1. Class 8. Oceans Figure: Ocean Depth (mean = 3.7 km)
bounded by continents
deep: difficult to make observations
Figure: Ocean Depth (mean = 3.7 km)

2. Ship-measurements Only a limited area covered bounded by continents
deep: difficult to make observations
Only a limited area covered

3. SST from buoys
drifter: can freely drift
moored: anchor

4. Ocean Surface Temperature from Remote Sensing (NOAA)
-2.0 C
16.1
cold water sinks
warm
- maximum insolation
- albedo of water ~ 7%
cold water sinks
strong gradient towards the poles
some structures: green cold tongue off the coast of california, Peru
source NOAA

5. Ocean Surface Salinity
Prep>Evap
Evap>Prep
strong gradient towards the poles
some structures: green cold tongue off the coast of california, Peru

6. ARGO: profiling the interior of the ocean (up to z=-2000 m)
drifter: can freely drift
moored: anchor

7. ARGO: profiling the interior of the ocean (up to z=-2000 m)
drifter: can freely drift
moored: anchor
Data products:
Temperature, salinity and density

8. Zonal average temperature in deep ocean
warm salty stratified lens of fluid
abyss z>1000 m
homogeneous mass of very cold water

9. Schematic of vertical structure
convection in the upper layer causes a vertically well mixed layer
strong vertical temperature gradient defines the thermocline
note: analogy to thermal inversion in the atmosphere
very cold water present below z<1000 m

10. Thermal expansion: Sea-level transgression scenarios for Bangladesh

11. Density (anomaly s), Temperature and Salinity
higher
density
salty water has a higher density
fresh water show dip in density
Fig. 9.2: Contours of seawater density anomalies (s=r-rref in kg/m3)
rref = 1000 kg/m3
PSU = Practical Salinity Unit ≈ g/kg grams of salt per kg of solution

12. Simplified equation of state (defined with respect to s0(T0,S0))

13. Simplified equation of state (defined with respect to s0(T0,S0))

14. Schematic of vertical structure
tendency due to
radiative heating
T = temperature
F = heat flux (Wm-2)
rw = density of water
cw = heat capacity of water μ

15. 1000
depth (m)
cold water -
deep convection
cold water
upwelling
900S
900N 00
latitude

16. P>E
P<E
1000
depth (m)
900S
900N 00
latitude
Low salinity if precipitation (P) exceeds evaporation (E)

17. Thermohaline circulation
arctic sea ice

18. Sea level height

19. Which balances do apply in the ocean?
Hydrostatic balance -> yes
Geostrophic balance?
Thermal "wind"?
Ekman pumping/suction?

20. Rossby and Reynolds number in the ocean
Far away from the equator, e.g. latitude = 400,
North-South length scale L = 2000 km (east-west larger)
Velocity scale U = 0.1 m/s

21. Pressure in the ocean mean density in water column high pressure
low pressure
geef eventueel dp/dz

22. Which sea level tilt is needed to explain U=0.1 m/s?
werk uit op bord
Example 1: assume density is constant

24. Geostrophic flow at depth
Example 2: assume density is NOT constant,
but varies in the x,y directions => r(x,y)=rref+s(x,y)
1000
depth (m)
900S
900N 00
latitude 23 24 25 26
26.5 27
1. Taylor Proudman
2. Thermal wind

25. Estimating the geostrophic wind from the density field: The dynamic method
This method allows for assessing geostrophic velocities relative to some reference level
One can assume that at a "sufficiently" deep height ug=0
1. Taylor Proudman
2. Thermal wind

26. Geostrophic flow at depth z
Example 3: I) assume density is NOT constant,
but varies in the x,y directions => r(x,y)=rref+s(x,y)
II) surface height is NOT constant
1. Taylor Proudman
2. Thermal wind

27. Geostrophic flow
Example 1: In the ocean geostrophic flow applies (not too close to equator)
Pressure induced by surface height variations η
Example 2: Horizontal density gradients cause a vertical change in the
geostrophic flow velocity ("thermal" wind)
Example 3: In principle both height and density variations may apply
1: p184, above 9-11
2: 7-16 3:

28. Determining the ocean flow from floating plastic ducks?
1. Taylor Proudman
2. Thermal wind

29. 1. Taylor Proudman
2. Thermal wind

30. 1000
depth (m)
cold water -
deep convection
cold water
upwelling
900S
900N 00
latitude

31. Ekman pumping/suction
1. Taylor Proudman
2. Thermal wind

32. Wind-driven ocean flow
Equations with wind-stress

33. Wind-driven ocean flow
Equations with wind-stress
Split velocity in geostrophic ('g') and ageostrophic parts ('ag')
e.g.

34. Ekman transport

35. Ekman pumping (downwards)/suction
X wind into the screen

36. Ekman pumping (downwards)/suction
elevated sea level height
in convergence area
tropics
midlatitudes

37. Ekman pumping/suction due to wind stress
1. Taylor Proudman
2. Thermal wind

38. Ekman pumping/suction Explanation
mass conservation

39. Ekman pumping/suction Explanation
1. we do not assume that f is constant, but f=f(y)
2. variations in wind stress are much larger than in f

40. Ekman pumping/suction Example
= 32 m/year

41. Ekman pumping/suction from wind stress climatology
downward
upward
f=0