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Rotating Fluid -Part II A “GFD view” of the Ocean and the Atmosphere (a follow up Raymond’s Lectures) Arnaud Czaja

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**–see Raymond’s lectures**

Source / sink flows –see Raymond’s lectures “Basin” “Channel”

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**–see Raymond’s lectures**

Source / sink flows –see Raymond’s 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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**impinging at low than high**

The energy constraint Geometry: more energy impinging at low than high latitudes

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**Assume infra-red radiation and albedo is uniform Observations**

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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**oxygen distribution at 2500m**

A classic: oxygen distribution at 2500m (from Wüst, 1935).

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**oxygen distribution at 2500m**

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 ocean’s 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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**yields Ho≈1PW as required**

Heat Transport Up Mo ≈ 20 Sv & Δθ≈10K yields Ho≈1PW as required Warm water North Cold water 26N East

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**Are there basins in the atmosphere?**

Z Density profile H~7km 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 <dP/dx> = 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 Zonally symmetric motions are the key energy carriers in the Tropics Transient eddies Stationnary eddies Axisymmetric motions

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**Zonally averaged atmospheric circulation (annual mean)**

Ω 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 Eddy motions are the key energy carriers in midlatitudes 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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**P T V “Shallow” Ocean (heat trspt ≠0) “Deep” Ocean (heat trspt=0)**

Height V Longitude

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