Description of the upgrade

The IFS Cycle 50r1, will bring  major changes to the IFS model and data assimilation system, including among many others:

• New ocean and sea ice models  based on NEMO4-SI ³
• Updates of the wave model including: n ew wave interaction with sea ice and ocean currents and revised wave model bathymetry
• Modified Stochastically Perturbed Parametrisation (SPP) configuration to reduce 10-metre wind spread in the ensemble
• New ocean and sea ice ensemble analysis system & outer loop coupling of ocean/sea-ice
• Reintroduction of stratospheric humidity assimilation from radiosondes up to 60 hPa
• Weak constraint formulation extended to the boundary layer allowing the increased use of T2m observations 

After making the high-resolution forecast (HRES) and 'control' member of medium range ensemble forecast (ENS control) identical in IFS Cycle 49r1, with this model upgrade we will stop producing the current ENS control, and the data stream that was formerly called the HRES will be called ENS control instead.

More detailed information will be made available in the coming weeks.

For  any questions, please contact us via the ECMWF Support Portal.

#IFS50r1 #newfcsystem @ECMWF

News

Datasets affected

• ENS Control (ex-HRES) (day 1-15)

• ENS (day 1-15)

• ENS Sub-seasonal (day 1-46)

• Control-WAM (ex-HRES-WAM) (day 1-15)

• ENS-WAM (day 1-15)

• ENS-WAM Sub-seasonal (day 1-46)

Resolution

There will be no resolution changes in this cycle.

Dissemination schedule

ENS control forecast will be disseminated earlier than currently, in the same schedule of the ex-HRES.

Meteorological content

Assimilation

• New ocean and sea ice ensemble analysis system
• Outer-loop coupled Data Assimilation of ocean and sea-ice
• A weak constraint formulation is extended to the boundary layer which allows for assimilation of many more T2m observations than in previous cycles
• Coupled ocean-atmosphere assimilation of microwave imagers and geostationary infrared data giving increments to ocean and sea-ice as well as upper air
• EDA configuration change: perturbed members' resolution reduction (TL399 to TL255)
• Scale-selective EDA re-centring to address issues with tropical cyclone initialisation arising from high-resolution EDA outer loop
• Single precision trajectories in 4DVar
• Introduction of time-varying correction in Weak Constraint 4D-Var with extension to the troposphere
• Reintroduction of stratospheric humidity assimilation from radiosondes up to 60 hPa
• An upgrade of the Radiative Transfer for TOVS (RTTOV) model to version 14, improving the simulation of satellite radiances for assimilation
• Increased number of wave observations being assimilated

Observations

• Upper air observations
  • Allowing specific humidity increments above the tropopause constrained by high quality radiosondes
  • The length of the observation timeslots has been reduced from 30 minutes to 15 minutes, allowing for a more accurate comparison between the model and the observations.  
  • Introduction of wind tracing with-ozone sensitive data
• Ocean observations
  • Activation of in situ temperature/salinity profiles (e.g. ARGO, moored buoy, ship subsurface, mammal, gliders, AXBTs etc)
  • Activation of Sea Level Anomaly (SLA) along-track products from Altika/Cryosat-2/Jason-3/Sentinel-3a/Sentinel-3b

Model

• New ocean and sea ice model based on NEMO4-SI³ (see more here), with the updates including:

  • Improved numerical schemes and physical parametrisation
  • Introduction of multi-category sea ice model with prognostic salinity and melt pond dynamics
  • Replacement of the LIM2 sea ice model with the more advanced SI³ model
  • Climatological sea ice albedo replaced with albedo diagnosed by sea ice model SI³
  • Introduction of the Generic Length Scale (GLS) turbulence scheme for better vertical mixing processes
  • Use of the extended tripolar ORCA grid (eORCA025) (grid extends further towards the South Pole) 
• New ensemble analysis system for ocean and sea ice based on ORAS6 reanalysis (see more here).
  This is used for initialising both the forecasts and the re-forecasts.
  The updates include:
  • Hourly surface forcing from ERA5 atmospheric reanalysis. This allows much more accurate representation of short-term variability, such as diurnal cycle of sea surface temperature, which is not captured with daily forcing used in earlier systems.
  • Introduction of a flow-dependent background error covariance using ensemble of data assimilations
  • First-time use of variational assimilation of sea surface temperature (SST) with flow-dependent errors.
• Wave model:  
  • New waves and sea ice interaction
  • Revised wave model bathymetry  
• New glacier parametrisation scheme for ecLand component replaces the previous binary glacier mask with one that accounts for how much of the grid area is covered by ice and uses a four-layer land-ice scheme
• Snow (single layer representation) on sea ice tile – in NWP, reduces the warm bias seen in winter over the ice surface especially in cloud free situations
• Modified Stochastically Perturbed Parametrisation (SPP) configuration to reduce 10-metre wind spread in the ensemble, and related misalignment of wind speed and wave height in perturbed members
• Model physics:
  • Convection and microphysics changes to improve the propagation of precipitation from ocean across land
  • Physics call reordering with vertical diffusion now called last
  • Reduced vertical diffusion in stable conditions in the stratosphere
• Coupling:
  • Coupling of snow depth and sea ice thickness from the sea ice model to the atmosphere, to allow snow over sea ice and variable ice thickness to be represented in the atmospheric forecast model
  • Partial coupling is switched off to enable fully coupled ocean-atmosphere forecasts, meaning the atmosphere now uses sea surface temperatures (SSTs) directly from the ocean model

Meteorological impact

Medium range

• Improvements to forecasts of light precipitation
• Better representation of convective precipitation: the revised convection / cloud-microphysics scheme reduces “stationary” convective precipitation, improving inland propagation of rainfall
• Improved tropical upper-air temperature and wind forecasts (at 850 hPa and 250 hPa) by up to ~7%, thanks to updates in aerosol climatology, convection, and physics ordering
• Improvement of temperature and humidity forecasts around the tropopause due to assimilation of stratospheric humidity from radiosondes up to 60 hPa
• Reduction of the known SST warm bias in the Southern Ocean  
• Improved Western Boundary Currents (e.g. Gulf Stream), and related large SST biases. 
• Dynamic evolution of marine variables (e.g. SST/SIC) in the analysis consistent with validity time
• Forecasts of total cloud cover, dewpoint temperature and 10-metre winds over sea improved by 1-2%, largely due to changes in the physics of the model
• Reduced ensemble wind spread at 10 m: the revised Stochastically Perturbed Parametrisation (SPP) scheme yields more realistic ensemble spread, particularly reducing excessive near-surface wind extremes 

Sub-seasonal range

• Increased forecast skill for quasi-biennial oscillation (QBO) in tropical stratospheric winds — stronger amplitude and more realistic vertical descent
• More realistic stratospheric dynamics 

Evaluation

Interactive scorecards presenting the new cycle performance are coming soon.

Key configuration changes

Atmospheric model

• ENS Control run (stream = enfo, type=cf) will become stream=oper type=fc

• There will be no change in vertical or horizontal resolution nor steps of the Atmospheric model  

Wave model

• There will be no change in horizontal resolution nor steps of the Wave model

Technical content

Changes to GRIB encoding

The GRIB model identifiers (generating process identification number) for cycle 50r1 will be changed as follows:

Resources

Webinars

References

• Upgrade to IFS Cycle 50r1, Polichtchouk, I.,  Massart, S., Kipling, Z., ECMWF Newsletter No 185 - Autumn 2025
• The introduction of waves in sea ice, Kousal, J., Bidlot, J., Steer, J., Rabault, J. (Norwegian Meteorological Institute), Müller, M. (Norwegian Meteorological Institute and The University of Oslo), ECMWF Newsletter No 185 - Autumn 2025
• Visible radiances in ECMWF's analysis, Necker, T., Lupu, C., Quesada-Ruiz, S., Firat, V., Scheck L. (DWD), Benedetti A., ECMWF Newsletter, No 184 - Summer 2025    
• Reintroducing the analysis of humidity in the stratosphere, Semane, N., Bonavita, M ., ECMWF Newsletter No 183 - Spring 2025
• Analysing humidity in the stratosphere improves forecasts , ECMWF News item, 23 June 2025
• Solar eclipses in IFS forecasts and (re)analyses , Lopez, P., ECMWF Newsletter No 181 - Autumn 2024
• Introduction of a new ocean and sea-ice model based on NEMO4-SI3, Keeley , S., Mogensen K., Bidlot J.R ., Boussetta S., Alonso Balmaseda, M., Hatfield S., ECMWF Newsletter No 180 - Summer 2024
• ECMWF’s next ensemble reanalysis system for ocean and sea ice: ORAS6 , Zuo, H., Alonso Balmaseda, M., De Boisséson, E., Browne, P., Chrust, M., Keeley, S., Mogensen, K., Pelletier, C., De Rosnay, P., Takakura, T., ECMWF Newsletter No 180 - Summer 2024
• Plans for high-resolution forecast (HRES) and ensemble forecast (ENS) control run , ECMWF In focus item, 5 March 2024

For any questions, please contact us via the ECMWF Support Portal .