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The BADC File-naming Convention for ERA-40 Re-analysis data


The BADC has developed a new file-naming convention for its ECMWF ERA-40 Re-analysis archive. This document explains the how the file names are derived, presents a table of parameter codes, gives some examples of file names and explains the directory structure for the ERA-40 data.

File names

The ERA-40 files are held in individual files for each time-step and parameter. This allows the user to identify the contents of each file specifically from its name alone. The file-naming convention for ERA-40 files is as follows:


AA    is the grid type.
B    denotes whether the file contains analysis or forecast data.
C    is the level type.
YYYY    is the year (e.g. 1994).
MM    is the month (from 01 to 12).
DD    is the day of the month (from 01 to 31).
TT    is the time of day (either 00, 06, 12 or 18).
P[PPPP]    is the parameter name (from one to five characters).
[_SSh]    is the forecast time step (SS is number of hours since analysis). This field is only included for forecast fields where B is 'f'. 'h' represents the unit hours. .EXT    is the file extension, denoting the file format. The main archive is stored in GRIB format (.grb) although some data will be available in NetCDF format (.nc).

Table 1 shows the codes for each grid, field and level type.

Table 1.   Grid, field and level types in the ERA-40 file names.
Grid type Field type Level type
ggN80 Reduced Gaussian Grid aAnalysis (at the zero time-step) mModel level data
spSpectral T159 Resolution -- sSurface or single level data
gpRegular 1.0° x 1.0° Grid fForecast pPressure level data
liRegular 2.5° x 2.5° Grid -- tPotential temperature level data
lfRegular 1.125° x 1.125° Grid -- vPotential vorticity level data
* See explanation of forecast files for more details.

Parameter abbreviations are used in the file names. These vary in length from one to five characters. Table 2 shows a complete list of the ERA-40 parameter names, abbreviations, numeric ECMWF codes and units.

Table 2.   Parameters details in the ERA-40 file names.
Parameter name Parameter code (abbreviation) ECMWF code (numeric) Units
Potential temperaturePT3K
Low vegetation coverLVC27(0-1)
High vegetation coverHVC28(0-1)
Low vegetation type (table index)LVT29index
High vegetation type (table index)HVT30index
Sea ice fraction (1 = full ice, 0 = no ice)CI31(0, 1)
Snow albedoASN32-
Snow densityRSN33kg
Sea surface temperatureSSTK34K
Sea ice temperature layer 1ISTL135K
Sea ice temperature layer 2ISTL236K
Sea ice temperature layer 3ISTL337K
Sea ice temperature layer 4ISTL438K
Soil moisture level 1 (volumetric)SWVL139m3/m3
Soil moisture level 2 (volumetric)SWVL240m3/m3
Soil moisture level 3 (volumetric)SWVL341m3/m3
Soil moisture level 4 (volumetric)SWVL442m3/m3
Snow evaporation (accum.)ES44m
Snow melt (accum.)SMLT45m
Wind gusts at 10 m10FG49m s-1
Large scale precipitation fraction (accum.)LSPF50s
Montgomery potentialMONT53m2 s-2
Potential vorticityPV60m2 s-1 K kg-1
Geopotential (at the surface = orography)Z129m2 s-2
Specific humidityQ133kg/kg
Vertical velocityW135Pa s-1
Total column waterTCW136kg/m2
Total column water vapourTCWV137kg/m2
Vorticity (relative)VO138s-1
Soil temperature level 1STL1139K
Snow DepthSD141m (of water equivalent)
Large scale precipitation (accum.)LSP142m
Convective precipitation (accum.)CP143m
Snow fall (accum.)SF144m (of water equivalent)
Boundary layer dissipation (accum.)BLD145W m-2s
Surface sensible heat flux (accum.)SSHF146W m-2s
Surface latent heat flux (accum.)SLHF147W m-2s
Charnock parameterCHNK148-
Mean sea level pressureMSL151Pa
Log surface pressureLNSP152-
Relative humidityR157%
Boundary layer heightBLH159m
Standard deviation of subgrid scale orographySDOR160-
Anisotropy of subgrid scale orographyISOR161-
Angle of subgrid scale orographyANOR162-
Slope of subgrid scale orographySLOR163-
Total cloud coverTCC164(0-1)
10 metre u-wind component10U165m s-1
10 metre v-wind component10V166m s-1
2 metre temperature2T167K
2 metre dewpoint temperature2D168K
Downward surface solar radiation (accum.)SSRD169W m-2s
Soil temperature level 2STL2170K
Land/sea maskLSM172(0, 1)
Surface roughnessSR173m
Downward surface thermal radiation (accum.)STRD175W m-2s
Surface solar radiation (accum.)SSR176W m-2s
Surface thermal radiation (accum.)STR177W m-2s
Top solar radiation (accum.)TSR178W m-2s
Top thermal radiation (accum.)TTR179W m-2s
East/West surface stress (accum.)EWSS180N m-2s
North/South surface stress (accum.)NSSS181N m-2s
Evaporation (accum.)E182m (of water)
Soil temperature level 3STL3183K
Low cloud coverLCC186(0-1)
Medium cloud coverMCC187(0-1)
High cloud coverHCC188(0-1)
Sunshine duration since last post-processing stepSUND189s
Latitudinal component of gravity wave stress (accum.)LGWS195N m-2s
Meridional component of gravity wave stress (accum.)MGWS196N m-2s
Gravity wave dissipation (accum.)GWD197W m-2s
Skin reservoir contentSRC198m (of water)
Maximum temp. at 2m since previous post-processingMX2T201K
Minimum temp. at 2m since previous post-processingMN2T202K
Ozone mass mixing ratioO3203kg/kg
Runoff (accum.)RO205m
Total column ozoneTCO3206kg m-2
Top solar radiation clear sky (accum.)TSRC208W m-2s
Top thermal radiation clear sky (accum.)TTRC209W m-2s
Surface solar radiation clear sky (accum.)SSRC210W m-2s
Surface thermal radiation clear sky (accum.)STRC211W m-2s
Instantaneous X surface stressIEWS229N m-2s
Instantaneous Y surface stressINSS230N m-2s
Instantaneous surface heat fluxISHF231W/m2
Instantaneous surface moistrue flux (evaporation)IE232kg m-2s
Logarithm of surface roughness length for heatLSRH234-
Skin temperatureSKT235K
Soil temperature level 4STL4236K
Temperature of snow layerTSN238K
Convective snow fall (accum.)CSF239m (of water equivalent)
Large scale snow fall (accum.)LSF240m (of water equivalent)
Forecast albedoFAL243-
Forecast surface roughnessFSR244m
Forecast logarithm of surface roughness for heatFLSR245-
Cloud liquid water contentCLWC246kg/kg
Cloud ice water contentCIWC247kg/kg
Cloud coverCC248(0-1)

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Example file names

Since the file-naming system is rather complicated some examples are given below:

ggap1992010618o3.grb   - N80 Reduced Gaussian Grid, Analysis, Pressure Levels, 6 January 1992, 18:00 hours, Ozone Mass Mixing Ratio field, GRIB format.

spat1962102712vo.grb   - T159 Spectral resolution, Analysis, Potential Temperature Levels, 27 October 1962, 12:00 hours, Vorticity (relative), GRIB format.

ggfm1974123100ciwc_24h.grb   - N80 Reduced Gaussian Grid, Forecast, Model Levels, 31 December 1974, 00:00 hours (start time of forecast), 24 hours (forecast step time), therefore valid time of data is 1974-12-31 00:00 + 24 hours = 1975-01-01 00:00, Cloud Ice Water Content field, GRIB format.

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Directory names and structure

The directory system for the ERA-40 archive uses the following structure:


AA    is the grid type.
B    denotes whether the file contains analysis or forecast data.
C    is the level type.
YYYY    is the year (e.g. 1994).
MM    is the month (from 01 to 12).
DD    is the day of the month (from 01 to 31).
file_name    is the file name as discussed above (e.g. spat1991041700pres.grb).

Note that if you accessing the data via the BADC web-interface (BADC registered users only), the data can be found at:

The directory system beyond the data directory is as above:


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