WPS v4.0 w. ERA5 - metgrid.exe latitude error

Having problems running the WRF Preprocessing System (WPS)?

WPS v4.0 w. ERA5 - metgrid.exe latitude error

Postby orndui » Fri Aug 17, 2018 11:09 am

First-time user here.

I'm trying to initialize WRF v4.0 using ERA5 reanalysis data. I'm following the user guide in combination with this guide.

I've reached the stage of running metgrid.exe and it returns the following error:

Code: Select all
> ./metgrid.exe
Processing domain 1 of 2
 Processing 2016-12-02_00
Oops, something is not right with the Gaussian latitude computation.
The input data gave the starting latitude as   56.443.
This routine computed the starting latitude as +-  89.570.
The difference is larger than 0.01 degrees, which is not expected.
ERROR: Gaussian_latitude_computation
Note: The following floating-point exceptions are signalling: IEEE_OVERFLOW_FLAG

So far I've found this similar post which suggests that a solution might be to use the global dataset instead of a limited area as I have done (see namelist.wps below). However, as noted in the linked post, using a spatial subset (esp. for such a small area as I require) is a massive reduction in file size and processing time. Since I'm trying to run the model on my laptop this is of even more importance to me.

Would it be a good idea to try to run this using an older version such as v3.9?

My namelist.wps:
Code: Select all
 wrf_core = 'ARW',
 max_dom = 2,
 start_date = '2016-12-02_00:00:00','2016-12-02_00:00:00',
 end_date   = '2016-12-03_18:00:00','2016-12-03_18:00:00',
 interval_seconds = 151200,
 io_form_geogrid = 2,

 parent_id         =   1,   1,
 parent_grid_ratio =   1,   3,
 i_parent_start    =   1,  31,
 j_parent_start    =   1,  17,
 e_we              =  74, 112,
 e_sn              =  61,  97,

 geog_data_res = 'default','default',
 dx = 30000,
 dy = 30000,
 map_proj = 'lambert',
 ref_lat   =  51.97,
 ref_lon   =   4.93,
 truelat1  =  40.0,
 truelat2  =  60.0,
 stand_lon =   5.0,
 geog_data_path = '/media/username/WPS_GEOG/'

 out_format = 'WPS',
 prefix = 'FL',

 fg_name = 'FL','PRES',
 io_form_metgrid = 2,
Posts: 2
Joined: Fri Aug 17, 2018 10:41 am

Re: WPS v4.0 w. ERA5 - metgrid.exe latitude error

Postby MeteoAdriatic » Sun Nov 18, 2018 9:41 am


I just encountered this problem using ERA1. The same fix most probably will work on ERA5 also.

You need to fix subset files with wgrib2. This is how:

First, use grid_defn.pl script to find out your grib definition:
http://ftp.cpc.ncep.noaa.gov/wd51we/wgr ... id_defn.pl
Code: Select all
grid_defn.pl small.grb2

Then, use reply from this script to recreate same grid definition with wgrib2; basically, you will rewrite same grid from original file, but wgrib2 will do it's magic to fix whatever needs to be fixed.

Code: Select all
wgrib2 small.grb2 -new_grid gaussian 0.000000:512:0.703000 89.463000:256 simple.grb2.temp

In this example, my grid definition is "gaussian 0.000000:512:0.703000 89.463000:256". That will be the same for all your ERA files (obviously, use whatever grid_defn.pl gives to you).

Now I've got simple packing gribs from above command which means they are still little bit too large for archiving purposes. So, I also change packing with:

Code: Select all
wgrib2 simple.grb2.temp -set_grib_type c2 -grib_out original_filename.grb2

You can probably combine regridding and packing type into single command.

After you do this for all your input grib files, I believe metgrid will be able to use them.

Posts: 19
Joined: Wed Apr 30, 2008 6:07 pm

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