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Multi-decadal variability in a long integration with the MPI-OM1 ocean model

Multi-decadal variability in a long integration with the MPI-OM1 ocean model. Philip Kruse Jakobsen (pkj@dmi.dk) and Torben Schmith (ts@dmi.dk) Danish Meteorological Institute. Variability in Atlantic Meridional Overturning Circulation.

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Multi-decadal variability in a long integration with the MPI-OM1 ocean model

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  1. Multi-decadal variability in a long integration with the MPI-OM1 ocean model Philip Kruse Jakobsen (pkj@dmi.dk) and Torben Schmith (ts@dmi.dk) Danish Meteorological Institute

  2. Variability in Atlantic Meridional Overturning Circulation

  3. Multidecadal variability:Observations in the North Atlantic • Observed temperatures: Schlesinger & Ramankutty (1994), Mann & Park(1994), Delworth&Knutson (2000) • Paleo-temperatures: Mann et al. (1995) (Schlesinger&Ramankutty, 1994) (Delworth & Knutson, 2000)

  4. Multidecadal variability:Observations in the Arctic • Arctic temperatures: Polyakov&Johnson(2000) • Fram Strait ice export: Schmith&Hansen (2003) Schmith&Hansen(2003)

  5. Hypotheses • Internal self-sustained ocean mode • e.g. Delworth et al. (1993) • Damped ocean oscillatory mode stochastilly exited by atmospheric forcing • e.g. Mikolajewitz&Maier-Reimer (1990) • Coupled ocean-atmosphere mode • e.g. Timmermann et al. (1998) • Externally forced oscillations • e.g. solar activity (Gleissberg-cycles ))

  6. MPI-OM1 (C-HOPE) Primitive eq. with 30 z-levels (partial cells). Hibler-type ice model Bottom Boundary Layer-scheme, Isopycnal diffusion, and eddy induced mixing Experiment Integrated 2000 years incl. 1000 years of spinup OMIP-forcing, precip. from Xie and Arkin (1996) SSS-restoring (39days) to monthly climatology (PHC) in ice-free regions Experimental setup

  7. Variability in Atlantic Meridional Overturning Circulation

  8. Variability in MOC II

  9. Nordic Seas

  10. Nordic Seas Salinity vs MOC strength

  11. Arctic Ocean

  12. Arctic Ocean: sea ice thicknessInterannual variability

  13. Arctic Ocean: sea ice thicknessEOF-analysis

  14. Arctic Ocean: Salinity near the pyknocline • Interannual variability of salinity at100m (shown to the right) has maximum along TPDS • This is interpretated as vertical displacements of the pyknocline

  15. Arctic Ocean: Salinity near the pyknocline • POP analysis shows propagation of signals with multidecadal period. Propagation time: around 20 years

  16. Concluding remarks • Flow anomalies in the Atlantic Overturning circulation of 2-3 Sv with a period of about 80 year exist in an experiment forced with intraannual variability only. • Involves the Nordic Seas and the Arctic Ocean surface layers • Antlantic inflows to Arctic Ocean does not seem to be the trigger .

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