Dear Jonathan, thanks for a good and constructive discussion!
Please find my comments inline. Best regards, Markus _______________________________________ Dr. Markus Fiebig Senior Scientist Dept. Atmospheric and Climate Research (ATMOS) Norwegian Institute for Air Research (NILU) P.O. Box 100 N-2027 Kjeller Norway Tel.: +47 6389-8235 Fax : +47 6389-8050 e-mail: [email protected] skype: markus.fiebig -----Original Message----- From: CF-metadata [mailto:[email protected]] On Behalf Of Jonathan Gregory Sent: Donnerstag, 17. Oktober 2013 11:05 To: [email protected] Subject: [CF-metadata] standard names for surface aerosol optical properties Dear Markus Thanks for your comments. > 1) > "surface_particle_number_concentration_at_stp_in_aerosol (and other similar > names). Could this be said more clearly as > surface_number_concentration_of_aerosol_in_air_at_stp? > That would be consistent with existing names e.g. > number_concentration_of_coarse_mode_ambient_aerosol_in_air" > > The standard names I proposed use the term "aerosol" according to its proper > textbook definition, i.e. meaning the system of particles and carrier gas. > Your wording implies that "aerosol" consists of particles only, which is a > common, but colloquial jargon use of the term. I respect the use of "aerosol" > in standard names so far, so I worded the proposed names to be backward > compatible. I agree with you about the textbook definition but it appears that existing CF names are not consistent. We have some names with a construction number_concentration_of_X_aerosol_in_air and some with atmosphere_number_content_of_aerosol_particles The difference between concentration and content is that the first is 3D and the second a vertical integral, so that's not a problem. We could change the first construction in existing names e.g. number_concentration_of_ambient_aerosol_in_air to number_concentration_of_X_aerosol_particles_in_air i.e. insert "particles". Would that be correct? I suppose that in_air is needed because aerosol is not necessarily in air (although the word looks like it should be). It could be any gas. Then for consistency, could you use number_concentration_of_aerosol_particles_at_stp_in_air in your new names? MF: Yes, that would be an option, and probably also a rather consistent and correct one! A few questions to this consensus from my side: a) I realized that I partly used the "_in_air" qualifier in my proposed standard names and partly not. I don't have any particular preference on using it or not. In the geophysical context, I can't think of any other carrier gas for an aerosol than air, so omitting "_in_air" would probably be ok. On the other hand, we may also keep it in for the sake of precision in wording. Should I consistently use "in_air" in my proposed names or not? b) In my proposed names for atmospheric aerosol optical properties, I referred only to "aerosol", e.g. volume_absorption_coefficient_in_air_due_to_dried_aerosol even though the variable is supposed to refer to the absorption coefficient of the particle phase only. Should I change these names as well, e.g. to volume_absorption_coefficient_of_dried_aerosol_particles_at_stp_in_air ? > 2) > You draw attention to the inclusion of "surface" in the above, but I'm not > clear why it's there. Is the measurement actually exactly at the ground? If > not, surface should be omitted, and the height indicated by a numerical > coordinate, or some other phrase e.g. in_atmosphere_boundary_layer (that one > already appears in the stdname table). > > The term "surface" is used according to the description given in the > "Guidelines for Construction of CF Standard Names" at > http://cf-pcmdi.llnl.gov/documents/cf-standard-names/guidelines 4-5 m above the ground is not really the surface. The constructions surface_ and _at_surface mean the same thing; they're chosen according to which seems to be easier to read in the context concerned. So I'd prefer > 2) Include in the definition the requirement that the > sampling height needs to be included as numerical > coordinate. That's what we do with screen-height temperature, for example. Although it is often called "surface air temperature", its standard name is air_temperature and it has a height coordinate (e.g. 1.5 m or 2.0 m). MF: Ok, I see the problem. I would in any case swap the "surface_" qualifier with "_at_surface" to avoid confusion, and requiring a height coordinate makes sense anyway. I'm still not quite happy with dropping "_at_surface" altogether. When the standard name is used in a data discovery portal independently of a file, having this information included in the name will be a big help to the user. He will see immediately what's in the file without opening it. You say that "_at_surface" means the exact interface of atmosphere and ground. However, even for models, this definition will depend very much on model resolution. "_at_surface" for a GCM will be very different from "_at_surface" for a microscale boundary layer model. How's that different from my proposed use of "_at_surface? Could I use "_at_surface" AND require stating the sampling height as vertical coordinate? > 3) > Clouds do not usually occur at the surface, so "surface" is surprising for > CCN. > > Not really. The number of cloud condensation nuclei active at a given water > vapour supersaturation is independent of the actual existence of a cloud. The > instrument measuring this property exposes the aerosol particles to a > generated, defined supersaturation, i.e. generates its own "cloud" inside the > instrument. OK, I see. MF: Solved! > 4) > electrical_mobility_particle_diameter. I think the "electrical" here refers > to the means of measurement. Usually the CF standard name describes the > geophysical quantity itself. Would it be OK to say aerosol_particle_diameter? > > The electrical mobility particle diameter is one of many aerosol particle > diameters, as opposed to for example the aerodynamic particle diameter (how a > particle follows a streamline) or the optical particle diameter (how the > particle scatters light). By only saying "aerosol particle diameter", the > property is somewhat ill-defined since most aerosol particles aren't > spherical. The proposed name avoids this ambiguity. OK. So it's really part of the definition of a geophysical quantity, not a method of measurement. MF: Solved! > 5) > sizing_relative_humidity. Could "sizing" be omitted? The definition of your > standard names can specify what the role of the RH is. > > This standard name would be used together with reporting particle size > resolved CCN concentrations, i.e. CCN concentrations as function of both, > supersaturation and dry particle size. In this context, we need to > distinguish between the RH for which the CCN concentration is measured (a few > 10ths above 100%), and the RH at which the particle size is selected (usually > below or just above 40%). I couldn't find any other way of distinguishing > this easily except defining a separate standard name. I see the need for two distinct standard names. However I wonder if sizing_relative_humidity could be made more self-explanatory somehow, and also whether for the other RH you also need a new and more explicit standard name, in order to make the distinction clearer? MF: I pondered this one for a good while. I think a separate humidity variable for indicating the humidity of a CCN concentration would add confusion. After all, this "relative_humidity" would be a co-ordinate variable to the CCN concentration or CCN number size distribution, so it's clear immediately what is meant. The "sizing_relative_humidity" would be auxiliary information. I could rename it to "relative_humidity_at aerosol_particle_size_selection", which would be rather self-explaining. Would that be ok? P Please consider the environment before printing this email and attachments _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
