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Sea-surface temperature (SST) and ice concentration

Sea-surface temperature are initialised using analyses received daily from the Met Office (OSTIA, 5 km resolution). Additionally NEMO, and the LIM2 subprogram within it, forecast changes in the sea-surface temperature (SST) and sea ice evolution.  Output from these programs are used interactively by all IFS atmospheric models.  HRES uses the same initial ice extent as ENS. Note: ECMWF uses LIM2 which is an earlier version of the Louvain-la-Neuve sea ice model currently available (Version 3.6)    

The impacts of differently-evolving SST and ice cover distributions should be considered when comparing different forecasts, even when they are from the same data time.



Fig2.1.4.8-1: Sequence of sea-ice and sea-surface temperatures from the ENS CTRL run data time 00 UTC 27 April 2017.   T+0hr (00UTC 27 April 17), T+120hr (00UTC 02 May 17),  T+240hr (00UTC 07 May 17), and  T+360hr (00UTC 12 May 17).  On such plots the climatological average sea ice cover is shown in pink (contour and stippling, for >50%), just discernible in the northern Gulf of Bothnia and in the White Sea.   Dark purple areas (SST between 0C and -2C) are prone to ice formation if not already in existence.   Areas of sea ice are shown as turquoise. 

Note:  

  • Movement of ice (turquoise) in the northern Gulf of Bothnia  due to the winds.
  • Steady rise of sea-surface temperatures in the Black Sea, and especially in the shallow waters of both the Sea of Azov and the northern Caspian Sea.  In the White Sea (east of Finland, top of plot) sea ice cover is less than the climatological average for this time of year.  Using these plots, the user can assess where sea ice cover is above/below average.


In general the LIM2 sea ice model tends to melt sea ice too slowly, particularly over the Bering Straits side of the Arctic basin where the analysis tends to have a bias towards greater ice thickness.

Fig2.1.4.8-2: Typical chart of sea surface temperature and sea ice.  The sea ice areas only show sea ice cover above 50% which gives the impression that there is no sea ice outside this area.  However, patchy ice and bergs are likely in the surrounding waters.

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