subset.tcl - A subset and conversion utility based on Convsh

A description of the 'subset.tcl' command that accesses Xconv/Convsh utilities.

Introduction

The Xconv/Convsh provides a number of user defined options that allow such features as data subsetting and conversions between formats. The subset.tcl command can be executed at the command line on login.badc.rl.ac.uk to:

Read files in formats: NetCDF, GRIB, UM format, PP, DRS and GrADS format.
Write files in formats: NetCDF, DRS, UTF and GrADS format.
Read multiple files from a Unix file/directory glob (allowing the user to select a range of files from multiple directories).
Subset data in the horizontal domain (i.e. select a rectangular region in x and y co-ordinates).
Interpolate and regrid data in the horizontal domain.
Subset in the vertical co-ordinate (allowing extraction of required atmospheric levels).
Selection of individual parameters from a file containing many.
Creation of zonal or meridional means.
Any combination of the above options.

Usage

All the options presented above are defined by the user as arguments at the command line. The available arguments are as follows:

subset.tcl -i infile(s) -o outfile [-of outformat] [-zm] [-mm] [-xs xstart -xe xend -xi xinc] [-ys ystart -ye yend -yi yinc] [-levs levs] [-p parameters]

All arguments within square brackets are optional. Where more than one argument exists within one set of square brackets, all the arguments inside must be used if that option is defined. Below is a more detailed list of the options available:

   -i : input file name(s) (and path) - can be more than one.
   -o : output file name (and path)
   -of : output file format (netcdf, grads, drs or utf) - Defaults to NetCDF.
   -zm : create zonal means
   -mm : create meridional means
   -xs : x-dimension start - i.e. first grid point
   -xe : x-dimension end - i.e. last grid point
   -xi : x-dimension increment - i.e. spacing between grid points (must be >=0.5)
   -ys, -ye and -yi are the same as above but for the y-dimension.
   -p : parameter codes (can be a comma separated list, e.g. t,q,u). Note that parameter codes that begin with a number are not allowed so you should reference them with the letter character(s) precede the number(s) (e.g. '10u' should be called 'u10').
   -levs : selected output levels (e.g. from model levels, pressure levels or potential temperature levels). Individual levels can be separated by commas. For model levels ranges can be used (e.g. 1-7,20-24).

Note: To create a subset across the 0 degree Meridian, you should use a negative value (i.e. degrees West) as the -xs argument and a positive value as the -xe argument.

Version history

Version 1 of subset.tcl was written at the BADC on 22 April 2002. It was initially designed for use with the BADC archive of ECMWF data (e.g. ERA-40). However, your feedback is welcomed if you have suggestions or have encountered problems with the subset.tcl utility.

Version 1.1 - BADC, 01 August 2002: Updated to allow level subsetting of BADC archives of ECMWF ERA-15 and Operational data.

Version 1.2 - BADC, 30 April 2003: Updated to allow creation of zonal or meridional means.

Source code

If you have downloaded Xconv/Convsh and would like to run subset.tcl on your own system the source code is also available.

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