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 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)