[Rnomads-user] Extract SOILW 4 layers from GFS analysis

[Daniel Bowman]

Hi Cheyenne,

I am sorry I took so long to get back to you.  I am able to read the file:
str(export_data)
List of 9
 $ model.run.date: chr [1:87995] "2018-01-01 00:00:00" "2018-01-01
00:00:00" "2018-01-01 00:00:00" "2018-01-01 00:00:00" ...
 $ forecast.date : chr [1:87995] "2018-01-01 06:00:00" "2018-01-01
06:00:00" "2018-01-01 06:00:00" "2018-01-01 06:00:00" ...
 $ variables     : chr [1:87995] "SOILW" "SOILW" "SOILW" "SOILW" ...
 $ levels        : chr [1:87995] "0.1-0.4 m below ground" "0.1-0.4 m
below ground" "0.1-0.4 m below ground" "0.1-0.4 m below ground" ...
 $ lon           : num [1:87995] 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 ...
 $ lat           : num [1:87995] -90 -90 -90 -90 -90 -90 -90 -90 -90 -90 ...
 $ value         : num [1:87995] 1 1 1 1 1 1 1 1 1 1 ...
 $ meta.data     : chr "None - this field is used for grib1 files"
 $ grib.type     : chr "grib2"

Can you give me the results of:

library(rNOMADS)
sessionInfo()

Maybe that will give us clues about the difference between our
operating systems or R versions.

In my experience, GFS data are in Kelvin.  I suppose either way is
fine as long as the units are clear.

Best,

Danny

On Wed, Apr 11, 2018 at 11:23 AM, Xiaoyan Shao <shaox at us.ibm.com> wrote:
> Dear rNOMADS users,
>
> I am relatively new to GFS grib2 data processing. Need some help here.
> Thanks in advance.
>
> I ran into some difficulty in extracting the 4 soil water content parameters
> from GFS reanalysis files.
>
> Here is the download link for a specific file I am testing:
> https://nomads.ncdc.noaa.gov/data/gfsanl/201801/20180101/gfsanl_4_20180101_0000_006.grb2
>
> I would like to extract 4 parameters using this R package. I have the grb2
> file downloaded to my local computer.
>
> library(rNOMADS)
> fpath<-"gfsanl_4_20180101_0000_006.grb2"
> variables<-c("SOILW")
> levels<-c("0.1-0.4 m below ground") # I want to test one parameter first
> export_data<- ReadGrib(fpath,levels=levels,variables=variables)
>
>> str(export_data)
> List of 9
> $ model.run.date: chr(0)
> $ forecast.date : chr(0)
> $ variables     : chr(0)
> $ levels        : chr(0)
> $ lon           : num(0)
> $ lat           : num(0)
> $ value         : chr(0)
> $ meta.data     : chr "None - this field is used for grib1 files"
> $ grib.type     : chr "grib2"
>
> What did I do wrong here?
>
> There are 4 SOILW parameters at different levels:
> [271] "271:43400382:d=2018010100:SOILW:0-0.1 m below ground:6 hour fcst:"
> [273] "273:43583330:d=2018010100:SOILW:0.1-0.4 m below ground:6 hour fcst:"
> [275] "275:43764744:d=2018010100:SOILW:0.4-1 m below ground:6 hour fcst:"
> [277] "277:43943879:d=2018010100:SOILW:1-2 m below ground:6 hour fcst:"
>
> When I change the variables to the 4th layer above, then it returns some
> data. It also works with the other 3 variables I am interested shown below:
> [286] "286:45186361:d=2018010100:TMAX:2 m above ground:0-6 hour max fcst:"
> [287] "287:45421594:d=2018010100:TMIN:2 m above ground:0-6 hour min fcst:"
> [293] "293:46556801:d=2018010100:APCP:surface:0-6 hour acc fcst:"
>
> Also gdal_translate will get the data out, for example temperature will be
> in C unit, but if I use the above command for the TMAX and TMIN, the unit
> seems to be K?
>
> Thanks & Regards,
> Cheyenne