres
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10-yr average sea surface height deviation from
geoid
Subpolar gyres
Antarctic Circumpolar Current
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ARGO floats (since yr 2000)
T/S/P profiles every 10 days
Coverage by lifetime
Coverage by depths
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All in-situ observations can be interpolated
dynamically using numerical ocean models
Overturning Streamfunction (Atlantic only)
From Wunsch (2000)
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RAPID WATCH array at 26N
Q2
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RAPID WATCH array at 26N
14 millions
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The movie
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Fridays session