1. Coastal Ocean Dynamics Baltic Sea Research Warnemünde
Second course:
North Sea dynamics
Hans Burchard
Leibniz Institute for
Baltic Sea Research Warnemünde

2. North Sea
bathymetry
Source: Werner Alpers

3. Exclusive Economic Zones
North Sea
catchment areas
and
Exclusive Economic Zones
Weser
Elbe
Rhine
Source: OSPAR Commission

4. Annual cycle of sea surface temperature in North Sea

5. Generation of the semi-diurnal lunar (M2) tide

6. Generation of the semi-diurnal solar (S2) tide

7. Tidal chart for the M2 tide (phase lines)

9. Why do the tides in the North Sea look like this ?
Tidal waves enter into North Sea through
northern boundary and English Channel.
Phase propagation is c = (g * depth)1/2, g = 9.81 m/s2
(depth = 40 m  c = 20 m/s = 72 km/h)
Due to Earth rotation, tidal waves are Kelvin waves,
leaning on a coast to the right.
Energy loss due to bed friction: tidal waves loose
power during their journey through the North Sea.

10. Tidal chart for the M2 tide full lines: amplitude dashed: phase
(Source: POL)

11. Tidal chart for the M2 tide (phase lines)

12. M2 tidal chart of Southern North Sea
Amphidromic point
M2 tidal chart of Southern North Sea
Prandle, 1981

13. Tidal propagation into the Baltic Sea is blocked !

14. Tides in the Wadden Sea (as seen in 200 m resolution model)

15. Wadden Sea model: M4 tidal elevations (phase and amplitude)
as validation data.
Gräwe et al., in prep.

16. Seasonality of tidal forcing
How does this affect
sediment transport
due to tidal asymmetries (M4)?
Gräwe et al. (in prep.)
Müller et al. (in prep.)

17. Stratification in the North Sea Besides tides, seasonal stratification is characteristic for the North Sea dynamics.
Annual cycle of temprature
stratification in the
Northern North Sea
(as seen from a 1D model)
Bolding and Burchard (2002)

18. Stratification is spatially not homogeneous
Tidal front
Doggerbank
Doggerbank
Model results by Burchard & Bolding, 2002

19. Tidal fronts
Tidal fronts (stratified in deep, mixed in shallow water) are an environmentally very important phenomenon.
Thus, in shallow water the bottom sediment is in direct contact with the surface waters, whereas in deeper waters, the bottom layers are clearly separated from the surface wates.

20. What determines the position of tidal fronts ?
Stabilising: water depth H, surface buoyancy flux Q
(heat flux, net precipitation).
Destabilising: tides given as tidal velocity amplitude u.
Important parameter by dimensional analysis:
(Q * H) / u3
Large: stably stratified; Small: mixed
Note: H / u3 is the famous Simpson-Hunter (1974) parameter.

21. Tidal mixing fronts in the Irish Sea
stratified & deep
mixed & shallow
mixed & very shallow & warm or
stratified due to river run-off
Satellite images courtesy Alejandro Souza

22. Tidal Mixing fronts in the Irish Sea
Stratification Simpson-Hunter parameter
Numerical model result, Souza et al., in press.

23. Environmental effects of seasonal thermal stratification
Surface heat flux (cumulated)
during FLEX‘76
Burchard, 2002

24. FLEX 1976 Lateral effects are small, such that one-dimensional
modelling may be
successful
Burchard, 2002

25. Summer stratification along 56°North Sea transect

26. Summer chlorophyll conc. along 56°North Sea transect

27. Northern North Sea: Annual cycle of stratification and
primary production
Burchard et al., 2005
Burchard, 2002

28. Rotating bulk shear in Monterey Bay
Itsweire et al. (1989)

29. PROVESS-NNS study site (observations: Sep-Nov 1998)
Wind
ADCP, CTD, MST

30. Bulk property observations in NNS
Wind
Bulk shear squared
Bulk shear direction
vs.
inertial rotation

31. Theory I
1D dynamic equations:
Layer averaging:

32. Dynamic equation for bulk shear squared:
Conclusion:
Assuming bed stress being small, bulk shear is generated
by the alignment of wind vector and shear vector.

33. Application of
theory to
observations

34. Impact of bulk shear on diapycnal mixing Conclusion:
Increased interfacial
mixing rates correlate
with high shear.
Can we resolve this
in 3D models?

35. Transect in NNS Observations (Scanfish data from BSH)
Model results (GETM with adaptive coordinates)
Gräwe et al. (in prep.)