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
coordinate 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> 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> -----
>>>
>>>> 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 -----
>>> _______________________________________________
>>> CF-metadata mailing list
>>> CF-metadata at cgd.ucar.edu
>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <
http://mailman.cgd.ucar.edu/pipermail/cf-metadata/attachments/20130529/9e25b879/attachment-0001.html>
Received on Wed May 29 2013 - 09:06:28 BST
