Rotating Fluid -Part II A

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Rotating Fluid -Part IIA GFD view of the
Ocean and the Atmosphere (a follow up Raymonds
Lectures)

• Arnaud Czaja

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Source / sink flows see Raymonds lectures
Basin
Channel
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Source / sink flows see Raymonds lectures
Basin
Channel
No distinction between Ocean Atmosphere
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Central idea

• Constraint 1 Ocean Atmosphere are rapidly
  rotating fluids geostrophy is the leading order
  dynamics.
• Constraint 2 The two fluids must transport
  energy poleward (cold parcels move equatorward
  and warm parcels poleward)

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Central idea

• This brings a key distinction between basins
  (ocean) and channel (atmosphere)s geometry
• Basins walls provide dP/dx and a large
  scale (eddy free) geostrophic heat transport is
  possible.
• Channels no zonally integrated dP/dx and the
  heat transport must involve eddies and / or
  ageostrophic effects (e.g., Hadley cell).

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Outline

• The energy constraint
• Basin dynamics
• Channel dynamics

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The energy constraint
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The energy constraint
Geometry more energy impinging at low than high
latitudes
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ASR
IR
Assume infra-red radiation and albedo is uniform
Observations
Stone, 1978.
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The energy constraint
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The energy constraint
Poleward motion in ocean atmosphere
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Basin Northern Oceans, Atmosphere

• Background
• Geostrophic mass transport calculation
• Heat transport
• Complications

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A classic oxygen distribution at 2500m (from
Wüst, 1935).
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A classic oxygen distribution at 2500m (from
Wüst, 1935).
-Spreading from high latitude North Atlantic
source region -Large spatial scale of tongue
considering the narrowness of ocean currents
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More recent section along the great tongue
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The great oceanic conveyor belt
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The great oceanic conveyor belt
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Broecker, 2005
NB 1 Amazon River 0.2 Million m3/s
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Atlantic oceans meridional overturning
streamfunction
NB From an OGCM constrained by data (Wunsch,
2000)
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Can we measure the ocean circulation in basins
using the Geostrophic calculation?

• All you need is the thermal wind

Coriolis parameter
East-west density gradient
North-South velocity Gradient with height
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Global inverse ocean circulatioin and heat
transport
Ganachaud and Wunsch, 2003
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RAPID WATCH array at 26N
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RAPID array calculation
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RAPID array calculation
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Blackboard calculations
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Heat Transport
Up
Warm water
North
Cold water
26N
East
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Heat Transport
Up
Mo 20 Sv ??10K yields Ho1PW as required
Warm water
North
Cold water
26N
East
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Are there basins in the atmosphere?
Z
Density profile H7km
X
OCEAN
ATMOSPHERE
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Different situation in the Tropics
Trade wind inversion
2-3km
isolated low level layer
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East-African Highlands the Indian Monsoon
Orography
Northward flow across the equator
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Low level winds climatology (June-August)
ERA40 Atlas
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Channel Atmosphere, Southern Ocean
How to satisfy the energy constraint In a
geometry in which ltdP/dxgt 0?

• Hadley cell
• Oceanic atmospheric eddies

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Zonally averaged atmospheric circulation (annual
mean)
100Sv
NB Ocean 10-20Sv
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Zonally symmetric motions are the key energy
carriers in the Tropics
Total
Transient eddies
Stationnary eddies
Axisymmetric motions
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Zonally averaged atmospheric circulation (annual
mean)
O
Eq
df/dy max at equator
Frictional effects dominate
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Zonally averaged atmospheric circulation (annual
mean)
Inertial effects dominate
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Critical (moist) temperature distributions
leading to the onset of Hadley cell
Emanuel (1995)
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Poleward heat transport in Hadley cell see Q3
High gz
Low gz
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Eumetsat/MetOffice infrared picture (daily
composite)
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Eddy motions are the key energy carriers in
midlatitudes
Total
Transient eddies
Stationnary eddies
Axisymmetric motions
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Ocean eddies the Movie
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Ocean eddy heat transport from a ¼ º ocean GCM
Total heat transport
Eddy heat transport
From Jayne Marotzke (2002)
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Shallow Ocean (heat trspt ?0)
Deep Ocean (heat trspt0)
P
T
Height
V
Longitude
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