Example netCDF files

Below we provide links to some sample netCDF files. These may be useful to developers of netCDF tools who want to test their tool on real data rather than small artificial examples. Some of these files are quite large, which is another characteristic of real data. To access small subsets of large datasets remotely, you need to use an OPeNDAP client to an OPeNDAP data server or a Java netCDF client to an HTTP server. Since version 4.1.1, the netCDF C library also supports remote client access to data on OPeNDAP servers. The netCDF-4 file format also supports internal compression, which means you can access small subsets of large files efficiently, without uncompressing the whole file.

For some examples from the NOAA National Oceanographic Data Center (NODC), see the NODC NetCDF Templates, which show good examples of use of netCDF Climate and Forecast (CF) conventions as well as conventions for dataset discovery.

Note that netCDF files may contain additional attributes not mentioned by the particular conventions with which they comply. This is not a violation of the conventions, which typically specify minimal requirements.

CF conventions

Several groups have created metadata standards for netCDF files. A recent comprehensive example is the Climate and Forecast (CF) metadata standards, developed through an international collaboration. Documents describing the latest CF conventions are available from CF Conventions and Metadata. The CF conventions have been adopted by the Program for Climate Model Diagnosis and Intercomparison (PCMDI), the Programme for Integrated Earth System Modeling (PRISM), the Earth System Modeling Framework (ESMF), NCAR, Hadley Centre, GFDL, and various EU projects. The Centre for Environmental Data Archival (CEDA) has provided a good introduction to CF. Coupled ocean-atmosphere general circulation models intended for use in Intergovernmental Panel on Climate Change (IPCC) assessments are required to produce output that conforms to the CF conventions.

Here are a few sample files using the CF conventions:

Sample files following CF conventions
CDL (metadata) netCDF file Description
sresa1b_ncar_ccsm3-example.cdl (11882 bytes) sresa1b_ncar_ccsm3-example.nc (2.8 MB) From the Community Climate System Model (CCSM), one time step of precipitation flux, air temperature, and eastward wind. More details.
ECMWF_ERA-40_subset.cdl(6695 bytes) ECMWF_ERA-40_subset.nc (22.2 MB) Surface data for July 2002 from the ECMWF 40 Years Re-Analysis, daily fields. (ECMWF ERA-40 data used in this study/project have been obtained from the ECMWF data server which has these conditions of use.)
cami_0000-09-01_64x128_L26_c030918.cdl (10625 bytes) cami_0000-09-01_64x128_L26_c030918.nc (18.4 MB) Initialization data for a CAM 3.0 model run
tos_O1_2001-2002.cdl(4515 bytes) tos_O1_2001-2002.nc (2.9 MB) Sea surface temperatures collected by PCMDI for use by the IPCC.
test_echam_spectral.cdl (29266 bytes) test_echam_spectral.nc (281.4 MB) Example model output from the ECHAM general circulation model. Almost CF, but not quite. Has a spectral coordinate for variables such as temperature (st) and vorticity (svo).



COARDS conventions

The CF conventions generalize and extend an earlier standard, the COARDS conventions. Many organizations make available data that conforms to the COARDS conventions, including the popular NCEP/NCAR Reanalysis Project data from the NOAA-CIRES Climate Diagnostics Center (CDC), who specify CDC netCDF Conventions: Gridded Data. The Naval Oceanographic Office NetCDF Standard v1.0 is an extension of COARDS conventions.

Sample files following COARDS conventions
CDL (metadata) netCDF file Description
rhum.2003.cdl (7088 bytes) rhum.2003.nc (61.4 MB) NCEP/NCAR Reanalysis 1 data for relative humidity at multiple levels, daily averages for 2003
smith_sandwell_topo_v8_2.cdl (1937 bytes) smith_sandwell_topo_v8_2.nc (136.9 MB) Smith & Sandwell v. 8.2: 1/30-degree topography and bathymetry



Other conventions

Sample files following other conventions
CDL (metadata) netCDF file Description
madis-hydro.cdl (25003 bytes) madis-hydro.nc (1.1 MB) Meteorological Assimilation Data Ingest System (MADIS) hydro data for a single hour within a flood control district. The MADIS data emphasizes quality control and uses AWIPS conventions.
madis-maritime.cdl (53171 bytes) madis-maritime.nc (472208 bytes) MADIS maritime data for a single hour.
madis-mesonet.cdl (60683 bytes) madis-mesonet.nc (5.2 MB) MADIS mesonet data for a single hour.
madis-metar.cdl (43563 bytes) madis-metar.nc (3.7 MB) MADIS METAR data for a single hour.
madis-profiler.cdl (15880 bytes) madis-profiler.nc (319648 bytes) MADIS profiler data for a single hour.
madis-raob.cdl (50027 bytes) madis-raob.nc (150612 bytes) MADIS RAOB data for a single hour.
madis-sao.cdl (43056 bytes) madis-sao.nc (266032 bytes) MADIS SAO data for a single hour.
GLASS.cdl (42473 bytes) GLASS.nc (296932 bytes) NCAR Mobile GLASS atmospheric sounding generated from the ASPEN system. This file is an upsonde (ground release). Dropsondes have a similar format.
WMI_Lear.cdl (4460 bytes) WMI_Lear.nc (10824 bytes) Aircraft track files used by Zebra and IDV from BAMEX field project. A flight is broken down into separate hourly files (based on clock time not flight time).
04091217_ruc.cdl (9807 bytes) 04091217_ruc.nc (7.3 MB) Output from Rapid Update Cycle model run, uses NUWG conventions.
GOTEX.C130-example.cdl (67108 bytes) GOTEX.C130-example.nc (8.3 MB) An example of sensor data from instruments on an aircraft, stored using NCAR-RAF/nimbus conventions.
ncswp_SPOL_RHI_.cdl (8966 bytes), ncswp_SPOL_PPI_.cdl (8966 bytes) ncswp_SPOL_RHI_.nc (836228 bytes), ncswp_SPOL_PPI_.nc (2.0 MB) NCAR S-band dual-polarized (S-Pol) radar netCDF sweep file format. Range Height Indicator (RHI) files are vertical scans, Plan Position Indicator (PPI) files are horizontal scans. Each file contains one sweep (azimuth (up/down) for RHI or elevation (horizontal) for PPI).
HRDL_iop12-example.cdl (2263 bytes) HRDL_iop12-example.nc (4.5 MB) HRDL Lidar Data collected during the CASES-99 Experiment near Leon, Kansas. Uses unspecified conventions: more details.
wrfout_v2_Lambert.cdl (16831 bytes) wrfout_v2_Lambert.nc (81.7 MB) WRF output with staggered axes. Grids that are offset from each other, such as in the WRF model output, are currently difficult to deal with because no commonly used convention expresses the relations between staggered grids.
slim_100897_198.cdl (2723 bytes) slim_100897_198.nc (5.4 MB) SLIMCAT Reference Atmosphere for UTLS-Ozone, see catalog record
sgpsondewnpnC1.cdl (4649 bytes) sgpsondewnpnC1.nc (181836 bytes) Atmospheric Radiation Measurement (ARM) sounding file. ARM uses netCDF extensively.
19981111_0045.cdl (846 bytes) 19981111_0045.nc (1.1 MB) Single-banded satellite image example from the NWS AWIPS system.
IMAGE0002.cdl (1924 bytes) IMAGE0002.nc (8.6 MB) Multi-banded satellite image generated by McIDAS program.



Example netCDF-4 files

Sample netCDF-4 files
CDL (metadata) netCDF file Description
test_hgroups.cdl (8052 bytes) test_hgroups.nc (90645 bytes) A couple of aircraft flight data sets stored as individual groups. For the sake of experimenting, the first group has its dimension (recNum) and the time variable defined at root level. All other groups have all dimensions stored inside the group.
OMI-Aura_L2-example.cdl (29057 bytes) OMI-Aura_L2-example.nc (239738 bytes) Example of a satellite data file with averaging kernels. Has variables with two dimensions of the same name in it (short O3.COLUMN.PARTIAL_AVK(DATETIME, PRESSURE, PRESSURE)).
test_echam_spectral-deflated.cdl (46079 bytes) test_echam_spectral-deflated.nc (120.7 MB) Example model output from the ECHAM general circulation model. Same as test_echam_spectral.nc netCDF-classic format file above, but this uses netCDF-4 chunking and compression to store the same data in a smaller file, only 43% as large. Subsets of the data can be accessed efficiently without uncompressing the whole file.



Miscellaneous netCDF files used for testing

Plans are to expand this list to a more extensive collection of test files for developers to test features. These test files follow no conventions.

Sample files for testing
CDL (metadata) netCDF file Description
testrh.cdl (61875 bytes) testrh.nc (40080 bytes) File with one variable of type float that compresses well and for which shuffling improves compression.

Last modified: Fri May 1 11:32:10 MDT 2015