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Re: [ferret_users] annual totals from monthly time series

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.


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


Andy Jacobson wrote:

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", ...


(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?



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