Hi Don:
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
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."
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.
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.
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 for your help.
Don
