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Re: 360 day years



Hi Thijs,

The quick solution is is to "associate" your model time axis with a corresponding
Gregorian time axis for purposes of plotting. The details:

The spacing of points in time on your days-360 time axis would be correctly
represented by

    DEFINE AXIS/T=15-FEB-1900:15-FEB-2000:90/units=days t360_seasons

But this leads to the problem you are seeing -- as illustrated by this look at
the "Feb" season each year, which "drifts" about 5 days per year

     yes? show axis/l=1:20:4 t360_seasons
      name       axis              # pts   start                end
      T360_SEASONS TIME            407 r   15-FEB-1900    02-MAR-2000
     T0 = 01-JAN-1900
                L     T                 BOX_SIZE       TIME_STEP (DAYS)
                1>  15-FEB-1900 00:00:00  90             45
                5>  10-FEB-1901 00:00:00  90             405
                9>  05-FEB-1902 00:00:00  90             765
               13>  31-JAN-1903 00:00:00  90             1125
               17>  26-JAN-1904 00:00:00  90             1485

Now, a Gregorian seasonal time axis with 4 equal-length seasons could be defined
with

yes? DEFINE AXIS/T=15-FEB-1900:15-FEB-2000:`365.2485/4,prec=9`/units=days tGreg_seasons

and has no long term "drift" problems:

     yes? show axis/l=1:200:`4*10` tGreg_seasons
      name       axis              # pts   start                end
      TGREG_SEASONS TIME           401 r   15-FEB-1900    15-FEB-2000
     T0 = 01-JAN-1900
                L     T                 BOX_SIZE       TIME_STEP (DAYS)
                1>  15-FEB-1900 00:00:00  91.31213       45
               41>  15-FEB-1910 11:38:27  91.31213       3697.485
               81>  15-FEB-1920 23:16:54  91.31213       7349.97
              121>  15-FEB-1930 10:55:22  91.31213       11002.46
              161>  15-FEB-1940 22:33:49  91.31213       14654.94


(A more exact time axis is explained in

 http://ferret.wrc.noaa.gov/Ferret/Documentation/Users_Guide/v50/partII.html#V5.0_DEFINE AXIS$/EDGES)

If you have a variable, MY_VAR, defined on a time axis like t360_seasons you can
make a nice plot of it using

    yes? PLOT MY_VAR[GT=tGreg_seasons@ASN]

where the "@ASN" denotes regridding by association.

Note that we are working on more automated solutions to this problem for future
versions of Ferret.

Thanks for your question.

    - steve

================================================

Thijs van Reenen wrote:

> Hello,
>
> My model produces seasonal output, each season (jfm, amj, ...) lasting for 90
> days. I would like to Ferret to use the 360-day model year so that the
> time-references on the plots will correspond to the model months.
>
> How can I achieve this?
>
> Thanks!
> --
>    ____________________________________________________________
>   |                                                            |
>   | Name   : Thijs van Reenen                                  |_
>   | Adress : Royal Netherlands Meteorological Institute (KNMI) | |
>   |          P.O. Box 201, 3730 AE De Bilt, The Netherlands    | |
>   | Tel    : +31 30 2206366                                    | |
>   | Fax    : +31 30 2202570                                    | |
>   | Email  : reenenv@knmi.nl                                   | |
>   | URL    : www.knmi.nl/~reenenv/                             | |
>   |____________________________________________________________| |
>     |____________________________________________________________|

--

                |  NOAA/PMEL               |  ph. (206) 526-6080
Steve Hankin    |  7600 Sand Point Way NE  |  FAX (206) 526-6744
                |  Seattle, WA 98115-0070  |  hankin@pmel.noaa.gov




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