wrfout_to_cf.ncl - Overview

An NCL based script to create new CF based NetCDF files from native wrfout NetCDF files.

The problem:

The native WRFOUT files are not the easiest NetCDF files to use.
      • The variables are based on WRF development history and not necessarily community acceptance.
      • Several of the key variables (i.e. u and v wind) are on the staggered WRF horizontal grid.
      • The vertical levels are on the native eta vertical coordinate.
      • A large number of variables are included in the WRFOUT files related to the WRF simulation and not the applicable science.
      • The associated NetCDF attributes may not be helpful.
      • The WRFOUT files can often be considerably larger than required for a research project, especially when building an archive of simulations for a study.
Modifying the Registry can change the variables included in the WRFOUT files.
      • It can be a tedious and potentially messy process to make significant modifications to the Registry.
      • Some variables are included in WRFOUT for reasons the user may never know.  Removing the variables may create unintended consequences.
      • The variables are still on the staggered grid and on the model vertical levels.

What it is - one solution:

wrfout_to_cf is an NCL based script designed to create CF compliant NetCDF files with user selectable variables, time reference, vertical levels, and spatial and temporal subsetting.

There are a number of WRF post-processing utilities to create output files and/or graphics for scientific use (e.g. NCEP UPP, RIP4, ARWpost, VAPOR).  wrfout_to_cf is just one solution to create post-processed WRF output files that are more convenient to work with on a research project.

This is not the most computationally efficient post-processing utility. This utility does not fit all applications. It is designed to be a simple and user flexible post-processing utility.

CF compliant (http://cf-pcmdi.llnl.gov/):

Climate and Forecast (CF) is a metadata convention designed to promote the sharing and utilization of similar NetCDF data files.  CF conventions have been adopted by a number of research projects and groups as a primary standard.  Some graphics programs (e.g. IDV) can readily read CF compliant NetCDF files.

The CF convention does not standardize variable names.  The selected variable names for this post-processing script are partially based on WRF conventions, consistency amongst the variables, a self-describing simple approach, and standardized meteorological variables.
 
The data in CF files are described by specifying standard attributes for the variables.
units
standard_name
long_name
_FillValue
missing_value
valid_max
valid_min
valid_range

The variables contain coordinate information accessed through the coordinate attribute.

The time in encoded with units specified by a specified "time_unit" since a given "reference_time.
TimeUnits = "hours since 2001-01-01 00:00:00"


NCL Based (http://www.ncl.ucar.edu/):

NCL is a free interpreted language designed for scientific data processing and visualization.  NCL Is available for a variety of operating systems including Linux, Mac OS X, and Cygwin/X running on Windows.

wrfout_to_cf heavily leverages the WRF-ARW NCL scripts and functions that are included in the NCL libraries.  These built-in NCL functions include diagnostics and tools for unstaggering the grids and interpolating to pressure levels.




Overview Usage Variables Add a Variable Release Notes TO DO Download