Model configurations

The IFS models the dynamics of the atmosphere and the physical processes that occur, and also other processes that influence the weather e.g. atmospheric composition, surface energy fluxes, the marine environment and processes at the atmosphere/surface interface (then scroll down to soil/surface section).  Several configurations of the atmospheric model are used, each tailored towards a specific aim:

• Medium Range ensemble to investigate detail and uncertainty in the forecast during the first 15 days.
• Sub-seasonal ensemble to give probability of general conditions to 46 days ahead.
• Seasonal ensemble to give probability of general conditions at longer ranges.

There are some slight differences, but generally the same model structure is used in each of the different model configurations.  The relative skill of the models and their strengths have been investigated.

Upgrades in latest cycle of Integrated Forecast System (IFS) model Cy49r1. 

Some major model changes were made to the IFS with the introduction of Cy49r1 in October 2024.  These are:

• Medium range ensemble forecast system
  • The name of both the HRES and the unperturbed control member of the ensemble forecast is replaced by Ensemble Control Forecast (ex-HRES).
  • Ensemble Control Forecast (ex-HRES), or equally any individual perturbed ensemble member, may be considered as a possible detailed solution during the first 15 days.
  • HRES and the Ensemble Control Forecast (ex-HRES) are scientifically, structurally and computationally identical with the same unperturbed analyses.
  • 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  It is labelled HRES for the convenience of users but the name will be withdrawn in a future update cycle.
  • Unchanged are: 
    • the horizontal resolution remains at 9 Km.
    • the vertical resolution remains at 137 model levels. 
    • the number of ensemble members remains at 50 members plus the control member.
    • the medium range ensembles are run daily:
      • Day0 to Day15 based on 00UTC and 12UTC data
      • Day-0 to Day6 based on 06UTC and 18UTC data. Results from these runs are:
        • used in Early cut off analysis (SCDA) and Long window data analysis (LWDA).
        • disseminated T+0 to T+72
    • documentation gives details of Ensemble Control Forecast (ex-HRES) products and dissemination schedules.
    • documentation gives details of Medium Range ensemble products and dissemination schedules.

• Sub-seasonal range ensemble (formerly extended range) forecast system:
  • The name of the extended range ensemble and associated forecast period is replaced by sub-seasonal range ensemble and associated forecast period.  The forecast system itself is unchanged.
  • Unchanged are: 
    • the horizontal resolution remains at 36 km.
    • the vertical resolution remains at 137 model levels.
    • the number of ensemble members is 100 members plus a control member.
    • the sub-seasonal range ensemble is run daily from Day0 to Day46 based on 00UTC data.
    • documentation gives details of sub-seasonal range products and dissemination schedules.

    • the sub-seasonal range forecasts are not just an extension of the medium-range forecasts but are completely separate systems each starting from their own analyses.  

• Wave model system:
  • the horizontal resolution is increased to 9km for the medium range and to 36km for the sub-seasonal range.  The resolutions are the same as the corresponding atmospheric model.
  • the number of medium range 2D wave spectra is reduced from 36 to 29. The first 29 frequencies in previous cycles are output but the remaining 7 frequencies are not.
  • the wave model ensembles are run daily Day0 to Day15 based on 00UTC and 12UTC data and Day0 to Day6 based on 06UTC and 18UTC data.
  • Unchanged are: 
    • the number of directions remains at 36.
    • documentation gives details of wave forecast products and dissemination schedules.
    • documentation gives details of ocean forecast products and dissemination schedules.

• Re-forecast systems for medium and sub-seasonal ranges:
  • There are two sets of re-forecasts, one for the medium range and one for the sub-seasonal range.  There is an increase in frequency; both are run over the past 20 years on fixed days of the month: 
    • Sub-seasonal range every two days: 1/3/5/7/9/11/13/15/17/19/21/23/25/27/29/31 (excluding 29 February).
    • Medium range every four days: 1/5/9/13/17/21/25/29 (excluding 29 February).

• An updated convection model package.
  • CAPE output is limited to the most unstable convective available potential energy (MUCAPE) and the associated convective inhibition (MUCIN) together with associated derived products. 

• An amended and updated land surface model package
  • • An urban tile is added to the set of land cover tiles in HTESSEL to deal with the effects of built up areas.
• Assimilation of observed 2m (screen) temperatures.

• Extension of Clear Air Turbulence to include non-orographic gravity wave outside convection.An atmospheric composition package.
• Activation of the Stochastically Perturbed Parameterisations (SPP) package dealing with uncertainty in all ensemble configurations.

(FUG Associated with Cy49r1)