PV
                                      --

9/08

The potential vorticity is not readily available on the web.  Here
are directions on how to generate it.

(1) download the sigma files from either

    ftp://nomad1.ncep.noaa.gov/pub/reanalysis-1/6hr/sigma/
    ftp://nomad1.ncep.noaa.gov/pub/reanalysis-2/6hr/sig/

    The files are stored in monthly tar files.

(2) Install the post-processor (igb.tgz) to convert from sigma to 
    isentropic surfaces (linux compatible)

    ftp://ftp.cpc.ncep.noaa.gov/wd51we/reanl_software/

(3) If on a little endian machine, install swap.c

    ftp://ftp.cpc.ncep.noaa.gov/wd51we/reanl_software/swap.c

(4) On little endian machine: run swap on the sigma file

(5) Run igb to make isentropic analysis
         igb.sh (sigma file) (isentropic analysis)

The output is in grib format.

Note: read ftp://ftp.cpc.ncep.noaa.gov/wd51we/reanal/random_notes/calc.pv
ftp://ftp.cpc.ncep.noaa.gov/wd51we/reanal/random_notes/calc.pv