Re: ferret question

[Ansley Manke <ansley.b.manke@xxxxxxxx>]

Hi Mark,
Yes you can do this. This is a great Ferret example.  You want to regrid 
the climatology
data onto the time axis of the daily data, and subtract the result from 
the daily series.  Do
you want to create the climatology time series as a step function so 
that you subtract the
climatological  January from each January point in the daily time 
series, and so on? Here's
an example of how to do that.  I'll use the coads_climatology dataset 
and create a daily
time series variable. Here I'm putting a signal into the random daily 
time series, but it illustrates
the method.


   ! create a daily time series variable
   yes? define axis/t=1-jan-1990:1-jan-2000:1/units=days dayt
   yes? let tt = 0.5* randu(t[gt=dayt]) - 0.25

   ! define the regridding transformation to put the
   ! climatology onto the daily series

   yes? use coads_climatology
   yes? let sstday = sst[x=181,y=1,gt=dayt@NRST] - 28.3

   ! look at the different components

   yes? plot sstday
   yes? plot/t=1-jan-1990:1-jan-1992 tt, sstday

   ! Subtract the climatology from the daily data

   yes? plot/t=1-jan-1990:1-jan-1992 tt - sstday

You should look at different regridding transformations and decide which
one to use to put the climatology data onto the long  daily time axis.  
Compare
the result if you use the @LIN regridding transform (the default)  
rather than
@NRST.

Ansley Manke

Mark Carson wrote:

> Hi all,
>
> I hope I can pose this question somewhat clearly.  I have a 
> temperature dataset that is gridded in time only with a grid spacing 
> of 1 day over 50 years span (18628 time points).  I would like to 
> subtract the WOA01 monthly mean climatology from the data, but it is 
> gridded in 12 time points - months.  How can I subtract the proper 
> month's value from my dataset when, say, January occurs over and over 
> again throughout the 50 years, and making sure I'm subtracting it from 
> the proper days that would be the days of January in each year?  Is 
> this doable in Ferret?
>
> Thanks for any thoughts or info!
>
> Mark Carson