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Potential temperature ( o C, Levitus 1994) Surface Global zonal mean.

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Presentation on theme: "Potential temperature ( o C, Levitus 1994) Surface Global zonal mean."— Presentation transcript:

1 Potential temperature ( o C, Levitus 1994) Surface Global zonal mean

2 Salinity (psu, Levitus 1994) Surface Global zonal mean

3 Evaporation – precipitation

4 Density as function of temp, salinity and pressure max density freezing point ρ–1000 kg m –3

5 Potential density (  -1000 kg m –3, Levitus 1994) Surface Global zonal mean

6 Mixed layer depth

7 Seasonal variation of mixed layer depth

8 World ocean currents Map shows vertically averaged currents around the world oceans

9 Western boundary currents: Gulf Stream Benjamin Franklin’s map (Richardson, Science1980) SST satellite image, from U. Miami RSMAS

10 Surface wind (NCEP, m/s) January July

11 Ekman spiral

12 Coastal upwelling due to Ekman transport

13 Observed asymmetry of gyres what one might expect what one observes westerlies trades

14 Annual mean Ekman pumping (m/year)

15 Friction in western boundary current

16 World ocean overturning and heat transport Results from a numerical model (Boccaletti et. al 2005) mass flux (Sv) heat flux (PW) Eq40N80N40S80S

17 Atlantic salinity and flow

18 The Great Conveyor Belt

19 Ocean heat transport by basin

20 Lumpkin and Speer (2007) The present perception of Southern Ocean overturning: it makes global the global thermohaline circulation possible Speer et al., 2000; Sloyan and Rintoul, 2001ab

21 Warm sources have to be deeper than cold ones: The Sandström’s theorem Mixing is crucial: A scenario with a surface buoyancy forcing of NADW upwelling is problematic NADWFormationNADWConsumption Mixing No THC Intense THC

22 “[…] understanding the physics related to the spatial and temporal distribution of mixing is one of the most important research frontiers in physical oceanography.” Huang (2004) Mixing is crucial: Different scenarios for the NADW upwelling a) Pushing by deepwater formation b) Pulling by deep mixing c) Pulling by wind stress & surface waves

23 A simple model of the thermohaline circulation  = flow strength, proportional to density difference ,  adim. constants temperature difference salinity difference

24 Multiple equilibria

25 Change in surface temperature 30 years after thermohaline shutdown

26 Tropical Pacific sea-surface temperature

27 Equatorial temperature cross section

28 Equatorial currents Surface Meridional cross section Equatorial undercurrent

29 Driving the undercurrent

30 Water parcel trajectories

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