Hi Seth, et al.,
air_pressure_of_lifted_parcel_at_origin
air_pressure_of_lifted_parcel_at_finish
Would it make sense to replace 'origin' with 'start'? I can think of a
couple of ways 'origin' might cause confusion: it can refer to the (0,0) point
in a coordinate system, and a parcel involved in convection (eg over
California) might have originated far away over Alaska. I think most people
would quickly figure out what you mean, but since 'start' is typically paired
with 'finish' anyway, why not use 'start'?
Best wishes,
Philip
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Dr Philip Cameron-Smith, [email protected], Lawrence Livermore National Lab.
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-----Original Message-----
From: CF-metadata [mailto:[email protected]] On Behalf Of Seth
McGinnis
Sent: Friday, May 24, 2013 4:58 PM
To: [email protected]
Subject: [CF-metadata] new standard names for CIN, LFC,LCL; update to CAPE
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
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