Description of the upgrade
In the IFS Cycle 47r2 single-precision for ENS (forecast up to day 46 and hindcast) and HRES (forecast) will be introduced. Moreover, the ENS vertical levels will be increased to 137 to bring it in line with HRES.
Users of ENS model levels (in particular users of Time-Critical Applications or customers retrieving or receiving model levels) are advised to check the Technical content below.
A set of 12 auxiliary surface fields will be added to the ENS control forecast.
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#IFS47r2 #newfcsystem @ECMWF
NEWS!
A summary of the cycle performance is now available
'Introducing ECMWF CY47r2' webinars
- 2nd December 2020 at 14:30 UTC: join the webinar
- 15th December 2020 at 08:30 UTC: join the webinar
IFS Cycle 47r2 content and implementation timeline announced
Implementation timeline
Meteorological content
In this model cycle single-precision for ENS (forecast up to d+46 and hindcast) and HRES (forecast) will be introduced. Research carried out at the University of Oxford, Météo-France and ECMWF has shown that it is possible to significantly reduce the arithmetic precision of many of the calculations performed in numerical weather prediction models without compromising the quality of weather forecasts. ‘Single precision’ forecasts have the advantage of being computationally less expensive than traditional ‘double precision’ forecasts. Such efficiency savings will greatly facilitate the introduction of higher-resolution ensemble forecasts and other model improvements in line with ECMWF’s Strategy to 2025. The article 'Progress in using single precision in the IFS' provides additional information.
Moreover, the ENS vertical levels will be increased to 137 to bring it in line with HRES.
Meteorological impact
Evaluation of 47r2
The two changes at 47r2 were a reduction to single precision in our HRES and ENS forecasts and (with the computational savings made) an increase from 91 to 137 levels in the ENS forecast. Our deterministic and ensemble analyses, including background forecasts, remain at double precision, and so are unaffected.
The change to single precision leads to no significant change in forecast skill, but there are benefits of the increased levels in the ENS. These benefits include:
- Reduction in westerly bias at 200hPa over the tropical Indian Ocean and West Pacific (e.g. 20% at day 2). This is coincident with better maintenance of the amplitude of the Madden Julian Oscillation (MJO), increased MJO spread, and improved MJO skill to day 30 (statistically significant throughout the first two weeks).
- Reduction in Stratospheric cold bias out to week 4 (e.g. 30% at day 10 at 50hPa) due to better resolving the vertical structure of gravity waves.
- Improved regional reliability (particularly in 850hPa subtropical temperatures) due to better resolving the boundary layer inversion.
- Deeper tropical cyclones, with reduced intensity errors and increased intensity spread, which result in better forecast reliability. Tropical Cyclone tracks are unchanged on average.
- An overall improvement in Continuous Rank Probability Score (CRPS) when considering all variables, all lead times and all regions (North Hemisphere, Southern Hemisphere, Tropics).
- Although the operational seasonal system is unchanged at 47r2, research experiments are showing improved teleconnections between the Quasi-Biennial Oscillation (QBO) and the North Atlantic oscillation (NAO).
New parameters
The table contains the list of parameters expected to be available with the model implementation. They will be available as part of the test data.
Param ID | Short Name | Name | Unit | Component & type | GRIB edition | Level type | MARS | Added to Catalogue | ecCharts | Dissemination |
|---|---|---|---|---|---|---|---|---|---|---|
aluvpi | UV visible albedo for direct radiation, isotropic component | (0-1) | ENS CF | 1 | sfc |
| TBC | | TBC | |
aluvpv | UV visible albedo for direct radiation, volumetric component | (0-1) | ENS CF | 1 | sfc |
| TBC | | TBC | |
aluvpg | UV visible albedo for direct radiation, geometric component | (0-1) | ENS CF | 1 | sfc |
| TBC | | TBC | |
alnipi | Near IR albedo for direct radiation, isotropic component | (0-1) | ENS CF | 1 | sfc |
| TBC | | TBC | |
alnipv | Near IR albedo for direct radiation, volumetric component | (0-1) | ENS CF | 1 | sfc |
| TBC | | TBC | |
alnipg | Near IR albedo for direct radiation, geometric component | (0-1) | ENS CF | 1 | sfc |
| TBC | | TBC | |
sdfor | Standard deviation of filtered subgrid orography | m | ENS CF 1 | 1 | sfc |
| TBC | | TBC | |
sdor | Standard deviation of orography | - | ENS CF 1 | 1 | sfc |
| TBC | | TBC | |
isor | Anisotropy of sub-gridscale orography | - | ENS CF 1 | 1 | sfc |
| TBC | | TBC | |
anor | Angle of sub-gridscale orography | radians | ENS CF 1 | 1 | sfc |
| TBC | | TBC | |
slor | Slope of sub-gridscale orography | - | ENS CF 1 | 1 | sfc |
| TBC | | TBC | |
lsrh | Logarithm of surface roughness length for heat | - | ENS CF 1 | 1 | sfc |
| TBC | | TBC |
1 Available at step 0 only.
Technical content
Increase of ENS vertical resolution to 137 model levels
With this cycle upgrade the number of vertical model levels in ensemble forecasts (ENS) increases from 91 to 137, bringing it to the same vertical resolution as HRES. The L137 model level definitions and the correspondence between the L91 and L137 model levels are available online. Please note that the L137 model level data cannot be converted back to GRIB edition 1 without the loss of information.
Users getting ENS data on model levels are advised to check their data requests and processing. Getting all model levels, 137 instead of 91, will increase the amount of data by a factor of 1.5. This will affect resources like disc space, array sizes, processing and transfer times. Users should adapt any limits and requirements, e.g. wallclock time, memory, accordingly.
Users getting specific model levels should revise their selection based on the correspondence between the L91 and L137 model levels.
Availability of IFS cycle 47r2 test data
The release candidate test data and products, which are expected to be made available in February 2021, will be generated daily, shortly behind operational high resolution and ensemble runs and based on the operational dissemination requirements. The availability of the test data does not follow any strict schedule.
Resources
Peter D. Dueben, Michail Diamantakis, Simon Lang, Sami Saarinen, Irina Sandu, Nils Wedi and Tomas Wilhelmson. Progress in using single precision in the IFS. ECMWF Newsletter, 2018.
Filip Vana, Glenn Carver, Peter D. Dueben, Simon Lang, Tim Palmer, Martin Leutbecher, and Deborah Salmond. Single-precision IFS. ECMWF Newsletter, 148, 2016