Chapter 8: Post-Processing Utilities

Table of Contents

·       Introduction

·       NCL

·       RIP4

·       ARWpost

·       WPP

·       VAPOR

·       Utility: read_wrf_nc

·       Utility: iowrf

·       Utility: p_interp

·       Tools


Introduction

There are a number of visualization tools available to display WRF-ARW (http://wrf-model.org/) model data. Model data in netCDF format, can essentially be displayed using any tool capable of displaying this data format.

 

Currently the following post-processing utilities are supported, NCL, RIP4, ARWpost (converter to GrADS and Vis5D), WPP, and VAPOR.

 

NCL, RIP4 and VAPOR can currently only read data in netCDF format, while ARWpost can read data in netCDF and GRIB1 format, and WPP can read data in netCDF and binary format.

Required software

The only library that is always required is the netCDF package from Unidata (http://www.unidata.ucar.edu/: login > Downloads > NetCDF - registration login required).

 

netCDF stands for Network Common Data Form. This format is platform independent, i.e., data files can be read on both big-endian and little-endian computers, regardless of where the file was created. To use the netCDF libraries, ensure that the paths to these libraries are set correct in your login scripts as well as all Makefiles.

 

Additional libraries required by each of the supported post-processing packages:

 

·       NCL (http://www.ncl.ucar.edu)

·       GrADS (http://grads.iges.org/home.html)

·       Vis5D (http://www.ssec.wisc.edu/~billh/vis5d.html)

·       GEMPAK (http://my.unidata.ucar.edu/content/software/gempak/index.html)

·       VAPOR (http://www.vapor.ucar.edu)


 

NCL

With the use of NCL Libraries (http://www.ncl.ucar.edu), WRF-ARW data can easily be displayed.

 

The information on these pages has been put together to help users generate NCL scripts to display their WRF-ARW model data.

 

Some example scripts are available online (http://www.mmm.ucar.edu/wrf/OnLineTutorial/Graphics/NCL/NCL_examples.htm), but in order to fully utilize the functionality of the NCL Libraries, users should adapt these for their own needs, or write their own scripts.

 

NCL can process WRF ARW static, input and output files, as well as WRF-Var output data. Both single and double precision data can be processed.

 

What is NEW?

 

In July 2007, the WRF-NCL processing scripts have been incorporated into the NCL Libraries, thus only the NCL Libraries, are now needed. NCL version 4.3.1 or higher is required. (NOTE: Since the release of NCL version 4.3.1, the WRFUserARW.ncl script incorporated in the NCL libraries has been updated significantly, and users should get a new version of this script from the WRF-ARW web site - http://www.mmm.ucar.edu/wrf/OnLineTutorial/Graphics/NCL/Examples/WRFUserARW.ncl).

 

With the NCL version 4.3.1 release all WRF related functions / procedures needed to plot WRF-ARW are now located in "$NCARG_ROOT/lib/ncarg/nclscripts/wrf/WRFUsersARW.ncl".

 

All the FORTRAN subroutines used for diagnostics and interpolation (previously located in wrf_user_fortran_util_0.f) has been re-coded into NCL in-line functions. This means users no longer need to compile these routines.

 

What is NCL

 

The NCAR Command Language (NCL) is a free interpreted language designed specifically for scientific data processing and visualization. NCL has robust file input and output. It can read in netCDF, HDF4, HDF4-EOS, GRIB, binary and ASCII data. The graphics are world class and highly customizable.

 

It runs on many different operating systems including Solaris, AIX, IRIX, Linux, MacOSX, Dec Alpha, and Cygwin/X running on Windows. The NCL binaries are freely available at: http://www.ncl.ucar.edu/Download/

 

To read more about NCL, visit: http://www.ncl.ucar.edu/overview.shtml

 

Necessary software

NCL libraries, version 4.3.1 or higher. Version 5.0.0 is recommended.

 

Environment Variable

Set the environment variable NCARG_ROOT to the location where you installed the NCL libraries. Typically (for cshrc shell):

 

setenv NCARG_ROOT /usr/local/ncl

 

.hluresfile

Create a file called .hluresfile in your $HOME directory. This file controls the color / background / fonts and basic size of your plot. For more information regarding this file, see: http://www.ncl.ucar.edu/Document/Graphics/hlures.shtml.

 

NOTE: This file must reside in your $HOME directory and not where you plan on running NCL.

 

Below is the .hluresfile used in the example scripts posted on the web (scripts are available at: http://www.mmm.ucar.edu/wrf/users/graphics/NCL/NCL.htm). If a different color table is used, the plots will appear different. Copy the following to your ~/.hluresfile. (A copy of this file is available at: http://www.mmm.ucar.edu/wrf/OnLineTutorial/Graphics/NCL/.hluresfile)
  

*wkColorMap : BlAqGrYeOrReVi200

*wkBackgroundColor : white

*wkForegroundColor : black

*FuncCode : ~

*TextFuncCode : ~

*Font : helvetica

*wkWidth : 900

*wkHeight : 900



NOTE:

If your image has a black background with white lettering, your .hluresfile has not been created correctly, or it is in the wrong location.

 

wkColorMap, as set in your .hluresfile can be overwritten in any NCL script with the use of the function “gsn_define_colormap”, so you do not need to change your .hluresfile if you just want to change the color map for a single plot.

 

Create NCL scripts

The basic outline of any NCL script will look as follows:

load external functions and procedures

 

begin

; Open input file(s)

; Open graphical output

; Read variables

; Set up plot resources & Create plots

; Output graphics

end

 

 

For example, let’s create a script to plot Surface Temperature, Sea Level Pressure and Wind as shown in the picture below.