# Re: [ferret_users] Calculations between different time axis

Hi people, Thanks for the explanations. What I mean to say was that I was wondering to solve it with a single command line. Each suggestion is enough. I prefered to define a "generic year" time axis. This way I get results (differences, graphs, etc) independet of the year.

Best regards,
Paulo Santiago

2009/8/11 Paul Young
Hi Paulo,

I see I missed out a bit in my example. Note, my method does not require you to define a new time axis - I simply re-grid var_yr2 onto the time axis of var_yr1. This works fine so long as the time axis is of the same number of points in both.

Corrected example - using the @asn regridding:

use "model_output_year_1.nc"
use "model_output_year_2.nc"

let var_yr1 = var[d=1]
let var_yr2 = var[d=2]
let var_yr2_new_t = var_yr[gt=var_yr1@asn]      !"blindy" associate yr1's time axis with y2 data

!Plot differences
fill/z=1000/l=1 var_yr1 - var_yr2_new_t

On Aug 11, 2009, at 2:50 PM, Paulo Santiago wrote:

Hi Paul,

I defined a new time axis and assigned to my variables.

define axis/t="15-JAN":"15-DEC":1/units=months mytax

I was wondering if I could solve it without defining a new axis.

Cheers,
Paulo

2009/8/11 Paul Young
Hi Paulo,

You need to re-grid the data to a common time axis. The simplest way is to re-grid the data from year 2 onto the year 1 time axis. I'll illustrate with a hypothetical ferret session:

use "model_output_year_1.nc"
use "model_output_year_2.nc"

let var_yr1 = var[d=1]
let var_yr2 = var[d=2]
let var_yr2_new_t = var_yr[gt=var_yr1]

!Plot differences
fill/z=1000/l=1 var_yr1 - var_yr2_new_t

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Take a look at the ferret documentation on re-gridding - ferret makes it quite straightforward for all kinds of re-gridding operations.

http://ferret.pmel.noaa.gov/Ferret/documentation/users-guide/Grids-Regions/GRIDS#_VPID_197

Cheers,

Paul

On Aug 11, 2009, at 1:11 PM, Paulo Santiago wrote:

Hi Ferreters,

I wou differences between data with different time axis.

The data are results from the same model (same xyz grid) for different years.

I believe there's a simple and elegant way to do this task with Ferret, but I can't imagine how.

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Paulo Santiago

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Paulo Santiago

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Paul Young

Chemistry and Climate Processes
Chemical Sciences Division
NOAA Earth System Research Laboratory
Boulder CO 80305-3328
USA

Fax:   +1 303-497-5686

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Paulo Santiago