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Description of upgrade

IFS Cycle 46r1 is an upgrade with many scientific contributions, including changes in data assimilation (both in the EDA and the 4DVAR), in the use of observations, and in modelling. The new cycle only includes meteorological changes; there are no technical changes, e.g. new resolutions. This upgrade does not apply to the ECMWF seasonal forecasting system or to the CAMS global forecasting system.

The page will be updated as required. It was last changed on 31.01.2018. We would encourage you to click the "watch" button (above right in this page) to receive notification of further updates.

For a record of changes made to this page please refer to  Document versions.

Further information and advice regarding the upgrade can be obtained from User Support.


Cycle 46r1 live-streamed seminars

We will organise two live-streamed seminars to introduce the new IFS cycle 46r1. The first seminar will mainly cover the Scientific changes made in the new Cycle and will take place on Tuesday, 26 Feb. 2019 at 09:30 UTC and repeated on Thursday, 07 Mar. 2019 at 17 :30 UTC. The second seminar will focus more on the meteorological impact and scores of the new cycle, with details on how to access the Cycle 46r1 release candidate  test data. This second seminar will be organised about one month before the implementation date and will also be repeated a second time. Dates for the second seminar will be confirmed. You will have the opportunity to raise any questions during all these seminars.

To attend any of these seminars, please follow the link below:

There is no need to pre-register.

Timetable for implementation

The planned timetable for the implementation of the cycle 46r1 is as follows:

January 2019Initial announcement
26 February and 07 March 2019Live-streamed seminar 1
May 2019Availability of test data in dissemination
Live-streamed seminar 2
June 2019

Expected date of implementation

The timetable represents current expectations and may change in light of actual progress made.

Meteorological content of the new cycle


  • Continuous data assimilation. Number of 4D-Var outer loops increased from 3 to 4. Early delivery assimilation window length increased from 6 to 8 hours. Observation cut off time extended.
  • Ensemble of Data Assimilations (EDA) increased from 25 members to 50 members.
  • Weakly coupled data assimilation introduced for sea-surface temperature in the tropics only.
  • Consistent spatial interpolation of the model to observation locations in trajectories and minimisations. Interpolation in nonlinear trajectories changed from bicubic to bilinear interpolation.
  • RTTOV upgraded from v12.1 to v12.2.


  • Assimilation of SMOS neural network soil moisture product.
  • Assimilation of SSMIS-F17 150h GHz and GMI 166 v/h GHz.
  • Improved use of land sea mask in the field of view for microwave imagers.
  • Introduction of interchannel observation error correlations for ATMS.
  • Introduction of interchannel observation error correlations for geostationary water vapour channels.
  • Slant path calculations for geostationary radiances.
  • Extend usage of geostationary radiances to higher zenith angles.
  • Consistent infrared aerosol detection

For further details, read Main Contributions in data assimilation and observations.


  • Improvements in convection scheme (entrainment, CAPE closure, shallow convection).
  • Activate LW scattering in radiation scheme.
  • 3D aerosol climatology replaces 2D climatology.
  • Correct scaling of dry mass flux in diffusion scheme.
  • Improvement of the TL/AD of the semi-Lagrangian departure point scheme in the polar cap area.
  • Fix instability in 2m temperature diagnostic related to wet tile.
  • Bug fix in the computation of rain amount that could freeze when intercepted by the snow-pack.
  • New parameterizations for wind input and deep water dissipation for the wave model.
  • Limit on wave spectrum for very shallow water and minimum depth set to 3m.
  • ENS makes use of 50 EDA-members and initial perturbations are made exchangeable.
  • ENS radiation time-step is reduced from 3 hours to 1 hour, to be consistent with HRES.

For further details, read Main Contributions in modelling


The new IFS cycle 46r1 will use the ERA5 data to initialize the re-forecasts and also use ERA5 EDA to perturb the re-forecast initial condition

Document versions


DateReason for update
31.01.2019Initial version
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  1. The first seminar  ... will take place on Tuesday, 26 Feb. 2019 at 09:30 

    Which time zone?

  2. UTC. Added this to the document. Thanks.