> -----Original Message-----
> From: Tomoo Ogura [mailto:[email protected]]
> Sent: Thursday, March 03, 2011 7:23 PM
> To: Cameron-smith, Philip; Jonathan Gregory
> Cc: Jennifer Kay; Yoko Tsushima; [email protected]; Tomoo Ogura
> Subject: Re: [CF-metadata] Proposal for new standard names
>
> Hi Philip,
>
> > This seems a reasonable distinction. I assume that your
> > proposal is that the existing std_names with 'precipitation'
> > should now be defined to exclude sedimentation of clouds
> > and aerosols. I suspect that this is probably how
> > people have already used them, so I would not object.
> > But there may be someone else who has a different opinion.
> > Either way, we should request that the description of
> > those 'precipitation' names be amended to reflect
> > the change.
>
> I agree with you - thanks for this.
>
> Regarding the definition of rain and cloud liquid water,
> I should have been more careful about whether it is established
> or not, since I'm not certain about it - I'm sorry for this.
> I just wanted to mention the description in the Glossary
> of Meteorology of American Meteorological Society.
> It may not be part of CF yet.
>
> raindrop
> A drop of water of diameter greater than 0.2 (or 0.5)mm
> falling through the atmosphere.
>
> cloud drop
> A spherical particle of liquid water, from a few
> micrometers to a few tens of micrometers diameter.
> A diameter of 0.2mm has been suggested as an upper
> limit to the size of drops.
>
> Best wishes,
>
> Tomoo
Hi Tomoo,
I would like to make sure that the definitions are appropriate to aerosols too.
I therefore suggest that the CF definition of precipitation and settling be in
terms of 'particles with aerodynamic diameter less (more) than X'.
The only aerosols I know of that get bigger than 200 microns (0.2mm) are in
dust storms, and even then are few in number, so almost all aerosols would be
classified as 'sedimenting', which is what I think most aerosol people would
expect. A 500 micron (0.5mm) cut-off would given an even bigger margin, but the
distinction between cloud drop and rain is probably more important.
Best wishes,
Philip
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