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Re: your mail : 360_DAY calendar & climatology

Hi Wendy Wang,
                Time axis is always a concern. Ferret needs the source
(your variable) and destination (climatological time axis) time axis 
to be defined over the same calendar type to do "MODULO" regridding.
>From the error message you have got it is clear that your variable is
on a "360_DAY" calendar. But the "month_reg" defined in climatological_
axes.cdf is "GREGORIAN". So the better way to get the climatology is to
define a "360_DAY" climatological axis. If you want more details about
the calendar types/attributes inf Ferret/NetCDF please have look at
Ferret user manual : Ch4 Sec2.2.  Time axes and calendars. 

      How to decide the calendar type of your variable in NetCDF file ?
There are two ways

           1. open the dataset in Ferret and use RETURN (will work with
                 only the recent versions of Ferret..i think)

                yes? use SWmn.nc
                yes? say `chl,RETURN=calendar`

           2. use netcdf utility "ncdump" to see the time axis definition

                [wendy@wendysmachine]$ ncdump -h SWmn.nc | more
                look for the "calendar" attribute. Please remember that
                if there is no calendar attribute in your NetCDF file,
                Ferret will take it as "GREGORIAN" calendar. 

  The example below illustrates the method to find climatology by 
defining a "climatological time axis" with proper /CALENDAR qualifier.
If you have any doubts/problems please let me know.

Hope This Helps 

With Regards


\ cancel mode verify

  ! create a variable "var" defined on a "360_DAY" (monthly) calendar axis

     define axis/t="16-JAN-1990:00":"16-DEC-1994":`360/12`/units=days/\
           calendar=360_DAY/T0="30-DEC-1989:00" tax

     let var      = t[gt=tax]
     say `var,r=calendar`

  ! define a proper climatological(monthly) axis

     define axis/t="16-JAN-0001:00":"16-DEC-0001":`360/12`/units=days/\
           calendar=360_DAY/T0="30-DEC-0000:00"/MODULO tclim    

     let var_clim = var[gt=tclim@MOD]  ! get the climatology
     list var_clim

!---end of example.jnl-------------------------------

On Mon, 20 Dec 2004, Wendy Wang wrote:

> Hi Ferret_users,
> I try to do monthly climatology of chlorophyll from >6 years monthly means.
> 16-SEP-1997 /  1:    ....
>   16-OCT-1997 /  2:  0.1552
>   16-NOV-1997 /  3:  0.0511
>   16-DEC-1997 /  4:  0.0636
>   .
> .
>   16-NOV-2003 / 75:  0.1932
>   16-DEC-2003 / 76:  0.1704
> But I got the following error:
> yes? use SWmn.nc
> yes? USE climatological_axes
>   *** NOTE: regarding /cdisk/d9/wwang/FERRET/go/climatological_axes.cdf ...
>   *** NOTE: Climatological axes SEASONAL_REG, MONTH_REG, and MONTH_IRREG 
> defined
> yes? CANCEL DATA climatological_axes
> yes? let cl_time=chl[t=16-jan-1998:16-dec-2003]
> yes? let clm=cl_time[gt=month_reg@mod]
> yes? list/x=140w/y=0 clm
>   **ERROR: regridding:  only @ASN, @LIN, or @NRST regridding between 
> calendar types: 360_DAY, GREGORIAN
> Could someone tell me where the problem is? Thanks.
> Wendy Wang


    Jaison Kurian                           
    Centre for Atmospheric and Oceanic Sciences
    Indian Institute of Science
    B A N G A L O R E   560 012
    Ph: +91-80-3942505

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