ERA-Interim production stopped on 31st August 2019

For ERA-Interim (1st January 1979 to 31st August 2019) access through the ECMWF Web API stopped on 01 June 2023

Its successor ERA5 is available from the Climate Data Store (CDS) (What are the changes from ERA-Interim to ERA5?) and users are strongly advised to migrate to ERA5 (How to download ERA5).

For those users who still need access to ERA-Interim after 01 June 2023 (subject to further notice), they can do so via the Climate Data Store (CDS) API.

Table of Contents

Introduction

Here we document the ERA-Interim dataset, which, covers the period from 1st January 1979 to 31st August 2019.

ERA-interim was produced using cycle 31r2 of the Integrated Forecast System (IFS - CY31R2) 2006, with 60 vertical levels, with the top level at 0.01 hPa. Atmospheric data are available on these levels and they are also interpolated to 37 pressure, 16 potential temperature and 1 potential vorticity

level(s). "Surface or single level" data are also available, containing 2D parameters such as precipitation, 2m temperature, top of atmosphere radiation and vertical integrals over the entire atmosphere.

Generally, the data are available at a sub-daily and monthly frequency and consist of analyses and 10-day forecasts, initialised twice daily at 00 and 12 UTC. Most analysed parameters are also available from the forecasts. There are a number of forecast parameters, e.g. mean rates and accumulations, that are not available from the analyses.

How to download ERA-Interim

The data are archived in the ECMWF data archive MARS and datasets are available until 31 May 2023 through both the ECMWF Web interface and the ECMWF WebAPI, which is the programmatic way of retrieving data from the archive.

Until further notice, ERA-Interim is also available via the API of the C3S Climate Data Store.

Documentation is available on How to download ERA-Interim data from the ECMWF data archive (Member State users can access the data directly from MARS, in the usual manner).

The IFS and data assimilation

The model documentation for CY31r2 (choose Cy31r1) is at https://www.ecmwf.int/en/publications/ifs-documentation.

The 4D-Var data assimilation uses 12 hour windows from 15 UTC to 03 UTC and 03 UTC to 15 UTC (the following day).

The model time step is 30 minutes.

Data organisation

The data can be accessed from MARS using the keywords class=ei. Subdivisions of the data are labelled using stream, type and levtype.

Stream:

  • oper: sub-daily products
  • wave: sub-daily ocean-waves products
  • mnth: synoptic monthly means
  • moda: monthly means of daily means
  • mdfa: monthly means of daily forecast accumulations

Type:

  • an: analyses
  • fc: forecasts

Levtype:

  • sfc: surface or single level
  • pl: pressure levels
  • pt: potential temperature levels
  • pv: potential vorticity levels
  • ml: model levels


In MARS: the date and time of the data is specified with three MARS keywords:

  • date
  • time
  • step

For analyses date and time, specify the analysis time and step equal to 0 hours. For forecasts date and time, choose the forecast start time and then step specifies the number of hours since that start time. The combination of date, time and forecast step defines the validity time. For analyses, the validity time is equal to the analysis time.

Spatial grid

The horizontal grid spacing of ERA-Interim atmospheric model and reanalysis system is around 80 km (reduced Gaussian grid N128) which became around 83km ( \( 0.75^{\circ} \) ) when interpolated to a regular lat/lon grid.

Depending on the parameter, the data are archived either as the full T255 spectral resolution and on the corresponding N128 reduced Gaussian grid, depending on their basic representation in the model. The coupled ocean-wave model data are produced and archived on a reduced \( 1.0^{\circ}\times 1.0^{\circ} \) latitude/longitude grid. For more information see ERA-Interim archive report Version 2.0, Section 2.

It is possible to specify the grid when downloading data. Available options are:

  • GRIB1 format  (native format): native grid, different Gaussian grids, and regular lat/lon grids. Data will be interpolated to your chosen grid if different to the native one.
  • NetCDF format: NetCDF only supports regular lat/lon grids. Data is transformed to a regular lat/lon grid, interpolated to your selected resolution, and converted from the native GRIB1 format to NetCDF.

Longitudes range from 0 to 360, which is equivalent to -180 to +180 in Geographic coordinate systems.

Spatial reference systems

The ECMWF model assumes the Earth is a perfect sphere, but the geodetic latitude/longitude of the surface elevation datasets are used as if they were the spherical latitude/longitude of the ECMWF model.

ECMWF data is referenced in the horizontal with respect to the WGS84 ellipse (which defines the major/minor axes) but in the vertical it is referenced to the Geoid (EGM96).

Earth model

For data in GRIB1 format (as is the case with ERA-Interim data) the earth model is a sphere with radius = 6367.47 km, as defined in the WMO GRIB Edition 1 specifications, Table 7, GDS Octet 17

For data in NetCDF format (i.e. converted from the native GRIB format to NetCDF), the earth model is inherited from the GRIB data.

Temporal frequency

Analyses of atmospheric fields on model levels, pressure levels, potential temperature and potential vorticity, are available every 6 hours at 00, 06, 12,  and 18 UTC. Forecasts run twice at 00 and 12 UTC and provide 3 hours output for surface and pressure level parameters up to 24 hours, with decreasing frequency to 10 days.


Wave spectra

The ERA-Interim atmospheric model is coupled ocean-wave model resolving 30 wave frequencies and 24 wave directions at the nodes of its reduced \( 1.0^{\circ}\times 1.0^{\circ} \) latitude/longitude grid.

Download from ERA-Interim

Wave data can be downloaded using the same mechanisms as atmospheric data. Please see How to download ERA-Interim

For wave spectra you need to specify the additional parameters 'direction' and 'frequency'. If you want to download the data in NetCDF format, please add the 'format' and 'grid' parameters.

Decoding 2D wave spectra in GRIB

To decode wave spectra in GRIB format we recommend ecCodes. Wave spectra are encoded in a specific way that other tools might not decode correctly.

In GRIB, the parameter is called 2d wave spectra (single) because in GRIB, the data are stored as a single global field per each spectral bin (a given frequency and direction), but in NetCDF, the fields are nicely recombined to produce a 2d matrix representing the discretized spectra at each grid point.

The wave spectra are encoded in GRIB using a local table specific to ECMWF. Because of this, the conversion of the meta data containing the information about the frequencies and the directions are not properly converted from GRIB to NetCDF format. So rather than having the actual values of the frequencies and directions, values show index numbers (1,1) : first frequency, first direction, (1,2) first frequency, second direction, etc ....

For ERA, because there are a total of 24 directions, the direction increment is 15 degrees with the first direction given by half the increment, namely 7.5 degree, where direction 0. means going towards the north and 90 towards the east (Oceanographic convention), or more precisely, this should be expressed in gradient since the spectra are in m^2 /(Hz radian)
The first frequency is 0.03453 Hz and the following ones are : f(n) = f(n-1)*1.1, n=2,30

Also note that it is NOT the spectral density that is encoded but rather log10 of it, so to recover the spectral density, expressed in m^2 /(radian Hz), one has to take the power 10 (10^) of the NON missing decoded values. Missing data are for all land points, but also, as part of the GRIB compression, all small values below a certain threshold have been discarded and so those missing spectral values are essentially 0. m^2 /(gradient Hz).

Decoding 2D wave spectra in NetCDF

The NetCDF wave spectra file will have the dimensions longitude, latitude, direction, frequency and time.

However, the direction and frequency bins are simply given as 1 to 24 and 1 to 30, respectively.

The direction bins start at 7.5 degree and increase by 15 degrees until 352.5, with 90 degree being towards the east (Oceanographic convention).

The frequency bins are non-linearly spaced. The first bin is 0.03453 Hz and the following bins are: f(n) = f(n-1)*1.1; n=2,30. The data provided is the log10 of spectra density. To obtain the spectral density one has to take to the power 10 (10 ** data). This will give the units 2D wave spectra as m**2 s radian**-1 . Very small values are discarded and set as missing values. These are essentially 0 m**2 s radian**-1.

This recoding can be done with the Python xarray package, for example:

import xarray as xr
import numpy as np
da = xr.open_dataarray('2d_spectra_201601.nc')
da = da.assign_coords(direction=np.arange(7.5, 352.5 + 15, 15))
da = da.assign_coords(frequency=np.full(30, 0.03453) * (1.1 ** np.arange(0, 30)))
da = 10 ** da
da = da.fillna(0)
da.to_netcdf(path='2d_spectra_201601_recoded.nc')

Units of 2D wave spectra

Once decoded, the units of 2D wave spectra are m2 s radian-1


Instantaneous and Accumulated parameters

Instantaneous parameters represent an average over the model time step (30min). Accumulated parameters are accumulated from the start of the forecast, ie. from 00 UTC or 12 UTC to the time step selected. All the analysed fields are instantaneous instead forecast data could be either instantaneous or accumulated, depending on the parameter. More detailed information on parameters are shown in Parameter listing.

Minimum/maximum since the previous post processing

In ERA-Interim there are some parameters named '...since previous post-processing', for example 'Maximum temperature at 2 metres since previous post-processing'. This represents the maximum temperature between the previous archived forecast 'Step' and the forecast 'Step'. For example, 'Maximum temperature at 2 metres since previous post-processing' with start time 00 UTC and Step=9, is the maximum 2m temperature in the 3-hour period between 06 UTC and 09 UTC.

Monthly means

ERA-interim sub-daily data are monthly averaged on data with valid times or accumulation periods that fall within the calendar month in question. The different monthly means are:

  • Synoptic Monthly Means (stream=mnth) are the monthly averages:
    • for each analysis time (at the four main synoptic hours - 00, 06, 12, and 18 UTC)
    • for each forecast start time (00 and 12 UTC) and step (3, 6, 9, 12 etc).
  • Monthly Means of Daily Means (stream=moda) are only available for analysis and instantaneous forecast data.
  • Monthly Means of Daily Forecast Accumulations (stream=mdfa) are similar to Monthly Means of Daily Means but are for accumulated fields (eg precipitation, radiation) and three step ranges are available.

See also Section 3 of the ERA-Interim archive documentation.

Data format

Model level fields are in GRIB2 format. All other fields are in GRIB1, unless otherwise indicated.

Level listings

Pressure levels: 1000/975/950/925/900/875/850/825/800/775/750/700/650/600/550/500/450/400/350/300/250/225/200/175/150/125/100/70/50/30/20/10/7/5/3/2/1

Potential temperature levels: 265/275/285/300/315/320/330/350/370/395/430/475/530/600/700/850

Model levels: 1/to/60, which are described at L60 model level definitions

Potential vorticity level: \( PV=\pm 2PVU \)

Parameter listings

Tables 1-6 below describe the surface and single level parameters (levtype=sfc), Table 7 describes wave parameters, Table 8 describes the monthly mean exceptions for surface and single level and wave parameters and Tables 9-13 describe upper air parameters on various levtypes. Information on all ECMWF parameters is available from the ECMWF parameter database.

Parameters described as "instantaneous"  below, are valid at the specified time.

Instantaneous, invariant, surface and single level parameters table

count

name

an

fc

paramId

units

1

Low vegetation cover

x


27

(0-1)

2

High vegetation cover

x


28

(0-1)

3

Low vegetation type (table index - see Table 10.1 in IFS CY31R1 Documentation)

x


29

index

4

High vegetation type (table index - see Table 10.1 in IFS CY31R1 Documentation)

x


30

index

5

Standard deviation of filtered subgrid orography

x


74

m

6

Surface geopotential

x

x

129

m2s-2

7

Standard deviation of orography

x


160

m

8

Anisotropy of orography X

x


161

~

9

Angle of sub-grid scale orography

x


162

~

10

Slope of sub-grid scale orography

x


163

~

11

Land-sea mask

x

x

172

(0 - 1)

Instantaneous, varying, surface and single level parameters table

count

name

an

fc

paramId

units

1

Sea ice fraction

x

x

31

(0 - 1)

2

Snow albedo

x

x

32

(0 - 1)

3

Snow density

x

x

33

kg m-3

4

Sea surface temperature

x

x

34

K

5

Sea ice temperature layer 11

x

x

35

K

6

Sea ice temperature layer 21

x

x

36

K

7

Sea ice temperature layer 31

x

x

37

K

8

Sea ice temperature layer 41

x

x

38

K

9

Volumetric soil water level 12

x

x

39

m3 m-3

10

Volumetric soil water level 22

x

x

40

m3 m-3

11

Volumetric soil water level 32

x

x

41

m3 m-3

12

Volumetric soil water level 42

x

x

42

m3 m-3

13

Convective available potential energy (CAPE)


x

59

J kg-1

14

Total column liquid water


x

78

kg m-2

15

Total column ice water


x

79

kg m-2

16

Surface pressure3

x

x

134

Pa

17total column waterxx136kg m-2
18total column water vapourxx137kg m-2

19

Soil temperature level 1

x

x

139

K

20

Snow depth

x

x

141

m of water equivalent

21

Charnock parameter

x

x

148

~

22

Mean sea level pressure

x

x

151

Pa

23

Boundary layer height


x

159

m

24

Total cloud cover

x

x

164

(0 - 1)

25

10 metre U wind component

x

x

165

m s-1

26

10 metre V wind component

x

x

166

m s-1

27

2 metre temperature

x

x

167

K

28

2 metre dewpoint temperature

x

x

168

K

29

Soil temperature level 2

x

x

170

K

30Surface roughnessx
173m
31Albedo (climate)x
174~

32

Soil temperature level 3

x

x

183

K

33

Low cloud cover

x

x

186

(0 - 1)

34

Medium cloud cover

x

x

187

(0 - 1)

35

High cloud cover

x

x

188

(0 - 1)

36

Skin reservoir content

x

x

198

m of water equivalent

37

Total column ozone

x

x

206

kg m-2

38

Instantaneous eastward turbulent surface stress


x

229

N m-2

39

Instantaneous northward turbulent surface stress


x

230

N m-2

40

Instantaneous surface heat flux


x

231

W m-2

41

Instantaneous moisture flux (evaporation)


x

232

kg m-2 s

42Log. surface roughness length (m) for heatx
234~

43

Skin temperature

x

x

235

K

44

Soil temperature level 4

x

x

236

K

45

Temperature of snow layer

x

x

238

K

46

Forecast albedo


x

243

~

47

Forecast surface roughness


x

244

m

48

Forecast logarithm of surface roughness for heat


x

245

~

1

LayerRange
Layer 10 - 7 cm
Layer 27 - 28 cm
Layer 328 - 100 cm
Layer 4100 - 150 cm

2

LayerRange
Layer 10 - 7 cm
Layer 27 - 28 cm
Layer 328 - 100 cm
Layer 4100 - 289 cm

3Forecasts are only available up to a range of 12-hours

Forecast accumulated surface and single level parameters

count

name

paramId

units

1Clear sky surface photosynthetically active radiation20W m-2s
2Snow evaporation44m
3Snow melt45m
4

Large-scale precipitation fraction

50

s

5

Downward UV radiation at the surface

57

W m-2 s

6Surface photosynthetically active radiation58W m-2 s
7Large-scale precipitation142m of water
8Convective precipitation143m of water
9Snowfall144m of water equivalent
10

Boundary layer dissipation

145

W m-2 s

11

Surface sensible heat flux

146

W m-2 s

12

Surface latent heat flux

147

W m-2 s

13

Downward surface solar radiation

169

W m-2 s

14

Downward surface thermal radiation

175

W m-2 s

15

Surface solar radiation

176

W m-2 s

16

Surface thermal radiation

177

W m-2 s

17

Top solar radiation

178

W m-2 s

18

Top thermal radiation

179

W m-2 s

19

East-West turbulent surface stress

180

N m-2 s

20

North-South turbulent surface stress

181

N m-2 s

21

East-West gravity wave surface stress

195

N m-2 s

22

North-South gravity wave surface stress

196

N m-2 s

23

Gravity wave dissipation

197

W m-2 s

24Runoff205m of water

25

Top net solar radiation, clear sky

208

W m-2 s

26

Top net thermal radiation, clear sky

209

W m-2 s

27

Surface solar radiation, clear sky

210

W m-2 s

28

Surface thermal radiation, clear sky

211

W m-2 s

29

TOA incident solar radiation

212

W m-2 s

30

Total precipitation

228

m of water

31

Convective snowfall

239

m of water equivalent

32

Large-scale snowfall

240

m of water equivalent

Forecast minimum/maximum surface and single level parameters

count

name

paramId

units

1

Wind gusts at 10 m

49

m s-1

2

Max. temp. at 2 m since previous post-processing

201

K

3

Min. temp. at 2 m since previous post-processing

202

K

Vertical single level integrals for budgets

count

name

units

paramId

an

fc

1

Vertical integral of mass of atmosphere

kg m-2

53

x

x

2

Vertical integral of temperature

K kg m-2

54

x

x

3Vertical integral of water vapourkg m-255xx
4Vertical integral of cloud liquid waterkg m-256xx
5Vertical integral of cloud frozen waterkg m-257xx
6Vertical integral of ozonekg m-258xx

7

Vertical integral of kinetic energy

J m-2

59

x

x

8

Vertical integral of thermal energy

J m-2

60

x

x

9

Vertical integral of potential+internal energy

J m-2

61

x

x

10

Vertical integral of potential+internal+latent energy

J m-2

62

x

x

11

Vertical integral of total energy

J m-2

63

x

x

12

Vertical integral of energy conversion

W m-2

64

x

x

13

Vertical integral of eastward mass flux

kg m-1 s-1

65

x

x

14

Vertical integral of northward mass flux

kg m-1s-1

66

x

x

15

Vertical integral of eastward kinetic energy flux

W m-1

67

x

x

16

Vertical integral of northward kinetic energy flux

W m-1

68

x

x

17

Vertical integral of eastward heat flux

W m-1

69

x

x

18

Vertical integral of northward heat flux

W m-1

70

x

x

19

Vertical integral of eastward water vapour flux

kg m-1 s-1

71

x

x

20

Vertical integral of northward water vapour flux

kg m-1 s-1

72

x

x

21

Vertical integral of eastward geopotential flux

W m-1

73

x

x

22

Vertical integral of northward geopotential flux

W m-1

74

x

x

23

Vertical integral of eastward total energy flux

W m-1

75

x

x

24

Vertical integral of northward total energy flux

W m-1

76

x

x

25

Vertical integral of eastward ozone flux

kg m-1 s-1

77

x

x

26

Vertical integral of northward ozone flux

kg m-1 s-1

78

x

x

27

Vertical integral of divergence of cloud liquid water flux

kg m-2 s-1

79

x

x

28

Vertical integral of divergence of cloud frozen water flux

kg m-2 s-1

80

x

x

29

Vertical integral of divergence of mass flux

kg m-2 s-1

81

x

x

30

Vertical integral of divergence of kinetic energy flux

W m-2

82

x

x

31

Vertical integral of divergence of thermal energy flux

W m-2

83

x

x

32

Vertical integral of divergence of moisture flux

kg m-2 s-1

84

x

x

33

Vertical integral of divergence of geopotential flux

W m-2

85

x

x

34

Vertical integral of divergence of total energy flux

W m-2

86

x

x

35

Vertical integral of divergence of ozone flux

kg m-2 s-1

87

x

x

36

Vertical integral of eastward cloud liquid water flux

kg m-1 s-1

88

x

x

37

Vertical integral of northward cloud liquid water flux

kg m-1 s-1

89

x

x

38

Vertical integral of eastward cloud frozen water flux

kg m-1 s-1

90

x

x

39

Vertical integral of northward cloud frozen water flux

kg m-1 s-1

91

x

x

40

Vertical integral of mass tendency

kg m-2 s-1

92

x


Wave and gridded ERS altimeter parameters

count

name

units

paramId

an

fc

20

Model bathymetry

m

219

x


21

Mean wave period based on first moment

s

220

x

x

22

Mean wave period based on second moment

s

221

x

x

23

Wave spectral directional width

~

222

x

x

24

Mean wave period based on first moment for wind waves

s

223

x

x

25

Mean wave period based on second moment for wind waves

s

224

x

x

26

Wave spectral directional width for wind waves

~

225

x

x

27

Mean wave period based on first moment for swell

s

226

x

x

28

Mean wave period based on second moment for swell

s

227

x

x

29

Wave spectral directional width for swell

~

228

x

x

30

Significant height of combined wind waves and swell

m

229

x

x

31

Mean wave direction

degrees

230

x

x

32

Peak wave period

s

231

x

x

33

Mean wave period

s

232

x

x

34

Coefficient of drag with waves

~

233

x

x

35

Significant height of wind waves

m

234

x

x

36

Mean direction of wind waves

degrees

235

x

x

37

Mean period of wind waves

s

236

x

x

38

Significant height of total swell

m

237

x

x

39

Mean direction of total swell

degrees

238

x

x

40

Mean period of total swell

s

239

x

x

41

Mean square slope of waves

dimensionless

244

x

x

42

10 metre wind speed1

m s-1

245

x

x

43

Gridded ERS altimeter wave height2

m

246

x


44

Gridded corrected ERS altimeter corrected wave height2

m

247

x


45

Gridded ERS altimeter range relative correction2

~

248

x


46

2D wave spectra (single)3

m2 s radians-1

251

x

x

47

Wave spectral kurtosis

~

252

x

x

48

Benjamin-Feir index

~

253

x

x

49

Wave spectral peakedness

s-1

254

x

x

1Forecasts are also available at a range of 3-hours

2Available from late 1991

3Available for 30 frequencies and 24 directions

Monthly mean surface and single level parameters: Exceptions from Tables 1-4

count

name

an

fc

paramId

units

1

Magnitude of surface stress (accumulated)


x

48

N m-2 s

2

Wind gusts at 10 m


no mean

49

m s-1

3

Geopotential

x

no mean

129

m-2 s-2

4

Land/sea mask

x

no mean

172

(0,1)

5

Max. temp. at 2 m since previous post-processing


no mean

201

K

6

Min. temp. at 2 m since previous post-processing


no mean

202

K

7

10 metre wind speed

x

x

207

m s-1

Accumulated model full levels parameters to validate clear sky radiation

count

name

an

fc

paramId

units

1

Short wave radiative tendency

x

x

100

K

2

Long wave radiative tendency

x

x

101

K

3

Clear sky short wave radiative tendency

x

x102

K

4

Clear sky long wave radiative tendency

x

x

103

K

Accumulated model half or model full levels parameters to support chemical transport modelling

count

name

an

fc

paramId

units

Surfaces

1

Updraught mass flux

x

x

104

kg m-2half levels

2

Downdraught mass flux

x

x

105

kg m-2

half levels

3

Updraught detrainment rate

x

x

106

kg m-2

full levels

4

Downdraught detrainment rate

x

x

107

kg m-2

full levels

5

Total precipitation profile

x

x

108

kg m-2

half levels

6

Turbulent diffusion coefficient for heat

x

x

109

m2

half levels

Accumulated model full levels net tendencies

count

name

an

fc

paramId

units

1

T tendency

x

x

110

K

2

q tendency

x

x

111

kg kg-1

3

u tendency

x

x

112

m s-1

4

v tendency

x

x

113

m s-1

Parameters on isentropic surfaces

count

name

gg1

sh2

paramId

units

1

Montgomery potential


x

53

m2 s-2

2

Pressure


x

54

Pa

3

Potential vorticity3

x


60

m2 s-1 K kg-1

4

Eastward wind component



131

m s-2

5

Northward wind component



132

m s-2

6

Specific humidity

x


133

kg/kg

7Vorticity
x138s-1
8Divergence
x155s-1
9ozone mass mixing ratiox
203kg/kg

1Gaussian grid

2Spherical harmonics

3Only PV is archived at 320 K

Parameters on the PV = ± 2 PVU surface

count

name

paramId

units

1

Potential temperature

3

K

2

Pressure

54

Pa

3

Geopotential

129

m2 s-2

4

Eastward wind component

131

m s-2

5

Northward wind component

132

m s-2

6

Specific humidity

133

kg/kg

79ozone mass mixing ratio203kg/kg

Observations

The observations (satellite and in-situ) used as input into ERA-Interim are listed in tables below.

Satellite Data

SensorSatelliteSatellite agencyData provider+

Measurement

(sensitivities exploited in ERA5 / variables analysed)

Satellite radiances (infrared and microwave)



AIRSAQUANASANOAABT (T, humidity and ozone)
AMSREAQUAJAXA

BT  (column water vapour, cloud liquid water,

precipitation and ocean surface wind speed)

AMSUANOAA-15/16/17/18/19, AQUA, METOP-ANOAA,ESA,EUMETSAT
BT (T)
AMSUBNOAA-16/17NOAA
BT (humidity)
HIRSMETOP-A, NOAA-10/11/12/14/15/16/17/18/19NOAA
BT (T, humidity and ozone)
MHSNOAA-18/19, METOP-ANOAA, EUMETSAT/ESA
BT (humidity and precipitation)
MSUNOAA-10/11/12/14

BT (T)
SSM/IDMSP-8/10/11/13/14/15/16US NavyNOAA,CMSAF

BT (column water vapour, cloud liquid water,

precipitation and ocean surface wind speed)

SSMISDMSP-16US NavyNOAA

BT (T,  humidity,  column water vapour,

cloud liquid water, precipitation and ocean surface wind speed)

SSUNOAA-11/14NOAA
BT (T)
MVIRIMETEOSAT 5/7EUMETSAT/ESAEUMETSATBT (water vapour, surface/cloud top T)
SEVIRIMETEOSAT-8/9EUMETSAT/ESAEUMETSATBT (water vapour, surface/cloud top T)
GOES IMAGERGOES-8/9/10/11/12/13/15NOAACIMMS,NESDISBT (water vapour, surface/cloud top T)
MTSAT IMAGERMTSAT-1RJMA
BT (water vapour, surface/cloud top T)
Satellite retrievals from radiance data



MVIRIMETEOSAT-4/5/7EUMETSAT/ESAEUMETSATwind vector
SEVIRIMETEOSAT-8/9/10EUMETSAT/ESAEUMETSATwind vector
GOES IMAGERGOES-8/9/10/12NOAACIMMS,NESDISwind vector
GMS IMAGERGMS-3/4/5JMA
wind vector
MTSAT IMAGERMTSAT-1RJMA
wind vector
AHIHimawari-8JMAJMAwind vector
AVHRRNOAA-7 /9/10/11/12/14 to 18, METOP-ANOAACIMMS,EUMETSATwind vector
MODISAQUA/TERRANASANESDIS,CIMMSwind vector
GOMEERS-2*ESA
Ozone
MIPASENVISAT*ESA
Ozone
MLSEOS-AURA*NASA
Ozone
OMIEOS-AURA*NASA
Ozone
SBUVNIMBUS-7*,NOAA*9/11/14/16/17/18NOAANASAOzone
SCIAMACHYENVISAT*ESA
Ozone
TOMSNIMBUS-7*,METEOR-3,ADEOS-1*,EARTH PROBENASA
Ozone
Satellite GPS-Radio Occultation data



BlackJackCHAMPDLR,NASA/DLR,NASA/COMAEGFZ,UCARBending angle
GRASMETOP-AEUMETSAT/ESAEUMETSATBending angle
IGORCOSMIC-1 to 6NSPO/NOAAGFZ,UCARBending angle
Satellite Altimeter data



RAERS-1*/2*ESA
Wave Height
RA-2ENVISAT*ESA
Wave Height
Poseidon-2JASON-1*CNES/NASACNESWave Height

In-situ data, provided by WMO WIS

Dataset nameObservation typeMeasurement
SYNOPLand stationSurface Pressure, Temperature, wind, humidity
METARLand stationSurface Pressure, Temperature, wind,humidity
DRIBU/DRIBU-BATHY/DRIBU-TESAC/BUFR Drifting BuoyDrifting buoys10m-wind, Surface Pressure
BUFR Moored BuoyMoored buoys10m-wind, Surface Pressure
SYNOP SHIPship stationSurface Pressure, Temperature, wind, humidity
Land/ship PILOTRadiosondeswind profiles
American Wind ProfilerRadarwind profiles
European Wind ProfilerRadarwind profiles
Japanese Wind ProfilerRadarwind profiles
TEMP SHIPRadiosondesTemperature, wind, humidity profiles
DROP SondeAircraft-sondesTemperature, wind profiles
Land/Mobile TEMPRadiosondesTemperature, wind, humidity profiles
AIREPAircraft dataTemperature, wind profiles
AMDARAircraft dataTemperature, wind profiles
ACARSAircraft dataTemperature, wind profiles, humidity
WIGOS AMDARAircraft dataTemperature, wind profiles
Ground based radarRadar precipitation compositesRain rates

Computation of near-surface humidity and snow cover

Near-surface humidity

Near-surface humidity is not archived directly in ERA datasets, but the archive contains near-surface (2m from the surface) temperature (T), dew point temperature (Td), and surface pressure (sp) from which you can calculate specific and relative humidity at 2m:

  • Specific humidity can be calculated over water and ice using equations 6.4 and 6.5 from Part IV, Physical processes section (Chapter 6, section 6.6.1b) in the documentation of the IFS for CY31R1. Use the 2m dew point temperature and surface pressure (which is approximately equal to the pressure at 2m) in these equations.
  • Relative humidity should be calculated: RH = 100 * es(Td)/es(T)

The relative humidity can be calculated with respect to saturation over water, ice or mixed phase by defining es(T) with respect to saturation over water, ice or mixed phase (water and ice). The usual practice is to define near-surface relative humidity with respect to saturation over water.

Snow Cover

In the ECMWF model (IFS), snow is represented by an additional layer on top of the uppermost soil level. The whole grid box may not be covered in snow. The snow cover gives the fraction of the grid box that is covered in snow. The method for calculating snow cover depends on the particular version of the IFS and for ERA-Interim is computed directly using snow water equivalent (ie parameter SD (141.128)) as:

ERA5 Snow cover formula

snow_cover (SC) = min(1, RW*SD/15 )

where RW is density of water equal to 1000 and RSN is density of snow (parameter 33.128).

The Physical depth of snow where there is snow cover is equal to RW*SD/(RSN*SC) where RSN = density of snow (parameter 33.128). For more in depth information see:

Surface elevation and orography

In ERA-Interim, and often in meteorology, altitudes (the altitude of the land and sea surface, or specific altitudes in the atmosphere) are not represented as geometric altitude (in metres above the spheroid), but as geopotential height (in metres above the geoid). However, ECMWF archive the geopotential (in  m2/s2), not the geopotential height.

In order to calculate the geopotential height of the land and sea surface (the so called surface geopotential height, or orography):

  • First, download the surface geopotential (i.e. the geopotential of the land and sea surface): surface geopotential is available on model levels (at level=1), where it is archived in spectral form.
  • Then divide the surface geopotential by g=9.80665 to obtain the surface geopotential height in metres.

In order to define the surface geopotential in ERA-Interim, the ECMWF model uses surface elevation data interpolated from GTOPO30, with some fixes for Antarctica and Greenland. See Chapter 10 Climatological data, of Part IV. Physical processes, of the ERA-Interim model documentation at  https://www.ecmwf.int/search/elibrary/part?solrsort=sort_label%20asc&title=part&secondary_title=31r1.

Notes

Known issues

Please see the ERA-Interim known issues page for guidance and workarounds.

How to acknowledge and cite ERA-Interim

Guidelines

In addition to the terms and conditions of the license(s), users must:

  • cite the CDS catalogue entry:

Copernicus Climate Change Service (2023): ERA-Interim atmospheric reanalysis. Copernicus Climate Change Service (C3S) Climate Data Store (CDS), DOI: 10.24381/cds.f2f5241d (Accessed on DD-MMM-YYYY)

  • provide clear and visible attribution to the Copernicus programme and to each data product used:

Copernicus programme:

[Generated using/Contains modified] Copernicus Climate Change Service information [year]. Neither the European Commission nor ECMWF is responsible for any use that may be made of the Copernicus information or data it contains.

Products:

Dee, D.P., Uppala, S.M., Simmons, A.J., Berrisford, P., Poli, P., Kobayashi, S., Andrae, U., Balmaseda, M.A., Balsamo, G., Bauer, P., Bechtold, P., Beljaars, A.C.M., van de Berg, L., Bidlot, J., Bormann, N., Delsol, C., Dragani, R., Fuentes, M., Geer, A.J., Haimberger, L., Healy, S.B., Hersbach, H., Hólm, E.V., Isaksen, L., Kållberg, P., Köhler, M., Matricardi, M., McNally, A.P., Monge-Sanz, B.M., Morcrette, J.J., Park, B.K., Peubey, C., de Rosnay, P., Tavolato, C., Thépaut, J.N. and Vitart, F. (2011): ERA-Interim global atmospheric reanalysis. Copernicus Climate Change Service (C3S) Climate Data Store (CDS), DOI: 10.24381/cds.f2f5241d (Accessed on DD-MMM-YYYY)

Reports

2004-2007

2008

2009

2010

2011

2014

References

  • Please use this as the main scientific reference to ERA-Interim:

    Dee, D. P., Uppala, S. M., Simmons, A. J., Berrisford, P., Poli, P., Kobayashi, S., Andrae, U., Balmaseda, M. A., Balsamo, G., Bauer, P., Bechtold, P., Beljaars, A. C. M., van de Berg, L., Bidlot, J., Bormann, N., Delsol, C., Dragani, R., Fuentes, M., Geer, A. J., Haimberger, L., Healy, S. B., Hersbach, H., Hólm, E. V., Isaksen, L., Kållberg, P., Köhler, M., Matricardi, M., McNally, A. P., Monge-Sanz, B. M., Morcrette, J.-J., Park, B.-K., Peubey, C., de Rosnay, P., Tavolato, C., Thépaut, J.-N. and Vitart, F. (2011), The ERA-Interim reanalysis: configuration and performance of the data assimilation system. Q.J.R. Meteorol. Soc., 137: 553–597. doi: 10.1002/qj.828

    For a more technical documentation of the contents of the ERA-Interim dataset please use:

    Berrisford, P, Dee, DP, Poli, P, Brugge, R, Fielding, K, Fuentes, M, Kållberg, PW, Kobayashi, S, Uppala, S, Simmons, A (2011): The ERA-Interim archive Version 2.0. ERA Report Series 1, http://www.ecmwf.int/en/elibrary/8174-era-interim-archive-version-20


  • Berrisford, P., P. Kållberg,  S. Kobayashi, D. Dee, S. Uppala, A. J. Simmons, P. Poli,  and H. Sato, 2011: Atmospheric conservation properties in ERA-Interim. Q.J.R. Meteorol. Soc., 137: 1381–1399. doi: 10.1002/qj.864
  • Dee, D. P., and Coauthos, 2011: The ERA-Interim reanalysis: configuration and performance of the data assimilation system. Q.J.R. Meteorol. Soc., 137: 553–597. doi:10.1002/qj.828
  • Further references available from the ECMWF website


This document has been produced in the context of the Copernicus Climate Change Service (C3S).

The activities leading to these results have been contracted by the European Centre for Medium-Range Weather Forecasts, operator of C3S on behalf of the European Union (Delegation agreement signed on 11/11/2014). All information in this document is provided "as is" and no guarantee or warranty is given that the information is fit for any particular purpose.

The users thereof use the information at their sole risk and liability. For the avoidance of all doubt, the European Commission and the European Centre for Medium-Range Weather Forecasts have no liability in respect of this document, which is merely representing the author's view.