Hi Seth,
It seems to me that you cleverly kill two birds (std_names) with one stone, in that you include details in the description on how to modify the std_name if it doesn't start at the surface.
However I haven't seen that before. I suggest it would be cleaner to just propose two std_names which each have their own definition, ie:
temperature_difference_between_ambient_air_and_air_lifted_adiabatically
temperature_difference_between_ambient_air_and_air_lifted_adiabatically_from_the_surface
Best wishes,
Philip
-----------------------------------------------------------------------
Dr Philip Cameron-Smith, pjc at llnl.gov, Lawrence Livermore National Lab.
-----------------------------------------------------------------------
From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Jonathan Wrotny
Sent: Wednesday, May 29, 2013 8:06 AM
To: Seth McGinnis
Cc: cf-metadata at cgd.ucar.edu
Subject: Re: [CF-metadata] new standard name: lifted_index
Hi Seth,
Finally getting back to you e-mail after a long weekend...
You raise a good point about the two levels used for many of the stability indices. You're right, it would be nice to have this information in the definition for the these data products in case data users/modelers need it. I think adding your two proposed standard names for the start and finish height is a good idea. I've taken my proposed definition of lifted index and added the sentence you suggested. Also, I added an additional sentence to discuss the scenario where the parcel is not lifted "from the surface" but from another pressure level. Here is my current proposal:
Standard Name: temperature_difference_between_ambient_air_and_air_lifted_adiabatically_from_the_surface
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_of_lifted_parcel_at_finish can be specified to indicate the specific air pressure that the temperature difference is calculated at. If the start point of the lifted parcel is not the ?surface,? then the phrase ?from_the_surface? is removed from the standard name and a c
oordinate variable of air_pressure_of_lifted_parcel_at_start can be specified to indicate the specific air pressure at which the parcel lifting starts.
Canonical Units: K
And, just to include them in this e-mail, the standard names/definitions/units for the two coordinate variables:
Standard_names:
air_pressure_of_lifted_parcel_at_origin
air_pressure_of_lifted_parcel_at_finish
Definitions:
Various stability and convective potential indices are calculated by
"lifting" a parcel of air: moving it dry adiabatically from a starting
height (often the surface) to the Lifting Condensation Level, and then
wet adiabatically from there to an ending height (often the top of
the data/model/atmosphere). air_pressure_of_lifted_parcel_at_origin
[finish] is the pressure height at the start [end] of lifting.
Canonical units: Pa
I will also revise the definition of the total totals index that I recently submitted and includes the coordinate variables in two other stability indices that I will post this week.
How does this look now?
Thanks again.
-Jonathan
On 5/24/2013 7:17 PM, Seth McGinnis wrote:
Hi Jonathan,
I would like to suggest a small modification to your proposal for the
lifted index (LI) standard_name.
I'm working on proposals for standard_names for CAPE, CIN, LCL, and
LFC, all of which, like LI, are based on lifting a parcel of air
adiabatically from one height to another.
The unusual thing about these variables is that they're not associated
with a single vertical coordinate, but with two of them: the starting
height and the ending height. So if you want to record both end
points, you need to do it in some way that lets you distinguish them.
I thought about trying to do it with cell_bounds, but that doesn't
seem like a good fit, because these aren't fields that exists within
the cell and are being summarized, but things that are only defined
relative to those two endpoints. So I think a better approach is to
use a scalar auxilliary coordinate, analogous to the way that
forecast_reference_time is used in example 5.11 in the CF spec.
For that, we need two new standard_names:
air_pressure_of_lifted_parcel_at_origin
air_pressure_of_lifted_parcel_at_finish
Which would have the following definitions:
Various stability and convective potential indices are calculated by
"lifting" a parcel of air: moving it dry adiabatically from a starting
height (often the surface) to the Lifting Condensation Level, and then
wet adiabatically from there to an ending height (often the top of
the data/model/atmosphere). air_pressure_of_lifted_parcel_at_origin
[finish] is the pressure height at the start [end] of lifting.
Both would have canonical units of Pa
I would then like to modify the last sentence in the definition of your
LI standard_name to say "A coordinate variable of
air_pressure_of_lifted_parcel_at_finish can be specified to indicate
the specific air pressure that the temperature difference is
calculated at."
Does that seem like a good way to handle this aspect of your LI
variable?
It would then be consistent with other lifted parcel variables (once
they get defined), and if anyone ever wanted to calculate LI from some
starting point other than the ground, they could just lop off the
"_from_the_surface" suffix from the standard_name and add the starting
coordinate. (The wikipedia article on LI talks about it being
calculated from "the portion of the PBL that lies below the morning
inversion", so it seems like a possibility.)
Cheers,
--Seth
On Wed, 22 May 2013 12:40:20 -0400
Jonathan Wrotny <jwrotny at aer.com><mailto:jwrotny at aer.com> wrote:
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><mailto:jwrotny at aer.com> -----
Date: Wed, 22 May 2013 11:29:34 -0400
From: Jonathan Wrotny <jwrotny at aer.com><mailto: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><mailto:j.m.gregory at reading.ac.uk>
CC: cf-metadata at cgd.ucar.edu<mailto: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
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