[ncl-talk] How to convert the value of a NetCDF file to zero

[Dave Allured - NOAA Affiliate]

Setareh, with simple 1-D coordinate variables, you would easily do this
with coordinate range subscripting.  Read about that in the NCL ref
manual.  Here is an example that writes directly into an existing file,
rather than making a new file.

      f->MSEBIO_ISOP( {0,10}, {10,30} ) = 0

However, the coordinates in your particular file are 3-D, so you have to
use extra code.  Here is the simplest way.  This is also the slowest, but
if you are only working with a small amount of data, it is better to keep
the code simple.  This example also writes directly into the existing
file.  Not tested:

      lat1 = 0
      lat2 = 10
      lon1 = 10
      lon2 = 30

      do t = 0, ntimes-1
         do i = 0, nlats-1
            do j = 0, nlons-1
               if ( (XLAT(t,i,j) .ge. lat1) .and. (XLAT(t,i,j) .le. lat2) \
                  .and. (XLONG(t,i,j) .ge. lon1) .and. (XLONG(t,i,j) .le.
lon2) ) then
                     f->MSEBIO_ISOP(t,i,j) = 0
                          ! You can add more variables here
               end if
            end do
         end do
      end do


On Thu, Jan 25, 2024 at 1:04 PM Setareh Rahimi <setareh.rahimi at gmail.com>
wrote:

> Dear Dave,
>
> So many thanks for your help. I just checked it and it worked.
>
> May I ask you please to advise me on how to only convert the values of all
> variables to zero for a specific region and not whole the domain? (for
> example lat[0,10], and lon[10,30])?
>
> Thanks in advance.
> Kind regards,
>
> On Thu, Jan 25, 2024 at 11:18 PM Dave Allured - NOAA Affiliate <
> dave.allured at noaa.gov> wrote:
>
>> The problem is that Dennis's program did not copy the file global
>> attributes, which contain part of the georeferencing.  Just add this line
>> near the top of the program, after the line "print (vNames)":
>>
>>       copy_VarAtts (f, fout)
>>
>>
>> On Thu, Jan 25, 2024 at 11:07 AM Ehsan Taghizadeh via ncl-talk <
>> ncl-talk at mailman.ucar.edu> wrote:
>>
>>> Dear Setareh,
>>> I suggest you read the variables from the fout file again. For example,
>>> if there is a variable named "V10" in fout, you just need to read that
>>> variable from fout, as follows:
>>> V10_zero=fout->V10
>>>
>>> This V10_zero has the same coordinates as V10 in the original file, but
>>> its values are zero.
>>> I hope this is correct.
>>>
>>>
>>> On Thursday, January 25, 2024 at 06:17:12 PM GMT+3:30, Setareh Rahimi
>>> via ncl-talk <ncl-talk at mailman.ucar.edu> wrote:
>>>
>>> Dear Dennis,
>>> I noticed an issue. When I use the attached script it converts all
>>> values to zero, but the data is no georefrenced any more. So how can I fix
>>> this please?
>>> Thanks in advance.
>>> Best regards,
>>>
>>> S.Rahimi
>>>
>>>
>>> On Sun, Jan 21, 2024 at 18:44 Dennis Shea <shea at ucar.edu> wrote:
>>>
>>> Attached is a script that does what you requested.
>>>
>>>
>>> On Sat, Jan 20, 2024 at 6:40 AM Setareh Rahimi via ncl-talk <
>>> ncl-talk at mailman.ucar.edu> wrote:
>>>
>>>
>>> Dear NCL users,
>>>
>>> I have a NetCDF file (attached) that contains some variables. I
>>> would like to change the values of all variables to zero for all grid
>>> points. So how can I do this using NCL, please?
>>>
>>> This file is an input file for the WRF-Chem model, and I do not want to
>>> change the format of the file, only want to change the values to zero.
>>>
>>> Please kindly advise me in this regard.
>>>
>>> Thanks in advance.
>>> Kind regards,
>>> --
>>> S.Rahimi
>>>
>>>
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