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, pjc at llnl.gov, Lawrence Livermore National Lab.
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-----Original Message-----
From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf Of Seth McGinnis
Sent: Friday, May 24, 2013 4:58 PM
To: cf-metadata at cgd.ucar.edu
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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Received on Sat May 25 2013 - 01:25:49 BST
