[CF-metadata] standard names for ocean model turbulent quantities

From: Tuomas Karna <karnat>
Date: Tue, 26 Mar 2013 15:26:09 -0700

Dear Allison,

I agree on your comment about giving a better definition to 'small
scale'. The turbulence closure models are derived from the primitive
equations via Reynolds decomposition, separating mean flow and random
fluctuations. Therefore I think that defining an upper length scale for
the turbulent fluctuations is not very straightforward. I guess in
practice the turbulent mixing length is used as a descriptive length scale.

Perhaps one solution could be to drop the "small scale" and stress the
random nature of turbulence instead:
"Turbulent kinetic energy" is the kinetic energy of chaotic turbulent
fluctuations of the flow ?

Tuomas Karna

Post-Doctoral Fellow
Center for Coastal Margin Observation and Prediction (CMOP)
Oregon Health and Science University
karnat at stccmop.org


On 03/19/2013 05:32 AM, alison.pamment at stfc.ac.uk wrote:
> Dear Tuomas,
>
> Thank you for working on the definitions. I take your point that 'turbulent' does not necessarily mean 'subgrid scale'. I think your suggested text is basically fine but it would be helpful if we could also include an upper limit on what you mean by 'small'.
>
> Best wishes,
> Alison
>
> ------
> Alison Pamment Tel: +44 1235 778065
> NCAS/British Atmospheric Data Centre Email: alison.pamment at stfc.ac.uk
> STFC Rutherford Appleton Laboratory
> R25, 2.22
> Harwell Oxford, Didcot, OX11 0QX, U.K.
>
>
>
>> -----Original Message-----
>> From: CF-metadata [mailto:cf-metadata-bounces at cgd.ucar.edu] On Behalf
>> Of Tuomas Karna
>> Sent: 15 March 2013 16:50
>> To: cf-metadata at cgd.ucar.edu
>> Subject: Re: [CF-metadata] standard names for ocean model turbulent
>> quantities
>>
>> Dear Allison,
>>
>> Thank you for your comments. I'd propose some further changes to the
>> definitions:
>>
>> 1. "specific_turbulent_kinetic_energy_of_sea_water (m2 s-2)"
>> As turbulent kinetic energy is not necessary equivalent to model's
>> subgrid scale eddy kinetic energy, I'd formulate the definition as:
>> ' "Specific" means per unit mass. "Turbulent kinetic energy" is the
>> kinetic energy of small scale turbulent fluctuations of the flow. '
>>
>> 2. "specific_turbulent_kinetic_energy_dissipation_in_sea_water (W kg-1)"
>> The definition would then become:
>> ' "Specific" means per unit mass. "Turbulent kinetic energy" is the
>> kinetic energy of small scale turbulent fluctuations of the flow. The
>> dissipation of kinetic energy arises in ocean models as a result of the
>> viscosity of sea water.'
>>
>> 3. "turbulent_mixing_length_of_sea_water (m)"
>> ' "Turbulent mixing length" is used in models to describe the macro
>> length scale of energy-containing eddies in a turbulent flow. '
>>
>> If these definitions seems too vague, I can try to elaborate them futher.
>>
>>
>> Best regards,
>>
>> Tuomas Karna
>>
>> Post-Doctoral Fellow
>> Center for Coastal Margin Observation and Prediction (CMOP)
>> Oregon Health and Science University
>> karnat at stccmop.org
>>
Received on Tue Mar 26 2013 - 16:26:09 GMT