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

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

3. –see Raymond’s lectures
Source / sink flows
–see Raymond’s lectures
“Basin”
“Channel”
No distinction between
Ocean & Atmosphere…

4. 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)

5. 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).

6. Outline
The energy constraint
Basin dynamics
Channel dynamics

7. The energy constraint

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

9. Assume infra-red radiation and albedo is uniform Observations
ASR IR
Assume infra-red
radiation and albedo
is uniform
Observations
Stone, 1978.

10. The energy constraint

11. The energy constraint
Poleward motion
in ocean & atmosphere

12. Basin: Northern Oceans, Atmosphere
Background
Geostrophic mass transport calculation
Heat transport
Complications…

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

14. 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

15. More recent section
along the `great tongue’

18. The “great oceanic conveyor belt”

19. The “great oceanic conveyor belt”

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

21. Atlantic ocean’s meridional overturning streamfunction
NB: From an OGCM
constrained by data
(Wunsch, 2000)

22. 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

23. Global “inverse” ocean circulatioin and heat transport
Ganachaud and Wunsch, 2003

24. RAPID – WATCH array at 26N

25. RAPID array calculation

26. RAPID array calculation

27. Blackboard calculations…

28. Heat Transport Up
Warm water
North
Cold water
26N
East

29. 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

30. Are there basins in the atmosphere?Z
Density profile
H~7km X
OCEAN
ATMOSPHERE

31. Different situation in the Tropics
Trade wind
inversion
2-3km
… “isolated” low level layer

32. East-African Highlands & the Indian Monsoon
Orography
Northward flow across the equator

33. Low level winds climatology (June-August)
ERA40 Atlas

34. Channel: Atmosphere, Southern Ocean
How to satisfy the energy constraint
In a geometry in which <dP/dx> = 0?
Hadley cell
Oceanic & atmospheric eddies

35. Zonally averaged atmospheric circulation (annual mean)
~100Sv
NB: Ocean: ~10-20Sv

36. 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

37. Zonally averaged atmospheric circulation (annual mean)Ω Eq
df/dy max
at equator
Frictional
effects
dominate

38. Zonally averaged atmospheric circulation (annual mean)
Inertial
effects
dominate

39. Critical (moist) temperature distributions leading to the onset of
Hadley cell
Emanuel (1995)

40. Poleward heat transport in Hadley cell –see Q3
High gz
Low gz

41. Eumetsat/MetOffice infrared picture (daily composite)

42. 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

43. Ocean eddies: the Movie

44. Ocean eddy heat transport from a ¼ º ocean GCM
Total heat
transport
Eddy
heat
transport
From Jayne & Marotzke (2002)

45. P T V “Shallow” Ocean (heat trspt ≠0) “Deep” Ocean (heat trspt=0)
Height V
Longitude