ECMWF analysis over Atlantic-Africa regions

ECMWF meteorological products from the operational analysis are available over a large Atlantic Africa area and over West Africa (AMMA regions), for all the AMMA scientific community. Products have been extracted at ECWMF on regular latitude/longitude grid and converted from GRIB (meteorological format) to Netcdf (self-describing format, widely used in modelers community).

The access to this dataset is restricted to AMMA-INT members. Please sign in to access this dataset. If you don't have an ID yet, you can apply for an account at : the AMMA databases mainsite

 

Temporal and spatial coverages

The products are available over two geographical areas with two different temporal coverages:

Atlantic Africa area: 100W to 50E, 47N to 25S
regular longitude-latitude mesh: 0.5x0.5deg
Time period: 2005, 2006, 2007 to be stored

West Africa area: 25W to 25E, 25N to 5S
regular longitude-latitude mesh: 0.25x0.25deg
Time period: May to September 2006

4 times daily (4xdaily) products:

Times : 0 6 12 18 h
step : 0 h

Times : 12 h
Steps :12, 18, 24, 30, 36 h

 

For the forecast variables, there are 5 forecast times per day : 0, 6, 12, 18 and 24h corresponding to the 5 forecasting steps (12, 18, 24, 30, 36h) starting at the reference time 12h of the day before.

Levels

Model levels

  • 60 levels before 01/02/2006
  • 91 levels after 01/02/2006 included

 

The ECMWF model uses a hybrid vertical coordinate that reduces smoothly from a terrain-following sigma coordinate in the lower troposphere to a pressure coordinate in the stratosphere.


To represent the vertical variation of the dependent variables Chap2_Discretization75.gif , Chap2_Discretization20.gif , Chap2_Discretization25.gif and Chap2_Discretization30.gif , the atmosphere is divided into Chap2_Discretization50.gif layers. These layers are defined by the pressures at the interfaces between them (the `half-levels'), and these pressures are given by

Chap2_Discretization56.gif (1)



for Chap2_Discretization61.gif . The Chap2_Discretization66.gif and Chap2_Discretization71.gif are constants whose values effectively define the vertical coordinate and Chap2_Discretization114.gif is the surface pressure field.


The values of the Chap2_Discretization5.gif and Chap2_Discretization15.gif for all Chap2_Discretization99.gif allow the reconstruction of the `full-level' pressure Chap2_Discretization104.gif associated with each model level (middle of layer) from Chap2_Discretization119.gif (Chap2_Discretization109.gif )by using equation (1) and the surface pressure field.

 

Pressure levels

  • 21 levels (in hPa) : 1000, 925, 850, 700, 500, 400, 300, 250, 200, 150, 100, 70, 50, 30, 20, 10, 7, 5, 3, 2,1

The fields have been interpolated to standard pressure levels from the original model levels.


Available products

Surface

* =tr>
Long name Grib id Netcdf name
Units Dataset* Level type*
Mean sea level pressure 151 msl Pascal AN SF
Temperature at 2 meters 167 t2 degK AN SF
Dew point at 2 meters 168 d2 degK AN SF
Soil temperature level1
139 stl1 degK AN SF Soil temperature level2 170
stl2
degK AN SF
Soil temperature level3 183
stl3
degK AN SF
Soil temperature level4 236
stl4
degK AN SF
Volumetric soil water level 1
39
swvl1
m**3 s**-3 AN SF
Volumetric soil water level 2
40
swvl2 m**3 s**-3 AN SF
Volumetric soil water level 3
42
swvl3 m**3 s**-3 AN SF
Volumetric soil water level 4
42
swvl4 m**3 s**-3 AN SF
Geopotentiel
129
geopt
m**2 s**-2 AN SF
10m U wind component 165 u10 m/s AN SF
10m V wind component 166 v10 m/s AN SF
Albedo 174 al -
AN SF
Land/sea mask 172
lsm
(0,1)
AN
SF
Sea surface temperature
24
sstk
degK
AN
SF
Skin temperature
235
skt
degK
AN
SF
Total column water vapor 137 tcwv kg/m^2 AN
SF
Snow depth 141
sd
m of water equivalent AN
SF
Evaporation 182 e m of water FC SF
Large scale precipitation 142 lsp m FC SF
Convective precipitation 143 cp m FC SF
Surface solar radiation 176 ssr (W/m^2)s FC SF
Surface thermal radiation 177 str (W/m^2)s FC SF
Top solar radiation 178 tsr (W/m^2)s FC SF
Top thermal radiation 179 ttr (W/m^2)s FC SF
Surface latent heat flux 147 slhfl (W/m^2)s FC SF
Surface sensible heat flux 146 sshfl (W/m^2)s FC SF
East /West surface stress 180 ewss (N/m^2)s FC SF
North/South surface stress 181 nsss (N/m^2)s FC SF
Downward surface solar radiation 169
ssrd
W/m^2 s FC
SF
Downward surface thermal radiation 175
strd
W/m^2 s FC
SF
Boundary layer height 159
blh
m
FC
SF

Pressure level

Long name Grib id Netcdf name
Units Dataset* Level type*
Geopotentiel 129 geopt m^2/s^2 AN PL
Temperature 130 ta degK AN PL
U-velocity 131 u m/s AN PL
V-velocity 132 v m/s AN PL
Vertical velocity 135 w
Pascal/s AN PL
Vorticity (relative) 138 vo s^-1 AN PL
Divergence 155 d s^-1 AN PL
Relative humidity 157 r % AN PL
Potential vorticity
164
pv
m^2 s^-1 K kg^-1 AN
PL

Model level

Long name Grib id Netcdf name Units Dataset*
Level type*
Log surface pressure 152 lnsp - AN ML(1st level)
Cloud liquid water content 246 clwc kg/kg AN ML
Cloud ice water content 247 ciwc kg/kg AN ML
Cloud cover 248 cc (0-1) AN ML

Specific humidity

133 q kg/kg AN ML(1st level)

Temperature

130 ta degK AN ML(1st level)

*AN: Analysis
*FC: Forecats
*SF: surface
*PL: pressure level
*ML: model level

Access

The access to this dataset is restricted to the members of the AMMA_INT group. Please sign in to access this dataset. If you don't have an ID yet, you can apply for an account at the AMMA databases main site.

Once you have got your login and password, you can access data by several ways :

  • With your WEB browser :ftp:// This e-mail address is being protected from spam bots, you need JavaScript enabled to view it /. You will be prompted for your password, then the system will log you on top of the ECMWF tree structure. Go into AMMAMOD/priv/ECMWF/OPERA/. To download a file, click on the file name with your right mouse button.

  • With the UNIX ftp command : type : ftp ftp.bddamma.ipsl.polytechnique.fr you will be prompted for you name and password, and logged on top of the above described file tree. Navigate the tree with the command cd. Go into AMMAMOD/priv/ECMWF/OPERA/. Download the file(s) with the commands get or mget.

  • With sophisticated ftp tools : Once you are familiar with this directory structure, you can use other ftp tools which allow you to download files in the background, during night, and which are able to restart the transfer in case of interrupts. At IPSL we used GNU wget.

Format

The data files are in the netCDF format and are compatible with the CF convention. It defines the meaning of attributes, the naming of variables, the units, the coordinate variables.

The files are organized by variable, by month for analysis and by day for forecast. One file contains one variable, during one month at the 4 synoptic hours for analyses and during one day at the 5 forecast steps for forecast, at all levels for the mutli-level fields. The geophysical values of variables (called unpacked values) are coded on 2 bytes (packed values).
The vast majority of the data that we distribute in netCDF files have been packed into short integers to save space. You must unpack that data to get the correct floating point representation of the data. Each netCDF variable (except some of them) that has been packed has an add_offset and scale_factor attribute associated with it. The scale_factor and add_offset can vary with each netCDF file even for the same variable from the same data set, though this doesn't happen often.

The formula to unpack the data is:

unpacked value = add_offset + ( (packed value) * scale_factor )

Related file Naming and Structure information

The ECMWF data are stored on the directory: AMMAMOD/priv/ECMWF/OPERA

  • The subdirectories are the following:

/FFF/GEO_RES/XXX/AA_LL/YYYY/name_file

FFF: format (NETCDF)
GEO: geographical area (ATLAFR for Atlantic Africa area and WESTAFR for West Africa area)
RES: resolution (05 for 0.5 degrees and 025 for 0.25 degrees)
XXX: is the temporal resolution (4xdaily)
AA_LL: AA is the type of data (AN for Analysis or FC for Forecast)
LL is the level type (SF, PL, ML)

SF: surface
PL: Pressure level
ML:Model level

YYYY: year

  • File names:

NAME.YYYY[MM][DD].ABC.[GEO_RES].EXT

NAME: is the netcdf parameter name (see table)
YYYY: year
MM: month
DD: day
A: type(a: analysis, f:forecast)
B: level type (s:surface,v: surface pv, t: isentropic level, p: pressure level, m: model level)
C: temporal resolution (h: 4 x daily, d: daily mean, m: monthly mean)
GEO: geographical area (ATLAFR for Atlantic Africa area and WESTAFR for West Africa area)
RES: resolution (05 for 0.5 degrees and 025 for 0.25 degrees)
EXT: format (.nc forNetcdf)

Original source

European Centre for Medium-Range Weather Forecasts.

Usage restrictions

The ECMWF data are restricted to non-commercial use. For additional information or permission to use ECMWF data, contact the European Centre for Medium-Range Weather Forecasts

Contact

Sophie Cloché-IPSL
Ecole Polytechnique
91128 Palaiseau cedex
FRANCE
Tel: 33 (1) 69 33 51 31
mail: This e-mail address is being protected from spam bots, you need JavaScript enabled to view it
Last Updated ( Monday, 02 June 2008 )