NARCCAP Data Overview
NARCCAP data is stored in CF-compliant NetCDF format. Filenames
are of the form
Each file contains data for a single variable. For 3-D data, a
file covers one month. For 2-D data, a file covers 5 years, ending
in a year that ends in 0 or 5. (Files covering the beginning and
ending of the run may not contain a full five years of data.)
VariableName is the IPCC/CF-convention Variable Name
as listed in the data tables
ModelName is the 4-character RCM identifier
Time is the starting time of the file, in the form
So, for example,
tas_RCM3_1981010103.nc contains data
tas from the RegCM3 regional model starting
at 03 UTC on January 1st, 1981 and ending at 00 UTC on January 1st,
NetCDF is a data format for storing array-oriented scientific data,
particularly geophysical data. It is highly portable,
widely-understood, and has built-in metadata that makes the files
The main data array has associated coodinate arrays, xc, yc,
and time, for each of its dimensions. Time is an unlimited or
record dimension (important for some tools). Each variable in
a NetCDF file can have attributes associated with it.
-- produced by
ncdump -h pr_WRFP_1979090103.nc
Outputs contents of a netCDF file as ascii. From Unidata, part of
the NetCDF libraries. http://www.unidata.ucar.edu/software/netcdf/index.html
ncdump -h -- prints headers
ncdump -v variable -- prints a variable
ncdump -f n1,n2 -- specify precision of output
ncdump -l length -- specify line length of output
Example output: pr-ncdump.csv -- produced using
ncdump -p 5,5 -l 2000 pr_WRFP_2001010103_clim.nc
NCO is a package of command-line utilities for manipulating netCDF
files. Each NCO command does one very specific kind of manipulation,
but you can combine them to powerful effect.
There are a number of options common to most or all NCO commands.
These include -v for specifying the variable and -d for choosing a
dimensional slice. Some NCO commands make use of a "record"
dimension. This needs to be the first dimension and is unlimited in
extent. In NARCCAP data, this is always the time dimension.
- ncap and ncap2: netCDF Arithmetic Processors (examples) -- algebraic manipulation of data
- ncatted: netCDF Attribute Editor (examples) -- modify metadata
- ncbo: netCDF Binary Operator (includes ncadd, ncsubtract, ncmultiply, ncdivide) -- (examples) -- math involving two files
- ncea: netCDF Ensemble Averager (examples) -- average across multiple input files
- ncecat: netCDF Ensemble Concatenator (examples) -- combine files into a single record
- ncflint: netCDF File Interpolator (examples) -- combine inputs via weighted interpolation
- ncks: netCDF Kitchen Sink (examples) -- copies data to ascii or output file
- ncpdq: netCDF Permute Dimensions Quickly, Pack Data Quietly (examples) -- rearrange dimensions or pack data
- ncra: netCDF Record Averager (examples) -- average across time (record dimension)
- ncrcat: netCDF Record Concatenator (examples) -- combine sequential files
- ncrename: netCDF Renamer (examples) -- rename dimensions, variables, or attributes
- ncwa: netCDF Weighted Averager (examples) -- weighted average over one file
seasonal-average -- Shellscript using NCO commands to generate seasonal climatology
NCL is an interpreted programming language for scientific analysis and
visualization. It is designed with NetCDF in mind and allows easy and
transparent access to NetCDF data files. It has a large and powerful
plotting library oriented toward geophysical data.
NCL's syntax is FORTRAN-like. It supports the idea of coordinate
variables and attributes associated with variables. Most parameters
are passed to functions via "resource" attributes.
2d-time-plot.ncl Plot a timeslice from a file. Used in NARCCAP QC process. Example results.
Extensive reference and support materials are available on the NCL
There are a number of other tools for working with netCDF data.
Importing NARCCAP Data into GIS
Data Download Walkthrough