[CF-metadata] Non-real-world calendars

From: Jonathan Gregory <j.m.gregory>
Date: Mon, 1 Jul 2013 18:16:45 +0100

Dear Richard

Issues like these have been raised before, and in fact there are two open
tickets (96 and 101) which I think relate to your points 2 and 3. Perhaps
you could have a look at them? I would not be surprised if point 1 has been
raised somewhere, but I can't remember! Is this exclusion really necessary?
Time-zones probably aren't needed for non-real-world calendars, which are
typically used in climate models only - but do they do any harm, if they
are simply defined as offsets in hours? An hour is a well-defined unit.
Perhaps the argument would be that time-zones involve summer time (daylight-
saving), and in the non-real-world calendar it wouldn't be clear when summer
time applies.

Best wishes

Jonathan

----- Forwarded message from "Hattersley, Richard" <richard.hattersley at metoffice.gov.uk> -----

> From: "Hattersley, Richard" <richard.hattersley at metoffice.gov.uk>
> To: "cf-metadata at cgd.ucar.edu" <cf-metadata at cgd.ucar.edu>
> Date: Mon, 1 Jul 2013 13:26:22 +0000
> Subject: [CF-metadata] Non-real-world calendars
>
> Hi everyone,
>
> I'd like to propose a trac ticket or two to clarify the meaning when using alternative calendars. But before I do that I'd like to check for community opinion (or even consensus!?) ...
>
> 1. Time zones should be excluded/banned when using non-real-world calendars. For example, the statement in section 4.4 of "if the time zone is omitted the default is UTC" should not apply.
>
> 2. The "months since" and "years since" semantics for non-real-world calendars need defining/outlawing. e.g. The UDUNITS definition of a year as 365.242198781 days makes no sense at all for a 360-day calendar, but in this particular case a year could be unambiguously defined as 360 days.
>
> 3. The year-zero semantics for non-real-world calendars need defining. From section 7.4, "Year 0 may be a valid year in non-real-world calendars".
Received on Mon Jul 01 2013 - 11:16:45 BST