[CF-metadata] new standard names for CIN, LFC,LCL; update to CAPE

From: Seth McGinnis <mcginnis>
Date: Fri, 28 Jun 2013 17:14:59 -0600

On Mon, 17 Jun 2013 13:49:30 +0100
 Jonathan Gregory <j.m.gregory at reading.ac.uk> wrote:
>Dear Seth
>
>Thanks for the updated list of names. This all looks logical to me.
>
>I now wonder whether, in the names, wrt_surface would convey the meaning more
>obviously than from_the_surface. It's not obvious until you read the
>definition
>why it's "from", I think. I feel that "wrt" would more immediately indicate
>
>As you note
>> atmosphere_specific_convective_available_potential_energy
>> [update to existing standard_name]
>is an existing standard name. The existing definition is not clear, but I
>suspect it might be interpreted as the whole-atmos version i.e. wrt surface.
>What do you think? In that case, this update would be a redefinition, not a
>clarification, and we should avoid redefining existing names. If that is the
>case, it could be avoided by adding another phrase to the name for the version
>when the parcel does not come from the surface. Then the existing name could
>be made an alias of the new "wrt surface" name. What do you think?
>
>Best wishes and thanks
>
>Jonathan
>

Hi Jonathan,

I think you're right, _wrt_surface is probably clearer than _from_the_surface.
 It's
also shorter, which is never a bad thing.

I can't think of a good suffix for the general (non-surface-based) names, but I
think we can still avoid redefining the existing name by removing _specific_
from my proposed new names. It seems to have been added simply because
CAPE has units with kg in the denominator, rather than because it needs to
be distinguished from some kind of non-specific CAPE. (Likewise, the sentence
in the definition defining potential energy seems to be automatic boilerplate,
rather than an important clarification.)

So I've revised the definitions below to remove _specific_ from the CAPE &
CIN names, and have made sure that it's clear from the definitions why they
have the units they do (since it's not obvious from the explanation of how
they are calculated).

If that's an acceptable way to handle this issue, we can then make
atmosphere_specific_convective_available_potential_energy an alias to
atmosphere_convective_available_potential_energy_wrt_surface.

Cheers,

--Seth


#####

original_air_pressure_of_lifted_parcel
        
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 a final height (often the top of the
troposphere). original_air_pressure_of_lifted_parcel is the pressure
height at the start of lifting.

canonical units: Pa


#####

final_air_pressure_of_lifted_parcel

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
troposphere). final_air_pressure_of_lifted_parcel is the pressure
height at the end of lifting.

canonical units: Pa


#####

atmosphere_convective_inhibition

Convective inhibition is the amount of energy per unit mass 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
temperature difference between the surrounding atmosphere and a parcel
of air lifted adiabatically from a given starting height to its
equilibrium level. A coordinate variable of
original_air_pressure_of_lifted_parcel should be specified to indicate
the starting height of the lifted parcel.

canonical units: J kg-1


#####

atmosphere_convective_inhibition_wrt_surface

Convective inhibition is the amount of energy per unit mass 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
temperature difference between the surrounding atmosphere and a parcel
of air lifted adiabatically from the surface to its equilibrium level.

canonical units: J kg-1


#####

atmosphere_lifting_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%. A coordinate variable of original_air_pressure_of_lifted_parcel
should be specified to indicate the starting height of the lifted
parcel.

canonical units: m


#####

atmosphere_lifting_condensation_level_wrt_surface

The lifting condensation level is the height at which the relative
humidity of an air parcel cooled by dry adiabatic lifting from the
surface would reach 100%.

canonical units: m


#####

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 (lifting
condensation level), then moist adiabatically until the parcel
temperature is equal to the ambient temperature. A coordinate
variable of original_air_pressure_of_lifted_parcel should be specified
to indicate the starting height of the lifted parcel.

canonical units: m


#####

atmosphere_level_of_free_convection_wrt_surface

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 from the surface to the LCL
(lifting condensation level), then moist adiabatically until the
parcel temperature is equal to the ambient temperature.

canonical units: m


#####

[This new standard_name replaces
atmosphere_specific_convective_available_potential_energy]

atmosphere_convective_available_potential_energy

Convective(ly) available potential energy (often abbreviated CAPE) is
a stability measure calculated by integrating the positive temperature
difference between the surrounding atmosphere and a parcel of air
lifted adiabatically from a given starting height to its equilibrium
level. A coordinate variable of original_air_pressure_of_lifted_parcel
should be specified to indicate the starting height of the lifted
parcel. CAPE exists under conditions of potential instability, and
measures the potential energy per unit mass that would be released by
the unstable parcel if it were able to convect upwards to equilibrium.

canonical units: J kg-1


#####

atmosphere_convective_available_potential_energy_wrt_surface

Convective(ly) available potential energy (often abbreviated CAPE) is
a stability measure calculated by integrating the positive temperature
difference between the surrounding atmosphere and a parcel of air
lifted adiabatically from the surface to its equilibrium level. CAPE
exists under conditions of potential instability, and measures the
potential energy per unit mass that would be released by the unstable
parcel if it were able to convect upwards to equilibrium.

canonical units: J kg-1

#####
Received on Fri Jun 28 2013 - 17:14:59 BST