Standard names: *Turbulent kinetic energy (atmosphere)*

[sol1105]

TKE (turbulent kinetic energy) is part of the COSMO model output, and yet lacking a specific standard name.

Proposer's name: Martin Schupfner

Date: March 08, 2023

- Term: specific_turbulent_kinetic_energy_of_atmosphere_layer specific_turbulent_kinetic_energy_of_air

- Description: Specific means per unit mass. "Turbulent kinetic energy" is the kinetic energy of chaotic fluctuations of the fluid flow. "Layer" means any layer with upper and lower boundaries that have constant values in some vertical coordinate. There must be a vertical coordinate variable indicating the extent of the layer(s). If the layers are model layers, the vertical coordinate can be model_level_number, but it is recommended to specify a physical coordinate (in a scalar or auxiliary coordinate variable) as well.

- Units: m2 s-2

- Comment: I used the expression “chaotic fluctuations of the fluid flow” from the sea water example below. If "fluid flow" is too general, maybe one could substitute it by “air flow”.

- Related terms:

atmosphere_kinetic_energy_content [J m-2] Content indicates a quantity per unit area. The "atmosphere content" of a quantity refers to the vertical integral from the surface to the top of the atmosphere. For the content between specified levels in the atmosphere, standard names including content_of_atmosphere_layer are used.

specific_turbulent_kinetic_energy_of_sea_water [m2 s-2] Specific means per unit mass. "Turbulent kinetic energy" is the kinetic energy of chaotic fluctuations of the fluid flow.

kinetic_energy_content_of_atmosphere_layer [J m-2] Content indicates a quantity per unit area. "Layer" means any layer with upper and lower boundaries that have constant values in some vertical coordinate. There must be a vertical coordinate variable indicating the extent of the layer(s). If the layers are model layers, the vertical coordinate can be model_level_number, but it is recommended to specify a physical coordinate (in a scalar or auxiliary coordinate variable) as well.

specific_kinetic_energy_of_air [m2 s-2] "specific" means per unit mass.

[jeremygibbs]

I politely and pedantically suggest that "turbulence kinetic energy" is the more appropriate term. I believe "turbulent kinetic energy" seemingly denotes some kinetic energy that is itself turbulent, while "turbulence kinetic energy" makes it clear that one is describing the kinetic energy associated with turbulence.

While both have been used interchangeably in the literature, I think "turbulence kinetic energy" should be the preferred standard name. Many canonical authors / sources in the atmospheric sciences use this version. See, e.g.,

• American Meteorological Society's "Glossary of Meteorology".
• Stull, R.B. (1988). Some Mathematical & Conceptual Tools: Part 1. Statistics. In: Stull, R.B. (eds) An Introduction to Boundary Layer Meteorology (p. 45). Atmospheric Sciences Library, vol 13. Springer, Dordrecht. https://doi.org/10.1007/978-94-009-3027-8_2
• Wyngaard, J. (2010). Conservation equations for covariances. In Turbulence in the Atmosphere (p. 101). Cambridge: Cambridge University Press. doi:10.1017/CBO9780511840524.006
• Deardorff, J. (1970). A numerical study of three-dimensional turbulent channel flow at large Reynolds numbers. Journal of Fluid Mechanics, 41(2), 453-480. doi:10.1017/S0022112070000691
• Golitsyn, G.S. (1998). Convection in Viscous and Rotating Fluids from the Viewpoint of the Forced Flow Theory. In: Plate, E.J., Fedorovich, E.E., Viegas, D.X., Wyngaard, J.C. (eds) Buoyant Convection in Geophysical Flows. NATO ASI Series, vol 513. Springer, Dordrecht. https://doi.org/10.1007/978-94-011-5058-3_6
• It is also defined this way on Wikipedia and CFD Online.

[JonathanGregory]

Dear Martin @sol1105

Thanks for your proposal. I think there are two possible quantities you might want to name - both of them sensible - and I am not sure which you intend. Do you mean turbulent_kinetic_energy_content_of_atmosphere_layer in J m-2 = kg s-2, which depends on the vertical extent of the layer, or is it specific_turbulent_kinetic_energy_of_air in J kg-1 = m2 s-2, which is an intensive property?

Dear @jeremygibbs

If turbulence is agreed for the new standard name, for consistency it would require changing the existing names specific_turbulent_kinetic_energy_dissipation_in_sea_water and specific_turbulent_kinetic_energy_of_sea_water, and perhaps turbulent_mixing_length_of_sea_water. This could be done, with aliases, if we agree it is useful to make that change. Thanks for raising this point.

Best wishes

Jonathan

[sol1105]

@JonathanGregory Thank you for your reply. The model variable is provided on model layers and in units [m2 s-2] . specific_turbulent_kinetic_energy_of_air would also be fine if something speaks against specific_turbulent_kinetic_energy_of_atmosphere_layer.

@jeremygibbs Thank you for commenting. I do not oppose the change to specific_turbulence_kinetic_energy_of_atmosphere_layer/of_air, but I cannot take part in the discussion whether it is useful to change existing standard_names or not.

[JonathanGregory]

Dear Martin @sol1105

If it's in m2 s-2 = J kg-1 then specific_turbulent_kinetic_energy_of_air would be right. The model layers have boundaries in some coordinate, presumably, and this is an intensive property which is representative of the air in the layer - right? It's the same kind of property as air_temperature, for instance. In a model, air_temperature is likewise provided on model layers, but that isn't relevant to the definition of the quantity itself.

If you multiply specific_turbulent_kinetic_energy_of_air by air_density you get a quantity in m2 s-2 kg m-3 = J m-3. This quantity doesn't have a standard name at present. It would be the concentration of turbulent KE. If you calculate the vertical integral of that within the model layer, you get something in J m-2. That would be probably be given the standard name turbulent_kinetic_energy_content_of_atmosphere_layer. We already have a similar quantity in the standard name table without turbulent_.

Best wishes

Jonathan

[sol1105]

@JonathanGregory Thank you, I adjusted the term and description:

- Term: specific_turbulent_kinetic_energy_of_air

- Description: Specific means per unit mass. "Turbulent kinetic energy" is the kinetic energy of chaotic fluctuations of the fluid flow.

- Units: m2 s-2

[JonathanGregory]

Thanks, @sol1105. This looks fine to me - clear and simple, following previous patterns. If no-one expresses concerns in the next week or two it should be accepted for inclusion in the standard name table. @jeremygibbs, I suggest that question of whether "turbulent" should be "turbulence", which doesn't affect only this name, should be regarded as a different issue; please raise one if you would like. Thanks, both.

[github-actions[bot]]

This issue has had no activity in the last 30 days. This is a reminder to please comment on standard name requests to assist with agreement and acceptance. Standard name moderators are also reminded to review @feggleton @japamment

[feggleton]

Thanks for this proposal and discussion. I have added this to the editor, apologies for the delay.

The standard phrase for Turbulent kinetic energy is '"Turbulent kinetic energy" is the kinetic energy of all eddy-induced motion that is not resolved on the grid scale of the model.' @sol1105 Are you ok if I change this in the description?

[sol1105]

@feggleton Thank you for your reply. After the initial comments, the standard_name term is an adjustment of specific_turbulent_kinetic_energy_of_sea_water. And the description is that of said term (Specific means per unit mass. "Turbulent kinetic energy" is the kinetic energy of chaotic fluctuations of the fluid flow.). I consulted the modelers if they agree with '"Turbulent kinetic energy" is the kinetic energy of all eddy-induced motion that is not resolved on the grid scale of the model and will get back to you with their reply.

[sol1105]

@feggleton I received the feedback from the modelers, the new description fits perfectly, thank you.

[japamment]

@sol1105 @feggleton

The name proposed and agreed in this issue will be included in V82 of the standard name table, currently in preparation.

Best wishes

Alison

[sol1105]

@japamment That's great news, thank you :+1:

[japamment]

I am closing this issue as the name has been published in V82 of the standard name table.