Hi Jonathan,
Looks good to me! I'm happy that it's useful for your case as well
as the ones I'm proposing.
Philip has suggested we switch from _at_origin to _at_start for the
standard_names, arguing that it's less ambiguous.
Any thoughts on that?
Cheers,
--Seth
On Wed, 29 May 2013 11:06:28 -0400
Jonathan Wrotny <jwrotny at aer.com> wrote:
>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
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>
Received on Wed May 29 2013 - 12:26:51 BST
