[MITgcm-support] advective and diffusive diagnostics

[Martin Losch]

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
>> ***************************************************
>>
>>
>>
>> _______________________________________________
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>> MITgcm-support at mitgcm.org
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>
> ---
> 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
>
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