Implementation of IFS Cycle 43r1

#newfcsystem

Description of upgrade

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 18.10.2016. Latest change: Meteorological impact of the new cycle and update to New model output parameters.

The next update to this page is expected to be on 24.10.2016.

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.

Timetable for implementation

The planned timetable for the implementation of IFS cycle 43r1 is as follows:

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

Meteorological content of the new cycle

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 T_L399 (previously T_L159) 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 global momentum, energy and moisture conservation properties.

Technical changes

• ecCodes replaces grib_api for encoding and decoding model output in GRIB.

New model output parameters

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.

• The magnitude and direction of the wave energy flux that is responsible for the impact of the waves on coastlines and offshore structures.
• Significant wave height of all waves in six different period ranges to help with detection of low-frequency wave energy.

All the new output fields are available at the usual post-processing time steps except where specified otherwise in the table:

• HRES, HRES-WAM and HRES-SAW: analysis and forecast - 3-hourly from T+0 to T+144 and 6 hourly from T+150 to T+240.
• ENS and ENS-WAM: 3-hourly from T+0 to T+144 and 6 hourly from T+150 to T+360.
• ENS-extended and ENS-WAM-extended: 6 hourly from T+366 to T+1104.

Further technical information is provided in the table.

paramId	shortName	name	description	units	GRIB edition	Component	Test data available	Dissemination	Proposed for Catalogue
260109	ceil	Ceiling	Cloud-base height relative to the ground.	m	2	HRES / ENS		TBC	TBC
228046	hcct	Height of convective cloud top		m	1	HRES / ENS		TBC	TBC
228047	hwbt0	Height of zero-degree wet-bulb temperature	See 43r1 new parameters: Height of zero-degree (and one-degree) wet-bulb temperature	m	1	HRES / ENS		TBC	TBC
228048	hwbt1	Height of one-degree wet-bulb temperature	See 43r1 new parameters: Height of zero-degree (and one-degree) wet-bulb temperature	m	1	HRES / ENS		TBC	TBC
47	dsrp	Direct solar radiation	Incident on a plane perpendicular to the sun's direction. This is an accumulated field.	J/m2	1	HRES / ENS NB: only forecast		TBC	TBC
140112	wefxm	Wave energy flux magnitude	Integral over all frequencies and directions of the product of the group speed and the two-dimensional energy wave spectrum.	W/m	1	HRES-WAM / ENS-WAM / HRES-SAW		TBC	TBC
140113	wefxd	Wave energy flux mean direction	Spectral mean direction over all frequencies and direction of the product of the group velocity vector and the two-dimensional energy wave spectrum.	Degree true	1	HRES-WAM / ENS-WAM / HRES-SAW		TBC	TBC
140114	h1012	Significant wave height of all waves with periods within the inclusive range from 10 to 12 seconds	Significant wave height of all waves with periods within the inclusive range from 10 to 12 seconds, where the significant wave height is defined as 4 times the square root of the integral over all directions and all frequencies between 1/12 and 1/10 Hz of the two-dimension wave spectrum	m	1	HRES-WAM / ENS-WAM / HRES-SAW		TBC	TBC
140115	h1214	Significant wave height of all waves with periods within the inclusive range from12 to 14 seconds	Significant wave height of all waves with periods within the inclusive range from 12 to 14 seconds, where the significant wave height is defined as 4 times the square root of the integral over all directions and all frequencies between 1/14 and 1/12 Hz of the two-dimension wave spectrum	m	1	HRES-WAM / ENS-WAM / HRES-SAW		TBC	TBC
140116	h1417	Significant wave height of all waves with periods within the inclusive range from 14 to 17 seconds	Significant wave height of all waves with periods within the inclusive range from 14 to 17 seconds, where the significant wave height is defined as 4 times the square root of the integral over all directions and all frequencies between 1/17 and 1/14 Hz of the two-dimension wave spectrum	m	1	HRES-WAM / ENS-WAM / HRES-SAW		TBC	TBC
140117	h1721	Significant wave height of all waves with periods within the inclusive range from 17 to 21 seconds	Significant wave height of all waves with periods within the inclusive range from 17 to 21 seconds, where the significant wave height is defined as 4 times the square root of the integral over all directions and all frequencies between 1/21 and 1/17 Hz of the two-dimension wave spectrum	m	1	HRES-WAM / ENS-WAM / HRES-SAW		TBC	TBC
140118	h2125	Significant wave height of all waves with periods within the inclusive range from 21 to 25 seconds	Significant wave height of all waves with periods within the inclusive range from 21 to 25 seconds, where the significant wave height is defined as 4 times the square root of the integral over all directions and all frequencies between 1/25 and 1/21 Hz of the two-dimension wave spectrum	m	1	HRES-WAM / ENS-WAM / HRES-SAW		TBC	TBC
140119	h2530	Significant wave height of all waves with periods within the inclusive range from 25 to 30 seconds	Significant wave height of all waves with periods within the inclusive range from 25 to 30 seconds, where the significant wave height is defined as 4 times the square root of the integral over all directions and all frequencies between 1/30 and 1/25 Hz of the two-dimension wave spectrum	m	1	HRES-WAM / ENS-WAM / HRES-SAW		TBC	TBC

The following new variable resolution parameter is also provided in the ensemble forecast variable resolution overlap stream (STREAM=EFOV) at T+360 (STEP=360) from the Monday and Thursday runs of the ensemble forecast monthly extension.

paramId	shortName	name	description	units	GRIB edition	Component	Test data available	Dissemination	Proposed for Catalogue
230047	dsrpvar	Direct solar radiation (variable resolution)	Variable resolution companion to dsrp.	J/m2	1	ENS (STREAM=EFOV)		TBC	TBC

Meteorological impact of the new cycle

Comparison of scores between IFS cycle 43r1 and IFS cycle 41r2 for HRES can be found in the IFS Cycle 43r1scorecard.

Upper air

The new model cycle provides improved high-resolution forecasts (HRES) and ensemble forecasts (ENS) throughout the troposphere and lower stratosphere. In the extra-tropics, error reductions of the order of 0.5-1% are found for most upper-air parameters and levels. The improvement in the primary headline score for the HRES (lead time at which the 500 hPa geopotential anomaly correlation drops below 80%) is about 1 h.

Improvements are most consistently seen in verification against the model analysis. In the tropics, there is a small degradation (both against analysis and observations) of temperature near the tropopause in terms of root mean square error (RMSE) but not in terms of anomaly correlation. This is due to a slight cooling caused by a modification in the treatment of cloud effects in the vertical diffusion scheme, which overall leads to improved cloud cover. While there is a consistent gain for upper-air parameters on the hemispheric scale, some continental-scale areas, such as North America and East Asia, show statistically significant improvements only at some levels and for some parameters.

Increases in upper-air skill of the ENS are generally similar to the HRES, with a substantial gain for mean sea level pressure. The improvement in the primary headline score for the ENS (lead time at which the CRPSS of the 850 hPa temperature drops below 25%) is small (of the order of 0.5 h). The spread-error relationship is generally improved, partly due to reduced error and partly due to increased spread. For some parameters this improvement is quite significant, such as the 850 hPa wind speed in the tropics, where the under-dispersion is reduced by about 20% in the medium range.

Weather parameters and waves

The new model cycle yields consistent gains in forecast performance in the tropics and extra-tropics for total cloud cover, mostly due to a reduction of the negative bias in low cloud cover.  

Changes in precipitation over land areas are small and overall neutral.

The increase in forecast skill for 2m temperature is most pronounced in the short and medium range, where it amounts to ~1% reduction of the RMSE in the northern hemisphere extra-tropics, and up to 2% over some land areas such as Europe and North America. In the tropics there is an increase of 0.5-1% in the RMSE for 2m temperature, connected to a slight increase of the overall cold bias at low latitudes. In the ENS there is a significant improvement in 2m temperature amounting to a 3% reduction in the continuous ranked probability score (CRPS) in Europe.

There is an increase of the RMSE of 2m humidity by about 1% in winter associated with the introduction of limited evapotranspiration when the uppermost soil layer is frozen. This change contributes to the improvements in 2m temperature.  

10m wind speed shows error reductions of 0.5-1% over the ocean, leading to improvements in significant wave height and mean wave period, especially in the tropics and southern hemisphere. Over land areas, changes in 10m wind speed forecast skill are generally neutral to slightly positive.

Monthly forecast

Verification results show a modest positive effect on skill scores although the differences are not statistically significant. There is a substantial improvement in the skill scores for the Madden-Julian Oscillation (MJO), corresponding to a gain in lead time of 0.5-1 day at a forecast range of 4 weeks. Also, MJO spread is increased, bringing it closer to the RMSE. Verification of precipitation against analysis shows some degradation in the tropics which is not statistically significant, and a reduction of precipitation biases in the northwest Pacific.

Sea ice

The new cycle introduces a prognostic sea-ice model, leading to a significant reduction of the RMSE of sea ice fraction in the later medium range.

Technical details of the new cycle

Upgrade to the dynamical ocean model

The medium-range ensemble and its monthly extension see a major upgrade in the dynamical ocean model.  The main changes are summarised in the table.

ORAS5 complements the current ocean reanalysis system (ORAS4) until there is no longer need for the ORAS4 output.

Changes to GRIB encoding

Model identifiers

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

Software

EMOSLIB

EMOSLIB 443 is needed to  interpolate successfully the wave energy flux mean direction (wefxd) parameter introduced at IFS Cycle 43r1.

GRIB API

GRIB API version 1.17.0 provides full support for the new model output parameters introduced in IFS Cycle 43r1. 

Older versions of GRIB API can decode the IFS Cycle 43r1 products successfully but users are advised to use at least GRIB API version 1.14.5, which provides full support for the octahedral reduced Gaussian grid.

ecCodes

ecCodes version 2.0.0 provides full support for the new model output parameters introduced in IFS Cycle 43r1.

Availability of test data from the IFS Cycle 43r1 test suites

Test data in MARS

Test data from the IFS Cycle 43r1 test suites are available in MARS. The data are available with experiment version 0070 (MARS keyword EXPVER=0070) starting from 06 UTC on 10 August 2016. Currently these data are from the beta testing stage.

The data can be accessed in MARS from:

• HRES (class=od, stream=oper, expver=70)
• Wave HRES (class=od, stream=wave, expver=70)
• ENS (class=od, stream=enfo, expver=70)
  • 00 UTC cycle only
• ENS Wave (class=od, stream=waef, expver=70)
  • 00 UTC cycle only

Only registered users of ECMWF computing systems will be able to access the test data sets in MARS.

The data are intended for testing technical aspects only and should not be used for operational forecasting.  Please report any problems you find with this data to User Support.

Test data in dissemination

Availability of test data from the release candidate testing stage in dissemination is expected to be announced during the week beginning 24 October 2016.

Document versions