Cycle 43r3

This upgrade of ECMWF’s Integrated Forecasting System (IFS) implemented on 11 July improves forecast skill in medium-range and monthly forecasts. IFS Cycle 43r3 includes changes in the model and in the assimilation of weather observations.

Model changes include a new radiation scheme, improvements in the modelling of convection and a new aerosol climatology.

Changes in data assimilation and in the way dropsonde observations are handled have improved the accuracy of the initial conditions on which forecasts are based. This is especially true of tropical cyclones.

The new cycle only includes meteorological changes; there are no technical changes, e.g. new resolutions.

Implementation date: 11 July 2017See News article
Detailed description of changes 
Key characteristics of our current forecasting system 


  • Atmospheric (unchanged)

    • HRES: O1280
    • ENS Days 1 - 15: O640
    • ENS extended (Days 16 - 46): O320
  • Wave (unchanged)
    • HRES-WAM: 0.125°
    • HRES SAW: 0.1°
    • ENS-WAM: 0.25°
    • ENS-WAM Extended: 0.5°
  • Ocean (unchanged)
    • NEMO: 0.25°


  • Atmospheric (unchanged)
    • HRES: L137
    • ENS: L91





  • Ocean (unchanged)
    • NEMO: 75

Data set affected

  • HRES
  • ENS
Scorecard for 43r3
Meteorological changes

Data Assimilation     

  • Improved humidity background error variances directly from the EDA like for all other variables.
  • Revised wavelet filtering of background error variances and revised quality control of drop-sonde wind observations in 4DVAR to improve tropical cyclone structures.


  • Increased use of microwave humidity sounding data by adding new sensors (SAPHIR, GMI 183 GHz channels).
  • Activation of 118 GHz channels over land from MWHS-2 instrument on-board FY-3C.
  • Harmonised data usage over land and sea-ice for microwave sounders (adding MHS channel 4 over snow, adding some ATMS channels, lower observation errors for MHS data over land).
  • Improved screening of infrared observations for anomalously high atmospheric concentrations of hydrogen cyanide (HCN) from wildfires.
  • Improved quality control for radio occultation observations and radiosonde data.

Model changes    

  • New, more efficient radiation scheme with reduced noise and more accurate longwave radiation transfer calculation.
  • New aerosol climatology based on ‘tuned’ CAMS aerosol re-analysis including dependence on relative humidity.
  • Increased super-cooled liquid water at colder temperatures (down to -38C) from the convection scheme.
  • Visibility calculation changed to use ‘tuned’ CAMS aerosol climatology.
Meteorological impacts

Upper air

Results for the HRES from alpha- and beta-testing are positive, with many of the scores over North Hemisphere, South Hemisphere and Europe indicating statistically significant improvements at the 95% level up to about forecast day 5 when forecasts are verified against own analysis. When forecasts are verified against observations, the positive impact of 43r3 is also evident.

Improvements are larger in summer than in winter and are to a large extent due to improvements in the humidity background error, as well as changes to the deep convection scheme and the aerosol climatology, which improved the temperature gradient between extra-tropics and tropics.

Improvements are significant for temperature and vector wind throughout the extra-tropical troposphere.

In the tropics there is some deterioration in temperature and humidity at certain vertical levels associated with the changes to the deep convection scheme.

Surface parameters show partially statistically significant improvements both in the tropics and extra-tropics (2-m humidity, 10-m wind speed, total cloud cover, precipitation), except for 2-m temperature which shows neutral results.

Weather parameters and waves

Over the ocean, statistically significant improvements are seen for verification against own analysis for 10-m wind speed, significant wave height, and mean wave period.


Results for the ENS based on alpha-testing are mainly positive and similar to the HRES both for upper-air and surface variables for the North Hemisphere, South Hemisphere and Europe when verified against analysis.

In the tropics there is some deterioration in upper tropospheric wind speed and lower tropospheric temperature associated with reduced spread. There are also some slight deteriorations in tropical 2-m temperature and precipitation scores.

Tropical cyclones

Changes in the tropical cyclone analysis are notable, with the cyclone structure defined in a better way. At forecast day 1 there is a marginally significant improvement in position error; the improvement is undetectable thereafter.

Tropical cyclone intensity (as measured by central pressure) is slightly reduced from day 2 onwards: for lead times beyond four days this has a beneficial effect since it reduces the existing negative bias in tropical cyclone central pressure in such forecasts.

You can find statistics on the Cycle 43r3 tropical cyclones forecast performance in  TCPerformance_43r3_43r1.pdf.

Technical changes
  • Upgrade to the dynamical ocean model used for the medium-range ensemble and its monthly extension
  • Changes to GRIB encoding
  • Changes to forecast products
    • new model output
Model ID
  • Atmospheric: 148
  • Ocean wave:  113
  • HRES standalone ocean wave: 213
New disseminated model outputThere are no new parameters introduced with cycle 43r3.
e-suite experiment number 0071