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Re: [ferret_users] regridding in time

This is done in Ferret with a regridding operation. Have a look at "regridding" in the documentation. Define the new time axis, and regrid your data to that axis. If you are happy with a regularly-spaced output axis, which will be only approximately the 3-month intervals, you could do it this way:

define axis/t=1-jan-1958:31-dec-1958/npoints=4/edges/units=days  seas_1958
let newDCHL = DCHL[gt=seas_1958]

Or you could look at the documentation under "monthly axis", creating for how to make an axis with time steps that include exactly the months JFM, AMJ, etc.

The other thing you can do is a "climatological regridding".  It sounds as if your data spans less than a year, but if it were several years, what this would do is average all the data in Jan-Feb-Mar into the first timestep, and all the April-May-June,  into the second, etc.  This operation is described in  the section on Climatological, also known as Modulo regridding.


On 5/23/2013 4:50 AM, Igaratza Fraile wrote:

Dear ferreters


I´m using a netCDF file for one year with data for every 5 days (73 time steps).


yes? Sh da

            currently SET data sets:

            1> .\dchl_ORCA2-levitus_DFS4_1958.nc <default>

Name   title                              I           J          K          L

DCHL   Tracer as simulated…    1:360    1:180    1:31      1:73


 I would like to get average values for every 3 month (Jan-Feb-Mar, Apr-may-Jun, Jul-aug-Sep and Oct-Nov-dec). I tried to use @ave transformation, but for some reason the results is not what I expected.


yes? let newDCHL=DCHL[L=1:72:18@ave]  (I ignored the last day)


However the average value is not the same as 1:18@ave, 19:36@ave…


yes? list/i=1/j=1/k=1 DCHL[L=1:18@ave], DCHL[L=1:18:18@ave], newDCHL[L=1]

            DCHL               DCHL               newDCHL

I / *:      1.864E-06         2.644E-06         2.644E-06


The value I was expecting is the first one. Why is that difference? And how can I regrid my data to get average values for every three months?

Thanks in advance



Igaratza Fraile
Unidad de investigación Marina
T. +34 667 174 464
Herrera Kaia, Portualdea z/g

E-20110 Pasaia, Gipuzkoa.
Mail: ifraileo@xxxxxxx





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