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The dynamic ocean model used for medium-range and seasonal forecasts of ocean structure is the Nucleus for European Modelling of the Ocean (NEMO). It is coupled with all IFS forecast models (medium range ENS, extended range ENS, Seasonal). NEMO is a three-dimensional general circulation ocean model and can reproduce the general features of the circulation and the thermal structure of the ocean and their seasonal and inter-annual variations.
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Throughout the forecast period the changing extent of sea-ice and the variation of the ice shelf with time have important effects upon the energy and moisture balance at the atmosphere/surface boundary. The Louvain-la-Neuve Sea Ice Model (LIM2) is a prognostic sea-ice model that deals with the dynamic and thermodynamic evolution of the sea surface so that sea-ice cover evolves dynamically. It is incorporated into the dynamic ocean model. The ice extent will change through the forecast period in response to sea temperatures and air temperatures, ocean currents and wind.
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- analyses received daily from the Met Office (OSTIA, 5 km resolution).
- NEMO, and the LIM2 subprogram within it.
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Note: ECMWF uses LIM2 which is an earlier version of the Louvain-la-Neuve sea ice model that is currently available (Version 3.6, LIM3)
Fig2.1.11: Sequence of sea-ice and sea-surface temperatures from the ENS CTRL run data time 00UTC 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.
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The Operational Sea Surface Temperature and Sea-Ice Analysis (OSTIA) provides sea-ice information. This is combined with the NEMOVAR ocean assimilation to give initial conditions for coupled model and also to provide a first guess for the next NEMOVAR assimilation cycle. The ocean analysis system consists of a reanalysis stream (ORAS5) and a real-time stream (ORTS5).
Observed sea-surface temperatures are not assimilated directly but a strong relaxation towards the OSTIA sea-surface temperature data is applied during the outer loops of the data assimilation cycle.
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- For more information on the 75 ORCA ocean model levels (section2.3).
- Read an in-depth description of the NEMOVAR ocean data assimilation system.
- Read more on Coupling of NEMO and IFS.
- See Met Office OSTIA site.
- An explanation of LIM2 and download full text (non ECMWF source).
- An explanation of NEMO (non ECMWF source).
Sea-ice evaluation of NEMO-Nordic 1.0: a NEMO–LIM3.6 based ocean–sea ice model setup for the North Sea and Baltic Sea.(non ECMWF source).
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