Horizontal resolution
Horizontal resolution
Hello,
I wanted to know what is real output data resolution. For example, if I am doing nesting up to 3 km grid spacing and then extracted data and then placed to arcgis, length between points are not 3 km.
For Latitude
http://imgur.com/sa6fEkw
For Longitude
http://imgur.com/sa6fEkw
What is the real horizontal resolution?
I wanted to know what is real output data resolution. For example, if I am doing nesting up to 3 km grid spacing and then extracted data and then placed to arcgis, length between points are not 3 km.
For Latitude
http://imgur.com/sa6fEkw
For Longitude
http://imgur.com/sa6fEkw
What is the real horizontal resolution?
Re: Horizontal resolution
So no ideas? or is it just a unwritten rule where you should write in the scientific article "approximately 3 km resolution" ?
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Re: Horizontal resolution
It depends on what grid you chose.
DX and DY values from namelist.wps are, quoting WRF ARW user's guide:
I hope this helps.
DX and DY values from namelist.wps are, quoting WRF ARW user's guide:
For NMM, "resolution in km" is given by diagonal distance between mass points; which then has to be calculated from DX and DY, like this (quoting NMM user's guide):10. DX : A real value specifying the grid distance in the x-direction where the map scale factor is 1. For ARW, the grid distance is in meters for the 'polar', 'lambert', and 'mercator' projection, and in degrees longitude for the 'lat-lon' projection; for NMM, the grid distance is in degrees longitude. Grid distances for nests are determined recursively based on values specified for parent_grid_ratio and parent_id. No default value.
11. DY : A real value specifying the nominal grid distance in the y-direction where the map scale factor is 1. For ARW, the grid distance is in meters for the 'polar', 'lambert', and 'mercator' projection, and in degrees latitude for the 'lat-lon' projection; for NMM, the grid distance is in degrees latitude. Grid distances for nests are determined recursively based on values specified for parent_grid_ratio and parent_id. No default value.
So, for NMM core, "grid resolution" does not correspond to lenght between two next grid cell corners neither in N-S, neither in E-W direction.Assuming 111 km/degree (a reasonable assumption for the rotated latitude-longitude grid) the grid spacing in km is approximately equal to:
111.0 * (SQRT (DX**2 + DY**2))
I hope this helps.
Re: Horizontal resolution
I used Lambert Conformal projection (ARW core).
What I understand that my grids real values goes along x-direction.
Is there some kind of equation or other method to get the real values?
What I understand that my grids real values goes along x-direction.
But I am not sure where to find the values of longitude.. :/10. DX : A real value specifying the grid distance in the x-direction where the map scale factor is 1.
Is there some kind of equation or other method to get the real values?
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Re: Horizontal resolution
What is your contents of namelist.wps inside static directory? dx and dy values?
Re: Horizontal resolution
Here you go: Dx and Dy = 27000. I guess these values you need
Code: Select all
&share
wrf_core = 'ARW'
max_dom = 3
start_date = '2010-08-07_00:00:00', '2010-08-07_00:00:00', '2010-08-07_00:00:00'
end_date = '2010-08-09_00:00:00', '2010-08-07_00:00:00', '2010-08-07_00:00:00'
interval_seconds = 21600
io_form_geogrid = 2
opt_output_from_geogrid_path = '/home/virmantas/wrfems/runs/hurricane/static/'
debug_level = 0
/
&geogrid
parent_id = 1, 1, 2
parent_grid_ratio = 1, 3, 3
i_parent_start = 1, 86, 93
j_parent_start = 1, 69, 73
e_we = 250, 238, 226
e_sn = 200, 190, 178
geog_data_res = 'modis_lakes+modis_30s+10m', 'modis_lakes+modis_30s+5m', 'modis_lakes+modis_30s+30s'
dx = 27000
dy = 27000
map_proj = 'lambert'
ref_lat = 55.159
ref_lon = 20.691
truelat1 = 55.159
truelat2 = 55.159
stand_lon = 20.691
ref_x = 125
ref_y = 100
geog_data_path = '/home/virmantas/wrfems/data/geog'
opt_geogrid_tbl_path = '/home/virmantas/wrfems/runs/hurricane/static/'
/
&ungrib
out_format = 'WPS'
prefix = 'FILE'
/
&metgrid
fg_name = CFSR, CFSRPTILE
io_form_metgrid = 2
constants_name = TAVGSFC, ICE5MIN:2010-08-07_00:00, SSTHR:2010-08-07_00:00
opt_output_from_metgrid_path = '/home/virmantas/wrfems/runs/hurricane/wpsprd'
opt_metgrid_tbl_path = '/home/virmantas/wrfems/runs/hurricane'
process_only_bdy =
/
&mod_levs
press_pa = 200100, 201300, 100000, 97500, 95000, 92500, 90000, 87500, 85000, 82500, 80000, 77500, 75000, 70000, 65000, 60000, 55000, 50000, 45000, 40000, 35000, 30000, 25000, 22500, 20000, 17500, 15000, 12500, 10000, 7000, 5000, 3000, 2000, 1000
/
&domain_wizard
grib_data_path = 'null'
grib_vtable = 'Vtable.GFS'
dwiz_center_over_gmt = true
dwiz_desc = hurricane
dwiz_gridpt_dist_km = 27.0
dwiz_latlon_linecolor = -8355712
dwiz_latlon_space_in_deg = 10
dwiz_map_horiz_scrollbar_pos = 802
dwiz_map_scale_pct = 12.5
dwiz_map_vert_scrollbar_pos = 0
dwiz_mpi_command = null
dwiz_name = hurricane
dwiz_show_political = true
dwiz_user_rect_x1 = 941
dwiz_user_rect_x2 = 1318
dwiz_user_rect_y1 = 69
dwiz_user_rect_y2 = 323
dwiz_modis = true
dwiz_tcvitals = null
dwiz_bigmap = Y
dwiz_lakes = true
/
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Re: Horizontal resolution
That looks good. Now please give small chunk of "wgrib2 -V yourgribfile" output, like this one:
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73:4449316:vt=2015100206:300 mb:anl:VGRD V-Component of Wind [m/s]:
ndata=205781:undef=0:mean=-2.68005:min=-43.1:max=33.2
grid_template=30:winds(grid):
Lambert Conformal: (529 x 389) input WE:SN output WE:SN res 56
Lat1 33.783000 Lon1 349.745000 LoV 10.200000
LatD 48.700000 Latin1 48.700000 Latin2 48.700000
LatSP 0.000000 LonSP 0.000000
North Pole (529 x 389) Dx 7300.000000 m Dy 7300.000000 m mode 56
Re: Horizontal resolution
This one will be alright?
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1106:30976417:vt=2010080706:975 mb:6 hour fcst:VGRD V-Component Of Wind [m/s]:
ndata=39825:undef=0:mean=3.96969:min=-13.29:max=12.84
grid_template=30:winds(grid):
Lambert Conformal: (225 x 177) input WE:SN output WE:SN res 56
Lat1 53.297000 Lon1 17.125000 LoV 20.691000
LatD 55.159000 Latin1 55.159000 Latin2 55.159000
LatSP 0.000000 LonSP 0.000000
North Pole (225 x 177) Dx 3000.000000 m Dy 3000.000000 m mode 56
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- Posts: 1604
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Re: Horizontal resolution
That all looks good. Your grid distance appears to really be 3000m in both directions in grib file.
I'm not familiar with your method of checking, but I did quick try in Qgis over my ARW grib file with dx=dy=9800m:
Those are results (first segments lengths - upper numbers):


It is clearly 9.8km in both directions, as it should be.
I'm not familiar with your method of checking, but I did quick try in Qgis over my ARW grib file with dx=dy=9800m:
Code: Select all
1276:71264433:vt=2015050215:surface:3 hour fcst:WTMP Water Temperature [K]:
ndata=117806:undef=0:mean=290.821:min=269.1:max=323.6
grid_template=30:winds(grid):
Lambert Conformal: (394 x 299) input WE:SN output WE:SN res 56
Lat1 33.417000 Lon1 349.882000 LoV 10.200000
LatD 48.700000 Latin1 48.700000 Latin2 48.700000
LatSP 0.000000 LonSP 0.000000
North Pole (394 x 299) Dx 9800.000000 m Dy 9800.000000 m mode 56


It is clearly 9.8km in both directions, as it should be.
Re: Horizontal resolution
well... I did convert .ctl file to .nc (with GRADS) to get a few variables and then imported to arcgis. Could convertion with Grads distort the resolution?
By the way, these links to the screenshots of distance (which I posted earlier). The points defines the middle of the GRID not the corners or something.
By the way, these links to the screenshots of distance (which I posted earlier). The points defines the middle of the GRID not the corners or something.