Re: [ferret_users] error converting monthly to yearly values

[samir pokhrel <pokhrelsamir@xxxxxxxxx>]

Thanks a lot Ansley,

I have gone through the FAQ and tried to define axis based on days1900

DEFINE AXIS/EDGES/T0=1-jan-1900/UNITS=days tann79_10 = DAYS1900(X[i=1979:2010:1],1,1)

let yr=mn[gt=tann79_10@ave]

but this is giving 31 records instead of 32 records.

Also I feel if I use repeat command to calculate the average of every alternate 12 records like 

repeat /name=nm/range=1:384:12 (let evp_yr = evp[l=`nm`:`nm+11`@ave]; save /file=yr_79_10.nc/append yr)

which will give me perfect result but I am not able to append it in time, how to do it?

Samir

On Tue, Jun 12, 2012 at 11:27 PM, Ansley Manke <ansley.b.manke@xxxxxxxx> wrote:

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

-- 
Samir Pokhrel
Climate and Global Modelling Division
Indian Institute of Tropical Meteorology
NCL Post, Pashan
Pune-411008
INDIA