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• Initial sea surface temperatures and sea ice concentration are given by NEMOVAR.  In practice the following procedures are adopted to deliver the T+0 fields used as the starting point for the coupled model forecasts:
  
  • For Sea-Ice, the ocean analysis assimilates OSTIA sea-ice fields and in effect is blending blended with the background (as happens in atmospheric assimilation).
  • For Sea Surface Temperature (SST), the latest OSTIA sea surface temperature analysis (re-gridded) is used but the approach depends on latitude.  Between 20S and 20N the NEMO ocean sea surface temperature analysis is relaxed towards the latest OSTIA sea surfacer temperature surface temperature analysis.  North of 25N and South of 25S, the latest OSTIA sea surface temperature analysis is used unchanged.  Between 20 and 25 degrees a hybrid of these approaches is used.
    
• Throughout the forecast period, NEMO provides the oceanic temperature structure near and at the surface.  ECWAM provides wave data, and therefore an indication of surface roughness.  From these, fluxes of heat, moisture and momentum are evaluated for passing to the lowest layers of the atmosphere.  The formation, evolution and decay of ice over open waters is controlled by LIM2 (part of NEMO).  In effect, NEMO and LIM2 together move ice around (according to ocean drift etc.) and melt or form ice (according to sea-surface temperatures etc.).  The albedo over the sea-ice surface uses a climatology prescribed in the IFS rather than the model albedo of LIM2 (this is because LIM2 does not model some of the key processes important for albedo such as melt ponds).  Note: ECMWF uses LIM2 which is an earlier version of the Louvain-la-Neuve sea ice model currently available (Version 3.6)  
  

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