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20041019: Bug in ut_calendar?



Dennis,

>Date: Tue, 19 Oct 2004 11:47:42 -0600 (MDT)
>From: Dennis Shea <address@hidden>
>Organization: UCAR
>To: address@hidden
>Subject: Re: 20041019: Bug in ut_calendar? 

The above message contained the following:

> I was the one who 1st reported this to Mary Haley.
> I recently obtained the dataset from the Climate Research Unit.
> It is one of the datasets used in the IPCC assessments.
> 
> http://www.cru.uea.ac.uk/cru/data/temperature/#datdow
> 
> specifically: hadcrut2v.nc
> 
> netcdf hadcrut2v {
> dimensions:
>         lat = 36 ;
>         lon = 72 ;
>         time = 1616 ;
> variables:
>         short temanom(time, lat, lon) ;
>                 temanom:long_name = "temperature_anomaly" ;
>                 temanom:units = "celsius" ;
>                 temanom:scale_factor = 0.01 ;
>                 temanom:valid_min = -9000 ;
>                 temanom:missing_value = -9999 ;
>         float lat(lat) ;
>                 lat:units = "degrees_north" ;
>         float lon(lon) ;
>                 lon:units = "degrees_east" ;
>         short time(time) ;
>                 time:units = "months since 1870-1-1" ;
> data:
> 
>  time = 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 
>     20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 
> [snip]
> 
> =================
> I am sure they [me, Mary, others I have talked to] assumed that 
>      time=0   ==> 187001
>           1       187002
>               etc
> 
> I can see that this is erroneous based upon the above.
> 
> I would lay odds that errors have been made as a result.
> Seems "months since ..." is a bad unit to use. 

Yup.  People (scientists even) have some odd ideas of what constitutes
a unit of a physical quantity.  I had one person who thought "flight
level" should be a unit.

> Mary ... maybe NCL's documentation for the udunits
> software should contain some explicit mention of this issue.

Regards,
Steve Emmerson


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