Files should be provided in compressed NetCDF format, a self-describing, machine-independent data format that support the creation, access, and sharing of array-oriented scientific data. It can be read/written/processed for example by:
ncdump (inspecting NetCDF headers and raw data) belonging to NetCDF software
ncview (simple data exploration and graphics)
command line tools, e.g. Climate Data Operators (CDO) (Help), netCDF Operator (NCO) and UVCDAT: show, convert, split, merge, write and perform arithmetic and statistical operations on NetCDF data
command line graphics, e.g. NCAR Command Language (NCL), UVCDAT and R
other applications, e.g. Matlab, Ferret, Panoply and many more
Requirements for NetCDF files
gridded NetCDF4 classic internally zipped, if internal compression is not possible deliver unzipped files
global grid ranges 89.75 to -89.75° latitude, and ‐179.75 to 179.75° longitude, i.e. 0.5° grid spacing, 360 rows and 720 columns, or 259200 grid cells total. (corresponding to the resolution of the climate input data)
gridtype: lonlat (not generic)
variable precision is float
regional model teams should interpolate their output data to the same, common 0.5x0.5° grid and submit only the region of interest
single grid cell (one‐point) time series have to be embedded onto a 1x1 point grid with properly set coordinates
pixels you do not simulate should be filled with the missing_value and _FillValue marker (1.e+20f)
relative time axis with reference time 1661-01-01, 00:00:00
time increment according to temporal resolution of the data, e.g. “[days|months|years] since 1661-01-01 00:00:00” for daily, monthly or annual data
dimensions and variables all lowercase
preferable calendar is “proleptic_gregorian”. Please specify the calendar used and, if needed, an explanation of what to do with leap days. calendar = "proleptic_gregorian"
add and fill institution and contact as global attribute
add global comments at own will with additional information about the run. Preferred global attribute is "comment" (avoid the attribute "description" – it is used during ESGF publication)
NetCDF4 internally chunks the data into subsets. Usually one chunk is defined by a record, i.e. a combination of one horizontal field at one time step and one vertical layer. Chunking the data differently make operations on the data extremely more time consuming. Check the chunk sizes of a variable with ncdump -hs FILE
for 2d data it should give you:
variable:_ChunkSizes = 1, 360, 720 ;
for 3d data it should give you:
variable:_ChunkSizes = 1, 10, 360, 720 ;
(assuming 10 vertical layers)
if necessary, rewrite the data with
- 2d: nccopy -k4 -d1 -c "time/1,lat/360,lon/720" IFILE OFILE
- 3d: nccopy -k4 -d1 -c "time/1,depth/10,lat/360,lon/720" IFILE OFILE
Time Interval
non-daily and/or non-global output should be reported as single files per experiment and climate scenario
for daily global model output only, split data into decadal chunks starting with year one of the decade and ending with year zero of the next decade or the first or last year of the climate scenario period. Files containing a single year have both identifiers filled with the same year. Examples: 1861_1870, 2001_2005, 2006_2010, 2091_2099, 2100_2100, 2101_2110
under the upload folder /path/to/UploadArea/sector/model/_tmp/ you will find four subfolders corresponding to the time periods listed below. Be sure to place your files in the correct folders:
- pre-industrial: 1661-1860
- historical: 1861-2005
- future: 2006-2099
- future_extended: 2100-2299
Dimension
NetCDF internal name; standard_name; long_name; Unit
X; lon; longitude; longitude; degrees_east
Y; lat; latitude; latitude; degrees_north
Time; time; time; [no long name]; [Relative to reference date+time]
NetCDF header
A proper NetCDF header for daily global data shown with ncdump -h FILE should look like this:
