Hi John and all,
ESMF has a mature time management library with calendars that are commonly
used in climate/weather/related modeling. It supports the following: 360
day,
no leap, Gregorian (proleptic), Julian, Julian day, modified Julian day,
and custom
(including custom calendars that may change the length of days). ESMF,
like CESM,
doesn't support the standard Gregorian calendar because it doesn't make
sense for modeling groups who may need to cross the Julian/Gregorian
weirdness line (we've never gotten a request to support standard
Gregorian from
modelers). ESMF has calendar, time, time interval, clock, and alarm
constructs,
can run time forward or backward, and prints times and time intervals in
ISO8601
format. CESM/CAM, NASA, NOAA, Navy and other codes use it.
The most complete interface to the time lib is Fortran, and there are
some basic
time functions exposed in C (the lib is actually written in C++).
However, we could
wrap the time functions in Python and include them in ESMP, which is
currently a
set of ESMF regridding functions wrapped in Python. We could probably do
that
in the late/winter spring timeframe, with some guidance on what
functions were
desired and a pass through our prioritization board.
Best,
-- Cecelia
On 12/5/2012 12:25 PM, John Caron wrote:
> Hi all:
>
> Its probably the right thing to do to make gregorian ("Mixed
> Gregorian/Julian calendar") the default calendar for COARDS/CF, for
> backwards compatibility. However, CDM may leave proleptic_gregorian
> (ISO8601) as its default.
>
> And I would strongly suggest that data writers stop using "time since
> 1-1-1". Ive never seen a dataset where "time since 1-1-1" using the
> mixed gregorian calendar was actually needed. If any one has a real
> example, Id like to hear about it.
>
> If you really need "historical accuracy", then put in an ISO8601
> formatted string, and an explicit calendar attribute. CDM handles
> those ok. CF should be upgraded to allow ISO strings also. "time since
> reference date" is not good for very large ranges of time.
>
> Ill just add that udunits never wanted to be a calendaring library,
> and shouldnt be used anymore for that. Im relying on joda-time (and
> its successor threeten) to be the expert in calendering, so i dont
> have to. I think the netcdf-C library now uses some CDAT (?) code for
> its calendaring, but Im sure theres other standard libraries that
> could be used. Anyone have candidate libraries in C or Python for
> robust calendering>
>
> In short, we should rely on clear encoding standards (eg ISO8601) with
> reference software, rather than implementations like udunits that
> eventually go away.
>
> John
>
> PS: I think ill cross post to cf, just to throw some gasoline on the
> fire ;), and maybe some broader viewpoints.
>
> On 12/5/2012 10:24 AM, Don Murray (NOAA Affiliate) wrote:
>> Hi Gerry-
>>
>> On 12/5/12 9:42 AM, Gerry Creager - NOAA Affiliate wrote:
>>> There are other datasets with reference to 1-1-1. I've seen them most
>>> recently in some ocean models.
>>
>> And the ESRL/PSD NCEP reanalysis datasets use it.
>>
>> Don
>>
>>> On Wed, Dec 5, 2012 at 10:16 AM, Don Murray (NOAA Affiliate)
>>> <don.murray at noaa.gov <mailto:don.murray at noaa.gov>> wrote:
>>>
>>> John-
>>>
>>> I meant to send this to support-netcdf-java, but perhaps others on
>>> the list might have the same problem.
>>>
>>>
>>> On 12/4/12 4:51 PM, John Caron wrote:
>>>
>>> On 12/4/2012 4:09 PM, Don Murray (NOAA Affiliate) wrote:
>>>
>>> Hi-
>>>
>>> I was just trying to access the NOAA/ESRL/PSD Outgoing
>>> Longwave
>>> Radiation (OLR) data using netCDF-Java 4.3 ToolsUI and
>>> noticed that the
>>> times are wrong. If you open:
>>>
>>>
>>> dods://www.esrl.noaa.gov/psd/__thredds/dodsC/Datasets/__uninterp_OLR/olr.day.mean.nc
>>>
>>>
>>>
>>> <http://www.esrl.noaa.gov/psd/thredds/dodsC/Datasets/uninterp_OLR/olr.day.mean.nc>
>>>
>>>
>>>
>>>
>>>
>>> in the ToolsUI grid viewer, the last time in the file is
>>> shown as
>>> 2012-12-04 00Z. However, the last time in the file is
>>> actually
>>> 2012-12-02 00Z. Here is the time variable in that file:
>>>
>>> double time(time=3989);
>>> :units = "hours since 1-1-1 00:00:0.0";
>>> :long_name = "Time";
>>> :actual_range = 1.7540448E7, 1.763616E7; // double
>>> :delta_t = "0000-00-01 00:00:00";
>>> :avg_period = "0000-00-01 00:00:00";
>>> :standard_name = "time";
>>> :axis = "T";
>>>
>>> netCDF-Java 4.2 and ncdump -t -v time (C version) show the
>>> correct
>>> date/times.
>>>
>>>
>>> hours from 1-1-1 is rather problematic, since you are crossing
>>> the
>>> julian/gregorian weirdness line (i think thats the technical
>>> term ;)
>>>
>>> Im guessing the trouble lies here:
>>>
>>> "Default calendar: for udunits, and therefore for CF, the
>>> default
>>> calendar is gregorian ("Mixed Gregorian/Julian calendar"). For
>>> CDM, the
>>> default calendar is proleptic_gregorian (ISO8601 standard).
>>> This
>>> only
>>> matters for dates before 1582."
>>>
>>>
>>> Joda time supports the GJ calendar (Historically accurate calendar
>>> with Julian followed by Gregorian) which seems it would be backward
>>> compatible with the CF/udunits. Perhaps that should be the default
>>> for backward compatibility.
>>>
>>>
>>> I have to say relying uncritically on a calendar
>>> implementation like
>>> udunits is a mistake. putting the reference date
>>> unnecessarily to
>>> include the problem is, um, unnecessary.
>>>
>>>
>>> But it is historically accurate. For climate datasets, this would
>>> be important.
>>>
>>>
>>> is there any way those files can be updated? specifying the
>>> gregorian
>>> calendar explicitly should do it, but changing to use a
>>> reference date
>>> after 1582 would be much better.
>>>
>>>
>>> How's your FORTRAN? ;-) I'm not sure why this was chosen
>>> originally, but it doesn't seem reasonable to make people change
>>> their datasets.
>>>
>>> Does anyone else on the list know of datasets (other than
>>> climatologies) that might use a reference of 1-1-1 that will be
>>> affected by this change?
>>>
>>>
>>>
>>> BTW, is there an easier way to see human readable dates
>>> through toolsUI
>>> than loading it into the grid viewer (akin to ncdump -t)?
>>>
>>>
>>> open in coordSys tab; in bottom table, select time coord,
>>> right-click
>>> and choose "show values as date"
>>>
>>>
>>> Thanks, that's easier.
>>>
>>>
>>> Don
>>> --
>>> Don Murray
>>> NOAA/ESRL/PSD and CIRES
>>> 303-497-3596 <tel:303-497-3596>
>>> http://www.esrl.noaa.gov/psd/__people/don.murray/
>>> <http://www.esrl.noaa.gov/psd/people/don.murray/>
>>>
>>> _________________________________________________
>>> netcdf-java mailing list
>>> netcdf-java at unidata.ucar.edu <mailto:netcdf-java at unidata.ucar.edu>
>>> For list information or to unsubscribe, visit:
>>> http://www.unidata.ucar.edu/__mailing_lists/
>>> <http://www.unidata.ucar.edu/mailing_lists/>
>>>
>>>
>>
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--
===================================================================
Cecelia DeLuca
NESII/CIRES/NOAA Earth System Research Laboratory
325 Broadway, Boulder 80305-337
Email: cecelia.deluca at noaa.gov
Phone: 303-497-3604
Received on Wed Dec 05 2012 - 15:01:17 GMT
