Handling NetCDF files¶

PISM takes one or more NetCDF files as input, performs some computation, and then produces one or more NetCDF files as output. However, other tools are usually needed to help to extract meaning from NetCDF files, and yet more NetCDF tools help with creating PISM input files or post-processing PISM output files.

Here we list a number of NetCDF tools that can be useful in preparing input data for use with PISM and post-processing results; see Table 20.

Table 20 A selection of tools for viewing and modifying NetCDF files.¶
Tool	Function
`ncdump` (part of NetCDF)	dump binary NetCDF as `.cdl` (text) file
`ncgen` (part of NetCDF)	convert `.cdl` file to binary NetCDF
ncview	quick graphical view
CDO	Climate Data Operators; command-line tools, including conservative re-mapping
IDV	more complete visualization
NCO	NetCDF Operators; command-line tools for pre- and post-processing
NCL	NCAR Command Language
PyNGL	Python version of NCL

The PISM authors use ncview and “ncdump -h” for quick visualization and metadata examination. NCO has powerful command-line manipulation of NetCDF files, but requires some learning. Another such command-line tool is CDO, but to use CDO on PISM files first run the script nc2cdo.py, from the util/ PISM directory, on the file to fix the metadata so that CDO will understand the mapping. Finally, Python scripts using the netcdf4-python package (see Installing PISM) are often the best way to non-trivially change a NetCDF file or make publishable figures from it. MATLAB also has good NetCDF I/O capabilities.

See Table 4 in section A hierarchy of simplifying assumptions for grounded ice flow for an overview on the data necessary for modeling. For more information on the format of input files for PISM, see section Initialization and bootstrapping.