computing monthly anomalies

[James Boyle <boyle@xxxxxxxxxxxxxx>]

What I want to do is this.

Given 6 years of data - 72 months 
(1) compute the seasonal cycle ( 12 months - each an average of the 6 Jan, Febs ... etc.)
(2) compute the anomalies from the climatology - 72 months of data - (eg jan 79 - jan climo ....)

I can do (1) easily using the modulo regridding, so far any way of doing (2) has
eluded me.

I'm sure this has been done many times but I can't see any elegant solution.


Thanks for any help.

Jim