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The ECMWF Integrated Forecasting System (IFS) consists of several components coupled together in various different ways:

• an atmospheric model which is run at various resolutions appropriate to the forecast length:
  • medium range ensemble (ENS) forecast (Day 0 to Day 15). 
  • Ensemble Control Forecast (ex-HRES) (Day 0 to Day 15).  HRES and Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical.  The Ensemble Control Forecast (ex-HRES) output runs on the schedule of HRES in Cy48 and earlier.   It runs before the medium range ensemble starts.  It is labelled HRES for the convenience of users but the name will be withdrawn in a future update cycle.
  • sub-seasonal range forecast (Day 0 to Day 46).
  • seasonal forecast (month 0 to month 7 or month 0 to month 13).
• an ocean wave model (ECWAM).
• an ocean model (NEMO) including a sea ice model, the Louvain-la-Neuve Sea Ice Model (LIM2).
• a land surface model (HTESSEL) including a lake model (FLake).
• a data analysis system (4D-VAR).
• perturbation techniques for generation of the ensembles.
  
  

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• the land is the lower boundary for the atmosphere for a less extensive area than the sea but it has a complex orography and exhibits far more temporal and spatial variability in the characteristics of energy storage and exchange.
• the lower boundary gives important feedback to the atmosphere if accurately modelled (important for short and long-range forecasting).
• the state of the landmasses (including soil moisture, cover and depth of snow, and lake ice) can change on a daily timescale and these variations can be important in certain situations during the forecast evolution.  Important aspects of the modelled state of the land that can affect the atmospheric evolution include:
  • rainfall absorption and soil moisture (give more information on boundary moisture flux),
  • ice variations on sea and lakes (gives more information on albedo and boundary heat and moisture fluxes),
  • land/lake temperature variations for evaluation of heat fluxes,
  • snow variations and extent (gives more information on albedo and boundary heat and moisture fluxes).
     

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