Dear Heinke, Christiane, Jonathan and Luca, Please see below for my comments on the various optical_thickness names, some of which raise important questions regarding their definitions.
optical_thickness and absorption_optical_thickness ************************************************** atmosphere_optical_thickness_due_to_ambient_aerosol; 1 The standard name table already contains the name atmosphere_optical_thickness_due_to_aerosol. Under the thread 'Modification of some existing CF standard names for chemical constituents' it was agreed that any older aerosol names (which existed prior to the introduction of the dry/ambient aerosol distinction) should be aliased to 'ambient_aerosol' names. Therefore, the name would become atmosphere_optical_thickness_due_to_ambient_aerosol as proposed. So far, so good. However, complications arise when considering the definition of this name. Currently, the definition of atmosphere_optical_thickness_due_to_aerosol reads as follows: 'The specification of a physical process by the phrase due_to_process means that the quantity named is a single term in a sum of terms which together compose the general quantity named by omitting the phrase. The optical thickness is the integral along the path of radiation of a volume scattering/absorption/attenuation coefficient. The radiative flux is reduced by a factor exp(-optical_thickness) on traversing the path. The atmosphere optical thickness applies to radiation passing through the entire atmosphere. "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets).' The addition of 'ambient' to the name would lead to the following two sentences being added to the end of the definition: '"Ambient aerosol" is aerosol that has taken up ambient water through hygroscopic growth. The extent of hygroscopic growth depends on the relative humidity and the composition of the aerosol.' This is fine and doesn't pose any problems. I think the difficulty arises in the definition of 'optical_thickness', specifically the sentence 'The optical thickness is the integral along the path of radiation of a volume scattering/absorption/attenuation coefficient.' This seems to imply that integration of any of the coefficients can be called simply optical_thickness, i.e. it is a generic term for both 'total' optical thickness and any of its components. However, in this thread we now have proposals for separate absorption_optical_thickness and optical_thickness names, where optical_thickness is the sum of scattering and absorption (and allows for the introduction of scattering_optical_thickness names if needed in future). Furthermore, Christiane has suggested adding a sentence to the definition of optical_thickness saying something like "Optical thickness is the sum of scattering and absorption components." The problem is that this proposed addition, while making perfect sense on its own, seems to conflict with the existing definition. I think that simply adding the new sentence will create a definition that contradicts itself, which isn't acceptable. However, if we delete the words 'scattering' and 'absorption' from the existing sentence so that it reads 'The optical thickness is the integral along the path of radiation of a volume attenuation coefficient' we are effectively changing the meaning of the name which will affect any existing data that use it, and that also wouldn't be acceptable! It's not clear to me how to resolve this question over the definition and I'd welcome any thoughts on the matter. atmosphere_optical_thickness_due_to_sulfate_ambient_aerosol; 1 The name is fine but the question about the 'optical_thickness' definition also applies to this name. atmosphere_absorption_optical_thickness_due_to_ambient_aerosol; 1 atmosphere_absorption_optical_thickness_due_to_dust_ambient_aerosol; 1 atmosphere_absorption_optical_thickness_due_to_particulate_organic_matte r_ambient_aerosol; 1 atmosphere_absorption_optical_thickness_due_to_sulfate_ambient_aerosol; 1 atmosphere_absorption_optical_thickness_due_to_seasalt_ambient_aerosol; 1 atmosphere_absorption_optical_thickness_due_to_black_carbon_ambient_aero sol; 1 These names are all accepted - I think new, more specific, names can be introduced regardless of how we decide to treat the 'total' optical thickness definitions. atmosphere_absorption_optical_thickness_due_to_water_ambient_aerosol; 1 I note the earlier conversation about the use of '_in_', which resulted in it being deleted from all these names. However, I think it shouldn't have been deleted from this last one, so it should read: atmosphere_absorption_optical_thickness_due_to_water_in_ambient_aerosol like the existing name atmosphere_optical_thickness_due_to_water_in_ambient_aerosol. Does everyone agree? optical_thickness and absorption_optical_thickness(mode) ******************************************************** Heinke, in her 16 December 2008 posting gives the following possible alternatives for these names: atmosphere_absorption_optical_thickness_due_to_accumulation_mode_ambient _aerosol; 1 or atmosphere_absorption_optical_thickness_due_to_accumulation_soluble_mode _ambient_aerosol; 1 atmosphere_absorption_optical_thickness_due_to_accumulation_mode_dry_aer osol; 1 or atmosphere_absorption_optical_thickness_due_to_accumulation_insoluble_mo de_ambient_aerosol; 1 atmosphere_absorption_optical_thickness_due_to_coarse_mode_ambient_aeros ol; 1 or atmosphere_absorption_optical_thickness_due_to_coarse_soluble_mode_ambie nt_aerosol; 1 atmosphere_absorption_optical_thickness_due_to_coarse_mode_dry_aerosol; 1 or atmosphere_absorption_optical_thickness_due_to_coarse_insoluble_mode_amb ient_aerosol; 1 atmosphere_absorption_optical_thickness_due_to_aitken_mode_ambient_aeros ol; 1 or atmosphere_absorption_optical_thickness_due_to_aitken_soluble_mode_ambie nt_aerosol; 1 atmosphere_absorption_optical_thickness_due_to_aitken_mode_dry_aerosol; 1 or atmosphere_absorption_optical_thickness_due_to_aitken_insoluble_mode_amb ient_aerosol; 1 atmosphere_optical_thickness_due_to_accumulation_mode_ambient_aerosol; 1 or atmosphere_optical_thickness_due_to_accumulation_soluble_mode_ambient_ae rosol; 1 atmosphere_optical_thickness_due_to_accumulation_mode_dry_aerosol; 1 or atmosphere_optical_thickness_due_to_accumulation_insoluble_mode_ambient_ aerosol; 1 atmosphere_optical_thickness_due_to_coarse_mode_ambient_aerosol; 1 or atmosphere_optical_thickness_due_to_coarse_soluble_mode_ambient_aerosol; 1 atmosphere_optical_thickness_due_to_coarse_mode_dry_aerosol; 1 or atmosphere_optical_thickness_due_to_coarse_insoluble_mode_ambient_aeroso l; 1 atmosphere_optical_thickness_due_to_aitken_mode_ambient_aerosol; 1 or atmosphere_optical_thickness_due_to_aitken_soluble_mode_ambient_aerosol; 1 atmosphere_optical_thickness_due_to_aitken_mode_dry_aerosol; 1 or atmosphere_optical_thickness_due_to_aitken_insoluble_mode_ambient_aeroso l; 1 There are three issues regarding these names and their definitions: 1) The question of whether to use a) dry_aerosol or insoluble_mode_ambient_aerosol b) ambient_aerosol or soluble_mode_ambient_aerosol Luca (2 December 2008) wrote: > > The definition "accumulation_mode_ambient_aerosol" and "accumulation_mode_ambient_aerosol" may be confusing, as one could understand the difference > between these two variables is just the presence of water on the same distribution of particles. But in fact I would like two describe two > different. particle distributions, both are at ambient conditions but one is composed of particles which can uptake water (soluble particles), and > another one which cannot uptake water in ambitn conditions (insoluble particles). So one possibility for the variables above is: > atmosphere_optical_thickness_due_to_accumulation_soluble_mode_ambient_ae rosol > atmosphere_optical_thickness_due_to_accumulation_insoluble_mode_ambient_ aerosol' > >From this I understand that 'insoluble' aerosol must always be dry because it cannot take up water. I am not clear, however, whether the 'soluble' aerosol has indeed taken up water because it is in ambient conditions, or simply that it is capable of doing so. I assume the former, but it would be helpful if someone could confirm that. Currently standard names definitions describe 'dry_aerosol' as follows: ' "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). Aerosol takes up ambient water (a process known as hygroscopic growth) depending on the relative humidity and the composition of the aerosol. "Dry aerosol" means aerosol without water.' The description of 'ambient_aerosol' is ' "Aerosol" means the suspended liquid or solid particles in air (except cloud droplets). "Ambient aerosol" is aerosol that has taken up ambient water through hygroscopic growth. The extent of hygroscopic growth depends on the relative humidity and the composition of the aerosol.' The current descriptions say nothing about whether a particular dry aerosol species is actually capable of taking up water. However, Luca needs to make this distinction. Perhaps we could do this by introducing the terms 'dry_insoluble_aerosol' and 'dry_soluble_aerosol' instead of simply 'dry_aerosol' in cases where the distinction is important. I assume that, by definition, ambient aerosol is soluble so I think we could probably just stick to calling it 'ambient_aerosol'. If we were to follow this suggestion we would introduce names such as: atmosphere_optical_thickness_due_to_accumulation_mode_ambient_aerosol (instead of soluble_mode_ambient_aerosol) atmosphere_optical_thickness_due_to_accumulation_mode_dry_insoluble_aero sol (instead of insoluble_mode_ambient_aerosol). I think this syntax is also better because it reunites the word 'mode' with 'accumulation', 'aitken', etc. 2) The question of the definition of aitken and coarse modes. It has been agreed that the terms 'aitken mode' and 'coarse mode' are sufficiently widely used to merit their inclusion in standard names. However, Christiane on 23 November 2008, wrote: > >I think it is however impossible to prescribe the definition in CF as >people use different limits in their model. Would it be possible to >request the exact definition in the comment of this name? under >discussion > This issue is similar to the question of how to deal with families of chemical species. I think it would be OK to put something in the definition that makes it clear that these quantities can vary between models. Is the definition of 'accumulation mode' similarly vague? 3) In her original posting in this thread Heinke wrote: > > for variables TAU_MODE and ABS_MODE, we should remove atmosphere, > because they are 3d, and in each model layer is given the optical depth > and is not the integration along the all atmosphere. > Am I correct in thinking that this remark refers to these coarse/aitken/accumulation mode names? These comments seem to conflict with the sentence in the current definition of optical_thickness which reads 'The atmosphere optical thickness applies to radiation passing through the entire atmosphere.' One possibility would be to use 'atmosphere_layer' for these names as follows: optical_thickness_due_to_accumulation_mode_ambient_aerosol_in_atmosphere _layer optical_thickness_due_to_accumulation_mode_dry_insoluble_aerosol_in_atmo sphere_layer. However, others have expressed the view that atmosphere_layer names should be deprecated in favour of using 'atmosphere' plus a vertical coordinate bounds variable. This has been discussed earlier in the ECHAM5-hammoz thread and in the medium 'atmosphere' thread. It seems appropriate here to include the discussion of the existing name optical_thickness_of_atmosphere_layer_due_to_aerosol which took place in the 'Modification of some existing CF standard names for chemical constituents' thread. Christiane wrote: > -> old: optical_thickness_of_atmosphere_layer_due_to_aerosol > FROM ME > >> The other optical thickness names are built like this: > >> atmosphere_optical_thickness_due_to_X > >> For consistency, I would suggest to change the first name to > >> atmosphere_layer_optical_thickness_due_to_aerosol > > > FROM JONATHaN > > I don't agree with that because all the existing 31 names with > > atmosphere_layer > > have of_atmosphere_layer or in_atmosphere_layer. However I have thought > > for some time that we don't really need the "atmosphere layer" names. We > > could just specify "atmosphere" and allow the bounds of the vertical > > coordinate to indicate what layer it means. That would be a simplification. > > Maybe we could alias this name with > atmosphere_optical_extinction_due_to_X because usually optical thickness > refers to the whole column of the atmosphere and is the vertical > integral the extinction. This way, the layer-question would vanish and > the name would be more physical. I wonder whether Christiane's approach could be used for these mode names, which would give us names of the form: atmosphere_optical_extinction_due_to_accumulation_mode_ambient_aerosol atmosphere_optical_thickness_due_to_accumulation_mode_dry_insoluble_aero sol I would welcome further comments on these names and definitions. Best wishes, Alison ------ Alison Pamment Tel: +44 1235 778065 NCAS/British Atmospheric Data Centre Fax: +44 1235 446314 Rutherford Appleton Laboratory Email: [email protected] Chilton, Didcot, OX11 0QX, U.K. -- Scanned by iCritical. _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
