On 1/29/2014 9:26 AM, Jonathan Gregory wrote:
> Dear Steve
>
>> In practice I do not think that
>> standard_name=depth and positive=up are necessarily in conflict (see
>> bold text below). We fairly commonly encounter ocean model outputs
>> in which the depths are encoded as negatives:
>>
>> 0
>> -10
>> -20
>> ...
>>
>> There are merits to this encoding -- especially apparent in coupled
>> ocean/atmosphere situations. (Also it preserves the right-handed
>> coordinate system.) It would be quite peculiar (and a frequent
>> source of error) to insist that an ocean model output file name its
>> Z axis as "altitude", simply because it has encoded the depth values
>> as negatives. The purpose of the 'positive' attribute is to inform
>> the application when the encoding of values and the physical
>> interpretation of the Z axis are reversed from one another.
> Maybe it's annoying, but I can't agree with that. I would say that such depth
> values are wrong. The standard_name depth is defined as "the vertical distance
> below the surface". -10 m means 10 m above the surface. There's no point in
> having standard names unless we use them correctly, and this is one of the
> kinds of imprecision standard names can help eliminate. It's fine for the ocean
> model to encode -10 m for 10 m below the surface if it wants to, but then it
> should use the standard_name of height instead (or altitude, since distance
> above the surface and above the geoid is approx the same thing in ocean areas).
> In all the ocean model data I work with (mostly from CMIP), depth is a positive
> number, as it should be.
Hi Jonathan,
Yes, respectfully, we do disagree on this.
Isn't the purpose of the standard name is to capture the semantics of a
variable -- i.e. its physical interpretation? You are suggesting that
a user of the file (or a search engine) should attach a different
meaning to the concept of "DEPTH" in an ocean model based upon whether
it is encoded as a positive or negative value. Do we attach a
different interpretation to "TIME" because it is encoded as "days"
versus "hours"?
- Steve
>
> Best wishes
>
> Jonathan
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Received on Wed Jan 29 2014 - 10:41:01 GMT
