[pyngl-talk] reading wrf output without lat lon variables

[Bill Ladwig]

Hi Huseyin,

Without that information in the files, you're going to have to calculate
the latitude and longitude values. Since you're using Python, you can use
wrf-python which contains a xy_to_ll routine that converts grid points to
latitude and longitude points, as long as you're using one of the standard
WRF projections, which it looks like you are (
https://wrf-python.readthedocs.io/en/latest/user_api/generated/wrf.xy_to_ll.html#wrf.xy_to_ll
)

Note that this will only work if you have the map projection global
parameters still in your file. If not, there is an xy_to_ll_proj version
where you can specify the parameters yourself. (
https://wrf-python.readthedocs.io/en/latest/user_api/generated/wrf.ll_to_xy_proj.html#wrf.ll_to_xy_proj
).

Hope this helps,

Bill

On Mon, Oct 29, 2018 at 7:17 AM Huseyin Ozdemir via pyngl-talk <
pyngl-talk at ucar.edu> wrote:

> Hi everyone,
>
> I have a problem with reading wrf output file (Projection is Polar
> Stereographic); i want to compare wrf model output with observations at
> specific latitude-longitude coordinates, but output netcdf file has no
> latitude and longitude variables.
>
> I am using my python environment for reading this netcdf file, where PyNGL
> and PyNIO are already installed. As an example, temp variable in this
> output has attributes below:
>
> short T2 [ Time|1, south_north|150, west_east|150 ]
>       FieldType : 104
>       MemoryOrder : XY
>       description : TEMP at 2 M
>       units : K
>       stagger :
>       coordinates : XLONG XLAT XTIME
>       add_offset : 273.8086
>       scale_factor : -0.0005068767
>
> Here, T2 variable has “Time", “south_north" and “west_east” dimensions and
> “south_north" and "west _east" dimensions have both 150 grids.  There is no
> XLAT and XLONG variables in the netcdf output, so how can i get the
> temperatures at any lat-lon points with just grid numbers?
>
> Thanks in advance,
>
> Huseyin
>
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