Re: [ExternalEmail] [ferret_users] Proleptic Gregorian Calendars overridden

["Ansley C. Manke" <ansley.b.manke@xxxxxxxx>]

Hi,
We had somehow glossed over this distinction between PROLEPTIC_GREGORIAN and GREGORIAN, instead as you found handling a PROLEPTIC_GREGORIAN specifier as if it's GREGORIAN.  We'll work on getting the correct behavior into Ferret; as given in the CF standard:

gregorian or standard

Mixed Gregorian/Julian calendar as defined by Udunits. This is the default.

proleptic_gregorian

A Gregorian calendar extended to dates before 1582-10-15. That is, a year is a leap year if either (i) it is divisible by 4 but not by 100 or (ii) it is divisible by 400.

Ansley

On 10/21/2018 10:01 PM, Russ Fiedler wrote:

Hi,

Furthermore from the CMIP6 metadata requirements

https://docs.google.com/document/d/1os9rZ11U0ajY7F8FWtgU4B49KcB59aFlBVGfLC4ahXs/edit

Section 17.c.

ote that if a model has a gregorian calendar and the base time is defined as a date prior to 1582, then the user should specify 'proleptic_gregorian', rather than 'gregorian' for the calendar attribute.

That's a pretty good reason for proleptic_gregorian to be treated correctly.

Russ

On 22/10/18 2:02 pm, Russ Fiedler wrote:

Hi,


I've got a time series  with the time definition


    double time(time) ;
        time:long_name = "time" ;
        time:cartesian_axis = "T" ;
        time:calendar_type = "PROLEPTIC_GREGORIAN" ;
        time:calendar = "PROLEPTIC_GREGORIAN" ;
        time:bounds = "time_bounds" ;
        time:units = "days since 0001-01-01 00:00:01" ;

Now, Ferret is a bit odd in its behaviour with respect to standard/gregorian calendars in that it uses the Proleptic Gregorian calendar EXCEPT when the starting date

is 0001-jan-01 when it and times are after 1582 when reverts to the cf compliant mixed gregorian/julian.


https://www.pmel.noaa.gov/maillists/tmap/ferret_users/fu_2005/msg00625.html

https://ferret.pmel.noaa.gov/Ferret/documentation/users-guide/Grids-Regions/GRIDS#_VPINDEXENTRY_634

http://cfconventions.org/Data/cf-conventions/cf-conventions-1.7/cf-conventions.html#calendar


I can handle the odd behaviour for legacy reasons but, surely, if I specify PROLEPTIC_GREGORIAN Ferret should respect that attribute and not muck about with the calendar.

Al the least I'd like a way to turn off this behaviour.

Maybe something like


SET  AXIS/CF_COMPLIANT_CALENDAR taxis



to get proper axis specifications no matter what (or if the "Conventions" attribute  "CF-X.X" is found then do it according to that convention).


Cheers,

Russ