Re: [ferret_users] error converting monthly to yearly values

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

Hi -
Do the edges of the grid cells on the input monthly time axis line up 
with the edges of the yearly axis you have defined?  If not, you could 
be seeing a discrepancy in the average from that, with contributions 
from parts of grid cells at the start and end of each year.

Try this:

  yes? show axis/t=1-jan-1979:1-jan-1981 t[gt=mn]  ! shows axis details 
for the input monthly time axis

  yes? show axis/t tax  ! shows the box edges and step size for the 
axis you defined

Do the values of TBOXLO at the start of the years match?  This FAQ might 
be helpful:
http://ferret.pmel.noaa.gov/Ferret/faq/regridding-a-time-series-with-ave

Ansley

On 6/12/2012 6:04 AM, samir pokhrel wrote:
> Dear Ferret users,
>
> I am trying to convert monthly fields to yearly fields by defining 
> axis of 360 calender days
>
> define axis/t=1-jan-1979:30-dec-2010:12/unit=month/cal=360_days/edges tax
>
> let yr = mn[gt=tax@ave]
>
> This seems to be much closer than other approach, still there is a 
> difference if i check the values by averaging every alternate 12 
> records or by using CDO.
>
> Is there any other efficient way to make it more reliable
>
> Thanks in advance
>
> Samir Pokhrel
>
> Climate and Global Modelling Division
> Indian Institute of Tropical Meteorology
> NCL Post, Pashan
> Pune-411008
> INDIA