Talk:CF Standard Names - Discussed Atmospheric Chemistry and Aerosol Terms

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Go to Agreed Items of Discussion on Proposed Atmospheric Chemistry and Aerosol Terms.

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Important issues are marked in RED , please COMMENT!

NOy

Vincent-Henri PEUCH VHP - CT - Jonathan Gregory JG - Frank Dentener FD - David Stevenson DS, June/July 2006

(VHP) There is always the problem that "NOy" has no fully agreed definition in the literature... It is perhaps unwise to use it in the name? Could we use "total_nitrogen_oxides" instead?

(JG) I think it's a good idea to avoid the word "total" if we can, as it is not always obvious what aspect is being totalled! total_nitrogen_oxides is probably clear enough, but maybe all_nitrogen_oxides might be better?

(CT) But what does 'all' include? anyway, I changed it.

(FD) NOy it is a matter of defining accurately. Total Nitrogen is a very confusing term, in biological applications it may mean something completely different. NOy=NO+NO2+HNO3+NO3aerosol+2 N2O5 + NO3(radical) + HNO4 + PAN + other organic nitrates.

(CT) some models might not have all these species, I define it now as:

standard_name: atmosphere_mole_fraction_of_all_nitrogen_oxides

explanation: volume mixing ratio of nitrogen oxides NOy, i.e., sum of moles_fractions of all simulated oxidized nitrogen species, (NO, NO2, HNO3, NO3aerosol, N2O5, NO3(radical), HNO4, PAN, other organic nitrates) (N2O5 is only counted once!)

(CT) Another difficulty arises from N2O5, that contains to N atmos. Frank wrote 2*N2O5 in his definition, but if we count in mole or kg - not kgN!, this is not correct. Therefore, I have added (N2O5 is only counted once!)

(DS) Follow Frank's definition, this is widely used. This is valid for all species expressed as mole fractions (or volume mixing ratios). This is the most common usage in atmospheric chemistry.

(JG) I don't think you have to list them all explicitly, do you? Different people might have different lists of things in NOy. Can you state generally that it is expressed in moles of N, to get round the multiple counting?

(CT) But this is not UDUNITS!?!

Tropopause definition - tropospheric column of gas phase species

Christiane Textor CT - Jonathan Gregory JG, June/July 2006

• JG: You have a number of names of the form up_to_chemical_tropopause_content_of_X_in_air. This order is rather unnatural, I'd say. Also in_air probably isn't right, as here you mean a large-scale quantity. I know that we discussed whether "atmosphere" goes at the start or the end, and I remarked it usually was at the start, but a complete phrase is more awkward at the start. Would you consider X_content_of_chemical_troposphere or X_content_of_atmosphere_below_chemical_tropopause?

CT: I have put in_air because satellites only see the fraction in the gas phase, so atmosphere is not correct. below_chemical_tropopause sounds good. This would lead to X_mole_content_below_chemical_tropopause_in_air or X_mole_content_in_air_below_chemical_tropopause. What do you think?

JG: X_mole_content_in_air_below_chemical_tropopause is fine

CT: tropopause not yet defined!

VHP: troposphere_content

Vincent-Henri PEUCH VHP - CT - DS, June/July 2006

The description of the "troposphere_content*" variables is not enough detailed because it is indeed verticaly integrated, but up to the tropopause only. We can specify in the explanation "up to the tropopause level", but we probably also have to specify the tropopause definition to be used (2PVU,380K ?) as the value is quite sensitive to the specific criterion used (for species with strong vertical gradients at the tropopause like ozone). A drawback of specifying is that any other type of hypotheses (other "tropopause" definition : 150 ppb of ozone, 100 hPa,...) or other ways of computation (specific tracer in the model) would then no longer fit with the name. I don't know the solution...

CT: The 150ppb O3 isosurface is a good measure for atmospheric chemsitry problems and has been used in ACCENT/PHOTOCOMP.

DS: We used the monthly mean 150 ppbv O3 isosurface as a post-processing mask on all monthly mean 3-D fields in the ACCENT work. This worked well, but may be less appropriate for instantaneous model fields, and/or in high resolution models (e.g. boundary layer ozone in a very polluted episode may exceed 150 ppbv; and a recently incorporated tropopause fold may also). We also had to be careful to define the mask for one case (e.g. the year 2000 base scenario) and then use it for all cases (e.g. various future emissions scenarios), otherwise the mass (or volume) of tropospheric air changes. One disadvantage is that the mass (or volume) of the troposphere then varies between models; this problem will occur for any definition, but perhaps shows less variation for better known definitions such as the WMO tropopause. We chose the chemical tropopause method because it had been used previously (IPCC 2001) and was easy to implement in post-processing (i.e. it didn't rely on modellers). If you are asking modellers to define tropospheric column amounts then that is open to problems. I would just ask for full model 3-D fields and calculate tropospheric columns in a consistent way in post-processing. If a variety of tropopause definitions is also asked for (WMO, 2PVU, 380K...) then you can use whichever you like when it comes down to it. But don't ask the modellers to do it, as they will all do something different.

CT: Thank you very much for you comment, it sound very good to me. I will post your suggestion to the GEMS people.

CT: Several tropopause definitions exist

CT, June/July 2006

- chemical tropopause (150 ppb O3 isosurface)

- lapse rate tropopause (the lowest level at which the lapse rate decreases to 2 °C/km or less,

provided that the average lapse rate between this level and all higher levels within 2 km does not exceed 2 °C/km. WMO definition of Tropopause)

- potential vorticity (PVU2 (at the 2 PVU surface) or PVU1.5 (at the 1.5 PVU surface))

- potential temperature surface

DS: Ask for them all, as suggested above. You don't need to use them all.

JG: tropopause_defined_by_...

JG- CT, June/July 2006

If you need to distinguish different definitions of the tropopause, this could be done by defining different standard names. This issue is rather like the definition of the ocean mixed layer, for which we have several standard names:

ocean_mixed_layer_thickness_defined_by_mixing_scheme

ocean_mixed_layer_thickness_defined_by_sigma_t

ocean_mixed_layer_thickness_defined_by_sigma_theta

ocean_mixed_layer_thickness_defined_by_temperature

If there are particular numbers which are needed for the definition (like your 150 ppb O3) they could be specified as standard name parameters (but we still haven't agreed the mechanism for this!).

CT: This would then give X_mole_content_in_air_below_tropopause_defined_by_150ppv_O3_iso_surface.

JG: For X_mole_content_in_air_below_tropopause_defined_by_150ppv_O3_iso_surface: I was thinking it is better avoid putting "parameter" like 150 ppb in the name. When it is necessary to record such parameters to define a standard name, we should use some other attribute. This has come up before and I refer to them as "standard name parameters" but we have not decided how it should be done! For instance, it could be a new attribute, or it could be a scalar coordinate variable. This needs to be debated. I think a generic name such as X_mole_content_in_air_below_tropopause_defined_by_ozone_mole_fraction would be all right, and we could mention the 150 ppb in the definition (for the moment).

CT: X_mole_content_in_air_below_tropopause_defined_by_ozone_mole_fraction is the new name so far, but the tropopause definition is still not agreed on, it could be:

tropopause_defined_by_ozone_mole_fraction

tropopause_defined_by_temperature_lapse_rate

tropopause_defined_by_potential_vorticity

tropopause_defined_by_potential_temperature

VHP: mole_fraction_of_ozone_from_stratosphere_in troposphere

VHP-JG, June/July 2006

The variable "mole_fraction_of_ozone_from_stratosphere_in troposphere" is a modeler's concept, with no chance of being measured. The way it is implemented in a model has an impact on the actual values, due to non linearities etc... I would not be in favor of including it as a standard variable. What do you think?

JG "The variable mole_fraction_of_ozone_from_stratosphere_in troposphere is a modeler's concept." Yes, that is true, but if modellers want to store this quantity, and compare it among models, then it should be given a standard name. There are many quantities like this, which aren't really observable. To begin with CF was designed for models, rather than the real world!

Construction of deposition flux names

Jonathan Gregory - Christiane Textor (CT), June/July 2006

• I would suggest that due_to_turbulence comes after of_X, because there could be a quantity dry_deposition_flux_of_X, of which dry_deposition_flux_of_X_due_to_turbulence is a part.

(CT) It is :dry_deposition_mole_flux_of_X=dry_deposition_mole_flux_of_X_due_to_turbulence+dry_deposition_mole_flux_of_X_due_to_sedimentation, so I would rather like to leave the due_to_turbulence and due_to_sedimentation close to deposition, so I would like to change it to dry_deposition_mole_flux_of_X=dry_deposition_due_to_turbulence_mole_flux_of_X+dry_deposition_due_to_sedimentation_mole_flux_of_X, ok?

Grid box area

Jonathan Gregory JG - Christiane Textor CT - Martin Schultz MS,June/July 2006

JG: Do you have a data variable containing area? If the only purpose of this is to provide weights, you can use cell_measures to supply the area variable (CF 7.2). However if you do have them as data variables, I agree you need a standard name. I'd suggest surface_area. I think this is really the quantity, isn't it. It is analogous to sea_ice_area (m2), for example. These are extensive quantities in space; they implicitly depend on the size of the grid box.

CT: I reread the CF documentation yesterday and realized the possibility of using the cell methods for the grid information, sorry for that. We do not need an additional standard_name.

MS: I am not convinced that this is a good decision. In atmospheric chemistry, the term "surface area" is much more common for "surface_area_of_leaves" (i.e. for calculating biogenic emissions), or "aerosol_surface_area" (i.e. for computing heterogeneous reaction rates). I think that the term gridbox_area is much more clear in describing what the variable contains. A really detailed standard name might be "gridbox_surface_area".

DS: Also ask for 'gridbox_volume' and 'gridbox_mass'. These are very useful for calculating integrated quantities without having to worry about model grids (especially vertical grids).

total atmospheric columns

VHP - CT, June/July 2006

VHP: we could add, for ozone at least, "total_atmosphere_content_of_*_in_air" (in Dobson units for ozone, mol/m2 for others if needed).

CT: I have added "atmosphere_content_of_*_in_air" in mole/m2. total_ is not necessary, this is already included in atmospere if there is no other specification. Dobson units are not possible within the concept of CF which is based on UDUNITS, see also the discussion on units.

3d emissions

CT - JG, July 2006

CT: I have defined surface_ and atmosphere_ emissions, e.g.

surface_emission_mole_flux_of_ozone mole/m2/s

atmosphere_emission_mole_flux_of_ozone mole/m3/s.

Is it allowed to have a flux per m3?

JG: Interesting! It's not really a flux, is it - not a flow through an area, which is what flux means to me. I think we may need to consider using a different word. What word is usually used in atmos chem for this?

CT: It is still an emission, and to my knowledge we would call it 3d-emissions. Maybe we would call it simply 'source' to distinguish from 'flux'? Or delete 'flux' in all names related to deposition and emission. We should be consistent with chemical_gross_mole_fraction_production_rate_of_G_in_air [1/s]. Question forwarded to GEMS-evaluators...