On Tue, Nov 2, 2010 at 5:19 AM, John <washa...@gmail.com> wrote:
> Maybe I should also follow up on this and indicate that one variable I
> really want is the Veg Type defiinitions from the files. It exists in
> the file from joewheatley's example, (VGTYP_P0_L1_GGA0) but it is on a
> Gaussian lat/lon grid. I've downloaded some of the gfs files from the
> 0.5 x 0.5 degree output, but I don't find the variable.
>
> Thanks again!
>
> On Tue, Nov 2, 2010 at 10:33 AM, John <washa...@gmail.com> wrote:
> > Folks,
> >
> > I'm trying to find documentation online that provides guidance on what
> > all the variables are that are in the NCEP model output grib files.
> > There are many NCEP models, so to be clear, I'm referring to the GFS
> > 0.5x0.5 degree product. I was looking at this nice blog:
> >
> > http://joewheatley.net/ncep-global-forecast-system/
> >
> > and the files that are available here:
> > ftp://ftp.ncep.noaa.gov/pub/data/nccf/com/gfs/prod
> >
> > And I see this link:
> > http://www.nco.ncep.noaa.gov/pmb/products/gfs/
> >
> > But looking at a file and the variables:
> > In [112]: ncep.variables.keys()
> > Out[112]:
> > ['PRES_P8_L223_GLL0_avg',
> > 'TOZNE_P0_L200_GLL0',
> > 'PRES_P0_L242_GLL0',
> > 'HGT_P0_L100_GLL0',
> > 'VVEL_P0_L100_GLL0',
> > 'UGRD_P0_L6_GLL0',
> > 'HGT_P0_L7_GLL0',
> > 'CIN_P0_2L108_GLL0',
> > 'ULWRF_P8_L8_GLL0_avg',
> > 'PRES_P0_L109_GLL0',
> > (snip)
> >
> > is somewhat clear in most cases, but is there a table which directly
> > maps these online?. Also, you can of course look at the 'long_name',
> > 'level', and 'level_type' attributes of each variable, but I'm looking
> > more or less for an online table showing all this. Maybe I need to
> > script it quickly ;)
> >
> > Thanks,
> > john
> >
>
>
John,
GRIB files are an interesting beast. It has been awhile since I have dealt
with them, but I will try to help you with what I can recall. First, the
data records in the files are indicated by:
1. Record number
2. Position in bytes
3. Date (YYMMDDHH).
4. Parameter name (LAND=land/sea mask)
5. Indicator of parameter and units (grib PDS octet 9)
6. Type of level/layer (grib PDS octet 10)
7. Height, pressure, etc (grib PDS octets 11-12)
8. Time Range (grib PDS octet 21)
9. Period of time 1, (grib PDS octet 19)
10. Period of time 2, (grib PDS octet 20)
11. Forecast time unit (grib PDS octet 18)
12. level
13. anl=analysis, fcst=forecast
14. NAve (number of grids used to make average)
The "type of level/layer" I believe is the grid projection type. Anyway,
these things can be mixed and matched, so all we need to do is find your
parameter in the grid projection that you want (or you will have to
re-project the data).
The operational models appear to have VGTYP, but the reanalysis products do
not appear to have this. Maybe this is causing your confusion?
This page might be more useful to you:
http://www.cpc.noaa.gov/products/wesley/wgrib.html
I hope this is useful,
Ben Root
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