Standard names: atmosphere-wave-ocean coupling diagnostics

[ukmo-ansaulter]

Proposer's name: Andy Saulter
Date: 1st February 2021

The terms below describe various diagnostics used to analyse/model coupled momentum transfer from atmosphere to waves and waves to ocean

Term: eastward_friction_velocity
Unit: m s-1
A velocity is a vector quantity. "Eastward" indicates a vector component which is positive when directed eastward (negative westward). Friction velocity is a reference wind velocity derived from the relationship between air density and downward stress and is usually applied at a level close to the surface where stress is assumed to independent of height and approximately proportional to the square of mean velocity.

Term: northward_friction_velocity
Unit: m s-1
A velocity is a vector quantity. "Northward" indicates a vector component which is positive when directed northward (negative southward). Friction velocity is a reference wind velocity derived from the relationship between air density and downward stress and is usually applied at a level close to the surface where stress is assumed to independent of height and approximately proportional to the square of mean velocity.

Term: sea_surface_wave_mean_wavenumber_from_variance_spectral_density_first_wavenumber_moment
Unit: m-1
The wave directional spectrum can be written as a five dimensional function S(t,x,y,k,theta) where t is time, x and y are horizontal coordinates (such as longitude and latitude), k is wavenumber and theta is direction. S has the standard name sea_surface_wave_directional_variance_spectral_density. S can be integrated over direction to give S1= integral(S dtheta) and this quantity has the standard name sea_surface_wave_variance_spectral_density. Wavenumber is the number of oscillations of a wave per unit distance. Wavenumber moments, M(n) of S1 can then be calculated as follows: M(n) = integral(S1 k^n dk), where k^n is k to the power of n. The mean wavenumber, k(1), is calculated as the ratio M(1)/M(0).

Term: sea_surface_wave_sxx_radiation_stress
Unit: Pa
“Sea surface wave radiation stress” describes the excess momentum flux caused by sea surface waves. Radiation stresses behave as a second-order tensor. “Sxx” indicates the component of the tensor along the grid x_ axis.

Term: sea_surface_wave_syy_radiation_stress
Unit: Pa
“Sea surface wave radiation stress” describes the excess momentum flux caused by sea surface waves. Radiation stresses behave as a second-order tensor. “Syy” indicates the component of the tensor along the grid y_ axis.

Term: sea_surface_wave_sxy_radiation_stress
Unit: Pa
“Sea surface wave radiation stress” describes the excess momentum flux caused by sea surface waves. Radiation stresses behave as a second-order tensor. “Sxy” indicates the lateral contributions to x_ and y_ components of the tensor.

[JonathanGregory]

Dear Andy Thanks for these proposals. I have some comments. (1) I suggest that the friction velocity should have _in_air at the end. (2) While it's quite correct that all waves radiate, I fear the word "radiation" is liable to be misunderstood. It's currently used in eight standard names, in all of which it means "electromagnetic radiation". It is not qualified in five of them, and the other three mention infrared. Is there any alternative phrasing which could avoid possible misapprehension? (3) For the tensor components I would propose _xx_ _yy_ and _xy; _xy_ is used already in a handful of names. Is that what you mean? Best wishes Jonathan

[ukmo-ansaulter]

Thanks as always @JonathanGregory

Re your comments:

(1) Yes I agree, should add _in_air

(2) radiation_stress in this context is a very specific and well-used term for those that work with wave data (see Coastal Wiki and Wikipedia entries). The sea_surface_wave phrasing should make it clear that we are talking about this instance?

(3) I don't see an issue with adopting the xx, yy, xy convention

Cheers
Andy

[feggleton]

Hi Andy, thank you for your proposal and to Jonathan for your help there. I have now added these terms to the cfeditor (http://cfeditor.ceda.ac.uk/proposals/1) and added the changes discussed above. Any further comments and discussion are welcome.

[feggleton]

Hi all, do let me know if you're happy with the terms above or if there are any further discussions. If there are no further comments in the next 7 days then these can be accepted.

[feggleton]

These terms have now been accepted into the next update.

[japamment]

Changes applied in version 78 of the standard name table.