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Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling. Part I Ocean and Climate (heat transport and storage). Net energy loss at top-of-the atmosphere. =. +. Poleward energy transport. Ha. Ho.

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Presentation Transcript
slide1
Ocean circulationArnaud Czaja1. Ocean and Climate2. Key observations3. Mechanisms of ocean-atmosphere coupling
slide3

Net energy loss at

top-of-the atmosphere

=

+

Poleward energy

transport

Ha

Ho

Imbalance between and

= energy (heat) storage

poleward heat transport and storage are small
Poleward heat transport and storage are small…

Energy exchanged at

top-of-atmosphere :

Planetary albedo

Solar constant

slide7

Ha+Ho

Ha

Northward heat transport

Ho

70N

50N

10N

30N

Vonder Haar & Oort, JPO 1973.

GERBE

approved!

slide8

NB: 1PW = 10^15 W

“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 Earth’s budget”.

Hall & Bryden, 1982; Bryden et al., 1991.

slide9

GERBE

approved!

(ask more to Chris D.!)

Trenberth & Caron, 2001

slide10

GERBE

approved!

Ha+Ho

Ho

Ha

Wunsch, JCl. 2005.

sometimes effects of heat storage and transport are hard to disentangle
Sometimes effects of heat storage and transport are hard to disentangle
  • Is the Gulf Stream responsible for “mild” European winters?
slide13

WARM!

COLD!

Eddy surface air

temperature from

NCAR reanalysis

(January, CI=3K)

“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”

model set up seager et al 2002
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

slide15

Q3

Seager et al.

(2002)

heat storage and climate change
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

the ocean is conservative below the surface 100m layer
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.
conservative nature of the ocean

Salinity on 1027.6 kg/m3 surface

Conservative nature of the ocean

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)

slide29

Q6

Broecker, 2005

NB: 1 Amazon River ≈ 0.2 Million m3/s

circulation scheme1
“Circulation” scheme

Two “sources” of deep water:

NADW: North Atlantic

Deep Water

AABW: Antarctic Bottom

Water

Williams & Follows (2009)

in situ velocity measurements
In – situ velocity measurements

Amplitude of

time variability

Location of “long”

(~2yr) currentmeters

Depth

NB: Energy at period < 1 day

was removed

From Wunsch (1997, 1999)

slide32

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)

slide33

Direct ship

observations

NB: 1m/s = 3.6kmh = 2.2mph = 1.9 knot

surface currents measured from space
Surface currents measured from Space

“Geostrophic balance”

Standard deviation of sea surface height

Time mean sea surface height

momentum balance
Momentum balance

Rotation

rate f/2

East to west

acceleration

f V

East to west

deceleration

up

North

NB: f = 2 Ω sinθ

East

geostrophic balance
Geostrophic balance!

Rotation

rate f/2

High

Pressure

Low

Pressure

East to west

acceleration

f V

East to west

deceleration

up

North

East

10 yr average sea surface height deviation from geoid1
10-yr average sea surface height deviation from geoid

Subpolar gyres

Antarctic Circumpolar

Current

argo floats since yr 2000
ARGO floats (since yr 2000)

T/S/P profiles every 10 days

Coverage

by lifetime

Coverage

by depths

slide40

All in-situ observations can be interpolated dynamically using numerical ocean models

Overturning

Streamfunction

(Atlantic only)

From Wunsch (2000)

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