Hello All,
We require four additional standard names for AerChemMIP, for 3 parameters plus one for a threshold. (1) lossn2o: Monthly Loss of atmospheric Nitrous Oxide [mol m-3 s-1] This is very similar to the existing CF Standard name for methane loss rate: tendency_of_atmosphere_mole_concentration_of_methane_due_to_chemical_destruction, so we propose: "tendency_of_atmosphere_of_mole_concentration_of_nitrous_oxide_due_to_chemical_destruction" (2) bs550aer: Aerosol backscatter coefficient [m-1 sr-1] Description: The intensity (flux per unit solid angle) of scattered radiation per unit length of scattering medium, normalised by the incident radiation flux, at an angle of 180 degrees to the incident radiation, and at a wavelength of 550nm, for scattering off ambient aerosol particles. This can be encoded using a variable with coordinates specifying scattering_angle=180 degrees and a radiation_wavelength=550nm. The phrases "backward scattering" and "backscattering" are used in the CF standard name list to refer to "the sum of scattering into all backward angles i.e. scattering_angle exceeding pi/2 radians", so cannot be used here. There are 3 existing CF names with units of "m-1 sr-1". Two of these are defined as sums over all backward angles (volume_attenuated_backwards_scattering_function_in_air and volume_attenuated_backwards_scattering_function_in_air_assuming_no_aerosol_or_cloud), so are not relevant here. The third is "volume_scattering_function_of_radiative_flux_in_sea_water", which provides a pattern for a new name. The help text for this name refers to the “fraction of incident radiative flux scattered into unit solid angle per unit path length”, which I find slightly misleading because we are dealing with the intensity of reflected radiation per ster radian, not an amount reflected into a finite solid angle, so I would like to update this wording. Proposed name: volume_scattering_function_in_air_due_to_ambient_aerosol_particles "The volume scattering function is the intensity (flux per unit solid angle) of scattered radiation per unit length of scattering medium, normalised by the incident radiation flux. The (range of) direction(s) of scattering can be specified by a coordinate of scattering_angle. A coordinate variable of radiation_wavelength or radiation_frequency can be specified to indicate that the scattering applies at specific wavelengths or frequencies.” (3a) pod0: Phytotoxic ozone dose [mol m-2 s-1] Accumulated stomatal ozone flux over the threshold of 0 mol m-2 s-1; Computation: Time Integral of (hourly above canopy ozone concentration * stomatal conductance * Rc/(Rb+Rc). The direction of the flux is implicitly into the plant. The proposal is to follow the approach used for variables such as rainfall_flux and not mention the direction of the flux in the name, but make it explicit in the description, since it may not be obvious to everyone that stomatal flux of ozone is necessarily inwards. Proposed name: integral_wrt_time_of_stomatal_ozone_flux_excess The CF standard name definition would then be: The phrase "integral_wrt_X_of_Y" means int Y dX. The data variable should have an axis for X specifying the limits of the integral as bounds. The term "wrt" means “with respect to”. The chemical formula for ozone is O3. The stomatal ozone flux excess is the stomatal ozone flux into the plant minus the threshold value, where only positive values are included in the integral. This parameter is often called the “phytotoxic ozone dose (POD)”. The data variable carrying this standard name should have a scalar coordinate variable or a size-one coordinate variable with the standard name of stomatal_ozone_flux_threshold, to indicate the threshold. (3b) stomatal_ozone_flux_threshold [mol m-2 s-1] A standard name to be used on variable specifying a threshold value of stomatal ozone flux. regards, Martin ________________________________ From: Michael Schulz <[email protected]> Sent: 17 April 2018 10:25 To: Juckes, Martin (STFC,RAL,RALSP) Subject: Re: AerChemMIP data request: clarifications and standard names Hi Martin, "per ster radian" is fine with me ! I think its important to put attention to this unit aspect. I was citing from this standard name: volume_attenuated_backwards_scattering_function_in_air "The volume scattering function is the fraction of incident radiative flux scattered into unit solid angle per unit path length.” which is probably not a good example. best wishes Michael On 16 Apr 2018, at 12:42, Martin Juckes - UKRI STFC <[email protected]<mailto:[email protected]>> wrote: Hello Michael, I'm sorry, but I'm not happy with that phrase. If an aerosol particle is at, say, 20km altitude, then a cone subtending one ster radian will intersect the Earth's surface with a circle that has an area of approximately 400 km2. Not exactly 400km2, because of geometric factors, but clearly larger than the receiving dish on the lidar. There is no way that the lidar can measure the radiation reflected into a unit solid angle. As you say, the units "sr-1" imply "per ster radian", so we should say that into the name. The phrase "scattered into unit solid angle" is not saying the same thing. regards, Martin ________________________________ From: Michael Schulz <[email protected]<mailto:[email protected]>> Sent: 16 April 2018 10:18 To: Juckes, Martin (STFC,RAL,RALSP) Subject: Re: AerChemMIP data request: clarifications and standard names HI Martin, sorry for delays —— Actually, I thought that the unit sr-1 corresponds to ".. fraction of incident radiative flux scattered into unit solid angle …" The lidar light backscattered is measured in a certain observation angle, and thus per ster radians. Therefore I thought that backscatter coefficients needed this wording. Does this sound reasonable? greetings Michael On 3 Apr 2018, at 13:30, Martin Juckes - UKRI STFC <[email protected]<mailto:[email protected]><mailto:[email protected]>> wrote: Hello Michael, I changed the wording because I'm uncomfortable with the phrase ".. fraction of incident radiative flux scattered into unit solid angle ...". These words refer to a quantity of radiation scattered into a portion of space which subtends one steradian. Surely what the lidar measures is more like the intensity of the reflected radiation reflected back? The description I suggested would be suitable for the MIP tables ... I agree that we need something more structured for the CF standard name list. Here is a modification of your text, replacing the above text with reference to intensity of scattered radiation: "The volume scattering function is the intensity (flux per unit solid angle) of scattered radiation normalised by the incident radiation flux. A scattering_angle should be specified with this quantity [otherwise it is assumed to be at 180 degrees of incident beam]. A wavelength should be specified with this quantity[, otherwise it is assumed to be 550 nm]. "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 quantity corresponds to the backscattering coefficient used in lidar retrievals. I'd prefer not to have defaults of 180 degrees and 550nm in the standard name because it can create ambiguity if angles and wavelengths sometimes have to be specified, but not always: it is impossible to automatically test whether an omitted value is an error or an intentional use of the default. But, if you want, we could put this question to the CF discussion list (the names have to go through the CF discussion list -- but hopefully that will not take long now that we have agreed the main points), regards, Martin ________________________________ From: Michael Schulz <[email protected]<mailto:[email protected]><mailto:[email protected]>> Sent: 29 March 2018 19:44 To: Juckes, Martin (STFC,RAL,RALSP) Subject: Re: AerChemMIP data request: clarifications and standard names Hi Martin, I agree with the standard name: volume_scattering_function_in_air_due_to_ambient_aerosol_particles Your description is fine, but it misses maybe somethings. I am wondering if the description should follow other wordings in CF. Eg I would have written. "The volume scattering function is the fraction of incident radiative flux scattered into unit solid angle per unit path length. A scattering_angle should be specified with this quantity otherwise it is assumed to be at 180 degrees of incident beam. A wavelength should be specified with this quantity, otherwise it is assumed to be 550 nm. "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 quantity corresponds to the backscattering coefficient used in lidar retrievals. Unit m-1 sr-1 I think the standard name could this way also be used for other scattering angles. It might create confusion that backscatter coefficient is not appearing in the description. I wonder thus if one should add a sentence like I have done. The radar community also made their imprint in the description of the attenuated backscatter quantity. best wishes Michael On 27 Mar 2018, at 14:13, [email protected]<mailto:[email protected]><mailto:[email protected]><mailto:[email protected]> wrote: Hello Michael, thanks. There appears to be a conflict with the terminology used in the existing CF Standard Names, where, in the words of the convention "Backwards scattering refers to the sum of scattering into all backward angles i.e. scattering_angle exceeding pi/2 radians". The definition of volume_attenuated_backwards_scattering_function_in_air_assuming_no_aerosol_or_cloud includes the sentences "Backwards scattering refers to the sum of scattering into all backward angles i.e. scattering_angle exceeding pi/2 radians. A scattering_angle should not be specified with this quantity", so we can't use it here. For the amount of radiation scattered into a specific range of angles, there is the term "volume_scattering_function": "The volume scattering function is the fraction of incident radiative flux scattered into unit solid angle per unit path length. The (range of) direction(s) of scattering can be specified by a coordinate of scattering_angle." [I'm not sure if this description, which comes from the existing definition of volume_scattering_function_of_radiative_flux_in_sea_water, is really clear -- since we are talking about an amount scattered per unit solid angle, not a fraction scattered into a finite solid angle: it might be clearer to say: "The volume scattering function is the intensity (flux per unit solid angle) of scattered radiation normalised by the incident radiation flux".] So, the solution might be a new standard name: volume_scattering_function_in_air_due_to_ambient_aerosol_particles with a scattering_angle coordinate set to 180 degrees and a radiative_wavelength set to 550nm. Would it be accurate to summarise the variable as: "The intensity (flux per unit solid angle) of scattered radiation normalised by the incident radiation flux, at an angle of 180 degrees to the incident radiation, and at a wavelength of 550nm, for scattering off ambient aerosol particles"? regards, Martin ________________________________ From: Michael Schulz <[email protected]<mailto:[email protected]><mailto:[email protected]><mailto:[email protected]>> Sent: 26 March 2018 15:05 To: Juckes, Martin (STFC,RAL,RALSP) Subject: Re: AerChemMIP data request: clarifications and standard names Hi Martin, (2) bs550aer: Aerosol backscatter coefficient [m-1 sr-1] Description: Aerosol Backscatter at 550nm and 180 degrees, computed from extinction and lidar ratio You have suggested: volume_lidar_backwards_scattering_coefficient_in_air_due_to_ambient_aerosol_particles Q1: Can you explain to me what the meaning of "extinction and lidar ratio" is in the description? Are you asking people to calculate this from an emulated lidar? Actually the “lidar" shall indicate the 180 degree angle for which the backward scattering shall be calculated. It could be done with a lidar emulator, but it can also come from a Mie calculation. There is still no standard name indeed for this rather standard parameter in atmospheric science. the most similar is: volume_backwards_scattering_coefficient_in_air_due_to_dried_aerosol_particles unit m-1 But then it should be *_due_to_ambient_aerosol_particles * and it should indicate the 180 degree angle, * with the unit: m-1 sr-1 Not sure how to solve this. The wavelength of 550 nm is good and can be implicit. Although for aerosol optical thickness one needs to add: "A coordinate variable of radiation_wavelength or radiation_frequency can be specified to indicate that the optical thickness applies at specific wavelengths or frequencies. “ Q2: Is the quantity somehow specific to lidar measurements, other than through the choice of 550nm wavelength? If not, then could "_lidar_" be omitted from the standard name:volume_backwards_scattering_coefficient_in_air_due_to_ambient_aerosol_particles? I think omitting lidar is ok, but then the unit is not consistent. EG [cid:[email protected]]volume_attenuated_backwards_scattering_function_in_air_assuming_no_aerosol_or_cloud has the unit m-1 sr-1 Does this make sense? kind regards Michael <arrow_down.gif> _______________________________________________ CF-metadata mailing list [email protected] http://mailman.cgd.ucar.edu/mailman/listinfo/cf-metadata
