[CF-metadata] Proposing new standard names.

alison.pamment at stfc.ac.uk alison.pamment at stfc.ac.uk
Wed Nov 24 06:12:23 MST 2010

Dear Bruno,

Thank you for proposing the names and definitions for liquid water quantities in air.  I think the names themselves are fine.

As regards the various droplet sizes, I found the following definitions in the AMS Glossary (http://amsglossary.allenpress.com/glossary). 

Cloud drop - "A spherical particle of liquid water, a few micrometers to a few tens of micrometers diameter" but later it says "A diameter of 0.2 mm has been suggested as an upper limit to the size of drops that shall be regarded as cloud drops; larger drops fall rapidly enough so that only very strong updrafts can sustain them. Any such division is somewhat arbitrary, and active cumulus clouds sometimes contain cloud drops much larger than this."

Drizzle drop - A drop of water of diameter 0.2-0.5 mm (0.008-0.02 in.) falling usually (but not always) from low stratus or stratocumulus cloud.

Rain drop - A drop of water of diameter greater than 0.5 mm falling through the atmosphere.

The range of rain drop diameters is similar to that suggested in your own explanations, but the division between cloud drops and drizzle is rather different. Would the AMS diameters be acceptable to you?  Whatever size ranges we choose to quote, I think that all the standard name explanations will need to make clear that the numbers should be regarded as indicative rather than definitive.

Best wishes,

Alison Pamment                          Tel: +44 1235 778065
NCAS/British Atmospheric Data Centre    Fax: +44 1235 446314
Rutherford Appleton Laboratory          Email: alison.pamment at stfc.ac.uk
Chilton, Didcot, OX11 0QX, U.K.

> -----Original Message-----
> From: cf-metadata-bounces at cgd.ucar.edu [mailto:cf-metadata-
> bounces at cgd.ucar.edu] On Behalf Of Bruno PIGUET
> Sent: 24 November 2010 09:45
> To: cf-metadata
> Subject: [CF-metadata] Proposing new standard names.
> Dear all,
>    Last month, I wrote about the lack of variable name for a local
> measurement of liquid water content.
>    Jonathan Gregory made some constructive remarks, and, since then,
> nobody opposed.
>    So, I would like to have these names added in the the next version
> of the official list. What is the proper procedure ? Is there some kind
> of formal proposal to write (a RFC) ?
> I recall hereafter what we came up to. Definition and size limits are
> my own, I couldn't find any definitive and authoritative numerical
> values, so I used "commonly accepted" ones. Do yous think that we
> should add "about" ou "approximately" before the numbers in the
> definition ?
> mass_concentration_of_cloud_liquid_water_in_air
>   Mass concentration means mass per unit volume. Cloud_liquid_water
> means droplet that are not large enough to fall under common
> circonstances (up to 40 µm diameter).
> mass_concentration_of_drizzle_in_air
>   Mass concentration means mass per unit volume. Drizzle means droplets
> with diameter between 40 and 700 µm.
> mass_concentration_of_rain_in_air
>   Mass concentration means mass per unit volume. Rain means drops of
> diameter larger than 0.7 mm. This quantity  corresponds to
> mass_fraction_of_rain_in_air (which is expressed as ratio of the mass
> of rain to the mass of air plus rain).
> mass_concentration_of_liquid_water_in_air
>   Mass concentration means mass per unit volume. All kinds of droplets
> and drops are taken into account, whatever their sizes or falling
> speed.
> Bruno.
> --
> Bruno PIGUET
>  Mèl : bruno.piguet at meteo.fr |  GAME : URA CNRS & METEO-FRANCE
>  Tel : +33 (0)5 61 07 96 59  |       CNRM/GMEI/TRAMM
>  Fax : +33 (0)5 61 07 96 27  |       42 Av. G. Coriolis
>  Sec : +33 (0)5 61 07 96 63  |     31057  TOULOUSE cedex 1
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