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Inconsistent specification of pole_lon in rotated lat-lon projection

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Chris Thomas

New member
geogrid does not appear to correctly use the pole_lon namelist variable when specifying a rotated lat-lon projection.

My geogrid namelist (attached) reads:

Code:
&geogrid
 parent_id         =    1,    1,   2,
 parent_grid_ratio =    1,    5,   4,
 i_parent_start    =    1,  245, 125,
 j_parent_start    =    1,   90, 110,
 e_we              =  540,  381, 641,
 e_sn              =  363,  501, 601
 geog_data_res     = 'default','default','default',
 dx = 0.176
 dy = 0.176
 map_proj = 'lat-lon',
 ref_lat   =  -24.26,
 ref_lon   = 147.63,
 pole_lat= 60.31
 pole_lon= 321.38
 stand_lon = 32.37,
geog_data_path = '/projects/WRF/data/WPS_GEOG/'
/

but it is apparent from the XLAT_M and XLONG_M data in the resulting geo_em files (attached) that the actual pole coordinates used were:

pole_lat = 60.31
pole_lon = 147.63 (instead of the requested 141.38)

For lat-lon coordinates, page 3-10 of WRFUsersGuideV4.2 says the transformation is controlled by parameters pole_lat, pole_lon and stand_lon. I had therefore assumed that ref_lat and ref_lon were redundant for a lat-lon projection. It looks to me like the WPS has either used ref_lon as the pole longitude or has used 180 - stand_lon (which is a guideline only, on 3-13 of user guide). Furthermore the global attributes in the geo_em files (attached) are listed as:

:STAND_LON = 32.37f ;
:pOLE_LAT = 60.31f ;
:pOLE_LON = 321.38f ;

which are those requested in the namelist but NOT those actually used.
 

Attachments

  • namelist.wps
    902 bytes · Views: 32
  • geo_em.d01.NARCliM20-4NSW.nc
    13.6 MB · Views: 37
  • geo_em.d02.NARCliM20-4NSW.nc
    31.2 MB · Views: 34
Would you please change your namlelist options as follows:
ref_lat = -24.26,
ref_lon = 147.63,
pole_lat = 65.74
pole_lon= -38.62
stand_lon = 32.37,
Then rerun geogrid.exe? Please see whether you can get correct results.
 
Please ignore or delete this thread. It was based on the results of a piece of software that did not faithfully represent
the WPS geographic <-> computational coordinate transformation. My apologies for wasting your time.

Chris
 
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