IFS Cycle 43r1 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.
With this cycle upgrade, the medium-range ensemble and its monthly extension see a major upgrade in the dynamical ocean model (NEMO): the resolution is increased from 1 degree and 42 layers to 0.25 degrees and 75 layers (ORCA025Z75). Furthermore, NEMO model version v3.4.1 with the interactive sea-ice model (LIM2) is implemented. The ocean and sea-ice components of the ENS initial conditions are provided by the new ocean analysis and reanalysis suite ORAS5, which uses the new ocean model and revised ensemble perturbation method.
The page will be updated as required. It was last changed on 19.09.2016.
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.
Data Assimilation methodology (atmosphere, land and ocean)
The sea-surface temperature (SST) perturbations used in the EDA have been upgraded to a recently developed climatology based on the HadISST.2 dataset. This makes the perturbations statistically consistent with the error characteristics of the analysis cycles.
The EDA-derived background error estimates used in 4DVAR are now computed at spectral resolution TL399 (previously TL159) and a new wavelet-based filtering algorithm is used to control sampling noise. The background error variance has been increased by ~16%.
The weak constraint option of 4DVAR has been reactivated using a model error forcing term active in the stratosphere above 40 hPa and a new estimate of the model error covariance matrix.
The land surface assimilation of SYNOP screen level observations now accounts for the vertical distance between the observations and model grid points. A new vertical structure function has been introduced that follows the approach used at Environment Canada and at Météo-France in MESAN-SAFRAN. The vertical correlation is expressed as a Gaussian function, consistent with that used for snow depth analysis. This gives more weight to observations from stations that are vertically closer to the model grid point (and less to observations less representative of the model altitude).
A new ocean analysis/re-analysis (ORAS5), based on NEMOVAR with a higher-resolution version of the ocean model NEMO (0.25 degrees with 75 vertical layers: ORCA025Z75) has been implemented. This uses the same ocean model version (NEMO v3.4.1) as ENS. ORAS5 uses a new perturbation strategy for the surface fluxes and to simulate observation errors. It also includes an improved quality-control scheme for ocean observations. Sea ice is assimilated within NEMOVAR, with a weakly coupled assimilation to the ocean dynamics.The analyses have been run from 1975 and continue in real-time to provide initial conditions for the ENS forecasts and re-forecasts.
Observations
Radiance assimilation will now take the viewing geometry more fully into account, by evaluating the radiative transfer along slantwise paths (instead of vertically). This is done for all clear-sky sounder radiances when interpolating model fields to observation locations.
A better treatment of observation uncertainty for IASI and CrIS has led to updated observation error covariance matrices and a change of ozone anchor channels in bias correction.
The channel selection for the hyperspectral infrared instrument CrIS has been revised and now uses 117 rather than 77 channels
The aerosol detection scheme for IASI has been revised making it independent of the bias correction. The scheme is also applied to both CrIS and AIRS.
Model changes
A new CAMS ozone climatology is now used, consisting of monthly means of a re-analysis of atmospheric constituents (CAMSiRA) for the period 2003 to 2014.
Changes to boundary layer cloud for marine stratocumulus and at high latitudes.
Modifications to surface coupling for 2 metre temperature.
Assimilation of snowfall from the NEXRAD RADAR network over the USA.
New model output fields include four cloud and freezing diagnostics (for aviation), a new direct-beam solar radiation diagnostic and improvements to the sunshine duration diagnostic.
Medium-range/monthly ensemble (ENS)
The horizontal and vertical resolutions of the ocean model (NEMO v3.4.1) used by ENS is increased from 1 degree and 42 layers to 0.25 degree and 75 layers (ORCA025Z75). An interactive sea-ice model (the Louvain-la-Neuve Sea Ice Model - LIM2) is introduced so that sea-ice cover evolves dynamically. Previously it was persisted for 15 days; over the next 30 days of the forecast, it was relaxed towards the climatology of the previous 5 years.
Ocean initial conditions are taken from ORAS5 instead of ORAS4.
A global fix for tendency perturbations in the stochastic model error scheme SPPT to improve conservation of humidity.
New model output fields for HRES and ENS comprise four cloud and freezing diagnostics (for aviation), and a new direct-beam solar radiation diagnostic
In addition, eight new wave model output fields are provided.
Parameters are available at the usual post-processing time steps. Further technical information is provided in the table.
| Date | Reason for update |
|---|---|
| 19.09.2016 | Initial version |