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Re: [ferret_users] error converting monthly to yearly values

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:


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

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