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Hans Burchard 1,3 , Frank Janssen 2 , Karsten Bolding 3 , Lars Umlauf 1 , and Hannes Rennau 1

Estimates of vertical mixing due to dense bottom currents in the Western Baltic Sea. Hans Burchard 1,3 , Frank Janssen 2 , Karsten Bolding 3 , Lars Umlauf 1 , and Hannes Rennau 1 1. Baltic Sea Research Institute Warnemünde 2. Bundesamt für Seeschifffahrt und Hydrographie

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Hans Burchard 1,3 , Frank Janssen 2 , Karsten Bolding 3 , Lars Umlauf 1 , and Hannes Rennau 1

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  1. Estimates of vertical mixing due to dense bottom currents in the Western Baltic Sea Hans Burchard1,3, Frank Janssen2, Karsten Bolding3, Lars Umlauf1, and Hannes Rennau1 1. Baltic Sea Research Institute Warnemünde 2. Bundesamt für Seeschifffahrt und Hydrographie 3. Bolding & Burchard Hydrodynamics hans.burchard@io-warnemuende.de

  2. Kriegers Flak Motivation: wind farms in the Western Baltic Sea Goal: Quantify natural mixing for evaluating additional mixing effects due to offshore constructions. Method: Three-dimensional numerical modelling.

  3. GETM is a 3D numerical model for estuarine, • coastal and shelf sea hydrodynamics with • Coupling to GOTM Turbulence Module • Generalised vertical coordinates • High-resolution advection schemes • Parallel execution • …

  4. GETM Western Baltic Sea hindcast Model setup: Meteo: 7 km (DWD) BC/IC: 3 nm Baltic Sea model based on MOM-3 Period: Sep 2003-May 2004 Resolution: 0.5 nm # of layers: 50 GVC

  5. GETM Western Baltic Sea hindcast

  6. GETM Western Baltic Sea hindcast

  7. Western Baltic Sea monitoring stations Farvandsvæsenet Drogden Sill: 8 m + MARNET (IOW/BSH) + + Arkona Buoy: 48 m Darss Sill: 19 m

  8. Model validation: Darss Sill

  9. Model validation: Drogden Sill

  10. Model validation: Arkona Buoy

  11. Model validation: Section across Kriegers Flak

  12. Quantification of vertical mixing Non-averaged salinity equation: Reynolds decomposition: Mean salinity equation

  13. Micro-structure salinity variance equation: Vertically integrated mean salinity variance: Vertically integrated salinity variance equation:

  14. Model derived annual mean vertically integrated salinity variance decay in Western Baltic Sea

  15. Alternative measure for vertical mixing: Vertically integrated turbulent salt flux

  16. Model derived annual mean vertically integrated vertical turbulent salt flux in Western Baltic Sea

  17. Conclusions: Density currents in Western Baltic Sea are highly variable, show a complex transverse structure (see Umlauf et al.) and induce substantial natural transports and mixing. A suitable model-based quantification of vertical mixing is given by the decay of the vertically integrated mean salinity variance. Next question: How big is the additional numerically-induced mixing ?

  18. RV Gauss leaving Warnemünde for its last research cruise

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