Implementation Date: 18 May 2011
The new cycle includes both meteorological and technical changes. The main technical change is that from this cycle onwards the WMO FM-92 GRIB edition 2 (GRIB-2) is used for the encoding of model-level data.
Observation processing
See the Observation Data Base documentation.
Data assimilation
Chapter 1: Overview
Chapter 2: 4D variational assimilation
Chapter 3: Tangent-linear physics
Chapter 4: Background term
Chapter 5: Observation operators and observation cost function (Jo )
Chapter 6: Background, analysis and forecast errors
Chapter 7: Gravity-wave control
Chapter 8: Diagnostics
Chapter 9: Observation processing
Chapter 10: Observation screening
Chapter 11: Land-surface analysis
Chapter 12: Analysis of sea-ice concentration and sea surface temperature
Chapter 13: Data flow
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Dynamics and numerical procedures
Chapter 1: Introduction
Chapter 2: Basic equations and discretization
Chapter 3: Semi-Lagrangian formulation
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Physical processes
Chapter 1: Overview
Chapter 2: Radiation
Chapter 3: Turbulent transport and interactions with the surface
Chapter 4: Subgrid-scale orographic drag
Chapter 5: Non-orographic gravity wave drag
Chapter 6: Convection
Chapter 7: Clouds and large-scale precipitation
Chapter 8: Surface parametrization
Chapter 9: Methane oxidation
Chapter 10: Ozone chemistry parametrization
Chapter 11: Climatological data
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Ensemble Prediction System
Chapter 1: Methodology
Chapter 2: Computational details: initial perturbations
Chapter 3: Computational details: non-linear integrations
References
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Technical and Computational Procedures
Chapter 1: Structure, data flow and standards
Chapter 2: Parallel implementation
Appendix A: Structure, data flow and standards
Appendix B: Message Passing Library (MPL)
Appendix C: The TRANS package
Appendix D: FullPos user guide
Appendix E: FullPos technical guide
Appendix F: Coding standards
Appendix G: The Perforce source code management system user guide
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Wave Model
Chapter 1: Introduction
Chapter 2 The kinematic part of the energy balance equation
Chapter 3 Parametrization of source terms and the energy balance in a growing wind sea
Chapter 4 Data assimilation in WAM
Chapter 5 Numerical scheme
Chapter 6 WAM model software package
Chapter 7 Wind wave interaction at ECMWF
Chapter 8 Extreme wave forecasting
Chapter 9 Second-order spectrum
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Meteorological Changes
- Background error variances from the ensemble of data assimilations (EDA) used by the deterministic 4D-Var assimilation
- Improvements to cloud scheme formulation
- Changes to all-sky assimilation of microwave data
- Reduction of AMSU-A observation errors and adjustments to MODIS AMVs
- Accounting for tangent point drift in GPS radio occultation
Changes specifically to the ENS
There are no specific changes to the ENS configuration apart from the model changes described above. The impact on the ENS is a small reduction in spread throughout the forecast range. The change is neutral in terms of probabilistic scores.
Technical Aspects
From cycle 37r2, ECMWF uses WMO FM-92 GRIB edition 2 (GRIB-2) encoding for its model level fields for the deterministic forecast and the EPS, including monthly forecasts. GRIB-1 model-level data will no longer be produced and disseminated. This applies to model level products only; all other operational data will remain in GRIB-1.
The EMOS library GRIBEX routine cannot handle GRIB-2 fields. In order to be able to handle both GRIB-1 and GRIB-2 fields, it is recommended to use grib_api. Download the latest version of the grib_api library
EMOSLIB
In order to be able to interpolate GRIB-2 fields, users must upgrade to version 000381 (released on 22 March 2011) or higher of EMOSLIB.
Second-order packing
Encoding of second order packed data in GRIB-1 and GRIB-2 has been implemented in version 1.9.8 of grib_api.
- GRIB-1 second order data encoded with grib_api can be decoded by GRIBEX.
- Encoding of GRIB-2 second order data is not fully compliant with the WMO FM-92 specifications and therefore a local template has been designed for it. For further details, see GRIB API keys for GRIB edition 2.
- Decoding of second order packed data produced by GRIBEX has been fully implemented in previous grib_api versions.
Latitude and longitude values for reduced Gaussian grids in GRIB-2
Latitude and longitude values of the first and last point are encoded in millidegrees in GRIB-1 and in micro-degrees in GRIB-2. As those values are encoded with the highest possible accuracy in each GRIB edition users should expect to get different values in GRIB-1 and GRIB-2 fields.
The latitudes and longitudes for each grid point can be obtained from grib_api with high accuracy using the keys latitudes, longitudes, distinctLatitudes, distinctLongitudes or using the grib_get_data Fortran functions or the grib_iterator C functions.
As grib_api is computing latitudes and longitudes from the order N of the Gaussian grid the values are identical in both editions and they are very accurate. Definitions of the various Gaussian grids in use at ECMWF can be found here.
Coding of negative longitude values in GRIB-2
According to the WMO FM-92 GRIB edition 2, only positive values of longitudeOfFirstGridPoint, longitudeOfLastGridPoint, longitudeOfSouthernPole are allowed. Negative values of longitudeOfFirstGridPointInDegrees, longitudeOfLastGridPointInDegrees, longitudeOfSouthernPoleInDegrees are converted by grib_api to positive values by adding 360 to the value before encoding.
Conversion
Please see GRIB edition 1 to 2 conversion. GRIB-2 to GRIB-1
PrepIFS experiments
PrepIFS experiments for IFS cycle 37r2 and above produce data in GRIB-2 for model level parameters and GRIB-1 for the rest.
Discontinuation
- The trajectory module in Metview 3 and the corresponding trajectory database have not been migrated to GRIB-2. The trajectory database has been discontinued.
- The 'multi-analysis suite' producing forecasts from other global NWP centres' analyses has been discontinued. Such data was stored in MARS as stream = AMAP / MAED / MAWV.
Meteorological impact
The impact of the new cycle on the performance of the forecasting system has been tested in research mode during the period June to December 2010, and in pre-operational runs during the period since 1 January 2011. The new cycle shows clear benefit in terms of objective upper-air scores in the medium range in both hemispheres: temperature and winds are improved throughout the troposphere. Tropical wind scores are also improved. The improvements to the cloud scheme increase the humidity in the upper troposphere. This results in some increase in bias, but overall provides a better fit to observations and improves humidity scores in the extra-tropics in the early forecast range.