The Annual NCEP/NCAR CD-ROMs are an easy way to acquire data Reanalysis.
However, many people would like to analyze multi-year time series.
Making long time series is easy because you can concatinate GRIB files.
This page gives more detailed instructions for a unix machine.
Some of GRIB files on CD-ROM contain multiple variables on
multiple levels. It is possible to eliminate unwanted variables
and levels using a wgrib as a filter.
Making GrADS control and index files can be done using grib2ctl.pl and gribmap.
Comments: wesley.ebisuzaki@noaa.gov
Without Filtering
ex. cp /cdrom/data/monthly/prs/all.prs /disk3/data/all.prs
ex. cat /cdrom/data/monthly/prs/all.prs >>/disk3/data/all.prs
With Filtering
ex. cp /cdrom/data/monthly/prs/all.prs /disk3/data/tmpfile
ex. keep 500 mb heights
wgrib /disk3/data/tmpfile -s | grep ":HGT:500 mb:" | \
wgrib /disk3/data/tmpfile -s -i -grib -o /disk3/data/z500.grib
ex. cp /cdrom/data/monthly/prs/all.prs /disk3/data/tmpfile
ex. wgrib /disk3/data/tmpfile -s | grep ":HGT:500 mb:" | \
wgrib /disk3/data/tmpfile -s -i -grib -append -o /disk3/data/z500.grib
grib2ctl.pl z500.grib >z500.ctl
gribmap -i z500.ctl -0
Making long time series: the easy way
The previous proceedure was written when disk space was a precious
commodity. Now PCs come with 60 GB drives and saving a few
hundred megabytes just doesn't seem that important. This
example shows how to make a 2 year time series of the "monthly/all.prs"
dataset.
$ cp data/monthly/prs/all.prs allprs.grb
$ cp ctl/monthly/prs/all.prs allprs.ctl
(mount the next year's cd-rom)
$ cat data/monthly/prs/all.prs >>allprs.grb
change
from: dset ^../../../data/monthly/prs/all.prs
to: dset ^allprs.grb
change
from: index ^../../../index/monthly/prs/all.prs
to: index ^allprs.idx
change:
from: tdef 12 linear 00z01jan79 1mo
to: tdef 24 linear 00z01jan1979 1mo
(You should change 24 and 1979 to the appropriate values.)
$ gribmap -0 -i allprs.ctl