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: