NACLIM annual meeting 2013, Trieste
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Transcript of NACLIM annual meeting 2013, Trieste
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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
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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
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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
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Prediction system
Subpolar gyre index: Minimum of subpolar barotropic streamfunction (maximum gyre strength)
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Predictability of subpolar gyre strength
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Predictability of subpolar gyre strength
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Predictability of subpolar gyre strength Subpolar gyre index: assimilation run, individual hindcasts, mean of hindcasts
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Predictability of subpolar gyre strength Subpolar gyre index: assimilation run, individual hindcasts, mean of hindcasts
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Why mid-1990s weakening with respect to area-averaged gyre strength less predictable?
Predictability of subpolar gyre strength
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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
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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.)
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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
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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).
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Prediction system