[CF-metadata] Fwd: Two-variable integer Time in CF? (V. Balaji)

[Philip J. Cameron-smith]

Hi,

The unit 'days' is so central to atmospheric behavior that it would be a 
shame to lose it.  However, to complicate the mix further, there is even 
an alternative Earth day: the sidereal day (the time it takes for 
the Earth to spin once and face the same stars, as opposed to the sun). 
The difference is about 4 minutes less than a calendar day.

Best wishes,

      Philip

On Fri, 2 Nov 2007, David Stuebe wrote:

> I support Rich and Balaji in creating a two integer time standard. I think
> the tick_length as a attribute is a great idea for non-rational times, and I
> agree with Rich that the major unit should be specified by the user - Days,
> Second, Hours, Years etc...
>
> Concerning Days and earth-centric time units in UDUNITS
>
> Days - or rather (Modified) Julian Date as defined using a two integer time
> variables is an extremely practical method of storing time information for
> many, but not all applications. A standard for time and date which includes
> the needed definition of Day and time origin is important, (leap seconds
> aside) although not general as you pointed out for ET models... A definition
> of Day should remain in UDUNITS. Is there a standard for setting time origin
> for MJD and JD?
>
> I found it difficult to set time origin using an attribute, the string gets
> complicated. I would suggest a seperate variable if it does not conform to
> some recognized standard like JD or MJD...
>
> About the choice of Millisecond as the minor unit, it is not arbitrary for
> storing MJD dates, there are more Microseconds in a day than can be stored
> in a 32-bit integer. To avoid dealing with long integers, I choose
> Milliseconds for FVCOM output, though in the model, the Time Type/Class uses
> 64-bit integers and microseconds.
>
> I don't see a type name for 64-bit integers in the NETCDF 3 docs - am I
> missing something?
>
> David
>

------------------------------------------------------------------------
Dr Philip Cameron-Smith        Energy & Environment Directorate
pjc at llnl.gov                   Lawrence Livermore National Laboratory
+1 925 4236634                 7000 East Avenue, Livermore, CA94550, USA
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