NCL-Is there a way to subtract same variable, diferent values (same file) from index information?

Question

I have a 3D nc variable PP = (time, lat, lon) of accumulated precipitation for an entire year and I want to calculate daily values.

I want to do something linke in the example, but culdn't find any examples.

I've tried to do a loop in which the subtraction should be between the values with [index+1] minus value [index] (like below)

t = f->time(:)   ;size = 365

pp = f->TOTALRAIN(:,:,:) ; time, lat, lon dimensions


do i = 0,dimsizes(t)-1

DailyPp = pp(i,:,:) - pp(i-1,:,:)

end do

but that way produces an error.

I need the daily values and only have accumulated precipitation as input information, and thought that a loop like that should be the best way.

How can I do the calculation from the variable???

I'm working with ncl but if you have cdo or nco propositions they're welcome.

Answer 1

you can do this with two NCO shell commands

the below command shifts the records up by one

ncks -v TOTALRAIN --msa_usr_rdr -d time,1,364 -d time,364 in.nc shift.nc

now use ncbo to find the difference

ncbo -v TOTALRAIN shift.nc in.nc diff.nc

now the netcdf file diff should contain your daily pp The final record of TOTALRAIN in this file will be zero's

...Henry

Answer 2

In cdo you can disaggregate accumulated variables using

cdo deltat in.nc diff.nc 

This is related to this question , please refer to the answers there for more details, including inserting the initial timestep.