Inconsistent dimension sizes of U&V in 850hp pressure level

[lslrsgis]

Dear WRF Community,

After running wrf using NARR as forcing, I am trying to extract U, V fields of 850hp from wrfout files. However, I have found they have different dimensions.

U850: [267] x [271]
V850: [268] x [270]

I am simply use the 6rd of 27 layers since 85000 is found as 6th in &mod_levs of namelist.wps.all_options. The ncl script (attached) is written as follows:
u850 = ull(6-1,:,*1.94386
v850 = vll(6-1,:,*1.94386

&mod_levs
press_pa = 201300 , 200100 , 100000 ,
95000 , 90000 ,
85000 , 80000 ,
75000 , 70000 ,
65000 , 60000 ,
55000 , 50000 ,
45000 , 40000 ,
35000 , 30000 ,
25000 , 20000 ,
15000 , 10000 ,
5000 , 1000
/

Is it reasonable? Why they have different dimensions? Thanks very much.

 

[hesselmans]

U and V are not defined at the center of a cell, but at east-west and north-south faces.
Dimension of U is 1 larger than the number of cells in x-direction.
Dimension of V is 1 larger than the number of cells in y-direction.
Please read the clarification at: https://www.openwfm.org/wiki/How_to_interpret_WRF_variables
Regards, Gerard

 

[Ming Chen]

WRF implements staggered grid structure. You can find the helpful information in the document here:
http://www2.mmm.ucar.edu/wrf/users/docs/technote/v4_technote.pdf