Part I Ocean heat storage and transport

1. Ocean circulation and coupling with the atmosphereArnaud Czaja1. Ocean heat storage & transport2. Key observations3. Ocean heat uptake and global warming4. Mechanisms of ocean-atmosphere coupling

2. Part IOcean heat storage and transport

3. Net energy loss at top-of-the atmosphere = + Poleward energy transport Ha Ho Imbalance between and = energy (heat) storage

4. Poleward heat transport and storage are small… Energy exchanged at top-of-atmosphere : Planetary albedo Solar constant

5. SeasonalHeat storage Q4

6. Trenberth & Caron, 2001

7. Ganachaud & Wunsch, 2003

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

9. 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”

10. 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

11. Q3 Seager et al. (2002)

12. Part IISome key oceanic observations

13. World Ocean Atlas surface temperature ºC

15. Thermocline

16. World Ocean Atlas Salinity (0-500m) psu

17. The “great oceanic conveyor belt”

18. Matsumoto, JGR 2007

19. “Circulation” scheme

20. Q5 Broecker, 2005 NB: 1 Amazon River ≈ 0.2 Million m3/s

21. 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)

22. Moorings in the North Atlantic interior (28N, 70W = MODE) 1 yr NB: Same velocity vectors but rotated Schmitz (1989)

23. Direct ship observations NB: 1m/s = 3.6kmh = 2.2mph = 1.9 knot

24. Surface currents measured from Space “Geostrophic balance” Standard deviation of sea surface height Time mean sea surface height

25. 10-yr average sea surface height deviation from geoid Subtropical gyres

26. 10-yr average sea surface height deviation from geoid Subpolar gyres Antarctic Circumpolar Current

27. ARGO floats (since yr 2000) T/S/P profiles every 10 days Coverage by lifetime Coverage by depths

28. All in-situ observations can be interpolated dynamically using numerical ocean models Overturning Streamfunction (Atlantic only) From Wunsch (2000)

29. RAPID – WATCH array at 26N Q2

30. RAPID – WATCH array at 26N 14 millions £

31. Part IIIOcean heat uptake and anthropogenic forcing of climate change

32. Heat storage and Climate change The surface warming due to +4Wm-2 (anthropogenic forcing) is not limited to the mixed layer. Heat exchanges between the mixed layer and deeper layers control the timescale of the surface warming.

33. Weak vertical ocean heat transport Anthropogenic forcing Net surface ocean heating Upper ocean cooling via mass exchange with deep ocean Upper ocean cooling via diabatic processes

34. Large vertical ocean heat transport Anthropogenic forcing Net surface ocean heating Upper ocean cooling via diabatic processes Upper ocean cooling via mass exchange with deep ocean

35. Atmosphere Extra Tropics Ocean Tropics The Environmental Physics Climate Model TA1 Heat content (J) http://www.sp.ph.ic.ac.uk/~aczaja/EP_ClimateModel.html

36. Upper (0-750m) ocean heat content vs TOA imbalance: observations Wong et al (2006)

37. Mechanisms of heat exchange between upper and deep layers • Wind driven circulation pumping down of warm subtropical waters; upwelling of cold, high latitude waters. • Buoyancy driven circulations sinking of dense water and upwelling of light water (= overturning circulations + eddy driven + convection). • Mixing isopycnal diffusion and breaking internal gravity waves. Q1

38. Ocean heat uptake in wind driven gyres • Global downward ocean heat transport driven by winds. • Strength: Williams & Follows (2012) Levitus (1988)

39. Buoyancy driven circulations and ocean heat uptake : Cooling • Total temperature change in the 10th decade after 2XCO2 (idealised ocean basin) • Temperature change due to change in ocean currents • Temperature change in absence of change in ocean currents. Xie and Vallis (2011)

40. Interior mixing & ocean heat uptake Upward heat flux Osborne (1998) +100 Vertical heat flux (Wm-2) deeper Downward heat flux -100 South Pole Equator North Pole

41. Motions in the ocean are not isotropic: “neutral” surfaces • In the simplest case of a waterworld at rest, a fluid parcel does work against the buoyancy force when displaced upward or downward. Motions along z=cst are energetically neutral. Z=h Z=0 Solid Earth where Reference density

42. Motions in the ocean are not isotropic: “neutral” surfaces • In the real ocean, neutral surfaces take the shape of a bowl due to the distortion of spheres by the seafloor topography, surface heating, cooling and winds. Neutral surfaces in the Atlantic NB: These surfaces can be approximated as surfaces of constant density (“isopycnals”). Neutrally energetic displacements WOCE A16

43. The movie…