Re: mean seasonal cycle

[Emilio Mayorga <emiliom@xxxxxxxxxxxxxxxx>]

Hi Joerg, how are the rains treating you at Stanford?

You've already received replies with the standard solutions to obtaining
the mean monthly climatology. I just wanted to add that you also need to
be careful with the time units you're using. I had problems using "months"
as the time step, because as Steve has pointed out already, this is an
ambiguous unit. I've had to switch to using hours as the time unit in my
netcdf files, uniform length months (I think Steve called them "abstract"
months, used in modeling), and a definition of a year that corresponds
exactly to Ferret's: a year is 365.2425 days, and a regular-length month
is 365.2425/12. The problems arise when you mix a "modulo" (climatology,
mean months) netcdf file created by ferret, and your own monthly netcdf
datasets that use month time units and where the length of the year
doesn't correspond to Ferret's. There's an accumulation of small errors
that takes place, which results in a lack of correspondence in the time
dimension.

If you use months as your time step in your models and therefore months as
the natural time unit in your netcdf files, this bit of information may
spare you some headaches.

Take care, give my regards to Chris Field & company.

Emilio Mayorga

________________________________________________________________
University of Washington	
School of Oceanography			emiliom@u.washington.edu
Box 357940				ph. (206) 543-5334
Seattle, WA  98195-7940	  USA		FAX (206) 685-3351
http://boto.ocean.washington.edu/staff_pages/emilio

On Wed, 25 Mar 1998, Joerg wrote:

> 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             
>