Implementation of IFS cycle 45r1

Description of upgrade

IFS Cycle 45r1 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.

The page will be updated as required. It was last changed on 21.03.2018.

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.

Timetable for implementation

The planned timetable for the implementation of the cycle 45r1 is as follows:

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

Current Status

The Alpha testing of cycle 45r1 will continue and the cycle is being passed to the Forecast Department to start the Beta testing.

Meteorological content of the new cycle

Assimilation

• Weakly coupled sea-ice atmosphere assimilation applied with the use of OCEAN5 sea-ice (instead of OSTIA) in the surface analysis of the high-resolution (HRES 4d-Var) and the ensemble of data assimilations (EDA) analyses;
• Relative humidity increments calculated using temperature instead of virtual temperature;
• Weak constraint model error forcing applied at every time step instead of every hour to avoid shocks in the model integration.

Observations

• Assimilation of non-surface-sensitive infra-red (IR) channels over land;
• Assimilation of all sky micro-wave (MW) sounding channels over coasts;
• Use of direct broadcast FY-3C MWHS2 data for better timeliness;
• Introduction of RTTOV-12 and new microwave instrument coefficients;
• Activation of constrained variational bias correction (VarBC);

• Retuning of the radiosonde observation error, and introduction of a scheme to account for radiosonde drift;

• Introduction of temperature bias correction of old-style AIREP observations; aircraft temperature varBC predictor upgraded to a three predictor model (cruise, ascent, descent); reduced thinning of aircraft data;

• Assimilation of JASON-3 and Sentinel-3A altimeters, and use of new altimeters for wave data assimilation;

Model

• Coupling of the 3-dimentional ocean and atmosphere: introduction of the coupling to the NEMO 3-dimentional ocean model also in the high-resolution forecast (HRES), with the same ocean model version used in the medium-range/monthly ensemble (ENS): NEMO3.4 in ORCA025_Z75 configuration; upgrade of the NEMO-IFS coupling strategy in both ENS and HRES to a full-coupling in the tropical region (partial-coupling-extra-tropics);
• Improved numerics for warm-rain cloud microphysics and vertical extrapolation for semi-lagrangian trajectory;
• Increased methane oxidation rate to improve (increase) water vapour in the stratosphere;
• Improved representation of super-cooled liquid water in convection, and minor convection updates;
• Improvements in the tangent forward and adjoint models linked to the convection scheme;
• Correction of soil thermal conductivity formulation and addition of soil ice dependency;
• New extended output parameters have been added. See below.
• Modified parameter for non-orographic gravity-wave drag scheme for 91 levels;
• Model error changes:
  • Stochastically perturbed parametrization tendency scheme (SPPT): improved flow-dependent error representation via reduced spread in clear skies regions (due to unperturbed radiative-tendency in clear sky), activation of tendency perturbations in stratosphere, and weaker tapering of perturbations in boundary layer; amplitude reduction of the SPPT perturbations patterns (by 20%);
  • EDA: cycling of stochastic physics random fields in the EDA, and adoption of the same SPPT configuration in EDA as in ENS;
  • Stochastic kinetic energy backscatter scheme (SKEB): deactivation of the stochastic backscatter (SKEB) scheme due to improved model error representation by the SPPT scheme (see above), leading to a 2.5% cost saving in the ENS;

Meteorological impact of the new cycle

The following evaluation of the new cycle is based on the alpha testing. Scorecards will be made available based on the beta testing phase.

Upper-air

The new cycle leads to improvements in HRES upper-air fields. Verified against the model analysis, a positive signal is seen throughout the troposphere for most parameters, except temperature in the lower troposphere at shorter ranges. The latter is mainly a result of changes to the analysis, as confirmed by corresponding neutral results against observations. Upper-air improvements are more pronounced in the tropics, especially for wind and temperature. Verified against observations, upper-air changes are overall positive in the tropics except for relative humidity, and neutral to slightly positive in the extratropics. Upper-air results for the ENS verified against analysis are mostly positive in the tropics but more neutral in the extratropics. The negative signal for temperature in the lower troposphere at shorter lead times is again mainly due to changes in the analysis. Against observations, results are mostly negative in the extratropics at early lead times and significantly positive in the tropics, with the exception of relative humidity at 700hPa. The negative impact in the extratropics is partly due to a slight reduction in ensemble spread associated with the transition to a physically more realistic SPPT scheme. Whether or not this reduced spread is genuinely detrimental depends on whether observation errors are taken into account in the verification which has not been done routinely so far. Experimental verification against radiosonde data that takes observation error into account indicates that a large fraction of the negative ENS results disappear or become statistically non-significant.

Weather parameters and waves

There is an overall improvement in 2m temperature both in the HRES and ENS, particularly for Europe. 2m humidity is largely neutral for HRES, but positive for ENS, particularly in the tropics. 10 m wind speed is largely neutral in the HRES and slightly negative in the ENS. Precipitation in the HRES is improved in terms of categorical verification (e.g. SEEPS), and near-coastal precipitation in warm-rain dominated situations is significantly improved due to changes in the cloud physics. However, these changes also lead to more activity at higher precipitation rates in active regions such as the East Asian monsoon, and as a result error measures such as RMSE or CRPS (for the ENS) are increased. The negative signal for significant wave height against analysis is a result of changes to the analysis from a large increase in observation usage, and verification against observations (buoys) shows the results are neutral for both HRES and ENS.

Tropical cyclones

The implementation of the ocean-atmosphere coupling in the HRES removes the overall negative bias in tropical cyclone central pressure and thereby reduces the mean absolute intensity error. The position error is slightly (and with marginal statistical significance) increased at longer time ranges.

Extended range

Changes in scores for the monthly system are generally positive across the range of parameters, with significance in week 1 for tropical winds. The only indication of a degradation is precipitation in the tropics with a consistent negative signal across all 4 weeks. There is an indication of a positive effect on skill across all parameters in the European domain. The MJO Index was significantly underspread, but changes in 45r1 to the SPPT scheme have brought the spread and error in close agreement throughout the 30 day forecast range. The underestimation of the MJO Index amplitude error has been significantly improved throughout the forecast.

Technical details of the new cycle

Changes to GRIB encoding

Model identifiers

The GRIB model identifiers (generating process identification number) for cycle 45r1 will be changed as follows:

New model output parameters

Extended output have been added in cycle 45r1, including precipitation rates, CAPE indices and a total lighting flash density.

paramId	Shortname	name	Description	units	GRIB edition	Component	Test data available	Dissemination	ecCharts	Proposed for Catalogue
228050	litoti	Instantaneous total lightning density	Total lightning flash density (instantaneous)	flashes km-2 day-1	2 (TBC)	HRES / ENS			TBC
228051	litota	Averaged total lightning density since previous post-processing	Total lightning flash density (averaged between consecutive post-processing time steps)	flashes km-2 day-1	2 (TBC)	HRES / ENS			TBC
228057	litota3	Averaged total lightning flash density over the past 3 hours	Averaged total (cloud-to-ground + intra-cloud) lightning flash density over the past 3 hours.	flashes km-2 day-1	2	HRES / ENS			TBC
228058	litota6	Averaged total lightning flash density over the past 6 hours	Averaged total (cloud-to-ground + intra-cloud) lightning flash density over the past 6 hours	flashes km-2 day-1	2	HRES / ENS			TBC
260048	tprate	Total precipitation rate	Total precipitation rate (instantaneous)	kg m-2 s-1	2	HRES / ENS			TBC
228035	mxcape6	maximum CAPE in the last 6 hours	Maximum CAPE in last 6 hours	J kg-1	2	HRES (TBC) / ENS			TBC
228036	mxcapes6	maximum CAPES in the last 6 hours	Maximum CAPESHEAR in last 6 hours	m2 s-2	2	HRES (TBC) / ENS			TBC

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