Grid cell corners into WRF

[maR_Kus]

Hi All,

I just have a quick question on the grid cell corners: I realized the variables XLAT_C and XLONG_C are computed by geogrid but their values are never used by WRF during the simulations.

float XLAT_C(Time, south_north_stag, west_east_stag) ;
XLAT_C:FieldType = 104 ;
XLAT_C:MemoryOrder = "XY " ;
XLAT_C:units = "degrees latitude" ;
XLAT_C:description = "Latitude at grid cell corners" ;
XLAT_C:stagger = "CORNER" ;
XLAT_C:sr_x = 1 ;
XLAT_C:sr_y = 1 ;

float XLONG_C(Time, south_north_stag, west_east_stag) ;
XLONG_C:FieldType = 104 ;
XLONG_C:MemoryOrder = "XY " ;
XLONG_C:units = "degrees longitude" ;
XLONG_C:description = "Longitude at grid cell corners" ;
XLONG_C:stagger = "CORNER" ;
XLONG_C:sr_x = 1 ;
XLONG_C:sr_y = 1 ;

I was wondering how can I retrieve the corner latitudes and longitudes runtime?

Thanks into advance for help,
Markus

 

[kwerner]

Hi Markus, Many apologies for the long delay in response. I believe you would need to use some sort of post-processing to find those values. There's an NCL script that can convert points from i,j to lat,lon, which may be useful. See slide 31 from this NCL presentation.

 

[maR_Kus]

Hi Kwerner,
thanks for the reply. Indeed I need this information runtime as I use WRF output to drive an another model. However, I will look how NCL computes the corners.
In the meantime I googled a while and I found these conversions:

X_corner(i,j) = real(0.5*(xlong_v(i-1,j)+xlong_v(i,j))
Y_corner(i,j) = real(0.5*(xlat_u(i,j-1)+xlat_u(i,j))

Nevertheless, the results I get with the above formulations are slightly different from the geogrid outputs.
Best,
Markus