All, Sorry to wade into this discussion late, but I believe part of the difficulty experienced in the discussions here are a consequence of mixing two distinct 'concepts':
1. Cloud Height Classification Based on Cloud Types There is a well-recognised allocations of cloud types to height-bands. These types and bands are nicely illustrated both in tabular form and visually on the Cloud Appreciation Society website at: http://cloudappreciationsociety.org/collecting/about-cloud-classificatio ns/ http://cloudappreciationsociety.org/collecting/ I believe that this allocation to height bands is sufficiently well-known to be characterized without attributing an owner (e.g. WMO) or an observation process (e.g. SYNOP), as Heiko argued. Thus, (if required) these should probably be given the standard names: low_type_cloud_area_fraction medium_type_cloud_area_fraction high_type_cloud_area_fraction *However*, at present I would argue that these can only be accurately determined by a human inspection of the sky, which leads us to the second concept... 2. Cloud Height Classification Based on Height Ranges Most automated systems, be they cloud base recorders, numerical models or other forecasting processes, will assign a cloud height class based on a height range. In this case, I would argue that the following set of standard names are more appropriate: low_cloud_area_fraction medium_cloud_area_fraction high_cloud_area_fraction I acknowledge that different height ranges will be adopted by different users, but, as Heiko states, this approach will at least allow Intercomparison, and the exact details of the height ranges used could be included as additional (non-CF Standard) metadata. Having presented these two 'concepts', I would suggest that the second is likely to be the most useful, in an age where the human observers are significantly outnumbered by automated observing and forecasting systems. However, there is no reason why both sets of standard names could not to adopted. My contribution to the debate - I hope it's helpful. Regards, Bruce -- Bruce Wright Strategic Advisor on Data Management Met Office FitzRoy Road Exeter EX1 3PB United Kingdom Tel: +44 (0)1392 886481 Fax: +44 (0)1392 885681 E-mail: [email protected] http://www.metoffice.gov.uk -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Heiko Klein Sent: 15 May 2012 09:10 To: Cameron-smith, Philip Cc: [email protected]; Jonathan Gregory Subject: Re: [CF-metadata] Standard_name for cloud-cover by phenomenon Philip, I agree that referring to versioned std_name tables is generally a good idea. The WMO members have (and still have) problems with versioning, in particularly when I think about grib-tables. I still have a bad feeling about using a name like wmosynop_high_cloud_area_fraction or isccp_high_cloud_area_fraction in particularly since they give a over-specification of a generally well understood phenomenons. Both wmosynop and isccp are measurements/measurement networks, and CF generally does not have enough metadata to cover all measurement-details. E.g. for air-temperature, it is from a measurement point of view often important what type of instrument has been measuring it (automatic, human, scale,...). We don't have a 'human_quicksilver_air_temperature' in CF (or a wmosynop_air_temperature). For comparing 'air_temperature' between measurements and possibly different models, the generally understood 'air_temperature' is best. With high-clouds, this is a similar problem. high, medium and low clouds is generally well understood and well documented in literature (a simple search on the net gives more than enough hits). From a model point of view, I cannot estimate if a cloud is exactly the one type or the other. There are often estimations like: sigma < 0.4 -> high cloud 0.4 > sigma > 0.7 -> medium cloud sigma > 0.7 -> low cloud It will be difficult for the modeller to say: This is a cloud according to the wmosynop definition. Therefore, I think we need at first a general CF-name for high/medium/low cloud to be able to compare in between measurement networks and models. ISCCP, WMO synop and models have already the concept of these clouds, they are not a 100% match, but close enough. If then one of these networks needs a more exact definition of high/medium/low clouds, they should ask for a std_name of their own. Best regards, Heiko _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
