[ncl-talk] grid_area_avg

[Kunal Bali]

Dear Haley Ma'am,

Thanks for providing the information and example.
But if I follow the getind_latlon2d function as I did, then it seems like I
followed the same procedure as given in the example
http://www.ncl.ucar.edu/Document/Functions/Contributed/getind_latlon2d.shtml

But still I am not getting the mean of the grid box on every time step or
am I reading incorrectly the result ?


regards
Kunal Bali






On Fri, Oct 13, 2017 at 12:11 AM, Mary Haley <haley at ucar.edu> wrote:

> 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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>
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