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Description of the upgrade

On 8 March 2016, ECMWF upgraded the horizontal resolution of its integrated forecasting system (IFS) including its high-resolution (HRES) and ensemble (ENS) forecasts. The upgraded horizontal resolution is about 9 km for the HRES and the data assimilation (the outer loop of the 4D-Var) and about 18 km for the ENS up to day 15 and about 36 km for the extended range (monthly). The resolution of the ensemble of data assimilations (EDA) is increased to 18 km.

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A new cycle of the IFS has been introduced to implement the horizontal resolution upgrade. This cycle is labelled 41r2, and includes a number of enhancements to the model and data assimilation. The main contents of IFS cycle 41r2 are:

  • The horizontal resolution is increased by using a cubic reduced Gaussian grid (with spectral truncation denoted by TC) instead of the current linear reduced Gaussian grid (denoted by TL).  With the cubic reduced Gaussian grid the shortest resolved wave is represented by four rather than two grid points.  In addition, a new form of the reduced Gaussian grid,  the octahedral grid, is used.  The octahedral grid is globally more uniform than the previously used reduced Gaussian grid.
  • The realism of the kinetic energy spectrum is significantly improved with more energy in the smaller scales due to a reduction of the diffusion and removal of the dealiasing filter, enabled by the change to using a cubic truncation for the spectral dynamics.
  • There is a significant revision to the specification of background error covariances (B) used in the HRES data assimilation due to the increased resolution of the EDA and the introduction of scale-dependence of the hybrid B (climatological and EDA), thereby relying more on the EDA "errors of the day" for the smaller scales.
  • There are improvements in the use and coverage of assimilated satellite data due to changes in observation selection and error representation (for GPS radio occultation data, all-sky microwave, AMSU-A, IASI and AMVs) and improved observation operators for radiance data from microwave sounders.
  • The stability of the semi-Lagrangian scheme near strong wind gradients is improved, reducing noise downstream of significant orography and in tropical cyclones.
  • The radiative heating/cooling at the surface is improved by introducing approximate updates on the full resolution grid at every timestep. This leads to a reduction in 2-metre temperature errors, particularly near coastlines.
  • Additionally there are changes to the triggering of deep convection, non-orographic wave drag and improvements to the linear physics in the data assimilation (for gravity wave drag, vertical diffusion and the surface exchange).

These upgrades

  • do not include any increase in the vertical resolution;
  • do not apply to the ECMWF seasonal forecasts;
  • do not apply to the standalone wave model (HRES-SAW);
  • do apply to products from the Boundary Condition Optional Programme.

Note

Implemented: 8 March 2016.

News

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10 March 2016

IFS cycle 41r2 has been implemented successfully in ECMWF operations. For further information see New forecast model cycle brings highest-ever resolution.

The first run with the new cycle was the 06 UTC "Boundary Condition" cycle on Tuesday 8 March 2016. The monthly forecast extension to the ensemble will be run with the new IFS cycle for the first time on Thursday 10 March 2016.

As announced previously, the IFS cycle 41r2 Ensemble re-forecasts for Thursday 10 March remain available in the test dissemination system as expver=69. They are also available in MARS with expver=1.

So far, two issues with products from the new cycle have been reported:

  1. The GRIB model identifiers (the generating process identification number) for the ECMWF ocean wave forecasts have not changed as previously announced and remain at 111 and 211 for the Ocean wave model and the HRES standalone wave model, respectively.
  2. A small number of parameters from the HRES surface analysis have been encoded with an incorrect GRIB model identifier.  These will be corrected during the week beginning Monday 14 March 2016.

ECMWF would be grateful for any further feedback from forecast users about data from the new cycle.

Finally, ECMWF wishes to thank all users for their efforts to prepare their systems for the change by using our test datasets.

1 March 2016


This is a final reminder that ECMWF's IFS will be upgraded to cycle 41r2 on Tuesday 8 March 2016.

The first operational run using the new cycle will be the 06 UTC analysis and forecast in the Boundary Conditions Optional Programme on 8 March followed by the 12 UTC main assimilation and forecast. The monthly forecast extension to the ensemble will be run with the new IFS cycle for the first time the following Thursday 10 March 2016.

  • Dissemination schedule unchanged
    There will be no changes to the dissemination schedule with the implementation of cycle 41r2. We will continue to work on further optimisations of our operational suites over the next few months and will review the schedule for ENS products after the HPC upgrade.
  • Suspension of changes to the dissemination requirements
    In order to manage the transition, changes to dissemination requirements will be suspended from 10 UTC on Monday 7 March 2016 to 10 UTC on Wednesday 9 March 2016..  On the day of implementation products will be disseminated based on users' current operational (i.e., IFS cycle 41r1) dissemination requirements.
  • Ensemble overlap products in dissemination
    For users of the ensemble overlap products, compatibility products will be provided at STEP=240 until the end of March 2016.  Users of these products are encouraged to change their requirements at the earliest opportunity to make best use of the harmonised resolution of the ENS products up to and including day 15.
  • Ensemble re-forecast products in dissemination
    On Monday 7 March 2016, the ensemble re-forecast products for Thursday 10 March 2016 will be disseminated as usual and based on the current (IFS cycle 41r1) operational requirements.  Users requiring ensemble re-forecast products based on the new (IFS cycle 41r2) cycle should take these from the test product dissemination system once the cycle upgrade has been confirmed.  There will be no re-transmission of the ensemble re-forecast products based on IFS cycle 41r2 for Thursday 10 March 2016.
  • Ensemble re-forecast products archived in MARS
    Following the upgrade, the ensemble re-forecast products archived in MARS for Thursday 10 March 2016, Monday 14 March 2016 and Thursday 17 March 2016 will be replaced with with those from IFS cycle 41r2 and so will correspond to the ensemble forecast monthly extension fields archived for those dates.
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10 February 2016

ECMWF is continuing to make good progress with the forthcoming introduction of IFS cycle 41r2.  The implementation is planned for Tuesday 8 March 2016.

The IFS cycle 41r2 detailed implementation page provides further information and the most recent updates on:

In addition, small corrections to the lake cover and leaf index constant surface specification files have been introduced for both HRES and ENS IFS 41r2 test data from 12 UTC on 10 February 2016.

Forecast users are encouraged to carry out their own tests with the new model data.  IFS cycle 41r2 test data can be accessed via MARS,  product dissemination and ecCharts.

14 January 2016

Test  product dissemination system has been fully opened to Member State users and the Data Services to request 41r2 test dissemination products. Products can be requested in the usual manner at https://ecpds-xmonitor.ecmwf.int/do/product/requirements.

Users can request dissemination products from a new 0.1 degree based grid from the high resolution forecast as well as 0.2 degree based grid from the ENS (days 1 to 15) and 0.4 degree based grid from the ENS Extended run. In addition, 0.125 degree based grid products have been made available from the global coupled wave model, 0.25 degree based products from the ENS-WAM and 0.1 degree based products from the HRES-SAW model.

As announced previously, please note that requesting Gaussian grid products has changed in the MARS language

  •    GAUSSIAN=regular,GRID=640 changes to GRID=F640
  •    GAUSSIAN=reduced,GRID=640 changes to GRID=N640

New octahedral grid based products can be requested by specifying GRID=O1280, etc. As before, any sub-area of the global field is supported.

Test dissemination products are generated within 41r2 e-suites and made available to users on https://ecpds-xmonitor.ecmwf.int/ . Users can trigger transmission of test products at their convenience.

23 December 2015

The problem with the GRIB encoding of some fields provided via the test dissemination system reported on 22 December 2015 has been resolved as of 23 December 2015.

22 December 2015

A problem has been found with the GRIB encoding of some fields provided via the test dissemination system.  Fields interpolated to a regular latitude-longitude grid have the first and last latitude points encoded incorrectly in the GRIB header. Typically, the values for fields on global grids are encoded with:

  •    latitudeOfFirstGridPointInDegrees = 89.946
  •    latitudeOfLastGridPointInDegrees = -90.054

instead of 90.0 and -90.0, respectively. Similar incorrect encodings of the latitudes are seen for fields interpolated to sub-areas of a regular latitude-longitude grid.

The issue is known to affect all surface parameters, pressure and model level grid point fields (such as specific humidity) and potential vorticity on theta surface. Analysts are investigating and will correct the encoding as soon as possible. 

8 December 2015

  • Formal start of the Release Candidate Phase of the pre-operational testing. Parallel product dissemination of 41r2 test data is now available.
  • ENS and ENS-WAM days 11 to 15 will be run at the same resolution as days 0 to 10. Resolution overlap products, EFOV, will be provided from day 14 to day 15 and these will be provided for the ENS Extended only. The ENS extension to 46 days will run twice a week (Mondays and Thursdays) as before. The specific ENS calibration / validation products are discontinued.
  • A new corrected land-sea mask (LSM) was introduced for both HRES and ENS IFS 41r2 test data from 12 UTC on 9 November 2015.

4 November 2015

  • HRES and ENS technical test data are now available in MARS for one calendar day, together with the software needed to decode and manipulate these data. At this stage, we invite you to do some technical tests with the octahedral grid or at the lat/lon resolutions you currently use.

Full technical and meteorological detail about the new cycle

Full technical and meteorological details can be found in the IFS cycle 41r2 detailed implementation  page.

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Timeline of the implementation

The planned timetable for the implementation of IFS cycle 41r2 is as follows:

Date

Event

4

...

Nov 2015Initial announcement to Member States and other

...

forecast users
8

...

Dec 2015Availability of test data in dissemination
14 Jan 2016Test data in dissemination available at upgraded resolution
9 Feb 2016Update of default software versions at ECMWF
8

...

Mar 2016

Expected date of implementation

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

Datasets affected

  • HRES
  • ENS
  • HRES-WAM
  • HRES-SAW
  • ENS-WAM

Resolution

Resolutions in bold increased/changed from previous IFS cycle.


Component

Horizontal resolution

Vertical resolution
[levels] 

Atmosphere

HRES

O1280

~9 km

137

ENS

O640

~18 km

91

ENS extended 

O320

~36 km

91

Wave

HRES-WAM

0.125°

~14 km

-


HRES SAW0.1°~11km

ENS-WAM 

0.25°

~28 km

-


ENS-WAM Extended

0.5° 

~55 km

-

Ocean

NEMO 3.4

0.25°

~28 km

75

Meteorological content

The main contents of IFS cycle 41r2 are:

  • The horizontal resolution is increased by using a cubic reduced Gaussian grid (with spectral truncation denoted by TC) instead of the current linear reduced Gaussian grid (denoted by TL).  With the cubic reduced Gaussian grid the shortest resolved wave is represented by four rather than two grid points.  In addition, a new form of the reduced Gaussian grid,  the octahedral grid, is used.  The octahedral grid is globally more uniform than the previously used reduced Gaussian grid.
  • The realism of the kinetic energy spectrum is significantly improved with more energy in the smaller scales due to a reduction of the diffusion and removal of the dealiasing filter, enabled by the change to using a cubic truncation for the spectral dynamics.
  • There is a significant revision to the specification of background error covariances (B) used in the HRES data assimilation due to the increased resolution of the EDA and the introduction of scale-dependence of the hybrid B (climatological and EDA), thereby relying more on the EDA "errors of the day" for the smaller scales.
  • There are improvements in the use and coverage of assimilated satellite data due to changes in observation selection and error representation (for GPS radio occultation data, all-sky microwave, AMSU-A, IASI and AMVs) and improved observation operators for radiance data from microwave sounders.
  • The stability of the semi-Lagrangian scheme near strong wind gradients is improved, reducing noise downstream of significant orography and in tropical cyclones.
  • The radiative heating/cooling at the surface is improved by introducing approximate updates on the full resolution grid at every timestep. This leads to a reduction in 2-metre temperature errors, particularly near coastlines.
  • Additionally there are changes to the triggering of deep convection, non-orographic wave drag and improvements to the linear physics in the data assimilation (for gravity wave drag, vertical diffusion and the surface exchange).

These upgrades

  • do not include any increase in the vertical resolution;
  • do not apply to the ECMWF seasonal forecasts;
  • do not apply to the standalone wave model (HRES-SAW);
  • do apply to products from the Boundary Condition Optional Programme.

See more details of the meteorological content of cycle 41r2 ...

Meteorological impact

See details of meteorological impacts of Cycle 41r2.

Evaluation

Comparison of scores between IFS cycle 41r2 and IFS cycle 41r1 for HRES and ENS can be found in the IFS cycle 41r2 scorecard.

New and changed parameters

See new and changed parameters within the technical changes section.

Technical content

Summary of technical changes

  • Resolution changes
  • New grid: the octahedral grid, for both HRES and ENS. See Introducing the octahedral reduced Gaussian grid for further details.
  • Changes to GRIB encoding
  • Changes to forecast products
    • increased field
    • new model output parameters
    • correction to solar zenith angle for the sunshine duration diagnostic
    • correction to the interpolation method used for the precipitation type diagnostic
  • Changes to software

See details of technical changes in Cycle 41r2. 

  • Atmospheric: 146
  • Ocean wave: 111 (unchanged)
  • Standalone ocean wave: 211 (unchanged)

Availability of IFS 41r2 test data


Time-critical applications

See details of time-critical applications within the technical changes section.

Resources 

Document versions

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4 November 2015
  • Initial version
8 December 2015
  • Announced start of Release Candidate testing phase
  • Test data available in dissemination and ecCharts
  • ENS Days 11 - 15 will be run at the same resolution as ENS Days 0 - 10
22 December 2015
  • Issue identified with test dissemination data.
23 December 2015
  • Issue identified on 22 December 2015 resolved.
14 January 2016
  • Full opening of test product dissemination system announced.
10 February 2016
  • Expected implementation date announced
  • Updates to default software versions at ECMWF
  • Updated HRES and ENS scorecard
1 March 2016
  • Implementation date confirmed as Tuesday 8 March 2016
10 March 2016
  • Successful implementation of IFS cycle 41r2 confirmed
28 July 2016
  • Links to ECMWF Newsletter articles.

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