John-
An example of how this could be handled (provided by Stuart Wier of
UNAVCO) is available here:
http://geon.unavco.org/unavco/geodynamics/Lithgow-Bertelloni_Richards_Mesozoic_Cenozoic_Plate_Velocities.cdl
described on the page:
http://geon.unavco.org/unavco/IDV_datasource_plates.html#c
Here, the time coordinate is listed as:
float time(time) ;
time:units = "Myear" ;
time:standard_name = "time" ;
with values of:
time = -170.0, -96.0, -94.0, -84.0, -74.0, -64.0, -56.0, -48.0, -43.0,
-25.0, -10.0 ;
The problem is that udunits ends up computing times for -64 Myear as:
63998634-12-14 00:00:00 BCE
so you lose precision on the year.
Don
On 8/19/11 10:45 AM, John Caron wrote:
>
>>> Regarding paleoclimate, a point I forgot is that some modellers may
>>> wish to
>>> have years which are very large negative numbers (many more than four
>>> digits)
>>> if they set up the model with the "true" date for the run. Although for
>>> geological timescales you might say that this isn't necessary and you
>>> might
>>> as well choose an arbitrary year, there is a good reason for it in
>>> Pleistocene
>>> when you might be using the dates to relate to orbital forcing or
>>> atmospheric
>>> composition.
>>
>> so the idea is that you are simulating some year, so you really need
>> time down to the hour or second. but the climate is from 5 million
>> years ago, so you need the year field to be able to handle that?
>
> Im just thinking that fitting this into the ISO date format
> "5000000-01-01 12:00" seems awkward, esp as it indicates unwarranted
> precision.
>
> seems something like "01-01 12:00 reference 50m BCE" would be better.
> What do paleo modellers actually use, eg in the figures that they publish?
> _______________________________________________
> CF-metadata mailing list
> CF-metadata at cgd.ucar.edu
> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
>
--
Don Murray
NOAA/ESRL/PSD and CIRES
303-497-3596
http://www.esrl.noaa.gov/psd/people/don.murray/
Received on Mon Aug 22 2011 - 09:16:39 BST
