[ncl-talk] Confusion on GFS files in GRIB2

[Lyndz]

Hi,

I'm not sure if this is an ncl question. You should have directed your
questions to the ncep help page (
https://www.ncep.noaa.gov/mail_dataquestions/)

*[1] *As far as I know, the .anl files are analyses files and were already
assimilated with observations.

*[2]* If you want to use the forecast, then use the files with the
following format (
https://nomads.ncep.noaa.gov/pub/data/nccf/com/gfs/prod/gfs.20210308/12/):

gfs.t12z.pgrb2.0p25.f000
<https://nomads.ncep.noaa.gov/pub/data/nccf/com/gfs/prod/gfs.20210308/12/gfs.t12z.pgrb2.0p25.f000>

gfs.t12z.pgrb2.0p25.f001
<https://nomads.ncep.noaa.gov/pub/data/nccf/com/gfs/prod/gfs.20210308/12/gfs.t12z.pgrb2.0p25.f001>

etc..

No need to download the other files!

ncl_filedump gfs.t12z.pgrb2.0p25.f000.grb will give you the contents
of the file.

If you want temperature, then look for the keyword "Temperature". This
will give u information about the variables such as below:

float TMP_P0_L102_GLL0 ( lv_AMSL1, lat_0, lon_0 )

         center :       US National Weather Service - NCEP (WMC)

         production_status :    Operational products

         long_name :    Temperature

         units :        K

         _FillValue :   1e+20

         grid_type :    Latitude/longitude

         parameter_discipline_and_category :    Meteorological
products, Temperature

         parameter_template_discipline_category_number :        ( 0, 0, 0, 0 )

         level_type :   Specific altitude above mean sea level (m)

         forecast_time :        72

         forecast_time_units :  hours

         initial_time : 03/08/2021 (00:00)

The variable name is the same for other GFS files, regardless of resolution.

*[3]* For documentation, check this:
https://www.emc.ncep.noaa.gov/emc/pages/numerical_forecast_systems/gfs/documentation.php

*[4] *The files are archived in rda.ucar.edu. For the 25km GFS, for
example, see this link:

https://rda.ucar.edu/datasets/ds084.1/#!docs



Hope this helps.

--Lyndz



On Mon, Mar 8, 2021 at 8:05 PM dr.hieronymus--- via ncl-talk <
ncl-talk at mailman.ucar.edu> wrote:

> Hello,
>
> I am trying to dig through GFS files in GRIB2 format on NCEP's FTP
> server (https://www.nco.ncep.noaa.gov/pmb/products/gfs/).
>
> Unfortunately, it is not very easy to get a proper overview. Therefore,
> my first question is whether there is documentation somewhere that
> describes the different formats/variants in detail.
>
> What one quickly notice and easy understand is that the GFS files are
> available in different resolutions (0.25°, 0.50°, 1.00°) and each GFS
> file is described by an index file. The GFS files with 0.25° resolution
> have an hourly granularity and the GFS files with 0.50° and 1.00°
> resolution have a three-hourly granularity.
>
> Then, there are the .anl and .f000 GFS files. I don't understand the
> difference between .anl and .f000. Is .f000 not a forecast? Furthermore,
> I noticed that the index files are different regarding .f000 and
> .f001-384 (0.25°) and .f000 and .f003-384 (0.50°, 1.00°).
>
> What also confuses me are the different GFS files, namely pgrb2, pgrb2b,
> pgrb2full and sfluxgrbfFFF. What are the differences exactly? According
> to the corresponding index files, the same physical variables are
> available in all different GFS files. Do these variables always have the
> same values ​​in all GFS files? Doesn't it matter which file I use when
> I have decided on a resolution?
>
> I am actually only interested in the temperature 2 meters above the
> ground. Which file should I simply use?
>
> In addition, I also wanted to know if the initial values for each model
> run (00, 06, 12, 18) are published somewhere.
>
> Thank you in advance for your help.
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