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

Model area

Model area Hot spot of water mass transformation

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

Main pathways Of dense bottom currents

Main pathways Of dense bottom currents

Main pathways Of dense bottom currents

Main pathways Of dense bottom currents

Main pathways Of dense bottom currents

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

Simulation of bottom salinity over nine months

Darss Sill Tracer vs. Drodgen Sill Tracer Tracer release positions

Darss Sill Tracer vs. Drodgen Sill Tracer Tracer release positions

Darss Sill Tracer vs. Drodgen Sill Tracer Tracer release positions

Darss Sill Tracer vs. Drodgen Sill Tracer Tracer release positions

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, 205-220, 2009.

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, 205-220, 2009.

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, 293-311, 2008.

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

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,…

Impact of bridge piles

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

Impact of bridge piles - modeling

Impact of bridge piles - modeling H.U. Lass et al. (2008) distance from pile / m 28 24 20 16 2000 1000 PILE 1000 2000 distance from pile / m

GETM 2D Slice Model

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

'Worst Case Study' with Offshore Windpark

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

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

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

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

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, …)

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

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)

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)

Main Focus for last year:

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, 293-311, 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, 205-220, 2009.