Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of...

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

Transcript of Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of...

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

Ocean circulation

Arnaud Czaja

1. Ocean and Climate

2. Key observations

3. Mechanisms of ocean-atmosphere coupling

Page 2: 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)

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

Ha Ho

+

Poleward energy transport

=

Net energy loss at top-of-the atmosphere

Imbalance between and = energy (heat) storage

Page 4: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Poleward heat transport and storage are small…

oaoP HHPWRS ,120)1( 2

Energy exchanged at top-of-atmosphere :

Planetary albedo Solar constant

Page 5: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

SeasonalHeat storage

)(10 A

o

SPW

dzdycTdxt

S

Q5

Page 6: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Bjerknes’ (1964) monograph. Data from Sverdrup (1957) & Houghton (1954)

Ha+Ho

Ha

Ho

PWdaycalunit 5.0/101 19

No

rth

wa

rd h

eat

tra

nsp

ort

EquatorPole

Heat transport: a long history of measurements…

Page 7: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Vonder Haar & Oort, JPO 1973.

PWyrcalunit 3.1/101 22

30N 50N 70N10N

No

rth

wa

rd h

eat

tra

nsp

ort

Ho

Ha

Ha+Ho

GERBEapproved!

Page 8: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Poleward heat transport at 24ºN

Pacific 0.76 +/- 0.3 PW

Atlantic 1.2 +/- 0.3 PW

Atlantic+Pacific 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 Earth’s budget”.

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

NB: 1PW = 10^15 W

Page 9: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Trenberth & Caron, 2001

GERBEapproved!

(ask more to Chris D.!)

Page 10: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Ha+Ho

Ha

Ho

Wunsch, JCl. 2005.

GERBEapproved!

Page 11: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Ganachaud & Wunsch, 2003

Page 12: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Sometimes effects of heat storage and transport are hard to

disentangle

• Is the Gulf Stream responsible for “mild” European winters?

Page 13: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

“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 windsof 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 evergreenrobes; while in the same latitude, on this side, the coasts of Labrador are fastbound in fetters of ice.”

Maury, 1855.

Eddy surface airtemperature from NCAR reanalysis(January, CI=3K)

WARM!

COLD!

Lieutenant Maury “The Pathfinder of the Seas”

Page 14: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

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

FseaairS

OOO QQt

ThC

Atmosphere

seaairQ

FQ

Page 15: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Seager et al. (2002)

Q3

Page 16: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Heat storage and Climate changeThe surface warming due to +4Wm-2 (anthropogenicforcing) 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 todownload and run the model :

http://sp.ph.ic.ac.uk/~arnaud

Page 17: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Ensemble mean model resultsfrom the IPCC-AR4 report

Q1

Page 18: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Strength of ocean overturning at 30N (A1B Scenario + constant after yr2100)

Q4

Page 19: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Part II

Some key oceanic observations

Page 20: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

World Ocean Atlas surface temperature

ºC

Page 21: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.
Page 22: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Thermocline

Page 23: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

World Ocean Atlas Salinity (0-500m)

psu

Page 24: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

The “great oceanic conveyor belt”

Page 25: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

• Temperature No heat exchange, only pressure effects.

• Salinity. No phase change in the range of observed concentration.

The ocean is conservative below the surface (≈100m) layer

Page 26: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Conservative nature of the ocean

50km 10km 2km

Spatial variations oftemperature and salinityare similar on scales fromseveral hundreds of kms to a few kms.

Salinity on 1027.6 kg/m3 surface

Ferrari & Polzin (2005)

Page 27: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Matsumoto, JGR 2007

Page 28: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

“Circulation” scheme

Page 29: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Broecker, 2005NB: 1 Amazon River ≈ 0.2 Million m3/s

Q6

Page 30: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

“Circulation” scheme

Two “sources” of deep water:

NADW: North Atlantic Deep Water

AABW: Antarctic Bottom Water

Williams & Follows (2009)

Page 31: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

In – situ velocity measurements

Location of “long”(~2yr) currentmeters

Dep

th

Amplitude oftime variability

From Wunsch (1997, 1999)NB: Energy at period < 1 day

was removed

Page 32: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

1 yr

NB: Same velocity vectors but rotated

Moorings in the North Atlantic interior (28N, 70W = MODE)

Schmitz (1989)

(ask more to Ute and Chris. O.!)

Page 33: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Direct ship observations

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

Page 34: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Surface currents measured from Space

y

Pfu

o

1

Time mean sea surface height Standard deviation of sea surface height

“Geostrophic balance”

Page 35: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Momentum balance

East to westacceleration

North

East

Rotationrate f/2

East to westdeceleration

f V up

NB: f = 2 Ω sinθ

Page 36: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Geostrophic balance!

East to westacceleration

North

East

Rotationrate f/2

East to westdeceleration

f V up

HighPressure

LowPressure

Page 37: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

10-yr average sea surface height deviation from geoid

Subtropical gyres

Page 38: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

10-yr average sea surface height deviation from geoid

Antarctic Circumpolar Current

Subpolar gyres

Page 39: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

ARGO floats (since yr 2000)

Coverage by depths

Coverage by lifetime

T/S/P profiles every 10 days

Page 40: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Sv2010max

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

136101 smSv

From Wunsch (2000)

Overturning Streamfunction(Atlantic only)

Page 41: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

RAPID – WATCH array at 26N

Q2

Page 42: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

RAPID – WATCH array at 26N

14 m

illion

s £

Page 43: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.
Page 44: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

The movie…

Page 45: Ocean circulation Arnaud Czaja 1. Ocean and Climate 2. Key observations 3. Mechanisms of ocean-atmosphere coupling.

Friday’s session