Re: [netcdf-java] problem with times in PSD dataset

  • To: Gerry Creager - NOAA Affiliate <gerry.creager@xxxxxxxx>
  • Subject: Re: [netcdf-java] problem with times in PSD dataset
  • From: "Don Murray (NOAA Affiliate)" <don.murray@xxxxxxxx>
  • Date: Wed, 05 Dec 2012 10:24:41 -0700
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.


On Wed, Dec 5, 2012 at 10:16 AM, Don Murray (NOAA Affiliate)
<don.murray@xxxxxxxx <mailto:don.murray@xxxxxxxx>> wrote:


    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:


            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:


            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

        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
        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
        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,
        and choose "show values as date"

    Thanks, that's easier.

    Don Murray
    303-497-3596 <tel:303-497-3596>

    netcdf-java mailing list
    netcdf-java@xxxxxxxxxxxxxxxx <mailto:netcdf-java@xxxxxxxxxxxxxxxx>
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Don Murray

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