Hi Jonathan,
Thanks a lot for the background on the CF conventions. This helps me
quite a bit to understand the ideas behind the process.
Yes, you are right about the surface question. The GOES-R product is
not referenced to a standard 'surface temperature' quantity, but just
the surface, in general. So, I think your proposal makes good sense.
So, to summarize, here the proposed standard name/definition/units for
this product:
Standard Name:
temperature_difference_between_ambient_air_and_air_lifted_adiabatically_from_the_surface
Defintion:
This quantity is defined as the temperature difference
between a parcel of air lifted adiabatically from the surface to a given
air pressure in the troposphere and the ambient air temperature at a
given air pressure in the troposphere. It is often called the lifted
index (LI) and provides a measure of the instability of the atmosphere.
The air parcel is "lifted" by moving the air parcel from the surface to
the Lifting Condensation Level (dry adiabatically) and then from the
Lifting Condensation Level to a given air pressure (wet adiabatically).
Air temperature is the bulk temperature of the air, not the surface
(skin) temperature. The term "surface" means the lower boundary of the
atmosphere. A coordinate variable of air_pressure can be specified to
indicate the specific air pressure that the temperature difference is
calculated at.
Canonical Units: K
Sincerely,
Jonathan
On 5/22/2013 12:09 PM, Jonathan Gregory wrote:
> Dear Jonathan
>
> Thanks for your thoughts. Actually I agree with you. I would not try to insist
> on a geophysical name in every case. It might be too contrived and it would not
> be helpful if there was very little chance that the generality would ever be
> useful. I prefer geophysically orientated general-purpose names whenever we
> can adopt them, because they are more self-explanatory and because they limit
> the number of names we have to define. We have to be pragmatic, and the result
> is that the standard name table reflects a mixture of approaches, some general,
> some very specific to applications. That's life.
>
> If you really mean "the surface", not "surface air" in the meteorological obs
> sense, perhaps it would be clearer as
>
> temperature_difference_between_ambient_air_and_air_lifted_adiabatically_from_the_surface
>
> That obviously avoids the need for a surface height coordinate. "The surface"
> (the bottom of the atmosphere), being a named well-defined surface, does not
> need a coordinate. It just has a name, and it appears in many standard names.
> So you have a need for only one coordinate, to specify the level of the ambient
> air. That could be a pressure coordinate or an altitude or anything you like -
> I think you could allow that flexibility in the definition.
>
> Best wishes
>
> Jonathan
>
> ----- Forwarded message from Jonathan Wrotny <jwrotny at aer.com> -----
>
>> Date: Wed, 22 May 2013 11:29:34 -0400
>> From: Jonathan Wrotny <jwrotny at aer.com>
>> User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:17.0) Gecko/20130509
>> Thunderbird/17.0.6
>> To: Jonathan Gregory <j.m.gregory at reading.ac.uk>
>> CC: cf-metadata at cgd.ucar.edu
>> Subject: Re: [CF-metadata] new standard name: lifted_index
>>
>> Hello Jonathan,
>>
>> I still think the standard names for the stability indices are a bit
>> of a conundrum, but I do understand the desire to attempt to devise
>> a general sounding name for each product. I believe that most
>> physical quantities are general enough to easily fit into the CF
>> standard naming paradigm, i.e. attempt to phrase a name with general
>> atmospheric terms combined with ampersands into something that, as
>> you described it, is almost a description (vs. a name). To me, there
>> are always some very specific quantities (e.g. stability indices,
>> NDVI, etc.) which are by definition *not* general and are one-off
>> ad-hoc quantities. I could see a scenario where these types of
>> products are their own special category with the CF - and, thus,
>> have unique, non-generalized, names - while the large majority are
>> more general and are easily adaptable to the CF naming paradigm. My
>> take is that you think that this type of product delineation in the
>> CF is not ideal in order to have cross-discipline use and
>> consistency for all the standard names, and thus are suggesting to
>> attempt to generalize each quantity if at all possible. This seems
>> to work in general but can cause issues with products like the
>> stability indices. The confusing aspect of this approach is that
>> now some of the stability index products will have general sounding
>> names (e.g. the proposed name for the lifted index) versus the total
>> totals index which is too complex to generalize. I'm not sure if
>> this is really a problem or not for the data users/modelers, but it
>> is a little strange. Maybe it is the only way to handle this
>> somewhat unique situation. Bottom line, I'm OK with your proposed
>> names - the general one for the lifted index and the specific one
>> for the total totals index, but wanted to present some of my
>> thoughts as I've worked through this myself. Maybe you will have
>> some comments.
>>
>> Re: the surface air, question. Yes, I forgot to reply to this
>> question in my last reply to you. The level of the "surface air' is
>> not the screen height in the GOES-R product but is from the NWP
>> surface pressure interpolated to the time of the GOES-R product and
>> the horizontal spatial grid. This information is not in the
>> delivered product, however. But, including the pressure level that
>> the lifted index is calculated could occur with a coordinate
>> variable. It appears that the proposed definition mentions a
>> coordinate variable that would include this level.
>>
>> Sincerely,
>>
>> Jonathan
>>
>>
>>
>> On 5/21/2013 5:34 PM, Jonathan Gregory wrote:
>>> Dear Jon
>>>
>>> Thanks for considering my comments on this one
>>>
>>>> Standard Name: temperature_difference_between_ambient_air_and_surface_air_lifted_adiabatically
>>> I'm glad you're happy with a general name in this case. I am interested in
>>> your response to Philip's question about how surface is defined here. It
>>> might mean "surface air" in the sense of "screen height", I suppose. In the
>>> standard name table, we do not actually have "surface air", because we expect
>>> the actual screen height to be explicitly given as a height coordinate (1.5 m
>>> or whatever). If that is the case, maybe this standard name should depend on
>>> two vertical coordinates, and maybe it should be further generalised to
>>> ..._and_air_lifted_adiabatically. But that might be too general! What do
>>> you think?
>>>
>>> Best wishes
>>>
>>> Jonathan
>>> _______________________________________________
>>> CF-metadata mailing list
>>> CF-metadata at cgd.ucar.edu
>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
> ----- End forwarded message -----
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