mean seasonal cycle

[Joerg <joerg@xxxxxxxxxxxxxxxxxxx>]

Dear ferreters,
how do I get a mean seasonal cycle from a couple of years of monthly data,
i.e. average of all Januaries, Februaries,... in a variable? And then, can I
subtract that variable from the original data to get the anomalies?
Any hints greatly appreciated,
thanks very much!
Ciao,
Joerg
--
Jörg Kaduk                           phone:  +1 (650) 325 1521 ext 416
Carnegie Institution of Washington   fax:    +1 (650) 325 6857
Department of Plant Biology
260 Panama Street                    e-mail: joerg@jasper.stanford.edu   
USA - Stanford, CA 94305