1. Nordic Seas Overflows in Models......

2. and Observations Rolf Käse, IfM - HH with support from Detlef Quadfasel, Nuno Serra, Matthias Köller a.o.

3. From Bob Dickson's 'Once upon a time' talk, 2003 There are some signs of effects on the Atlantic circulation … on the eastern Overflow..... but not yet the western :............. There, the 187 monthly means of flow speed collected from the overflow core since 1986 (z ≈2000m) show little sign of seasonal variability..... Neither has there been any obvious change in the transport of the overflow core.

4. Is this paradox in view of what we know today? A paradox is a statement or group of statements that leads to a contradiction or a situation which defies intuition. It's your turn to decide

5. Outline of the talk - A controlled volume box model based on hydraulic control - Hindcast of DSO with this model vs MPI-OM ensembles - Overflow east of Iceland -> in-phase or anti-phase to DSO? - Upstream pathways modification by NAO+ / - patterns

6. DSO Salinity on 27.8 surface

7. accumulation hydraulic outflow of DSO net inflow + production area Box Balance Leads to a non-linear Riccati equation for reservoir height NAO If h is linearized and Q S is white noise → h has a red noise spectrum

10. Comparison of Riccati-Box-Model terms and analysed from hi-resolution model with seasonal forcing Riccati-Model Hi-Resolution Model resolving hydraulics Overflow only about 10 % of Production for typical DSO reservoir height Principle balance between Production and Accumulation

11. Calculated from reservoir height (courtesy of H.Valdimarsson, S. Jonsson) by A. Macrander Girton et al. Ross O'73 R.Käse, GRL 2006

12. Unlagged correlation of DSO with model SSH Köhl et al. 2007, JPO MODEL Observable ?

13. Observations from different satellites and current measurements Köhl et al. 2007 Note: DSO stronger

14. MPI-OM results courtesy of J.Jungclaus/D.Matei Obs. courtesy of H. Valdimarsson,S.Jonsson,A.Macrander Yellow: 1 instrument at sill brown: 2 instr. Forcing: Annual NAO Riccati-Model NAO- NAO+ NAO- Models / Observations

15. Forcing: Annual NAO Riccati-Model Köhl et al, 2007 DSO from Altimetry

16. Main difference to observations in MPI-OM Too strong seasonal cycle butsomewhat improved by assimilation ??? No hydraulics ??? Same is true for Olsen et al. 2008 east of Iceland Agreement is much better in 'overflow' east of Iceland Anti-phase to DSO ? But:

17. Serra et al. submitted de-seasoned series DSO curl FSC Model again

18. Nuno Serra's North-Atlantic Model Mean dense pathways

19. Dense Water Transport Difference (2001-03) minus (1991-94) NAO- minus NAO+ ====>> Dense eastern branch (and FBC) is enhanced at NAO __

20. Summary: Overflows strongly linked to wind stress curl / NAO On time scales 4-6 years DSO and FBC in opposite phase But not after mid 1990's Models capture variability more or less

22. Kösters et al. GRL 2005 and Köller et al. 2009 submitted to Tellus

24. Variations in the Labrador/Irminger Sea subpolar gyre are highly correlated with Sea Ice

25. Air over Labrador Sea 'cold' leads Greenland Sea 'heat' by 10 years NCEP reanalysis data reveal Greenland Sea / Labrador Sea flip-flop