[ncl-talk] Filtering dates of a netcdf file (include number of gridpoints as additional criteria)

[Rashed Mahmood]

I think your condition (b) would be the only condition that is needed,
since if condition b is true then condition "a" must be true. So, it
appears that you do not need condition "a".
For example, if 80% of grid points for a given time and region has
precipitation values greater than zero, then for that particular time and
region area average value will always be above zero.

So I modified your script (see attached) and added a loop to find out those
time steps:

; condition b:

   dims      = dimsizes(rain_region)
   ntime     = dims(0)
   tot_point = dims(1)*dims(2)*1.
   ids_valid = new(ntime,integer)
   req_perc  = 80. ; 40.

   do n=0,ntime-1
      tmp_rain = rain_region(n,:,:)
      oneD     = ndtooned(tmp_rain)
      npnts    = 1.*dimsizes(ind(oneD.gt.0))
      perc     = 100.*(npnts/tot_point)

      if(perc.gt.req_perc)then
        ids_valid(n) = n
       else
        print(n+ " ... pertange of grid points is less than 80% = > "+perc)
      end if
      delete([/tmp_rain,oneD,npnts,perc/])
   end do

   if(.not.all(ismissing(ids_valid)))then
       n_thres  = ids_valid(ind(.not.ismissing(ids_valid)))
   else
     print(" No valid time step for the specified condition: Exiting")
    exit
   end if


You need to play with the variable    req_perc  = 80., by changing to lower
values such 40. or anything else to see how it works. In your data file no
time step would satisfy the 80% condition.
hope that helps.









On Mon, Sep 9, 2019 at 9:20 AM Lyndz <olagueralyndonmark429 at gmail.com>
wrote:

> Hi,
>
> This includes all time steps. But, in the file that I sent, I want to *count
> the number of gridpoints in each time step* with rainfall above 0. I have
> to include this in the time filter. Specifically, these two conditions: the
> area averaged rainfall is > 0 *and* at least 80% of the total gridpoints
> have rainfall > 0.
>
> Over the region I specified (rain_region), it has 40 x 30 x 10 (ntim x
> nlat x nlon).
> The above command you gave results to 5830.
> I can get a similar result by just doing this: a = num(rain_region.gt.0)
>
> Sincerely,
>
>
> On Tue, Sep 10, 2019 at 12:02 AM Rashed Mahmood <rashidcomsis at gmail.com>
> wrote:
>
>> Yes, there can be several ways of counting grid points with rainfall
>> above 0:
>>
>> e.g. say your variable name is "precp"
>>
>> oneD = ndtooned(precip)
>>
>>  nVal = dimsizes(ind(oneD.gt.0))
>>
>> nVal is the number of time precip is greater than 0. Does this makes
>> sense, let me know if does not.
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> On Mon, Sep 9, 2019 at 11:36 AM Lyndz via ncl-talk <ncl-talk at ucar.edu>
>> wrote:
>>
>>> Dear NCL experts,
>>>
>>> I would like to filter the dates in a NetCDF file when the following
>>> conditions are met:
>>> (a) Area averaged rainfall is greater than 0.
>>>
>>> Area:
>>>   latS = 12.5
>>>   latN = 20.0
>>>   lonL = 120.0
>>>   lonR = 122.5
>>>
>>> (b) At least 80% of the grid points within the specified area satisfies
>>> (a).
>>>
>>> Attached in this email is the script that I am currently working on.
>>> The sample data can be accessed here:
>>> https://www.dropbox.com/s/spfnwb4rhwjo90o/aphro_1979_AMJ.nc?dl=0
>>>
>>>
>>> *[Problem]*
>>> I was able to do the condition (a) but is there a way to count the
>>> number of grid points with rainfall above 0 over the specified region? How
>>> can I add this as another condition for the date filter?
>>>
>>> The time filter is like this:
>>>
>>>   rain_threshold = 0
>>>   rain_aave=wgt_areaave_Wrap(rain_region,1.0,1.0,0)
>>>   printVarSummary(rain_aave)
>>>   n_thres  = ind(rain_aave .gt. rain_threshold) ;time indices
>>>   print(n_thres)
>>>   print("=====")
>>>
>>> I'll appreciate any guidance about this.
>>>
>>> Sincerely,
>>> Lyndz
>>>
>>>
>>>
>>> _______________________________________________
>>> ncl-talk mailing list
>>> ncl-talk at ucar.edu
>>> List instructions, subscriber options, unsubscribe:
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>>
>>
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