Dear Alison, Thank-you for your comments. I apologize for my late responding, I was away from the net since Wednesday at noon.
I have no reason to oppose to the AMS diameters : I'm a data processor, not a cloud physics specialist. The limit I proposed for the distinction between cloud and drizzle comes from the growth mechanism : below 40 µm, coalescence is not efficient, and cloud droplets will remain stable for a long time, whereas larger droplets, while falling slowly (a few cm/s) will grow and eventually fall. But it is true that a 100µm droplet is usually considered as a cloudy one. 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 > > ------ > Alison Pamment Tel: +44 1235 778065 > NCAS/British Atmospheric Data Centre Fax: +44 1235 446314 > Rutherford Appleton Laboratory Email: alison.pamm...@stfc.ac.uk > Chilton, Didcot, OX11 0QX, U.K. > > > -----Original Message----- > > From: cf-metadata-boun...@cgd.ucar.edu [mailto:cf-metadata- > > boun...@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.pig...@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
signature.asc
Description: This is a digitally signed message part
_______________________________________________ CF-metadata mailing list CF-metadata@cgd.ucar.edu http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
