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 <[email protected]> -----
Date: Wed, 22 May 2013 11:29:34 -0400
From: Jonathan Wrotny <[email protected]>
User-Agent: Mozilla/5.0 (Windows NT 5.1; rv:17.0) Gecko/20130509
Thunderbird/17.0.6
To: Jonathan Gregory <[email protected]>
CC: [email protected]
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
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