[ncl-talk] grid_area_avg
Mary Haley
haley at ucar.edu
Thu Oct 12 12:41:24 MDT 2017
Kunal,
I created an example for you, showing three ways you can subset a WRF grid
(since I already had a similar example). It shows how to use the
getind_latlon2d function.
You have to be careful with subsetting curvilinear data, because specifying
a lat/lon box to take an average over can mean two different things. You
will be able to see the difference when you look at the graphic.
See example wrf_gsn_10.ncl at:
http://www.ncl.ucar.edu/Applications/wrfgsn.shtml#ex10
--Mary
On Wed, Oct 11, 2017 at 12:03 PM, Kunal Bali <kunal.bali9 at gmail.com> wrote:
> Dear NCL users,
>
> Single point coordinates values of 23.0 N and 77.0 E is extracted or print
> by using the script below
>
> ----------------------------------------------------------------------
> ; Main code
> ;----------------------------------------------------------------------
> dir = "./"
> fnames = systemfunc("ls " + dir + "maiactaot*.nc")
> print(fnames)
> a = addfile(fnames,"r")
> data = short2flt(a->Optical_Depth_055_grid1km)
> nFill = num(ismissing(data))
> lat2d = a->GridLat_grid1km
> lon2d = a->GridLon_grid1km
>
> ;---grid points of interest
> latv = (/23.0/)
> lonv = (/77.0 /)
>
> nm = getind_latlon2d (lat2d,lon2d, latv, lonv)
>
> do k=0,dimsizes(latv)-1
> n = nm(k,0)
> m = nm(k,1)
> print(lat2d(n,m)+" "+lon2d(n,m)) ; grid point location
> print(" "+data(:,n,m)) ; nearest grid point at
> all time steps
> print("-----")
> end do
>
>
> NOW, I want to extract the square grid box of 100 km around the
> coordinates (23N,77E) such as
> latv = (/22, 24.0, 24.0, 22.0, 22.0/)
> lonv = (/76, 76.0, 78.0, 78.0, 76.0 /)
>
>
> after that I want to do the area mean of the grid box. So that I can get
> one single point value of that grid box.
> So when I replacing
> latv = (/23.0/)
> lonv = (/77.0/)
>
> with
>
> latv = (/22, 24.0, 24.0, 22.0, 22.0/)
> lonv = (/76, 76.0, 78.0, 78.0, 76.0 /)
>
> then It's not giving mean of the square grid box.
>
> It shows the something like that (given below), which is incorrect. So
> please let me know how can I get the square grid box mean and then extract
> as asciiwrite or print?
>
> (0) 23.76603307545667 75.53995171540016
> (0) 0.179
> (1) 0.142
> (2) -28672
> (3) 0.169
> (4) -28672
> (5) -28672
> (6) -28672
> (0) -----
> (0) 24.00322458681621 75.99551564353467
> (0) 0.171
> (1) 0.16
> (2) -28672
> (3) 0.17
> (4) -28672
> (5) -28672
> (6) -28672
>
> etc..etc..
>
>
>
> regards
> Kunal Bali
>
>
>
>
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