As part of my current work I have been playing around with model output with PMEL’s Ferret software. One of the things that I wanted to do was to make a seasonal climatology from a time subset (e.g. quarterly averages centered on Feb, May, Aug, Oct for 1998-2007). If the data is defined using a standard calendar it’s fairly straightforward and is laid out in the Ferret FAQ.

However, this data is defined with a constant NOLEAP calendar, so we have to do a little more work. I was able to dig up some information on the Ferret mailing list archives where Jaison Kurian gave a nice example for making a custom modulo grid for a 360_DAY calendar. I was able to take his example and reshape it into what I needed for the NOLEAP data.

yes? define axis/t="16-FEB-0001:00":"16-OCT-0001":3\
/MODULO noleapseas
yes? let lsrat9807clim = lsrat9807[gt=noleapseas@MOD]
yes? list lsratclim[X=180,Y=30]
16-FEB      / 1:  0.1108
18-MAY      / 2:  0.1388
17-AUG      / 3:  0.1026
16-NOV      / 4:  0.0559

which checks out with a manual average spot check. Nice.