1. Numerical simulations of dense bottom currents in the Western Baltic Sea: Quantification of natural, structure-induced and numerical mixing
Hannes Rennau
Funded by:

2. Model area

3. Model area
Hot spot of water
mass transformation

4. Model area Hot spot of water mass transformation Drodgen Sill (~8m)
Darss Sill (~20m)

5. Main pathways
Of dense bottom
currents

6. Main pathways
Of dense bottom
currents

7. Main pathways
Of dense bottom
currents

8. Main pathways
Of dense bottom
currents

9. Main pathways
Of dense bottom
currents

10. Numerical Model typical ocean-circulation model GETM with state
of the art turbulence model GOTM (code developers for
both models at IOW)
Parallel execution on
IOW Linux Cluster

11. Simulation of bottom salinity over nine months

12. Darss Sill Tracer vs. Drodgen Sill Tracer
Tracer release
positions

13. Darss Sill Tracer vs. Drodgen Sill Tracer
Tracer release
positions

14. Darss Sill Tracer vs. Drodgen Sill Tracer
Tracer release
positions

15. Darss Sill Tracer vs. Drodgen Sill Tracer
Tracer release
positions

16. Model Validation x MARNET Arkona Station
Burchard, H., F. Janssen, K. Bolding, L. Umlauf, and H. Rennau, Model simulations of dense bottom currents in the Western Baltic Sea, Cont. Shelf Res., 29, , 2009.

17. Natural mixing in the numerical model
Significantly increased natural mixing:
in channels (Kriegers Flak, Bornholm Channel, …)
in the area of shallow sills
(Drodgen Sill,
Darss Sill, …)
Burchard, H., F. Janssen, K. Bolding, L. Umlauf, and H. Rennau, Model simulations of dense bottom currents in the Western Baltic Sea, Cont. Shelf Res., 29, , 2009.

18. found method to analyse numerical mixing
Physical mixing Numerical mixing
Rennau, H., and H. Burchard, Quantitative analysis of numerically induced mixing in a coastal model application, Ocean Dynamics, submitted December 2008.
Burchard, H., and H. Rennau, Comparative quantification of physically and numerically induced mixing in ocean models, Ocean Modelling, 20, , 2008.

19. Conclusions
Fundamental knowledge about propagation of dense bottom currents in
the western Baltic Sea
Model derived amount of physically induced mixing without offshore
foundations

20. Conclusions
Fundamental knowledge about propagation of dense bottom currents in
the western Baltic Sea
Model derived amount of physically induced mixing without offshore
foundations
numerically induced mixing and physical mixing have same orders of
magnitude but different horizontal distribution
enhanced numerical mixing –> less physical mixing
numerical techniques: adaptive vertical coordinates,…

21. Impact of bridge piles

22. Impact of bridge piles
distance from pile / m
Lass et al. (2008)

23. Impact of bridge piles - modeling

24. Impact of bridge piles - modeling
H.U. Lass et al. (2008)
distance from pile / m 28 24 20 16
PILE
distance from pile / m

25. GETM 2D Slice Model

26. Additional mixing due to Offshore windpark foundations
Local model at
University of Hannover
Regional model
at IOW
Parameterisaton?

27. 'Worst Case Study' with Offshore Windpark

28. Influence of Offshore wind park: 10. April, 2004
With windpark without windpark

29. „Worst Case“ Study – Simulation with Offshore Windpark
Snapshot:
bottom salinity (without windpark) –
bottom salinity (with windpark)
windpark

30. „Worst Case“ Study – Simulation with Offshore Windpark
Snapshot:
bottom salinity (without windpark) –
bottom salinity (with windpark)
windpark
+0.5

31. „Worst Case“ Study – Simulation with Offshore Windpark
Snapshot:
bottom salinity (without windpark) –
bottom salinity (with windpark)
windpark
-0.2
+0.5

32. Main conclusions - expected low additional mixing due to Offshore
Windpark foundations (needs further calibration
in parameterisation and longer time series)
- strength of additional mixing mainly dependent on:
(1) where to be build
(2) windfarm distribution (how many, …)

33. Main Focus for last year:
- Final results concerning additional mixing of offshore
windpark foundations in the Western Baltic Sea (publication
in preparation)

34. Main Focus for last year:
- Final results concerning additional mixing of offshore
windpark foundations in the Western Baltic Sea (publication
in preparation)
- Model nesting: 3D structure development of dense bottom
currents in channels (Kriegers Flak North and Bornholm
Channel) (publication in preparation)

35. Main Focus for last year:
- Final results concerning additional mixing of offshore
windpark foundations in the Western Baltic Sea (publication
in preparation)
- Model nesting: 3D structure development of dense bottom
currents in channels (Kriegers Flak North and Bornholm
Channel) (publication in preparation)
- Passive Tracer study (correlations for propagation time of
dense bottom currents) (publication in preparation)

36. Main Focus for last year:

37. Main Focus for last year:
- Final results concerning additional mixing of offshore
windpark foundations in the Western Baltic Sea (publication
in preparation)
- Model nesting: 3D structure development of dense bottom
currents in channels (Kriegers Flak North and Bornholm
Channel) (publication in preparation)
- Passive Tracer study (correlations for propagation time of
dense bottom currents) (publication in preparation)
Fehmarn Belt Project
Rennau, H., and H. Burchard, Quantitative analysis of numerically induced mixing in a coastal model application, Ocean Dynamics, submitted December 2008.
Burchard, H., and H. Rennau, Comparative quantification of physically and numerically induced mixing in ocean models, Ocean Modelling, 20, , 2008.
Burchard, H., F. Janssen, K. Bolding, L. Umlauf, and H. Rennau, Model simulations of dense bottom currents in the Western Baltic Sea, Cont. Shelf Res., 29, , 2009.