Hi Jonathan (Wrotny),
I am not sure if my last email got through. Is it possible to define the
vertical extent of 'surface' better? Eg, do you mean the bottom 1cm, 10m, 1km,
mixed layer?
We might not want to be too precise, so as to allow wiggle room for other ways
of generating the lifted index. It would just be nice for me to have some idea
of the scale involved if I wanted to generate it from my model.
Best wishes,
Philip
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Dr Philip Cameron-Smith, [email protected], Lawrence Livermore National Lab.
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From: CF-metadata [mailto:[email protected]] On Behalf Of
Jonathan Wrotny
Sent: Monday, May 20, 2013 1:31 PM
To: Jonathan Gregory
Cc: [email protected]
Subject: Re: [CF-metadata] new standard name: lifted_index
Hello Jonathan,
Thanks for your reply to this post. I see your point of view. I guess it
would be odd if a name "lifted_index" was adopted when the general naming
paradigm for the CF standard names is to attempt to phrase each quantity in
general atmospheric terms so that they are general purpose across all
disciplines. I can see the advantage of each approach you mention, but it does
seem best (if possible) to try to generally define each name. In terms of the
GOES-R atmospheric products, there will be four atmospheric stability indices
(of which I've only posted two so far). In thinking about them, I believe that
two of them could have general names - like the one you've suggested below -
while the other two are sufficiently complex that a name such as
"atmospheric_stability_total_totals_index" will be necessary.
The "lifted_index" is simple enough so that your proposed name should work
well. In light of your suggestions, these could be the name/definition/units:
Standard Name:
temperature_difference_between_ambient_air_and_surface_air_lifted_adiabatically
Definition: 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 5/18/2013 10:05 AM, Jonathan Gregory wrote:
Dear Jonathan
lifted_index
with the associated definition:
The Lifted Index (LI) is an index that provides a measure of the
instability of the atmosphere. The index is defined as the
temperature difference between a parcel of air lifted from the
surface to a given air pressure in the troposphere and the ambient
air temperature at a given air pressure in the troposphere.
I think this presents an example of a kind of problem we have had before with
the standard name table (and total_totals_index does too - in my next email),
that there's a conflict between (a) using a term that is in common use in its
field of application, but which is opaque jargon to anyone who is not familiar
with it, or (b) using something more descriptive, which would be understandable
to more people, but surprising to those who are familiar with the jargon term,
who might not recognise the quantity for what it is. The reason why we have
this conflict is that the standard name table, and CF-netCDF datasets, cover
many geophysical disciplines. Also I think the term "standard name" has often
been a cause of disappointed expectations, because actually many of them are
not names, but short definitions.
>From a generalistic perspective I tend to argue for (b) and domain experts
often argue for (a), not surprisingly! In this case, I would like to make a
(b)-type proposal. We could call this quantity
temperature_difference_between_ambient_air_and_surface_air_lifted_adiabatically
Would people who know "lifted index" recognise that as being the definition of
this quantity? Have I written that the right way round i.e. is it ambient air
temperature minus lifted surface air temperature? If we did adopt such a name,
then its definition would say that this is often called the "lifted index". But
it is also a general-purpose atmopheric quantity.
Cheers
Jonathan
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