Vertical levels in metgrid files

[Aurora_LagosD]

Hello everyone,

I ran a real simulation from February 1, 2021, to April 1, 2021, using three domains, with initial and boundary conditions based on ERA5 fields in GRIB format. I downloaded 29 vertical pressure levels along with some surface and subsurface fields. The GRIB files have the following dimensions:

Variables on pressure coordinates:
dimensions:
time = UNLIMITED ;
lon = 141 ;
lat = 117 ;
plev = 29 ;

and variables on surface and subsurface:
dimensions:
time = UNLIMITED ;
lon = 141 ;
lat = 117 ;
depth = 1 ;
bnds = 2 ;
depth_2 = 1 ;
depth_3 = 1 ;
depth_4 = 1 ;


The simulation completed successfully. The dimensions of the met_em.d0* files are as follows:

dimensions:
Time = UNLIMITED ;
DateStrLen = 19 ;
west_east = 120 ;
south_north = 120 ;
num_metgrid_levels = 38 ;
num_st_layers = 4 ;
num_sm_layers = 4 ;
south_north_stag = 121 ;
west_east_stag = 121 ;
z-dimension0003 = 3 ;
z-dimension0012 = 12 ;
z-dimension0016 = 16 ;
z-dimension0021 = 21 ;

I attempted to run another simulation using initual and boundary conditions from the ERA5 reanalysis in GRIB format, but this time from April 1, 2016, to August 2,2016, with a slightly larger domain. The dimensions of the downloaded GRIB files are the following:

Variables on pressure coordinates:
dimensions:
time = UNLIMITED ;
lon = 153 ;
lat = 169 ;
plev = 29 ;

and variables on surface and subsurface:
dimensions:
time = UNLIMITED ;
lon = 153 ;
lat = 169 ;
depth = 1 ;
bnds = 2 ;
depth_2 = 1 ;
depth_3 = 1 ;
depth_4 = 1 ;


As you can notice, the vertical coordinates of the GRIB files for both simulations are identical. The execution of metgrid.exe in this simulation completed successfully, but the met_em.d0* files have the following dimensions:

dimensions:
Time = UNLIMITED ; // (1 currently)
DateStrLen = 19 ;
west_east = 121 ;
south_north = 169 ;
num_metgrid_levels = 30 ;
num_st_layers = 4 ;
num_sm_layers = 4 ;
south_north_stag = 170 ;
west_east_stag = 122 ;
z-dimension0003 = 3 ;
z-dimension0012 = 12 ;
z-dimension0016 = 16 ;
z-dimension0021 = 21 ;


Although in both simulations the metgrid.log indicates a successful completion, the number of vertical levels in the met_em.d0* files differs, in the first one is 38 and the second is 30.

My question:​

Why are the vertical levels different between these simulations if the procedure was exactly the same?

nb: I attached both namelist.wps files

 

[Aurora_LagosD]

I download the ERA5 files in GRIB format using CDSAPI as follows:

import cdsapi

dataset = "reanalysis-era5-pressure-levels"
request = {
"product_type": ["reanalysis"],
"variable": [
"divergence",
"fraction_of_cloud_cover",
"geopotential",
"relative_humidity",
"specific_cloud_liquid_water_content",
"specific_humidity",
"specific_snow_water_content",
"temperature",
"u_component_of_wind",
"v_component_of_wind",
"vertical_velocity",
"vorticity"
],
"year": ["2016"],
"month": ["08"],
"day": [
"02"
],
"time": [
"00:00","03:00","06:00","09:00","12:00","15:00","18:00","21:00"
],
"pressure_level": [
"50", "70", "100",
"125", "150", "175",
"200", "225", "250",
"300", "350", "400",
"450", "500", "550",
"600", "650", "700",
"750", "775", "800",
"825", "850", "875",
"900", "925", "950",
"975", "1000"
],
"data_format": "grib",
"download_format": "unarchived",
"area": [-15, -95, -57, -57]
}

client = cdsapi.Client()
client.retrieve(dataset, request).download()

 

[Ming Chen]

Please see my answers below:

Hello everyone,

I ran a real simulation from February 1, 2021, to April 1, 2021, using three domains, with initial and boundary conditions based on ERA5 fields in GRIB format. I downloaded 29 vertical pressure levels along with some surface and subsurface fields. The GRIB files have the following dimensions:

Variables on pressure coordinates:
dimensions:
time = UNLIMITED ;
lon = 141 ;
lat = 117 ;
plev = 29 ;

and variables on surface and subsurface:
dimensions:
time = UNLIMITED ;
lon = 141 ;
lat = 117 ;
depth = 1 ;
bnds = 2 ;
depth_2 = 1 ;
depth_3 = 1 ;
depth_4 = 1 ;


The simulation completed successfully. The dimensions of the met_em.d0* files are as follows:

dimensions:
Time = UNLIMITED ;
DateStrLen = 19 ;
west_east = 120 ;
south_north = 120 ;
num_metgrid_levels = 38 ;
num_st_layers = 4 ;
num_sm_layers = 4 ;
south_north_stag = 121 ;
west_east_stag = 121 ;
z-dimension0003 = 3 ;
z-dimension0012 = 12 ;
z-dimension0016 = 16 ;
z-dimension0021 = 21 ;

The above case seems problematic. If the ERA5 data you ungrib only have 29 vertical levels, then it makes no sense that num_metgrid_levels = 38.
Please double check your ERA5 data, --- I am suspicious that the data have 37 vertical levels.

I attempted to run another simulation using initual and boundary conditions from the ERA5 reanalysis in GRIB format, but this time from April 1, 2016, to August 2,2016, with a slightly larger domain. The dimensions of the downloaded GRIB files are the following:

Variables on pressure coordinates:
dimensions:
time = UNLIMITED ;
lon = 153 ;
lat = 169 ;
plev = 29 ;

and variables on surface and subsurface:
dimensions:
time = UNLIMITED ;
lon = 153 ;
lat = 169 ;
depth = 1 ;
bnds = 2 ;
depth_2 = 1 ;
depth_3 = 1 ;
depth_4 = 1 ;


As you can notice, the vertical coordinates of the GRIB files for both simulations are identical. The execution of metgrid.exe in this simulation completed successfully, but the met_em.d0* files have the following dimensions:

dimensions:
Time = UNLIMITED ; // (1 currently)
DateStrLen = 19 ;
west_east = 121 ;
south_north = 169 ;
num_metgrid_levels = 30 ;
num_st_layers = 4 ;
num_sm_layers = 4 ;
south_north_stag = 170 ;
west_east_stag = 122 ;
z-dimension0003 = 3 ;
z-dimension0012 = 12 ;
z-dimension0016 = 16 ;
z-dimension0021 = 21 ;


Although in both simulations the metgrid.log indicates a successful completion, the number of vertical levels in the met_em.d0* files differs, in the first one is 38 and the second is 30.

This case is correct. num_metgrid_levels should be equal to the number of upper levels plus 1. In your case with plev = 29, num_metgrid_levels = 30 is correct.

My question:​

Why are the vertical levels different between these simulations if the procedure was exactly the same?

nb: I attached both namelist.wps files

vertical levels are dependent on input data. Again, please double check the input data you used for the two cases.