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ECMWF plans to upgrade the horizontal resolution of its integrated forecasting system (IFS) including its high-resolution (HRES) and ensemble (ENS) forecasts.The upgraded horizontal resolution will be 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) will be increased to 18 km.

A new cycle of the IFS will be 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 changing from linear (T_L) to cubic (T_C) spectral truncation and introducing an octahedral reduced Gaussian grid. With the cubic spectral truncation the shortest resolved wave is represented by four rather than two grid points and 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.

News

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:

the meteorological content of the new cycle
the forecast performance including an updated scorecard for HRES and now also for ENS
releases of supporting software, and
how to access IFS cycle 41r2 test data via product dissemination and ecCharts.

In addition, small corrections to the lake cover and leaf index constant surface specification files has 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.

Timetable for implementation

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

4 November 2015	Initial announcement to Member States and other customers
8 December 2015	Availability of test data in dissemination
8 March 2016	Expected date of implementation

Document versions

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