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Don There are other datasets with reference to 1-1-1. I've seen them most recently in some ocean models. Gerry On Wed, Dec 5, 2012 at 10:16 AM, Don Murray (NOAA Affiliate) < don.murray@xxxxxxxx> 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 > http://www.esrl.noaa.gov/psd/**people/don.murray/<http://www.esrl.noaa.gov/psd/people/don.murray/> > > ______________________________**_________________ > netcdf-java mailing list > netcdf-java@xxxxxxxxxxxxxxxx > 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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