[MITgcm-support] advective and diffusive diagnostics

[Dimitris Menemenlis]

Hi Martin, Zhan Su and I were puzzled by exactly the same question
and came across your MITgcm question, but no answer :-(

Ou points out that DFrE_TH contains the GM contribution to vertical
diffusivity computed “explicitly” in gmredi_rtransport.F, even when
implicitDiffusion=.TRUE.

Dimitris Menemenlis

> On Mar 2, 2007, at 12:45 AM, Martin Losch <Martin.Losch at awi.de> wrote:
> 
> Hi,
> let me add a related question:
> 
> for vertical diffusive flux there are two fields:
> 1. DFrI_TH, implicit diffusive flux of theta
> 2. DFrE_TH, explicit diffusive flux of theta
> 
> when I use a vertical mixing scheme that require implicit vertical diffusion such as KPP (in conjunction with GMredi), I expect that all diffusive flux is in DFrI_TH. But I still get a small contribution in DFrE_TH (explicit diffusive flux). Why is that so?
> 
> (Actually I have tried this only with passive tracers, so DFrITR01 and DFrETR01, but from looking a the code I don't see, why it should be different for theta).
> 
> Martin
> 
> On 1 Mar 2007, at 20:29, Patrick Heimbach wrote:
> 
>> 
>> To add to Baylor's description at the thread
>> http://forge.csail.mit.edu/pipermail/mitgcm-support/2007-February/004605.html
>> 
>> Quoting:
>> 1) UVELTH is just the correlation between U and T.
>> 2) UTHMASS is the correlation between U and T, weighted by 'mass', or
>> HFac, which gives free-surface corrections.
>> 3) ADVx_TH is the 'effect of advection'.  It includes flux-limiting
>> and diffusion from the numerical scheme.
>> 
>> there is a fourth diagnostic
>> 4) DFxE_TH
>> which could be termed "diffusive", i.e. it contains all
>> non-advective components in the dT/dt sum, such as diffusion due to
>> Laplacian or biharmonic diffusion (diffKh, diffK4) and due to GM/Redi.
>> 
>> The fields 3) and 4) (ADVx_TH, DFxE_TH) are mass-weighted as well
>> (yes, it's the mass of water in the grid cell),
>> so you don't have to worry about cell area, thickness or surface corrections
>> when computing sums or budgets.
>> 
>> 
>> -p.
>> 
>> 
>> 
>> On Mar 1, 2007, at 1:54 PM, Valerie Benesh wrote:
>> 
>>> I am currently trying to understand the units of the advective and diffusive fluxes in the available diagnostics.  What is the difference between mass-weighted transport of a tracer and the advective flux of the tracer?  Does the mass transport include diffusion? I take it mass-weighting involves the mass of water in the grid cell?   How exactly are the units (kg/kg)*(m/s) come by for mass-weighted transport?  How are the units (kg/kg)*(m^3/s) achieved for fluxes of the tracer?  Are these the fluxes themselves at each cell boundary?  Any help understanding these units is appreciated.  Thanks,
>>> 
>>> Val
>>> 
>>> 
>>> 
>>> ***************************************************
>>> Val Bennington
>>> Graduate Student
>>> Atmospheric and Oceanic Sciences
>>> University of Wisconsin-Madison
>>> benesh at wisc.edu
>>> ***************************************************
>>> 
>>> 
>>> 
>>> _______________________________________________
>>> MITgcm-support mailing list
>>> MITgcm-support at mitgcm.org
>>> http://mitgcm.org/mailman/listinfo/mitgcm-support
>> 
>> ---
>> Dr Patrick Heimbach | heimbach at mit.edu | http://www.mit.edu/~heimbach
>> MIT | EAPS, 54-1518 | 77 Massachusetts Ave | Cambridge, MA 02139, USA
>> FON: +1-617-253-5259 | FAX: +1-617-253-4464 | SKYPE: patrick.heimbach
>> 
>> 
>> _______________________________________________
>> MITgcm-support mailing list
>> MITgcm-support at mitgcm.org
>> http://mitgcm.org/mailman/listinfo/mitgcm-support
> 
> _______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mitgcm.org/mailman/listinfo/mitgcm-support
>