Re: [ferret_users] annual totals from monthly time series

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

Hi Andy,
The problem as I'm sure you know is that a "year" isn't the same length 
every year in the standard calendar. Have a look at this example from 
the Users Guide: (See "monthly axis, creating" in the index).  It 
defines a true monthly axis with edges at the exact start of each month, 
which is similar to what you want to do.  I imagine you can adapt it to 
create the true year axis that you want.

http://ferret.pmel.noaa.gov/Ferret/documentation/users-guide/commands-reference/DEFINE#_VPINDEXENTRY_1311

Write back if it doesn't see to work for some reason (or if it does, 
fill us in on the details!)


Ansley

Andy Jacobson wrote:
> Howdy,
>
> I'm trying to compute annual means from monthly time series.   My 
> strategy has been to define a time axis with yearly resolution, then 
> regrid to this time axis using the @ave transformation, like:
>
> define 
> axis/edges/t="01-Jan-2000:00:00:00":"01-Jan-2008:00:00:00":1/UNITS=years 
> tannual
> list nee[gt=tannual@ave]
>
> The regridding strategy works.  The only problem I have is that I'd 
> like the tannual axis edges to each fall right on 01-Jan 00:00 UTC, 
> but they drift as shown by the TBOXLO values below:
>
> show axis/l=1:9 tannual
>  name       axis              # pts   start                end
>  TANNUAL   TIME                 9 r   01-JUL-2000 14:54    01-JUL-2008 
> 13:28
> T0 = 15-JAN-1901
>    Axis span (to cell edges) = 9
>
>        L     T                   TBOX      TBOXLO                TSTEP 
> (YEARS)
>        1>  01-JUL-2000 14:54:36  1         01-JAN-2000 00:00:00   
> 99.46165
>        2>  01-JUL-2001 20:43:48  1         31-DEC-2000 05:49:12   
> 100.4616
>        3>  02-JUL-2002 02:33:00  1         31-DEC-2001 11:38:24   
> 101.4616
>        4>  02-JUL-2003 08:22:12  1         31-DEC-2002 17:27:36   
> 102.4616
>        5>  01-JUL-2004 14:11:24  1         31-DEC-2003 23:16:48   
> 103.4616
>        6>  01-JUL-2005 20:00:36  1         31-DEC-2004 05:06:00   
> 104.4616
>        7>  02-JUL-2006 01:49:48  1         31-DEC-2005 10:55:12   
> 105.4616
>        8>  02-JUL-2007 07:39:00  1         31-DEC-2006 16:44:24   
> 106.4616
>        9>  01-JUL-2008 13:28:12  1         31-DEC-2007 22:33:36   
> 107.4616
>
> I had hoped that I could specify the axis edges explicitly as in:
>
> define axis/edges/t 
> tannual={"01-Jan-2000:00:00:00","01-Jan-2001:00:00:00","01-Jan-2002:00:00:00","01-Jan-2003:00:00:00","01-Jan-2004:00:00:00","01-Jan-2005:00:00:00","01-Jan-2006:00:00:00","01-Jan-2007:00:00:00","01-Jan-2008:00:00:00"} 
>
>
> ...but ferret (v5.70 alpha, on OSX) emits:
>
>  **ERROR: illegal data type (float,string,...) for operation: 
> {"01-Jan-2000:00:00:00", ...
>
> So:
>
> (1) Is there a way to explicitly specify the dates of a time axis?
> (2) Am I thinking unferretly about how to compute annual totals?
>
> Thanks!
>
> Andy