Hi Seth,
Thanks for the consideration. Sincerely,
Jonathan Wrotny
On 6/13/2013 6:12 PM, Seth McGinnis wrote:
> Hi Jonathan,
>
> You have good timing; I'm hoping to post updated definitions soon.
>
> I'd be happy to adjust the wording to use "temperature difference", and
> leave it unspecified as to the details of whether it's calculated from
> potential temperature or virtual temperature or whatever. It's similar
> to the question of whether it's surface-based or most-unstable or
> max-theta-e CAPE -- wherever the parcel starts, it's all still CAPE.
>
> Cheers,
>
> --Seth
>
>
> On Thu, 13 Jun 2013 16:40:15 -0400
> Jonathan Wrotny <jwrotny at aer.com> wrote:
>> Dear Seth,
>>
>> I know that I am replying to late in the game to this e-mail from a few weeks
>> ago - sorry about this, but I wanted to make one comment regarding your
>> proposed modification to the definition for CAPE. As you might remember, I
>> recently proposed some new standard names which are related to the future
>> GOES-R platform. Another GOES-R output data product will be CAPE, so I perused
>> your proposed modification to the CAPE definition to see if it was consistent
>> with the GOES-R product.
>>
>> The first sentence of your definition says "...calculated by integrating the
>> positive differences in virtual temperature...". My concern about using
>> virtual temperature in the definition is that it is too specific since CAPE is
>> not always calculated using the virtual temperature. For example, in the
>> GOES-R product, potential temperature differences are used. The parcel
>> potential temperature is corrected for moisture in the parcel, but not in the
>> same way as calculating the virtual temperature of the parcel. I'm thinking
>> it might be good to attempt to generalize your proposed definition of CAPE.
>> Perhaps you could say that it is calculated by integrating the temperature
>> difference between the parcel and environment, where the parcel temperature
>> may be corrected due to the moisture content of the air parcel (e.g. the
>> virtual temperature). Using "temperature difference" as opposed to a specific
>> temperature, e.g. the virtual temperature, would help to generalize the
>> definition.
>>
>> Sincerely,
>>
>> Jonathan Wrotny
>>
>>
>> On 5/24/2013 7:57 PM, Seth McGinnis wrote:
>>> Greetings CF mailing list!
>>>
>>> I would like to propose some new standard_names related to convective
>>> instability indices.
>>>
>>> I apologize for sending such a long proposal right before a holiday
>>> weekend in the US, but I've been working on it for a while and it
>>> dovetails with the recent discussion of a standard_name for Lifted
>>> Index. In that discussion, I've proposed two new standard names to
>>> record the starting and ending points of a lifted parcel:
>>>
>>> air_pressure_of_lifted_parcel_at_origin
>>> air_pressure_of_lifted_parcel_at_finish
>>>
>>>
>>> Given this (or some other) way of specifying the lifted parcel, we can
>>> then handle variables recording various of its properties. I would like
>>> to propose three new standard_names for CIN, LCL, and LFC, and to
>>> add to the existing definition for CAPE, as follows:
>>>
>>>
>>> CIN:
>>>
>>> name: atmosphere_specific_convective_inhibition
>>>
>>> Convective inhibition is the amount of energy required to overcome the
>>> negatively buoyant energy exerted by the environment on a parcel of
>>> air. Convective inhibition is often abbreviated as "CIN" or "CINH".
>>> It is calculated by integrating the negative differences in virtual
>>> temperature between a parcel of air lifted adiabatically and its
>>> surroundings. If the start and/or end points of the lifted parcel are
>>> not specified using auxiliary coordinate variables with the
>>> standard_names air_pressure_of_lifted_parcel_at_origin (_finish), the
>>> parcel starts at the surface (lower boundary of the atmosphere) and
>>> ends at the top of the atmosphere.
>>>
>>> canonical units: J/kg
>>>
>>>
>>> LCL:
>>>
>>> name: atmosphere_lifted_condensation_level
>>>
>>> The lifting condensation level is the height at which the relative
>>> humidity of an air parcel cooled by dry adiabatic lifting would reach
>>> 100%. If the starting point of the lifted parcel is not specified
>>> using an auxiliary coordinate variable with the standard_name
>>> air_pressure_of_lifted_parcel_at_start, the parcel starts at the
>>> surface (lower boundary of the atmosphere).
>>>
>>> canonical units: m
>>>
>>>
>>> [Note that, wikipedia notwithstanding, Google reports "liftING
>>> condensation level" as more commonly used than "liftED condensation
>>> level" by about 5:4. Personally, I have no strong feelings about it
>>> one way or the other, and will gladly bow to anyone who has an opinion
>>> based on observations in the wild.]
>>>
>>>
>>> LFC:
>>>
>>> name: atmosphere_level_of_free_convection
>>>
>>> The level of free convection is the altitude where the temperature of
>>> the environment decreases faster than the moist adiabatic lapse rate
>>> of a saturated air parcel at the same level. It is calculated by
>>> lifting a parcel of air dry adiabatically to the LCL (lifted
>>> condensation level), then moist adiabatically until the parcel
>>> temperature is equal to the ambient temperature. If the starting
>>> point of the lifted parcel is not specified using an auxiliary
>>> coordinate variable with the standard_name
>>> air_pressure_of_lifted_parcel_at_start, the parcel starts at the
>>> surface (lower boundary of the atmosphere).
>>>
>>> canonical units: m
>>>
>>>
>>> CAPE:
>>>
>>> CAPE already exists in the standard name table as
>>> atmosphere_specific_convective_available_potential_energy
>>>
>>> There are apparently several different flavors of CAPE depending on
>>> how one chooses the starting point of the lifted parcel. (Among
>>> others, there's surface-based, most-unstable, and maximum-theta-e
>>> CAPE.) Rather than propose several new standard_names for the
>>> different flavors, I think they can be handled by simply adding an
>>> explanatory note in the metadata -- as long as the starting height of
>>> the parcel can be recorded.
>>>
>>> So I propose that we update the existing CAPE definition to default to
>>> being surface-based, and add an explanation of the whole lifted parcel
>>> business so that other flavors can be accommodated by noting the
>>> starting heights, as follows:
>>>
>>>
>>> Additions to definition of
>>> atmosphere_specific_convective_available_potential_energy:
>>>
>>> Convective(ly) available potential energy (often abbreviated CAPE) is
>>> a stability measure typically calculated by integrating the positive
>>> differences in virtual temperature between a parcel of air lifted
>>> adiabatically and its surroundings. If the start and/or end points of
>>> the lifted parcel are not specified using auxiliary coordinate
>>> variables with the standard_names
>>> air_pressure_of_lifted_parcel_at_origin (_finish), the parcel starts
>>> at the surface (lower boundary of the atmosphere) and ends at the top
>>> of the atmosphere. [remainder of existing definition goes here]
>>>
>>> Cheers,
>>>
>>> --Seth
>>> _______________________________________________
>>> CF-metadata mailing list
>>> CF-metadata at cgd.ucar.edu
>>> http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
Received on Fri Jun 14 2013 - 09:41:30 BST
