NACLIM annual meeting 2013, Trieste

Predictability of North Atlantic subpolar gyre strength with focus on the mid-1990s weakening

Katja Lohmann, Daniela Matei, Johann Jungclaus

MotivationBlue Whiting catches

Hatun et al., 2009

Mid-1990s weakening of subpolar gyre

• followed by large biogeographical shift in northeastern North Atlantic

• was caused not only by atmospheric forcing, but also ocean initial state

Construct time series according to lead time

Assimilation run:coupled model simulation with data assimilation (T and S anomalies from ocean model simulation forced with atmospheric reanalysis fields)

1948 2007 Initialized hindcasts:

• coupled model simulations with inititial conditions from assimilation run

• 1 hindcast every year every 5th year plus in 1990s: 3 hindcasts

10 years

Prediction system• PreCMIP5 prediction experiments (Matei et al., 2012a, b)

Matei et al. (2012b): Two tales of initializing decadal climate predictions experiments with the ECHAM5/MPI-OM model. Journal of Climate, 25, 8502-8523Matei et al. (2012a): Multiyear prediction of monthly mean Atlantic Meridional Overturning Circulation at 26.5oN. Science, 335 (6064), 76-79

Prediction system

Subpolar gyre index: Minimum of subpolar barotropic streamfunction (maximum gyre strength)

Predictability of subpolar gyre strength

Predictability of subpolar gyre strength

Predictability of subpolar gyre strength Subpolar gyre index: assimilation run, individual hindcasts, mean of hindcasts

Predictability of subpolar gyre strength Subpolar gyre index: assimilation run, individual hindcasts, mean of hindcasts

Why mid-1990s weakening with respect to area-averaged gyre strength less predictable?

Predictability of subpolar gyre strength

Conclusions

• Apart from predictive skill based on relatively long time series, predictability of certain events (case studies) is of interest

• Mid-1990s weakening of subpolar gyre, with respect to maximum gyre strength, mainly caused by ocean initial state and therefore more predictable than subpolar gyre strength in general

• Weakening of subpolar gyre is found in hindcasts from about 1991 on; ocean initial state in 1994 and 1995 sufficient to predict a realistic amplitude of weakening in all hindcasts

Construct time series according to lead time, which are compared to HadISST

1960 2010

Initialized hindcasts from CMIP5:Several hindcasts every 5th year

10 years

Predictability of sea surface temperature and sea ice in the Nordic Seas (Helene Langehaug et al.)

Predictability of sea surface temperature and sea ice in the Nordic Seas (Helene Langehaug et al.)

Inflow of warm Atlantic water leads to predictive skill of eastern Nordic Seas / Barents Sea sea surface temperature as well as Barents Sea sea ice?

COR skill sea surface temperature

Thank you!

The research leading to these results has received funding from the European Union 7th Framework Programme (FP7 2007-2013) under grant agreement n.308299 (NACLIM).

Prediction system