Ocean circulation and coupling with the atmosphere Arnaud Czaja 1. Ocean heat storage

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Ocean circulation and coupling with the
atmosphereArnaud Czaja1. Ocean heat storage
transport2. Key observations3. Ocean heat
uptake and global warming4. Mechanisms of
ocean-atmosphere coupling
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Part IOcean heat storage and transport
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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
Q4
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Trenberth Caron, 2001
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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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Part IISome key oceanic observations
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World Ocean Atlas surface temperature
ºC
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(No Transcript)
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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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Matsumoto, JGR 2007
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Circulation scheme
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Q5
Broecker, 2005
NB 1 Amazon River 0.2 Million m3/s
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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)
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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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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Part IIIOcean heat uptake and anthropogenic
forcing of climate change
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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. Heat exchanges between the mixed
layer and deeper layers control the timescale of
the surface warming.
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Weak vertical ocean heat transport
Anthropogenic forcing
Net surface ocean heating
Upper ocean cooling via mass exchange with deep
ocean
Upper ocean cooling via diabatic processes
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Large vertical ocean heat transport
Anthropogenic forcing
Net surface ocean heating
Upper ocean cooling via diabatic processes
Upper ocean cooling via mass exchange with deep
ocean
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The Environmental Physics Climate Model
TA1
Heat content (J)
http//www.sp.ph.ic.ac.uk/aczaja/EP_ClimateModel.
html
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Upper (0-750m) ocean heat content vs TOA
imbalance observations
Wong et al (2006)
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Mechanisms of heat exchange between upper and
deep layers

• Wind driven circulation
• pumping down of warm subtropical waters
  upwelling of cold, high latitude waters.
• Buoyancy driven circulations
• sinking of dense water and upwelling of light
  water
• ( overturning circulations eddy driven
  convection).
• Mixing
• isopycnal diffusion and breaking internal
  gravity waves.

Q1
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Ocean heat uptake in wind driven gyres
Williams Follows (2012)

• Global downward ocean heat transport driven by
  winds.
• Strength

Levitus (1988)
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Buoyancy driven circulations and ocean heat
uptake
Cooling

• Total temperature change in the 10th decade after
  2XCO2 (idealised ocean basin)
• Temperature change due to change in ocean
  currents
• Temperature change in absence of change in ocean
  currents.

Xie and Vallis (2011)
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Interior mixing ocean heat uptake
Upward heat flux
Osborne (1998)
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Vertical heat flux (Wm-2)
deeper
Downward heat flux
-100
Equator
South Pole
North Pole
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Motions in the ocean are not isotropic neutral
surfaces

• In the simplest case of a waterworld at rest, a
  fluid parcel does work against the buoyancy force
  when displaced upward or downward. Motions along
  zcst are energetically neutral.

Zh
Z0
Solid Earth
where
Reference density
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Motions in the ocean are not isotropic neutral
surfaces

• In the real ocean, neutral surfaces take the
  shape of a bowl due to the distortion of spheres
  by the seafloor topography, surface heating,
  cooling and winds.

Neutral surfaces in the Atlantic
NB These surfaces can be approximated as
surfaces of constant density (isopycnals).
Neutrally energetic displacements
WOCE A16
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The movie