Ocean%20circulation%20Arnaud%20Czaja%201.%20Ocean%20and%20Climate%202.%20Key%20observations%203.%20Key%20physics

1
Ocean circulationArnaud Czaja1. Ocean and
Climate2. Key observations3. Key physics
2
Part IOcean and Climate(heat transport and
storage)
3
Net energy loss at top-of-the atmosphere


Poleward energy transport
Ha
Ho
Imbalance between and energy (heat)
storage
4
Poleward heat transport and storage are small
Energy exchanged at top-of-atmosphere
Planetary albedo
Solar constant
5
SeasonalHeat storage
Q5
6
Bjerknes (1964) monograph. Data from Sverdrup
(1957) Houghton (1954)
Heat transport a long history of measurements
HaHo
Ha
Northward heat transport
Ho
Equator
Pole
7
HaHo
Ha
Northward heat transport
Ho
70N
50N
30N
10N
Vonder Haar Oort, JPO 1973.
GERBE approved!
8
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.
9
GERBE approved!
(ask more to Chris D.!)
Trenberth Caron, 2001
10
GERBE approved!
HaHo
Ho
Ha
Wunsch, JCl. 2005.
11
Ganachaud Wunsch, 2003
12
Sometimes effects of heat storage and transport
are hard to disentangle

• Is the Gulf Stream responsible for mild
  European winters?

13
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
14
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
15
Q3
Seager et al. (2002)
16
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
17
Ensemble mean model resultsfrom the IPCC-AR4
report
Q1
18
Strength of ocean overturning at 30N (A1B
Scenario constant after yr2100)
Q4
19
Part IISome key oceanic observations
20
World Ocean Atlas surface temperature
ºC
21
(No Transcript)
22
Thermocline
23
World Ocean Atlas Salinity (0-500m)
psu
24
The great oceanic conveyor belt
25
The ocean is conservative below the surface
(100m) layer

• Temperature Not changed by absorption/emission of
  photons.
• Salinity. No phase change in the range of
  observed concentration.

26
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)
27
Matsumoto, JGR 2007
28
Circulation scheme
29
Circulation scheme
Two sources of deep water NADW North
Atlantic Deep Water AABW
Antarctic Bottom Water
Williams Follows (2009)
30
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)
31
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)
32
Direct ship observations
NB 1m/s 3.6kmh 2.2mph 1.9 knot
33
Surface currents measured from Space
Geostrophic balance
Standard deviation of sea surface height
Time mean sea surface height
34
Momentum balance
Rotation rate f/2
East to west acceleration
f V
East to west deceleration
up
North
NB f 2 O sin?
East
35
Geostrophic balance!
Rotation rate f/2
High Pressure
Low Pressure
East to west acceleration
f V
East to west deceleration
up
North
East
36
10-yr average sea surface height deviation from
geoid
Subtropical gyres
37
10-yr average sea surface height deviation from
geoid
Subpolar gyres
Antarctic Circumpolar Current
38
ARGO floats (since yr 2000)
T/S/P profiles every 10 days
Coverage by lifetime
Coverage by depths
39
All in-situ observations can be interpolated
dynamically using numerical ocean models
Overturning Streamfunction (Atlantic only)
From Wunsch (2000)
40
RAPID WATCH array at 26N
Q2
41
RAPID WATCH array at 26N
14 millions
42
The movie
43
Part IIIKey physics
44
Because T is conserved by fluid motion the
temperature structure simply reflects transport
by waves and mean currents
Downward heat transport
Upward heat transport

Sea surface
Zo
No internal heat source/sink
Z
Ocean bottom
X, Y
45
This simply happens when warm water goes up or
cold water goes down
Downward heat transport
Upward heat transport

Sea surface
Zo
No internal heat source/sink
Z
Ocean bottom
X, Y
46
This happens when warm water goes down or cold
water goes up
Downward heat transport
Upward heat transport

Sea surface
Zo
No internal heat source/sink
Z
Ocean bottom
X, Y
47
Requires mechanical forcing (winds/tides)!
Downward heat transport
Upward heat transport

Sea surface
Zo
No internal heat source/sink
Z
Ocean bottom
X, Y
48
Historical view
Sea surface
Zo
Z
Ocean bottom
X, Y
49
Historical view
Conveyor-belt upwelling/downwelling
Sea surface
Zo
Z
Ocean bottom
X, Y
50
Q6
Broecker, 2005
NB 1 Amazon River 0.2 Million m3/s
51
Historical view
C
W
z
x,y
Small scale wave breaking
Conveyor-belt upwelling/downwelling

Sea surface
Zo
Z
Ocean bottom
Q7
X, Y
52
Internal waves

• Waves inducing displacement of density surfaces
  whose restoring mechanism is gravity.
• Frequency of linear wave is between the Coriolis
  frequency f (T10h in midlatitudes) and the
  buoyancy frequency N (T10mn in upper ocean
  100mn in deep ocean)

53
Small scale wavebreaking strength
(Naveira-Garabato, 2006)
54
Numerical model results
Conveyor belt strength
-2ºX2º horizontal resolution -Single basin -No
wind -Surface heating-cooling -Small scale
wave breaking parameterised by a
constant diffusivity coefficient K
2/3
K
slope
(Sv)
(cm²/s)
From Vallis (2000)
55
Historical view
z
x,y
Small scale wave breaking
Conveyor-belt upwelling/downwelling

Sea surface
Zo
Z
Ocean bottom
X, Y
56
Historical view
A very bold statement! -Is the ocean
circulation driven by tides? -Can hurricanes
drive the conveyor belt?
z
x,y
Small scale wave breaking
Conveyor-belt upwelling

Sea surface
Zo
Z
Ocean bottom
X, Y
57
Historical view
10,000km
km
z
x,y
Small scale wave breaking
Conveyor-belt upwelling

Sea surface
Zo
Z
Ocean bottom
X, Y
58
In-situ observations are dominated by a
meso-scale (100km)
KE spectra (surface)
Infrared based surface temperature
59
Alternative paradigm
Zo
Z
Ocean bottom
X, Y
60
Alternative paradigm
Meso-scale waves upwelling/downwelling
Zo
Z
Ocean bottom
X, Y
61
Alternative paradigm

Wind forced pumping
Meso-scale waves upwelling/downwelling
Zo
Z
Ocean bottom
X, Y
62
Momentum balance
Rotation rate f/2
East to west acceleration
f V
East to west deceleration
up
North
East
63
Ekman balance!
Rotation rate f/2
East to west acceleration
Windstress
f V
East to west deceleration
up
North
East
64
Wind forced pumping
Westerly winds ( 45º latitude)
Trade winds (10º latitude)
X
Sea surface
Ekman layer
Upwelling
Upwelling
Downwelling
65
Alternative paradigm

Wind forced pumping
Meso-scale waves upwelling/downwelling
Zo
Z
Ocean bottom
X, Y
66
Lab experiments
-Rotating tank -Pump warm fluid down from a
more slowly rotating disk
Depth of warm lens
Wind strength
From Marshall (2003)
67
Results from realistic coupled models

• Upper ocean 0-2500m,
• wT by the resolved
• flow is downward and
• balanced by upward
• heat flux due to eddy
• advection.
• Abyssal ocean below
• 2500m, very weak but
• positive upward heat
• transport by the
• resolved flow, opposed
• by downward diffusive
• heat transport.

NB gt0 means upward
Gnanadesikan et al. (2007)
68
Fridays session