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

[Lyndz]

Dear Rashed and NCL experts,

I tried adding another condition on the above script:
(a) OLR < 240 W/m2 and the number of grid points with rainfall above 0
mm/day should be at least 10%.


Like this:
     olr_threshold = 240
     olr_aave=wgt_areaave_Wrap(olr_region,1.0,1.0,0)





*     if((perc.gt.req_perc) .and. (olr_aave.lt.olr_threshold))then
ids_valid(n) = n       else        print(n+ " ... pertange of grid points
is less than 80% = > "+perc)      end if*

I am getting the following errors:


*fatal:Conditional statements (if and do while) require SCALAR logical
values, see all and any functionsfatal:["Execute.c":8637]:Execute: Error
occurred at or near line 66 in file date_filter.ncl*

Line 66 is the end if part of the script.

I uploaded the olr data here:
https://www.dropbox.com/s/ufdzfk4ky2gfmz8/olr_1979_AMJ.nc?dl=0

and the script is attached in this email.

Any suggestions on how to do this correctly in NCL?
I'll appreciate any help.

Sincerely,
Lyndz


On Tue, Sep 10, 2019 at 1:28 PM Lyndz <olagueralyndonmark429 at gmail.com>
wrote:

> Dear Rashed,
>
> Thank you so much for your help!
> This works. I just need to tweak the threshold.
>
> Sincerely,
> Lyndz
>
>
> On Tue, Sep 10, 2019 at 3:15 AM Rashed Mahmood <rashidcomsis at gmail.com>
> wrote:
>
>>
>> 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:
>>>>> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>>>>
>>>>
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